* Re: [PATCH v4 0/5] implement lightweight guard pages
From: SeongJae Park @ 2024-10-28 18:24 UTC (permalink / raw)
To: Lorenzo Stoakes
Cc: SeongJae Park, Andrew Morton, Liam R . Howlett, Matthew Wilcox,
Vlastimil Babka, Paul E . McKenney, Jann Horn, David Hildenbrand,
linux-mm, linux-kernel, Muchun Song, Richard Henderson,
Matt Turner, Thomas Bogendoerfer, James E . J . Bottomley,
Helge Deller, Chris Zankel, Max Filippov, Arnd Bergmann,
linux-alpha, linux-mips, linux-parisc, linux-arch, Shuah Khan,
Christian Brauner, linux-kselftest, Sidhartha Kumar, Jeff Xu,
Christoph Hellwig, linux-api, John Hubbard
In-Reply-To: <cover.1730123433.git.lorenzo.stoakes@oracle.com>
On Mon, 28 Oct 2024 14:13:26 +0000 Lorenzo Stoakes <lorenzo.stoakes@oracle.com> wrote:
> Userland library functions such as allocators and threading implementations
> often require regions of memory to act as 'guard pages' - mappings which,
> when accessed, result in a fatal signal being sent to the accessing
> process.
>
> The current means by which these are implemented is via a PROT_NONE mmap()
> mapping, which provides the required semantics however incur an overhead of
> a VMA for each such region.
>
> With a great many processes and threads, this can rapidly add up and incur
> a significant memory penalty. It also has the added problem of preventing
> merges that might otherwise be permitted.
>
> This series takes a different approach - an idea suggested by Vlasimil
> Babka (and before him David Hildenbrand and Jann Horn - perhaps more - the
Nit. s/Vlasimil/Vlastimil/ ;)
Thanks,
SJ
[...]
^ permalink raw reply
* Re: [PATCH v6 2/5] pidfd: add PIDFD_SELF_* sentinels to refer to own thread/process
From: Lorenzo Stoakes @ 2024-10-28 16:06 UTC (permalink / raw)
To: Christian Brauner
Cc: Oleg Nesterov, Christian Brauner, Shuah Khan, Liam R . Howlett,
Suren Baghdasaryan, Vlastimil Babka, pedro.falcato,
linux-kselftest, linux-mm, linux-fsdevel, linux-api, linux-kernel,
Oliver Sang, John Hubbard
In-Reply-To: <20241028-gesoffen-drehmoment-5314faba9731@brauner>
On Mon, Oct 28, 2024 at 04:34:33PM +0100, Christian Brauner wrote:
> On Sat, Oct 26, 2024 at 08:24:58AM +0100, Lorenzo Stoakes wrote:
> > It is useful to be able to utilise the pidfd mechanism to reference the
> > current thread or process (from a userland point of view - thread group
> > leader from the kernel's point of view).
> >
> > Therefore introduce PIDFD_SELF_THREAD to refer to the current thread, and
> > PIDFD_SELF_THREAD_GROUP to refer to the current thread group leader.
> >
> > For convenience and to avoid confusion from userland's perspective we alias
> > these:
> >
> > * PIDFD_SELF is an alias for PIDFD_SELF_THREAD - This is nearly always what
> > the user will want to use, as they would find it surprising if for
> > instance fd's were unshared()'d and they wanted to invoke pidfd_getfd()
> > and that failed.
> >
> > * PIDFD_SELF_PROCESS is an alias for PIDFD_SELF_THREAD_GROUP - Most users
> > have no concept of thread groups or what a thread group leader is, and
> > from userland's perspective and nomenclature this is what userland
> > considers to be a process.
> >
> > Due to the refactoring of the central __pidfd_get_pid() function we can
> > implement this functionality centrally, providing the use of this sentinel
> > in most functionality which utilises pidfd's.
> >
> > We need to explicitly adjust kernel_waitid_prepare() to permit this (though
> > it wouldn't really make sense to use this there, we provide the ability for
> > consistency).
> >
> > We explicitly disallow use of this in setns(), which would otherwise have
> > required explicit custom handling, as it doesn't make sense to set the
> > current calling thread to join the namespace of itself.
> >
> > As the callers of pidfd_get_pid() expect an increased reference count on
> > the pid we do so in the self case, reducing churn and avoiding any breakage
> > from existing logic which decrements this reference count.
> >
> > This change implicitly provides PIDFD_SELF_* support in the waitid(P_PIDFS,
> > ...), process_madvise(), process_mrelease(), pidfd_send_signal(), and
> > pidfd_getfd() system calls.
> >
> > Things such as polling a pidfs and general fd operations are not supported,
> > this strictly provides the sentinel for APIs which explicitly accept a
> > pidfd.
> >
> > Suggested-by: Pedro Falcato <pedro.falcato@gmail.com>
> > Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> > ---
>
> Currently, a pidfd based system call like pidfd_send_signal() would
> simply do:
>
> fdget(pidfd);
> // use struct pid
> fdput(pidfd);
>
> Where the lifetime of @pid is guaranteed by @file. And in the regular
> case where there's only a single thread the file code will avoid taking
> a reference. Thus, there's no reference count bump on fdget(), nor a
> drop on fdput(), nor a get_pid() or put_pid().
Right I missed that fdget() wouldn't take a reference count I assumed it
would be equivalent, my mistake.
>
> With your patch series you will always cause reference counts on @pid to
> be taken for everyone. And I wouldn't be surprised if we get performance
> regressions for this.
This was in response to you review saying I can't pass around a pointer to
the fd, originally I didn't do this.
This was the only way I could find to de-jank and make my shared function
not end up problematic in the light of wanting to keep the fd within a
single scope, I didn't realise that passing that by value would be ok.
But obviously hadn't realised that fdget()/fdput() sometimes doesn't change
a reference count, mea culpa on that not an fs person...
>
> In one of my earlier mails I had mused about a fdput() like primitive.
> What I roughly, hastily, and under the influence of the flu, sketched in
> the _completey untested_ patch I appended illustrates roughly what I had
> been thinking about.
OK, I was really uncertain as to what you meant regarding the scope of this
value so had assumed we couldn't do something like assigning the value like
that.
I guess I'll try to adapt that and respin a v7 when I get a chance.
>
> > include/linux/pid.h | 8 ++++--
> > include/uapi/linux/pidfd.h | 10 ++++++++
> > kernel/exit.c | 4 ++-
> > kernel/nsproxy.c | 1 +
> > kernel/pid.c | 51 ++++++++++++++++++++++++--------------
> > 5 files changed, 53 insertions(+), 21 deletions(-)
> >
> > diff --git a/include/linux/pid.h b/include/linux/pid.h
> > index d466890e1b35..3b2ac7567a88 100644
> > --- a/include/linux/pid.h
> > +++ b/include/linux/pid.h
> > @@ -78,11 +78,15 @@ struct file;
> > * __pidfd_get_pid() - Retrieve a pid associated with the specified pidfd.
> > *
> > * @pidfd: The pidfd whose pid we want, or the fd of a /proc/<pid> file if
> > - * @alloc_proc is also set.
> > + * @alloc_proc is also set, or PIDFD_SELF_* to refer to the current
> > + * thread or thread group leader.
> > * @allow_proc: If set, then an fd of a /proc/<pid> file can be passed instead
> > * of a pidfd, and this will be used to determine the pid.
> > +
> > * @flags: Output variable, if non-NULL, then the file->f_flags of the
> > - * pidfd will be set here.
> > + * pidfd will be set here or If PIDFD_SELF_THREAD is set, this is
> > + * set to PIDFD_THREAD, otherwise if PIDFD_SELF_THREAD_GROUP then
> > + * this is set to zero.
> > *
> > * Returns: If successful, the pid associated with the pidfd, otherwise an
> > * error.
> > diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h
> > index 565fc0629fff..6fe1d63b2086 100644
> > --- a/include/uapi/linux/pidfd.h
> > +++ b/include/uapi/linux/pidfd.h
> > @@ -29,4 +29,14 @@
> > #define PIDFD_GET_USER_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 9)
> > #define PIDFD_GET_UTS_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 10)
> >
> > +/*
> > + * Special sentinel values which can be used to refer to the current thread or
> > + * thread group leader (which from a userland perspective is the process).
> > + */
> > +#define PIDFD_SELF PIDFD_SELF_THREAD
> > +#define PIDFD_SELF_PROCESS PIDFD_SELF_THREAD_GROUP
> > +
> > +#define PIDFD_SELF_THREAD -10000 /* Current thread. */
> > +#define PIDFD_SELF_THREAD_GROUP -20000 /* Current thread group leader. */
> > +
> > #endif /* _UAPI_LINUX_PIDFD_H */
> > diff --git a/kernel/exit.c b/kernel/exit.c
> > index 619f0014c33b..e4f85ec4ba78 100644
> > --- a/kernel/exit.c
> > +++ b/kernel/exit.c
> > @@ -71,6 +71,7 @@
> > #include <linux/user_events.h>
> > #include <linux/uaccess.h>
> >
> > +#include <uapi/linux/pidfd.h>
> > #include <uapi/linux/wait.h>
> >
> > #include <asm/unistd.h>
> > @@ -1739,7 +1740,8 @@ int kernel_waitid_prepare(struct wait_opts *wo, int which, pid_t upid,
> > break;
> > case P_PIDFD:
> > type = PIDTYPE_PID;
> > - if (upid < 0)
> > + if (upid < 0 && upid != PIDFD_SELF_THREAD &&
> > + upid != PIDFD_SELF_THREAD_GROUP)
> > return -EINVAL;
> >
> > pid = pidfd_get_pid(upid, &f_flags);
> > diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
> > index dc952c3b05af..d239f7eeaa1f 100644
> > --- a/kernel/nsproxy.c
> > +++ b/kernel/nsproxy.c
> > @@ -550,6 +550,7 @@ SYSCALL_DEFINE2(setns, int, fd, int, flags)
> > struct nsset nsset = {};
> > int err = 0;
> >
> > + /* If fd is PIDFD_SELF_*, implicitly fail here, as invalid. */
> > if (!fd_file(f))
> > return -EBADF;
> >
> > diff --git a/kernel/pid.c b/kernel/pid.c
> > index 94c97559e5c5..0a1861b4422c 100644
> > --- a/kernel/pid.c
> > +++ b/kernel/pid.c
> > @@ -535,33 +535,48 @@ struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
> > }
> > EXPORT_SYMBOL_GPL(find_ge_pid);
> >
> > +static struct pid *pidfd_get_pid_self(unsigned int pidfd, unsigned int *flags)
>
> The @flags argument is unused afaict.
Oops will rework on v7.
>
> > +{
> > + bool is_thread = pidfd == PIDFD_SELF_THREAD;
> > + enum pid_type type = is_thread ? PIDTYPE_PID : PIDTYPE_TGID;
> > + struct pid *pid = *task_pid_ptr(current, type);
> > +
> > + /* The caller expects an elevated reference count. */
> > + get_pid(pid);
> > + return pid;
> > +}
>
> Fwiw, what you've done here is essentially reimplement the already
> existing get_task_pid() helper that you could simply use.
We're looking up PIDFD_SELF_* values here. So presumably you mean the:
struct pid *pid = *task_pid_ptr(current, type);
/* The caller expects an elevated reference count. */
get_pid(pid);
Bit is duplicated vs. get_task_pid()?
I did that because it wasn't clear doing that under the RCU lock was
necessary or useful?
It seems useful still to have the PIDFD_SELF stuff qseparate, I can replace
those two lines with a call to get_task_pid() if you prefer? Unless you
meant something else?
>
> > +
> > struct pid *__pidfd_get_pid(unsigned int pidfd, bool allow_proc,
> > unsigned int *flags)
> > {
> > - struct pid *pid;
> > - struct fd f = fdget(pidfd);
> > - struct file *file = fd_file(f);
> > + if (pidfd == PIDFD_SELF_THREAD || pidfd == PIDFD_SELF_THREAD_GROUP) {
> > + return pidfd_get_pid_self(pidfd, flags);
> > + } else {
>
> I think the else can just go and we can save an indentation level.
This has been raised a couple times before by other reviewers, this is just
so we can declare variables, especially the fd variable, which you were
very clear _must_ retain scope only where it used.
Otherwise I have to do something like;
struct fd f = {};
if (...) { return ...; }
f = fdget(...);
This way we don't need to do that.
I mean probably the compiler would do the right thing but it just seems
ugly to assign/reassign a stack value like that.
Ah, I see struct fd is just a wrapper around an unsigned long, so probably
not a big deal to just leave it unassigned then.
This was the only reason I did this, I usually much prefer the guard
pattern.
OK if you're fine with this value being assigned like that then no problem
will change!
>
> > + struct pid *pid;
> > + struct fd f = fdget(pidfd);
> > + struct file *file = fd_file(f);
> >
> > - if (!file)
> > - return ERR_PTR(-EBADF);
> > + if (!file)
> > + return ERR_PTR(-EBADF);
> >
> > - pid = pidfd_pid(file);
> > - /* If we allow opening a pidfd via /proc/<pid>, do so. */
> > - if (IS_ERR(pid) && allow_proc)
> > - pid = tgid_pidfd_to_pid(file);
> > + pid = pidfd_pid(file);
> > + /* If we allow opening a pidfd via /proc/<pid>, do so. */
> > + if (IS_ERR(pid) && allow_proc)
> > + pid = tgid_pidfd_to_pid(file);
> >
> > - if (IS_ERR(pid)) {
> > + if (IS_ERR(pid)) {
> > + fdput(f);
> > + return pid;
> > + }
> > +
> > + /* Pin pid before we release fd. */
> > + get_pid(pid);
> > + if (flags)
> > + *flags = file->f_flags;
> > fdput(f);
> > +
> > return pid;
> > }
> > -
> > - /* Pin pid before we release fd. */
> > - get_pid(pid);
> > - if (flags)
> > - *flags = file->f_flags;
> > - fdput(f);
> > -
> > - return pid;
> > }
> >
> > /**
> > --
> > 2.47.0
^ permalink raw reply
* Re: [PATCH v6 2/5] pidfd: add PIDFD_SELF_* sentinels to refer to own thread/process
From: Christian Brauner @ 2024-10-28 15:34 UTC (permalink / raw)
To: Lorenzo Stoakes, Oleg Nesterov
Cc: Christian Brauner, Shuah Khan, Liam R . Howlett,
Suren Baghdasaryan, Vlastimil Babka, pedro.falcato,
linux-kselftest, linux-mm, linux-fsdevel, linux-api, linux-kernel,
Oliver Sang, John Hubbard
In-Reply-To: <8eceec08eb64b744b24bf2aa09d4535e77e1ba47.1729926229.git.lorenzo.stoakes@oracle.com>
[-- Attachment #1: Type: text/plain, Size: 8458 bytes --]
On Sat, Oct 26, 2024 at 08:24:58AM +0100, Lorenzo Stoakes wrote:
> It is useful to be able to utilise the pidfd mechanism to reference the
> current thread or process (from a userland point of view - thread group
> leader from the kernel's point of view).
>
> Therefore introduce PIDFD_SELF_THREAD to refer to the current thread, and
> PIDFD_SELF_THREAD_GROUP to refer to the current thread group leader.
>
> For convenience and to avoid confusion from userland's perspective we alias
> these:
>
> * PIDFD_SELF is an alias for PIDFD_SELF_THREAD - This is nearly always what
> the user will want to use, as they would find it surprising if for
> instance fd's were unshared()'d and they wanted to invoke pidfd_getfd()
> and that failed.
>
> * PIDFD_SELF_PROCESS is an alias for PIDFD_SELF_THREAD_GROUP - Most users
> have no concept of thread groups or what a thread group leader is, and
> from userland's perspective and nomenclature this is what userland
> considers to be a process.
>
> Due to the refactoring of the central __pidfd_get_pid() function we can
> implement this functionality centrally, providing the use of this sentinel
> in most functionality which utilises pidfd's.
>
> We need to explicitly adjust kernel_waitid_prepare() to permit this (though
> it wouldn't really make sense to use this there, we provide the ability for
> consistency).
>
> We explicitly disallow use of this in setns(), which would otherwise have
> required explicit custom handling, as it doesn't make sense to set the
> current calling thread to join the namespace of itself.
>
> As the callers of pidfd_get_pid() expect an increased reference count on
> the pid we do so in the self case, reducing churn and avoiding any breakage
> from existing logic which decrements this reference count.
>
> This change implicitly provides PIDFD_SELF_* support in the waitid(P_PIDFS,
> ...), process_madvise(), process_mrelease(), pidfd_send_signal(), and
> pidfd_getfd() system calls.
>
> Things such as polling a pidfs and general fd operations are not supported,
> this strictly provides the sentinel for APIs which explicitly accept a
> pidfd.
>
> Suggested-by: Pedro Falcato <pedro.falcato@gmail.com>
> Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> ---
Currently, a pidfd based system call like pidfd_send_signal() would
simply do:
fdget(pidfd);
// use struct pid
fdput(pidfd);
Where the lifetime of @pid is guaranteed by @file. And in the regular
case where there's only a single thread the file code will avoid taking
a reference. Thus, there's no reference count bump on fdget(), nor a
drop on fdput(), nor a get_pid() or put_pid().
With your patch series you will always cause reference counts on @pid to
be taken for everyone. And I wouldn't be surprised if we get performance
regressions for this.
In one of my earlier mails I had mused about a fdput() like primitive.
What I roughly, hastily, and under the influence of the flu, sketched in
the _completey untested_ patch I appended illustrates roughly what I had
been thinking about.
> include/linux/pid.h | 8 ++++--
> include/uapi/linux/pidfd.h | 10 ++++++++
> kernel/exit.c | 4 ++-
> kernel/nsproxy.c | 1 +
> kernel/pid.c | 51 ++++++++++++++++++++++++--------------
> 5 files changed, 53 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/pid.h b/include/linux/pid.h
> index d466890e1b35..3b2ac7567a88 100644
> --- a/include/linux/pid.h
> +++ b/include/linux/pid.h
> @@ -78,11 +78,15 @@ struct file;
> * __pidfd_get_pid() - Retrieve a pid associated with the specified pidfd.
> *
> * @pidfd: The pidfd whose pid we want, or the fd of a /proc/<pid> file if
> - * @alloc_proc is also set.
> + * @alloc_proc is also set, or PIDFD_SELF_* to refer to the current
> + * thread or thread group leader.
> * @allow_proc: If set, then an fd of a /proc/<pid> file can be passed instead
> * of a pidfd, and this will be used to determine the pid.
> +
> * @flags: Output variable, if non-NULL, then the file->f_flags of the
> - * pidfd will be set here.
> + * pidfd will be set here or If PIDFD_SELF_THREAD is set, this is
> + * set to PIDFD_THREAD, otherwise if PIDFD_SELF_THREAD_GROUP then
> + * this is set to zero.
> *
> * Returns: If successful, the pid associated with the pidfd, otherwise an
> * error.
> diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h
> index 565fc0629fff..6fe1d63b2086 100644
> --- a/include/uapi/linux/pidfd.h
> +++ b/include/uapi/linux/pidfd.h
> @@ -29,4 +29,14 @@
> #define PIDFD_GET_USER_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 9)
> #define PIDFD_GET_UTS_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 10)
>
> +/*
> + * Special sentinel values which can be used to refer to the current thread or
> + * thread group leader (which from a userland perspective is the process).
> + */
> +#define PIDFD_SELF PIDFD_SELF_THREAD
> +#define PIDFD_SELF_PROCESS PIDFD_SELF_THREAD_GROUP
> +
> +#define PIDFD_SELF_THREAD -10000 /* Current thread. */
> +#define PIDFD_SELF_THREAD_GROUP -20000 /* Current thread group leader. */
> +
> #endif /* _UAPI_LINUX_PIDFD_H */
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 619f0014c33b..e4f85ec4ba78 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -71,6 +71,7 @@
> #include <linux/user_events.h>
> #include <linux/uaccess.h>
>
> +#include <uapi/linux/pidfd.h>
> #include <uapi/linux/wait.h>
>
> #include <asm/unistd.h>
> @@ -1739,7 +1740,8 @@ int kernel_waitid_prepare(struct wait_opts *wo, int which, pid_t upid,
> break;
> case P_PIDFD:
> type = PIDTYPE_PID;
> - if (upid < 0)
> + if (upid < 0 && upid != PIDFD_SELF_THREAD &&
> + upid != PIDFD_SELF_THREAD_GROUP)
> return -EINVAL;
>
> pid = pidfd_get_pid(upid, &f_flags);
> diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
> index dc952c3b05af..d239f7eeaa1f 100644
> --- a/kernel/nsproxy.c
> +++ b/kernel/nsproxy.c
> @@ -550,6 +550,7 @@ SYSCALL_DEFINE2(setns, int, fd, int, flags)
> struct nsset nsset = {};
> int err = 0;
>
> + /* If fd is PIDFD_SELF_*, implicitly fail here, as invalid. */
> if (!fd_file(f))
> return -EBADF;
>
> diff --git a/kernel/pid.c b/kernel/pid.c
> index 94c97559e5c5..0a1861b4422c 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -535,33 +535,48 @@ struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
> }
> EXPORT_SYMBOL_GPL(find_ge_pid);
>
> +static struct pid *pidfd_get_pid_self(unsigned int pidfd, unsigned int *flags)
The @flags argument is unused afaict.
> +{
> + bool is_thread = pidfd == PIDFD_SELF_THREAD;
> + enum pid_type type = is_thread ? PIDTYPE_PID : PIDTYPE_TGID;
> + struct pid *pid = *task_pid_ptr(current, type);
> +
> + /* The caller expects an elevated reference count. */
> + get_pid(pid);
> + return pid;
> +}
Fwiw, what you've done here is essentially reimplement the already
existing get_task_pid() helper that you could simply use.
> +
> struct pid *__pidfd_get_pid(unsigned int pidfd, bool allow_proc,
> unsigned int *flags)
> {
> - struct pid *pid;
> - struct fd f = fdget(pidfd);
> - struct file *file = fd_file(f);
> + if (pidfd == PIDFD_SELF_THREAD || pidfd == PIDFD_SELF_THREAD_GROUP) {
> + return pidfd_get_pid_self(pidfd, flags);
> + } else {
I think the else can just go and we can save an indentation level.
> + struct pid *pid;
> + struct fd f = fdget(pidfd);
> + struct file *file = fd_file(f);
>
> - if (!file)
> - return ERR_PTR(-EBADF);
> + if (!file)
> + return ERR_PTR(-EBADF);
>
> - pid = pidfd_pid(file);
> - /* If we allow opening a pidfd via /proc/<pid>, do so. */
> - if (IS_ERR(pid) && allow_proc)
> - pid = tgid_pidfd_to_pid(file);
> + pid = pidfd_pid(file);
> + /* If we allow opening a pidfd via /proc/<pid>, do so. */
> + if (IS_ERR(pid) && allow_proc)
> + pid = tgid_pidfd_to_pid(file);
>
> - if (IS_ERR(pid)) {
> + if (IS_ERR(pid)) {
> + fdput(f);
> + return pid;
> + }
> +
> + /* Pin pid before we release fd. */
> + get_pid(pid);
> + if (flags)
> + *flags = file->f_flags;
> fdput(f);
> +
> return pid;
> }
> -
> - /* Pin pid before we release fd. */
> - get_pid(pid);
> - if (flags)
> - *flags = file->f_flags;
> - fdput(f);
> -
> - return pid;
> }
>
> /**
> --
> 2.47.0
[-- Attachment #2: 0001-UNTESTED-SKETCH-DRAFT.patch --]
[-- Type: text/x-diff, Size: 5457 bytes --]
From 120b45b3900d28880b65b776f7a188cab4b38250 Mon Sep 17 00:00:00 2001
From: Christian Brauner <brauner@kernel.org>
Date: Mon, 28 Oct 2024 15:34:59 +0100
Subject: [PATCH] UNTESTED, SKETCH, DRAFT
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
fs/pidfs.c | 42 +++++++++++++++++++++++++++++++++++++
include/linux/pidfs.h | 29 +++++++++++++++++++++++++
kernel/signal.c | 49 ++++++++++++-------------------------------
3 files changed, 84 insertions(+), 36 deletions(-)
diff --git a/fs/pidfs.c b/fs/pidfs.c
index 80675b6bf884..de7e9e6bbd22 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -22,6 +22,48 @@
#include "internal.h"
#include "mount.h"
+struct pid_fd pidfd_get(int fd)
+{
+ struct fd f;
+ struct pid *pid;
+
+ /* handle PIDFD_SELF_* cases */
+ if (fd < 0) {
+ if (fd == PIDFD_SELF_THREAD)
+ return (struct pid_fd){ .fd = EMPTY_FD, .pid = get_task_pid(current, PIDTYPE_PID) };
+ if (fd == PIDFD_SELF_THREAD_GROUP)
+ return (struct pid_fd){ .fd = EMPTY_FD, .pid = get_task_pid(current, PIDTYPE_TGID) };
+ return (struct pid_fd){ .fd = EMPTY_FD, .pid = ERR_PTR(-EBADF) };
+ }
+
+ /* handle the regular case */
+ f = fdget(fd);
+ if (!fd_file(f))
+ return (struct pid_fd){ .fd = EMPTY_FD, .pid = ERR_PTR(-EBADF) };
+
+ pid = pidfd_pid(fd_file(f));
+ if (IS_ERR(pid)) {
+ fdput(f);
+ return (struct pid_fd) { .fd = EMPTY_FD, .pid = pid };
+ }
+
+ return (struct pid_fd) { .fd = f, pid = pid } ;
+}
+
+void pidfd_put(struct pid_fd fd)
+{
+ /*
+ * Handle PIDFD_SELF_* where the struct pid hasn't been attached
+ * to a file.
