* Re: Extending clone_args for clone3()
From: Arnd Bergmann @ 2025-06-04 8:29 UTC (permalink / raw)
To: Yury Khrustalev, linux-kernel
Cc: Christian Brauner, Mark Brown, Mark Rutland, linux-api
In-Reply-To: <aCs65ccRQtJBnZ_5@arm.com>
On Mon, May 19, 2025, at 16:06, Yury Khrustalev wrote:
>
> This seems fragile and may call for writing cumbersome code. In essence,
> we will have to have clone30(), clone31(), clone32()... wrappers which
> probably defeats the point of why clone3 was added:
>
>
> if (clone32_supported && clone32(...) == -1 && errno == E2BIG)
> {
> clone32_supported = false;
> /* ... */
> }
> else if (clone31_supported && clone31(...) == -1 && errno == E2BIG)
> {
> clone12_supported = false;
> /* ... */
> }
> ...
>
> Is there a neat way to work around this? What was the idea for extending
> clone_args in practice?
>
> I suppose we can't rely on kernel version because support for extended
> clone_args can be backported. In any case, we'd have to do a syscall
> for this (it would probably be great to have kernel version in auxv).
I don't think there is a generic way to handle extended syscalls
from libc, it really depends on the specific feature it's trying
to use that requires the additional fields to be nonzero: some features
may have a reasonable fallback implementation in libc, other features
still require an error to be passed back to the caller.
As I understand the shadow stack feature, we want this to be enabled
whenever the kernel and hardware supports it, completely transparent
to an application, right?
I think ideally we'd check for HWCAP_GCS on arm64 or the equivalent
feature on other architectures and expect clone3 to support the
longer argument whenever that is set, but it looks like that would
break on current kernels that already support HWCAP_GCS but not
the clone3 argument.
Adding one more hwcap flag would be ugly, but that seems to be
the easiest way. That way, glibc can just test for the new hwcap
flag only use the extra clone3 word if all prerequisites (hardware
support, kernel gcs support, clone3 argument support) are there.
Arnd
^ permalink raw reply
* Re: Extending clone_args for clone3()
From: Mark Brown @ 2025-06-04 11:05 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Yury Khrustalev, linux-kernel, Christian Brauner, Mark Rutland,
linux-api
In-Reply-To: <71c9bd77-85fd-4f00-a36a-8621640ebbb5@app.fastmail.com>
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On Wed, Jun 04, 2025 at 10:29:48AM +0200, Arnd Bergmann wrote:
> As I understand the shadow stack feature, we want this to be enabled
> whenever the kernel and hardware supports it, completely transparent
> to an application, right?
Slightly more involved, but roughly. The application and all libraries
linked into it should be built targeting shadow stacks (most binaries
will already be compatible but it's possible they wouldn't be so we
can't just asssume that) then if everything is compatible shadow stacks
will be enabled transparently by libc if the system supports them.
> I think ideally we'd check for HWCAP_GCS on arm64 or the equivalent
> feature on other architectures and expect clone3 to support the
> longer argument whenever that is set, but it looks like that would
> break on current kernels that already support HWCAP_GCS but not
> the clone3 argument.
> Adding one more hwcap flag would be ugly, but that seems to be
> the easiest way. That way, glibc can just test for the new hwcap
> flag only use the extra clone3 word if all prerequisites (hardware
> support, kernel gcs support, clone3 argument support) are there.
We'd also have to add something similar for x86 since that's had the
support even longer, and the RISC-V series looks like it's getting near
to being merged too so we'll likely have the same problem there given
that the clone3() series is not progressing super fast.
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^ permalink raw reply
* Re: [DISCUSSION] proposed mctl() API
From: Johannes Weiner @ 2025-06-04 12:00 UTC (permalink / raw)
To: Barry Song
Cc: Matthew Wilcox, Lorenzo Stoakes, Andrew Morton, Shakeel Butt,
Liam R . Howlett, David Hildenbrand, Vlastimil Babka, Jann Horn,
Arnd Bergmann, Christian Brauner, SeongJae Park, Usama Arif,
Mike Rapoport, linux-mm, linux-arch, linux-kernel, linux-api,
Pedro Falcato
In-Reply-To: <CAGsJ_4yKDqUu8yZjHSmWBz3CpQhU6DM0=EhibfTwHbTo+QWvZA@mail.gmail.com>
On Fri, May 30, 2025 at 07:52:28PM +1200, Barry Song wrote:
> On Fri, May 30, 2025 at 9:14 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
> >
> > On Thu, May 29, 2025 at 04:28:46PM +0100, Matthew Wilcox wrote:
> > > Barry's problem is that we're all nervous about possibly regressing
> > > performance on some unknown workloads. Just try Barry's proposal, see
> > > if anyone actually compains or if we're just afraid of our own shadows.
