* Re: [PATCH v7 5/6] selftests: pidfd: add tests for PIDFD_SELF_*
From: Shakeel Butt @ 2025-02-05 5:27 UTC (permalink / raw)
To: Lorenzo Stoakes
Cc: Christian Brauner, Shuah Khan, Liam R . Howlett,
Suren Baghdasaryan, Vlastimil Babka, pedro.falcato,
linux-kselftest, linux-mm, linux-fsdevel, linux-api, linux-kernel,
Oliver Sang, John Hubbard, Tejun Heo, Johannes Weiner,
Michal Koutny, Andrew Morton
In-Reply-To: <7ab0e48b26ba53abf7b703df2dd11a2e99b8efb2.1738268370.git.lorenzo.stoakes@oracle.com>
On Thu, Jan 30, 2025 at 08:40:30PM +0000, Lorenzo Stoakes wrote:
> Add tests to assert that PIDFD_SELF* correctly refers to the current
> thread and process.
>
> We explicitly test pidfd_send_signal(), however We defer testing of
> mm-specific functionality which uses pidfd, namely process_madvise() and
> process_mrelease() to mm testing (though note the latter can not be
> sensibly tested as it would require the testing process to be dying).
>
> We also correct the pidfd_open_test.c fields which refer to .request_mask
> whereas the UAPI header refers to .mask, which otherwise break the import
> of the UAPI header.
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
^ permalink raw reply
* Re: [PATCH v7 6/6] selftests/mm: use PIDFD_SELF in guard pages test
From: Shakeel Butt @ 2025-02-05 5:28 UTC (permalink / raw)
To: Lorenzo Stoakes
Cc: Christian Brauner, Shuah Khan, Liam R . Howlett,
Suren Baghdasaryan, Vlastimil Babka, pedro.falcato,
linux-kselftest, linux-mm, linux-fsdevel, linux-api, linux-kernel,
Oliver Sang, John Hubbard, Tejun Heo, Johannes Weiner,
Michal Koutny, Andrew Morton
In-Reply-To: <69fbbe088d3424de9983e145228459cb05a8f13d.1738268370.git.lorenzo.stoakes@oracle.com>
On Thu, Jan 30, 2025 at 08:40:31PM +0000, Lorenzo Stoakes wrote:
> Now we have PIDFD_SELF available for process_madvise(), make use of it in
> the guard pages test.
>
> This is both more convenient and asserts that PIDFD_SELF works as expected.
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
^ permalink raw reply
* Re: [PATCH v7 0/6] introduce PIDFD_SELF* sentinels
From: Christian Brauner @ 2025-02-05 9:29 UTC (permalink / raw)
To: Suren Baghdasaryan
Cc: Lorenzo Stoakes, Shuah Khan, Liam R . Howlett, Vlastimil Babka,
pedro.falcato, linux-kselftest, linux-mm, linux-fsdevel,
linux-api, linux-kernel, Oliver Sang, John Hubbard, Tejun Heo,
Johannes Weiner, Michal Koutny, Andrew Morton, Shakeel Butt,
Elliott Hughes
In-Reply-To: <CAJuCfpEUusRt_ss7RtxRPP9q_LRwi+Lw+SOq32EUA58s3JOx1A@mail.gmail.com>
On Tue, Feb 04, 2025 at 09:43:31AM -0800, Suren Baghdasaryan wrote:
> On Tue, Feb 4, 2025 at 2:01 AM Lorenzo Stoakes
> <lorenzo.stoakes@oracle.com> wrote:
> >
> > On Tue, Feb 04, 2025 at 10:46:35AM +0100, Christian Brauner wrote:
> > > On Thu, 30 Jan 2025 20:40:25 +0000, Lorenzo Stoakes wrote:
> > > > If you wish to utilise a pidfd interface to refer to the current process or
> > > > thread it is rather cumbersome, requiring something like:
> > > >
> > > > int pidfd = pidfd_open(getpid(), 0 or PIDFD_THREAD);
> > > >
> > > > ...
> > > >
> > > > [...]
> > >
> > > Updated merge message. I've slightly rearranged pidfd_send_signal() so
> > > we don't have to call CLASS(fd, f)(pidfd) unconditionally anymore.
> >
> > Sounds good and thank you! Glad to get this in :)
>
> Sorry, a bit late to the party...
>
> We were discussing MADV_GUARD_INSTALL use with Android Bionic team and
> the possibility of caching pidfd_open() result for reuse when
> installing multiple guards, however doing that in libraries would pose
> issues as we can't predict the user behavior, which can fork() in
> between such calls. That would be an additional reason why having
> these sentinels is beneficial.
Ok, added this to the cover letter as well.
Note that starting with v6.14 pidfs supports file handles.
This works because pidfs provides each pidfd with a unique 64bit inode
number that is exposed in statx(). On 64-bit the ->st_ino simply is the
inode number. On 32-bit the unique identifier can be reconstructed using
->st_ino and the inode generation number which can be retrieved via the
FS_IOC_GETVERSION ioctl. So the 64-bit identifier on 32-bit is
reconstructed by using ->st_ino as the lower 32-bits and the 32-bit
generation number as the upper 32-bits.
Also note that since the introduction of pidfs each struct pid will
refer to a different inode but the same struct pid will refer to the
same inode if it's opened multiple times. In contrast to pre-pidfs
pidfds where each struct pid refered to the same inode.
IOW, with pidfs statx() is sufficient to compare to pidfds whether they
refer to the same process. On 64-bit it's sufficient to do the usual
st1->st_dev == st2->st_dev && st1->st_ino == st2->st_ino and on 32-bit
you will want to also compare the generation number:
TEST_F(pidfd_bind_mount, reopen)
{
int pidfd;
char proc_path[PATH_MAX];
sprintf(proc_path, "/proc/self/fd/%d", self->pidfd);
pidfd = open(proc_path, O_RDONLY | O_NOCTTY | O_CLOEXEC);
ASSERT_GE(pidfd, 0);
ASSERT_GE(fstat(self->pidfd, &self->st2), 0);
ASSERT_EQ(ioctl(self->pidfd, FS_IOC_GETVERSION, &self->gen2), 0);
ASSERT_TRUE(self->st1.st_dev == self->st2.st_dev && self->st1.st_ino == self->st2.st_ino);
ASSERT_TRUE(self->gen1 == self->gen2);
ASSERT_EQ(close(pidfd), 0);
}
Plus, you can bind-mount them now.