+ */
+ if (fd_empty(fd.fd) && pidfd_valid(fd))
+ put_pid(fd.pid);
+
+ /* Can call unconditionally safely. */
+ fdput(fd.fd);
+
+}
+
#ifdef CONFIG_PROC_FS
/**
* pidfd_show_fdinfo - print information about a pidfd
diff --git a/include/linux/pidfs.h b/include/linux/pidfs.h
index 75bdf9807802..ad86b69ee1ea 100644
--- a/include/linux/pidfs.h
+++ b/include/linux/pidfs.h
@@ -2,6 +2,35 @@
#ifndef _LINUX_PID_FS_H
#define _LINUX_PID_FS_H
+#include <linux/file.h>
+#include <linux/cleanup.h>
+
+#define PIDFD_SELF PIDFD_SELF_THREAD
+#define PIDFD_SELF_PROCESS PIDFD_SELF_THREAD_GROUP
+
+#define PIDFD_SELF_THREAD -10000 /* Current thread. */
+#define PIDFD_SELF_THREAD_GROUP -20000 /* Current thread group leader. */
+
+struct pid_fd {
+ struct fd fd;
+ struct pid *pid;
+};
+
+static inline struct pid *pid_fd_pid(struct pid_fd pfd)
+{
+ return pfd.pid;
+}
+
+static inline bool pidfd_valid(struct pid_fd pfd)
+{
+ return !IS_ERR(pid_fd_pid(pfd));
+}
+
+struct pid_fd pidfd_get(int fd);
+void pidfd_put(struct pid_fd fd);
+
+DEFINE_CLASS(pid_fd, struct pid_fd, pidfd_put(_T), pidfd_get(fd), int fd)
+
struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags);
void __init pidfs_init(void);
diff --git a/kernel/signal.c b/kernel/signal.c
index 4344860ffcac..16b10e726038 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -47,6 +47,7 @@
#include <linux/cgroup.h>
#include <linux/audit.h>
#include <linux/sysctl.h>
+#include <linux/pidfs.h>
#include <uapi/linux/pidfd.h>
#define CREATE_TRACE_POINTS
@@ -3875,17 +3876,6 @@ static int copy_siginfo_from_user_any(kernel_siginfo_t *kinfo,
return copy_siginfo_from_user(kinfo, info);
}
-static struct pid *pidfd_to_pid(const struct file *file)
-{
- struct pid *pid;
-
- pid = pidfd_pid(file);
- if (!IS_ERR(pid))
- return pid;
-
- return tgid_pidfd_to_pid(file);
-}
-
#define PIDFD_SEND_SIGNAL_FLAGS \
(PIDFD_SIGNAL_THREAD | PIDFD_SIGNAL_THREAD_GROUP | \
PIDFD_SIGNAL_PROCESS_GROUP)
@@ -3908,7 +3898,6 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
siginfo_t __user *, info, unsigned int, flags)
{
int ret;
- struct fd f;
struct pid *pid;
kernel_siginfo_t kinfo;
enum pid_type type;
@@ -3921,25 +3910,18 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
if (hweight32(flags & PIDFD_SEND_SIGNAL_FLAGS) > 1)
return -EINVAL;
- f = fdget(pidfd);
- if (!fd_file(f))
- return -EBADF;
-
- /* Is this a pidfd? */
- pid = pidfd_to_pid(fd_file(f));
- if (IS_ERR(pid)) {
- ret = PTR_ERR(pid);
- goto err;
- }
+ CLASS(pid_fd, pid_fd)(pidfd);
+ if (!pidfd_valid(pid_fd))
+ return PTR_ERR(pid_fd_pid(pid_fd));
- ret = -EINVAL;
+ pid = pid_fd_pid(pid_fd);
if (!access_pidfd_pidns(pid))
- goto err;
+ return -EINVAL;
switch (flags) {
case 0:
/* Infer scope from the type of pidfd. */
- if (fd_file(f)->f_flags & PIDFD_THREAD)
+ if (pidfd > 0 && fd_file(pid_fd.fd)->f_flags & PIDFD_THREAD)
type = PIDTYPE_PID;
else
type = PIDTYPE_TGID;
@@ -3958,28 +3940,23 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
if (info) {
ret = copy_siginfo_from_user_any(&kinfo, info);
if (unlikely(ret))
- goto err;
+ return ret;
- ret = -EINVAL;
if (unlikely(sig != kinfo.si_signo))
- goto err;
+ return -EINVAL;
/* Only allow sending arbitrary signals to yourself. */
- ret = -EPERM;
if ((task_pid(current) != pid || type > PIDTYPE_TGID) &&
(kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL))
- goto err;
+ return -EPERM;
} else {
prepare_kill_siginfo(sig, &kinfo, type);
}
if (type == PIDTYPE_PGID)
- ret = kill_pgrp_info(sig, &kinfo, pid);
- else
- ret = kill_pid_info_type(sig, &kinfo, pid, type);
-err:
- fdput(f);
- return ret;
+ return kill_pgrp_info(sig, &kinfo, pid);
+
+ return kill_pid_info_type(sig, &kinfo, pid, type);
}
static int
--
2.45.2
^ permalink raw reply related
* [PATCH v4 1/5] mm: pagewalk: add the ability to install PTEs
From: Lorenzo Stoakes @ 2024-10-28 14:13 UTC (permalink / raw)
To: Andrew Morton
Cc: Suren Baghdasaryan, Liam R . Howlett, Matthew Wilcox,
Vlastimil Babka, Paul E . McKenney, Jann Horn, David Hildenbrand,
linux-mm, linux-kernel, Muchun Song, Richard Henderson,
Matt Turner, Thomas Bogendoerfer, James E . J . Bottomley,
Helge Deller, Chris Zankel, Max Filippov, Arnd Bergmann,
linux-alpha, linux-mips, linux-parisc, linux-arch, Shuah Khan,
Christian Brauner, linux-kselftest, Sidhartha Kumar, Jeff Xu,
Christoph Hellwig, linux-api, John Hubbard
In-Reply-To: <cover.1730123433.git.lorenzo.stoakes@oracle.com>
The existing generic pagewalk logic permits the walking of page tables,
invoking callbacks at individual page table levels via user-provided
mm_walk_ops callbacks.
This is useful for traversing existing page table entries, but precludes
the ability to establish new ones.
Existing mechanism for performing a walk which also installs page table
entries if necessary are heavily duplicated throughout the kernel, each
with semantic differences from one another and largely unavailable for use
elsewhere.
Rather than add yet another implementation, we extend the generic pagewalk
logic to enable the installation of page table entries by adding a new
install_pte() callback in mm_walk_ops. If this is specified, then upon
encountering a missing page table entry, we allocate and install a new one
and continue the traversal.
If a THP huge page is encountered at either the PMD or PUD level we split
it only if there are ops->pte_entry() (or ops->pmd_entry at PUD level),
otherwise if there is only an ops->install_pte(), we avoid the unnecessary
split.
We do not support hugetlb at this stage.
If this function returns an error, or an allocation fails during the
operation, we abort the operation altogether. It is up to the caller to
deal appropriately with partially populated page table ranges.
If install_pte() is defined, the semantics of pte_entry() change - this
callback is then only invoked if the entry already exists. This is a useful
property, as it allows a caller to handle existing PTEs while installing
new ones where necessary in the specified range.
If install_pte() is not defined, then there is no functional difference to
this patch, so all existing logic will work precisely as it did before.
As we only permit the installation of PTEs where a mapping does not already
exist there is no need for TLB management, however we do invoke
update_mmu_cache() for architectures which require manual maintenance of
mappings for other CPUs.
We explicitly do not allow the existing page walk API to expose this
feature as it is dangerous and intended for internal mm use only. Therefore
we provide a new walk_page_range_mm() function exposed only to
mm/internal.h.
We take the opportunity to additionally clean up the page walker logic to
be a little easier to follow.{
Reviewed-by: Jann Horn <jannh@google.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
{# modified: mm/pagewalk.c
---
include/linux/pagewalk.h | 18 ++-
mm/internal.h | 6 +
mm/pagewalk.c | 246 ++++++++++++++++++++++++++++-----------
3 files changed, 201 insertions(+), 69 deletions(-)
diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h
index f5eb5a32aeed..9700a29f8afb 100644
--- a/include/linux/pagewalk.h
+++ b/include/linux/pagewalk.h
@@ -25,12 +25,15 @@ enum page_walk_lock {
* this handler is required to be able to handle
* pmd_trans_huge() pmds. They may simply choose to
* split_huge_page() instead of handling it explicitly.
- * @pte_entry: if set, called for each PTE (lowest-level) entry,
- * including empty ones
+ * @pte_entry: if set, called for each PTE (lowest-level) entry
+ * including empty ones, except if @install_pte is set.
+ * If @install_pte is set, @pte_entry is called only for
+ * existing PTEs.
* @pte_hole: if set, called for each hole at all levels,
* depth is -1 if not known, 0:PGD, 1:P4D, 2:PUD, 3:PMD.
* Any folded depths (where PTRS_PER_P?D is equal to 1)
- * are skipped.
+ * are skipped. If @install_pte is specified, this will
+ * not trigger for any populated ranges.
* @hugetlb_entry: if set, called for each hugetlb entry. This hook
* function is called with the vma lock held, in order to
* protect against a concurrent freeing of the pte_t* or
@@ -51,6 +54,13 @@ enum page_walk_lock {
* @pre_vma: if set, called before starting walk on a non-null vma.
* @post_vma: if set, called after a walk on a non-null vma, provided
* that @pre_vma and the vma walk succeeded.
+ * @install_pte: if set, missing page table entries are installed and
+ * thus all levels are always walked in the specified
+ * range. This callback is then invoked at the PTE level
+ * (having split any THP pages prior), providing the PTE to
+ * install. If allocations fail, the walk is aborted. This
+ * operation is only available for userland memory. Not
+ * usable for hugetlb ranges.
*
* p?d_entry callbacks are called even if those levels are folded on a
* particular architecture/configuration.
@@ -76,6 +86,8 @@ struct mm_walk_ops {
int (*pre_vma)(unsigned long start, unsigned long end,
struct mm_walk *walk);
void (*post_vma)(struct mm_walk *walk);
+ int (*install_pte)(unsigned long addr, unsigned long next,
+ pte_t *ptep, struct mm_walk *walk);
enum page_walk_lock walk_lock;
};
diff --git a/mm/internal.h b/mm/internal.h
index c4c884d61024..41b60204b059 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -12,6 +12,7 @@
#include <linux/mm.h>
#include <linux/mm_inline.h>
#include <linux/pagemap.h>
+#include <linux/pagewalk.h>
#include <linux/rmap.h>
#include <linux/swap.h>
#include <linux/swapops.h>
@@ -1502,4 +1503,9 @@ static inline void accept_page(struct page *page)
}
#endif /* CONFIG_UNACCEPTED_MEMORY */
+/* pagewalk.c */
+int walk_page_range_mm(struct mm_struct *mm, unsigned long start,
+ unsigned long end, const struct mm_walk_ops *ops,
+ void *private);
+
#endif /* __MM_INTERNAL_H */
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 5f9f01532e67..e478777c86e1 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -3,9 +3,14 @@
#include <linux/highmem.h>
#include <linux/sched.h>
#include <linux/hugetlb.h>
+#include <linux/mmu_context.h>
#include <linux/swap.h>
#include <linux/swapops.h>
+#include <asm/tlbflush.h>
+
+#include "internal.h"
+
/*
* We want to know the real level where a entry is located ignoring any
* folding of levels which may be happening. For example if p4d is folded then
@@ -29,9 +34,23 @@ static int walk_pte_range_inner(pte_t *pte, unsigned long addr,
int err = 0;
for (;;) {
- err = ops->pte_entry(pte, addr, addr + PAGE_SIZE, walk);
- if (err)
- break;
+ if (ops->install_pte && pte_none(ptep_get(pte))) {
+ pte_t new_pte;
+
+ err = ops->install_pte(addr, addr + PAGE_SIZE, &new_pte,
+ walk);
+ if (err)
+ break;
+
+ set_pte_at(walk->mm, addr, pte, new_pte);
+ /* Non-present before, so for arches that need it. */
+ if (!WARN_ON_ONCE(walk->no_vma))
+ update_mmu_cache(walk->vma, addr, pte);
+ } else {
+ err = ops->pte_entry(pte, addr, addr + PAGE_SIZE, walk);
+ if (err)
+ break;
+ }
if (addr >= end - PAGE_SIZE)
break;
addr += PAGE_SIZE;
@@ -81,6 +100,8 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
pmd_t *pmd;
unsigned long next;
const struct mm_walk_ops *ops = walk->ops;
+ bool has_handler = ops->pte_entry;
+ bool has_install = ops->install_pte;
int err = 0;
int depth = real_depth(3);
@@ -89,11 +110,14 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
again:
next = pmd_addr_end(addr, end);
if (pmd_none(*pmd)) {
- if (ops->pte_hole)
+ if (has_install)
+ err = __pte_alloc(walk->mm, pmd);
+ else if (ops->pte_hole)
err = ops->pte_hole(addr, next, depth, walk);
if (err)
break;
- continue;
+ if (!has_install)
+ continue;
}
walk->action = ACTION_SUBTREE;
@@ -109,18 +133,25 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
if (walk->action == ACTION_AGAIN)
goto again;
-
- /*
- * Check this here so we only break down trans_huge
- * pages when we _need_ to
- */
- if ((!walk->vma && (pmd_leaf(*pmd) || !pmd_present(*pmd))) ||
- walk->action == ACTION_CONTINUE ||
- !(ops->pte_entry))
+ if (walk->action == ACTION_CONTINUE)
continue;
+ if (!has_handler) { /* No handlers for lower page tables. */
+ if (!has_install)
+ continue; /* Nothing to do. */
+ /*
+ * We are ONLY installing, so avoid unnecessarily
+ * splitting a present huge page.
+ */
+ if (pmd_present(*pmd) &&
+ (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)))
+ continue;
+ }
+
if (walk->vma)
split_huge_pmd(walk->vma, pmd, addr);
+ else if (pmd_leaf(*pmd) || !pmd_present(*pmd))
+ continue; /* Nothing to do. */
err = walk_pte_range(pmd, addr, next, walk);
if (err)
@@ -140,6 +171,8 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
pud_t *pud;
unsigned long next;
const struct mm_walk_ops *ops = walk->ops;
+ bool has_handler = ops->pmd_entry || ops->pte_entry;
+ bool has_install = ops->install_pte;
int err = 0;
int depth = real_depth(2);
@@ -148,11 +181,14 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
again:
next = pud_addr_end(addr, end);
if (pud_none(*pud)) {
- if (ops->pte_hole)
+ if (has_install)
+ err = __pmd_alloc(walk->mm, pud, addr);
+ else if (ops->pte_hole)
err = ops->pte_hole(addr, next, depth, walk);
if (err)
break;
- continue;
+ if (!has_install)
+ continue;
}
walk->action = ACTION_SUBTREE;
@@ -164,14 +200,26 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
if (walk->action == ACTION_AGAIN)
goto again;
-
- if ((!walk->vma && (pud_leaf(*pud) || !pud_present(*pud))) ||
- walk->action == ACTION_CONTINUE ||
- !(ops->pmd_entry || ops->pte_entry))
+ if (walk->action == ACTION_CONTINUE)
continue;
+ if (!has_handler) { /* No handlers for lower page tables. */
+ if (!has_install)
+ continue; /* Nothing to do. */
+ /*
+ * We are ONLY installing, so avoid unnecessarily
+ * splitting a present huge page.
+ */
+ if (pud_present(*pud) &&
+ (pud_trans_huge(*pud) || pud_devmap(*pud)))
+ continue;
+ }
+
if (walk->vma)
split_huge_pud(walk->vma, pud, addr);
+ else if (pud_leaf(*pud) || !pud_present(*pud))
+ continue; /* Nothing to do. */
+
if (pud_none(*pud))
goto again;
@@ -189,6 +237,8 @@ static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
p4d_t *p4d;
unsigned long next;
const struct mm_walk_ops *ops = walk->ops;
+ bool has_handler = ops->pud_entry || ops->pmd_entry || ops->pte_entry;
+ bool has_install = ops->install_pte;
int err = 0;
int depth = real_depth(1);
@@ -196,18 +246,21 @@ static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
do {
next = p4d_addr_end(addr, end);
if (p4d_none_or_clear_bad(p4d)) {
- if (ops->pte_hole)
+ if (has_install)
+ err = __pud_alloc(walk->mm, p4d, addr);
+ else if (ops->pte_hole)
err = ops->pte_hole(addr, next, depth, walk);
if (err)
break;
- continue;
+ if (!has_install)
+ continue;
}
if (ops->p4d_entry) {
err = ops->p4d_entry(p4d, addr, next, walk);
if (err)
break;
}
- if (ops->pud_entry || ops->pmd_entry || ops->pte_entry)
+ if (has_handler || has_install)
err = walk_pud_range(p4d, addr, next, walk);
if (err)
break;
@@ -222,6 +275,9 @@ static int walk_pgd_range(unsigned long addr, unsigned long end,
pgd_t *pgd;
unsigned long next;
const struct mm_walk_ops *ops = walk->ops;
+ bool has_handler = ops->p4d_entry || ops->pud_entry || ops->pmd_entry ||
+ ops->pte_entry;
+ bool has_install = ops->install_pte;
int err = 0;
if (walk->pgd)
@@ -231,18 +287,21 @@ static int walk_pgd_range(unsigned long addr, unsigned long end,
do {
next = pgd_addr_end(addr, end);
if (pgd_none_or_clear_bad(pgd)) {
- if (ops->pte_hole)
+ if (has_install)
+ err = __p4d_alloc(walk->mm, pgd, addr);
+ else if (ops->pte_hole)
err = ops->pte_hole(addr, next, 0, walk);
if (err)
break;
- continue;
+ if (!has_install)
+ continue;
}
if (ops->pgd_entry) {
err = ops->pgd_entry(pgd, addr, next, walk);
if (err)
break;
}
- if (ops->p4d_entry || ops->pud_entry || ops->pmd_entry || ops->pte_entry)
+ if (has_handler || has_install)
err = walk_p4d_range(pgd, addr, next, walk);
if (err)
break;
@@ -334,6 +393,11 @@ static int __walk_page_range(unsigned long start, unsigned long end,
int err = 0;
struct vm_area_struct *vma = walk->vma;
const struct mm_walk_ops *ops = walk->ops;
+ bool is_hugetlb = is_vm_hugetlb_page(vma);
+
+ /* We do not support hugetlb PTE installation. */
+ if (ops->install_pte && is_hugetlb)
+ return -EINVAL;
if (ops->pre_vma) {
err = ops->pre_vma(start, end, walk);
@@ -341,7 +405,7 @@ static int __walk_page_range(unsigned long start, unsigned long end,
return err;
}
- if (is_vm_hugetlb_page(vma)) {
+ if (is_hugetlb) {
if (ops->hugetlb_entry)
err = walk_hugetlb_range(start, end, walk);
} else
@@ -380,47 +444,14 @@ static inline void process_vma_walk_lock(struct vm_area_struct *vma,
#endif
}
-/**
- * walk_page_range - walk page table with caller specific callbacks
- * @mm: mm_struct representing the target process of page table walk
- * @start: start address of the virtual address range
- * @end: end address of the virtual address range
- * @ops: operation to call during the walk
- * @private: private data for callbacks' usage
- *
- * Recursively walk the page table tree of the process represented by @mm
- * within the virtual address range [@start, @end). During walking, we can do
- * some caller-specific works for each entry, by setting up pmd_entry(),
- * pte_entry(), and/or hugetlb_entry(). If you don't set up for some of these
- * callbacks, the associated entries/pages are just ignored.
- * The return values of these callbacks are commonly defined like below:
- *
- * - 0 : succeeded to handle the current entry, and if you don't reach the
- * end address yet, continue to walk.
- * - >0 : succeeded to handle the current entry, and return to the caller
- * with caller specific value.
- * - <0 : failed to handle the current entry, and return to the caller
- * with error code.
- *
- * Before starting to walk page table, some callers want to check whether
- * they really want to walk over the current vma, typically by checking
- * its vm_flags. walk_page_test() and @ops->test_walk() are used for this
- * purpose.
- *
- * If operations need to be staged before and committed after a vma is walked,
- * there are two callbacks, pre_vma() and post_vma(). Note that post_vma(),
- * since it is intended to handle commit-type operations, can't return any
- * errors.
- *
- * struct mm_walk keeps current values of some common data like vma and pmd,
- * which are useful for the access from callbacks. If you want to pass some
- * caller-specific data to callbacks, @private should be helpful.
+/*
+ * See the comment for walk_page_range(), this performs the heavy lifting of the
+ * operation, only sets no restrictions on how the walk proceeds.
*
- * Locking:
- * Callers of walk_page_range() and walk_page_vma() should hold @mm->mmap_lock,
- * because these function traverse vma list and/or access to vma's data.
+ * We usually restrict the ability to install PTEs, but this functionality is
+ * available to internal memory management code and provided in mm/internal.h.
*/
-int walk_page_range(struct mm_struct *mm, unsigned long start,
+int walk_page_range_mm(struct mm_struct *mm, unsigned long start,
unsigned long end, const struct mm_walk_ops *ops,
void *private)
{
@@ -479,6 +510,80 @@ int walk_page_range(struct mm_struct *mm, unsigned long start,
return err;
}
+/*
+ * Determine if the walk operations specified are permitted to be used for a
+ * page table walk.
+ *
+ * This check is performed on all functions which are parameterised by walk
+ * operations and exposed in include/linux/pagewalk.h.
+ *
+ * Internal memory management code can use the walk_page_range_mm() function to
+ * be able to use all page walking operations.
+ */
+static bool check_ops_valid(const struct mm_walk_ops *ops)
+{
+ /*
+ * The installation of PTEs is solely under the control of memory
+ * management logic and subject to many subtle locking, security and
+ * cache considerations so we cannot permit other users to do so, and
+ * certainly not for exported symbols.
+ */
+ if (ops->install_pte)
+ return false;
+
+ return true;
+}
+
+/**
+ * walk_page_range - walk page table with caller specific callbacks
+ * @mm: mm_struct representing the target process of page table walk
+ * @start: start address of the virtual address range
+ * @end: end address of the virtual address range
+ * @ops: operation to call during the walk
+ * @private: private data for callbacks' usage
+ *
+ * Recursively walk the page table tree of the process represented by @mm
+ * within the virtual address range [@start, @end). During walking, we can do
+ * some caller-specific works for each entry, by setting up pmd_entry(),
+ * pte_entry(), and/or hugetlb_entry(). If you don't set up for some of these
+ * callbacks, the associated entries/pages are just ignored.
+ * The return values of these callbacks are commonly defined like below:
+ *
+ * - 0 : succeeded to handle the current entry, and if you don't reach the
+ * end address yet, continue to walk.
+ * - >0 : succeeded to handle the current entry, and return to the caller
+ * with caller specific value.
+ * - <0 : failed to handle the current entry, and return to the caller
+ * with error code.
+ *
+ * Before starting to walk page table, some callers want to check whether
+ * they really want to walk over the current vma, typically by checking
+ * its vm_flags. walk_page_test() and @ops->test_walk() are used for this
+ * purpose.
+ *
+ * If operations need to be staged before and committed after a vma is walked,
+ * there are two callbacks, pre_vma() and post_vma(). Note that post_vma(),
+ * since it is intended to handle commit-type operations, can't return any
+ * errors.
+ *
+ * struct mm_walk keeps current values of some common data like vma and pmd,
+ * which are useful for the access from callbacks. If you want to pass some
+ * caller-specific data to callbacks, @private should be helpful.
+ *
+ * Locking:
+ * Callers of walk_page_range() and walk_page_vma() should hold @mm->mmap_lock,
+ * because these function traverse vma list and/or access to vma's data.
+ */
+int walk_page_range(struct mm_struct *mm, unsigned long start,
+ unsigned long end, const struct mm_walk_ops *ops,
+ void *private)
+{
+ if (!check_ops_valid(ops))
+ return -EINVAL;
+
+ return walk_page_range_mm(mm, start, end, ops, private);
+}
+
/**
* walk_page_range_novma - walk a range of pagetables not backed by a vma
* @mm: mm_struct representing the target process of page table walk
@@ -494,7 +599,7 @@ int walk_page_range(struct mm_struct *mm, unsigned long start,
* walking the kernel pages tables or page tables for firmware.
