* Re: [PATCH v3 07/12] man/man2/fsmount.2: document "new" mount API
From: Askar Safin @ 2025-08-20 11:53 UTC (permalink / raw)
To: Aleksa Sarai
Cc: Alejandro Colomar, Michael T. Kerrisk, Alexander Viro, Jan Kara,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <2025-08-20.1755686261-lurid-sleepy-lime-quarry-j42HLU@cyphar.com>
---- On Wed, 20 Aug 2025 14:38:48 +0400 Aleksa Sarai <cyphar@cyphar.com> wrote ---
> The reason I wanted to include the comparison is that you can create
> multiple mount objects from the same underlying object using
> open_tree(2) but that's not possible with fsmount(2) (at least, not
> without creating a new filesystem context each time).
Okay, you may write that.
--
Askar Safin
https://types.pl/@safinaskar
^ permalink raw reply
* Re: [PATCH v3 00/12] man2: document "new" mount API
From: Askar Safin @ 2025-08-20 11:37 UTC (permalink / raw)
To: Aleksa Sarai
Cc: alx, brauner, dhowells, g.branden.robinson, jack, linux-api,
linux-fsdevel, linux-kernel, linux-man, mtk.manpages, viro,
Ian Kent, autofs mailing list
In-Reply-To: <2025-08-17.1755446479-rotten-curled-charms-robe-vWOBH5@cyphar.com>
---- On Sun, 17 Aug 2025 20:16:04 +0400 Aleksa Sarai <cyphar@cyphar.com> wrote ---
> They are not tested by fstests AFAICS, but that's more of a flaw in
> fstests (automount requires you to have a running autofs daemon, which
> probably makes testing it in fstests or selftests impractical) not the
> feature itself.
I suggest testing automounts in fstests/selftests using "tracing" automount.
This is what I do in my reproducers.
> The automount behaviour of tracefs is different to the general automount
> mechanism which is managed by userspace with the autofs daemon.
Yes. But I still was able to write reproducers using "tracing", so this
automount point is totally okay for tests. (At least for some tests,
such as RESOLVE_NO_XDEV.)
--
Askar Safin
https://types.pl/@safinaskar
^ permalink raw reply
* Re: [PATCH v5 3/3] man/man2/mremap.2: describe previously undocumented shrink behaviour
From: Lorenzo Stoakes @ 2025-08-20 11:24 UTC (permalink / raw)
To: Alejandro Colomar
Cc: linux-man, Andrew Morton, Peter Xu, Alexander Viro,
Christian Brauner, Jan Kara, Liam R . Howlett, Vlastimil Babka,
Jann Horn, Pedro Falcato, Rik van Riel, linux-mm, linux-kernel,
linux-api
In-Reply-To: <jmjlamoqau6rs32ldggra4ojiwim7b7h7xtgzh63m64xejsid4@cdnae7mjdeh3>
On Wed, Aug 20, 2025 at 12:50:25PM +0200, Alejandro Colomar wrote:
> Hi Lorenzo,
>
> On Tue, Aug 19, 2025 at 09:37:39PM +0100, Lorenzo Stoakes wrote:
> > > > diff --git a/man/man2/mremap.2 b/man/man2/mremap.2
> > > > index 6d14bf627..53d4eda29 100644
> > > > --- a/man/man2/mremap.2
> > > > +++ b/man/man2/mremap.2
> > > > @@ -47,8 +47,35 @@ The
> > > > .B MREMAP_DONTUNMAP
> > > > flag may also be specified.
> > > > .P
> > > > -If the operation is not
> > > > -simply moving mappings,
> > > > +Equally, if the operation performs a shrink,
>
> I've changed s/Equally/Similarly/
>
> > > > +that is if
> > >
> > > Missing comma.
> >
> > Could you fix that up? Thnks!
> >
> > >
> > > > +.I old_size
> > > > +is greater than
> > > > +.IR new_size ,
> > > > +then
> > > > +.I old_size
> > > > +may also span multiple mappings
> > > > +which do not have to be
> > > > +adjacent to one another.
> > >
> > > I'm wondering if there's a missing comma or not before 'which'.
> > > The meaning of the sentence would be different.
> > >
> > > So, I should ask:
> > >
> > > Does old_size > new_size mean that old_size may span multiple mappings
> > > and you're commenting that multiple mappings need not be adjacent?
> >
> > Yes.
> >
> > >
> > > Or are multiple mappings always allowed and old_size > new_size allows
> > > non-adjacent ones?
> >
> > No.
> >
> > >
> > > I suspect it's the former, right? Then, it's missing a comma, right?
> >
> > Yes could you fix that up?
>
> Yup.
>
> >
> > >
> > >
> > > Other than this, the patch looks good.
> >
> > Thanks!
>
> Thanks for the patch! I've applied it with those amendments.
> <https://www.alejandro-colomar.es/src/alx/linux/man-pages/man-pages.git/commit/?h=contrib&id=21b1c7188ce1d66ef294eb1681361315a35e8070>
All sounds good, thanks for doing that and also for applies for other patches in
series :)
Cheers, Lorenzo
>
>
> Have a lovely day!
> Alex
>
> --
> <https://www.alejandro-colomar.es/>
^ permalink raw reply
* Re: [PATCH v3 08/12] man/man2/move_mount.2: document "new" mount API
From: Askar Safin @ 2025-08-20 11:18 UTC (permalink / raw)
To: Aleksa Sarai
Cc: Alejandro Colomar, Michael T. Kerrisk, Alexander Viro, Jan Kara,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <2025-08-12.1755009210-quick-best-oranges-coats-BNJpCV@cyphar.com>
---- On Tue, 12 Aug 2025 18:36:53 +0400 Aleksa Sarai <cyphar@cyphar.com> wrote ---
> > "Filesystem root" can be understood as "root of superblock".
> > So, please, change this to "root directory" or something.
>
> Maybe I should borrow the "root mount" terminology from pivot_root(2)?
I don't like this. For me "root mount" is initial root mount, i. e. initramfs.
It is not what you mean here.
> I didn't like using "rootfs" as
> shorthand in a man-page.
I agree.
What you mean by "filesystem root" here? "Thing, which is changed by chroot(2)", right?
Then, please, write "root directory" (or "root"), this is standard term for that thing.
Or you can just write "/".
--
Askar Safin
https://types.pl/@safinaskar
^ permalink raw reply
* Re: [PATCH v5 3/3] man/man2/mremap.2: describe previously undocumented shrink behaviour
From: Alejandro Colomar @ 2025-08-20 10:50 UTC (permalink / raw)
To: Lorenzo Stoakes
Cc: linux-man, Andrew Morton, Peter Xu, Alexander Viro,
Christian Brauner, Jan Kara, Liam R . Howlett, Vlastimil Babka,
Jann Horn, Pedro Falcato, Rik van Riel, linux-mm, linux-kernel,
linux-api
In-Reply-To: <fb880acd-25df-4386-a13c-9b68640477ef@lucifer.local>
[-- Attachment #1: Type: text/plain, Size: 1714 bytes --]
Hi Lorenzo,
On Tue, Aug 19, 2025 at 09:37:39PM +0100, Lorenzo Stoakes wrote:
> > > diff --git a/man/man2/mremap.2 b/man/man2/mremap.2
> > > index 6d14bf627..53d4eda29 100644
> > > --- a/man/man2/mremap.2
> > > +++ b/man/man2/mremap.2
> > > @@ -47,8 +47,35 @@ The
> > > .B MREMAP_DONTUNMAP
> > > flag may also be specified.
> > > .P
> > > -If the operation is not
> > > -simply moving mappings,
> > > +Equally, if the operation performs a shrink,
I've changed s/Equally/Similarly/
> > > +that is if
> >
> > Missing comma.
>
> Could you fix that up? Thnks!
>
> >
> > > +.I old_size
> > > +is greater than
> > > +.IR new_size ,
> > > +then
> > > +.I old_size
> > > +may also span multiple mappings
> > > +which do not have to be
> > > +adjacent to one another.
> >
> > I'm wondering if there's a missing comma or not before 'which'.
> > The meaning of the sentence would be different.
> >
> > So, I should ask:
> >
> > Does old_size > new_size mean that old_size may span multiple mappings
> > and you're commenting that multiple mappings need not be adjacent?
>
> Yes.
>
> >
> > Or are multiple mappings always allowed and old_size > new_size allows
> > non-adjacent ones?
>
> No.
>
> >
> > I suspect it's the former, right? Then, it's missing a comma, right?
>
> Yes could you fix that up?
Yup.
>
> >
> >
> > Other than this, the patch looks good.
>
> Thanks!
Thanks for the patch! I've applied it with those amendments.
<https://www.alejandro-colomar.es/src/alx/linux/man-pages/man-pages.git/commit/?h=contrib&id=21b1c7188ce1d66ef294eb1681361315a35e8070>
Have a lovely day!
Alex
--
<https://www.alejandro-colomar.es/>
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^ permalink raw reply
* Re: [PATCH v3 07/12] man/man2/fsmount.2: document "new" mount API
From: Aleksa Sarai @ 2025-08-20 10:38 UTC (permalink / raw)
To: Askar Safin
Cc: Alejandro Colomar, Michael T. Kerrisk, Alexander Viro, Jan Kara,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <198c6e76d3e.113f774e874302.5490092759974557634@zohomail.com>
[-- Attachment #1: Type: text/plain, Size: 831 bytes --]
On 2025-08-20, Askar Safin <safinaskar@zohomail.com> wrote:
> ---- On Tue, 12 Aug 2025 18:33:04 +0400 Aleksa Sarai <cyphar@cyphar.com> wrote ---
> > Unlike open_tree(2) with OPEN_TREE_CLONE, fsmount() can only be called
> > once in the lifetime of a filesystem context.
>
> Weird. open_tree doesn't get filesystem context as argument at all.
> I suggest just this:
>
> fsmount() can only be called
> once in the lifetime of a filesystem context.
The reason I wanted to include the comparison is that you can create
multiple mount objects from the same underlying object using
open_tree(2) but that's not possible with fsmount(2) (at least, not
without creating a new filesystem context each time).
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/
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^ permalink raw reply
* Re: [PATCH v3 07/12] man/man2/fsmount.2: document "new" mount API
From: Askar Safin @ 2025-08-20 9:55 UTC (permalink / raw)
To: Aleksa Sarai
Cc: Alejandro Colomar, Michael T. Kerrisk, Alexander Viro, Jan Kara,
G. Branden Robinson, linux-man, linux-api, linux-fsdevel,
linux-kernel, David Howells, Christian Brauner
In-Reply-To: <2025-08-12.1755007445-rural-feudal-spacebar-forehead-28QkCN@cyphar.com>
---- On Tue, 12 Aug 2025 18:33:04 +0400 Aleksa Sarai <cyphar@cyphar.com> wrote ---
> Unlike open_tree(2) with OPEN_TREE_CLONE, fsmount() can only be called
> once in the lifetime of a filesystem context.
Weird. open_tree doesn't get filesystem context as argument at all.
I suggest just this:
fsmount() can only be called
once in the lifetime of a filesystem context.
--
Askar Safin
https://types.pl/@safinaskar
^ permalink raw reply
* Re: [PATCH v5 3/3] man/man2/mremap.2: describe previously undocumented shrink behaviour
From: Lorenzo Stoakes @ 2025-08-19 20:37 UTC (permalink / raw)
To: Alejandro Colomar
Cc: linux-man, Andrew Morton, Peter Xu, Alexander Viro,
Christian Brauner, Jan Kara, Liam R . Howlett, Vlastimil Babka,
Jann Horn, Pedro Falcato, Rik van Riel, linux-mm, linux-kernel,
linux-api
In-Reply-To: <uvh2e2jjdk44tdwrhmnd46atwgdzwwmny4kczxqv2vm33gjqpp@63lsupn6y2u6>
On Fri, Aug 15, 2025 at 11:36:26PM +0200, Alejandro Colomar wrote:
> Hi Lorenzo,
>
> On Mon, Aug 11, 2025 at 03:59:39PM +0100, Lorenzo Stoakes wrote:
> > There is pre-existing logic that appears to be undocumented for an mremap()
> > shrink operation, where it turns out that the usual 'input range must span
> > a single mapping' requirement no longer applies.
> >
> > In fact, it turns out that the input range specified by [old_address,
> > old_address + old_size) may span any number of mappings.
> >
> > If shrinking in-place (that is, neither the MREMAP_FIXED nor
> > MREMAP_DONTUNMAP flags are specified), then the new span may also span any
> > number of VMAs - [old_address, old_address + new_size).
> >
> > If shrinking and moving, the range specified by [old_address, old_address +
> > new_size) must span a single VMA.
> >
> > There must be at least one VMA contained within the [old_address,
> > old_address + old_size) range, and old_address must be within the range of
> > a VMA.
> >
> > Explicitly document this.