In any case, this allows us to create file handles that are unique for
the lifetime of the system. Please see
tools/testing/selftests/pidfd/pidfd_file_handle_test.c
for how that works. The gist is that decoding and encoding for pidfs is
unprivileged and the only requirement we have is that the process the
file handle resolves to must be valid in the caller's pid namespace
hierarchy:
TEST_F(file_handle, file_handle_child_pidns)
{
int mnt_id;
struct file_handle *fh;
int pidfd = -EBADF;
struct stat st1, st2;
fh = malloc(sizeof(struct file_handle) + MAX_HANDLE_SZ);
ASSERT_NE(fh, NULL);
memset(fh, 0, sizeof(struct file_handle) + MAX_HANDLE_SZ);
fh->handle_bytes = MAX_HANDLE_SZ;
ASSERT_EQ(name_to_handle_at(self->child_pidfd2, "", fh, &mnt_id, AT_EMPTY_PATH), 0);
ASSERT_EQ(fstat(self->child_pidfd2, &st1), 0);
pidfd = open_by_handle_at(self->pidfd, fh, 0);
ASSERT_GE(pidfd, 0);
ASSERT_EQ(fstat(pidfd, &st2), 0);
ASSERT_TRUE(st1.st_dev == st2.st_dev && st1.st_ino == st2.st_ino);
ASSERT_EQ(close(pidfd), 0);
pidfd = open_by_handle_at(self->pidfd, fh, O_CLOEXEC);
ASSERT_GE(pidfd, 0);
ASSERT_EQ(fstat(pidfd, &st2), 0);
ASSERT_TRUE(st1.st_dev == st2.st_dev && st1.st_ino == st2.st_ino);
ASSERT_EQ(close(pidfd), 0);
pidfd = open_by_handle_at(self->pidfd, fh, O_NONBLOCK);
ASSERT_GE(pidfd, 0);
ASSERT_EQ(fstat(pidfd, &st2), 0);
ASSERT_TRUE(st1.st_dev == st2.st_dev && st1.st_ino == st2.st_ino);
ASSERT_EQ(close(pidfd), 0);
free(fh);
}
So you don't need to keep the fd open.
>
>
> >
> > >
> > > ---
> > >
> > > Applied to the vfs-6.15.pidfs branch of the vfs/vfs.git tree.
> > > Patches in the vfs-6.15.pidfs branch should appear in linux-next soon.
> > >
> > > Please report any outstanding bugs that were missed during review in a
> > > new review to the original patch series allowing us to drop it.
> > >
> > > It's encouraged to provide Acked-bys and Reviewed-bys even though the
> > > patch has now been applied. If possible patch trailers will be updated.
> > >
> > > Note that commit hashes shown below are subject to change due to rebase,
> > > trailer updates or similar. If in doubt, please check the listed branch.
> > >
> > > tree: https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
> > > branch: vfs-6.15.pidfs
> > >
> > > [1/6] pidfd: add PIDFD_SELF* sentinels to refer to own thread/process
> > > https://git.kernel.org/vfs/vfs/c/e6e4ed42f8d8
> > > [2/6] selftests/pidfd: add missing system header imcludes to pidfd tests
> > > https://git.kernel.org/vfs/vfs/c/c9f04f4a251d
> > > [3/6] tools: testing: separate out wait_for_pid() into helper header
> > > https://git.kernel.org/vfs/vfs/c/fb67fe44116e
> > > [4/6] selftests: pidfd: add pidfd.h UAPI wrapper
> > > https://git.kernel.org/vfs/vfs/c/ac331e56724d
> > > [5/6] selftests: pidfd: add tests for PIDFD_SELF_*
> > > https://git.kernel.org/vfs/vfs/c/881a3515c191
> > > [6/6] selftests/mm: use PIDFD_SELF in guard pages test
> > > https://git.kernel.org/vfs/vfs/c/b4703f056f42
^ permalink raw reply
* Re: [PATCH v7 2/6] selftests/pidfd: add missing system header imcludes to pidfd tests
From: Peter Seiderer @ 2025-02-05 12:06 UTC (permalink / raw)
To: Lorenzo Stoakes
Cc: Christian Brauner, Shuah Khan, Liam R . Howlett,
Suren Baghdasaryan, Vlastimil Babka, pedro.falcato,
linux-kselftest, linux-mm, linux-fsdevel, linux-api, linux-kernel,
Oliver Sang, John Hubbard, Tejun Heo, Johannes Weiner,
Michal Koutny, Andrew Morton, Shakeel Butt
In-Reply-To: <fab8843ea8664b5089f95ccfdcfd5bd7a5a6bb0b.1738268370.git.lorenzo.stoakes@oracle.com>
Hello *,
On Thu, 30 Jan 2025 20:40:27 +0000, Lorenzo Stoakes <lorenzo.stoakes@oracle.com> wrote:
> The pidfd_fdinfo_test.c and pidfd_setns_test.c tests appear to be missing
> fundamental system header imports required to execute correctly. Add these.
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> ---
> tools/testing/selftests/pidfd/pidfd_fdinfo_test.c | 1 +
> tools/testing/selftests/pidfd/pidfd_setns_test.c | 1 +
> 2 files changed, 2 insertions(+)
>
> diff --git a/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c b/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c
> index f062a986e382..f718aac75068 100644
> --- a/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c
> +++ b/tools/testing/selftests/pidfd/pidfd_fdinfo_test.c
> @@ -13,6 +13,7 @@
> #include <syscall.h>
> #include <sys/wait.h>
> #include <sys/mman.h>
> +#include <sys/mount.h>
>
> #include "pidfd.h"
> #include "../kselftest.h"
Predated patch already available, see
https://lore.kernel.org/linux-kselftest/20250115105211.390370-1-ps.report@gmx.net/
> diff --git a/tools/testing/selftests/pidfd/pidfd_setns_test.c b/tools/testing/selftests/pidfd/pidfd_setns_test.c
> index 222f8131283b..a55f6641e0b6 100644
> --- a/tools/testing/selftests/pidfd/pidfd_setns_test.c
> +++ b/tools/testing/selftests/pidfd/pidfd_setns_test.c
> @@ -14,6 +14,7 @@
> #include <sys/prctl.h>
> #include <sys/wait.h>
> #include <unistd.h>
> +#include <sys/ioctl.h>
> #include <sys/socket.h>
> #include <sys/stat.h>
> #include <linux/ioctl.h>
and predated patch available, see
https://lore.kernel.org/linux-kselftest/20250115105211.390370-2-ps.report@gmx.net/
Regards,
Peter
^ permalink raw reply
* [PATCH RFT v14 0/8] fork: Support shadow stacks in clone3()
From: Mark Brown @ 2025-02-06 11:38 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook, Kees Cook, Shuah Khan
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.
Please note that the x86 portions of this code are build tested only, I
don't appear to have a system that can run CET available to me.