*
* Note: Be careful to walk the kernel pages tables, the caller may be need to
- * take other effective approache (mmap lock may be insufficient) to prevent
+ * take other effective approaches (mmap lock may be insufficient) to prevent
* the intermediate kernel page tables belonging to the specified address range
* from being freed (e.g. memory hot-remove).
*/
@@ -513,6 +618,8 @@ int walk_page_range_novma(struct mm_struct *mm, unsigned long start,
if (start >= end || !walk.mm)
return -EINVAL;
+ if (!check_ops_valid(ops))
+ return -EINVAL;
/*
* 1) For walking the user virtual address space:
@@ -556,6 +663,8 @@ int walk_page_range_vma(struct vm_area_struct *vma, unsigned long start,
return -EINVAL;
if (start < vma->vm_start || end > vma->vm_end)
return -EINVAL;
+ if (!check_ops_valid(ops))
+ return -EINVAL;
process_mm_walk_lock(walk.mm, ops->walk_lock);
process_vma_walk_lock(vma, ops->walk_lock);
@@ -574,6 +683,8 @@ int walk_page_vma(struct vm_area_struct *vma, const struct mm_walk_ops *ops,
if (!walk.mm)
return -EINVAL;
+ if (!check_ops_valid(ops))
+ return -EINVAL;
process_mm_walk_lock(walk.mm, ops->walk_lock);
process_vma_walk_lock(vma, ops->walk_lock);
@@ -623,6 +734,9 @@ int walk_page_mapping(struct address_space *mapping, pgoff_t first_index,
unsigned long start_addr, end_addr;
int err = 0;
+ if (!check_ops_valid(ops))
+ return -EINVAL;
+
lockdep_assert_held(&mapping->i_mmap_rwsem);
vma_interval_tree_foreach(vma, &mapping->i_mmap, first_index,
first_index + nr - 1) {
--
2.47.0
^ permalink raw reply related
* [PATCH v4 0/5] implement lightweight guard pages
From: Lorenzo Stoakes @ 2024-10-28 14:13 UTC (permalink / raw)
To: Andrew Morton
Cc: Suren Baghdasaryan, Liam R . Howlett, Matthew Wilcox,
Vlastimil Babka, Paul E . McKenney, Jann Horn, David Hildenbrand,
linux-mm, linux-kernel, Muchun Song, Richard Henderson,
Matt Turner, Thomas Bogendoerfer, James E . J . Bottomley,
Helge Deller, Chris Zankel, Max Filippov, Arnd Bergmann,
linux-alpha, linux-mips, linux-parisc, linux-arch, Shuah Khan,
Christian Brauner, linux-kselftest, Sidhartha Kumar, Jeff Xu,
Christoph Hellwig, linux-api, John Hubbard
Userland library functions such as allocators and threading implementations
often require regions of memory to act as 'guard pages' - mappings which,
when accessed, result in a fatal signal being sent to the accessing
process.
The current means by which these are implemented is via a PROT_NONE mmap()
mapping, which provides the required semantics however incur an overhead of
a VMA for each such region.
With a great many processes and threads, this can rapidly add up and incur
a significant memory penalty. It also has the added problem of preventing
merges that might otherwise be permitted.
This series takes a different approach - an idea suggested by Vlasimil
Babka (and before him David Hildenbrand and Jann Horn - perhaps more - the
provenance becomes a little tricky to ascertain after this - please forgive
any omissions!) - rather than locating the guard pages at the VMA layer,
instead placing them in page tables mapping the required ranges.
Early testing of the prototype version of this code suggests a 5 times
speed up in memory mapping invocations (in conjunction with use of
process_madvise()) and a 13% reduction in VMAs on an entirely idle android
system and unoptimised code.
We expect with optimisation and a loaded system with a larger number of
guard pages this could significantly increase, but in any case these
numbers are encouraging.
This way, rather than having separate VMAs specifying which parts of a
range are guard pages, instead we have a VMA spanning the entire range of
memory a user is permitted to access and including ranges which are to be
'guarded'.
After mapping this, a user can specify which parts of the range should
result in a fatal signal when accessed.
By restricting the ability to specify guard pages to memory mapped by
existing VMAs, we can rely on the mappings being torn down when the
mappings are ultimately unmapped and everything works simply as if the
memory were not faulted in, from the point of view of the containing VMAs.
This mechanism in effect poisons memory ranges similar to hardware memory
poisoning, only it is an entirely software-controlled form of poisoning.
The mechanism is implemented via madvise() behaviour - MADV_GUARD_INSTALL
which installs page table-level guard page markers - and
MADV_GUARD_REMOVE - which clears them.
Guard markers can be installed across multiple VMAs and any existing
mappings will be cleared, that is zapped, before installing the guard page
markers in the page tables.
There is no concept of 'nested' guard markers, multiple attempts to install
guard markers in a range will, after the first attempt, have no effect.
Importantly, removing guard markers over a range that contains both guard
markers and ordinary backed memory has no effect on anything but the guard
markers (including leaving huge pages un-split), so a user can safely
remove guard markers over a range of memory leaving the rest intact.
The actual mechanism by which the page table entries are specified makes
use of existing logic - PTE markers, which are used for the userfaultfd
UFFDIO_POISON mechanism.
Unfortunately PTE_MARKER_POISONED is not suited for the guard page
mechanism as it results in VM_FAULT_HWPOISON semantics in the fault
handler, so we add our own specific PTE_MARKER_GUARD and adapt existing
logic to handle it.
We also extend the generic page walk mechanism to allow for installation of
PTEs (carefully restricted to memory management logic only to prevent
unwanted abuse).
We ensure that zapping performed by MADV_DONTNEED and MADV_FREE do not
remove guard markers, nor does forking (except when VM_WIPEONFORK is
specified for a VMA which implies a total removal of memory
characteristics).
It's important to note that the guard page implementation is emphatically
NOT a security feature, so a user can remove the markers if they wish. We
simply implement it in such a way as to provide the least surprising
behaviour.
An extensive set of self-tests are provided which ensure behaviour is as
expected and additionally self-documents expected behaviour of guard
ranges.
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Suggested-by: Jann Horn <jannh@google.com>
Suggested-by: David Hildenbrand <david@redhat.com>
v4
* Use restart_syscall() to implement -ERESTARTNOINTR to ensure correctly
handled by kernel - tested this code path and confirmed it works
correctly. Thanks to Vlastimil for pointing this issue out!
* Updated the vector_madvise() handler to not unnecessarily invoke
cond_resched() as suggested by Vlastimil.
* Updated guard page tests to add a test for a vector operation which
overwrites existing mappings. Tested this against the -ERESTARTNOINTR
case and confirmed working.
* Improved page walk logic further, refactoring handling logic as suggested
by Vlastimil.
* Moved MAX_MADVISE_GUARD_RETRIES to mm/madvise.c as suggested by Vlastimil.
v3
* Cleaned up mm/pagewalk.c logic a bit to make things clearer, as suggested
by Vlastiml.
* Explicitly avoid splitting THP on PTE installation, as suggested by
Vlastimil. Note this has no impact on the guard pages logic, which has
page table entry handlers at PUD, PMD and PTE level.
* Added WARN_ON_ONCE() to mm/hugetlb.c path where we don't expect a guard
marker, as suggested by Vlastimil.
* Reverted change to is_poisoned_swp_entry() to exclude guard pages which
has the effect of MADV_FREE _not_ clearing guard pages. After discussion
with Vlastimil, it became apparent that the ability to 'cancel' the
freeing operation by writing to the mapping after having issued an
MADV_FREE would mean that we would risk unexpected behaviour should the
guard pages be removed, so we now do not remove markers here at all.
* Added comment to PTE_MARKER_GUARD to highlight that memory tagged with
the marker behaves as if it were a region mapped PROT_NONE, as
highlighted by David.
* Rename poison -> install, unpoison -> remove (i.e. MADV_GUARD_INSTALL /
MADV_GUARD_REMOVE over MADV_GUARD_POISON / MADV_GUARD_REMOVE) at the
request of David and John who both find the poison analogy
confusing/overloaded.
* After a lot of discussion, replace the looping behaviour should page
faults race with guard page installation with a modest reattempt followed
by returning -ERESTARTNOINTR to have the operation abort and re-enter,
relieving lock contention and avoiding the possibility of allowing a
malicious sandboxed process to impact the mmap lock or stall the overall
process more than necessary, as suggested by Jann and Vlastimil having
raised the issue.
* Adjusted the page table walker so a populated huge PUD or PMD is
correctly treated as being populated, necessitating a zap. In v2 we
incorrectly skipped over these, which would cause the logic to wrongly
proceed as if nothing were populated and the install succeeded.
Instead, explicitly check to see if a huge page - if so, do not split but
rather abort the operation and let zap take care of things.
* Updated the guard remove logic to not unnecessarily split huge pages
either.
* Added a debug check to assert that the number of installed PTEs matches
expectation, accounting for any existing guard pages.
* Adapted vector_madvise() used by the process_madvise() system call to
handle -ERESTARTNOINTR correctly.
https://lore.kernel.org/all/cover.1729699916.git.lorenzo.stoakes@oracle.com/
v2
* The macros in kselftest_harness.h seem to be broken - __EXPECT() is
terminated by '} while (0); OPTIONAL_HANDLER(_assert)' meaning it is not
safe in single line if / else or for /which blocks, however working
around this results in checkpatch producing invalid warnings, as reported
by Shuah.
* Fixing these macros is out of scope for this series, so compromise and
instead rewrite test blocks so as to use multiple lines by separating out
a decl in most cases. This has the side effect of, for the most part,
making things more readable.
* Heavily document the use of the volatile keyword - we can't avoid
checkpatch complaining about this, so we explain it, as reported by
Shuah.
* Updated commit message to highlight that we skip tests we lack
permissions for, as reported by Shuah.
* Replaced a perror() with ksft_exit_fail_perror(), as reported by Shuah.
* Added user friendly messages to cases where tests are skipped due to lack
of permissions, as reported by Shuah.
* Update the tool header to include the new MADV_GUARD_POISON/UNPOISON
defines and directly include asm-generic/mman.h to get the
platform-neutral versions to ensure we import them.
* Finally fixed Vlastimil's email address in Suggested-by tags from suze to
suse, as reported by Vlastimil.
* Added linux-api to cc list, as reported by Vlastimil.
https://lore.kernel.org/all/cover.1729440856.git.lorenzo.stoakes@oracle.com/
v1
* Un-RFC'd as appears no major objections to approach but rather debate on
implementation.
* Fixed issue with arches which need mmu_context.h and
tlbfush.h. header imports in pagewalker logic to be able to use
update_mmu_cache() as reported by the kernel test bot.
* Added comments in page walker logic to clarify who can use
ops->install_pte and why as well as adding a check_ops_valid() helper
function, as suggested by Christoph.
* Pass false in full parameter in pte_clear_not_present_full() as suggested
by Jann.
* Stopped erroneously requiring a write lock for the poison operation as
suggested by Jann and Suren.
* Moved anon_vma_prepare() to the start of madvise_guard_poison() to be
consistent with how this is used elsewhere in the kernel as suggested by
Jann.
* Avoid returning -EAGAIN if we are raced on page faults, just keep looping
and duck out if a fatal signal is pending or a conditional reschedule is
needed, as suggested by Jann.
* Avoid needlessly splitting huge PUDs and PMDs by specifying
ACTION_CONTINUE, as suggested by Jann.
https://lore.kernel.org/all/cover.1729196871.git.lorenzo.stoakes@oracle.com/
RFC
https://lore.kernel.org/all/cover.1727440966.git.lorenzo.stoakes@oracle.com/
Lorenzo Stoakes (5):
mm: pagewalk: add the ability to install PTEs
mm: add PTE_MARKER_GUARD PTE marker
mm: madvise: implement lightweight guard page mechanism
tools: testing: update tools UAPI header for mman-common.h
selftests/mm: add self tests for guard page feature
arch/alpha/include/uapi/asm/mman.h | 3 +
arch/mips/include/uapi/asm/mman.h | 3 +
arch/parisc/include/uapi/asm/mman.h | 3 +
arch/xtensa/include/uapi/asm/mman.h | 3 +
include/linux/mm_inline.h | 2 +-
include/linux/pagewalk.h | 18 +-
include/linux/swapops.h | 24 +-
include/uapi/asm-generic/mman-common.h | 3 +
mm/hugetlb.c | 4 +
mm/internal.h | 6 +
mm/madvise.c | 239 ++++
mm/memory.c | 18 +-
mm/mprotect.c | 6 +-
mm/mseal.c | 1 +
mm/pagewalk.c | 246 +++-
tools/include/uapi/asm-generic/mman-common.h | 3 +
tools/testing/selftests/mm/.gitignore | 1 +
tools/testing/selftests/mm/Makefile | 1 +
tools/testing/selftests/mm/guard-pages.c | 1243 ++++++++++++++++++
19 files changed, 1751 insertions(+), 76 deletions(-)
create mode 100644 tools/testing/selftests/mm/guard-pages.c
--
2.47.0
^ permalink raw reply
* [PATCH v4 2/5] mm: add PTE_MARKER_GUARD PTE marker
From: Lorenzo Stoakes @ 2024-10-28 14:13 UTC (permalink / raw)
To: Andrew Morton
Cc: Suren Baghdasaryan, Liam R . Howlett, Matthew Wilcox,
Vlastimil Babka, Paul E . McKenney, Jann Horn, David Hildenbrand,
linux-mm, linux-kernel, Muchun Song, Richard Henderson,
Matt Turner, Thomas Bogendoerfer, James E . J . Bottomley,
Helge Deller, Chris Zankel, Max Filippov, Arnd Bergmann,
linux-alpha, linux-mips, linux-parisc, linux-arch, Shuah Khan,
Christian Brauner, linux-kselftest, Sidhartha Kumar, Jeff Xu,
Christoph Hellwig, linux-api, John Hubbard
In-Reply-To: <cover.1730123433.git.lorenzo.stoakes@oracle.com>
Add a new PTE marker that results in any access causing the accessing
process to segfault.
This is preferable to PTE_MARKER_POISONED, which results in the same
handling as hardware poisoned memory, and is thus undesirable for cases
where we simply wish to 'soft' poison a range.
This is in preparation for implementing the ability to specify guard pages
at the page table level, i.e. ranges that, when accessed, should cause
process termination.
Additionally, rename zap_drop_file_uffd_wp() to zap_drop_markers() - the
function checks the ZAP_FLAG_DROP_MARKER flag so naming it for this single
purpose was simply incorrect.
We then reuse the same logic to determine whether a zap should clear a
guard entry - this should only be performed on teardown and never on
MADV_DONTNEED or MADV_FREE.
We additionally add a WARN_ON_ONCE() in hugetlb logic should a guard marker
be encountered there, as we explicitly do not support this operation and
this should not occur.
Acked-by: Vlastimil Babka <vbabkba@suse.cz>
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
include/linux/mm_inline.h | 2 +-
include/linux/swapops.h | 24 +++++++++++++++++++++++-
mm/hugetlb.c | 4 ++++
mm/memory.c | 18 +++++++++++++++---
mm/mprotect.c | 6 ++++--
5 files changed, 47 insertions(+), 7 deletions(-)
diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index 355cf46a01a6..1b6a917fffa4 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -544,7 +544,7 @@ static inline pte_marker copy_pte_marker(
{
pte_marker srcm = pte_marker_get(entry);
/* Always copy error entries. */
- pte_marker dstm = srcm & PTE_MARKER_POISONED;
+ pte_marker dstm = srcm & (PTE_MARKER_POISONED | PTE_MARKER_GUARD);
/* Only copy PTE markers if UFFD register matches. */
if ((srcm & PTE_MARKER_UFFD_WP) && userfaultfd_wp(dst_vma))
diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index cb468e418ea1..96f26e29fefe 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -426,9 +426,19 @@ typedef unsigned long pte_marker;
* "Poisoned" here is meant in the very general sense of "future accesses are
* invalid", instead of referring very specifically to hardware memory errors.
* This marker is meant to represent any of various different causes of this.
+ *
+ * Note that, when encountered by the faulting logic, PTEs with this marker will
+ * result in VM_FAULT_HWPOISON and thus regardless trigger hardware memory error
+ * logic.
*/
#define PTE_MARKER_POISONED BIT(1)
-#define PTE_MARKER_MASK (BIT(2) - 1)
+/*
+ * Indicates that, on fault, this PTE will case a SIGSEGV signal to be
+ * sent. This means guard markers behave in effect as if the region were mapped
+ * PROT_NONE, rather than if they were a memory hole or equivalent.
+ */
+#define PTE_MARKER_GUARD BIT(2)
+#define PTE_MARKER_MASK (BIT(3) - 1)
static inline swp_entry_t make_pte_marker_entry(pte_marker marker)
{
@@ -464,6 +474,18 @@ static inline int is_poisoned_swp_entry(swp_entry_t entry)
{
return is_pte_marker_entry(entry) &&
(pte_marker_get(entry) & PTE_MARKER_POISONED);
+
+}
+
+static inline swp_entry_t make_guard_swp_entry(void)
+{
+ return make_pte_marker_entry(PTE_MARKER_GUARD);
+}
+
+static inline int is_guard_swp_entry(swp_entry_t entry)
+{
+ return is_pte_marker_entry(entry) &&
+ (pte_marker_get(entry) & PTE_MARKER_GUARD);
}
/*
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 906294ac85dc..2c8c5da0f5d3 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6353,6 +6353,10 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
ret = VM_FAULT_HWPOISON_LARGE |
VM_FAULT_SET_HINDEX(hstate_index(h));
goto out_mutex;
+ } else if (WARN_ON_ONCE(marker & PTE_MARKER_GUARD)) {
+ /* This isn't supported in hugetlb. */
+ ret = VM_FAULT_SIGSEGV;
+ goto out_mutex;
}
}
diff --git a/mm/memory.c b/mm/memory.c
index 2d32023d4eb8..75c2dfd04f72 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1455,7 +1455,7 @@ static inline bool should_zap_folio(struct zap_details *details,
return !folio_test_anon(folio);
}
-static inline bool zap_drop_file_uffd_wp(struct zap_details *details)
+static inline bool zap_drop_markers(struct zap_details *details)
{
if (!details)
return false;
@@ -1476,7 +1476,7 @@ zap_install_uffd_wp_if_needed(struct vm_area_struct *vma,
if (vma_is_anonymous(vma))
return;
- if (zap_drop_file_uffd_wp(details))
+ if (zap_drop_markers(details))
return;
for (;;) {
@@ -1671,7 +1671,15 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
* drop the marker if explicitly requested.
*/
if (!vma_is_anonymous(vma) &&
- !zap_drop_file_uffd_wp(details))
+ !zap_drop_markers(details))
+ continue;
+ } else if (is_guard_swp_entry(entry)) {
+ /*
+ * Ordinary zapping should not remove guard PTE
+ * markers. Only do so if we should remove PTE markers
+ * in general.
+ */
+ if (!zap_drop_markers(details))
continue;
} else if (is_hwpoison_entry(entry) ||
is_poisoned_swp_entry(entry)) {
@@ -4003,6 +4011,10 @@ static vm_fault_t handle_pte_marker(struct vm_fault *vmf)
if (marker & PTE_MARKER_POISONED)
return VM_FAULT_HWPOISON;
+ /* Hitting a guard page is always a fatal condition. */
+ if (marker & PTE_MARKER_GUARD)
+ return VM_FAULT_SIGSEGV;
+
if (pte_marker_entry_uffd_wp(entry))
return pte_marker_handle_uffd_wp(vmf);
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 6f450af3252e..516b1d847e2c 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -236,9 +236,11 @@ static long change_pte_range(struct mmu_gather *tlb,
} else if (is_pte_marker_entry(entry)) {
/*
* Ignore error swap entries unconditionally,
- * because any access should sigbus anyway.
+ * because any access should sigbus/sigsegv
+ * anyway.
*/
- if (is_poisoned_swp_entry(entry))
+ if (is_poisoned_swp_entry(entry) ||
+ is_guard_swp_entry(entry))
continue;
/*
* If this is uffd-wp pte marker and we'd like
--
2.47.0
^ permalink raw reply related
* [PATCH v4 5/5] selftests/mm: add self tests for guard page feature
From: Lorenzo Stoakes @ 2024-10-28 14:13 UTC (permalink / raw)
To: Andrew Morton
Cc: Suren Baghdasaryan, Liam R . Howlett, Matthew Wilcox,
Vlastimil Babka, Paul E . McKenney, Jann Horn, David Hildenbrand,
linux-mm, linux-kernel, Muchun Song, Richard Henderson,
Matt Turner, Thomas Bogendoerfer, James E . J . Bottomley,
Helge Deller, Chris Zankel, Max Filippov, Arnd Bergmann,
linux-alpha, linux-mips, linux-parisc, linux-arch, Shuah Khan,
Christian Brauner, linux-kselftest, Sidhartha Kumar, Jeff Xu,
Christoph Hellwig, linux-api, John Hubbard
In-Reply-To: <cover.1730123433.git.lorenzo.stoakes@oracle.com>
Utilise the kselftest harmness to implement tests for the guard page
implementation.
We start by implement basic tests asserting that guard pages can be
installed, removed and that touching guard pages result in SIGSEGV. We also
assert that, in removing guard pages from a range, non-guard pages remain
intact.
We then examine different operations on regions containing guard markers
behave to ensure correct behaviour:
* Operations over multiple VMAs operate as expected.
* Invoking MADV_GUARD_INSTALL / MADV_GUARD_REMOVE via process_madvise() in
batches works correctly.
* Ensuring that munmap() correctly tears down guard markers.
* Using mprotect() to adjust protection bits does not in any way override
or cause issues with guard markers.
* Ensuring that splitting and merging VMAs around guard markers causes no
issue - i.e. that a marker which 'belongs' to one VMA can function just
as well 'belonging' to another.
* Ensuring that madvise(..., MADV_DONTNEED) and madvise(..., MADV_FREE)
do not remove guard markers.
* Ensuring that mlock()'ing a range containing guard markers does not
cause issues.
* Ensuring that mremap() can move a guard range and retain guard markers.
* Ensuring that mremap() can expand a guard range and retain guard
markers (perhaps moving the range).
* Ensuring that mremap() can shrink a guard range and retain guard markers.
* Ensuring that forking a process correctly retains guard markers.
* Ensuring that forking a VMA with VM_WIPEONFORK set behaves sanely.
* Ensuring that lazyfree simply clears guard markers.
* Ensuring that userfaultfd can co-exist with guard pages.
* Ensuring that madvise(..., MADV_POPULATE_READ) and
madvise(..., MADV_POPULATE_WRITE) error out when encountering
guard markers.
* Ensuring that madvise(..., MADV_COLD) and madvise(..., MADV_PAGEOUT) do
not remove guard markers.
If any test is unable to be run due to lack of permissions, that test is
skipped.
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
tools/testing/selftests/mm/.gitignore | 1 +
tools/testing/selftests/mm/Makefile | 1 +
tools/testing/selftests/mm/guard-pages.c | 1243 ++++++++++++++++++++++
3 files changed, 1245 insertions(+)
create mode 100644 tools/testing/selftests/mm/guard-pages.c
diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore
index 689bbd520296..8f01f4da1c0d 100644
--- a/tools/testing/selftests/mm/.gitignore
+++ b/tools/testing/selftests/mm/.gitignore
@@ -54,3 +54,4 @@ droppable
hugetlb_dio
pkey_sighandler_tests_32
pkey_sighandler_tests_64
+guard-pages
diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index 02e1204971b0..15c734d6cfec 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -79,6 +79,7 @@ TEST_GEN_FILES += hugetlb_fault_after_madv
TEST_GEN_FILES += hugetlb_madv_vs_map
TEST_GEN_FILES += hugetlb_dio
TEST_GEN_FILES += droppable
+TEST_GEN_FILES += guard-pages
ifneq ($(ARCH),arm64)
TEST_GEN_FILES += soft-dirty
diff --git a/tools/testing/selftests/mm/guard-pages.c b/tools/testing/selftests/mm/guard-pages.c
new file mode 100644
index 000000000000..7cdf815d0d63
--- /dev/null
+++ b/tools/testing/selftests/mm/guard-pages.c
@@ -0,0 +1,1243 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#define _GNU_SOURCE
+#include "../kselftest_harness.h"
+#include <asm-generic/mman.h> /* Force the import of the tools version. */
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/userfaultfd.h>
+#include <setjmp.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sys/syscall.h>
+#include <sys/uio.h>
+#include <unistd.h>
+
+/*
+ * Ignore the checkpatch warning, as per the C99 standard, section 7.14.1.1:
+ *
+ * "If the signal occurs other than as the result of calling the abort or raise
+ * function, the behavior is undefined if the signal handler refers to any
+ * object with static storage duration other than by assigning a value to an
+ * object declared as volatile sig_atomic_t"
+ */
+static volatile sig_atomic_t signal_jump_set;
+static sigjmp_buf signal_jmp_buf;
+
+/*
+ * Ignore the checkpatch warning, we must read from x but don't want to do
+ * anything with it in order to trigger a read page fault. We therefore must use
+ * volatile to stop the compiler from optimising this away.