> >
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> > ---
> > man/man2/mremap.2 | 31 +++++++++++++++++++++++++++++--
> > 1 file changed, 29 insertions(+), 2 deletions(-)
> >
> > diff --git a/man/man2/mremap.2 b/man/man2/mremap.2
> > index 6d14bf627..53d4eda29 100644
> > --- a/man/man2/mremap.2
> > +++ b/man/man2/mremap.2
> > @@ -47,8 +47,35 @@ The
> > .B MREMAP_DONTUNMAP
> > flag may also be specified.
> > .P
> > -If the operation is not
> > -simply moving mappings,
> > +Equally, if the operation performs a shrink,
> > +that is if
>
> Missing comma.
Could you fix that up? Thnks!
>
> > +.I old_size
> > +is greater than
> > +.IR new_size ,
> > +then
> > +.I old_size
> > +may also span multiple mappings
> > +which do not have to be
> > +adjacent to one another.
>
> I'm wondering if there's a missing comma or not before 'which'.
> The meaning of the sentence would be different.
>
> So, I should ask:
>
> Does old_size > new_size mean that old_size may span multiple mappings
> and you're commenting that multiple mappings need not be adjacent?
Yes.
>
> Or are multiple mappings always allowed and old_size > new_size allows
> non-adjacent ones?
No.
>
> I suspect it's the former, right? Then, it's missing a comma, right?
Yes could you fix that up?
>
>
> Other than this, the patch looks good.
Thanks!
>
>
> Have a lovely night!
> Alex
>
> > +If this shrink is performed
> > +in-place,
> > +that is,
> > +neither
> > +.BR MREMAP_FIXED ,
> > +nor
> > +.B MREMAP_DONTUNMAP
> > +are specified,
> > +.I new_size
> > +may also span multiple VMAs.
> > +However, if the range is moved,
> > +then
> > +.I new_size
> > +must span only a single mapping.
> > +.P
> > +If the operation is neither a
> > +.B MREMAP_FIXED
> > +move
> > +nor a shrink,
> > then
> > .I old_size
> > must span only a single mapping.
> > --
> > 2.50.1
> >
>
> --
> <https://www.alejandro-colomar.es/>
^ permalink raw reply
* [PATCH v19 8/8] selftests/clone3: Test shadow stack support
From: Mark Brown @ 2025-08-19 16:21 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook, Shuah Khan
In-Reply-To: <20250819-clone3-shadow-stack-v19-0-bc957075479b@kernel.org>
Add basic test coverage for specifying the shadow stack for a newly
created thread via clone3(), including coverage of the newly extended
argument structure. We check that a user specified shadow stack can be
provided, and that invalid combinations of parameters are rejected.
In order to facilitate testing on systems without userspace shadow stack
support we manually enable shadow stacks on startup, this is architecture
specific due to the use of an arch_prctl() on x86. Due to interactions with
potential userspace locking of features we actually detect support for
shadow stacks on the running system by attempting to allocate a shadow
stack page during initialisation using map_shadow_stack(), warning if this
succeeds when the enable failed.
In order to allow testing of user configured shadow stacks on
architectures with that feature we need to ensure that we do not return
from the function where the clone3() syscall is called in the child
process, doing so would trigger a shadow stack underflow. To do this we
use inline assembly rather than the standard syscall wrapper to call
clone3(). In order to avoid surprises we also use a syscall rather than
the libc exit() function., this should be overly cautious.
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
tools/testing/selftests/clone3/clone3.c | 143 +++++++++++++++++++++-
tools/testing/selftests/clone3/clone3_selftests.h | 63 ++++++++++
2 files changed, 205 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/clone3/clone3.c b/tools/testing/selftests/clone3/clone3.c
index 5b8b7d640e70..6fd2b3238e2c 100644
--- a/tools/testing/selftests/clone3/clone3.c
+++ b/tools/testing/selftests/clone3/clone3.c
@@ -3,6 +3,7 @@
/* Based on Christian Brauner's clone3() example */
#define _GNU_SOURCE
+#include <asm/mman.h>
#include <errno.h>
#include <inttypes.h>
#include <linux/types.h>
@@ -11,6 +12,7 @@
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
+#include <sys/mman.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/un.h>
@@ -19,8 +21,12 @@
#include <sched.h>
#include "../kselftest.h"
+#include "../ksft_shstk.h"
#include "clone3_selftests.h"
+static bool shadow_stack_supported;
+static size_t max_supported_args_size;
+
enum test_mode {
CLONE3_ARGS_NO_TEST,
CLONE3_ARGS_ALL_0,
@@ -28,6 +34,10 @@ enum test_mode {
CLONE3_ARGS_INVAL_EXIT_SIGNAL_NEG,
CLONE3_ARGS_INVAL_EXIT_SIGNAL_CSIG,
CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG,
+ CLONE3_ARGS_SHADOW_STACK,
+ CLONE3_ARGS_SHADOW_STACK_MISALIGNED,
+ CLONE3_ARGS_SHADOW_STACK_NO_TOKEN,
+ CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY,
};
typedef bool (*filter_function)(void);
@@ -44,6 +54,44 @@ struct test {
filter_function filter;
};
+
+/*
+ * We check for shadow stack support by attempting to use
+ * map_shadow_stack() since features may have been locked by the
+ * dynamic linker resulting in spurious errors when we attempt to
+ * enable on startup. We warn if the enable failed.
+ */
+static void test_shadow_stack_supported(void)
+{
+ long ret;
+
+ ret = syscall(__NR_map_shadow_stack, 0, getpagesize(), 0);
+ if (ret == -1) {
+ ksft_print_msg("map_shadow_stack() not supported\n");
+ } else if ((void *)ret == MAP_FAILED) {
+ ksft_print_msg("Failed to map shadow stack\n");
+ } else {
+ ksft_print_msg("Shadow stack supportd\n");
+ shadow_stack_supported = true;
+
+ if (!shadow_stack_enabled)
+ ksft_print_msg("Mapped but did not enable shadow stack\n");
+ }
+}
+
+static void *get_shadow_stack_page(unsigned long flags)
+{
+ unsigned long long page;
+
+ page = syscall(__NR_map_shadow_stack, 0, getpagesize(), flags);
+ if ((void *)page == MAP_FAILED) {
+ ksft_print_msg("map_shadow_stack() failed: %d\n", errno);
+ return 0;
+ }
+
+ return (void *)page;
+}
+
static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
{
struct __clone_args args = {
@@ -57,6 +105,7 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
} args_ext;
pid_t pid = -1;
+ void *p;
int status;
memset(&args_ext, 0, sizeof(args_ext));
@@ -89,6 +138,26 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
case CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG:
args.exit_signal = 0x00000000000000f0ULL;
break;
+ case CLONE3_ARGS_SHADOW_STACK:
+ p = get_shadow_stack_page(SHADOW_STACK_SET_TOKEN);
+ p += getpagesize() - sizeof(void *);
+ args.shadow_stack_token = (unsigned long long)p;
+ break;
+ case CLONE3_ARGS_SHADOW_STACK_MISALIGNED:
+ p = get_shadow_stack_page(SHADOW_STACK_SET_TOKEN);
+ p += getpagesize() - sizeof(void *) - 1;
+ args.shadow_stack_token = (unsigned long long)p;
+ break;
+ case CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY:
+ p = malloc(getpagesize());
+ p += getpagesize() - sizeof(void *);
+ args.shadow_stack_token = (unsigned long long)p;
+ break;
+ case CLONE3_ARGS_SHADOW_STACK_NO_TOKEN:
+ p = get_shadow_stack_page(0);
+ p += getpagesize() - sizeof(void *);
+ args.shadow_stack_token = (unsigned long long)p;
+ break;
}
memcpy(&args_ext.args, &args, sizeof(struct __clone_args));
@@ -102,7 +171,12 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
if (pid == 0) {
ksft_print_msg("I am the child, my PID is %d\n", getpid());
- _exit(EXIT_SUCCESS);
+ /*
+ * Use a raw syscall to ensure we don't get issues
+ * with manually specified shadow stack and exit handlers.
+ */
+ syscall(__NR_exit, EXIT_SUCCESS);
+ ksft_print_msg("CHILD FAILED TO EXIT PID is %d\n", getpid());
}
ksft_print_msg("I am the parent (%d). My child's pid is %d\n",
@@ -184,6 +258,26 @@ static bool no_timenamespace(void)
return true;
}
+static bool have_shadow_stack(void)
+{
+ if (shadow_stack_supported) {
+ ksft_print_msg("Shadow stack supported\n");
+ return true;
+ }
+
+ return false;
+}
+
+static bool no_shadow_stack(void)
+{
+ if (!shadow_stack_supported) {
+ ksft_print_msg("Shadow stack not supported\n");
+ return true;
+ }
+
+ return false;
+}
+
static size_t page_size_plus_8(void)
{
return getpagesize() + 8;
@@ -327,6 +421,50 @@ static const struct test tests[] = {
.expected = -EINVAL,
.test_mode = CLONE3_ARGS_NO_TEST,
},
+ {
+ .name = "Shadow stack on system with shadow stack",
+ .size = 0,
+ .expected = 0,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK,
+ .filter = no_shadow_stack,
+ },
+ {
+ .name = "Shadow stack with misaligned address",
+ .flags = CLONE_VM,
+ .size = 0,
+ .expected = -EINVAL,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK_MISALIGNED,
+ .filter = no_shadow_stack,
+ },
+ {
+ .name = "Shadow stack with normal memory",
+ .flags = CLONE_VM,
+ .size = 0,
+ .expected = -EFAULT,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY,
+ .filter = no_shadow_stack,
+ },
+ {
+ .name = "Shadow stack with no token",
+ .flags = CLONE_VM,
+ .size = 0,
+ .expected = -EINVAL,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK_NO_TOKEN,
+ .filter = no_shadow_stack,
+ },
+ {
+ .name = "Shadow stack on system without shadow stack",
+ .flags = CLONE_VM,
+ .size = 0,
+ .expected = -EFAULT,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY,
+ .filter = have_shadow_stack,
+ },
};
int main(int argc, char *argv[])
@@ -334,9 +472,12 @@ int main(int argc, char *argv[])
size_t size;
int i;
+ enable_shadow_stack();
+
ksft_print_header();
ksft_set_plan(ARRAY_SIZE(tests));
test_clone3_supported();
+ test_shadow_stack_supported();
for (i = 0; i < ARRAY_SIZE(tests); i++)
test_clone3(&tests[i]);
diff --git a/tools/testing/selftests/clone3/clone3_selftests.h b/tools/testing/selftests/clone3/clone3_selftests.h
index 939b26c86d42..8151c4fc971a 100644
--- a/tools/testing/selftests/clone3/clone3_selftests.h
+++ b/tools/testing/selftests/clone3/clone3_selftests.h
@@ -31,12 +31,75 @@ struct __clone_args {
__aligned_u64 set_tid;
__aligned_u64 set_tid_size;
__aligned_u64 cgroup;
+#ifndef CLONE_ARGS_SIZE_VER2
+#define CLONE_ARGS_SIZE_VER2 88 /* sizeof third published struct */
+#endif
+ __aligned_u64 shadow_stack_token;
+#ifndef CLONE_ARGS_SIZE_VER3
+#define CLONE_ARGS_SIZE_VER3 96 /* sizeof fourth published struct */
+#endif
};
+/*
+ * For architectures with shadow stack support we need to be
+ * absolutely sure that the clone3() syscall will be inline and not a
+ * function call so we open code.
+ */
+#ifdef __x86_64__
+static __always_inline pid_t sys_clone3(struct __clone_args *args, size_t size)
+{
+ register long _num __asm__ ("rax") = __NR_clone3;
+ register long _args __asm__ ("rdi") = (long)(args);
+ register long _size __asm__ ("rsi") = (long)(size);
+ long ret;
+
+ __asm__ volatile (
+ "syscall\n"
+ : "=a"(ret)
+ : "r"(_args), "r"(_size),
+ "0"(_num)
+ : "rcx", "r11", "memory", "cc"
+ );
+
+ if (ret < 0) {
+ errno = -ret;
+ return -1;
+ }
+
+ return ret;
+}
+#elif defined(__aarch64__)
+static __always_inline pid_t sys_clone3(struct __clone_args *args, size_t size)
+{
+ register long _num __asm__ ("x8") = __NR_clone3;
+ register long _args __asm__ ("x0") = (long)(args);
+ register long _size __asm__ ("x1") = (long)(size);
+ register long arg2 __asm__ ("x2") = 0;
+ register long arg3 __asm__ ("x3") = 0;
+ register long arg4 __asm__ ("x4") = 0;
+
+ __asm__ volatile (
+ "svc #0\n"
+ : "=r"(_args)
+ : "r"(_args), "r"(_size),
+ "r"(_num), "r"(arg2),
+ "r"(arg3), "r"(arg4)
+ : "memory", "cc"
+ );
+
+ if ((int)_args < 0) {
+ errno = -((int)_args);
+ return -1;
+ }
+
+ return _args;
+}
+#else
static pid_t sys_clone3(struct __clone_args *args, size_t size)
{
return syscall(__NR_clone3, args, size);
}
+#endif
static inline void test_clone3_supported(void)
{
--
2.39.5
^ permalink raw reply related
* [PATCH v19 7/8] selftests/clone3: Allow tests to flag if -E2BIG is a valid error code
From: Mark Brown @ 2025-08-19 16:21 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250819-clone3-shadow-stack-v19-0-bc957075479b@kernel.org>
The clone_args structure is extensible, with the syscall passing in the
length of the structure. Inside the kernel we use copy_struct_from_user()
to read the struct but this has the unfortunate side effect of silently
accepting some overrun in the structure size providing the extra data is
all zeros. This means that we can't discover the clone3() features that
the running kernel supports by simply probing with various struct sizes.