[1] https://lore.kernel.org/linux-arm-kernel/20241001-arm64-gcs-v13-0-222b78d87eee@kernel.org/T/#mc58f97f27461749ccf400ebabf6f9f937116a86b
Signed-off-by: Mark Brown <broonie@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 | 62 +++++-
arch/x86/include/asm/shstk.h | 11 +-
arch/x86/kernel/process.c | 2 +-
arch/x86/kernel/shstk.c | 57 +++++-
include/asm-generic/cacheflush.h | 11 ++
include/linux/sched/task.h | 17 ++
include/uapi/linux/sched.h | 10 +-
kernel/fork.c | 96 +++++++--
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, 635 insertions(+), 81 deletions(-)
---
base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b
change-id: 20231019-clone3-shadow-stack-15d40d2bf536
Best regards,
--
Mark Brown <broonie@kernel.org>
^ permalink raw reply
* [PATCH RFT v14 1/8] arm64/gcs: Return a success value from gcs_alloc_thread_stack()
From: Mark Brown @ 2025-02-06 11:38 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook
In-Reply-To: <20250206-clone3-shadow-stack-v14-0-805b53af73b9@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 f50660603ecf5dc09a92740062df3a089b02b219..d8923b5f03b776252aca76ce316ef57399d71fa9 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 42faebb7b712328a8bebd25c47b01f09daae3861..45130ea7ea6e8090f09297a32fa71fe86e6532b9 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -297,7 +297,7 @@ 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;
@@ -305,9 +305,9 @@ static int copy_thread_gcs(struct task_struct *p,
p->thread.gcs_base = 0;
p->thread.gcs_size = 0;
- 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;
p->thread.gcs_el0_mode = current->thread.gcs_el0_mode;
p->thread.gcs_el0_locked = current->thread.gcs_el0_locked;
diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c
index 5c46ec527b1cdaa8f52cff445d70ba0f8509d086..1f633a482558b59aac5427963d42b37fce08c8a6 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 RFT v14 2/8] Documentation: userspace-api: Add shadow stack API documentation
From: Mark Brown @ 2025-02-06 11:38 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250206-clone3-shadow-stack-v14-0-805b53af73b9@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>
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 b1395d94b3fd0a7d43a3a9a9afa329d467675ae5..c491f332d289e6333675b6e41ab7d55b7e108829 100644
--- a/Documentation/userspace-api/index.rst
+++ b/Documentation/userspace-api/index.rst
@@ -60,6 +60,7 @@ 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 0000000000000000000000000000000000000000..65c665496624c7d9c33dbd8c714b8dc88c2032b3
--- /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 RFT v14 3/8] selftests: Provide helper header for shadow stack testing
From: Mark Brown @ 2025-02-06 11:38 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250206-clone3-shadow-stack-v14-0-805b53af73b9@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>
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 0000000000000000000000000000000000000000..fecf91218ea51edd30c220d4d94e5814e2d69c9e
--- /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 RFT v14 4/8] fork: Add shadow stack support to clone3()
From: Mark Brown @ 2025-02-06 11:38 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook
In-Reply-To: <20250206-clone3-shadow-stack-v14-0-805b53af73b9@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 the 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. 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.
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>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/mm/gcs.c | 54 +++++++++++++++++++++-
arch/x86/include/asm/shstk.h | 11 +++--
arch/x86/kernel/process.c | 2 +-
arch/x86/kernel/shstk.c | 57 +++++++++++++++++++++---
include/asm-generic/cacheflush.h | 11 +++++
include/linux/sched/task.h | 17 +++++++
include/uapi/linux/sched.h | 10 +++--
kernel/fork.c | 96 +++++++++++++++++++++++++++++++++++-----
8 files changed, 232 insertions(+), 26 deletions(-)
diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c
index 1f633a482558b59aac5427963d42b37fce08c8a6..10ee92390ea1702793bef471452352463e464d2d 100644
--- a/arch/arm64/mm/gcs.c
+++ b/arch/arm64/mm/gcs.c
@@ -43,8 +43,24 @@ 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_pointer)
+ 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_pointer) {
+ tsk->thread.gcs_base = 0;
+ tsk->thread.gcs_size = 0;
+ tsk->thread.gcspr_el0 = args->shadow_stack_pointer;
return 0;
+ }
if (!task_gcs_el0_enabled(tsk))
return 0;
@@ -68,6 +84,42 @@ 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;
+
+ /* Ensure that a token written as a result of a pivot is visible */
+ gcsb_dsync();
+
+ gcspr_el0 = args->shadow_stack_pointer;
+ if (!gcs_consume_token(vma, page, gcspr_el0))
+ return -EINVAL;
+
+ tsk->thread.gcspr_el0 = gcspr_el0 + sizeof(u64);
+
+ /* Ensure that our token consumption visible */
+ gcsb_dsync();
+
+ 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 4cb77e004615dff003426a2eb594460ca1015f4e..252feeda69991e939942c74556e23e27c835e766 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 6da6769d7254a46d87118ac016ede70d3f56f020..b56188ef5db27b5b5cf9fb4dfafce3746571a598 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -208,7 +208,7 @@ 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 059685612362d7b1865eabf400888fbfa0659c1e..056e2c9ec30531d0901297da07f1842b47d2fcd5 100644
--- a/arch/x86/kernel/shstk.c
+++ b/arch/x86/kernel/shstk.c
@@ -191,18 +191,65 @@ 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 = kmap_local_page(page);
+ int offset;
+ unsigned long addr, ssp;
+ u64 expected;
+
+ if (!features_enabled(ARCH_SHSTK_SHSTK))
+ return 0;
+
+ ssp = args->shadow_stack_pointer;
+ addr = ssp - SS_FRAME_SIZE;
+ expected = ssp | BIT(0);
+ offset = offset_in_page(addr);
+
+ if (!cmpxchg_to_user_page(vma, page, addr, (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_pointer)
+ 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_pointer) {
+ shstk->base = 0;
+ shstk->size = 0;
+ return args->shadow_stack_pointer;
+ }
/*
* For CLONE_VFORK the child will share the parents shadow stack.
@@ -222,7 +269,7 @@ 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 7ee8a179d1036e1d8010b8b18a8f3022e41c1695..96cc0c7a5c90fd7e899d0c5fe7c706302265efcf 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 0f2aeb37bbb047335a399326b31bc8df81b75a3a..cd36389619d5c97401f7b90e177c6027c232783b 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
@@ -43,6 +44,7 @@ struct kernel_clone_args {
void *fn_arg;
struct cgroup *cgrp;
struct css_set *cset;
+ unsigned long shadow_stack_pointer;
};
/*
@@ -236,4 +238,19 @@ 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 359a14cc76a4038aeacef14b2915d5ce60d0cf44..586a1c05a4e4ca05584d4d500223bcf6c3add54c 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -84,6 +84,8 @@
* 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_pointer: Value to use for shadow stack pointer in the
+ * child process.
*
* The structure is versioned by size and thus extensible.
* New struct members must go at the end of the struct and
@@ -101,12 +103,14 @@ struct clone_args {
__aligned_u64 set_tid;
__aligned_u64 set_tid_size;
__aligned_u64 cgroup;
+ __aligned_u64 shadow_stack_pointer;
};
#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 735405a9c5f323b16fdac3832320c255649b6e23..17eb698beaa7f0e3ff42887c5e44d848d91d4417 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2136,6 +2136,51 @@ static void rv_task_fork(struct task_struct *p)
#define rv_task_fork(p) do {} while (0)
#endif
+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_pointer)
+ return 0;
+
+ mm = get_task_mm(p);
+ if (!mm)
+ return -EFAULT;
+
+ mmap_read_lock(mm);
+
+ addr = untagged_addr_remote(mm, args->shadow_stack_pointer);
+ 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.
@@ -2410,6 +2455,9 @@ __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;
@@ -2973,7 +3021,9 @@ noinline static 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_pointer) !=
+ CLONE_ARGS_SIZE_VER3);
+ BUILD_BUG_ON(sizeof(struct clone_args) != CLONE_ARGS_SIZE_VER3);
if (unlikely(usize > PAGE_SIZE))
return -E2BIG;
@@ -3006,16 +3056,17 @@ noinline static 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_pointer = args.shadow_stack_pointer,
};
if (args.set_tid &&
@@ -3056,6 +3107,27 @@ 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_pointer)
+ return true;
+
+ if (!IS_ALIGNED(kargs->shadow_stack_pointer, sizeof(void *)))
+ return false;
+
+ /*
+ * The architecture must check support on the specific
+ * machine.