+ */
+#define FORCE_READ(x) (*(volatile typeof(x) *)x)
+
+static int userfaultfd(int flags)
+{
+ return syscall(SYS_userfaultfd, flags);
+}
+
+static void handle_fatal(int c)
+{
+ if (!signal_jump_set)
+ return;
+
+ siglongjmp(signal_jmp_buf, c);
+}
+
+static int pidfd_open(pid_t pid, unsigned int flags)
+{
+ return syscall(SYS_pidfd_open, pid, flags);
+}
+
+/*
+ * Enable our signal catcher and try to read/write the specified buffer. The
+ * return value indicates whether the read/write succeeds without a fatal
+ * signal.
+ */
+static bool try_access_buf(char *ptr, bool write)
+{
+ bool failed;
+
+ /* Tell signal handler to jump back here on fatal signal. */
+ signal_jump_set = true;
+ /* If a fatal signal arose, we will jump back here and failed is set. */
+ failed = sigsetjmp(signal_jmp_buf, 0) != 0;
+
+ if (!failed) {
+ if (write)
+ *ptr = 'x';
+ else
+ FORCE_READ(ptr);
+ }
+
+ signal_jump_set = false;
+ return !failed;
+}
+
+/* Try and read from a buffer, return true if no fatal signal. */
+static bool try_read_buf(char *ptr)
+{
+ return try_access_buf(ptr, false);
+}
+
+/* Try and write to a buffer, return true if no fatal signal. */
+static bool try_write_buf(char *ptr)
+{
+ return try_access_buf(ptr, true);
+}
+
+/*
+ * Try and BOTH read from AND write to a buffer, return true if BOTH operations
+ * succeed.
+ */
+static bool try_read_write_buf(char *ptr)
+{
+ return try_read_buf(ptr) && try_write_buf(ptr);
+}
+
+FIXTURE(guard_pages)
+{
+ unsigned long page_size;
+};
+
+FIXTURE_SETUP(guard_pages)
+{
+ struct sigaction act = {
+ .sa_handler = &handle_fatal,
+ .sa_flags = SA_NODEFER,
+ };
+
+ sigemptyset(&act.sa_mask);
+ if (sigaction(SIGSEGV, &act, NULL))
+ ksft_exit_fail_perror("sigaction");
+
+ self->page_size = (unsigned long)sysconf(_SC_PAGESIZE);
+};
+
+FIXTURE_TEARDOWN(guard_pages)
+{
+ struct sigaction act = {
+ .sa_handler = SIG_DFL,
+ .sa_flags = SA_NODEFER,
+ };
+
+ sigemptyset(&act.sa_mask);
+ sigaction(SIGSEGV, &act, NULL);
+}
+
+TEST_F(guard_pages, basic)
+{
+ const unsigned long NUM_PAGES = 10;
+ const unsigned long page_size = self->page_size;
+ char *ptr;
+ int i;
+
+ ptr = mmap(NULL, NUM_PAGES * page_size, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANON, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /* Trivially assert we can touch the first page. */
+ ASSERT_TRUE(try_read_write_buf(ptr));
+
+ ASSERT_EQ(madvise(ptr, page_size, MADV_GUARD_INSTALL), 0);
+
+ /* Establish that 1st page SIGSEGV's. */
+ ASSERT_FALSE(try_read_write_buf(ptr));
+
+ /* Ensure we can touch everything else.*/
+ for (i = 1; i < NUM_PAGES; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_TRUE(try_read_write_buf(curr));
+ }
+
+ /* Establish a guard page at the end of the mapping. */
+ ASSERT_EQ(madvise(&ptr[(NUM_PAGES - 1) * page_size], page_size,
+ MADV_GUARD_INSTALL), 0);
+
+ /* Check that both guard pages result in SIGSEGV. */
+ ASSERT_FALSE(try_read_write_buf(ptr));
+ ASSERT_FALSE(try_read_write_buf(&ptr[(NUM_PAGES - 1) * page_size]));
+
+ /* Remove the first guard page. */
+ ASSERT_FALSE(madvise(ptr, page_size, MADV_GUARD_REMOVE));
+
+ /* Make sure we can touch it. */
+ ASSERT_TRUE(try_read_write_buf(ptr));
+
+ /* Remove the last guard page. */
+ ASSERT_FALSE(madvise(&ptr[(NUM_PAGES - 1) * page_size], page_size,
+ MADV_GUARD_REMOVE));
+
+ /* Make sure we can touch it. */
+ ASSERT_TRUE(try_read_write_buf(&ptr[(NUM_PAGES - 1) * page_size]));
+
+ /*
+ * Test setting a _range_ of pages, namely the first 3. The first of
+ * these be faulted in, so this also tests that we can install guard
+ * pages over backed pages.
+ */
+ ASSERT_EQ(madvise(ptr, 3 * page_size, MADV_GUARD_INSTALL), 0);
+
+ /* Make sure they are all guard pages. */
+ for (i = 0; i < 3; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+
+ /* Make sure the rest are not. */
+ for (i = 3; i < NUM_PAGES; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_TRUE(try_read_write_buf(curr));
+ }
+
+ /* Remove guard pages. */
+ ASSERT_EQ(madvise(ptr, NUM_PAGES * page_size, MADV_GUARD_REMOVE), 0);
+
+ /* Now make sure we can touch everything. */
+ for (i = 0; i < NUM_PAGES; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_TRUE(try_read_write_buf(curr));
+ }
+
+ /*
+ * Now remove all guard pages, make sure we don't remove existing
+ * entries.
+ */
+ ASSERT_EQ(madvise(ptr, NUM_PAGES * page_size, MADV_GUARD_REMOVE), 0);
+
+ for (i = 0; i < NUM_PAGES * page_size; i += page_size) {
+ char chr = ptr[i];
+
+ ASSERT_EQ(chr, 'x');
+ }
+
+ ASSERT_EQ(munmap(ptr, NUM_PAGES * page_size), 0);
+}
+
+/* Assert that operations applied across multiple VMAs work as expected. */
+TEST_F(guard_pages, multi_vma)
+{
+ const unsigned long page_size = self->page_size;
+ char *ptr_region, *ptr, *ptr1, *ptr2, *ptr3;
+ int i;
+
+ /* Reserve a 100 page region over which we can install VMAs. */
+ ptr_region = mmap(NULL, 100 * page_size, PROT_NONE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr_region, MAP_FAILED);
+
+ /* Place a VMA of 10 pages size at the start of the region. */
+ ptr1 = mmap(ptr_region, 10 * page_size, PROT_READ | PROT_WRITE,
+ MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr1, MAP_FAILED);
+
+ /* Place a VMA of 5 pages size 50 pages into the region. */
+ ptr2 = mmap(&ptr_region[50 * page_size], 5 * page_size,
+ PROT_READ | PROT_WRITE,
+ MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr2, MAP_FAILED);
+
+ /* Place a VMA of 20 pages size at the end of the region. */
+ ptr3 = mmap(&ptr_region[80 * page_size], 20 * page_size,
+ PROT_READ | PROT_WRITE,
+ MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr3, MAP_FAILED);
+
+ /* Unmap gaps. */
+ ASSERT_EQ(munmap(&ptr_region[10 * page_size], 40 * page_size), 0);
+ ASSERT_EQ(munmap(&ptr_region[55 * page_size], 25 * page_size), 0);
+
+ /*
+ * We end up with VMAs like this:
+ *
+ * 0 10 .. 50 55 .. 80 100
+ * [---] [---] [---]
+ */
+
+ /*
+ * Now mark the whole range as guard pages and make sure all VMAs are as
+ * such.
+ */
+
+ /*
+ * madvise() is certifiable and lets you perform operations over gaps,
+ * everything works, but it indicates an error and errno is set to
+ * -ENOMEM. Also if anything runs out of memory it is set to
+ * -ENOMEM. You are meant to guess which is which.
+ */
+ ASSERT_EQ(madvise(ptr_region, 100 * page_size, MADV_GUARD_INSTALL), -1);
+ ASSERT_EQ(errno, ENOMEM);
+
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr1[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+
+ for (i = 0; i < 5; i++) {
+ char *curr = &ptr2[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+
+ for (i = 0; i < 20; i++) {
+ char *curr = &ptr3[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+
+ /* Now remove guar pages over range and assert the opposite. */
+
+ ASSERT_EQ(madvise(ptr_region, 100 * page_size, MADV_GUARD_REMOVE), -1);
+ ASSERT_EQ(errno, ENOMEM);
+
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr1[i * page_size];
+
+ ASSERT_TRUE(try_read_write_buf(curr));
+ }
+
+ for (i = 0; i < 5; i++) {
+ char *curr = &ptr2[i * page_size];
+
+ ASSERT_TRUE(try_read_write_buf(curr));
+ }
+
+ for (i = 0; i < 20; i++) {
+ char *curr = &ptr3[i * page_size];
+
+ ASSERT_TRUE(try_read_write_buf(curr));
+ }
+
+ /* Now map incompatible VMAs in the gaps. */
+ ptr = mmap(&ptr_region[10 * page_size], 40 * page_size,
+ PROT_READ | PROT_WRITE | PROT_EXEC,
+ MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+ ptr = mmap(&ptr_region[55 * page_size], 25 * page_size,
+ PROT_READ | PROT_WRITE | PROT_EXEC,
+ MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /*
+ * We end up with VMAs like this:
+ *
+ * 0 10 .. 50 55 .. 80 100
+ * [---][xxxx][---][xxxx][---]
+ *
+ * Where 'x' signifies VMAs that cannot be merged with those adjacent to
+ * them.
+ */
+
+ /* Multiple VMAs adjacent to one another should result in no error. */
+ ASSERT_EQ(madvise(ptr_region, 100 * page_size, MADV_GUARD_INSTALL), 0);
+ for (i = 0; i < 100; i++) {
+ char *curr = &ptr_region[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+ ASSERT_EQ(madvise(ptr_region, 100 * page_size, MADV_GUARD_REMOVE), 0);
+ for (i = 0; i < 100; i++) {
+ char *curr = &ptr_region[i * page_size];
+
+ ASSERT_TRUE(try_read_write_buf(curr));
+ }
+
+ /* Cleanup. */
+ ASSERT_EQ(munmap(ptr_region, 100 * page_size), 0);
+}
+
+/*
+ * Assert that batched operations performed using process_madvise() work as
+ * expected.
+ */
+TEST_F(guard_pages, process_madvise)
+{
+ const unsigned long page_size = self->page_size;
+ pid_t pid = getpid();
+ int pidfd = pidfd_open(pid, 0);
+ char *ptr_region, *ptr1, *ptr2, *ptr3;
+ ssize_t count;
+ struct iovec vec[6];
+
+ ASSERT_NE(pidfd, -1);
+
+ /* Reserve region to map over. */
+ ptr_region = mmap(NULL, 100 * page_size, PROT_NONE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr_region, MAP_FAILED);
+
+ /*
+ * 10 pages offset 1 page into reserve region. We MAP_POPULATE so we
+ * overwrite existing entries and test this code path against
+ * overwriting existing entries.
+ */
+ ptr1 = mmap(&ptr_region[page_size], 10 * page_size,
+ PROT_READ | PROT_WRITE,
+ MAP_FIXED | MAP_ANON | MAP_PRIVATE | MAP_POPULATE, -1, 0);
+ ASSERT_NE(ptr1, MAP_FAILED);
+ /* We want guard markers at start/end of each VMA. */
+ vec[0].iov_base = ptr1;
+ vec[0].iov_len = page_size;
+ vec[1].iov_base = &ptr1[9 * page_size];
+ vec[1].iov_len = page_size;
+
+ /* 5 pages offset 50 pages into reserve region. */
+ ptr2 = mmap(&ptr_region[50 * page_size], 5 * page_size,
+ PROT_READ | PROT_WRITE,
+ MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr2, MAP_FAILED);
+ vec[2].iov_base = ptr2;
+ vec[2].iov_len = page_size;
+ vec[3].iov_base = &ptr2[4 * page_size];
+ vec[3].iov_len = page_size;
+
+ /* 20 pages offset 79 pages into reserve region. */
+ ptr3 = mmap(&ptr_region[79 * page_size], 20 * page_size,
+ PROT_READ | PROT_WRITE,
+ MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr3, MAP_FAILED);
+ vec[4].iov_base = ptr3;
+ vec[4].iov_len = page_size;
+ vec[5].iov_base = &ptr3[19 * page_size];
+ vec[5].iov_len = page_size;
+
+ /* Free surrounding VMAs. */
+ ASSERT_EQ(munmap(ptr_region, page_size), 0);
+ ASSERT_EQ(munmap(&ptr_region[11 * page_size], 39 * page_size), 0);
+ ASSERT_EQ(munmap(&ptr_region[55 * page_size], 24 * page_size), 0);
+ ASSERT_EQ(munmap(&ptr_region[99 * page_size], page_size), 0);
+
+ /* Now guard in one step. */
+ count = process_madvise(pidfd, vec, 6, MADV_GUARD_INSTALL, 0);
+
+ /* OK we don't have permission to do this, skip. */
+ if (count == -1 && errno == EPERM)
+ ksft_exit_skip("No process_madvise() permissions, try running as root.\n");
+
+ /* Returns the number of bytes advised. */
+ ASSERT_EQ(count, 6 * page_size);
+
+ /* Now make sure the guarding was applied. */
+
+ ASSERT_FALSE(try_read_write_buf(ptr1));
+ ASSERT_FALSE(try_read_write_buf(&ptr1[9 * page_size]));
+
+ ASSERT_FALSE(try_read_write_buf(ptr2));
+ ASSERT_FALSE(try_read_write_buf(&ptr2[4 * page_size]));
+
+ ASSERT_FALSE(try_read_write_buf(ptr3));
+ ASSERT_FALSE(try_read_write_buf(&ptr3[19 * page_size]));
+
+ /* Now do the same with unguard... */
+ count = process_madvise(pidfd, vec, 6, MADV_GUARD_REMOVE, 0);
+
+ /* ...and everything should now succeed. */
+
+ ASSERT_TRUE(try_read_write_buf(ptr1));
+ ASSERT_TRUE(try_read_write_buf(&ptr1[9 * page_size]));
+
+ ASSERT_TRUE(try_read_write_buf(ptr2));
+ ASSERT_TRUE(try_read_write_buf(&ptr2[4 * page_size]));
+
+ ASSERT_TRUE(try_read_write_buf(ptr3));
+ ASSERT_TRUE(try_read_write_buf(&ptr3[19 * page_size]));
+
+ /* Cleanup. */
+ ASSERT_EQ(munmap(ptr1, 10 * page_size), 0);
+ ASSERT_EQ(munmap(ptr2, 5 * page_size), 0);
+ ASSERT_EQ(munmap(ptr3, 20 * page_size), 0);
+ close(pidfd);
+}
+
+/* Assert that unmapping ranges does not leave guard markers behind. */
+TEST_F(guard_pages, munmap)
+{
+ const unsigned long page_size = self->page_size;
+ char *ptr, *ptr_new1, *ptr_new2;
+
+ ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /* Guard first and last pages. */
+ ASSERT_EQ(madvise(ptr, page_size, MADV_GUARD_INSTALL), 0);
+ ASSERT_EQ(madvise(&ptr[9 * page_size], page_size, MADV_GUARD_INSTALL), 0);
+
+ /* Assert that they are guarded. */
+ ASSERT_FALSE(try_read_write_buf(ptr));
+ ASSERT_FALSE(try_read_write_buf(&ptr[9 * page_size]));
+
+ /* Unmap them. */
+ ASSERT_EQ(munmap(ptr, page_size), 0);
+ ASSERT_EQ(munmap(&ptr[9 * page_size], page_size), 0);
+
+ /* Map over them.*/
+ ptr_new1 = mmap(ptr, page_size, PROT_READ | PROT_WRITE,
+ MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr_new1, MAP_FAILED);
+ ptr_new2 = mmap(&ptr[9 * page_size], page_size, PROT_READ | PROT_WRITE,
+ MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr_new2, MAP_FAILED);
+
+ /* Assert that they are now not guarded. */
+ ASSERT_TRUE(try_read_write_buf(ptr_new1));
+ ASSERT_TRUE(try_read_write_buf(ptr_new2));
+
+ /* Cleanup. */
+ ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
+}
+
+/* Assert that mprotect() operations have no bearing on guard markers. */
+TEST_F(guard_pages, mprotect)
+{
+ const unsigned long page_size = self->page_size;
+ char *ptr;
+ int i;
+
+ ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /* Guard the middle of the range. */
+ ASSERT_EQ(madvise(&ptr[5 * page_size], 2 * page_size,
+ MADV_GUARD_INSTALL), 0);
+
+ /* Assert that it is indeed guarded. */
+ ASSERT_FALSE(try_read_write_buf(&ptr[5 * page_size]));
+ ASSERT_FALSE(try_read_write_buf(&ptr[6 * page_size]));
+
+ /* Now make these pages read-only. */
+ ASSERT_EQ(mprotect(&ptr[5 * page_size], 2 * page_size, PROT_READ), 0);
+
+ /* Make sure the range is still guarded. */
+ ASSERT_FALSE(try_read_buf(&ptr[5 * page_size]));
+ ASSERT_FALSE(try_read_buf(&ptr[6 * page_size]));
+
+ /* Make sure we can guard again without issue.*/
+ ASSERT_EQ(madvise(&ptr[5 * page_size], 2 * page_size,
+ MADV_GUARD_INSTALL), 0);
+
+ /* Make sure the range is, yet again, still guarded. */
+ ASSERT_FALSE(try_read_buf(&ptr[5 * page_size]));
+ ASSERT_FALSE(try_read_buf(&ptr[6 * page_size]));
+
+ /* Now unguard the whole range. */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_REMOVE), 0);
+
+ /* Make sure the whole range is readable. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_TRUE(try_read_buf(curr));
+ }
+
+ /* Cleanup. */
+ ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
+}
+
+/* Split and merge VMAs and make sure guard pages still behave. */
+TEST_F(guard_pages, split_merge)
+{
+ const unsigned long page_size = self->page_size;
+ char *ptr, *ptr_new;
+ int i;
+
+ ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /* Guard the whole range. */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_INSTALL), 0);
+
+ /* Make sure the whole range is guarded. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+
+ /* Now unmap some pages in the range so we split. */
+ ASSERT_EQ(munmap(&ptr[2 * page_size], page_size), 0);
+ ASSERT_EQ(munmap(&ptr[5 * page_size], page_size), 0);
+ ASSERT_EQ(munmap(&ptr[8 * page_size], page_size), 0);
+
+ /* Make sure the remaining ranges are guarded post-split. */
+ for (i = 0; i < 2; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+ for (i = 2; i < 5; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+ for (i = 6; i < 8; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+ for (i = 9; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+
+ /* Now map them again - the unmap will have cleared the guards. */
+ ptr_new = mmap(&ptr[2 * page_size], page_size, PROT_READ | PROT_WRITE,
+ MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr_new, MAP_FAILED);
+ ptr_new = mmap(&ptr[5 * page_size], page_size, PROT_READ | PROT_WRITE,
+ MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr_new, MAP_FAILED);
+ ptr_new = mmap(&ptr[8 * page_size], page_size, PROT_READ | PROT_WRITE,
+ MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr_new, MAP_FAILED);
+
+ /* Now make sure guard pages are established. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+ bool result = try_read_write_buf(curr);
+ bool expect_true = i == 2 || i == 5 || i == 8;
+
+ ASSERT_TRUE(expect_true ? result : !result);
+ }
+
+ /* Now guard everything again. */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_INSTALL), 0);
+
+ /* Make sure the whole range is guarded. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+
+ /* Now split the range into three. */
+ ASSERT_EQ(mprotect(ptr, 3 * page_size, PROT_READ), 0);
+ ASSERT_EQ(mprotect(&ptr[7 * page_size], 3 * page_size, PROT_READ), 0);
+
+ /* Make sure the whole range is guarded for read. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_FALSE(try_read_buf(curr));
+ }
+
+ /* Now reset protection bits so we merge the whole thing. */
+ ASSERT_EQ(mprotect(ptr, 3 * page_size, PROT_READ | PROT_WRITE), 0);
+ ASSERT_EQ(mprotect(&ptr[7 * page_size], 3 * page_size,
+ PROT_READ | PROT_WRITE), 0);
+
+ /* Make sure the whole range is still guarded. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+
+ /* Split range into 3 again... */
+ ASSERT_EQ(mprotect(ptr, 3 * page_size, PROT_READ), 0);
+ ASSERT_EQ(mprotect(&ptr[7 * page_size], 3 * page_size, PROT_READ), 0);
+
+ /* ...and unguard the whole range. */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_REMOVE), 0);
+
+ /* Make sure the whole range is remedied for read. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_TRUE(try_read_buf(curr));
+ }
+
+ /* Merge them again. */
+ ASSERT_EQ(mprotect(ptr, 3 * page_size, PROT_READ | PROT_WRITE), 0);
+ ASSERT_EQ(mprotect(&ptr[7 * page_size], 3 * page_size,
+ PROT_READ | PROT_WRITE), 0);
+
+ /* Now ensure the merged range is remedied for read/write. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_TRUE(try_read_write_buf(curr));
+ }
+
+ /* Cleanup. */
+ ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
+}
+
+/* Assert that MADV_DONTNEED does not remove guard markers. */
+TEST_F(guard_pages, dontneed)
+{
+ const unsigned long page_size = self->page_size;
+ char *ptr;
+ int i;
+
+ ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /* Back the whole range. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ *curr = 'y';
+ }
+
+ /* Guard every other page. */
+ for (i = 0; i < 10; i += 2) {
+ char *curr = &ptr[i * page_size];
+ int res = madvise(curr, page_size, MADV_GUARD_INSTALL);
+
+ ASSERT_EQ(res, 0);
+ }
+
+ /* Indicate that we don't need any of the range. */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_DONTNEED), 0);
+
+ /* Check to ensure guard markers are still in place. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+ bool result = try_read_buf(curr);
+
+ if (i % 2 == 0) {
+ ASSERT_FALSE(result);
+ } else {
+ ASSERT_TRUE(result);
+ /* Make sure we really did get reset to zero page. */
+ ASSERT_EQ(*curr, '\0');
+ }
+
+ /* Now write... */
+ result = try_write_buf(&ptr[i * page_size]);
+
+ /* ...and make sure same result. */
+ ASSERT_TRUE(i % 2 != 0 ? result : !result);
+ }
+
+ /* Cleanup. */
+ ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
+}
+
+/* Assert that mlock()'ed pages work correctly with guard markers. */
+TEST_F(guard_pages, mlock)
+{
+ const unsigned long page_size = self->page_size;
+ char *ptr;
+ int i;
+
+ ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /* Populate. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ *curr = 'y';
+ }
+
+ /* Lock. */
+ ASSERT_EQ(mlock(ptr, 10 * page_size), 0);
+
+ /* Now try to guard, should fail with EINVAL. */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_INSTALL), -1);
+ ASSERT_EQ(errno, EINVAL);
+
+ /* OK unlock. */
+ ASSERT_EQ(munlock(ptr, 10 * page_size), 0);
+
+ /* Guard first half of range, should now succeed. */
+ ASSERT_EQ(madvise(ptr, 5 * page_size, MADV_GUARD_INSTALL), 0);
+
+ /* Make sure guard works. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+ bool result = try_read_write_buf(curr);
+
+ if (i < 5) {
+ ASSERT_FALSE(result);
+ } else {
+ ASSERT_TRUE(result);
+ ASSERT_EQ(*curr, 'x');
+ }
+ }
+
+ /*
+ * Now lock the latter part of the range. We can't lock the guard pages,
+ * as this would result in the pages being populated and the guarding
+ * would cause this to error out.
+ */
+ ASSERT_EQ(mlock(&ptr[5 * page_size], 5 * page_size), 0);
+
+ /*
+ * Now remove guard pages, we permit mlock()'d ranges to have guard
+ * pages removed as it is a non-destructive operation.
+ */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_REMOVE), 0);
+
+ /* Now check that no guard pages remain. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_TRUE(try_read_write_buf(curr));
+ }
+
+ /* Cleanup. */
+ ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
+}
+
+/*
+ * Assert that moving, extending and shrinking memory via mremap() retains
+ * guard markers where possible.
+ *
+ * - Moving a mapping alone should retain markers as they are.
+ */
+TEST_F(guard_pages, mremap_move)
+{
+ const unsigned long page_size = self->page_size;
+ char *ptr, *ptr_new;
+
+ /* Map 5 pages. */
+ ptr = mmap(NULL, 5 * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /* Place guard markers at both ends of the 5 page span. */
+ ASSERT_EQ(madvise(ptr, page_size, MADV_GUARD_INSTALL), 0);
+ ASSERT_EQ(madvise(&ptr[4 * page_size], page_size, MADV_GUARD_INSTALL), 0);
+
+ /* Make sure the guard pages are in effect. */
+ ASSERT_FALSE(try_read_write_buf(ptr));
+ ASSERT_FALSE(try_read_write_buf(&ptr[4 * page_size]));
+
+ /* Map a new region we will move this range into. Doing this ensures
+ * that we have reserved a range to map into.