We need to check this for the benefit of test systems which run newer
kselftests on old kernels.
Add a flag which can be set on a test to indicate that clone3() may return
-E2BIG due to the use of newer struct versions. Currently no tests need
this but it will become an issue for testing clone3() support for shadow
stacks, the support for shadow stacks is already present on x86.
Reviewed-by: Kees Cook <kees@kernel.org>
Tested-by: Kees Cook <kees@kernel.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
tools/testing/selftests/clone3/clone3.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/tools/testing/selftests/clone3/clone3.c b/tools/testing/selftests/clone3/clone3.c
index e066b201fa64..5b8b7d640e70 100644
--- a/tools/testing/selftests/clone3/clone3.c
+++ b/tools/testing/selftests/clone3/clone3.c
@@ -39,6 +39,7 @@ struct test {
size_t size;
size_function size_function;
int expected;
+ bool e2big_valid;
enum test_mode test_mode;
filter_function filter;
};
@@ -146,6 +147,11 @@ static void test_clone3(const struct test *test)
ksft_print_msg("[%d] clone3() with flags says: %d expected %d\n",
getpid(), ret, test->expected);
if (ret != test->expected) {
+ if (test->e2big_valid && ret == -E2BIG) {
+ ksft_print_msg("Test reported -E2BIG\n");
+ ksft_test_result_skip("%s\n", test->name);
+ return;
+ }
ksft_print_msg(
"[%d] Result (%d) is different than expected (%d)\n",
getpid(), ret, test->expected);
--
2.39.5
^ permalink raw reply related
* [PATCH v19 6/8] selftests/clone3: Factor more of main loop into test_clone3()
From: Mark Brown @ 2025-08-19 16:21 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250819-clone3-shadow-stack-v19-0-bc957075479b@kernel.org>
In order to make it easier to add more configuration for the tests and
more support for runtime detection of when tests can be run pass the
structure describing the tests into test_clone3() rather than picking
the arguments out of it and have that function do all the per-test work.
No functional change.
Reviewed-by: Kees Cook <kees@kernel.org>
Tested-by: Kees Cook <kees@kernel.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
tools/testing/selftests/clone3/clone3.c | 77 ++++++++++++++++-----------------
1 file changed, 37 insertions(+), 40 deletions(-)
diff --git a/tools/testing/selftests/clone3/clone3.c b/tools/testing/selftests/clone3/clone3.c
index e61f07973ce5..e066b201fa64 100644
--- a/tools/testing/selftests/clone3/clone3.c
+++ b/tools/testing/selftests/clone3/clone3.c
@@ -30,6 +30,19 @@ enum test_mode {
CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG,
};
+typedef bool (*filter_function)(void);
+typedef size_t (*size_function)(void);
+
+struct test {
+ const char *name;
+ uint64_t flags;
+ size_t size;
+ size_function size_function;
+ int expected;
+ enum test_mode test_mode;
+ filter_function filter;
+};
+
static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
{
struct __clone_args args = {
@@ -109,30 +122,40 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
return 0;
}
-static bool test_clone3(uint64_t flags, size_t size, int expected,
- enum test_mode test_mode)
+static void test_clone3(const struct test *test)
{
+ size_t size;
int ret;
+ if (test->filter && test->filter()) {
+ ksft_test_result_skip("%s\n", test->name);
+ return;
+ }
+
+ if (test->size_function)
+ size = test->size_function();
+ else
+ size = test->size;
+
+ ksft_print_msg("Running test '%s'\n", test->name);
+
ksft_print_msg(
"[%d] Trying clone3() with flags %#" PRIx64 " (size %zu)\n",
- getpid(), flags, size);
- ret = call_clone3(flags, size, test_mode);
+ getpid(), test->flags, size);
+ ret = call_clone3(test->flags, size, test->test_mode);
ksft_print_msg("[%d] clone3() with flags says: %d expected %d\n",
- getpid(), ret, expected);
- if (ret != expected) {
+ getpid(), ret, test->expected);
+ if (ret != test->expected) {
ksft_print_msg(
"[%d] Result (%d) is different than expected (%d)\n",
- getpid(), ret, expected);
- return false;
+ getpid(), ret, test->expected);
+ ksft_test_result_fail("%s\n", test->name);
+ return;
}
- return true;
+ ksft_test_result_pass("%s\n", test->name);
}
-typedef bool (*filter_function)(void);
-typedef size_t (*size_function)(void);
-
static bool not_root(void)
{
if (getuid() != 0) {
@@ -160,16 +183,6 @@ static size_t page_size_plus_8(void)
return getpagesize() + 8;
}
-struct test {
- const char *name;
- uint64_t flags;
- size_t size;
- size_function size_function;
- int expected;
- enum test_mode test_mode;
- filter_function filter;
-};
-
static const struct test tests[] = {
{
.name = "simple clone3()",
@@ -319,24 +332,8 @@ int main(int argc, char *argv[])
ksft_set_plan(ARRAY_SIZE(tests));
test_clone3_supported();
- for (i = 0; i < ARRAY_SIZE(tests); i++) {
- if (tests[i].filter && tests[i].filter()) {
- ksft_test_result_skip("%s\n", tests[i].name);
- continue;
- }
-
- if (tests[i].size_function)
- size = tests[i].size_function();
- else
- size = tests[i].size;
-
- ksft_print_msg("Running test '%s'\n", tests[i].name);
-
- ksft_test_result(test_clone3(tests[i].flags, size,
- tests[i].expected,
- tests[i].test_mode),
- "%s\n", tests[i].name);
- }
+ for (i = 0; i < ARRAY_SIZE(tests); i++)
+ test_clone3(&tests[i]);
ksft_finished();
}
--
2.39.5
^ permalink raw reply related
* [PATCH v19 5/8] selftests/clone3: Remove redundant flushes of output streams
From: Mark Brown @ 2025-08-19 16:21 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250819-clone3-shadow-stack-v19-0-bc957075479b@kernel.org>
Since there were widespread issues with output not being flushed the
kselftest framework was modified to explicitly set the output streams
unbuffered in commit 58e2847ad2e6 ("selftests: line buffer test
program's stdout") so there is no need to explicitly flush in the clone3
tests.
Reviewed-by: Kees Cook <kees@kernel.org>
Tested-by: Kees Cook <kees@kernel.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
tools/testing/selftests/clone3/clone3_selftests.h | 2 --
1 file changed, 2 deletions(-)
diff --git a/tools/testing/selftests/clone3/clone3_selftests.h b/tools/testing/selftests/clone3/clone3_selftests.h
index eeca8005723f..939b26c86d42 100644
--- a/tools/testing/selftests/clone3/clone3_selftests.h
+++ b/tools/testing/selftests/clone3/clone3_selftests.h
@@ -35,8 +35,6 @@ struct __clone_args {
static pid_t sys_clone3(struct __clone_args *args, size_t size)
{
- fflush(stdout);
- fflush(stderr);
return syscall(__NR_clone3, args, size);
}
--
2.39.5
^ permalink raw reply related
* [PATCH v19 4/8] fork: Add shadow stack support to clone3()
From: Mark Brown @ 2025-08-19 16:21 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook
In-Reply-To: <20250819-clone3-shadow-stack-v19-0-bc957075479b@kernel.org>
Unlike with the normal stack there is no API for configuring the shadow
stack for a new thread, instead the kernel will dynamically allocate a
new shadow stack with the same size as the normal stack. This appears to
be due to the shadow stack series having been in development since
before the more extensible clone3() was added rather than anything more
deliberate.
Add a parameter to clone3() specifying a shadow stack pointer to use
for the new thread, this is inconsistent with the way we specify the
normal stack but during review concerns were expressed about having to
identify where the shadow stack pointer should be placed especially in
cases where the shadow stack has been previously active. If no shadow
stack is specified then the existing implicit allocation behaviour is
maintained.
If a shadow stack pointer is specified then it is required to have an
architecture defined token placed on the stack, this will be consumed by
the new task, the shadow stack is specified by pointing to this token. If
no valid token is present then this will be reported with -EINVAL. This
token prevents new threads being created pointing at the shadow stack of
an existing running thread. On architectures with support for userspace
pivoting of shadow stacks it is expected that the same format and placement
of tokens will be used, this is the case for arm64 and x86.
If the architecture does not support shadow stacks the shadow stack
pointer must be not be specified, architectures that do support the
feature are expected to enforce the same requirement on individual
systems that lack shadow stack support.
Update the existing arm64 and x86 implementations to pay attention to
the newly added arguments, in order to maintain compatibility we use the
existing behaviour if no shadow stack is specified. Since we are now
using more fields from the kernel_clone_args we pass that into the
shadow stack code rather than individual fields.
Portions of the x86 architecture code were written by Rick Edgecombe.
Acked-by: Yury Khrustalev <yury.khrustalev@arm.com>
Tested-by: Yury Khrustalev <yury.khrustalev@arm.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/mm/gcs.c | 47 +++++++++++++++++++-
arch/x86/include/asm/shstk.h | 11 +++--
arch/x86/kernel/process.c | 2 +-
arch/x86/kernel/shstk.c | 53 ++++++++++++++++++++---
include/asm-generic/cacheflush.h | 11 +++++
include/linux/sched/task.h | 17 ++++++++
include/uapi/linux/sched.h | 9 ++--
kernel/fork.c | 93 ++++++++++++++++++++++++++++++++++------
8 files changed, 217 insertions(+), 26 deletions(-)
diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c
index 3abcbf9adb5c..249ff05bca45 100644
--- a/arch/arm64/mm/gcs.c
+++ b/arch/arm64/mm/gcs.c
@@ -43,8 +43,23 @@ int gcs_alloc_thread_stack(struct task_struct *tsk,
{
unsigned long addr, size;
- if (!system_supports_gcs())
+ if (!system_supports_gcs()) {
+ if (args->shadow_stack_token)
+ return -EINVAL;
+
return 0;
+ }
+
+ /*
+ * If the user specified a GCS then use it, otherwise fall
+ * back to a default allocation strategy. Validation is done
+ * in arch_shstk_validate_clone().
+ */
+ if (args->shadow_stack_token) {
+ tsk->thread.gcs_base = 0;
+ tsk->thread.gcs_size = 0;
+ return 0;
+ }
if (!task_gcs_el0_enabled(tsk))
return 0;
@@ -68,6 +83,36 @@ int gcs_alloc_thread_stack(struct task_struct *tsk,
return 0;
}
+static bool gcs_consume_token(struct vm_area_struct *vma, struct page *page,
+ unsigned long user_addr)
+{
+ u64 expected = GCS_CAP(user_addr);
+ u64 *token = page_address(page) + offset_in_page(user_addr);
+
+ if (!cmpxchg_to_user_page(vma, page, user_addr, token, expected, 0))
+ return false;
+ set_page_dirty_lock(page);
+
+ return true;
+}
+
+int arch_shstk_validate_clone(struct task_struct *tsk,
+ struct vm_area_struct *vma,
+ struct page *page,
+ struct kernel_clone_args *args)
+{
+ unsigned long gcspr_el0;
+ int ret = 0;
+
+ gcspr_el0 = args->shadow_stack_token;
+ if (!gcs_consume_token(vma, page, gcspr_el0))
+ return -EINVAL;
+
+ tsk->thread.gcspr_el0 = gcspr_el0 + sizeof(u64);
+
+ return ret;
+}
+
SYSCALL_DEFINE3(map_shadow_stack, unsigned long, addr, unsigned long, size, unsigned int, flags)
{
unsigned long alloc_size;
diff --git a/arch/x86/include/asm/shstk.h b/arch/x86/include/asm/shstk.h
index ba6f2fe43848..827e983430aa 100644
--- a/arch/x86/include/asm/shstk.h
+++ b/arch/x86/include/asm/shstk.h
@@ -6,6 +6,7 @@
#include <linux/types.h>
struct task_struct;
+struct kernel_clone_args;
struct ksignal;
#ifdef CONFIG_X86_USER_SHADOW_STACK
@@ -16,8 +17,8 @@ struct thread_shstk {
long shstk_prctl(struct task_struct *task, int option, unsigned long arg2);
void reset_thread_features(void);
-unsigned long shstk_alloc_thread_stack(struct task_struct *p, unsigned long clone_flags,
- unsigned long stack_size);
+unsigned long shstk_alloc_thread_stack(struct task_struct *p,
+ const struct kernel_clone_args *args);
void shstk_free(struct task_struct *p);
int setup_signal_shadow_stack(struct ksignal *ksig);
int restore_signal_shadow_stack(void);
@@ -28,8 +29,10 @@ static inline long shstk_prctl(struct task_struct *task, int option,
unsigned long arg2) { return -EINVAL; }
static inline void reset_thread_features(void) {}
static inline unsigned long shstk_alloc_thread_stack(struct task_struct *p,
- unsigned long clone_flags,
- unsigned long stack_size) { return 0; }
+ const struct kernel_clone_args *args)
+{
+ return 0;
+}
static inline void shstk_free(struct task_struct *p) {}
static inline int setup_signal_shadow_stack(struct ksignal *ksig) { return 0; }
static inline int restore_signal_shadow_stack(void) { return 0; }
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 1b7960cf6eb0..0a54af6c60df 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -209,7 +209,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
* is disabled, new_ssp will remain 0, and fpu_clone() will know not to
* update it.