> >
> > I actually explained why I think this is a terrible idea. But okay, I
> > tried the patch anyway.
> >
> > This is 'git log' on a hot kernel repo after a large IO stream:
> >
> > VANILLA BARRY
> > Real time 49.93 ( +0.00%) 60.36 ( +20.48%)
> > User time 32.10 ( +0.00%) 32.09 ( -0.04%)
> > System time 14.41 ( +0.00%) 14.64 ( +1.50%)
> > pgmajfault 9227.00 ( +0.00%) 18390.00 ( +99.30%)
> > workingset_refault_file 184.00 ( +0.00%) 236899.00 (+127954.05%)
> >
> > Clearly we can't generally ignore page cache hits just because the
> > mmaps() are intermittent.
>
> Hi Johannes,
> Thanks!
>
> Are you on v1, which lacks folio demotion[1], or v2, which includes it [2]?
>
> [1] https://lore.kernel.org/linux-mm/20250412085852.48524-1-21cnbao@gmail.com/
> [2] https://lore.kernel.org/linux-mm/20250514070820.51793-1-21cnbao@gmail.com/
The subthread is about whether the reference dismissal / demotion
should be unconditional (v1) or opt-in (v2).
I'm arguing for v2.
^ permalink raw reply
* Re: [DISCUSSION] proposed mctl() API
From: David Hildenbrand @ 2025-06-04 12:05 UTC (permalink / raw)
To: Johannes Weiner, Barry Song
Cc: Matthew Wilcox, Lorenzo Stoakes, Andrew Morton, Shakeel Butt,
Liam R . Howlett, Vlastimil Babka, Jann Horn, Arnd Bergmann,
Christian Brauner, SeongJae Park, Usama Arif, Mike Rapoport,
linux-mm, linux-arch, linux-kernel, linux-api, Pedro Falcato
In-Reply-To: <20250604120013.GA1431@cmpxchg.org>
On 04.06.25 14:00, Johannes Weiner wrote:
> On Fri, May 30, 2025 at 07:52:28PM +1200, Barry Song wrote:
>> On Fri, May 30, 2025 at 9:14 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
>>>
>>> On Thu, May 29, 2025 at 04:28:46PM +0100, Matthew Wilcox wrote:
>>>> Barry's problem is that we're all nervous about possibly regressing
>>>> performance on some unknown workloads. Just try Barry's proposal, see
>>>> if anyone actually compains or if we're just afraid of our own shadows.
>>>
>>> I actually explained why I think this is a terrible idea. But okay, I
>>> tried the patch anyway.
>>>
>>> This is 'git log' on a hot kernel repo after a large IO stream:
>>>
>>> VANILLA BARRY
>>> Real time 49.93 ( +0.00%) 60.36 ( +20.48%)
>>> User time 32.10 ( +0.00%) 32.09 ( -0.04%)
>>> System time 14.41 ( +0.00%) 14.64 ( +1.50%)
>>> pgmajfault 9227.00 ( +0.00%) 18390.00 ( +99.30%)
>>> workingset_refault_file 184.00 ( +0.00%) 236899.00 (+127954.05%)
>>>
>>> Clearly we can't generally ignore page cache hits just because the
>>> mmaps() are intermittent.
>>
>> Hi Johannes,
>> Thanks!
>>
>> Are you on v1, which lacks folio demotion[1], or v2, which includes it [2]?
>>
>> [1] https://lore.kernel.org/linux-mm/20250412085852.48524-1-21cnbao@gmail.com/
>> [2] https://lore.kernel.org/linux-mm/20250514070820.51793-1-21cnbao@gmail.com/
>
> The subthread is about whether the reference dismissal / demotion
> should be unconditional (v1) or opt-in (v2).
>
> I'm arguing for v2.