+ */
+ ptr_new = mmap(NULL, 5 * page_size, PROT_NONE, MAP_ANON | MAP_PRIVATE,
+ -1, 0);
+ ASSERT_NE(ptr_new, MAP_FAILED);
+
+ ASSERT_EQ(mremap(ptr, 5 * page_size, 5 * page_size,
+ MREMAP_MAYMOVE | MREMAP_FIXED, ptr_new), ptr_new);
+
+ /* Make sure the guard markers are retained. */
+ ASSERT_FALSE(try_read_write_buf(ptr_new));
+ ASSERT_FALSE(try_read_write_buf(&ptr_new[4 * page_size]));
+
+ /*
+ * Clean up - we only need reference the new pointer as we overwrote the
+ * PROT_NONE range and moved the existing one.
+ */
+ munmap(ptr_new, 5 * page_size);
+}
+
+/*
+ * Assert that moving, extending and shrinking memory via mremap() retains
+ * guard markers where possible.
+ *
+ * Expanding should retain guard pages, only now in different position. The user
+ * will have to remove guard pages manually to fix up (they'd have to do the
+ * same if it were a PROT_NONE mapping).
+ */
+TEST_F(guard_pages, mremap_expand)
+{
+ const unsigned long page_size = self->page_size;
+ char *ptr, *ptr_new;
+
+ /* Map 10 pages... */
+ ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+ /* ...But unmap the last 5 so we can ensure we can expand into them. */
+ ASSERT_EQ(munmap(&ptr[5 * page_size], 5 * page_size), 0);
+
+ /* Place guard markers at both ends of the 5 page span. */
+ ASSERT_EQ(madvise(ptr, page_size, MADV_GUARD_INSTALL), 0);
+ ASSERT_EQ(madvise(&ptr[4 * page_size], page_size, MADV_GUARD_INSTALL), 0);
+
+ /* Make sure the guarding is in effect. */
+ ASSERT_FALSE(try_read_write_buf(ptr));
+ ASSERT_FALSE(try_read_write_buf(&ptr[4 * page_size]));
+
+ /* Now expand to 10 pages. */
+ ptr = mremap(ptr, 5 * page_size, 10 * page_size, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /*
+ * Make sure the guard markers are retained in their original positions.
+ */
+ ASSERT_FALSE(try_read_write_buf(ptr));
+ ASSERT_FALSE(try_read_write_buf(&ptr[4 * page_size]));
+
+ /* Reserve a region which we can move to and expand into. */
+ ptr_new = mmap(NULL, 20 * page_size, PROT_NONE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr_new, MAP_FAILED);
+
+ /* Now move and expand into it. */
+ ptr = mremap(ptr, 10 * page_size, 20 * page_size,
+ MREMAP_MAYMOVE | MREMAP_FIXED, ptr_new);
+ ASSERT_EQ(ptr, ptr_new);
+
+ /*
+ * Again, make sure the guard markers are retained in their original positions.
+ */
+ ASSERT_FALSE(try_read_write_buf(ptr));
+ ASSERT_FALSE(try_read_write_buf(&ptr[4 * page_size]));
+
+ /*
+ * A real user would have to remove guard markers, but would reasonably
+ * expect all characteristics of the mapping to be retained, including
+ * guard markers.
+ */
+
+ /* Cleanup. */
+ munmap(ptr, 20 * page_size);
+}
+/*
+ * Assert that moving, extending and shrinking memory via mremap() retains
+ * guard markers where possible.
+ *
+ * Shrinking will result in markers that are shrunk over being removed. Again,
+ * if the user were using a PROT_NONE mapping they'd have to manually fix this
+ * up also so this is OK.
+ */
+TEST_F(guard_pages, mremap_shrink)
+{
+ const unsigned long page_size = self->page_size;
+ char *ptr;
+ int i;
+
+ /* Map 5 pages. */
+ ptr = mmap(NULL, 5 * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /* Place guard markers at both ends of the 5 page span. */
+ ASSERT_EQ(madvise(ptr, page_size, MADV_GUARD_INSTALL), 0);
+ ASSERT_EQ(madvise(&ptr[4 * page_size], page_size, MADV_GUARD_INSTALL), 0);
+
+ /* Make sure the guarding is in effect. */
+ ASSERT_FALSE(try_read_write_buf(ptr));
+ ASSERT_FALSE(try_read_write_buf(&ptr[4 * page_size]));
+
+ /* Now shrink to 3 pages. */
+ ptr = mremap(ptr, 5 * page_size, 3 * page_size, MREMAP_MAYMOVE);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /* We expect the guard marker at the start to be retained... */
+ ASSERT_FALSE(try_read_write_buf(ptr));
+
+ /* ...But remaining pages will not have guard markers. */
+ for (i = 1; i < 3; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_TRUE(try_read_write_buf(curr));
+ }
+
+ /*
+ * As with expansion, a real user would have to remove guard pages and
+ * fixup. But you'd have to do similar manual things with PROT_NONE
+ * mappings too.
+ */
+
+ /*
+ * If we expand back to the original size, the end marker will, of
+ * course, no longer be present.
+ */
+ ptr = mremap(ptr, 3 * page_size, 5 * page_size, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /* Again, we expect the guard marker at the start to be retained... */
+ ASSERT_FALSE(try_read_write_buf(ptr));
+
+ /* ...But remaining pages will not have guard markers. */
+ for (i = 1; i < 5; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_TRUE(try_read_write_buf(curr));
+ }
+
+ /* Cleanup. */
+ munmap(ptr, 5 * page_size);
+}
+
+/*
+ * Assert that forking a process with VMAs that do not have VM_WIPEONFORK set
+ * retain guard pages.
+ */
+TEST_F(guard_pages, fork)
+{
+ const unsigned long page_size = self->page_size;
+ char *ptr;
+ pid_t pid;
+ int i;
+
+ /* Map 10 pages. */
+ ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /* Establish guard apges in the first 5 pages. */
+ ASSERT_EQ(madvise(ptr, 5 * page_size, MADV_GUARD_INSTALL), 0);
+
+ pid = fork();
+ ASSERT_NE(pid, -1);
+ if (!pid) {
+ /* This is the child process now. */
+
+ /* Assert that the guarding is in effect. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+ bool result = try_read_write_buf(curr);
+
+ ASSERT_TRUE(i >= 5 ? result : !result);
+ }
+
+ /* Now unguard the range.*/
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_REMOVE), 0);
+
+ exit(0);
+ }
+
+ /* Parent process. */
+
+ /* Parent simply waits on child. */
+ waitpid(pid, NULL, 0);
+
+ /* Child unguard does not impact parent page table state. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+ bool result = try_read_write_buf(curr);
+
+ ASSERT_TRUE(i >= 5 ? result : !result);
+ }
+
+ /* Cleanup. */
+ ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
+}
+
+/*
+ * Assert that forking a process with VMAs that do have VM_WIPEONFORK set
+ * behave as expected.
+ */
+TEST_F(guard_pages, fork_wipeonfork)
+{
+ const unsigned long page_size = self->page_size;
+ char *ptr;
+ pid_t pid;
+ int i;
+
+ /* Map 10 pages. */
+ ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /* Mark wipe on fork. */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_WIPEONFORK), 0);
+
+ /* Guard the first 5 pages. */
+ ASSERT_EQ(madvise(ptr, 5 * page_size, MADV_GUARD_INSTALL), 0);
+
+ pid = fork();
+ ASSERT_NE(pid, -1);
+ if (!pid) {
+ /* This is the child process now. */
+
+ /* Guard will have been wiped. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_TRUE(try_read_write_buf(curr));
+ }
+
+ exit(0);
+ }
+
+ /* Parent process. */
+
+ waitpid(pid, NULL, 0);
+
+ /* Guard markers should be in effect.*/
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+ bool result = try_read_write_buf(curr);
+
+ ASSERT_TRUE(i >= 5 ? result : !result);
+ }
+
+ /* Cleanup. */
+ ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
+}
+
+/* Ensure that MADV_FREE retains guard entries as expected. */
+TEST_F(guard_pages, lazyfree)
+{
+ const unsigned long page_size = self->page_size;
+ char *ptr;
+ int i;
+
+ /* Map 10 pages. */
+ ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /* Guard range. */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_INSTALL), 0);
+
+ /* Ensure guarded. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+
+ /* Lazyfree range. */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_FREE), 0);
+
+ /* This should leave the guard markers in place. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+
+ /* Cleanup. */
+ ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
+}
+
+/* Ensure that MADV_POPULATE_READ, MADV_POPULATE_WRITE behave as expected. */
+TEST_F(guard_pages, populate)
+{
+ const unsigned long page_size = self->page_size;
+ char *ptr;
+
+ /* Map 10 pages. */
+ ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /* Guard range. */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_INSTALL), 0);
+
+ /* Populate read should error out... */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_POPULATE_READ), -1);
+ ASSERT_EQ(errno, EFAULT);
+
+ /* ...as should populate write. */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_POPULATE_WRITE), -1);
+ ASSERT_EQ(errno, EFAULT);
+
+ /* Cleanup. */
+ ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
+}
+
+/* Ensure that MADV_COLD, MADV_PAGEOUT do not remove guard markers. */
+TEST_F(guard_pages, cold_pageout)
+{
+ const unsigned long page_size = self->page_size;
+ char *ptr;
+ int i;
+
+ /* Map 10 pages. */
+ ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /* Guard range. */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_INSTALL), 0);
+
+ /* Ensured guarded. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+
+ /* Now mark cold. This should have no impact on guard markers. */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_COLD), 0);
+
+ /* Should remain guarded. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+
+ /* OK, now page out. This should equally, have no effect on markers. */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_PAGEOUT), 0);
+
+ /* Should remain guarded. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+
+ /* Cleanup. */
+ ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
+}
+
+/* Ensure that guard pages do not break userfaultd. */
+TEST_F(guard_pages, uffd)
+{
+ const unsigned long page_size = self->page_size;
+ int uffd;
+ char *ptr;
+ int i;
+ struct uffdio_api api = {
+ .api = UFFD_API,
+ .features = 0,
+ };
+ struct uffdio_register reg;
+ struct uffdio_range range;
+
+ /* Set up uffd. */
+ uffd = userfaultfd(0);
+ if (uffd == -1 && errno == EPERM)
+ ksft_exit_skip("No userfaultfd permissions, try running as root.\n");
+ ASSERT_NE(uffd, -1);
+
+ ASSERT_EQ(ioctl(uffd, UFFDIO_API, &api), 0);
+
+ /* Map 10 pages. */
+ ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANON | MAP_PRIVATE, -1, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+
+ /* Register the range with uffd. */
+ range.start = (unsigned long)ptr;
+ range.len = 10 * page_size;
+ reg.range = range;
+ reg.mode = UFFDIO_REGISTER_MODE_MISSING;
+ ASSERT_EQ(ioctl(uffd, UFFDIO_REGISTER, ®), 0);
+
+ /* Guard the range. This should not trigger the uffd. */
+ ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_INSTALL), 0);
+
+ /* The guarding should behave as usual with no uffd intervention. */
+ for (i = 0; i < 10; i++) {
+ char *curr = &ptr[i * page_size];
+
+ ASSERT_FALSE(try_read_write_buf(curr));
+ }
+
+ /* Cleanup. */
+ ASSERT_EQ(ioctl(uffd, UFFDIO_UNREGISTER, &range), 0);
+ close(uffd);
+ ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
+}
+
+TEST_HARNESS_MAIN
--
2.47.0
^ permalink raw reply related
* [PATCH v4 3/5] mm: madvise: implement lightweight guard page mechanism
From: Lorenzo Stoakes @ 2024-10-28 14:13 UTC (permalink / raw)
To: Andrew Morton
Cc: Suren Baghdasaryan, Liam R . Howlett, Matthew Wilcox,
Vlastimil Babka, Paul E . McKenney, Jann Horn, David Hildenbrand,
linux-mm, linux-kernel, Muchun Song, Richard Henderson,
Matt Turner, Thomas Bogendoerfer, James E . J . Bottomley,
Helge Deller, Chris Zankel, Max Filippov, Arnd Bergmann,
linux-alpha, linux-mips, linux-parisc, linux-arch, Shuah Khan,
Christian Brauner, linux-kselftest, Sidhartha Kumar, Jeff Xu,
Christoph Hellwig, linux-api, John Hubbard
In-Reply-To: <cover.1730123433.git.lorenzo.stoakes@oracle.com>
Implement a new lightweight guard page feature, that is regions of userland
virtual memory that, when accessed, cause a fatal signal to arise.
Currently users must establish PROT_NONE ranges to achieve this.
However this is very costly memory-wise - we need a VMA for each and every
one of these regions AND they become unmergeable with surrounding VMAs.
In addition repeated mmap() calls require repeated kernel context switches
and contention of the mmap lock to install these ranges, potentially also
having to unmap memory if installed over existing ranges.
The lightweight guard approach eliminates the VMA cost altogether - rather
than establishing a PROT_NONE VMA, it operates at the level of page table
entries - establishing PTE markers such that accesses to them cause a fault
followed by a SIGSGEV signal being raised.
This is achieved through the PTE marker mechanism, which we have already
extended to provide PTE_MARKER_GUARD, which we installed via the generic
page walking logic which we have extended for this purpose.
These guard ranges are established with MADV_GUARD_INSTALL. If the range in
which they are installed contain any existing mappings, they will be
zapped, i.e. free the range and unmap memory (thus mimicking the behaviour
of MADV_DONTNEED in this respect).
Any existing guard entries will be left untouched. There is therefore no
nesting of guarded pages.
Guarded ranges are NOT cleared by MADV_DONTNEED nor MADV_FREE (in both
instances the memory range may be reused at which point a user would expect
guards to still be in place), but they are cleared via MADV_GUARD_REMOVE,
process teardown or unmapping of memory ranges.
The guard property can be removed from ranges via MADV_GUARD_REMOVE. The
ranges over which this is applied, should they contain non-guard entries,
will be untouched, with only guard entries being cleared.
We permit this operation on anonymous memory only, and only VMAs which are
non-special, non-huge and not mlock()'d (if we permitted this we'd have to
drop locked pages which would be rather counterintuitive).
Racing page faults can cause repeated attempts to install guard pages that
are interrupted, result in a zap, and this process can end up being
repeated. If this happens more than would be expected in normal operation,
we rescind locks and retry the whole thing, which avoids lock contention in
this scenario.
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Suggested-by: Jann Horn <jannh@google.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
arch/alpha/include/uapi/asm/mman.h | 3 +
arch/mips/include/uapi/asm/mman.h | 3 +
arch/parisc/include/uapi/asm/mman.h | 3 +
arch/xtensa/include/uapi/asm/mman.h | 3 +
include/uapi/asm-generic/mman-common.h | 3 +
mm/madvise.c | 239 +++++++++++++++++++++++++
mm/mseal.c | 1 +
7 files changed, 255 insertions(+)
diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h
index 763929e814e9..1e700468a685 100644
--- a/arch/alpha/include/uapi/asm/mman.h
+++ b/arch/alpha/include/uapi/asm/mman.h
@@ -78,6 +78,9 @@
#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */
+#define MADV_GUARD_INSTALL 102 /* fatal signal on access to range */
+#define MADV_GUARD_REMOVE 103 /* unguard range */
+
/* compatibility flags */
#define MAP_FILE 0
diff --git a/arch/mips/include/uapi/asm/mman.h b/arch/mips/include/uapi/asm/mman.h
index 9c48d9a21aa0..b700dae28c48 100644
--- a/arch/mips/include/uapi/asm/mman.h
+++ b/arch/mips/include/uapi/asm/mman.h
@@ -105,6 +105,9 @@
#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */
+#define MADV_GUARD_INSTALL 102 /* fatal signal on access to range */
+#define MADV_GUARD_REMOVE 103 /* unguard range */
+
/* compatibility flags */
#define MAP_FILE 0
diff --git a/arch/parisc/include/uapi/asm/mman.h b/arch/parisc/include/uapi/asm/mman.h
index 68c44f99bc93..b6a709506987 100644
--- a/arch/parisc/include/uapi/asm/mman.h
+++ b/arch/parisc/include/uapi/asm/mman.h
@@ -75,6 +75,9 @@
#define MADV_HWPOISON 100 /* poison a page for testing */
#define MADV_SOFT_OFFLINE 101 /* soft offline page for testing */
+#define MADV_GUARD_INSTALL 102 /* fatal signal on access to range */
+#define MADV_GUARD_REMOVE 103 /* unguard range */
+
/* compatibility flags */
#define MAP_FILE 0
diff --git a/arch/xtensa/include/uapi/asm/mman.h b/arch/xtensa/include/uapi/asm/mman.h
index 1ff0c858544f..99d4ccee7f6e 100644
--- a/arch/xtensa/include/uapi/asm/mman.h
+++ b/arch/xtensa/include/uapi/asm/mman.h
@@ -113,6 +113,9 @@
#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */
+#define MADV_GUARD_INSTALL 102 /* fatal signal on access to range */
+#define MADV_GUARD_REMOVE 103 /* unguard range */
+
/* compatibility flags */
#define MAP_FILE 0
diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index 6ce1f1ceb432..1ea2c4c33b86 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -79,6 +79,9 @@
#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */
+#define MADV_GUARD_INSTALL 102 /* fatal signal on access to range */
+#define MADV_GUARD_REMOVE 103 /* unguard range */
+
/* compatibility flags */
#define MAP_FILE 0
diff --git a/mm/madvise.c b/mm/madvise.c
index e871a72a6c32..0ceae57da7da 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -37,6 +37,12 @@
#include "internal.h"
#include "swap.h"
+/*
+ * Maximum number of attempts we make to install guard pages before we give up
+ * and return -ERESTARTNOINTR to have userspace try again.
+ */
+#define MAX_MADVISE_GUARD_RETRIES 3
+
struct madvise_walk_private {
struct mmu_gather *tlb;
bool pageout;
@@ -60,6 +66,8 @@ static int madvise_need_mmap_write(int behavior)
case MADV_POPULATE_READ:
case MADV_POPULATE_WRITE:
case MADV_COLLAPSE:
+ case MADV_GUARD_INSTALL:
+ case MADV_GUARD_REMOVE:
return 0;
default:
/* be safe, default to 1. list exceptions explicitly */
@@ -1017,6 +1025,214 @@ static long madvise_remove(struct vm_area_struct *vma,
return error;
}
+static bool is_valid_guard_vma(struct vm_area_struct *vma, bool allow_locked)
+{
+ vm_flags_t disallowed = VM_SPECIAL | VM_HUGETLB;
+
+ /*
+ * A user could lock after setting a guard range but that's fine, as
+ * they'd not be able to fault in. The issue arises when we try to zap
+ * existing locked VMAs. We don't want to do that.
+ */
+ if (!allow_locked)
+ disallowed |= VM_LOCKED;
+
+ if (!vma_is_anonymous(vma))
+ return false;
+
+ if ((vma->vm_flags & (VM_MAYWRITE | disallowed)) != VM_MAYWRITE)
+ return false;
+
+ return true;
+}
+
+static bool is_guard_pte_marker(pte_t ptent)
+{
+ return is_pte_marker(ptent) &&
+ is_guard_swp_entry(pte_to_swp_entry(ptent));
+}
+
+static int guard_install_pud_entry(pud_t *pud, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ pud_t pudval = pudp_get(pud);
+
+ /* If huge return >0 so we abort the operation + zap. */
+ return pud_trans_huge(pudval) || pud_devmap(pudval);
+}
+
+static int guard_install_pmd_entry(pmd_t *pmd, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ pmd_t pmdval = pmdp_get(pmd);
+
+ /* If huge return >0 so we abort the operation + zap. */
+ return pmd_trans_huge(pmdval) || pmd_devmap(pmdval);
+}
+
+static int guard_install_pte_entry(pte_t *pte, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ pte_t pteval = ptep_get(pte);
+ unsigned long *nr_pages = (unsigned long *)walk->private;
+
+ /* If there is already a guard page marker, we have nothing to do. */
+ if (is_guard_pte_marker(pteval)) {
+ (*nr_pages)++;
+
+ return 0;
+ }
+
+ /* If populated return >0 so we abort the operation + zap. */
+ return 1;
+}
+
+static int guard_install_set_pte(unsigned long addr, unsigned long next,
+ pte_t *ptep, struct mm_walk *walk)
+{
+ unsigned long *nr_pages = (unsigned long *)walk->private;
+
+ /* Simply install a PTE marker, this causes segfault on access. */
+ *ptep = make_pte_marker(PTE_MARKER_GUARD);
+ (*nr_pages)++;
+
+ return 0;
+}
+
+static const struct mm_walk_ops guard_install_walk_ops = {
+ .pud_entry = guard_install_pud_entry,
+ .pmd_entry = guard_install_pmd_entry,
+ .pte_entry = guard_install_pte_entry,
+ .install_pte = guard_install_set_pte,
+ .walk_lock = PGWALK_RDLOCK,
+};
+
+static long madvise_guard_install(struct vm_area_struct *vma,
+ struct vm_area_struct **prev,
+ unsigned long start, unsigned long end)
+{
+ long err;
+ int i;
+
+ *prev = vma;
+ if (!is_valid_guard_vma(vma, /* allow_locked = */false))
+ return -EINVAL;
+
+ /*
+ * If we install guard markers, then the range is no longer
+ * empty from a page table perspective and therefore it's
+ * appropriate to have an anon_vma.
+ *
+ * This ensures that on fork, we copy page tables correctly.
+ */
+ err = anon_vma_prepare(vma);
+ if (err)
+ return err;
+
+ /*
+ * Optimistically try to install the guard marker pages first. If any
+ * non-guard pages are encountered, give up and zap the range before
+ * trying again.
+ *
+ * We try a few times before giving up and releasing back to userland to
+ * loop around, releasing locks in the process to avoid contention. This
+ * would only happen if there was a great many racing page faults.
+ *
+ * In most cases we should simply install the guard markers immediately
+ * with no zap or looping.
+ */
+ for (i = 0; i < MAX_MADVISE_GUARD_RETRIES; i++) {
+ unsigned long nr_pages = 0;
+
+ /* Returns < 0 on error, == 0 if success, > 0 if zap needed. */
+ err = walk_page_range_mm(vma->vm_mm, start, end,
+ &guard_install_walk_ops, &nr_pages);
+ if (err < 0)
+ return err;
+
+ if (err == 0) {
+ unsigned long nr_expected_pages = PHYS_PFN(end - start);
+
+ VM_WARN_ON(nr_pages != nr_expected_pages);
+ return 0;
+ }
+
+ /*
+ * OK some of the range have non-guard pages mapped, zap
+ * them. This leaves existing guard pages in place.
+ */
+ zap_page_range_single(vma, start, end - start, NULL);
+ }
+
+ /*
+ * We were unable to install the guard pages due to being raced by page
+ * faults. This should not happen ordinarily. We return to userspace and
+ * immediately retry, relieving lock contention.
+ */
+ return restart_syscall();
+}
+
+static int guard_remove_pud_entry(pud_t *pud, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ pud_t pudval = pudp_get(pud);
+
+ /* If huge, cannot have guard pages present, so no-op - skip. */
+ if (pud_trans_huge(pudval) || pud_devmap(pudval))
+ walk->action = ACTION_CONTINUE;
+
+ return 0;
+}
+
+static int guard_remove_pmd_entry(pmd_t *pmd, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ pmd_t pmdval = pmdp_get(pmd);
+
+ /* If huge, cannot have guard pages present, so no-op - skip. */
+ if (pmd_trans_huge(pmdval) || pmd_devmap(pmdval))
+ walk->action = ACTION_CONTINUE;
+
+ return 0;
+}
+
+static int guard_remove_pte_entry(pte_t *pte, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ pte_t ptent = ptep_get(pte);
+
+ if (is_guard_pte_marker(ptent)) {
+ /* Simply clear the PTE marker. */
+ pte_clear_not_present_full(walk->mm, addr, pte, false);
+ update_mmu_cache(walk->vma, addr, pte);
+ }
+
+ return 0;
+}
+
+static const struct mm_walk_ops guard_remove_walk_ops = {
+ .pud_entry = guard_remove_pud_entry,
+ .pmd_entry = guard_remove_pmd_entry,
+ .pte_entry = guard_remove_pte_entry,
+ .walk_lock = PGWALK_RDLOCK,
+};
+
+static long madvise_guard_remove(struct vm_area_struct *vma,
+ struct vm_area_struct **prev,
+ unsigned long start, unsigned long end)
+{
+ *prev = vma;
+ /*
+ * We're ok with removing guards in mlock()'d ranges, as this is a
+ * non-destructive action.