*/
- new_ssp = shstk_alloc_thread_stack(p, clone_flags, args->stack_size);
+ new_ssp = shstk_alloc_thread_stack(p, args);
if (IS_ERR_VALUE(new_ssp))
return PTR_ERR((void *)new_ssp);
diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
index 2ddf23387c7e..88ca9eaebc96 100644
--- a/arch/x86/kernel/shstk.c
+++ b/arch/x86/kernel/shstk.c
@@ -191,18 +191,61 @@ void reset_thread_features(void)
current->thread.features_locked = 0;
}
-unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, unsigned long clone_flags,
- unsigned long stack_size)
+int arch_shstk_validate_clone(struct task_struct *t,
+ struct vm_area_struct *vma,
+ struct page *page,
+ struct kernel_clone_args *args)
+{
+ /*
+ * SSP is aligned, so reserved bits and mode bit are a zero, just mark
+ * the token 64-bit.
+ */
+ void *maddr = page_address(page);
+ unsigned long token;
+ int offset;
+ u64 expected;
+
+ token = args->shadow_stack_token;
+ expected = (token + SS_FRAME_SIZE) | BIT(0);
+ offset = offset_in_page(token);
+
+ if (!cmpxchg_to_user_page(vma, page, token, (unsigned long *)(maddr + offset),
+ expected, 0))
+ return -EINVAL;
+ set_page_dirty_lock(page);
+
+ return 0;
+}
+
+unsigned long shstk_alloc_thread_stack(struct task_struct *tsk,
+ const struct kernel_clone_args *args)
{
struct thread_shstk *shstk = &tsk->thread.shstk;
+ unsigned long clone_flags = args->flags;
unsigned long addr, size;
/*
* If shadow stack is not enabled on the new thread, skip any
- * switch to a new shadow stack.
+ * implicit switch to a new shadow stack and reject attempts to
+ * explicitly specify one.
*/
- if (!features_enabled(ARCH_SHSTK_SHSTK))
+ if (!features_enabled(ARCH_SHSTK_SHSTK)) {
+ if (args->shadow_stack_token)
+ return (unsigned long)ERR_PTR(-EINVAL);
+
return 0;
+ }
+
+ /*
+ * If the user specified a shadow stack then use it, otherwise
+ * fall back to a default allocation strategy. Validation is
+ * done in arch_shstk_validate_clone().
+ */
+ if (args->shadow_stack_token) {
+ shstk->base = 0;
+ shstk->size = 0;
+ return args->shadow_stack_token + 8;
+ }
/*
* For CLONE_VFORK the child will share the parents shadow stack.
@@ -222,7 +265,7 @@ unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, unsigned long cl
if (!(clone_flags & CLONE_VM))
return 0;
- size = adjust_shstk_size(stack_size);
+ size = adjust_shstk_size(args->stack_size);
addr = alloc_shstk(0, size, 0, false);
if (IS_ERR_VALUE(addr))
return addr;
diff --git a/include/asm-generic/cacheflush.h b/include/asm-generic/cacheflush.h
index 7ee8a179d103..96cc0c7a5c90 100644
--- a/include/asm-generic/cacheflush.h
+++ b/include/asm-generic/cacheflush.h
@@ -124,4 +124,15 @@ static inline void flush_cache_vunmap(unsigned long start, unsigned long end)
} while (0)
#endif
+#ifndef cmpxchg_to_user_page
+#define cmpxchg_to_user_page(vma, page, vaddr, ptr, old, new) \
+({ \
+ bool ret; \
+ \
+ ret = try_cmpxchg(ptr, &old, new); \
+ flush_icache_user_page(vma, page, vaddr, sizeof(*ptr)); \
+ ret; \
+})
+#endif
+
#endif /* _ASM_GENERIC_CACHEFLUSH_H */
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index ea41795a352b..b501f752fc9a 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -16,6 +16,7 @@ struct task_struct;
struct rusage;
union thread_union;
struct css_set;
+struct vm_area_struct;
/* All the bits taken by the old clone syscall. */
#define CLONE_LEGACY_FLAGS 0xffffffffULL
@@ -44,6 +45,7 @@ struct kernel_clone_args {
struct cgroup *cgrp;
struct css_set *cset;
unsigned int kill_seq;
+ unsigned long shadow_stack_token;
};
/*
@@ -226,4 +228,19 @@ static inline void task_unlock(struct task_struct *p)
DEFINE_GUARD(task_lock, struct task_struct *, task_lock(_T), task_unlock(_T))
+#ifdef CONFIG_ARCH_HAS_USER_SHADOW_STACK
+int arch_shstk_validate_clone(struct task_struct *p,
+ struct vm_area_struct *vma,
+ struct page *page,
+ struct kernel_clone_args *args);
+#else
+static inline int arch_shstk_validate_clone(struct task_struct *p,
+ struct vm_area_struct *vma,
+ struct page *page,
+ struct kernel_clone_args *args)
+{
+ return 0;
+}
+#endif
+
#endif /* _LINUX_SCHED_TASK_H */
diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index 359a14cc76a4..9cf5c419e109 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -84,6 +84,7 @@
* kernel's limit of nested PID namespaces.
* @cgroup: If CLONE_INTO_CGROUP is specified set this to
* a file descriptor for the cgroup.
+ * @shadow_stack_token: Pointer to shadow stack token at top of stack.
*
* The structure is versioned by size and thus extensible.
* New struct members must go at the end of the struct and
@@ -101,12 +102,14 @@ struct clone_args {
__aligned_u64 set_tid;
__aligned_u64 set_tid_size;
__aligned_u64 cgroup;
+ __aligned_u64 shadow_stack_token;
};
#endif
-#define CLONE_ARGS_SIZE_VER0 64 /* sizeof first published struct */
-#define CLONE_ARGS_SIZE_VER1 80 /* sizeof second published struct */
-#define CLONE_ARGS_SIZE_VER2 88 /* sizeof third published struct */
+#define CLONE_ARGS_SIZE_VER0 64 /* sizeof first published struct */
+#define CLONE_ARGS_SIZE_VER1 80 /* sizeof second published struct */
+#define CLONE_ARGS_SIZE_VER2 88 /* sizeof third published struct */
+#define CLONE_ARGS_SIZE_VER3 96 /* sizeof fourth published struct */
/*
* Scheduling policies
diff --git a/kernel/fork.c b/kernel/fork.c
index af673856499d..d484ebeded33 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1907,6 +1907,51 @@ static bool need_futex_hash_allocate_default(u64 clone_flags)
return true;
}
+static int shstk_validate_clone(struct task_struct *p,
+ struct kernel_clone_args *args)
+{
+ struct mm_struct *mm;
+ struct vm_area_struct *vma;
+ struct page *page;
+ unsigned long addr;
+ int ret;
+
+ if (!IS_ENABLED(CONFIG_ARCH_HAS_USER_SHADOW_STACK))
+ return 0;
+
+ if (!args->shadow_stack_token)
+ return 0;
+
+ mm = get_task_mm(p);
+ if (!mm)
+ return -EFAULT;
+
+ mmap_read_lock(mm);
+
+ addr = untagged_addr_remote(mm, args->shadow_stack_token);
+ page = get_user_page_vma_remote(mm, addr, FOLL_FORCE | FOLL_WRITE,
+ &vma);
+ if (IS_ERR(page)) {
+ ret = -EFAULT;
+ goto out;
+ }
+
+ if (!(vma->vm_flags & VM_SHADOW_STACK) ||
+ !(vma->vm_flags & VM_WRITE)) {
+ ret = -EFAULT;
+ goto out_page;
+ }
+
+ ret = arch_shstk_validate_clone(p, vma, page, args);
+
+out_page:
+ put_page(page);
+out:
+ mmap_read_unlock(mm);
+ mmput(mm);
+ return ret;
+}
+
/*
* This creates a new process as a copy of the old one,
* but does not actually start it yet.
@@ -2182,6 +2227,9 @@ __latent_entropy struct task_struct *copy_process(
if (retval)
goto bad_fork_cleanup_namespaces;
retval = copy_thread(p, args);
+ if (retval)
+ goto bad_fork_cleanup_io;
+ retval = shstk_validate_clone(p, args);
if (retval)
goto bad_fork_cleanup_io;
@@ -2763,7 +2811,9 @@ static noinline int copy_clone_args_from_user(struct kernel_clone_args *kargs,
CLONE_ARGS_SIZE_VER1);
BUILD_BUG_ON(offsetofend(struct clone_args, cgroup) !=
CLONE_ARGS_SIZE_VER2);
- BUILD_BUG_ON(sizeof(struct clone_args) != CLONE_ARGS_SIZE_VER2);
+ BUILD_BUG_ON(offsetofend(struct clone_args, shadow_stack_token) !=
+ CLONE_ARGS_SIZE_VER3);
+ BUILD_BUG_ON(sizeof(struct clone_args) != CLONE_ARGS_SIZE_VER3);
if (unlikely(usize > PAGE_SIZE))
return -E2BIG;
@@ -2796,16 +2846,17 @@ static noinline int copy_clone_args_from_user(struct kernel_clone_args *kargs,
return -EINVAL;
*kargs = (struct kernel_clone_args){
- .flags = args.flags,
- .pidfd = u64_to_user_ptr(args.pidfd),
- .child_tid = u64_to_user_ptr(args.child_tid),
- .parent_tid = u64_to_user_ptr(args.parent_tid),
- .exit_signal = args.exit_signal,
- .stack = args.stack,
- .stack_size = args.stack_size,
- .tls = args.tls,
- .set_tid_size = args.set_tid_size,
- .cgroup = args.cgroup,
+ .flags = args.flags,
+ .pidfd = u64_to_user_ptr(args.pidfd),
+ .child_tid = u64_to_user_ptr(args.child_tid),
+ .parent_tid = u64_to_user_ptr(args.parent_tid),
+ .exit_signal = args.exit_signal,
+ .stack = args.stack,
+ .stack_size = args.stack_size,
+ .tls = args.tls,
+ .set_tid_size = args.set_tid_size,
+ .cgroup = args.cgroup,
+ .shadow_stack_token = args.shadow_stack_token,
};
if (args.set_tid &&
@@ -2846,6 +2897,24 @@ static inline bool clone3_stack_valid(struct kernel_clone_args *kargs)
return true;
}
+/**
+ * clone3_shadow_stack_valid - check and prepare shadow stack
+ * @kargs: kernel clone args
+ *
+ * Verify that shadow stacks are only enabled if supported.
+ */
+static inline bool clone3_shadow_stack_valid(struct kernel_clone_args *kargs)
+{
+ if (!kargs->shadow_stack_token)
+ return true;
+
+ if (!IS_ALIGNED(kargs->shadow_stack_token, sizeof(void *)))
+ return false;
+
+ /* Fail if the kernel wasn't built with shadow stacks */
+ return IS_ENABLED(CONFIG_ARCH_HAS_USER_SHADOW_STACK);
+}
+
static bool clone3_args_valid(struct kernel_clone_args *kargs)
{
/* Verify that no unknown flags are passed along. */
@@ -2868,7 +2937,7 @@ static bool clone3_args_valid(struct kernel_clone_args *kargs)
kargs->exit_signal)
return false;
- if (!clone3_stack_valid(kargs))
+ if (!clone3_stack_valid(kargs) || !clone3_shadow_stack_valid(kargs))
return false;
return true;
--
2.39.5
^ permalink raw reply related
* [PATCH v19 3/8] selftests: Provide helper header for shadow stack testing
From: Mark Brown @ 2025-08-19 16:21 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250819-clone3-shadow-stack-v19-0-bc957075479b@kernel.org>
While almost all users of shadow stacks should be relying on the dynamic
linker and libc to enable the feature there are several low level test
programs where it is useful to enable without any libc support, allowing
testing without full system enablement. This low level testing is helpful
during bringup of the support itself, and also in enabling coverage by
automated testing without needing all system components in the target root
filesystems to have enablement.
Provide a header with helpers for this purpose, intended for use only by
test programs directly exercising shadow stack interfaces.