+ */
+ 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. */
@@ -3078,7 +3150,7 @@ 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 RFT v14 5/8] selftests/clone3: Remove redundant flushes of output streams
From: Mark Brown @ 2025-02-06 11:38 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250206-clone3-shadow-stack-v14-0-805b53af73b9@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>
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 3d2663fe50ba56f011629e4f2eb68a72bcceb087..39b5dcba663c30b9fc2542d9a0d2686105ce5761 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 RFT v14 6/8] selftests/clone3: Factor more of main loop into test_clone3()
From: Mark Brown @ 2025-02-06 11:38 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250206-clone3-shadow-stack-v14-0-805b53af73b9@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>
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 e61f07973ce5e27aff30047b35e03b1b51875c15..e066b201fa64eb17c55939b7cec18ac5d109613b 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 RFT v14 7/8] selftests/clone3: Allow tests to flag if -E2BIG is a valid error code
From: Mark Brown @ 2025-02-06 11:38 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook, Kees Cook, Shuah Khan
In-Reply-To: <20250206-clone3-shadow-stack-v14-0-805b53af73b9@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>
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 e066b201fa64eb17c55939b7cec18ac5d109613b..5b8b7d640e70132242fc6939450669acd0c534f9 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 RFT v14 8/8] selftests/clone3: Test shadow stack support
From: Mark Brown @ 2025-02-06 11:38 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,
Yury Khrustalev, Wilco Dijkstra, linux-kselftest, linux-api,
Mark Brown, Kees Cook, Shuah Khan
In-Reply-To: <20250206-clone3-shadow-stack-v14-0-805b53af73b9@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>
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 5b8b7d640e70132242fc6939450669acd0c534f9..b0378d7418cc8b00caebc6f92f58280bc04b0f80 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_pointer = (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_pointer = (unsigned long long)p;
+ break;
+ case CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY:
+ p = malloc(getpagesize());
+ p += getpagesize() - sizeof(void *);
+ args.shadow_stack_pointer = (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_pointer = (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 = -EINVAL,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK,
+ .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 39b5dcba663c30b9fc2542d9a0d2686105ce5761..24d40860fe2a3c2e66731a8b2afe94c5d2dff278 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_pointer;
+#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
* Re: [PATCH v3 2/2] selftests/seccomp: validate uretprobe syscall passes through seccomp
From: Kees Cook @ 2025-02-06 21:18 UTC (permalink / raw)
To: Eyal Birger
Cc: Jiri Olsa, luto, wad, oleg, mhiramat, andrii, alexei.starovoitov,
cyphar, songliubraving, yhs, john.fastabend, peterz, tglx, bp,
daniel, ast, andrii.nakryiko, rostedt, rafi, shmulik.ladkani, bpf,
linux-api, linux-trace-kernel, x86, linux-kernel
In-Reply-To: <CAHsH6GtpzR5_X4e0KphnyNSkKqBdgivfvyGQ1mbtA8fpnuu5sg@mail.gmail.com>
On Sun, Feb 02, 2025 at 01:13:28PM -0800, Eyal Birger wrote:
> On Sun, Feb 2, 2025 at 12:51 PM Jiri Olsa <olsajiri@gmail.com> wrote:
> >
> > On Sun, Feb 02, 2025 at 08:29:21AM -0800, Eyal Birger wrote:
> >
> > SNIP
> >
> > > +TEST_F(URETPROBE, uretprobe_default_block)
> > > +{
> > > + struct sock_filter filter[] = {
> > > + BPF_STMT(BPF_LD|BPF_W|BPF_ABS,
> > > + offsetof(struct seccomp_data, nr)),
> > > + BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_exit_group, 1, 0),
> > > + BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_KILL),
> > > + BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
> > > + };
> > > + struct sock_fprog prog = {
> > > + .len = (unsigned short)ARRAY_SIZE(filter),
> > > + .filter = filter,
> > > + };
> > > +
> > > + ASSERT_EQ(0, run_probed_with_filter(&prog));
> > > +}
> > > +
> > > +TEST_F(URETPROBE, uretprobe_block_uretprobe_syscall)
> > > +{
> > > + struct sock_filter filter[] = {
> > > + BPF_STMT(BPF_LD|BPF_W|BPF_ABS,
> > > + offsetof(struct seccomp_data, nr)),
> > > +#ifdef __NR_uretprobe
> > > + BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, __NR_uretprobe, 0, 1),
> > > +#endif
> >
> > does it make sense to run these tests on archs without __NR_uretprobe ?
>
> I considered ifdefing them out, but then thought that given it's not
> a lot of code it'd be better for the tests to be compiling and
> ready in case support is added on a new platform than to have to
> worry about that at that point.
The trouble I had is that on other archs, the tests fail. I've added
this, which retains build coverage, but doesn't trigger failures without
__NR_uretprobe:
diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index bee4f424c5c3..14ba51b52095 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -4973,6 +4973,10 @@ FIXTURE_SETUP(URETPROBE)
ssize_t offset;
int type, bit;
+#ifndef __NR_uretprobe
+ SKIP(return, "__NR_uretprobe syscall not defined");
+#endif
+
if (!variant->attach)
return;
--
Kees Cook
^ permalink raw reply related
* Re: [PATCH v3 1/2] seccomp: passthrough uretprobe systemcall without filtering
From: Kees Cook @ 2025-02-06 21:20 UTC (permalink / raw)
To: Eyal Birger
Cc: luto, wad, oleg, mhiramat, andrii, jolsa, alexei.starovoitov,
olsajiri, cyphar, songliubraving, yhs, john.fastabend, peterz,
tglx, bp, daniel, ast, andrii.nakryiko, rostedt, rafi,
shmulik.ladkani, bpf, linux-api, linux-trace-kernel, x86,
linux-kernel, stable
In-Reply-To: <20250202162921.335813-2-eyal.birger@gmail.com>
On Sun, Feb 02, 2025 at 08:29:20AM -0800, Eyal Birger wrote:
> When attaching uretprobes to processes running inside docker, the attached
> process is segfaulted when encountering the retprobe.
>
> The reason is that now that uretprobe is a system call the default seccomp
> filters in docker block it as they only allow a specific set of known
> syscalls. This is true for other userspace applications which use seccomp
> to control their syscall surface.
>
> Since uretprobe is a "kernel implementation detail" system call which is
> not used by userspace application code directly, it is impractical and
> there's very little point in forcing all userspace applications to
> explicitly allow it in order to avoid crashing tracked processes.
>
> Pass this systemcall through seccomp without depending on configuration.
>
> Note: uretprobe isn't supported in i386 and __NR_ia32_rt_tgsigqueueinfo
> uses the same number as __NR_uretprobe so the syscall isn't forced in the
> compat bitmap.
>
> Fixes: ff474a78cef5 ("uprobe: Add uretprobe syscall to speed up return probe")
> Reported-by: Rafael Buchbinder <rafi@rbk.io>
> Link: https://lore.kernel.org/lkml/CAHsH6Gs3Eh8DFU0wq58c_LF8A4_+o6z456J7BidmcVY2AqOnHQ@mail.gmail.com/
> Link: https://lore.kernel.org/lkml/20250121182939.33d05470@gandalf.local.home/T/#me2676c378eff2d6a33f3054fed4a5f3afa64e65b
> Link: https://lore.kernel.org/lkml/20250128145806.1849977-1-eyal.birger@gmail.com/
> Cc: stable@vger.kernel.org
> Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
> ---
> v3: no change - deferring 32bit compat handling as there aren't plans to
> support this syscall in compat mode.