+ */
+ if (!is_valid_guard_vma(vma, /* allow_locked = */true))
+ return -EINVAL;
+
+ return walk_page_range(vma->vm_mm, start, end,
+ &guard_remove_walk_ops, NULL);
+}
+
/*
* Apply an madvise behavior to a region of a vma. madvise_update_vma
* will handle splitting a vm area into separate areas, each area with its own
@@ -1098,6 +1314,10 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
break;
case MADV_COLLAPSE:
return madvise_collapse(vma, prev, start, end);
+ case MADV_GUARD_INSTALL:
+ return madvise_guard_install(vma, prev, start, end);
+ case MADV_GUARD_REMOVE:
+ return madvise_guard_remove(vma, prev, start, end);
}
anon_name = anon_vma_name(vma);
@@ -1197,6 +1417,8 @@ madvise_behavior_valid(int behavior)
case MADV_DODUMP:
case MADV_WIPEONFORK:
case MADV_KEEPONFORK:
+ case MADV_GUARD_INSTALL:
+ case MADV_GUARD_REMOVE:
#ifdef CONFIG_MEMORY_FAILURE
case MADV_SOFT_OFFLINE:
case MADV_HWPOISON:
@@ -1490,6 +1712,23 @@ static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter,
while (iov_iter_count(iter)) {
ret = do_madvise(mm, (unsigned long)iter_iov_addr(iter),
iter_iov_len(iter), behavior);
+ /*
+ * An madvise operation is attempting to restart the syscall,
+ * but we cannot proceed as it would not be correct to repeat
+ * the operation in aggregate, and would be surprising to the
+ * user.
+ *
+ * As we have already dropped locks, it is safe to just loop and
+ * try again. We check for fatal signals in case we need exit
+ * early anyway.
+ */
+ if (ret == -ERESTARTNOINTR) {
+ if (fatal_signal_pending(current)) {
+ ret = -EINTR;
+ break;
+ }
+ continue;
+ }
if (ret < 0)
break;
iov_iter_advance(iter, iter_iov_len(iter));
diff --git a/mm/mseal.c b/mm/mseal.c
index ece977bd21e1..81d6e980e8a9 100644
--- a/mm/mseal.c
+++ b/mm/mseal.c
@@ -30,6 +30,7 @@ static bool is_madv_discard(int behavior)
case MADV_REMOVE:
case MADV_DONTFORK:
case MADV_WIPEONFORK:
+ case MADV_GUARD_INSTALL:
return true;
}
--
2.47.0
^ permalink raw reply related
* [PATCH v4 4/5] tools: testing: update tools UAPI header for mman-common.h
From: Lorenzo Stoakes @ 2024-10-28 14:13 UTC (permalink / raw)
To: Andrew Morton
Cc: Suren Baghdasaryan, Liam R . Howlett, Matthew Wilcox,
Vlastimil Babka, Paul E . McKenney, Jann Horn, David Hildenbrand,
linux-mm, linux-kernel, Muchun Song, Richard Henderson,
Matt Turner, Thomas Bogendoerfer, James E . J . Bottomley,
Helge Deller, Chris Zankel, Max Filippov, Arnd Bergmann,
linux-alpha, linux-mips, linux-parisc, linux-arch, Shuah Khan,
Christian Brauner, linux-kselftest, Sidhartha Kumar, Jeff Xu,
Christoph Hellwig, linux-api, John Hubbard
In-Reply-To: <cover.1730123433.git.lorenzo.stoakes@oracle.com>
Import the new MADV_GUARD_INSTALL/REMOVE madvise flags.
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
tools/include/uapi/asm-generic/mman-common.h | 3 +++
1 file changed, 3 insertions(+)
diff --git a/tools/include/uapi/asm-generic/mman-common.h b/tools/include/uapi/asm-generic/mman-common.h
index 6ce1f1ceb432..1ea2c4c33b86 100644
--- a/tools/include/uapi/asm-generic/mman-common.h
+++ b/tools/include/uapi/asm-generic/mman-common.h
@@ -79,6 +79,9 @@
#define MADV_COLLAPSE 25 /* Synchronous hugepage collapse */
+#define MADV_GUARD_INSTALL 102 /* fatal signal on access to range */
+#define MADV_GUARD_REMOVE 103 /* unguard range */
+
/* compatibility flags */
#define MAP_FILE 0
--
2.47.0
^ permalink raw reply related
* Re: [PATCH v3 3/5] mm: madvise: implement lightweight guard page mechanism
From: Lorenzo Stoakes @ 2024-10-28 12:40 UTC (permalink / raw)
To: Vlastimil Babka
Cc: Andrew Morton, Suren Baghdasaryan, Liam R . Howlett,
Matthew Wilcox, Paul E . McKenney, Jann Horn, David Hildenbrand,
linux-mm, linux-kernel, Muchun Song, Richard Henderson,
Matt Turner, Thomas Bogendoerfer, James E . J . Bottomley,
Helge Deller, Chris Zankel, Max Filippov, Arnd Bergmann,
linux-alpha, linux-mips, linux-parisc, linux-arch, Shuah Khan,
Christian Brauner, linux-kselftest, Sidhartha Kumar, Jeff Xu,
Christoph Hellwig, linux-api, John Hubbard
In-Reply-To: <c957ae63-6aa9-4a29-a191-1686ee31987e@lucifer.local>
On Fri, Oct 25, 2024 at 11:35:03PM +0100, Lorenzo Stoakes wrote:
> On Fri, Oct 25, 2024 at 11:56:52PM +0200, Vlastimil Babka wrote:
> > On 10/25/24 19:12, Lorenzo Stoakes wrote:
> > > On Wed, Oct 23, 2024 at 05:24:40PM +0100, Lorenzo Stoakes wrote:
> > >> Implement a new lightweight guard page feature, that is regions of userland
> > >> virtual memory that, when accessed, cause a fatal signal to arise.
> > >
> > > <snip>
> > >
> > > Hi Andrew - Could you apply the below fix-patch? I realise we must handle
> > > fatal signals and conditional rescheduling in the vector_madvise() special
> > > case.
> > >
> > > Thanks!
> > >
> > > ----8<----
> > > From 546d7e1831c71599fc733d589e0d75f52e84826d Mon Sep 17 00:00:00 2001
> > > From: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> > > Date: Fri, 25 Oct 2024 18:05:48 +0100
> > > Subject: [PATCH] mm: yield on fatal signal/cond_sched() in vector_madvise()
> > >
> > > While we have to treat -ERESTARTNOINTR specially here as we are looping
> > > through a vector of operations and can't simply restart the entire
> > > operation, we mustn't hold up fatal signals or RT kernels.
> >
> > For plain madvise() syscall returning -ERESTARTNOINTR does the right thing
> > and checks fatal_signal_pending() before returning, right?
>
> I believe so. But now you've caused me some doubt so let me double check
> and make absolutely sure :)
>
> >
> > Uh actually can we be just returning -ERESTARTNOINTR or do we need to use
> > restart_syscall()?
>
> Yeah I was wondering about that, but restart_syscall() seems to set
> TIF_SIGPENDING, and I wondered if that was correct... but then I saw other
> places that seemed to use it direct so it seemed so.
>
> Let's eliminiate doubt, will check this next week and make sure.
>
Yeah looks like we do actually, as the function is handled by
arch_do_signal_or_restart():
do_syscall_64()
-> sycall_exit_to_user_mode_work()
-> __sycall_exit_to_user_mode_work()
-> exit_to_user_mode_prepare()
-> exit_to_user_mode_loop()
-> arch_do_signal_or_restart()
-> (possibly) get_signal()
And arch_do_signal_or_restart() is only invoked by exit_to_user_mode_loop()
if _TIF_SIGPENDING or _TIF_NOTIFY_SIGNAL is set:
if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
arch_do_signal_or_restart(regs);
This is set by restart_syscall():
static inline int restart_syscall(void)
{
set_tsk_thread_flag(current, TIF_SIGPENDING);
return -ERESTARTNOINTR;
}
It's a nop if no signal is actually pending too, and it handily also deals
with signals...
> >
> > > ---
> > > mm/madvise.c | 8 +++++++-
> > > 1 file changed, 7 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/mm/madvise.c b/mm/madvise.c
> > > index 48eba25e25fe..127aa5d86656 100644
> > > --- a/mm/madvise.c
> > > +++ b/mm/madvise.c
> > > @@ -1713,8 +1713,14 @@ static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter,
> > > * we have already rescinded locks, it should be no problem to
> > > * simply try again.
> > > */
> > > - if (ret == -ERESTARTNOINTR)
> > > + if (ret == -ERESTARTNOINTR) {
> > > + if (fatal_signal_pending(current)) {
> > > + ret = -EINTR;
> > > + break;
> > > + }
> > > + cond_resched();
> >
> > Should be unnecessary as we're calling an operation that takes a rwsem so
> > there are reschedule points already. And with lazy preempt hopefully
> > cond_resched()s will become history, so let's not add more only to delete later.
>
> Ack will remove on respin.
>
> >
> > > continue;
> > > + }
> > > if (ret < 0)
> > > break;
> > > iov_iter_advance(iter, iter_iov_len(iter));
> > > --
> > > 2.47.0
> >
>
> For simplicitly with your other comments too I think I'll respin this next
> week.
So will respin to use restart_syscall() correctly (+ fix up your other points too).
Have tested and confirmed that failing to use restart_syscall() causes the
-ERESTARTINTR to be returned and no restart, but using it works.
^ permalink raw reply
* Re: [PATCH 2/6] futex: Implement FUTEX2_NUMA
From: Peter Zijlstra @ 2024-10-28 9:46 UTC (permalink / raw)
To: Christoph Lameter (Ampere)
Cc: tglx, linux-kernel, mingo, dvhart, dave, andrealmeid,
Andrew Morton, urezki, hch, lstoakes, Arnd Bergmann, linux-api,
linux-mm, linux-arch, malteskarupke, llong
In-Reply-To: <dce4d83c-fb3f-3581-71e4-33dad3f91e07@gentwo.org>
On Fri, Oct 25, 2024 at 12:28:54PM -0700, Christoph Lameter (Ampere) wrote:
> On Fri, 25 Oct 2024, Peter Zijlstra wrote:
>
> > Extend the futex2 interface to be numa aware.
> >
> > When FUTEX2_NUMA is specified for a futex, the user value is extended
> > to two words (of the same size). The first is the user value we all
> > know, the second one will be the node to place this futex on.
> >
> > struct futex_numa_32 {
> > u32 val;
> > u32 node;
> > };
> >
> > When node is set to ~0, WAIT will set it to the current node_id such
> > that WAKE knows where to find it. If userspace corrupts the node value
> > between WAIT and WAKE, the futex will not be found and no wakeup will
> > happen.
> >
> > When FUTEX2_NUMA is not set, the node is simply an extention of the
> > hash, such that traditional futexes are still interleaved over the
> > nodes.
>
>
> Would it be possible to follow the NUMA memory policy set up for a task
> when making these decisions? We may not need a separate FUTEX2_NUMA
> option. There are supportive functions in mm/mempolicy.c that will yield
> a node for the futex logic to use.
Using get_task_policy() seems very dangerous to me. It is explicitly
possible for different tasks in a process to have different policies,
which means (private) futexes would fail to work correctly.
We need something that is process wide consistent -- like the vma
policies. Except at current, those are to expensive to readily access.
^ permalink raw reply
* Re: [PATCH 2/6] futex: Implement FUTEX2_NUMA
From: Peter Zijlstra @ 2024-10-28 9:38 UTC (permalink / raw)
To: tglx, linux-kernel, mingo, dvhart, andrealmeid, Andrew Morton,
urezki, hch, lstoakes, Arnd Bergmann, linux-api, linux-mm,
linux-arch, malteskarupke, cl, llong
In-Reply-To: <i4ljhfndmqrdg5zevd4gf2chmzesfieflxvfj2io2qfhfj4vb7@nicvpjmcdtyu>
On Fri, Oct 25, 2024 at 11:30:26AM -0700, Davidlohr Bueso wrote:
> On Fri, 25 Oct 2024, Peter Zijlstra wrote:\n
>
> > static int __init futex_init(void)
> > {
> > - unsigned int futex_shift;
> > - unsigned long i;
> > + unsigned int order, n;
> > + unsigned long size, i;
> >
> > #ifdef CONFIG_BASE_SMALL
> > futex_hashsize = 16;
> > #else
> > - futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
> > + futex_hashsize = 256 * num_possible_cpus();
> > + futex_hashsize /= num_possible_nodes();
> > + futex_hashsize = roundup_pow_of_two(futex_hashsize);
> > #endif
> > + futex_hashshift = ilog2(futex_hashsize);
> > + size = sizeof(struct futex_hash_bucket) * futex_hashsize;
> > + order = get_order(size);
> > +
> > + for_each_node(n) {
>
> Probably want to skip nodes that don't have CPUs, those will never
> have the remote for .node value.
What if the CPU-less node is placed equidistant between two (or more)
regular nodes and it is the best location for a futex that is spanning
those nodes?
That is to say, just because it doesn't have CPUs, doesn't mean it is
never the right node.
Hmm?
^ permalink raw reply
* Re: [PATCH 2/6] futex: Implement FUTEX2_NUMA
From: Davidlohr Bueso @ 2024-10-28 1:59 UTC (permalink / raw)
To: Christoph Lameter (Ampere)
Cc: Peter Zijlstra, tglx, linux-kernel, mingo, dvhart, andrealmeid,
Andrew Morton, urezki, hch, lstoakes, Arnd Bergmann, linux-api,
linux-mm, linux-arch, malteskarupke, llong
In-Reply-To: <dce4d83c-fb3f-3581-71e4-33dad3f91e07@gentwo.org>
On Fri, 25 Oct 2024, Christoph Lameter (Ampere) wrote:\n
>Would it be possible to follow the NUMA memory policy set up for a task
>when making these decisions? We may not need a separate FUTEX2_NUMA
>option. There are supportive functions in mm/mempolicy.c that will yield
>a node for the futex logic to use.
With numa-awareness, when would lookups ever want to be anywhere but
local? mempolicy is about allocations, futexes are not that.
^ permalink raw reply
* Re: [PATCH v3 1/5] mm: pagewalk: add the ability to install PTEs
From: Lorenzo Stoakes @ 2024-10-26 7:42 UTC (permalink / raw)
To: David Hildenbrand
Cc: Andrew Morton, Suren Baghdasaryan, Liam R . Howlett,
Matthew Wilcox, Vlastimil Babka, Paul E . McKenney, Jann Horn,
linux-mm, linux-kernel, Muchun Song, Richard Henderson,
Matt Turner, Thomas Bogendoerfer, James E . J . Bottomley,
Helge Deller, Chris Zankel, Max Filippov, Arnd Bergmann,
linux-alpha, linux-mips, linux-parisc, linux-arch, Shuah Khan,
Christian Brauner, linux-kselftest, Sidhartha Kumar, Jeff Xu,
Christoph Hellwig, linux-api, John Hubbard
In-Reply-To: <c072049b-d6ef-47ce-b281-006ae0f721b3@redhat.com>
On Fri, Oct 25, 2024 at 09:08:24PM +0200, David Hildenbrand wrote:
> > >
> > > We already discussed in the past that we need a better and more efficient
> > > way to walk page tables. I have part of that on my TODO list, but I'm
> > > getting distracted.
> >
> > Yes I remember an LSF session on this, it's a really obvious area of improvement
> > that stands out at the moment for sure.
> >
> > Having worked several 12+ hour days in a row though recently I can relate to
> > workload making this difficult though :)
>
> Yes :)
>
> >
> > >
> > > *Inserting* (not walking/modifying existing things as most users to) as done
> > > in this patch is slightly different though, likely "on thing that fits all"
> > > will not apply to all page table walker user cases.
> >
> > Yeah, there's also replace scenarios which then have to do egregious amounts of
> > work to make sure we do everything right, in fact there's duplicates of this in
> > mm/madvise.c *grumble grumble*.
> >
> > >
> > > --
> > > Cheers,
> > >
> > > David / dhildenb
> > >
> >
> > OK so I guess I'll hold off my TODOs on this as you are looking in this area and
> > I trust you :)
>
> It will probably take me a while until I get to it, though. I'd focus on
> walking (and batching what we can) first, then on top modifying existing
> entries.
Yeah entirely understandable and that's the right order I think, the
modifying path is the trickier one especially with all the special cases
all over the place...
>
> The "install something where there is nothing yet" (incl. populating fresh
> page tables etc.) case probably deserves a separate "walker".
Yes this would avoid all the heavy handling a replace handler needs.
>
> If you end up having spare cycles and want to sync on a possible design for
> some part of that bigger task -- removing the old pagewalk logic -- please
> do reach out! :)
Thanks, I may have a play when I have a brief moment, as I feel quite
strongly we need to attack this (as do you I feel! :) will send some RFC or
some thoughts or whatever should I do so!
>
> --
> Cheers,
>
> David / dhildenb
>
Cheers!
^ permalink raw reply
* Re: [PATCH v3 3/5] mm: madvise: implement lightweight guard page mechanism
From: Lorenzo Stoakes @ 2024-10-26 7:40 UTC (permalink / raw)
To: Andrew Morton
Cc: Suren Baghdasaryan, Liam R . Howlett, Matthew Wilcox,
Vlastimil Babka, Paul E . McKenney, Jann Horn, David Hildenbrand,
linux-mm, linux-kernel, Muchun Song, Richard Henderson,
Matt Turner, Thomas Bogendoerfer, James E . J . Bottomley,
Helge Deller, Chris Zankel, Max Filippov, Arnd Bergmann,
linux-alpha, linux-mips, linux-parisc, linux-arch, Shuah Khan,
Christian Brauner, linux-kselftest, Sidhartha Kumar, Jeff Xu,
Christoph Hellwig, linux-api, John Hubbard
In-Reply-To: <20241025171131.9ceabcec32ff4c569d87875f@linux-foundation.org>
On Fri, Oct 25, 2024 at 05:11:31PM -0700, Andrew Morton wrote:
> On Thu, 24 Oct 2024 08:25:46 +0100 Lorenzo Stoakes <lorenzo.stoakes@oracle.com> wrote:
>
> > I actually do plan to extend this work to support shmem and file-backed
> > mappings in the future as a revision to this work.
>
> Useful, thanks. I pasted this in.
>
> > >
> > > (generally, it would be nice to include the proposed manpage update at
> > > this time, so people can review it while the code change is fresh in
> > > their minds)
> >
> > It'd be nice to have the man pages live somewhere within the kernel so we
> > can do this as part of the patch change as things evolve during review, but
> > obviously moving things about like that is out of scope for this discussion
> > :)
>
> Yes, that would be good. At present the linkage is so poor that things
> could get lost.
Things _have_ got lost. I don't see MADV_DONTNEED_LOCKED in the madvise()
man page for instance...
(I intend actually to send a patch for that alongside my changes.)
>
> I guess one thing we could do is to include the proposed manpage update
> within the changelogs. That way it's stored somewhere and gets reviewed
> alongside the patches themselves.
Hm it won't be a diff but I do like the idea... let me come up with
something.
>
> > I do explicitly intend to send a manpage update once this series lands
> > however.
>
> That's late, IMO. Sometimes reviewing manpage updates leads people to
> ask "hey. what about X" or "hey, that's wrong". Michael Kerrisk was
> good at finding such holes, back in the day.
>
Right, this is the problem with having the manpages in a separate repo, it
seems presumptious to _assume_ this will land in 6.13 though I hope it
does, but if I get a patch accepted in the manpages they may ship a version
that has information that is simply invalid...
Really would be nice to integrate it here :)
Michael Kerrisk is a hero, writes with a power of clarity I could only
dream of :) understandable that he may be rather tired of having to
maintain all this however...
^ permalink raw reply
* [PATCH v6 5/5] selftests: pidfd: add tests for PIDFD_SELF_*
From: Lorenzo Stoakes @ 2024-10-26 7:25 UTC (permalink / raw)
To: Christian Brauner
Cc: Shuah Khan, Liam R . Howlett, Suren Baghdasaryan, Vlastimil Babka,
pedro.falcato, linux-kselftest, linux-mm, linux-fsdevel,
linux-api, linux-kernel, Oliver Sang, John Hubbard
In-Reply-To: <cover.1729926229.git.lorenzo.stoakes@oracle.com>
Add tests to assert that PIDFD_SELF_* correctly refers to the current
thread and process.
This is only practically meaningful to pidfd_send_signal() and
pidfd_getfd(), but also explicitly test that we disallow this feature for
setns() where it would make no sense.
We cannot reasonably wait on ourself using waitid(P_PIDFD, ...) so while in
theory PIDFD_SELF_* would work here, we'd be left blocked if we tried it.
We defer testing of mm-specific functionality which uses pidfd, namely
process_madvise() and process_mrelease() to mm testing (though note the
latter can not be sensibly tested as it would require the testing process
to be dying).
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
tools/testing/selftests/pidfd/pidfd.h | 2 +
.../selftests/pidfd/pidfd_getfd_test.c | 141 ++++++++++++++++++
.../selftests/pidfd/pidfd_setns_test.c | 11 ++
tools/testing/selftests/pidfd/pidfd_test.c | 76 ++++++++--
4 files changed, 218 insertions(+), 12 deletions(-)
diff --git a/tools/testing/selftests/pidfd/pidfd.h b/tools/testing/selftests/pidfd/pidfd.h
index 0f3fc51cec73..1dbe48c1cf46 100644
--- a/tools/testing/selftests/pidfd/pidfd.h
+++ b/tools/testing/selftests/pidfd/pidfd.h
@@ -16,6 +16,8 @@
#include <sys/types.h>
#include <sys/wait.h>
+#include <linux/pidfd.h>
+
#include "../kselftest.h"
#include "pidfd_helpers.h"
diff --git a/tools/testing/selftests/pidfd/pidfd_getfd_test.c b/tools/testing/selftests/pidfd/pidfd_getfd_test.c
index cd51d547b751..48d224b13c01 100644
--- a/tools/testing/selftests/pidfd/pidfd_getfd_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_getfd_test.c
@@ -6,6 +6,7 @@
#include <limits.h>
#include <linux/types.h>
#include <poll.h>
+#include <pthread.h>
#include <sched.h>
#include <signal.h>
#include <stdio.h>
@@ -15,6 +16,7 @@
#include <sys/prctl.h>
#include <sys/wait.h>
#include <unistd.h>
+#include <sys/mman.h>
#include <sys/socket.h>
#include <linux/kcmp.h>
@@ -114,6 +116,94 @@ static int child(int sk)
return ret;
}
+static int __pidfd_self_thread_worker(unsigned long page_size)
+{
+ int memfd;
+ int newfd;
+ char *ptr;
+ int err = 0;
+
+ /*
+ * Unshare our FDs so we have our own set. This means
+ * PIDFD_SELF_THREAD_GROUP will fal.
+ */
+ if (unshare(CLONE_FILES) < 0) {
+ err = -errno;
+ goto exit;
+ }
+
+ /* Truncate, map in and write to our memfd. */
+ memfd = sys_memfd_create("test_self_child", 0);
+ if (memfd < 0) {
+ err = -errno;
+ goto exit;
+ }
+
+ if (ftruncate(memfd, page_size)) {
+ err = -errno;
+ goto exit_close_memfd;
+ }
+
+ ptr = mmap(NULL, page_size, PROT_READ | PROT_WRITE,
+ MAP_SHARED, memfd, 0);
+ if (ptr == MAP_FAILED) {
+ err = -errno;
+ goto exit_close_memfd;
+ }
+ ptr[0] = 'y';
+ if (munmap(ptr, page_size)) {
+ err = -errno;
+ goto exit_close_memfd;
+ }
+
+ /* Get a thread-local duplicate of our memfd. */
+ newfd = sys_pidfd_getfd(PIDFD_SELF_THREAD, memfd, 0);
+ if (newfd < 0) {
+ err = -errno;
+ goto exit_close_memfd;
+ }
+
+ if (memfd == newfd) {
+ err = -EINVAL;
+ goto exit_close_fds;
+ }
+
+ /* Map in new fd and make sure that the data is as expected. */
+ ptr = mmap(NULL, page_size, PROT_READ | PROT_WRITE,
+ MAP_SHARED, newfd, 0);
+ if (ptr == MAP_FAILED) {
+ err = -errno;
+ goto exit_close_fds;
+ }
+
+ if (ptr[0] != 'y') {
+ err = -EINVAL;
+ goto exit_close_fds;
+ }
+
+ if (munmap(ptr, page_size)) {
+ err = -errno;
+ goto exit_close_fds;
+ }
+
+exit_close_fds:
+ close(newfd);
+exit_close_memfd:
+ close(memfd);
+exit:
+ return err;
+}
+
+static void *pidfd_self_thread_worker(void *arg)
+{
+ unsigned long page_size = (unsigned long)arg;
+ int ret;
+
+ /* We forward any errors for the caller to handle. */
+ ret = __pidfd_self_thread_worker(page_size);
+ return (void *)(intptr_t)ret;
+}
+
FIXTURE(child)
{
/*
@@ -264,6 +354,57 @@ TEST_F(child, no_strange_EBADF)
EXPECT_EQ(errno, ESRCH);
}
+TEST(pidfd_self)
+{
+ int memfd = sys_memfd_create("test_self", 0);
+ unsigned long page_size = sysconf(_SC_PAGESIZE);
+ int newfd;
+ char *ptr;
+ pthread_t thread;
+ void *res;
+ int err;
+
+ ASSERT_GE(memfd, 0);
+ ASSERT_EQ(ftruncate(memfd, page_size), 0);
+
+ /*
+ * Map so we can assert that the duplicated fd references the same
+ * memory.