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Reviewed-by: Kees Cook <kees@kernel.org>
Tested-by: Kees Cook <kees@kernel.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
tools/testing/selftests/ksft_shstk.h | 98 ++++++++++++++++++++++++++++++++++++
1 file changed, 98 insertions(+)
diff --git a/tools/testing/selftests/ksft_shstk.h b/tools/testing/selftests/ksft_shstk.h
new file mode 100644
index 000000000000..fecf91218ea5
--- /dev/null
+++ b/tools/testing/selftests/ksft_shstk.h
@@ -0,0 +1,98 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Helpers for shadow stack enablement, this is intended to only be
+ * used by low level test programs directly exercising interfaces for
+ * working with shadow stacks.
+ *
+ * Copyright (C) 2024 ARM Ltd.
+ */
+
+#ifndef __KSFT_SHSTK_H
+#define __KSFT_SHSTK_H
+
+#include <asm/mman.h>
+
+/* This is currently only defined for x86 */
+#ifndef SHADOW_STACK_SET_TOKEN
+#define SHADOW_STACK_SET_TOKEN (1ULL << 0)
+#endif
+
+static bool shadow_stack_enabled;
+
+#ifdef __x86_64__
+#define ARCH_SHSTK_ENABLE 0x5001
+#define ARCH_SHSTK_SHSTK (1ULL << 0)
+
+#define ARCH_PRCTL(arg1, arg2) \
+({ \
+ long _ret; \
+ register long _num asm("eax") = __NR_arch_prctl; \
+ register long _arg1 asm("rdi") = (long)(arg1); \
+ register long _arg2 asm("rsi") = (long)(arg2); \
+ \
+ asm volatile ( \
+ "syscall\n" \
+ : "=a"(_ret) \
+ : "r"(_arg1), "r"(_arg2), \
+ "0"(_num) \
+ : "rcx", "r11", "memory", "cc" \
+ ); \
+ _ret; \
+})
+
+#define ENABLE_SHADOW_STACK
+static __always_inline void enable_shadow_stack(void)
+{
+ int ret = ARCH_PRCTL(ARCH_SHSTK_ENABLE, ARCH_SHSTK_SHSTK);
+ if (ret == 0)
+ shadow_stack_enabled = true;
+}
+
+#endif
+
+#ifdef __aarch64__
+#define PR_SET_SHADOW_STACK_STATUS 75
+# define PR_SHADOW_STACK_ENABLE (1UL << 0)
+
+#define my_syscall2(num, arg1, arg2) \
+({ \
+ register long _num __asm__ ("x8") = (num); \
+ register long _arg1 __asm__ ("x0") = (long)(arg1); \
+ register long _arg2 __asm__ ("x1") = (long)(arg2); \
+ register long _arg3 __asm__ ("x2") = 0; \
+ register long _arg4 __asm__ ("x3") = 0; \
+ register long _arg5 __asm__ ("x4") = 0; \
+ \
+ __asm__ volatile ( \
+ "svc #0\n" \
+ : "=r"(_arg1) \
+ : "r"(_arg1), "r"(_arg2), \
+ "r"(_arg3), "r"(_arg4), \
+ "r"(_arg5), "r"(_num) \
+ : "memory", "cc" \
+ ); \
+ _arg1; \
+})
+
+#define ENABLE_SHADOW_STACK
+static __always_inline void enable_shadow_stack(void)
+{
+ int ret;
+
+ ret = my_syscall2(__NR_prctl, PR_SET_SHADOW_STACK_STATUS,
+ PR_SHADOW_STACK_ENABLE);
+ if (ret == 0)
+ shadow_stack_enabled = true;
+}
+
+#endif
+
+#ifndef __NR_map_shadow_stack
+#define __NR_map_shadow_stack 453
+#endif
+
+#ifndef ENABLE_SHADOW_STACK
+static inline void enable_shadow_stack(void) { }
+#endif
+
+#endif
--
2.39.5
^ permalink raw reply related
* [PATCH v19 2/8] Documentation: userspace-api: Add shadow stack API documentation
From: Mark Brown @ 2025-08-19 16:21 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250819-clone3-shadow-stack-v19-0-bc957075479b@kernel.org>
There are a number of architectures with shadow stack features which we are
presenting to userspace with as consistent an API as we can (though there
are some architecture specifics). Especially given that there are some
important considerations for userspace code interacting directly with the
feature let's provide some documentation covering the common aspects.
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Kees Cook <kees@kernel.org>
Tested-by: Kees Cook <kees@kernel.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Yury Khrustalev <yury.khrustalev@arm.com>
Reviewed-by: Deepak Gupta <debug@rivosinc.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
Documentation/userspace-api/index.rst | 1 +
Documentation/userspace-api/shadow_stack.rst | 44 ++++++++++++++++++++++++++++
2 files changed, 45 insertions(+)
diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst
index b8c73be4fb11..0167e59b541e 100644
--- a/Documentation/userspace-api/index.rst
+++ b/Documentation/userspace-api/index.rst
@@ -62,6 +62,7 @@ Everything else
ELF
netlink/index
+ shadow_stack
sysfs-platform_profile
vduse
futex2
diff --git a/Documentation/userspace-api/shadow_stack.rst b/Documentation/userspace-api/shadow_stack.rst
new file mode 100644
index 000000000000..65c665496624
--- /dev/null
+++ b/Documentation/userspace-api/shadow_stack.rst
@@ -0,0 +1,44 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=============
+Shadow Stacks
+=============
+
+Introduction
+============
+
+Several architectures have features which provide backward edge
+control flow protection through a hardware maintained stack, only
+writeable by userspace through very limited operations. This feature
+is referred to as shadow stacks on Linux, on x86 it is part of Intel
+Control Enforcement Technology (CET), on arm64 it is Guarded Control
+Stacks feature (FEAT_GCS) and for RISC-V it is the Zicfiss extension.
+It is expected that this feature will normally be managed by the
+system dynamic linker and libc in ways broadly transparent to
+application code, this document covers interfaces and considerations.
+
+
+Enabling
+========
+
+Shadow stacks default to disabled when a userspace process is
+executed, they can be enabled for the current thread with a syscall:
+
+ - For x86 the ARCH_SHSTK_ENABLE arch_prctl()
+ - For other architectures the PR_SET_SHADOW_STACK_ENABLE prctl()
+
+It is expected that this will normally be done by the dynamic linker.
+Any new threads created by a thread with shadow stacks enabled will
+themselves have shadow stacks enabled.
+
+
+Enablement considerations
+=========================
+
+- Returning from the function that enables shadow stacks without first
+ disabling them will cause a shadow stack exception. This includes
+ any syscall wrapper or other library functions, the syscall will need
+ to be inlined.
+- A lock feature allows userspace to prevent disabling of shadow stacks.
+- Those that change the stack context like longjmp() or use of ucontext
+ changes on signal return will need support from libc.
--
2.39.5
^ permalink raw reply related
* [PATCH v19 1/8] arm64/gcs: Return a success value from gcs_alloc_thread_stack()
From: Mark Brown @ 2025-08-19 16:21 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook
In-Reply-To: <20250819-clone3-shadow-stack-v19-0-bc957075479b@kernel.org>
Currently as a result of templating from x86 code gcs_alloc_thread_stack()
returns a pointer as an unsigned int however on arm64 we don't actually use
this pointer value as anything other than a pass/fail flag. Simplify the
interface to just return an int with 0 on success and a negative error code
on failure.
Acked-by: Deepak Gupta <debug@rivosinc.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/include/asm/gcs.h | 8 ++++----
arch/arm64/kernel/process.c | 8 ++++----
arch/arm64/mm/gcs.c | 8 ++++----
3 files changed, 12 insertions(+), 12 deletions(-)
diff --git a/arch/arm64/include/asm/gcs.h b/arch/arm64/include/asm/gcs.h
index 5bc432234d3a..b4bbec9382a1 100644
--- a/arch/arm64/include/asm/gcs.h
+++ b/arch/arm64/include/asm/gcs.h
@@ -64,8 +64,8 @@ static inline bool task_gcs_el0_enabled(struct task_struct *task)
void gcs_set_el0_mode(struct task_struct *task);
void gcs_free(struct task_struct *task);
void gcs_preserve_current_state(void);
-unsigned long gcs_alloc_thread_stack(struct task_struct *tsk,
- const struct kernel_clone_args *args);
+int gcs_alloc_thread_stack(struct task_struct *tsk,
+ const struct kernel_clone_args *args);
static inline int gcs_check_locked(struct task_struct *task,
unsigned long new_val)
@@ -91,8 +91,8 @@ static inline bool task_gcs_el0_enabled(struct task_struct *task)
static inline void gcs_set_el0_mode(struct task_struct *task) { }
static inline void gcs_free(struct task_struct *task) { }
static inline void gcs_preserve_current_state(void) { }
-static inline unsigned long gcs_alloc_thread_stack(struct task_struct *tsk,
- const struct kernel_clone_args *args)
+static inline int gcs_alloc_thread_stack(struct task_struct *tsk,
+ const struct kernel_clone_args *args)
{
return -ENOTSUPP;
}
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 96482a1412c6..f0b1bea9c873 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -299,7 +299,7 @@ static void flush_gcs(void)
static int copy_thread_gcs(struct task_struct *p,
const struct kernel_clone_args *args)
{
- unsigned long gcs;
+ int ret;
if (!system_supports_gcs())
return 0;
@@ -310,9 +310,9 @@ static int copy_thread_gcs(struct task_struct *p,
p->thread.gcs_el0_mode = current->thread.gcs_el0_mode;
p->thread.gcs_el0_locked = current->thread.gcs_el0_locked;
- gcs = gcs_alloc_thread_stack(p, args);
- if (IS_ERR_VALUE(gcs))
- return PTR_ERR((void *)gcs);
+ ret = gcs_alloc_thread_stack(p, args);
+ if (ret != 0)
+ return ret;
return 0;
}
diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c
index 6e93f78de79b..3abcbf9adb5c 100644
--- a/arch/arm64/mm/gcs.c
+++ b/arch/arm64/mm/gcs.c
@@ -38,8 +38,8 @@ static unsigned long gcs_size(unsigned long size)
return max(PAGE_SIZE, size);
}
-unsigned long gcs_alloc_thread_stack(struct task_struct *tsk,
- const struct kernel_clone_args *args)
+int gcs_alloc_thread_stack(struct task_struct *tsk,
+ const struct kernel_clone_args *args)
{
unsigned long addr, size;
@@ -59,13 +59,13 @@ unsigned long gcs_alloc_thread_stack(struct task_struct *tsk,
size = gcs_size(size);
addr = alloc_gcs(0, size);
if (IS_ERR_VALUE(addr))
- return addr;
+ return PTR_ERR((void *)addr);
tsk->thread.gcs_base = addr;
tsk->thread.gcs_size = size;
tsk->thread.gcspr_el0 = addr + size - sizeof(u64);
- return addr;
+ return 0;
}
SYSCALL_DEFINE3(map_shadow_stack, unsigned long, addr, unsigned long, size, unsigned int, flags)
--
2.39.5
^ permalink raw reply related
* [PATCH v19 0/8] fork: Support shadow stacks in clone3()
From: Mark Brown @ 2025-08-19 16:21 UTC (permalink / raw)
To: Rick P. Edgecombe, Deepak Gupta, Szabolcs Nagy, H.J. Lu,
Florian Weimer, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
Mel Gorman, Valentin Schneider, Christian Brauner, Shuah Khan
Cc: linux-kernel, Catalin Marinas, Will Deacon, jannh, bsegall,
Andrew Morton, Yury Khrustalev, Wilco Dijkstra, linux-kselftest,
linux-api, Mark Brown, Kees Cook, Kees Cook, Shuah Khan
[ I think at this point everyone is OK with the ABI, and the x86
implementation has been tested so hopefully we are near to being
able to get this merged? If there are any outstanding issues let
me know and I can look at addressing them. The one possible issue
I am aware of is that the RISC-V shadow stack support was briefly
in -next but got dropped along with the general RISC-V issues during
the last merge window, rebasing for that is still in progress. I
guess ideally this could be applied on a branch and then pulled into
the RISC-V tree? ]
The kernel has recently added support for shadow stacks, currently
x86 only using their CET feature but both arm64 and RISC-V have
equivalent features (GCS and Zicfiss respectively), I am actively
working on GCS[1]. With shadow stacks the hardware maintains an
additional stack containing only the return addresses for branch
instructions which is not generally writeable by userspace and ensures
that any returns are to the recorded addresses. This provides some
protection against ROP attacks and making it easier to collect call
stacks. These shadow stacks are allocated in the address space of the
userspace process.
Our API for shadow stacks does not currently offer userspace any
flexiblity for managing the allocation of shadow stacks for newly
created threads, instead the kernel allocates a new shadow stack with
the same size as the normal stack whenever a thread is created with the
feature enabled. The stacks allocated in this way are freed by the
kernel when the thread exits or shadow stacks are disabled for the
thread. This lack of flexibility and control isn't ideal, in the vast
majority of cases the shadow stack will be over allocated and the
implicit allocation and deallocation is not consistent with other
interfaces. As far as I can tell the interface is done in this manner
mainly because the shadow stack patches were in development since before
clone3() was implemented.