+1
--
Cheers,
David / dhildenb
^ permalink raw reply
* Re: [DISCUSSION] proposed mctl() API
From: Johannes Weiner @ 2025-06-04 12:19 UTC (permalink / raw)
To: Vlastimil Babka
Cc: Matthew Wilcox, Lorenzo Stoakes, Andrew Morton, Shakeel Butt,
Liam R . Howlett, David Hildenbrand, Jann Horn, Arnd Bergmann,
Christian Brauner, SeongJae Park, Usama Arif, Mike Rapoport,
Barry Song, linux-mm, linux-arch, linux-kernel, linux-api,
Pedro Falcato, tj
In-Reply-To: <0aeb6d8b-2abb-43a7-b47d-448f37f8a3bf@suse.cz>
On Fri, May 30, 2025 at 12:31:35PM +0200, Vlastimil Babka wrote:
> On 5/29/25 23:14, Johannes Weiner wrote:
> > On Thu, May 29, 2025 at 04:28:46PM +0100, Matthew Wilcox wrote:
> >> Barry's problem is that we're all nervous about possibly regressing
> >> performance on some unknown workloads. Just try Barry's proposal, see
> >> if anyone actually compains or if we're just afraid of our own shadows.
> >
> > I actually explained why I think this is a terrible idea. But okay, I
> > tried the patch anyway.
> >
> > This is 'git log' on a hot kernel repo after a large IO stream:
> >
> > VANILLA BARRY
> > Real time 49.93 ( +0.00%) 60.36 ( +20.48%)
> > User time 32.10 ( +0.00%) 32.09 ( -0.04%)
> > System time 14.41 ( +0.00%) 14.64 ( +1.50%)
> > pgmajfault 9227.00 ( +0.00%) 18390.00 ( +99.30%)
> > workingset_refault_file 184.00 ( +0.00%) 236899.00 (+127954.05%)
> >
> > Clearly we can't generally ignore page cache hits just because the
> > mmaps() are intermittent.
> >
> > The whole point is to cache across processes and their various
> > apertures into a common, long-lived filesystem space.
> >
> > Barry knows something about the relationship between certain processes
> > and certain files that he could exploit with MADV_COLD-on-exit
> > semantics. But that's not something the kernel can safely assume. Not
> > without defeating the page cache for an entire class of file accesses.
>
> I've just read the previous threads about Barry's proposal and if doing this
> always isn't feasible, I'm wondering if memcg would be a better interface to
> opt-in for this kind of behavior than both prctl or mctl. I think at least
> conceptually it fits what memcg is doing? The question is if the
> implementation would be feasible, and if android puts apps in separate memcgs...
CCing Tejun.
Cgroups has been trying to resist flag settings like these. The cgroup
tree is a nested hierarchical structure designed for dividing up
system resources. But flag properties don't have natural inheritance
rules. What does it mean if the parent group says one thing and the
child says another? Which one has precedence?
Hence the proposal to make it a per-process property that propagates
through fork() and exec(). This also enables the container usecase (by
setting the flag in the container launching process), without there
being any confusion what the *effective* setting for any given process
in the system is.
^ permalink raw reply
* Re: [DISCUSSION] proposed mctl() API
From: Lorenzo Stoakes @ 2025-06-04 12:28 UTC (permalink / raw)
To: Matthew Wilcox
Cc: Andrew Morton, Shakeel Butt, Liam R . Howlett, David Hildenbrand,
Vlastimil Babka, Jann Horn, Arnd Bergmann, Christian Brauner,
SeongJae Park, Usama Arif, Mike Rapoport, Johannes Weiner,
Barry Song, linux-mm, linux-arch, linux-kernel, linux-api,
Pedro Falcato
In-Reply-To: <aDh9LtSLCiTLjg2X@casper.infradead.org>
On Thu, May 29, 2025 at 04:28:46PM +0100, Matthew Wilcox wrote:
> On Thu, May 29, 2025 at 03:43:26PM +0100, Lorenzo Stoakes wrote:
> > After discussions in various threads (Usama's series adding a new prctl()
> > in [0], and a proposal to adapt process_madvise() to do the same -
> > conception in [1] and RFC in [2]), it seems fairly clear that it would make
> > sense to explore a dedicated API to explicitly allow for actions which
> > affect the virtual address space as a whole.
> >
> > Also, Barry is implementing a feature (currently under RFC) which could
> > additionally make use of this API (see [3]).
>
> I think the reason that you're having trouble coming up with a good
> place to put these ideas is because they are all bad ideas. Do none of
> them. Problem solved.
>
> People should put more effort into allocating THPs automatically and
> monitoring where they're helping performance and where they're hurting
> performance, instead of coming up with these baroque reasons to blame
> the sysadmin for not having tweaked some magic knob.