+ */
+ ptr = mmap(NULL, page_size, PROT_READ | PROT_WRITE,
+ MAP_SHARED, memfd, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+ ptr[0] = 'x';
+ ASSERT_EQ(munmap(ptr, page_size), 0);
+
+ /* Now get a duplicate of our memfd. */
+ newfd = sys_pidfd_getfd(PIDFD_SELF_THREAD_GROUP, memfd, 0);
+ ASSERT_GE(newfd, 0);
+ ASSERT_NE(memfd, newfd);
+
+ /* Now map duplicate fd and make sure it references the same memory. */
+ ptr = mmap(NULL, page_size, PROT_READ | PROT_WRITE,
+ MAP_SHARED, newfd, 0);
+ ASSERT_NE(ptr, MAP_FAILED);
+ ASSERT_EQ(ptr[0], 'x');
+ ASSERT_EQ(munmap(ptr, page_size), 0);
+
+ /* Cleanup. */
+ close(memfd);
+ close(newfd);
+
+ /*
+ * Fire up the thread and assert that we can lookup the thread-specific
+ * PIDFD_SELF_THREAD (also aliased by PIDFD_SELF).
+ */
+ ASSERT_EQ(pthread_create(&thread, NULL, pidfd_self_thread_worker,
+ (void *)page_size), 0);
+ ASSERT_EQ(pthread_join(thread, &res), 0);
+ err = (int)(intptr_t)res;
+
+ ASSERT_EQ(err, 0);
+}
+
#if __NR_pidfd_getfd == -1
int main(void)
{
diff --git a/tools/testing/selftests/pidfd/pidfd_setns_test.c b/tools/testing/selftests/pidfd/pidfd_setns_test.c
index 7c2a4349170a..bbd39dc5ceb7 100644
--- a/tools/testing/selftests/pidfd/pidfd_setns_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_setns_test.c
@@ -752,4 +752,15 @@ TEST(setns_einval)
close(fd);
}
+TEST(setns_pidfd_self_disallowed)
+{
+ ASSERT_EQ(setns(PIDFD_SELF_THREAD, 0), -1);
+ EXPECT_EQ(errno, EBADF);
+
+ errno = 0;
+
+ ASSERT_EQ(setns(PIDFD_SELF_THREAD_GROUP, 0), -1);
+ EXPECT_EQ(errno, EBADF);
+}
+
TEST_HARNESS_MAIN
diff --git a/tools/testing/selftests/pidfd/pidfd_test.c b/tools/testing/selftests/pidfd/pidfd_test.c
index 9faa686f90e4..440447cf89ba 100644
--- a/tools/testing/selftests/pidfd/pidfd_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_test.c
@@ -42,12 +42,41 @@ static pid_t pidfd_clone(int flags, int *pidfd, int (*fn)(void *))
#endif
}
-static int signal_received;
+static pthread_t signal_received;
static void set_signal_received_on_sigusr1(int sig)
{
if (sig == SIGUSR1)
- signal_received = 1;
+ signal_received = pthread_self();
+}
+
+static int send_signal(int pidfd)
+{
+ int ret = 0;
+
+ if (sys_pidfd_send_signal(pidfd, SIGUSR1, NULL, 0) < 0) {
+ ret = -EINVAL;
+ goto exit;
+ }
+
+ if (signal_received != pthread_self()) {
+ ret = -EINVAL;
+ goto exit;
+ }
+
+exit:
+ signal_received = 0;
+ return ret;
+}
+
+static void *send_signal_worker(void *arg)
+{
+ int pidfd = (int)(intptr_t)arg;
+ int ret;
+
+ /* We forward any errors for the caller to handle. */
+ ret = send_signal(pidfd);
+ return (void *)(intptr_t)ret;
}
/*
@@ -56,8 +85,11 @@ static void set_signal_received_on_sigusr1(int sig)
*/
static int test_pidfd_send_signal_simple_success(void)
{
- int pidfd, ret;
+ int pidfd;
const char *test_name = "pidfd_send_signal send SIGUSR1";
+ pthread_t thread;
+ void *thread_res;
+ int err;
if (!have_pidfd_send_signal) {
ksft_test_result_skip(
@@ -66,25 +98,45 @@ static int test_pidfd_send_signal_simple_success(void)
return 0;
}
+ signal(SIGUSR1, set_signal_received_on_sigusr1);
+
+ /* Try sending a signal to ourselves via /proc/self. */
pidfd = open("/proc/self", O_DIRECTORY | O_CLOEXEC);
if (pidfd < 0)
ksft_exit_fail_msg(
"%s test: Failed to open process file descriptor\n",
test_name);
+ err = send_signal(pidfd);
+ if (err)
+ ksft_exit_fail_msg(
+ "%s test: Error %d on sending pidfd signal\n",
+ test_name, err);
+ close(pidfd);
- signal(SIGUSR1, set_signal_received_on_sigusr1);
+ /* Now try the same thing only using PIDFD_SELF_THREAD_GROUP. */
+ err = send_signal(PIDFD_SELF_THREAD_GROUP);
+ if (err)
+ ksft_exit_fail_msg(
+ "%s test: Error %d on PIDFD_SELF_THREAD_GROUP signal\n",
+ test_name, err);
- ret = sys_pidfd_send_signal(pidfd, SIGUSR1, NULL, 0);
- close(pidfd);
- if (ret < 0)
- ksft_exit_fail_msg("%s test: Failed to send signal\n",
+ /*
+ * Now try the same thing in a thread and assert thread ID is equal to
+ * worker thread ID.
+ */
+ if (pthread_create(&thread, NULL, send_signal_worker,
+ (void *)(intptr_t)PIDFD_SELF_THREAD))
+ ksft_exit_fail_msg("%s test: Failed to create thread\n",
test_name);
-
- if (signal_received != 1)
- ksft_exit_fail_msg("%s test: Failed to receive signal\n",
+ if (pthread_join(thread, &thread_res))
+ ksft_exit_fail_msg("%s test: Failed to join thread\n",
test_name);
+ err = (int)(intptr_t)thread_res;
+ if (err)
+ ksft_exit_fail_msg(
+ "%s test: Error %d on PIDFD_SELF_THREAD signal\n",
+ test_name, err);
- signal_received = 0;
ksft_test_result_pass("%s test: Sent signal\n", test_name);
return 0;
}
--
2.47.0
^ permalink raw reply related
* [PATCH v6 4/5] selftests: pidfd: add pidfd.h UAPI wrapper
From: Lorenzo Stoakes @ 2024-10-26 7:25 UTC (permalink / raw)
To: Christian Brauner
Cc: Shuah Khan, Liam R . Howlett, Suren Baghdasaryan, Vlastimil Babka,
pedro.falcato, linux-kselftest, linux-mm, linux-fsdevel,
linux-api, linux-kernel, Oliver Sang, John Hubbard
In-Reply-To: <cover.1729926229.git.lorenzo.stoakes@oracle.com>
Conflicts can arise between system fcntl.h and linux/fcntl.h, imported by
the linux/pidfd.h UAPI header.
Work around this by adding a wrapper for linux/pidfd.h to
tools/include/ which sets the linux/fcntl.h header guard ahead of
importing the pidfd.h header file.
Adjust the pidfd selftests Makefile to reference this include directory and
put it at a higher precidence than any make header installed headers to
ensure the wrapper is preferred.
This way we can directly import the UAPI header file without issue, use the
latest system header file without having to duplicate anything.
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
tools/include/linux/pidfd.h | 14 ++++++++++++++
tools/testing/selftests/pidfd/Makefile | 3 +--
2 files changed, 15 insertions(+), 2 deletions(-)
create mode 100644 tools/include/linux/pidfd.h
diff --git a/tools/include/linux/pidfd.h b/tools/include/linux/pidfd.h
new file mode 100644
index 000000000000..113c8023072d
--- /dev/null
+++ b/tools/include/linux/pidfd.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef _TOOLS_LINUX_PIDFD_H
+#define _TOOLS_LINUX_PIDFD_H
+
+/*
+ * Some systems have issues with the linux/fcntl.h import in linux/pidfd.h, so
+ * work around this by setting the header guard.
+ */
+#define _LINUX_FCNTL_H
+#include "../../../include/uapi/linux/pidfd.h"
+#undef _LINUX_FCNTL_H
+
+#endif /* _TOOLS_LINUX_PIDFD_H */
diff --git a/tools/testing/selftests/pidfd/Makefile b/tools/testing/selftests/pidfd/Makefile
index d731e3e76d5b..f5038c9dae14 100644
--- a/tools/testing/selftests/pidfd/Makefile
+++ b/tools/testing/selftests/pidfd/Makefile
@@ -1,8 +1,7 @@
# SPDX-License-Identifier: GPL-2.0-only
-CFLAGS += -g $(KHDR_INCLUDES) -pthread -Wall
+CFLAGS += -g -isystem $(top_srcdir)/tools/include $(KHDR_INCLUDES) -pthread -Wall
TEST_GEN_PROGS := pidfd_test pidfd_fdinfo_test pidfd_open_test \
pidfd_poll_test pidfd_wait pidfd_getfd_test pidfd_setns_test
include ../lib.mk
-
--
2.47.0
^ permalink raw reply related
* [PATCH v6 3/5] tools: testing: separate out wait_for_pid() into helper header
From: Lorenzo Stoakes @ 2024-10-26 7:24 UTC (permalink / raw)
To: Christian Brauner
Cc: Shuah Khan, Liam R . Howlett, Suren Baghdasaryan, Vlastimil Babka,
pedro.falcato, linux-kselftest, linux-mm, linux-fsdevel,
linux-api, linux-kernel, Oliver Sang, John Hubbard
In-Reply-To: <cover.1729926229.git.lorenzo.stoakes@oracle.com>
It seems tests other than the pidfd tests use the wait_for_pid() function
declared in pidfd.h.
Since we will shortly be modifying pidfd.h in a way that might clash with
other tests, separate this out and update tests accordingly.
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
tools/testing/selftests/cgroup/test_kill.c | 2 +-
.../pid_namespace/regression_enomem.c | 2 +-
tools/testing/selftests/pidfd/pidfd.h | 26 +------------
tools/testing/selftests/pidfd/pidfd_helpers.h | 39 +++++++++++++++++++
4 files changed, 42 insertions(+), 27 deletions(-)
create mode 100644 tools/testing/selftests/pidfd/pidfd_helpers.h
diff --git a/tools/testing/selftests/cgroup/test_kill.c b/tools/testing/selftests/cgroup/test_kill.c
index 0e5bb6c7307a..2367f645fe89 100644
--- a/tools/testing/selftests/cgroup/test_kill.c
+++ b/tools/testing/selftests/cgroup/test_kill.c
@@ -10,7 +10,7 @@
#include <unistd.h>
#include "../kselftest.h"
-#include "../pidfd/pidfd.h"
+#include "../pidfd/pidfd_helpers.h"
#include "cgroup_util.h"
/*
diff --git a/tools/testing/selftests/pid_namespace/regression_enomem.c b/tools/testing/selftests/pid_namespace/regression_enomem.c
index 7d84097ad45c..f3e6989c8069 100644
--- a/tools/testing/selftests/pid_namespace/regression_enomem.c
+++ b/tools/testing/selftests/pid_namespace/regression_enomem.c
@@ -12,7 +12,7 @@
#include <sys/wait.h>
#include "../kselftest_harness.h"
-#include "../pidfd/pidfd.h"
+#include "../pidfd/pidfd_helpers.h"
/*
* Regression test for:
diff --git a/tools/testing/selftests/pidfd/pidfd.h b/tools/testing/selftests/pidfd/pidfd.h
index 88d6830ee004..0f3fc51cec73 100644
--- a/tools/testing/selftests/pidfd/pidfd.h
+++ b/tools/testing/selftests/pidfd/pidfd.h
@@ -17,6 +17,7 @@
#include <sys/wait.h>
#include "../kselftest.h"
+#include "pidfd_helpers.h"
#ifndef P_PIDFD
#define P_PIDFD 3
@@ -68,31 +69,6 @@
#define PIDFD_SKIP 3
#define PIDFD_XFAIL 4
-static inline int wait_for_pid(pid_t pid)
-{
- int status, ret;
-
-again:
- ret = waitpid(pid, &status, 0);
- if (ret == -1) {
- if (errno == EINTR)
- goto again;
-
- ksft_print_msg("waitpid returned -1, errno=%d\n", errno);
- return -1;
- }
-
- if (!WIFEXITED(status)) {
- ksft_print_msg(
- "waitpid !WIFEXITED, WIFSIGNALED=%d, WTERMSIG=%d\n",
- WIFSIGNALED(status), WTERMSIG(status));
- return -1;
- }
-
- ret = WEXITSTATUS(status);
- return ret;
-}
-
static inline int sys_pidfd_open(pid_t pid, unsigned int flags)
{
return syscall(__NR_pidfd_open, pid, flags);
diff --git a/tools/testing/selftests/pidfd/pidfd_helpers.h b/tools/testing/selftests/pidfd/pidfd_helpers.h
new file mode 100644
index 000000000000..5637bfe888de
--- /dev/null
+++ b/tools/testing/selftests/pidfd/pidfd_helpers.h
@@ -0,0 +1,39 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __PIDFD_HELPERS_H
+#define __PIDFD_HELPERS_H
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "../kselftest.h"
+
+static inline int wait_for_pid(pid_t pid)
+{
+ int status, ret;
+
+again:
+ ret = waitpid(pid, &status, 0);
+ if (ret == -1) {
+ if (errno == EINTR)
+ goto again;
+
+ ksft_print_msg("waitpid returned -1, errno=%d\n", errno);
+ return -1;
+ }
+
+ if (!WIFEXITED(status)) {
+ ksft_print_msg(
+ "waitpid !WIFEXITED, WIFSIGNALED=%d, WTERMSIG=%d\n",
+ WIFSIGNALED(status), WTERMSIG(status));
+ return -1;
+ }
+
+ ret = WEXITSTATUS(status);
+ return ret;
+}
+
+#endif /* __PIDFD_HELPERS_H */
--
2.47.0
^ permalink raw reply related
* [PATCH v6 2/5] pidfd: add PIDFD_SELF_* sentinels to refer to own thread/process
From: Lorenzo Stoakes @ 2024-10-26 7:24 UTC (permalink / raw)
To: Christian Brauner
Cc: Shuah Khan, Liam R . Howlett, Suren Baghdasaryan, Vlastimil Babka,
pedro.falcato, linux-kselftest, linux-mm, linux-fsdevel,
linux-api, linux-kernel, Oliver Sang, John Hubbard
In-Reply-To: <cover.1729926229.git.lorenzo.stoakes@oracle.com>
It is useful to be able to utilise the pidfd mechanism to reference the
current thread or process (from a userland point of view - thread group
leader from the kernel's point of view).
Therefore introduce PIDFD_SELF_THREAD to refer to the current thread, and
PIDFD_SELF_THREAD_GROUP to refer to the current thread group leader.
For convenience and to avoid confusion from userland's perspective we alias
these:
* PIDFD_SELF is an alias for PIDFD_SELF_THREAD - This is nearly always what
the user will want to use, as they would find it surprising if for
instance fd's were unshared()'d and they wanted to invoke pidfd_getfd()
and that failed.
* PIDFD_SELF_PROCESS is an alias for PIDFD_SELF_THREAD_GROUP - Most users
have no concept of thread groups or what a thread group leader is, and
from userland's perspective and nomenclature this is what userland
considers to be a process.
Due to the refactoring of the central __pidfd_get_pid() function we can
implement this functionality centrally, providing the use of this sentinel
in most functionality which utilises pidfd's.
We need to explicitly adjust kernel_waitid_prepare() to permit this (though
it wouldn't really make sense to use this there, we provide the ability for
consistency).
We explicitly disallow use of this in setns(), which would otherwise have
required explicit custom handling, as it doesn't make sense to set the
current calling thread to join the namespace of itself.
As the callers of pidfd_get_pid() expect an increased reference count on
the pid we do so in the self case, reducing churn and avoiding any breakage
from existing logic which decrements this reference count.
This change implicitly provides PIDFD_SELF_* support in the waitid(P_PIDFS,
...), process_madvise(), process_mrelease(), pidfd_send_signal(), and
pidfd_getfd() system calls.
Things such as polling a pidfs and general fd operations are not supported,
this strictly provides the sentinel for APIs which explicitly accept a
pidfd.
Suggested-by: Pedro Falcato <pedro.falcato@gmail.com>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
include/linux/pid.h | 8 ++++--
include/uapi/linux/pidfd.h | 10 ++++++++
kernel/exit.c | 4 ++-
kernel/nsproxy.c | 1 +
kernel/pid.c | 51 ++++++++++++++++++++++++--------------
5 files changed, 53 insertions(+), 21 deletions(-)
diff --git a/include/linux/pid.h b/include/linux/pid.h
index d466890e1b35..3b2ac7567a88 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -78,11 +78,15 @@ struct file;
* __pidfd_get_pid() - Retrieve a pid associated with the specified pidfd.
*
* @pidfd: The pidfd whose pid we want, or the fd of a /proc/<pid> file if
- * @alloc_proc is also set.
+ * @alloc_proc is also set, or PIDFD_SELF_* to refer to the current
+ * thread or thread group leader.
* @allow_proc: If set, then an fd of a /proc/<pid> file can be passed instead
* of a pidfd, and this will be used to determine the pid.
+
* @flags: Output variable, if non-NULL, then the file->f_flags of the
- * pidfd will be set here.
+ * pidfd will be set here or If PIDFD_SELF_THREAD is set, this is
+ * set to PIDFD_THREAD, otherwise if PIDFD_SELF_THREAD_GROUP then
+ * this is set to zero.
*
* Returns: If successful, the pid associated with the pidfd, otherwise an
* error.
diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h
index 565fc0629fff..6fe1d63b2086 100644
--- a/include/uapi/linux/pidfd.h
+++ b/include/uapi/linux/pidfd.h
@@ -29,4 +29,14 @@
#define PIDFD_GET_USER_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 9)
#define PIDFD_GET_UTS_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 10)
+/*
+ * Special sentinel values which can be used to refer to the current thread or
+ * thread group leader (which from a userland perspective is the process).
+ */
+#define PIDFD_SELF PIDFD_SELF_THREAD
+#define PIDFD_SELF_PROCESS PIDFD_SELF_THREAD_GROUP
+
+#define PIDFD_SELF_THREAD -10000 /* Current thread. */
+#define PIDFD_SELF_THREAD_GROUP -20000 /* Current thread group leader. */
+
#endif /* _UAPI_LINUX_PIDFD_H */
diff --git a/kernel/exit.c b/kernel/exit.c
index 619f0014c33b..e4f85ec4ba78 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -71,6 +71,7 @@
#include <linux/user_events.h>
#include <linux/uaccess.h>
+#include <uapi/linux/pidfd.h>
#include <uapi/linux/wait.h>
#include <asm/unistd.h>
@@ -1739,7 +1740,8 @@ int kernel_waitid_prepare(struct wait_opts *wo, int which, pid_t upid,
break;
case P_PIDFD:
type = PIDTYPE_PID;
- if (upid < 0)
+ if (upid < 0 && upid != PIDFD_SELF_THREAD &&
+ upid != PIDFD_SELF_THREAD_GROUP)
return -EINVAL;
pid = pidfd_get_pid(upid, &f_flags);
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index dc952c3b05af..d239f7eeaa1f 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -550,6 +550,7 @@ SYSCALL_DEFINE2(setns, int, fd, int, flags)
struct nsset nsset = {};
int err = 0;
+ /* If fd is PIDFD_SELF_*, implicitly fail here, as invalid. */
if (!fd_file(f))
return -EBADF;
diff --git a/kernel/pid.c b/kernel/pid.c
index 94c97559e5c5..0a1861b4422c 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -535,33 +535,48 @@ struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
}
EXPORT_SYMBOL_GPL(find_ge_pid);
+static struct pid *pidfd_get_pid_self(unsigned int pidfd, unsigned int *flags)
+{
+ bool is_thread = pidfd == PIDFD_SELF_THREAD;
+ enum pid_type type = is_thread ? PIDTYPE_PID : PIDTYPE_TGID;
+ struct pid *pid = *task_pid_ptr(current, type);
+
+ /* The caller expects an elevated reference count. */
+ get_pid(pid);
+ return pid;
+}
+
struct pid *__pidfd_get_pid(unsigned int pidfd, bool allow_proc,
unsigned int *flags)
{
- struct pid *pid;
- struct fd f = fdget(pidfd);
- struct file *file = fd_file(f);
+ if (pidfd == PIDFD_SELF_THREAD || pidfd == PIDFD_SELF_THREAD_GROUP) {
+ return pidfd_get_pid_self(pidfd, flags);
+ } else {
+ struct pid *pid;
+ struct fd f = fdget(pidfd);
+ struct file *file = fd_file(f);
- if (!file)
- return ERR_PTR(-EBADF);
+ if (!file)
+ return ERR_PTR(-EBADF);
- pid = pidfd_pid(file);
- /* If we allow opening a pidfd via /proc/<pid>, do so. */
- if (IS_ERR(pid) && allow_proc)
- pid = tgid_pidfd_to_pid(file);
+ pid = pidfd_pid(file);
+ /* If we allow opening a pidfd via /proc/<pid>, do so. */
+ if (IS_ERR(pid) && allow_proc)
+ pid = tgid_pidfd_to_pid(file);
- if (IS_ERR(pid)) {
+ if (IS_ERR(pid)) {
+ fdput(f);
+ return pid;
+ }
+
+ /* Pin pid before we release fd. */
+ get_pid(pid);
+ if (flags)
+ *flags = file->f_flags;
fdput(f);
+
return pid;
}
-
- /* Pin pid before we release fd. */
- get_pid(pid);
- if (flags)
- *flags = file->f_flags;
- fdput(f);
-
- return pid;
}
/**
--
2.47.0
^ permalink raw reply related
* [PATCH v6 0/5] introduce PIDFD_SELF* sentinels
From: Lorenzo Stoakes @ 2024-10-26 7:24 UTC (permalink / raw)
To: Christian Brauner
Cc: Shuah Khan, Liam R . Howlett, Suren Baghdasaryan, Vlastimil Babka,
pedro.falcato, linux-kselftest, linux-mm, linux-fsdevel,
linux-api, linux-kernel, Oliver Sang, John Hubbard
If you wish to utilise a pidfd interface to refer to the current process or
thread it is rather cumbersome, requiring something like:
int pidfd = pidfd_open(getpid(), 0 or PIDFD_THREAD);
...
close(pidfd);
Or the equivalent call opening /proc/self. It is more convenient to use a
sentinel value to indicate to an interface that accepts a pidfd that we
simply wish to refer to the current process thread.
This series introduces sentinels for this purposes which can be passed as
the pidfd in this instance rather than having to establish a dummy fd for
this purpose.
It is useful to refer to both the current thread from the userland's
perspective for which we use PIDFD_SELF, and the current process from the
userland's perspective, for which we use PIDFD_SELF_PROCESS.
There is unfortunately some confusion between the kernel and userland as to
what constitutes a process - a thread from the userland perspective is a
process in userland, and a userland process is a thread group (more
specifically the thread group leader from the kernel perspective). We
therefore alias things thusly:
* PIDFD_SELF_THREAD aliased by PIDFD_SELF - use PIDTYPE_PID.
* PIDFD_SELF_THREAD_GROUP alised by PIDFD_SELF_PROCESS - use PIDTYPE_TGID.
In all of the kernel code we refer to PIDFD_SELF_THREAD and
PIDFD_SELF_THREAD_GROUP. However we expect users to use PIDFD_SELF and
PIDFD_SELF_PROCESS.
This matters for cases where, for instance, a user unshare()'s FDs or does
thread-specific signal handling and where the user would be hugely confused
if the FDs referenced or signal processed referred to the thread group
leader rather than the individual thread.
We ensure that pidfd_send_signal() and pidfd_getfd() work correctly, and
assert as much in selftests. All other interfaces except setns() will work
implicitly with this new interface, however it doesn't make sense to test
waitid(P_PIDFD, ...) as waiting on ourselves is a blocking operation.
In the case of setns() we explicitly disallow use of PIDFD_SELF* as it
doesn't make sense to obtain the namespaces of our own process, and it
would require work to implement this functionality there that would be of
no use.
We also do not provide the ability to utilise PIDFD_SELF* in ordinary fd
operations such as open() or poll(), as this would require extensive work
and be of no real use.
v6:
* Avoid static inline in UAPI header as suggested by Pedro.
* Place PIDFD_SELF values out of range of errors and any other sentinel as
suggested by Pedro.
v5:
* Fixup self test dependencies on pidfd/pidfd.h.
https://lore.kernel.org/linux-mm/cover.1729848252.git.lorenzo.stoakes@oracle.com/
v4:
* Avoid returning an fd in the __pidfd_get_pid() function as pointed out by
Christian, instead simply always pin the pid and maintain fd scope in the
helper alone.
* Add wrapper header file in tools/include/linux to allow for import of
UAPI pidfd.h header without encountering the collision between system
fcntl.h and linux/fcntl.h as discussed with Shuah and John.
* Fixup tests to import the UAPI pidfd.h header working around conflicts
between system fcntl.h and linux/fcntl.h which the UAPI pidfd.h imports,
as reported by Shuah.