Since clone3() is readily extensible let's add support for specifying a
shadow stack when creating a new thread or process, keeping the current
implicit allocation behaviour if one is not specified either with
clone3() or through the use of clone(). The user must provide a shadow
stack pointer, this must point to memory mapped for use as a shadow
stackby map_shadow_stack() with an architecture specified shadow stack
token at the top of the stack.
Yuri Khrustalev has raised questions from the libc side regarding
discoverability of extended clone3() structure sizes[2], this seems like
a general issue with clone3(). There was a suggestion to add a hwcap on
arm64 which isn't ideal but is doable there, though architecture
specific mechanisms would also be needed for x86 (and RISC-V if it's
support gets merged before this does). The idea has, however, had
strong pushback from the architecture maintainers and it is possible to
detect support for this in clone3() by attempting a call with a
misaligned shadow stack pointer specified so no hwcap has been added.
[1] https://lore.kernel.org/linux-arm-kernel/20241001-arm64-gcs-v13-0-222b78d87eee@kernel.org/T/#mc58f97f27461749ccf400ebabf6f9f937116a86b
[2] https://lore.kernel.org/r/aCs65ccRQtJBnZ_5@arm.com
Signed-off-by: Mark Brown <broonie@kernel.org>
---
Changes in v19:
- Rebase onto v6.17-rc1.
- Link to v18: https://lore.kernel.org/r/20250702-clone3-shadow-stack-v18-0-7965d2b694db@kernel.org
Changes in v18:
- Rebase onto v6.16-rc3.
- Thanks to pointers from Yuri Khrustalev this version has been tested
on x86 so I have removed the RFT tag.
- Clarify clone3_shadow_stack_valid() comment about the Kconfig check.
- Remove redundant GCSB DSYNCs in arm64 code.
- Fix token validation on x86.
- Link to v17: https://lore.kernel.org/r/20250609-clone3-shadow-stack-v17-0-8840ed97ff6f@kernel.org
Changes in v17:
- Rebase onto v6.16-rc1.
- Link to v16: https://lore.kernel.org/r/20250416-clone3-shadow-stack-v16-0-2ffc9ca3917b@kernel.org
Changes in v16:
- Rebase onto v6.15-rc2.
- Roll in fixes from x86 testing from Rick Edgecombe.
- Rework so that the argument is shadow_stack_token.
- Link to v15: https://lore.kernel.org/r/20250408-clone3-shadow-stack-v15-0-3fa245c6e3be@kernel.org
Changes in v15:
- Rebase onto v6.15-rc1.
- Link to v14: https://lore.kernel.org/r/20250206-clone3-shadow-stack-v14-0-805b53af73b9@kernel.org
Changes in v14:
- Rebase onto v6.14-rc1.
- Link to v13: https://lore.kernel.org/r/20241203-clone3-shadow-stack-v13-0-93b89a81a5ed@kernel.org
Changes in v13:
- Rebase onto v6.13-rc1.
- Link to v12: https://lore.kernel.org/r/20241031-clone3-shadow-stack-v12-0-7183eb8bee17@kernel.org
Changes in v12:
- Add the regular prctl() to the userspace API document since arm64
support is queued in -next.
- Link to v11: https://lore.kernel.org/r/20241005-clone3-shadow-stack-v11-0-2a6a2bd6d651@kernel.org
Changes in v11:
- Rebase onto arm64 for-next/gcs, which is based on v6.12-rc1, and
integrate arm64 support.
- Rework the interface to specify a shadow stack pointer rather than a
base and size like we do for the regular stack.
- Link to v10: https://lore.kernel.org/r/20240821-clone3-shadow-stack-v10-0-06e8797b9445@kernel.org
Changes in v10:
- Integrate fixes & improvements for the x86 implementation from Rick
Edgecombe.
- Require that the shadow stack be VM_WRITE.
- Require that the shadow stack base and size be sizeof(void *) aligned.
- Clean up trailing newline.
- Link to v9: https://lore.kernel.org/r/20240819-clone3-shadow-stack-v9-0-962d74f99464@kernel.org
Changes in v9:
- Pull token validation earlier and report problems with an error return
to parent rather than signal delivery to the child.
- Verify that the top of the supplied shadow stack is VM_SHADOW_STACK.
- Rework token validation to only do the page mapping once.
- Drop no longer needed support for testing for signals in selftest.
- Fix typo in comments.
- Link to v8: https://lore.kernel.org/r/20240808-clone3-shadow-stack-v8-0-0acf37caf14c@kernel.org
Changes in v8:
- Fix token verification with user specified shadow stack.
- Don't track user managed shadow stacks for child processes.
- Link to v7: https://lore.kernel.org/r/20240731-clone3-shadow-stack-v7-0-a9532eebfb1d@kernel.org
Changes in v7:
- Rebase onto v6.11-rc1.
- Typo fixes.
- Link to v6: https://lore.kernel.org/r/20240623-clone3-shadow-stack-v6-0-9ee7783b1fb9@kernel.org
Changes in v6:
- Rebase onto v6.10-rc3.
- Ensure we don't try to free the parent shadow stack in error paths of
x86 arch code.
- Spelling fixes in userspace API document.
- Additional cleanups and improvements to the clone3() tests to support
the shadow stack tests.
- Link to v5: https://lore.kernel.org/r/20240203-clone3-shadow-stack-v5-0-322c69598e4b@kernel.org
Changes in v5:
- Rebase onto v6.8-rc2.
- Rework ABI to have the user allocate the shadow stack memory with
map_shadow_stack() and a token.
- Force inlining of the x86 shadow stack enablement.
- Move shadow stack enablement out into a shared header for reuse by
other tests.
- Link to v4: https://lore.kernel.org/r/20231128-clone3-shadow-stack-v4-0-8b28ffe4f676@kernel.org
Changes in v4:
- Formatting changes.
- Use a define for minimum shadow stack size and move some basic
validation to fork.c.
- Link to v3: https://lore.kernel.org/r/20231120-clone3-shadow-stack-v3-0-a7b8ed3e2acc@kernel.org
Changes in v3:
- Rebase onto v6.7-rc2.
- Remove stale shadow_stack in internal kargs.
- If a shadow stack is specified unconditionally use it regardless of
CLONE_ parameters.
- Force enable shadow stacks in the selftest.
- Update changelogs for RISC-V feature rename.
- Link to v2: https://lore.kernel.org/r/20231114-clone3-shadow-stack-v2-0-b613f8681155@kernel.org
Changes in v2:
- Rebase onto v6.7-rc1.
- Remove ability to provide preallocated shadow stack, just specify the
desired size.
- Link to v1: https://lore.kernel.org/r/20231023-clone3-shadow-stack-v1-0-d867d0b5d4d0@kernel.org
---
Mark Brown (8):
arm64/gcs: Return a success value from gcs_alloc_thread_stack()
Documentation: userspace-api: Add shadow stack API documentation
selftests: Provide helper header for shadow stack testing
fork: Add shadow stack support to clone3()
selftests/clone3: Remove redundant flushes of output streams
selftests/clone3: Factor more of main loop into test_clone3()
selftests/clone3: Allow tests to flag if -E2BIG is a valid error code
selftests/clone3: Test shadow stack support
Documentation/userspace-api/index.rst | 1 +
Documentation/userspace-api/shadow_stack.rst | 44 +++++
arch/arm64/include/asm/gcs.h | 8 +-
arch/arm64/kernel/process.c | 8 +-
arch/arm64/mm/gcs.c | 55 +++++-
arch/x86/include/asm/shstk.h | 11 +-
arch/x86/kernel/process.c | 2 +-
arch/x86/kernel/shstk.c | 53 ++++-
include/asm-generic/cacheflush.h | 11 ++
include/linux/sched/task.h | 17 ++
include/uapi/linux/sched.h | 9 +-
kernel/fork.c | 93 +++++++--
tools/testing/selftests/clone3/clone3.c | 226 ++++++++++++++++++----
tools/testing/selftests/clone3/clone3_selftests.h | 65 ++++++-
tools/testing/selftests/ksft_shstk.h | 98 ++++++++++
15 files changed, 620 insertions(+), 81 deletions(-)
---
base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585
change-id: 20231019-clone3-shadow-stack-15d40d2bf536
Best regards,
--
Mark Brown <broonie@kernel.org>
^ permalink raw reply
* Re: [PATCH v3 00/12] man2: document "new" mount API
From: Aleksa Sarai @ 2025-08-19 8:50 UTC (permalink / raw)
To: Christian Brauner
Cc: Askar Safin, alx, dhowells, g.branden.robinson, jack, linux-api,
linux-fsdevel, linux-kernel, linux-man, mtk.manpages, viro,
Ian Kent, autofs mailing list
In-Reply-To: <20250819-erhitzen-knacken-e4d52248ca3e@brauner>
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On 2025-08-19, Christian Brauner <brauner@kernel.org> wrote:
> On Mon, Aug 18, 2025 at 02:16:04AM +1000, Aleksa Sarai wrote:
> > On 2025-08-17, Askar Safin <safinaskar@zohomail.com> wrote:
> > > I noticed that you changed docs for automounts. So I dig into
> > > automounts implementation. And I found a bug in openat2. If
> > > RESOLVE_NO_XDEV is specified, then name resolution doesn't cross
> > > automount points (i. e. we get EXDEV), but automounts still happen! I
> > > think this is a bug. Bug is reproduced in 6.17-rc1. In the end of this
> > > mail you will find reproducer. And miniconfig.
> >
> > Yes, this is a bug -- we check LOOKUP_NO_XDEV after traverse_mounts()
> > because we want to error out if we actually jumped to a different mount.
> > We should probably be erroring out in follow_automount() as well, and I
> > missed this when I wrote openat2().
> >
> > openat2() also really needs RESOLVE_NO_AUTOMOUNT (and probably
> > RESOLVE_NO_DOTDOT as well as some other small features). I'll try to
> > send something soon.
> >
> > > Are automounts actually used? Is it possible to deprecate or
> > > remove them? It seems for me automounts are rarely tested obscure
> > > feature, which affects core namei code.
> >
> > I use them for auto-mounting NFS shares on my laptop, and I'm sure there
> > are plenty of other users. They are little bit funky but I highly doubt
> > they are "unused". Howells probably disagrees in even stronger terms.
> > Most distributions provide autofs as a supported package (I think it
> > even comes pre-installed for some distros).
> >
> > They are not tested by fstests AFAICS, but that's more of a flaw in
> > fstests (automount requires you to have a running autofs daemon, which
> > probably makes testing it in fstests or selftests impractical) not the
> > feature itself.
> >
> > > This reproducer is based on "tracing" automount, which
> > > actually *IS* already deprecated. But automount mechanism
> > > itself is not deprecated, as well as I know.
> >
> > The automount behaviour of tracefs is different to the general automount
> > mechanism which is managed by userspace with the autofs daemon. I don't
> > know the history behind the deprecation, but I expect that it was
> > deprecated in favour of configuring it with autofs (or just enabling it
> > by default).
> >
> > > Also, I did read namei code, and I think that
> > > options AT_NO_AUTOMOUNT, FSPICK_NO_AUTOMOUNT, etc affect
> > > last component only, not all of them. I didn't test this yet.
> > > I plan to test this within next days.
> >
> > No, LOOKUP_AUTOMOUNT affects all components. I double-checked this with
> > Christian.
>
> Hm? I was asking the question in the chat because I was unsure and not
> in front of a computer you then said that it does affect all components. :)
Yeah I misunderstood what you said -- didn't mean to throw you under the
bus, sorry about that!
> > You would think that it's only the last component (like O_DIRECTORY,
> > O_NOFOLLOW, AT_SYMLINK_{,NO}FOLLOW) but follow_automount() is called for
> > all components (i.e., as part of step_into()). It hooks into the regular
> > lookup flow for mountpoints.
> >
> > Yes, it is quite funky that AT_NO_AUTOMOUNT is the only AT_* flag that
> > works this way -- hence why I went with a different RESOLVE_* namespace
> > for openat2() (which _always_ act on _all_ components).
> >
> > --
> > Aleksa Sarai
> > Senior Software Engineer (Containers)
> > SUSE Linux GmbH
> > https://www.cyphar.com/
>
>
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/
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^ permalink raw reply
* Re: [PATCH v3 00/12] man2: document "new" mount API
From: Christian Brauner @ 2025-08-19 8:31 UTC (permalink / raw)
To: Aleksa Sarai
Cc: Askar Safin, alx, dhowells, g.branden.robinson, jack, linux-api,
linux-fsdevel, linux-kernel, linux-man, mtk.manpages, viro,
Ian Kent, autofs mailing list
In-Reply-To: <2025-08-17.1755446479-rotten-curled-charms-robe-vWOBH5@cyphar.com>
On Mon, Aug 18, 2025 at 02:16:04AM +1000, Aleksa Sarai wrote:
> On 2025-08-17, Askar Safin <safinaskar@zohomail.com> wrote:
> > I noticed that you changed docs for automounts. So I dig into
> > automounts implementation. And I found a bug in openat2. If
> > RESOLVE_NO_XDEV is specified, then name resolution doesn't cross
> > automount points (i. e. we get EXDEV), but automounts still happen! I
> > think this is a bug. Bug is reproduced in 6.17-rc1. In the end of this
> > mail you will find reproducer. And miniconfig.