>
> Barry's problem is that we're all nervous about possibly regressing
> performance on some unknown workloads. Just try Barry's proposal, see
> if anyone actually compains or if we're just afraid of our own shadows.
>
So from my perspective - I very much agree with the concept of doing nothing
here, ideally :)
But I feel we need to look at this problem from both the short term and the
long term - in the long run I absolutely agree with what you say.
In the short term this proposal is broadly 'what is the least worst means
of establishing policy like this?'.
I think there is broad agreement that prctl() is sub-optimal, so an
mm-specific API makes sense.
So it comes down to a question of - how badly do we need to be able to do
this _now_?
^ permalink raw reply
* Re: [DISCUSSION] proposed mctl() API
From: Johannes Weiner @ 2025-06-04 13:21 UTC (permalink / raw)
To: Matthew Wilcox
Cc: Lorenzo Stoakes, Andrew Morton, Shakeel Butt, Liam R . Howlett,
David Hildenbrand, Vlastimil Babka, Jann Horn, Arnd Bergmann,
Christian Brauner, SeongJae Park, Usama Arif, Mike Rapoport,
Barry Song, linux-mm, linux-arch, linux-kernel, linux-api,
Pedro Falcato
In-Reply-To: <aD3nFMS9kWHp7a4F@casper.infradead.org>
On Mon, Jun 02, 2025 at 07:01:56PM +0100, Matthew Wilcox wrote:
> On Thu, May 29, 2025 at 05:14:23PM -0400, Johannes Weiner wrote:
> > On Thu, May 29, 2025 at 04:28:46PM +0100, Matthew Wilcox wrote:
> > > Barry's problem is that we're all nervous about possibly regressing
> > > performance on some unknown workloads. Just try Barry's proposal, see
> > > if anyone actually compains or if we're just afraid of our own shadows.
> >
> > I actually explained why I think this is a terrible idea. But okay, I
> > tried the patch anyway.
>
> Sorry, I must've missed that one ;-(
Apologies for my tone. The discussion is spread out over too many
threads...
> > This is 'git log' on a hot kernel repo after a large IO stream:
> >
> > VANILLA BARRY
> > Real time 49.93 ( +0.00%) 60.36 ( +20.48%)
> > User time 32.10 ( +0.00%) 32.09 ( -0.04%)
> > System time 14.41 ( +0.00%) 14.64 ( +1.50%)
> > pgmajfault 9227.00 ( +0.00%) 18390.00 ( +99.30%)
> > workingset_refault_file 184.00 ( +0.00%) 236899.00 (+127954.05%)
> >
> > Clearly we can't generally ignore page cache hits just because the
> > mmaps() are intermittent.
> >
> > The whole point is to cache across processes and their various
> > apertures into a common, long-lived filesystem space.
> >
> > Barry knows something about the relationship between certain processes
> > and certain files that he could exploit with MADV_COLD-on-exit
> > semantics. But that's not something the kernel can safely assume. Not
> > without defeating the page cache for an entire class of file accesses.
>
> So what about distinguishing between exited-normally processes (ie git
> log) vs killed-by-oom processes (ie Barry's usecase)? Update the
> referenced bit in the first case and not the second?
In cloud environments, it's common to restart a workload immediately
after an OOM kill.
The hosts tend to handle a fairly dynamic mix of batch jobs and
semi-predictable user request load, all while also trying to target
decent average host utilization. Adapting to external load peaks is
laggy (spawning new workers, rebalancing).
In such setups, OOM conditions are generally assumed to be highly
transient. And quick restarts are important to avoid cascading
failures in the worker pool during load peaks.
So I don't think OOM is a good universal signal that the workload is
gone and the memory is cold.
^ permalink raw reply
* Re: [DISCUSSION] proposed mctl() API
From: Johannes Weiner @ 2025-06-05 12:31 UTC (permalink / raw)
To: Vlastimil Babka
Cc: Matthew Wilcox, Lorenzo Stoakes, Andrew Morton, Shakeel Butt,
Liam R . Howlett, David Hildenbrand, Jann Horn, Arnd Bergmann,
Christian Brauner, SeongJae Park, Usama Arif, Mike Rapoport,
Barry Song, linux-mm, linux-arch, linux-kernel, linux-api,
Pedro Falcato, Tejun Heo
In-Reply-To: <20250604121923.GB1431@cmpxchg.org>
CCing Tejun - with the right mutt alias this time.