> v2: use action_cache bitmap and mode1 array to check the syscall
> ---
> kernel/seccomp.c | 24 +++++++++++++++++++++---
> 1 file changed, 21 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index f59381c4a2ff..09b6f8e6db51 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -734,13 +734,13 @@ seccomp_prepare_user_filter(const char __user *user_filter)
>
> #ifdef SECCOMP_ARCH_NATIVE
> /**
> - * seccomp_is_const_allow - check if filter is constant allow with given data
> + * seccomp_is_filter_const_allow - check if filter is constant allow with given data
> * @fprog: The BPF programs
> * @sd: The seccomp data to check against, only syscall number and arch
> * number are considered constant.
> */
> -static bool seccomp_is_const_allow(struct sock_fprog_kern *fprog,
> - struct seccomp_data *sd)
> +static bool seccomp_is_filter_const_allow(struct sock_fprog_kern *fprog,
> + struct seccomp_data *sd)
> {
> unsigned int reg_value = 0;
> unsigned int pc;
> @@ -812,6 +812,21 @@ static bool seccomp_is_const_allow(struct sock_fprog_kern *fprog,
> return false;
> }
>
> +static bool seccomp_is_const_allow(struct sock_fprog_kern *fprog,
> + struct seccomp_data *sd)
> +{
> +#ifdef __NR_uretprobe
> + if (sd->nr == __NR_uretprobe
> +#ifdef SECCOMP_ARCH_COMPAT
> + && sd->arch != SECCOMP_ARCH_COMPAT
> +#endif
> + )
> + return true;
> +#endif
> +
> + return seccomp_is_filter_const_allow(fprog, sd);
> +}
> +
> static void seccomp_cache_prepare_bitmap(struct seccomp_filter *sfilter,
> void *bitmap, const void *bitmap_prev,
> size_t bitmap_size, int arch)
I minimized the above to:
@@ -749,6 +749,15 @@ static bool seccomp_is_const_allow(struct sock_fprog_kern *fprog,
if (WARN_ON_ONCE(!fprog))
return false;
+ /* Our single exception to filtering. */
+#ifdef __NR_uretprobe
+#ifdef SECCOMP_ARCH_COMPAT
+ if (sd->arch == SECCOMP_ARCH_NATIVE)
+#endif
+ if (sd->nr == __NR_uretprobe)
+ return true;
+#endif
+
for (pc = 0; pc < fprog->len; pc++) {
struct sock_filter *insn = &fprog->filter[pc];
u16 code = insn->code;
> @@ -1023,6 +1038,9 @@ static inline void seccomp_log(unsigned long syscall, long signr, u32 action,
> */
> static const int mode1_syscalls[] = {
> __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
> +#ifdef __NR_uretprobe
> + __NR_uretprobe,
> +#endif
> -1, /* negative terminated */
> };
>
> --
> 2.43.0
>
-Kees
--
Kees Cook
^ permalink raw reply
* Re: [PATCH v3 0/2] seccomp: pass uretprobe system call through seccomp
From: Kees Cook @ 2025-02-06 21:21 UTC (permalink / raw)
To: luto, wad, oleg, mhiramat, andrii, jolsa, Eyal Birger
Cc: Kees Cook, olsajiri, cyphar, songliubraving, yhs, john.fastabend,
peterz, tglx, bp, daniel, ast, andrii.nakryiko, rostedt, rafi,
shmulik.ladkani, bpf, linux-api, linux-trace-kernel, x86,
linux-kernel
In-Reply-To: <20250202162921.335813-1-eyal.birger@gmail.com>
On Sun, 02 Feb 2025 08:29:19 -0800, Eyal Birger wrote:
> uretprobe(2) is an performance enhancement system call added to improve
> uretprobes on x86_64.
>
> Confinement environments such as Docker are not aware of this new system
> call and kill confined processes when uretprobes are attached to them.
>
> Since uretprobe is a "kernel implementation detail" system call which is
> not used by userspace application code directly, pass this system call
> through seccomp without forcing existing userspace confinement environments
> to be changed.
>
> [...]
With the changes I mentioned in each patch, I've applied this to
for-next/seccomp, with the intention of getting them into v6.14-rc2.
Thanks!
[1/2] seccomp: passthrough uretprobe systemcall without filtering
https://git.kernel.org/kees/c/cf6cb56ef244
[2/2] selftests/seccomp: validate uretprobe syscall passes through seccomp
https://git.kernel.org/kees/c/c2debdb8544f
Take care,
--
Kees Cook
^ permalink raw reply
* Re: [PATCH RFT v14 2/8] Documentation: userspace-api: Add shadow stack API documentation
From: Deepak Gupta @ 2025-02-06 21:58 UTC (permalink / raw)
To: Mark Brown
Cc: Rick P. Edgecombe, 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, linux-kernel,
Catalin Marinas, Will Deacon, jannh, Yury Khrustalev,
Wilco Dijkstra, linux-kselftest, linux-api, Kees Cook, Shuah Khan
In-Reply-To: <20250206-clone3-shadow-stack-v14-2-805b53af73b9@kernel.org>
On Thu, Feb 06, 2025 at 11:38:04AM +0000, Mark Brown wrote:
>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>
>Signed-off-by: Mark Brown <broonie@kernel.org>
>---
Reviewed-by: Deepak Gupta <debug@rivosinc.com>
> Documentation/userspace-api/index.rst | 1 +
> Documentation/userspace-api/shadow_stack.rst | 44 ++++++++++++++++++++++++++++
> 2 files changed, 45 insertions(+)
^ permalink raw reply
* Re: [PATCH v3 0/2] seccomp: pass uretprobe system call through seccomp
From: Eyal Birger @ 2025-02-07 1:06 UTC (permalink / raw)
To: Kees Cook
Cc: luto, wad, oleg, mhiramat, andrii, jolsa, olsajiri, cyphar,
songliubraving, yhs, john.fastabend, peterz, tglx, bp, daniel,
ast, andrii.nakryiko, rostedt, rafi, shmulik.ladkani, bpf,
linux-api, linux-trace-kernel, x86, linux-kernel
In-Reply-To: <173887689139.3506371.3849387827240027734.b4-ty@kernel.org>
On Thu, Feb 6, 2025 at 1:22 PM Kees Cook <kees@kernel.org> wrote:
>
> On Sun, 02 Feb 2025 08:29:19 -0800, Eyal Birger wrote:
> > uretprobe(2) is an performance enhancement system call added to improve
> > uretprobes on x86_64.
> >
> > Confinement environments such as Docker are not aware of this new system
> > call and kill confined processes when uretprobes are attached to them.
> >
> > Since uretprobe is a "kernel implementation detail" system call which is
> > not used by userspace application code directly, pass this system call
> > through seccomp without forcing existing userspace confinement environments
> > to be changed.
> >
> > [...]
>
> With the changes I mentioned in each patch, I've applied this to
> for-next/seccomp, with the intention of getting them into v6.14-rc2.
>
> Thanks!
Thank you very much for your help.
Eyal.