>
> Yes, this is a bug -- we check LOOKUP_NO_XDEV after traverse_mounts()
> because we want to error out if we actually jumped to a different mount.
> We should probably be erroring out in follow_automount() as well, and I
> missed this when I wrote openat2().
>
> openat2() also really needs RESOLVE_NO_AUTOMOUNT (and probably
> RESOLVE_NO_DOTDOT as well as some other small features). I'll try to
> send something soon.
>
> > Are automounts actually used? Is it possible to deprecate or
> > remove them? It seems for me automounts are rarely tested obscure
> > feature, which affects core namei code.
>
> I use them for auto-mounting NFS shares on my laptop, and I'm sure there
> are plenty of other users. They are little bit funky but I highly doubt
> they are "unused". Howells probably disagrees in even stronger terms.
> Most distributions provide autofs as a supported package (I think it
> even comes pre-installed for some distros).
>
> They are not tested by fstests AFAICS, but that's more of a flaw in
> fstests (automount requires you to have a running autofs daemon, which
> probably makes testing it in fstests or selftests impractical) not the
> feature itself.
>
> > This reproducer is based on "tracing" automount, which
> > actually *IS* already deprecated. But automount mechanism
> > itself is not deprecated, as well as I know.
>
> The automount behaviour of tracefs is different to the general automount
> mechanism which is managed by userspace with the autofs daemon. I don't
> know the history behind the deprecation, but I expect that it was
> deprecated in favour of configuring it with autofs (or just enabling it
> by default).
>
> > Also, I did read namei code, and I think that
> > options AT_NO_AUTOMOUNT, FSPICK_NO_AUTOMOUNT, etc affect
> > last component only, not all of them. I didn't test this yet.
> > I plan to test this within next days.
>
> No, LOOKUP_AUTOMOUNT affects all components. I double-checked this with
> Christian.
Hm? I was asking the question in the chat because I was unsure and not
in front of a computer you then said that it does affect all components. :)
>
> You would think that it's only the last component (like O_DIRECTORY,
> O_NOFOLLOW, AT_SYMLINK_{,NO}FOLLOW) but follow_automount() is called for
> all components (i.e., as part of step_into()). It hooks into the regular
> lookup flow for mountpoints.
>
> Yes, it is quite funky that AT_NO_AUTOMOUNT is the only AT_* flag that
> works this way -- hence why I went with a different RESOLVE_* namespace
> for openat2() (which _always_ act on _all_ components).
>
> --
> Aleksa Sarai
> Senior Software Engineer (Containers)
> SUSE Linux GmbH
> https://www.cyphar.com/
^ permalink raw reply
* Re: [PATCH v3 07/30] kho: add interfaces to unpreserve folios and physical memory ranges
From: Jason Gunthorpe @ 2025-08-18 13:55 UTC (permalink / raw)
To: Mike Rapoport
Cc: Pasha Tatashin, pratyush, jasonmiu, graf, changyuanl, dmatlack,
rientjes, corbet, rdunlap, ilpo.jarvinen, kanie, ojeda, aliceryhl,
masahiroy, akpm, tj, yoann.congal, mmaurer, roman.gushchin,
chenridong, axboe, mark.rutland, jannh, vincent.guittot, hannes,
dan.j.williams, david, joel.granados, rostedt, anna.schumaker,
song, zhangguopeng, linux, linux-kernel, linux-doc, linux-mm,
gregkh, tglx, mingo, bp, dave.hansen, x86, hpa, rafael, dakr,
bartosz.golaszewski, cw00.choi, myungjoo.ham, yesanishhere,
Jonathan.Cameron, quic_zijuhu, aleksander.lobakin, ira.weiny,
andriy.shevchenko, leon, lukas, bhelgaas, wagi, djeffery,
stuart.w.hayes, ptyadav, lennart, brauner, linux-api,
linux-fsdevel, saeedm, ajayachandra, parav, leonro, witu
In-Reply-To: <aJ756q-wWJV37fMm@kernel.org>
On Fri, Aug 15, 2025 at 12:12:10PM +0300, Mike Rapoport wrote:
> > Which is perhaps another comment, if this __get_free_pages() is going
> > to be a common pattern (and I guess it will be) then the API should be
> > streamlined alot more:
> >
> > void *kho_alloc_preserved_memory(gfp, size);
> > void kho_free_preserved_memory(void *);
>
> This looks backwards to me. KHO should not deal with memory allocation,
> it's responsibility to preserve/restore memory objects it supports.
Then maybe those are luo_ helpers
But having users open code __get_free_pages() and convert to/from
struct page, phys, etc is not a great idea.
The use case is simply to get some memory to preserve, it should work
in terms of void *. We don't support slab today so this has to be
emulated with full pages, but this detail should not leak out of the
API.
Jason
^ permalink raw reply
* Re: [PATCH v3 00/12] man2: document "new" mount API
From: Aleksa Sarai @ 2025-08-18 5:46 UTC (permalink / raw)
To: Askar Safin
Cc: alx, autofs, brauner, dhowells, g.branden.robinson, jack,
linux-api, linux-fsdevel, linux-kernel, linux-man, mtk.manpages,
raven, viro
In-Reply-To: <20250817185048.302679-1-safinaskar@zohomail.com>
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On 2025-08-17, Askar Safin <safinaskar@zohomail.com> wrote:
> I just sent to fsdevel fix for that RESOLVE_NO_XDEV bug.
Thanks, I've sent some review comments.
> if (!(lookup_flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY |
> LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT)) &&
>
> We never return -EISDIR in this "if" if we are in non-final component
> thanks to LOOKUP_PARENT here. We fall to finish_automount instead.
Grr, I re-read this conditional a few times and I still misunderstood
what it was doing. My bad.
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/
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^ permalink raw reply
* Re: [PATCH util-linux v2] fallocate: add FALLOC_FL_WRITE_ZEROES support
From: Zhang Yi @ 2025-08-18 2:17 UTC (permalink / raw)
To: Darrick J. Wong
Cc: linux-fsdevel, linux-block, dm-devel, linux-nvme, linux-scsi,
linux-kernel, linux-api, hch, tytso, bmarzins, chaitanyak,
shinichiro.kawasaki, brauner, martin.petersen, yi.zhang,
chengzhihao1, yukuai3, yangerkun
In-Reply-To: <20250815142908.GG7981@frogsfrogsfrogs>
On 8/15/2025 10:29 PM, Darrick J. Wong wrote:
> On Fri, Aug 15, 2025 at 05:29:19PM +0800, Zhang Yi wrote:
>> Thank you for your review comments!
>>
>> On 2025/8/15 0:52, Darrick J. Wong wrote:
>>> On Wed, Aug 13, 2025 at 10:40:15AM +0800, Zhang Yi wrote:
>>>> From: Zhang Yi <yi.zhang@huawei.com>
>>>>
>>>> The Linux kernel (since version 6.17) supports FALLOC_FL_WRITE_ZEROES in
>>>> fallocate(2). Add support for FALLOC_FL_WRITE_ZEROES to the fallocate
>>>> utility by introducing a new option -w|--write-zeroes.
>>>>
>>>> Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=278c7d9b5e0c
>>>> Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
>>>> ---
>>>> v1->v2:
>>>> - Minor description modification to align with the kernel.
>>>>
>>>> sys-utils/fallocate.1.adoc | 11 +++++++++--
>>>> sys-utils/fallocate.c | 20 ++++++++++++++++----
>>>> 2 files changed, 25 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/sys-utils/fallocate.1.adoc b/sys-utils/fallocate.1.adoc
>>>> index 44ee0ef4c..0ec9ff9a9 100644
>>>> --- a/sys-utils/fallocate.1.adoc
>>>> +++ b/sys-utils/fallocate.1.adoc
>>>> @@ -12,7 +12,7 @@ fallocate - preallocate or deallocate space to a file
>>>
>>> <snip all the long lines>
>>>
>>>> +*-w*, *--write-zeroes*::
>>>> +Zeroes space in the byte range starting at _offset_ and continuing
>>>> for _length_ bytes. Within the specified range, blocks are
>>>> preallocated for the regions that span the holes in the file. After a
>>>> successful call, subsequent reads from this range will return zeroes,
>>>> subsequent writes to that range do not require further changes to the
>>>> file mapping metadata.
>>>
>>> "...will return zeroes and subsequent writes to that range..." ?
>>>
>>
>> Yeah.
>>
>>>> ++
>>>> +Zeroing is done within the filesystem by preferably submitting write
>>>
>>> I think we should say less about what the filesystem actually does to
>>> preserve some flexibility:
>>>
>>> "Zeroing is done within the filesystem. The filesystem may use a
>>> hardware accelerated zeroing command, or it may submit regular writes.
>>> The behavior depends on the filesystem design and available hardware."
>>>
>>
>> Sure.
>>
>>>> zeores commands, the alternative way is submitting actual zeroed data,
>>>> the specified range will be converted into written extents. The write
>>>> zeroes command is typically faster than write actual data if the
>>>> device supports unmap write zeroes, the specified range will not be
>>>> physically zeroed out on the device.
>>>> ++
>>>> +Options *--keep-size* can not be specified for the write-zeroes
>>>> operation.
>>>> +
>>>> include::man-common/help-version.adoc[]
>>>>
>>>> == AUTHORS
>> [..]
>>>> @@ -429,6 +438,9 @@ int main(int argc, char **argv)
>>>> else if (mode & FALLOC_FL_ZERO_RANGE)
>>>> fprintf(stdout, _("%s: %s (%ju bytes) zeroed.\n"),
>>>> filename, str, length);
>>>> + else if (mode & FALLOC_FL_WRITE_ZEROES)
>>>> + fprintf(stdout, _("%s: %s (%ju bytes) write zeroed.\n"),
>>>
>>> "write zeroed" is a little strange, but I don't have a better
>>> suggestion. :)
>>>
>>
>> Hmm... What about simply using "zeroed", the same to FALLOC_FL_ZERO_RANGE?
>> Users should be aware of the parameters they have passed to fallocate(),
>> so they should not use this print for further differentiation.
>
> No thanks, different inputs should produce different outputs. :)
>
OK. perhaps "written as zeros." ? Sounds OK?
Thanks,
Yi.
^ permalink raw reply
* Re: [PATCH v3 00/12] man2: document "new" mount API
From: Askar Safin @ 2025-08-17 18:50 UTC (permalink / raw)
To: cyphar
Cc: alx, autofs, brauner, dhowells, g.branden.robinson, jack,
linux-api, linux-fsdevel, linux-kernel, linux-man, mtk.manpages,
raven, safinaskar, viro
In-Reply-To: <2025-08-17.1755446479-rotten-curled-charms-robe-vWOBH5@cyphar.com>
I just sent to fsdevel fix for that RESOLVE_NO_XDEV bug.
Aleksa Sarai <cyphar@cyphar.com>:
> No, LOOKUP_AUTOMOUNT affects all components. I double-checked this with
> Christian.
No. I just tested this. See tests (and miniconfig) in the end of this message.
statx always follows automounts in non-final components no matter what.
I tested this. And it follows automounts in final component depending on
AT_NO_AUTOMOUNT. I tested this too. Also, absolutely all other syscalls always
follow automounts in non-final components no matter what. With sole exception
for openat2 with RESOLVE_NO_XDEV. I didn't test this, but I conclude this
by reading code.
First of all, LOOKUP_PARENT's doc in kernel currently is wrong:
https://elixir.bootlin.com/linux/v6.17-rc1/source/include/linux/namei.h#L31
We see there:
#define LOOKUP_PARENT BIT(10) /* Looking up final parent in path */
This is not true. LOOKUP_PARENT means that we are resolving any non-final
component. LOOKUP_PARENT is set when we enter link_path_walk, which
is used for resolving everything except for final component.
And LOOKUP_PARENT is cleared when we leave link_path_walk.
Now let's look here:
https://elixir.bootlin.com/linux/v6.17-rc1/source/fs/namei.c#L1447
if (!(lookup_flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY |
LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT)) &&
We never return -EISDIR in this "if" if we are in non-final component
thanks to LOOKUP_PARENT here. We fall to finish_automount instead.
Again: if this is non-final component, then LOOKUP_PARENT is set, and thus
LOOKUP_AUTOMOUNT is ignored. If this is final component, then LOOKUP_AUTOMOUNT
may affect things.
Code below tests that:
- statx always follows non-final automounts
- statx follow final automounts depending on options
The code doesn't test other syscalls, they can be added if needed.
The code was tested in Qemu on Linux 6.17-rc1.
I'm not trying to insult you in any way.
Again: thank you a lot for your work! For openat2 and for these mans.