On Wed, Jun 04, 2025 at 08:19:28AM -0400, Johannes Weiner wrote:
> On Fri, May 30, 2025 at 12:31:35PM +0200, Vlastimil Babka wrote:
> > On 5/29/25 23:14, Johannes Weiner wrote:
> > > On Thu, May 29, 2025 at 04:28:46PM +0100, Matthew Wilcox wrote:
> > >> Barry's problem is that we're all nervous about possibly regressing
> > >> performance on some unknown workloads. Just try Barry's proposal, see
> > >> if anyone actually compains or if we're just afraid of our own shadows.
> > >
> > > I actually explained why I think this is a terrible idea. But okay, I
> > > tried the patch anyway.
> > >
> > > This is 'git log' on a hot kernel repo after a large IO stream:
> > >
> > > VANILLA BARRY
> > > Real time 49.93 ( +0.00%) 60.36 ( +20.48%)
> > > User time 32.10 ( +0.00%) 32.09 ( -0.04%)
> > > System time 14.41 ( +0.00%) 14.64 ( +1.50%)
> > > pgmajfault 9227.00 ( +0.00%) 18390.00 ( +99.30%)
> > > workingset_refault_file 184.00 ( +0.00%) 236899.00 (+127954.05%)
> > >
> > > Clearly we can't generally ignore page cache hits just because the
> > > mmaps() are intermittent.
> > >
> > > The whole point is to cache across processes and their various
> > > apertures into a common, long-lived filesystem space.
> > >
> > > Barry knows something about the relationship between certain processes
> > > and certain files that he could exploit with MADV_COLD-on-exit
> > > semantics. But that's not something the kernel can safely assume. Not
> > > without defeating the page cache for an entire class of file accesses.
> >
> > I've just read the previous threads about Barry's proposal and if doing this
> > always isn't feasible, I'm wondering if memcg would be a better interface to
> > opt-in for this kind of behavior than both prctl or mctl. I think at least
> > conceptually it fits what memcg is doing? The question is if the
> > implementation would be feasible, and if android puts apps in separate memcgs...
>
> CCing Tejun.
>
> Cgroups has been trying to resist flag settings like these. The cgroup
> tree is a nested hierarchical structure designed for dividing up
> system resources. But flag properties don't have natural inheritance
> rules. What does it mean if the parent group says one thing and the
> child says another? Which one has precedence?
>
> Hence the proposal to make it a per-process property that propagates
> through fork() and exec(). This also enables the container usecase (by
> setting the flag in the container launching process), without there
> being any confusion what the *effective* setting for any given process
> in the system is.
^ permalink raw reply
* [PATCH RFT v17 0/8] fork: Support shadow stacks in clone3()
From: Mark Brown @ 2025-06-09 12:54 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.
Yuri Khrustalev has raised questions from the libc side regarding
discoverability of extended clone3() structure sizes[2], this seems like
a general issue with clone3(). There was a suggestion to add a hwcap on
arm64 which isn't ideal but is doable there, though architecture
specific mechanisms would also be needed for x86 (and RISC-V if it's
support gets merged before this does).
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
[2] https://lore.kernel.org/r/aCs65ccRQtJBnZ_5@arm.com
Signed-off-by: Mark Brown <broonie@kernel.org>
---
Changes in v17:
- Rebase onto v6.16-rc1.
- Link to v16: https://lore.kernel.org/r/20250416-clone3-shadow-stack-v16-0-2ffc9ca3917b@kernel.org
Changes in v16:
- Rebase onto v6.15-rc2.
- Roll in fixes from x86 testing from Rick Edgecombe.
- Rework so that the argument is shadow_stack_token.
- Link to v15: https://lore.kernel.org/r/20250408-clone3-shadow-stack-v15-0-3fa245c6e3be@kernel.org
Changes in v15:
- Rebase onto v6.15-rc1.
- Link to v14: https://lore.kernel.org/r/20250206-clone3-shadow-stack-v14-0-805b53af73b9@kernel.org
Changes in v14:
- Rebase onto v6.14-rc1.
- Link to v13: https://lore.kernel.org/r/20241203-clone3-shadow-stack-v13-0-93b89a81a5ed@kernel.org
Changes in v13:
- Rebase onto v6.13-rc1.
- Link to v12: https://lore.kernel.org/r/20241031-clone3-shadow-stack-v12-0-7183eb8bee17@kernel.org
Changes in v12:
- Add the regular prctl() to the userspace API document since arm64
support is queued in -next.