^ permalink raw reply
* Re: [PATCH v3 0/2] seccomp: pass uretprobe system call through seccomp
From: Jiri Olsa @ 2025-02-07 13:24 UTC (permalink / raw)
To: Eyal Birger
Cc: Kees Cook, luto, wad, oleg, mhiramat, andrii, olsajiri, cyphar,
songliubraving, yhs, john.fastabend, peterz, tglx, bp, daniel,
ast, andrii.nakryiko, rostedt, rafi, shmulik.ladkani, bpf,
linux-api, linux-trace-kernel, x86, linux-kernel
In-Reply-To: <CAHsH6Gv7SLuy+v1hRzxH7sk-dVDRKA=iTyeabRBkoFuMGz7_YQ@mail.gmail.com>
On Thu, Feb 06, 2025 at 05:06:29PM -0800, Eyal Birger wrote:
> On Thu, Feb 6, 2025 at 1:22 PM Kees Cook <kees@kernel.org> wrote:
> >
> > On Sun, 02 Feb 2025 08:29:19 -0800, Eyal Birger wrote:
> > > uretprobe(2) is an performance enhancement system call added to improve
> > > uretprobes on x86_64.
> > >
> > > Confinement environments such as Docker are not aware of this new system
> > > call and kill confined processes when uretprobes are attached to them.
> > >
> > > Since uretprobe is a "kernel implementation detail" system call which is
> > > not used by userspace application code directly, pass this system call
> > > through seccomp without forcing existing userspace confinement environments
> > > to be changed.
> > >
> > > [...]
> >
> > With the changes I mentioned in each patch, I've applied this to
> > for-next/seccomp, with the intention of getting them into v6.14-rc2.
> >
> > Thanks!
>
> Thank you very much for your help.
great!
thanks,
jirka
^ permalink raw reply
* Re: [PATCH v3 0/2] seccomp: pass uretprobe system call through seccomp
From: Jann Horn @ 2025-02-07 15:27 UTC (permalink / raw)
To: Eyal Birger
Cc: kees, luto, wad, oleg, mhiramat, andrii, jolsa,
alexei.starovoitov, olsajiri, cyphar, songliubraving, yhs,
john.fastabend, peterz, tglx, bp, daniel, ast, andrii.nakryiko,
rostedt, rafi, shmulik.ladkani, bpf, linux-api,
linux-trace-kernel, x86, linux-kernel
In-Reply-To: <20250202162921.335813-1-eyal.birger@gmail.com>
On Sun, Feb 2, 2025 at 5:29 PM Eyal Birger <eyal.birger@gmail.com> wrote:
> uretprobe(2) is an performance enhancement system call added to improve
> uretprobes on x86_64.
>
> Confinement environments such as Docker are not aware of this new system
> call and kill confined processes when uretprobes are attached to them.
FYI, you might have similar issues with Syscall User Dispatch
(https://docs.kernel.org/admin-guide/syscall-user-dispatch.html) and
potentially also with ptrace-based sandboxes, depending on what kinda
processes you inject uprobes into. For Syscall User Dispatch, there is
already precedent for a bypass based on instruction pointer (see
syscall_user_dispatch()).
> Since uretprobe is a "kernel implementation detail" system call which is
> not used by userspace application code directly, pass this system call
> through seccomp without forcing existing userspace confinement environments
> to be changed.
This makes me feel kinda uncomfortable. The purpose of seccomp() is
that you can create a process that is as locked down as you want; you
can use it for some light limits on what a process can do (like in
Docker), or you can use it to make a process that has access to
essentially nothing except read(), write() and exit_group(). Even
stuff like restart_syscall() and rt_sigreturn() is not currently
excepted from that.
I guess your usecase is a little special in that you were already
calling from userspace into the kernel with SWBP before, which is also
not subject to seccomp; and the syscall is essentially an
arch-specific hack to make the SWBP a little faster.
If we do this, we should at least ensure that there is absolutely no
way for anything to happen in sys_uretprobe when no uretprobes are
configured for the process - the first check in the syscall
implementation almost does that, but the implementation could be a bit
stricter. It checks for "regs->ip != trampoline_check_ip()", but if no
uprobe region exists for the process, trampoline_check_ip() returns
`-1 + (uretprobe_syscall_check - uretprobe_trampoline_entry)`. So
there is a userspace instruction pointer near the bottom of the
address space that is allowed to call into the syscall if uretprobes
are not set up. Though the mmap minimum address restrictions will
typically prevent creating mappings there, and
uprobe_handle_trampoline() will SIGILL us if we get that far without a
valid uretprobe.
^ permalink raw reply
* Re: [PATCH v3 0/2] seccomp: pass uretprobe system call through seccomp
From: Eyal Birger @ 2025-02-07 16:20 UTC (permalink / raw)
To: Jann Horn, jolsa
Cc: kees, luto, wad, oleg, mhiramat, andrii, alexei.starovoitov,
olsajiri, cyphar, songliubraving, yhs, john.fastabend, peterz,
tglx, bp, daniel, ast, andrii.nakryiko, rostedt, rafi,
shmulik.ladkani, bpf, linux-api, linux-trace-kernel, x86,
linux-kernel
In-Reply-To: <CAG48ez1Pj6MT=RV-sogtNbw7WLLmCrC-3TkNfRjpcCif8iNGkA@mail.gmail.com>
Hi,
On Fri, Feb 7, 2025 at 7:27 AM Jann Horn <jannh@google.com> wrote:
>
> On Sun, Feb 2, 2025 at 5:29 PM Eyal Birger <eyal.birger@gmail.com> wrote:
> > uretprobe(2) is an performance enhancement system call added to improve
> > uretprobes on x86_64.
> >
> > Confinement environments such as Docker are not aware of this new system
> > call and kill confined processes when uretprobes are attached to them.
>
> FYI, you might have similar issues with Syscall User Dispatch
> (https://docs.kernel.org/admin-guide/syscall-user-dispatch.html) and
> potentially also with ptrace-based sandboxes, depending on what kinda
> processes you inject uprobes into. For Syscall User Dispatch, there is
> already precedent for a bypass based on instruction pointer (see
> syscall_user_dispatch()).
Thanks. This is interesting.
Do you know of confinement environments using this?
>
> > Since uretprobe is a "kernel implementation detail" system call which is
> > not used by userspace application code directly, pass this system call
> > through seccomp without forcing existing userspace confinement environments
> > to be changed.
>
> This makes me feel kinda uncomfortable. The purpose of seccomp() is
> that you can create a process that is as locked down as you want; you
> can use it for some light limits on what a process can do (like in
> Docker), or you can use it to make a process that has access to
> essentially nothing except read(), write() and exit_group(). Even
> stuff like restart_syscall() and rt_sigreturn() is not currently
> excepted from that.
Yes, this has been discussed at length in the threads mentioned
in the "Link" tags.
>
> I guess your usecase is a little special in that you were already
> calling from userspace into the kernel with SWBP before, which is also
> not subject to seccomp; and the syscall is essentially an
> arch-specific hack to make the SWBP a little faster.
Indeed. The uretprobe mechanism wasn't enforced by seccomp before
this syscall. This change preserves this.