* Use an int for pidfd_is_self_sentinel() to avoid any dependency on
stdbool.h in userland.
https://lore.kernel.org/linux-mm/cover.1729198898.git.lorenzo.stoakes@oracle.com/
v3:
* Do not fput() an invalid fd as reported by kernel test bot.
* Fix unintended churn from moving variable declaration.
https://lore.kernel.org/linux-mm/cover.1729073310.git.lorenzo.stoakes@oracle.com/
v2:
* Fix tests as reported by Shuah.
* Correct RFC version lore link.
https://lore.kernel.org/linux-mm/cover.1728643714.git.lorenzo.stoakes@oracle.com/
Non-RFC v1:
* Removed RFC tag - there seems to be general consensus that this change is
a good idea, but perhaps some debate to be had on implementation. It
seems sensible then to move forward with the RFC flag removed.
* Introduced PIDFD_SELF_THREAD, PIDFD_SELF_THREAD_GROUP and their aliases
PIDFD_SELF and PIDFD_SELF_PROCESS respectively.
* Updated testing accordingly.
https://lore.kernel.org/linux-mm/cover.1728578231.git.lorenzo.stoakes@oracle.com/
RFC version:
https://lore.kernel.org/linux-mm/cover.1727644404.git.lorenzo.stoakes@oracle.com/
Lorenzo Stoakes (5):
pidfd: extend pidfd_get_pid() and de-duplicate pid lookup
pidfd: add PIDFD_SELF_* sentinels to refer to own thread/process
tools: testing: separate out wait_for_pid() into helper header
selftests: pidfd: add pidfd.h UAPI wrapper
selftests: pidfd: add tests for PIDFD_SELF_*
include/linux/pid.h | 34 ++++-
include/uapi/linux/pidfd.h | 10 ++
kernel/exit.c | 4 +-
kernel/nsproxy.c | 1 +
kernel/pid.c | 65 +++++---
kernel/signal.c | 29 +---
tools/include/linux/pidfd.h | 14 ++
tools/testing/selftests/cgroup/test_kill.c | 2 +-
.../pid_namespace/regression_enomem.c | 2 +-
tools/testing/selftests/pidfd/Makefile | 3 +-
tools/testing/selftests/pidfd/pidfd.h | 28 +---
.../selftests/pidfd/pidfd_getfd_test.c | 141 ++++++++++++++++++
tools/testing/selftests/pidfd/pidfd_helpers.h | 39 +++++
.../selftests/pidfd/pidfd_setns_test.c | 11 ++
tools/testing/selftests/pidfd/pidfd_test.c | 76 ++++++++--
15 files changed, 371 insertions(+), 88 deletions(-)
create mode 100644 tools/include/linux/pidfd.h
create mode 100644 tools/testing/selftests/pidfd/pidfd_helpers.h
--
2.47.0
^ permalink raw reply
* [PATCH v6 1/5] pidfd: extend pidfd_get_pid() and de-duplicate pid lookup
From: Lorenzo Stoakes @ 2024-10-26 7:24 UTC (permalink / raw)
To: Christian Brauner
Cc: Shuah Khan, Liam R . Howlett, Suren Baghdasaryan, Vlastimil Babka,
pedro.falcato, linux-kselftest, linux-mm, linux-fsdevel,
linux-api, linux-kernel, Oliver Sang, John Hubbard
In-Reply-To: <cover.1729926229.git.lorenzo.stoakes@oracle.com>
The means by which a pid is determined from a pidfd is duplicated, with
some callers holding a reference to the (pid)fd, and others explicitly
pinning the pid.
Introduce __pidfd_get_pid() which narrows this to one approach of pinning
the pid, with an optional output parameters for file->f_flags to avoid the
need to hold onto a file to retrieve this.
Additionally, allow the ability to open a pidfd by opening a /proc/<pid>
directory, utilised by the pidfd_send_signal() system call, providing a
pidfd_get_pid_proc() helper function to do so.
Doing this allows us to eliminate open-coded pidfd pid lookup and to
consistently handle this in one place.
This lays the groundwork for a subsequent patch which adds a new sentinel
pidfd to explicitly reference the current process (i.e. thread group
leader) without the need for a pidfd.
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
include/linux/pid.h | 30 +++++++++++++++++++++++++++++-
kernel/pid.c | 42 ++++++++++++++++++++++++------------------
kernel/signal.c | 29 ++++++-----------------------
3 files changed, 59 insertions(+), 42 deletions(-)
diff --git a/include/linux/pid.h b/include/linux/pid.h
index a3aad9b4074c..d466890e1b35 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -2,6 +2,7 @@
#ifndef _LINUX_PID_H
#define _LINUX_PID_H
+#include <linux/file.h>
#include <linux/pid_types.h>
#include <linux/rculist.h>
#include <linux/rcupdate.h>
@@ -72,8 +73,35 @@ extern struct pid init_struct_pid;
struct file;
+
+/**
+ * __pidfd_get_pid() - Retrieve a pid associated with the specified pidfd.
+ *
+ * @pidfd: The pidfd whose pid we want, or the fd of a /proc/<pid> file if
+ * @alloc_proc is also set.
+ * @allow_proc: If set, then an fd of a /proc/<pid> file can be passed instead
+ * of a pidfd, and this will be used to determine the pid.
+ * @flags: Output variable, if non-NULL, then the file->f_flags of the
+ * pidfd will be set here.
+ *
+ * Returns: If successful, the pid associated with the pidfd, otherwise an
+ * error.
+ */
+struct pid *__pidfd_get_pid(unsigned int pidfd, bool allow_proc,
+ unsigned int *flags);
+
+static inline struct pid *pidfd_get_pid(unsigned int pidfd, unsigned int *flags)
+{
+ return __pidfd_get_pid(pidfd, /* allow_proc = */ false, flags);
+}
+
+static inline struct pid *pidfd_get_pid_proc(unsigned int pidfd,
+ unsigned int *flags)
+{
+ return __pidfd_get_pid(pidfd, /* allow_proc = */ true, flags);
+}
+
struct pid *pidfd_pid(const struct file *file);
-struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags);
int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret);
void do_notify_pidfd(struct task_struct *task);
diff --git a/kernel/pid.c b/kernel/pid.c
index 2715afb77eab..94c97559e5c5 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -36,6 +36,7 @@
#include <linux/pid_namespace.h>
#include <linux/init_task.h>
#include <linux/syscalls.h>
+#include <linux/proc_fs.h>
#include <linux/proc_ns.h>
#include <linux/refcount.h>
#include <linux/anon_inodes.h>
@@ -534,22 +535,32 @@ struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
}
EXPORT_SYMBOL_GPL(find_ge_pid);
-struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags)
+struct pid *__pidfd_get_pid(unsigned int pidfd, bool allow_proc,
+ unsigned int *flags)
{
- struct fd f;
struct pid *pid;
+ struct fd f = fdget(pidfd);
+ struct file *file = fd_file(f);
- f = fdget(fd);
- if (!fd_file(f))
+ if (!file)
return ERR_PTR(-EBADF);
- pid = pidfd_pid(fd_file(f));
- if (!IS_ERR(pid)) {
- get_pid(pid);
- *flags = fd_file(f)->f_flags;
+ pid = pidfd_pid(file);
+ /* If we allow opening a pidfd via /proc/<pid>, do so. */
+ if (IS_ERR(pid) && allow_proc)
+ pid = tgid_pidfd_to_pid(file);
+
+ if (IS_ERR(pid)) {
+ fdput(f);
+ return pid;
}
+ /* Pin pid before we release fd. */
+ get_pid(pid);
+ if (flags)
+ *flags = file->f_flags;
fdput(f);
+
return pid;
}
@@ -747,23 +758,18 @@ SYSCALL_DEFINE3(pidfd_getfd, int, pidfd, int, fd,
unsigned int, flags)
{
struct pid *pid;
- struct fd f;
int ret;
/* flags is currently unused - make sure it's unset */
if (flags)
return -EINVAL;
- f = fdget(pidfd);
- if (!fd_file(f))
- return -EBADF;
-
- pid = pidfd_pid(fd_file(f));
+ pid = pidfd_get_pid(pidfd, NULL);
if (IS_ERR(pid))
- ret = PTR_ERR(pid);
- else
- ret = pidfd_getfd(pid, fd);
+ return PTR_ERR(pid);
- fdput(f);
+ ret = pidfd_getfd(pid, fd);
+
+ put_pid(pid);
return ret;
}
diff --git a/kernel/signal.c b/kernel/signal.c
index 4344860ffcac..9a35b1cf40ad 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3875,17 +3875,6 @@ static int copy_siginfo_from_user_any(kernel_siginfo_t *kinfo,
return copy_siginfo_from_user(kinfo, info);
}
-static struct pid *pidfd_to_pid(const struct file *file)
-{
- struct pid *pid;
-
- pid = pidfd_pid(file);
- if (!IS_ERR(pid))
- return pid;
-
- return tgid_pidfd_to_pid(file);
-}
-
#define PIDFD_SEND_SIGNAL_FLAGS \
(PIDFD_SIGNAL_THREAD | PIDFD_SIGNAL_THREAD_GROUP | \
PIDFD_SIGNAL_PROCESS_GROUP)
@@ -3908,10 +3897,10 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
siginfo_t __user *, info, unsigned int, flags)
{
int ret;
- struct fd f;
struct pid *pid;
kernel_siginfo_t kinfo;
enum pid_type type;
+ unsigned int f_flags;
/* Enforce flags be set to 0 until we add an extension. */
if (flags & ~PIDFD_SEND_SIGNAL_FLAGS)
@@ -3921,16 +3910,10 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
if (hweight32(flags & PIDFD_SEND_SIGNAL_FLAGS) > 1)
return -EINVAL;
- f = fdget(pidfd);
- if (!fd_file(f))
- return -EBADF;
-
/* Is this a pidfd? */
- pid = pidfd_to_pid(fd_file(f));
- if (IS_ERR(pid)) {
- ret = PTR_ERR(pid);
- goto err;
- }
+ pid = pidfd_get_pid_proc(pidfd, &f_flags);
+ if (IS_ERR(pid))
+ return PTR_ERR(pid);
ret = -EINVAL;
if (!access_pidfd_pidns(pid))
@@ -3939,7 +3922,7 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
switch (flags) {
case 0:
/* Infer scope from the type of pidfd. */
- if (fd_file(f)->f_flags & PIDFD_THREAD)
+ if (f_flags & PIDFD_THREAD)
type = PIDTYPE_PID;
else
type = PIDTYPE_TGID;
@@ -3978,7 +3961,7 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
else
ret = kill_pid_info_type(sig, &kinfo, pid, type);
err:
- fdput(f);
+ put_pid(pid);
return ret;
}
--
2.47.0
^ permalink raw reply related
* Re: [PATCH v1 11/14] futex: Implement FUTEX2_NUMA
From: Peter Zijlstra @ 2024-10-26 7:21 UTC (permalink / raw)
To: Christoph Lameter (Ampere)
Cc: tglx, axboe, linux-kernel, mingo, dvhart, dave, andrealmeid,
Andrew Morton, urezki, hch, lstoakes, Arnd Bergmann, linux-api,
linux-mm, linux-arch, malteskarupke
In-Reply-To: <887eadb6-6142-3edf-0a25-d33b2219b90d@gentwo.org>
On Fri, Oct 25, 2024 at 12:36:28PM -0700, Christoph Lameter (Ampere) wrote:
>
> Sorry saw this after the other email.
>
> On Fri, 25 Oct 2024, Peter Zijlstra wrote:
>
> > > Could we follow NUMA policies like with other metadata allocations during
> > > systen call processing?
> >
> > I had a quick look at this, and since the mempolicy stuff is per vma,
> > and we don't have the vma, this is going to be terribly expensive --
> > mmap_lock and all that.
>
> There is a memory policy for the task as a whole that is used for slab
> allocations and allocations that are not vma bound in current->mempolicy.
> Use that.
> You can get a node number following the current task mempolicy by calling
> mempolicy_slab_node() and keep using that node for the future.
I'll look into the per task thing, which I'm hoping means per-process.
We need something that is mm wide consistent.
But since futexes play in the address space, I was really rather
thinking we ought to use the vma policy.
^ permalink raw reply
* Re: [PATCH v3 3/5] mm: madvise: implement lightweight guard page mechanism
From: Andrew Morton @ 2024-10-26 0:11 UTC (permalink / raw)
To: Lorenzo Stoakes
Cc: Suren Baghdasaryan, Liam R . Howlett, Matthew Wilcox,
Vlastimil Babka, Paul E . McKenney, Jann Horn, David Hildenbrand,
linux-mm, linux-kernel, Muchun Song, Richard Henderson,
Matt Turner, Thomas Bogendoerfer, James E . J . Bottomley,
Helge Deller, Chris Zankel, Max Filippov, Arnd Bergmann,
linux-alpha, linux-mips, linux-parisc, linux-arch, Shuah Khan,
Christian Brauner, linux-kselftest, Sidhartha Kumar, Jeff Xu,
Christoph Hellwig, linux-api, John Hubbard
In-Reply-To: <a10c26ea-3a48-452c-a02d-7522eefd494d@lucifer.local>
On Thu, 24 Oct 2024 08:25:46 +0100 Lorenzo Stoakes <lorenzo.stoakes@oracle.com> wrote:
> I actually do plan to extend this work to support shmem and file-backed
> mappings in the future as a revision to this work.
Useful, thanks. I pasted this in.
> >
> > (generally, it would be nice to include the proposed manpage update at
> > this time, so people can review it while the code change is fresh in
> > their minds)
>
> It'd be nice to have the man pages live somewhere within the kernel so we
> can do this as part of the patch change as things evolve during review, but
> obviously moving things about like that is out of scope for this discussion
> :)
Yes, that would be good. At present the linkage is so poor that things
could get lost.
I guess one thing we could do is to include the proposed manpage update
within the changelogs. That way it's stored somewhere and gets reviewed
alongside the patches themselves.
> I do explicitly intend to send a manpage update once this series lands
> however.
That's late, IMO. Sometimes reviewing manpage updates leads people to
ask "hey. what about X" or "hey, that's wrong". Michael Kerrisk was
good at finding such holes, back in the day.
^ permalink raw reply
* Re: [PATCH v3 3/5] mm: madvise: implement lightweight guard page mechanism
From: Lorenzo Stoakes @ 2024-10-25 22:35 UTC (permalink / raw)
To: Vlastimil Babka
Cc: Andrew Morton, Suren Baghdasaryan, Liam R . Howlett,
Matthew Wilcox, Paul E . McKenney, Jann Horn, David Hildenbrand,
linux-mm, linux-kernel, Muchun Song, Richard Henderson,
Matt Turner, Thomas Bogendoerfer, James E . J . Bottomley,
Helge Deller, Chris Zankel, Max Filippov, Arnd Bergmann,
linux-alpha, linux-mips, linux-parisc, linux-arch, Shuah Khan,
Christian Brauner, linux-kselftest, Sidhartha Kumar, Jeff Xu,
Christoph Hellwig, linux-api, John Hubbard
In-Reply-To: <7c7185ed-f997-484a-b1d1-91ae6c761266@suse.cz>
On Fri, Oct 25, 2024 at 11:56:52PM +0200, Vlastimil Babka wrote:
> On 10/25/24 19:12, Lorenzo Stoakes wrote:
> > On Wed, Oct 23, 2024 at 05:24:40PM +0100, Lorenzo Stoakes wrote:
> >> Implement a new lightweight guard page feature, that is regions of userland
> >> virtual memory that, when accessed, cause a fatal signal to arise.
> >
> > <snip>
> >
> > Hi Andrew - Could you apply the below fix-patch? I realise we must handle
> > fatal signals and conditional rescheduling in the vector_madvise() special
> > case.
> >
> > Thanks!
> >
> > ----8<----
> > From 546d7e1831c71599fc733d589e0d75f52e84826d Mon Sep 17 00:00:00 2001
> > From: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> > Date: Fri, 25 Oct 2024 18:05:48 +0100
> > Subject: [PATCH] mm: yield on fatal signal/cond_sched() in vector_madvise()
> >
> > While we have to treat -ERESTARTNOINTR specially here as we are looping
> > through a vector of operations and can't simply restart the entire
> > operation, we mustn't hold up fatal signals or RT kernels.
>
> For plain madvise() syscall returning -ERESTARTNOINTR does the right thing
> and checks fatal_signal_pending() before returning, right?
I believe so. But now you've caused me some doubt so let me double check
and make absolutely sure :)
>
> Uh actually can we be just returning -ERESTARTNOINTR or do we need to use
> restart_syscall()?
Yeah I was wondering about that, but restart_syscall() seems to set
TIF_SIGPENDING, and I wondered if that was correct... but then I saw other
places that seemed to use it direct so it seemed so.
Let's eliminiate doubt, will check this next week and make sure.
>
> > ---
> > mm/madvise.c | 8 +++++++-
> > 1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/madvise.c b/mm/madvise.c
> > index 48eba25e25fe..127aa5d86656 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -1713,8 +1713,14 @@ static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter,
> > * we have already rescinded locks, it should be no problem to
> > * simply try again.
> > */
> > - if (ret == -ERESTARTNOINTR)
> > + if (ret == -ERESTARTNOINTR) {
> > + if (fatal_signal_pending(current)) {
> > + ret = -EINTR;
> > + break;
> > + }
> > + cond_resched();
>
> Should be unnecessary as we're calling an operation that takes a rwsem so
> there are reschedule points already. And with lazy preempt hopefully
> cond_resched()s will become history, so let's not add more only to delete later.
Ack will remove on respin.
>
> > continue;
> > + }
> > if (ret < 0)
> > break;
> > iov_iter_advance(iter, iter_iov_len(iter));
> > --
> > 2.47.0
>
For simplicitly with your other comments too I think I'll respin this next
week.
^ permalink raw reply
* Re: [PATCH v5 2/5] pidfd: add PIDFD_SELF_* sentinels to refer to own thread/process
From: Lorenzo Stoakes @ 2024-10-25 22:17 UTC (permalink / raw)
To: John Hubbard
Cc: Pedro Falcato, Christian Brauner, Shuah Khan, Liam R . Howlett,
Suren Baghdasaryan, Vlastimil Babka, linux-kselftest, linux-mm,
linux-fsdevel, linux-api, linux-kernel, Oliver Sang
In-Reply-To: <330c0dae-fa8a-49e5-94b4-25b915f74e37@nvidia.com>
On Fri, Oct 25, 2024 at 02:51:29PM -0700, John Hubbard wrote:
> On 10/25/24 2:09 PM, Lorenzo Stoakes wrote:
> > On Fri, Oct 25, 2024 at 01:31:49PM -0700, John Hubbard wrote:
> > > On 10/25/24 12:49 PM, Lorenzo Stoakes wrote:
> > > > On Fri, Oct 25, 2024 at 11:44:34AM -0700, John Hubbard wrote:
> > > > > On 10/25/24 11:38 AM, Pedro Falcato wrote:
> > > > > > On Fri, Oct 25, 2024 at 6:41 PM John Hubbard <jhubbard@nvidia.com> wrote:
> > > ...
> > > I'll admit to being easily cowed by "you're breaking userspace" arguments.
> > > Even when they start to get rather absurd. Because I can't easily tell where
> > > the line is.
> > >
> > > Maybe "-std=c89 -pedantic" is on the other side of the line. I'd like it
> > > to be! :)
> >
> > Well, apparently not...
>
> Why not? Your arguments are clear and reasonable. Why shouldn't they prevail?
>
> Please don't think that I have some sort of firm position here. I'm simply
> looking for the right answer. And if that's different than something I
> proposed earlier, no problem. The best answer should win.
>
> ...
> > > > The bike shed should be blue! Wait no no, it should be red... Hang on
> > > > yellow yes! Yellow's great!
> > >
> > > Putting a header in the right location, so as to avoid breakage here or
> > > there, is not bikeshedding. Sorry.
> >
> > There are 312 uses of "static inline" already in UAPI headers, not all
> > quite as obscure as claimed.
> >
>
> OK, good. Let's lead with that. It seems very clear, then, that a new one
> won't cause a problem.
Right, sorry I thought I had made this point earlier, perhaps in a sub-thread of
a thread of thread. It felt as if you guys were acting as if that were
immaterial, which is why I highlighted it again.
>
> > Specifically requiring me and only me to support ansi C89 for a theorised
> > scenario is in my opinion bikeshedding, but I don't want to get into an
> > argument about something so petty :)
>
> An argument about the definition of bikeshedding sounds delightfully
> recursive, but yes, let's not. :)
:)
>
> ...
> > > > ANyway if you guys feel strong enough about this, I'll respin again and
> > > > just open-code this trivial check where it's used.
> > >
> > > No strong feelings, just hoping to help make a choice that gets you
> > > closer to getting your patches committed.
> >
> > I mean, you are saying I am breaking things and implying the series is
> > blocked on this, that sounds like a strong opinion, but again I'm not going
> > to argue.
>
> Actually, Pedro's request kicked this off, and I was hoping to dismiss
> it--again, in order to help move things along. My opinion is that we
> should shun ancient toolchains and ancient systems whenever possible.
>
> Somehow that got turned into "I'm trying to block the patchset". Really,
> whatever works, follows The Rules (whatever we eventually understand
> them to be), and doesn't cause someone *else* to come out of the
> woodwork and claim a problem, is fine with me.
Text is a poor medium, sorry!
I don't mean to say you're doing that purposefully on any level, I mean to
say that, by arguing here over something that feels kind of unimportant, we
are inadvertently doing that.
>
> >
> > As with the requirement that I, only for my part of the change, must fix up
> > test header import, while I disagree I should be doing the fix, I did it
> > anyway as I am accommodating and reasonable.
>
> I agree that pre-existing problems in selftests should not be your
> problem.
>
> By the way, I'm occasionally involved in helping fix up various
> selftest-related problems, especially when they impact mm. Send me a
> note if you have anything in mind that ought to be fixed up, I might be
> able to help head off future grief in that area.
Sure, and I'm passionate about tests (I've written _thousands_ of lines of
tests recently!) I mention this as a related example of something that
feels out of scope.
Equally as the pidfd.h test header already had other instances of exactly
what I did and thus really should have been solved as a separate series
(one that I'd have been happy to do myself), I feel this issue, if truly a
problem should be considered separately.
>
> >
> > So fine - I'll respin and just open-code this as it's trivial and there's
> > no (other) sensible place to put it anyway.
> >
> > A P.S. though - a very NOT theoretical issue with userspace is the import
> > of linux/fcntl.h in pidfd.h which seems to me to have been imported solely
> > for the kernel's sake.
> >
> > A gentle suggestion (it seems I can't win - gentle suggestions are ignored,
> > tongue-in-cheek parody is taken to be mean... but anyway) is to do
>
> Actually, these come across as sarcasm, especially in the context of
> these emails that show you are becoming quite distraught.
Yes, I get that, rather a Brit element to this, to be clear - I am not
distraught, merely mildly perturbed. Again text is a bloody awful medium!
This genuinely was meant to be tongue in cheek, BUT I realise it's a me
issue on this kind of thing - obviously written down like that it comes off
as possibly dripping with a kind of venom that was ABSOLUTELY not intended.
Whereas my intent was a sort of wry smile, 'come on guys this doesn't
matter' thing.
But since this is the second time now that I've said something intended
that way and having been received as quite something different - this is a
me thing - and I will refrain from dalliances into the rhetorical like this
in future!
Apologies if either you or Pedro took offence and I'm fine! Other than this
damn cold that wont' go away...
>
> I've met you several times at the conferences. We get along well. And
> your work is top notch. So please consider that I'm very much supportive
> of you and your work here.
And I consider you one of the loveliest people in the kernel and very very
sharp, and have enjoyed meeting you and your erstwhile colleague Jason :)
To be clear - I also have high regard for Pedro who I consider very smart,
and I don't say that lightly.
I mean this _whole series_ is his idea, for instance. I don't just write
series based on an idea on review for just anyone ;)
So this is not at all intended to be a critique of either of you, as I have
the utmost regard for you both...!
>
> I'm still trying to understand why you are recently sending these very
> strong emails (Vlastimil also took some heat), but I see that you also
> mentioned some long hours.
Well some of higher 'strength' have more basis than others that may be my
failing to communicate things quite as intended. We'd have to speak on a
case-by-case basis :)
But in Vlastimil's case, that was absolutely not intended. Again text is a
bad medium!
>
> If my feedback is making things worse here, I'll try to adjust.
> Selftests in general are a frustrating area.
No it's fine, I think just a comms thing here.
Please do carry on reviewing it is all much appreciated... I promise!
>
>
> thanks,
> --
> John Hubbard
>
>
> > something like:
> >
> > #ifdef __KERNEL__
> > #include <linux/fcntl.h>
> > #else
> > #include <fcntl.h>
> > #endif
> >
> > At the top of the pidfd.h header. This must surely sting a _lot_ of people
> > in userland otherwise.
> >
> > But this is out of scope for this change.
>
Anyway on this issue, as I said, and meant - I will respin with this taken
out to alleviate concerns.
The _far_ more pressing issue I think is the one Pedro raised about the
actual PIDFD_SELF* values. I may simply choose some arbitrary ones in the
range specified by Pedro on respin.
Thanks! And I guess I owe you both beers ;)
^ permalink raw reply
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