- Link to v11: https://lore.kernel.org/r/20241005-clone3-shadow-stack-v11-0-2a6a2bd6d651@kernel.org
Changes in v11:
- Rebase onto arm64 for-next/gcs, which is based on v6.12-rc1, and
integrate arm64 support.
- Rework the interface to specify a shadow stack pointer rather than a
base and size like we do for the regular stack.
- Link to v10: https://lore.kernel.org/r/20240821-clone3-shadow-stack-v10-0-06e8797b9445@kernel.org
Changes in v10:
- Integrate fixes & improvements for the x86 implementation from Rick
Edgecombe.
- Require that the shadow stack be VM_WRITE.
- Require that the shadow stack base and size be sizeof(void *) aligned.
- Clean up trailing newline.
- Link to v9: https://lore.kernel.org/r/20240819-clone3-shadow-stack-v9-0-962d74f99464@kernel.org
Changes in v9:
- Pull token validation earlier and report problems with an error return
to parent rather than signal delivery to the child.
- Verify that the top of the supplied shadow stack is VM_SHADOW_STACK.
- Rework token validation to only do the page mapping once.
- Drop no longer needed support for testing for signals in selftest.
- Fix typo in comments.
- Link to v8: https://lore.kernel.org/r/20240808-clone3-shadow-stack-v8-0-0acf37caf14c@kernel.org
Changes in v8:
- Fix token verification with user specified shadow stack.
- Don't track user managed shadow stacks for child processes.
- Link to v7: https://lore.kernel.org/r/20240731-clone3-shadow-stack-v7-0-a9532eebfb1d@kernel.org
Changes in v7:
- Rebase onto v6.11-rc1.
- Typo fixes.
- Link to v6: https://lore.kernel.org/r/20240623-clone3-shadow-stack-v6-0-9ee7783b1fb9@kernel.org
Changes in v6:
- Rebase onto v6.10-rc3.
- Ensure we don't try to free the parent shadow stack in error paths of
x86 arch code.
- Spelling fixes in userspace API document.
- Additional cleanups and improvements to the clone3() tests to support
the shadow stack tests.
- Link to v5: https://lore.kernel.org/r/20240203-clone3-shadow-stack-v5-0-322c69598e4b@kernel.org
Changes in v5:
- Rebase onto v6.8-rc2.
- Rework ABI to have the user allocate the shadow stack memory with
map_shadow_stack() and a token.
- Force inlining of the x86 shadow stack enablement.
- Move shadow stack enablement out into a shared header for reuse by
other tests.
- Link to v4: https://lore.kernel.org/r/20231128-clone3-shadow-stack-v4-0-8b28ffe4f676@kernel.org
Changes in v4:
- Formatting changes.
- Use a define for minimum shadow stack size and move some basic
validation to fork.c.
- Link to v3: https://lore.kernel.org/r/20231120-clone3-shadow-stack-v3-0-a7b8ed3e2acc@kernel.org
Changes in v3:
- Rebase onto v6.7-rc2.
- Remove stale shadow_stack in internal kargs.
- If a shadow stack is specified unconditionally use it regardless of
CLONE_ parameters.
- Force enable shadow stacks in the selftest.
- Update changelogs for RISC-V feature rename.
- Link to v2: https://lore.kernel.org/r/20231114-clone3-shadow-stack-v2-0-b613f8681155@kernel.org
Changes in v2:
- Rebase onto v6.7-rc1.
- Remove ability to provide preallocated shadow stack, just specify the
desired size.
- Link to v1: https://lore.kernel.org/r/20231023-clone3-shadow-stack-v1-0-d867d0b5d4d0@kernel.org
---
Mark Brown (8):
arm64/gcs: Return a success value from gcs_alloc_thread_stack()
Documentation: userspace-api: Add shadow stack API documentation
selftests: Provide helper header for shadow stack testing
fork: Add shadow stack support to clone3()
selftests/clone3: Remove redundant flushes of output streams
selftests/clone3: Factor more of main loop into test_clone3()
selftests/clone3: Allow tests to flag if -E2BIG is a valid error code
selftests/clone3: Test shadow stack support
Documentation/userspace-api/index.rst | 1 +
Documentation/userspace-api/shadow_stack.rst | 44 +++++
arch/arm64/include/asm/gcs.h | 8 +-
arch/arm64/kernel/process.c | 8 +-
arch/arm64/mm/gcs.c | 61 +++++-
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 | 9 +-
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, 633 insertions(+), 81 deletions(-)
---
base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
change-id: 20231019-clone3-shadow-stack-15d40d2bf536
Best regards,
--
Mark Brown <broonie@kernel.org>
^ permalink raw reply
* [PATCH RFT v17 1/8] arm64/gcs: Return a success value from gcs_alloc_thread_stack()
From: Mark Brown @ 2025-06-09 12:54 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: <20250609-clone3-shadow-stack-v17-0-8840ed97ff6f@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 f50660603ecf..d8923b5f03b7 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 a5ca15daeb8a..87e1547d7abf 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 5c46ec527b1c..1f633a482558 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 v17 2/8] Documentation: userspace-api: Add shadow stack API documentation
From: Mark Brown @ 2025-06-09 12:54 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: <20250609-clone3-shadow-stack-v17-0-8840ed97ff6f@kernel.org>
There are a number of architectures with shadow stack features which we are
presenting to userspace with as consistent an API as we can (though there
are some architecture specifics). Especially given that there are some
important considerations for userspace code interacting directly with the
feature let's provide some documentation covering the common aspects.