>
> If we do this, we should at least ensure that there is absolutely no
> way for anything to happen in sys_uretprobe when no uretprobes are
> configured for the process - the first check in the syscall
> implementation almost does that, but the implementation could be a bit
> stricter. It checks for "regs->ip != trampoline_check_ip()", but if no
> uprobe region exists for the process, trampoline_check_ip() returns
> `-1 + (uretprobe_syscall_check - uretprobe_trampoline_entry)`. So
> there is a userspace instruction pointer near the bottom of the
> address space that is allowed to call into the syscall if uretprobes
> are not set up. Though the mmap minimum address restrictions will
> typically prevent creating mappings there, and
> uprobe_handle_trampoline() will SIGILL us if we get that far without a
> valid uretprobe.
I'm not sure I understand your point. If creating mappings in that
area is prevented, what is the issue? also, this would be related to the
uretprobe syscall implementation in general, no?
To me this seems unrelated to the seccomp change.
Jiri, do you have any input on this?
Thanks!
Eyal.
^ permalink raw reply
* Re: [PATCH v3 0/2] seccomp: pass uretprobe system call through seccomp
From: Jann Horn @ 2025-02-07 16:50 UTC (permalink / raw)
To: Eyal Birger
Cc: jolsa, kees, luto, wad, oleg, mhiramat, andrii,
alexei.starovoitov, olsajiri, cyphar, songliubraving, yhs,
john.fastabend, peterz, tglx, bp, daniel, ast, andrii.nakryiko,
rostedt, rafi, shmulik.ladkani, bpf, linux-api,
linux-trace-kernel, x86, linux-kernel
In-Reply-To: <CAHsH6GtiwCGJevfkE5=VzzuQcusKp-ugnRD+AD+5a+8kqOGyZA@mail.gmail.com>
On Fri, Feb 7, 2025 at 5:20 PM Eyal Birger <eyal.birger@gmail.com> wrote:
> On Fri, Feb 7, 2025 at 7:27 AM Jann Horn <jannh@google.com> wrote:
> >
> > On Sun, Feb 2, 2025 at 5:29 PM Eyal Birger <eyal.birger@gmail.com> wrote:
> > > uretprobe(2) is an performance enhancement system call added to improve
> > > uretprobes on x86_64.
> > >
> > > Confinement environments such as Docker are not aware of this new system
> > > call and kill confined processes when uretprobes are attached to them.
> >
> > FYI, you might have similar issues with Syscall User Dispatch
> > (https://docs.kernel.org/admin-guide/syscall-user-dispatch.html) and
> > potentially also with ptrace-based sandboxes, depending on what kinda
> > processes you inject uprobes into. For Syscall User Dispatch, there is
> > already precedent for a bypass based on instruction pointer (see
> > syscall_user_dispatch()).
>
> Thanks. This is interesting.
>
> Do you know of confinement environments using this?
Not for Syscall User Dispatch; I think that was mostly intended for
stuff like emulating Windows syscalls in WINE. I'm not sure who
actually uses it, I just know a bit about the kernel side of it.
From what I know, ptrace sandboxing is a technique used by some
configurations of gVisor
(https://gvisor.dev/docs/architecture_guide/platforms/#ptrace), though
now I see that that page says that this configuration is no longer
supported. I am also not sure whether you'd ever have uprobes
installed in files from which instructions are executed in this
environment.
> > > Since uretprobe is a "kernel implementation detail" system call which is
> > > not used by userspace application code directly, pass this system call
> > > through seccomp without forcing existing userspace confinement environments
> > > to be changed.
> >
> > This makes me feel kinda uncomfortable. The purpose of seccomp() is
> > that you can create a process that is as locked down as you want; you
> > can use it for some light limits on what a process can do (like in
> > Docker), or you can use it to make a process that has access to
> > essentially nothing except read(), write() and exit_group(). Even
> > stuff like restart_syscall() and rt_sigreturn() is not currently
> > excepted from that.
>
> Yes, this has been discussed at length in the threads mentioned
> in the "Link" tags.
>
> >
> > I guess your usecase is a little special in that you were already
> > calling from userspace into the kernel with SWBP before, which is also
> > not subject to seccomp; and the syscall is essentially an
> > arch-specific hack to make the SWBP a little faster.
>
> Indeed. The uretprobe mechanism wasn't enforced by seccomp before
> this syscall. This change preserves this.
>
> >
> > If we do this, we should at least ensure that there is absolutely no
> > way for anything to happen in sys_uretprobe when no uretprobes are
> > configured for the process - the first check in the syscall
> > implementation almost does that, but the implementation could be a bit
> > stricter. It checks for "regs->ip != trampoline_check_ip()", but if no
> > uprobe region exists for the process, trampoline_check_ip() returns
> > `-1 + (uretprobe_syscall_check - uretprobe_trampoline_entry)`. So
> > there is a userspace instruction pointer near the bottom of the
> > address space that is allowed to call into the syscall if uretprobes
> > are not set up. Though the mmap minimum address restrictions will
> > typically prevent creating mappings there, and
> > uprobe_handle_trampoline() will SIGILL us if we get that far without a
> > valid uretprobe.
>
> I'm not sure I understand your point. If creating mappings in that
> area is prevented, what is the issue?
It is usually prevented, not always - root can do it depending on
system configuration.
Also, in a syscall like this that will be reachable in every sandbox,
I think we should try to be more careful about edge cases and avoid
things like this offset calculation on address -1.
> also, this would be related to the
> uretprobe syscall implementation in general, no?
Yes. I just think it is relevant to the seccomp change because
excepting a syscall from seccomp makes it more important that that
syscall is robust and correct.
> To me this seems unrelated to the seccomp change.
> Jiri, do you have any input on this?
>
> Thanks!
> Eyal.
^ permalink raw reply
* Re: [PATCH v3 0/2] seccomp: pass uretprobe system call through seccomp
From: Jiri Olsa @ 2025-02-08 0:03 UTC (permalink / raw)
To: Jann Horn
Cc: Eyal Birger, kees, luto, wad, oleg, mhiramat, andrii,
alexei.starovoitov, olsajiri, cyphar, songliubraving, yhs,
john.fastabend, peterz, tglx, bp, daniel, ast, andrii.nakryiko,
rostedt, rafi, shmulik.ladkani, bpf, linux-api,
linux-trace-kernel, x86, linux-kernel
In-Reply-To: <CAG48ez1Pj6MT=RV-sogtNbw7WLLmCrC-3TkNfRjpcCif8iNGkA@mail.gmail.com>
On Fri, Feb 07, 2025 at 04:27:09PM +0100, Jann Horn wrote:
> On Sun, Feb 2, 2025 at 5:29 PM Eyal Birger <eyal.birger@gmail.com> wrote:
> > uretprobe(2) is an performance enhancement system call added to improve
> > uretprobes on x86_64.
> >
> > Confinement environments such as Docker are not aware of this new system
> > call and kill confined processes when uretprobes are attached to them.
>
> FYI, you might have similar issues with Syscall User Dispatch
> (https://docs.kernel.org/admin-guide/syscall-user-dispatch.html) and
> potentially also with ptrace-based sandboxes, depending on what kinda
> processes you inject uprobes into. For Syscall User Dispatch, there is
> already precedent for a bypass based on instruction pointer (see
> syscall_user_dispatch()).
>
> > Since uretprobe is a "kernel implementation detail" system call which is
> > not used by userspace application code directly, pass this system call
> > through seccomp without forcing existing userspace confinement environments
> > to be changed.