Askar Safin
====
miniconfig:
CONFIG_64BIT=y
CONFIG_EXPERT=y
CONFIG_PRINTK=y
CONFIG_PRINTK_TIME=y
CONFIG_TTY=y
CONFIG_VT=y
CONFIG_VT_CONSOLE=y
CONFIG_FRAMEBUFFER_CONSOLE=y
CONFIG_PROC_FS=y
CONFIG_DEVTMPFS=y
CONFIG_SYSFS=y
CONFIG_TMPFS=y
CONFIG_DEBUG_FS=y
CONFIG_USER_EVENTS=y
CONFIG_FTRACE=y
CONFIG_MULTIUSER=y
CONFIG_NAMESPACES=y
CONFIG_USER_NS=y
CONFIG_PID_NS=y
CONFIG_SERIAL_8250=y
CONFIG_SERIAL_8250_CONSOLE=y
CONFIG_BLK_DEV_INITRD=y
CONFIG_RD_GZIP=y
CONFIG_BINFMT_ELF=y
CONFIG_BINFMT_SCRIPT=y
CONFIG_TRACEFS_AUTOMOUNT_DEPRECATED=y
CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
====
/*
Author: Askar Safin
Public domain
Make sure your kernel is compiled with CONFIG_TRACEFS_AUTOMOUNT_DEPRECATED=y
If all tests pass, the program
should print "All tests passed".
Any other output means that something gone wrong.
This program requires root in initial user namespace
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sched.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/mount.h>
#include <sys/syscall.h>
#include <linux/openat2.h>
#define MY_ASSERT(cond) do { \
if (!(cond)) { \
fprintf (stderr, "%s: assertion failed\n", #cond); \
exit (1); \
} \
} while (0)
bool
tracing_mounted (void)
{
struct statx tracing;
if (statx (AT_FDCWD, "/tmp/debugfs/tracing", AT_NO_AUTOMOUNT, 0, &tracing) != 0)
{
perror ("statx tracing");
exit (1);
}
if (!(tracing.stx_attributes_mask & STATX_ATTR_MOUNT_ROOT))
{
fprintf (stderr, "???\n");
exit (1);
}
return tracing.stx_attributes & STATX_ATTR_MOUNT_ROOT;
}
void
mount_debugfs (void)
{
if (mount (NULL, "/tmp/debugfs", "debugfs", 0, NULL) != 0)
{
perror ("mount debugfs");
exit (1);
}
MY_ASSERT (!tracing_mounted ());
}
void
umount_debugfs (void)
{
umount ("/tmp/debugfs/tracing"); // Ignore errors
if (umount ("/tmp/debugfs") != 0)
{
perror ("umount debugfs");
exit (1);
}
}
int
main (void)
{
// Init
{
if (chdir ("/") != 0)
{
perror ("chdir /");
exit (1);
}
if (unshare (CLONE_NEWNS) != 0)
{
perror ("unshare");
exit (1);
}
if (mount (NULL, "/", NULL, MS_REC | MS_PRIVATE, NULL) != 0)
{
perror ("mount(NULL, /, NULL, MS_REC | MS_PRIVATE, NULL)");
exit (1);
}
if (mount (NULL, "/tmp", "tmpfs", 0, NULL) != 0)
{
perror ("mount tmpfs");
exit (1);
}
}
if (mkdir ("/tmp/debugfs", 0777) != 0)
{
perror ("mkdir(/tmp/debugfs)");
exit (1);
}
// statx always follows automounts in non-final components. With AT_NO_AUTOMOUNT and without AT_NO_AUTOMOUNT
{
mount_debugfs();
{
struct statx readme;
if (statx (AT_FDCWD, "/tmp/debugfs/tracing/README", 0, 0, &readme) != 0)
{
perror ("statx");
exit (1);
}
}
MY_ASSERT (tracing_mounted ());
umount_debugfs();
mount_debugfs();
{
struct statx readme;
if (statx (AT_FDCWD, "/tmp/debugfs/tracing/README", AT_NO_AUTOMOUNT, 0, &readme) != 0)
{
perror ("statx");
exit (1);
}
}
MY_ASSERT (tracing_mounted ());
umount_debugfs();
}
// statx follows automounts in final components if AT_NO_AUTOMOUNT is not specified
{
mount_debugfs();
{
struct statx tracing;
if (statx (AT_FDCWD, "/tmp/debugfs/tracing", 0, 0, &tracing) != 0)
{
perror ("statx");
exit (1);
}
if (!(tracing.stx_attributes_mask & STATX_ATTR_MOUNT_ROOT))
{
fprintf (stderr, "???\n");
exit (1);
}
// Checking that this is new mount, not automount point itself
MY_ASSERT (tracing.stx_attributes & STATX_ATTR_MOUNT_ROOT);
}
MY_ASSERT (tracing_mounted ());
umount_debugfs ();
mount_debugfs();
{
struct statx tracing;
if (statx (AT_FDCWD, "/tmp/debugfs/tracing", AT_NO_AUTOMOUNT, 0, &tracing) != 0)
{
perror ("statx");
exit (1);
}
if (!(tracing.stx_attributes_mask & STATX_ATTR_MOUNT_ROOT))
{
fprintf (stderr, "???\n");
exit (1);
}
MY_ASSERT (!(tracing.stx_attributes & STATX_ATTR_MOUNT_ROOT));
}
MY_ASSERT (!tracing_mounted ());
umount_debugfs ();
}
printf ("All tests passed\n");
exit (0);
}
^ permalink raw reply
* Re: [PATCH v3 00/12] man2: document "new" mount API
From: Aleksa Sarai @ 2025-08-17 16:16 UTC (permalink / raw)
To: Askar Safin
Cc: alx, brauner, dhowells, g.branden.robinson, jack, linux-api,
linux-fsdevel, linux-kernel, linux-man, mtk.manpages, viro,
Ian Kent, autofs mailing list
In-Reply-To: <20250817075252.4137628-1-safinaskar@zohomail.com>
[-- Attachment #1: Type: text/plain, Size: 2946 bytes --]
On 2025-08-17, Askar Safin <safinaskar@zohomail.com> wrote:
> I noticed that you changed docs for automounts. So I dig into
> automounts implementation. And I found a bug in openat2. If
> RESOLVE_NO_XDEV is specified, then name resolution doesn't cross
> automount points (i. e. we get EXDEV), but automounts still happen! I
> think this is a bug. Bug is reproduced in 6.17-rc1. In the end of this
> mail you will find reproducer. And miniconfig.
Yes, this is a bug -- we check LOOKUP_NO_XDEV after traverse_mounts()
because we want to error out if we actually jumped to a different mount.
We should probably be erroring out in follow_automount() as well, and I
missed this when I wrote openat2().
openat2() also really needs RESOLVE_NO_AUTOMOUNT (and probably
RESOLVE_NO_DOTDOT as well as some other small features). I'll try to
send something soon.
> Are automounts actually used? Is it possible to deprecate or
> remove them? It seems for me automounts are rarely tested obscure
> feature, which affects core namei code.
I use them for auto-mounting NFS shares on my laptop, and I'm sure there
are plenty of other users. They are little bit funky but I highly doubt
they are "unused". Howells probably disagrees in even stronger terms.
Most distributions provide autofs as a supported package (I think it
even comes pre-installed for some distros).
They are not tested by fstests AFAICS, but that's more of a flaw in
fstests (automount requires you to have a running autofs daemon, which
probably makes testing it in fstests or selftests impractical) not the
feature itself.
> This reproducer is based on "tracing" automount, which
> actually *IS* already deprecated. But automount mechanism
> itself is not deprecated, as well as I know.
The automount behaviour of tracefs is different to the general automount
mechanism which is managed by userspace with the autofs daemon. I don't
know the history behind the deprecation, but I expect that it was
deprecated in favour of configuring it with autofs (or just enabling it
by default).
> Also, I did read namei code, and I think that
> options AT_NO_AUTOMOUNT, FSPICK_NO_AUTOMOUNT, etc affect
> last component only, not all of them. I didn't test this yet.
> I plan to test this within next days.
No, LOOKUP_AUTOMOUNT affects all components. I double-checked this with
Christian.
You would think that it's only the last component (like O_DIRECTORY,
O_NOFOLLOW, AT_SYMLINK_{,NO}FOLLOW) but follow_automount() is called for
all components (i.e., as part of step_into()). It hooks into the regular
lookup flow for mountpoints.
Yes, it is quite funky that AT_NO_AUTOMOUNT is the only AT_* flag that
works this way -- hence why I went with a different RESOLVE_* namespace
for openat2() (which _always_ act on _all_ components).
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/
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^ permalink raw reply
* Re: [PATCH] LoongArch: Increase COMMAND_LINE_SIZE to 4096
From: Xose Vazquez Perez @ 2025-08-17 7:57 UTC (permalink / raw)
To: Ming Wang; +Cc: LINUX_ARCH-ML, API-ML, KERNEL-ML, X86-ML
Ming Wang wrote:
> The default COMMAND_LINE_SIZE of 512, inherited from asm-generic, is
> too small for modern use cases. For example, kdump configurations or
> extensive debugging parameters can easily exceed this limit.
>
> Therefore, increase the command line size to 4096 bytes, aligning
> LoongArch with the MIPS architecture. This change follows a broader
> trend among architectures to raise this limit to support modern needs;
> for instance, PowerPC increased its value for similar reasons in
> commit a5980d064fe2 ("powerpc: Bump COMMAND_LINE_SIZE to 2048").
>
> Similar to the change made for RISC-V in commit 61fc1ee8be26
> ("riscv: Bump COMMAND_LINE_SIZE value to 1024"), this is considered
> a safe change. The broader kernel community has reached a consensus
> that modifying COMMAND_LINE_SIZE from UAPI headers does not
> constitute a uABI breakage, as well-behaved userspace applications
> should not rely on this macro.
>
> Suggested-by: Huang Cun <cunhuang@tencent.com>
> Signed-off-by: Ming Wang <wangming01@loongson.cn>
> ---
> arch/loongarch/include/uapi/asm/setup.h | 8 ++++++++
> 1 file changed, 8 insertions(+)
> create mode 100644 arch/loongarch/include/uapi/asm/setup.h
>
> diff --git a/arch/loongarch/include/uapi/asm/setup.h b/arch/loongarch/include/uapi/asm/setup.h
> new file mode 100644
> index 000000000000..d46363ce3e02
> --- /dev/null
> +++ b/arch/loongarch/include/uapi/asm/setup.h
> @@ -0,0 +1,8 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +
> +#ifndef _UAPI_ASM_LOONGARCH_SETUP_H
> +#define _UAPI_ASM_LOONGARCH_SETUP_H
> +
> +#define COMMAND_LINE_SIZE 4096
> +
> +#endif /* _UAPI_ASM_LOONGARCH_SETUP_H */
> --
> 2.43.0
A bit chaotic and arbitrary sizes:
$ git grep "define.*COMMAND_LINE_SIZE"
arch/alpha/include/uapi/asm/setup.h:#define COMMAND_LINE_SIZE 256
arch/arc/include/asm/setup.h:#define COMMAND_LINE_SIZE 256
arch/arm64/include/uapi/asm/setup.h:#define COMMAND_LINE_SIZE 2048
arch/arm/include/uapi/asm/setup.h:#define COMMAND_LINE_SIZE 1024
arch/m68k/include/asm/setup.h:#define CL_SIZE COMMAND_LINE_SIZE
arch/m68k/include/uapi/asm/setup.h:#define COMMAND_LINE_SIZE 256
arch/microblaze/include/uapi/asm/setup.h:#define COMMAND_LINE_SIZE 256
arch/mips/include/uapi/asm/setup.h:#define COMMAND_LINE_SIZE 4096
arch/mips/loongson64/reset.c:#define KEXEC_ARGV_SIZE COMMAND_LINE_SIZE
arch/parisc/include/uapi/asm/setup.h:#define COMMAND_LINE_SIZE 1024
arch/powerpc/boot/ops.h:#define BOOT_COMMAND_LINE_SIZE 2048
arch/powerpc/include/uapi/asm/setup.h:#define COMMAND_LINE_SIZE 2048
arch/riscv/include/uapi/asm/setup.h:#define COMMAND_LINE_SIZE 1024
arch/s390/include/asm/setup.h:#define COMMAND_LINE_SIZE CONFIG_COMMAND_LINE_SIZE
arch/s390/include/asm/setup.h:#define LEGACY_COMMAND_LINE_SIZE 896
arch/sparc/include/uapi/asm/setup.h:# define COMMAND_LINE_SIZE 2048
arch/sparc/include/uapi/asm/setup.h:# define COMMAND_LINE_SIZE 256
arch/um/include/asm/setup.h:#define COMMAND_LINE_SIZE 4096
arch/x86/include/asm/setup.h:#define COMMAND_LINE_SIZE 2048
arch/xtensa/include/uapi/asm/setup.h:#define COMMAND_LINE_SIZE 256
include/uapi/asm-generic/setup.h:#define COMMAND_LINE_SIZE 512
kernel/trace/ftrace.c:#define FTRACE_FILTER_SIZE COMMAND_LINE_SIZE
tools/power/x86/turbostat/turbostat.c:#define COMMAND_LINE_SIZE 2048
tools/testing/selftests/kho/init.c:#define COMMAND_LINE_SIZE 2048
Maybe they should be standardized ???
And for s390 it is configurable, see 622021cd6c560
^ permalink raw reply
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