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Kees Cook <kees@kernel.org>
Tested-by: Kees Cook <kees@kernel.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Yury Khrustalev <yury.khrustalev@arm.com>
Reviewed-by: Deepak Gupta <debug@rivosinc.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
---
Documentation/userspace-api/index.rst | 1 +
Documentation/userspace-api/shadow_stack.rst | 44 ++++++++++++++++++++++++++++
2 files changed, 45 insertions(+)
diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst
index b8c73be4fb11..0167e59b541e 100644
--- a/Documentation/userspace-api/index.rst
+++ b/Documentation/userspace-api/index.rst
@@ -62,6 +62,7 @@ Everything else
ELF
netlink/index
+ shadow_stack
sysfs-platform_profile
vduse
futex2
diff --git a/Documentation/userspace-api/shadow_stack.rst b/Documentation/userspace-api/shadow_stack.rst
new file mode 100644
index 000000000000..65c665496624
--- /dev/null
+++ b/Documentation/userspace-api/shadow_stack.rst
@@ -0,0 +1,44 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=============
+Shadow Stacks
+=============
+
+Introduction
+============
+
+Several architectures have features which provide backward edge
+control flow protection through a hardware maintained stack, only
+writeable by userspace through very limited operations. This feature
+is referred to as shadow stacks on Linux, on x86 it is part of Intel
+Control Enforcement Technology (CET), on arm64 it is Guarded Control
+Stacks feature (FEAT_GCS) and for RISC-V it is the Zicfiss extension.
+It is expected that this feature will normally be managed by the
+system dynamic linker and libc in ways broadly transparent to
+application code, this document covers interfaces and considerations.
+
+
+Enabling
+========
+
+Shadow stacks default to disabled when a userspace process is
+executed, they can be enabled for the current thread with a syscall:
+
+ - For x86 the ARCH_SHSTK_ENABLE arch_prctl()
+ - For other architectures the PR_SET_SHADOW_STACK_ENABLE prctl()
+
+It is expected that this will normally be done by the dynamic linker.
+Any new threads created by a thread with shadow stacks enabled will
+themselves have shadow stacks enabled.
+
+
+Enablement considerations
+=========================
+
+- Returning from the function that enables shadow stacks without first
+ disabling them will cause a shadow stack exception. This includes
+ any syscall wrapper or other library functions, the syscall will need
+ to be inlined.
+- A lock feature allows userspace to prevent disabling of shadow stacks.
+- Those that change the stack context like longjmp() or use of ucontext
+ changes on signal return will need support from libc.
--
2.39.5
^ permalink raw reply related
* [PATCH RFT v17 3/8] selftests: Provide helper header for shadow stack testing
From: Mark Brown @ 2025-06-09 12:54 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: <20250609-clone3-shadow-stack-v17-0-8840ed97ff6f@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 000000000000..fecf91218ea5
--- /dev/null
+++ b/tools/testing/selftests/ksft_shstk.h
@@ -0,0 +1,98 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Helpers for shadow stack enablement, this is intended to only be
+ * used by low level test programs directly exercising interfaces for
+ * working with shadow stacks.
+ *
+ * Copyright (C) 2024 ARM Ltd.