>
> This makes me feel kinda uncomfortable. The purpose of seccomp() is
> that you can create a process that is as locked down as you want; you
> can use it for some light limits on what a process can do (like in
> Docker), or you can use it to make a process that has access to
> essentially nothing except read(), write() and exit_group(). Even
> stuff like restart_syscall() and rt_sigreturn() is not currently
> excepted from that.
>
> I guess your usecase is a little special in that you were already
> calling from userspace into the kernel with SWBP before, which is also
> not subject to seccomp; and the syscall is essentially an
> arch-specific hack to make the SWBP a little faster.
>
> If we do this, we should at least ensure that there is absolutely no
> way for anything to happen in sys_uretprobe when no uretprobes are
> configured for the process - the first check in the syscall
> implementation almost does that, but the implementation could be a bit
> stricter. It checks for "regs->ip != trampoline_check_ip()", but if no
> uprobe region exists for the process, trampoline_check_ip() returns
> `-1 + (uretprobe_syscall_check - uretprobe_trampoline_entry)`. So
> there is a userspace instruction pointer near the bottom of the
> address space that is allowed to call into the syscall if uretprobes
> are not set up. Though the mmap minimum address restrictions will
> typically prevent creating mappings there, and
> uprobe_handle_trampoline() will SIGILL us if we get that far without a
> valid uretprobe.
nice catch, I think change below should fix that
thanks,
jirka
---
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 0c74a4d4df65..9b8837d8f06e 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -368,19 +368,21 @@ void *arch_uretprobe_trampoline(unsigned long *psize)
return &insn;
}
-static unsigned long trampoline_check_ip(void)
+static unsigned long trampoline_check_ip(unsigned long tramp)
{
- unsigned long tramp = uprobe_get_trampoline_vaddr();
-
return tramp + (uretprobe_syscall_check - uretprobe_trampoline_entry);
}
SYSCALL_DEFINE0(uretprobe)
{
struct pt_regs *regs = task_pt_regs(current);
- unsigned long err, ip, sp, r11_cx_ax[3];
+ unsigned long err, ip, sp, r11_cx_ax[3], tramp;
+
+ tramp = uprobe_get_trampoline_vaddr();
+ if (tramp == -1)
+ goto sigill;
- if (regs->ip != trampoline_check_ip())
+ if (regs->ip != trampoline_check_ip(tramp))
goto sigill;
err = copy_from_user(r11_cx_ax, (void __user *)regs->sp, sizeof(r11_cx_ax));
^ permalink raw reply related
* Re: [PATCH v3 0/2] seccomp: pass uretprobe system call through seccomp
From: Kees Cook @ 2025-02-08 20:35 UTC (permalink / raw)
To: Jiri Olsa
Cc: Jann Horn, Eyal Birger, luto, wad, oleg, mhiramat, andrii,
alexei.starovoitov, cyphar, songliubraving, yhs, john.fastabend,
peterz, tglx, bp, daniel, ast, andrii.nakryiko, rostedt, rafi,
shmulik.ladkani, bpf, linux-api, linux-trace-kernel, x86,
linux-kernel
In-Reply-To: <Z6afa2Z4IYlIAbJ2@krava>
On Sat, Feb 08, 2025 at 01:03:55AM +0100, Jiri Olsa wrote:
> On Fri, Feb 07, 2025 at 04:27:09PM +0100, Jann Horn wrote:
> > On Sun, Feb 2, 2025 at 5:29 PM Eyal Birger <eyal.birger@gmail.com> wrote:
> > > uretprobe(2) is an performance enhancement system call added to improve
> > > uretprobes on x86_64.
> > >
> > > Confinement environments such as Docker are not aware of this new system
> > > call and kill confined processes when uretprobes are attached to them.
> >
> > FYI, you might have similar issues with Syscall User Dispatch
> > (https://docs.kernel.org/admin-guide/syscall-user-dispatch.html) and
> > potentially also with ptrace-based sandboxes, depending on what kinda
> > processes you inject uprobes into. For Syscall User Dispatch, there is
> > already precedent for a bypass based on instruction pointer (see
> > syscall_user_dispatch()).
> >
> > > Since uretprobe is a "kernel implementation detail" system call which is
> > > not used by userspace application code directly, pass this system call
> > > through seccomp without forcing existing userspace confinement environments
> > > to be changed.
> >
> > This makes me feel kinda uncomfortable. The purpose of seccomp() is
> > that you can create a process that is as locked down as you want; you
> > can use it for some light limits on what a process can do (like in
> > Docker), or you can use it to make a process that has access to
> > essentially nothing except read(), write() and exit_group(). Even
> > stuff like restart_syscall() and rt_sigreturn() is not currently
> > excepted from that.
> >
> > I guess your usecase is a little special in that you were already
> > calling from userspace into the kernel with SWBP before, which is also
> > not subject to seccomp; and the syscall is essentially an
> > arch-specific hack to make the SWBP a little faster.
> >
> > If we do this, we should at least ensure that there is absolutely no
> > way for anything to happen in sys_uretprobe when no uretprobes are
> > configured for the process - the first check in the syscall
> > implementation almost does that, but the implementation could be a bit
> > stricter. It checks for "regs->ip != trampoline_check_ip()", but if no
> > uprobe region exists for the process, trampoline_check_ip() returns
> > `-1 + (uretprobe_syscall_check - uretprobe_trampoline_entry)`. So
> > there is a userspace instruction pointer near the bottom of the
> > address space that is allowed to call into the syscall if uretprobes
> > are not set up. Though the mmap minimum address restrictions will
> > typically prevent creating mappings there, and
> > uprobe_handle_trampoline() will SIGILL us if we get that far without a
> > valid uretprobe.
>
> nice catch, I think change below should fix that
Thanks! Please backport this to -stable too. :)
-Kees
>
> thanks,
> jirka
>
>
> ---
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index 0c74a4d4df65..9b8837d8f06e 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -368,19 +368,21 @@ void *arch_uretprobe_trampoline(unsigned long *psize)
> return &insn;
> }
>
> -static unsigned long trampoline_check_ip(void)
> +static unsigned long trampoline_check_ip(unsigned long tramp)
> {
> - unsigned long tramp = uprobe_get_trampoline_vaddr();
> -
> return tramp + (uretprobe_syscall_check - uretprobe_trampoline_entry);
> }
>
> SYSCALL_DEFINE0(uretprobe)
> {
> struct pt_regs *regs = task_pt_regs(current);
> - unsigned long err, ip, sp, r11_cx_ax[3];
> + unsigned long err, ip, sp, r11_cx_ax[3], tramp;
> +
> + tramp = uprobe_get_trampoline_vaddr();
> + if (tramp == -1)
> + goto sigill;
>
> - if (regs->ip != trampoline_check_ip())
> + if (regs->ip != trampoline_check_ip(tramp))
> goto sigill;
>
> err = copy_from_user(r11_cx_ax, (void __user *)regs->sp, sizeof(r11_cx_ax));
--
Kees Cook
^ permalink raw reply
* Re: The business loan-
From: David Song @ 2025-02-08 22:01 UTC (permalink / raw)
To: linux-api
Hello,
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Email: dsong@aa4financialservice.com
^ permalink raw reply
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