+ */
+
+#ifndef __KSFT_SHSTK_H
+#define __KSFT_SHSTK_H
+
+#include <asm/mman.h>
+
+/* This is currently only defined for x86 */
+#ifndef SHADOW_STACK_SET_TOKEN
+#define SHADOW_STACK_SET_TOKEN (1ULL << 0)
+#endif
+
+static bool shadow_stack_enabled;
+
+#ifdef __x86_64__
+#define ARCH_SHSTK_ENABLE 0x5001
+#define ARCH_SHSTK_SHSTK (1ULL << 0)
+
+#define ARCH_PRCTL(arg1, arg2) \
+({ \
+ long _ret; \
+ register long _num asm("eax") = __NR_arch_prctl; \
+ register long _arg1 asm("rdi") = (long)(arg1); \
+ register long _arg2 asm("rsi") = (long)(arg2); \
+ \
+ asm volatile ( \
+ "syscall\n" \
+ : "=a"(_ret) \
+ : "r"(_arg1), "r"(_arg2), \
+ "0"(_num) \
+ : "rcx", "r11", "memory", "cc" \
+ ); \
+ _ret; \
+})
+
+#define ENABLE_SHADOW_STACK
+static __always_inline void enable_shadow_stack(void)
+{
+ int ret = ARCH_PRCTL(ARCH_SHSTK_ENABLE, ARCH_SHSTK_SHSTK);
+ if (ret == 0)
+ shadow_stack_enabled = true;
+}
+
+#endif
+
+#ifdef __aarch64__
+#define PR_SET_SHADOW_STACK_STATUS 75
+# define PR_SHADOW_STACK_ENABLE (1UL << 0)
+
+#define my_syscall2(num, arg1, arg2) \
+({ \
+ register long _num __asm__ ("x8") = (num); \
+ register long _arg1 __asm__ ("x0") = (long)(arg1); \
+ register long _arg2 __asm__ ("x1") = (long)(arg2); \
+ register long _arg3 __asm__ ("x2") = 0; \
+ register long _arg4 __asm__ ("x3") = 0; \
+ register long _arg5 __asm__ ("x4") = 0; \
+ \
+ __asm__ volatile ( \
+ "svc #0\n" \
+ : "=r"(_arg1) \
+ : "r"(_arg1), "r"(_arg2), \
+ "r"(_arg3), "r"(_arg4), \
+ "r"(_arg5), "r"(_num) \
+ : "memory", "cc" \
+ ); \
+ _arg1; \
+})
+
+#define ENABLE_SHADOW_STACK
+static __always_inline void enable_shadow_stack(void)
+{
+ int ret;
+
+ ret = my_syscall2(__NR_prctl, PR_SET_SHADOW_STACK_STATUS,
+ PR_SHADOW_STACK_ENABLE);
+ if (ret == 0)
+ shadow_stack_enabled = true;
+}
+
+#endif
+
+#ifndef __NR_map_shadow_stack
+#define __NR_map_shadow_stack 453
+#endif
+
+#ifndef ENABLE_SHADOW_STACK
+static inline void enable_shadow_stack(void) { }
+#endif
+
+#endif
--
2.39.5
^ permalink raw reply related
* [PATCH RFT v17 4/8] fork: Add shadow stack support to clone3()
From: Mark Brown @ 2025-06-09 12:54 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: <20250609-clone3-shadow-stack-v17-0-8840ed97ff6f@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 | 53 +++++++++++++++++++++-
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 | 9 ++--
kernel/fork.c | 96 +++++++++++++++++++++++++++++++++++-----
8 files changed, 230 insertions(+), 26 deletions(-)
diff --git a/arch/arm64/mm/gcs.c b/arch/arm64/mm/gcs.c
index 1f633a482558..586494f7669b 100644
--- a/arch/arm64/mm/gcs.c
+++ b/arch/arm64/mm/gcs.c
@@ -43,8 +43,23 @@ int gcs_alloc_thread_stack(struct task_struct *tsk,
{
unsigned long addr, size;
- if (!system_supports_gcs())
+ if (!system_supports_gcs()) {
+ if (args->shadow_stack_token)
+ return -EINVAL;
+
+ return 0;
+ }
+
+ /*
+ * If the user specified a GCS then use it, otherwise fall
+ * back to a default allocation strategy. Validation is done
+ * in arch_shstk_validate_clone().
+ */
+ if (args->shadow_stack_token) {
+ tsk->thread.gcs_base = 0;
+ tsk->thread.gcs_size = 0;
return 0;
+ }
if (!task_gcs_el0_enabled(tsk))
return 0;
@@ -68,6 +83,42 @@ 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_token;
+ 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 ba6f2fe43848..827e983430aa 100644
--- a/arch/x86/include/asm/shstk.h
+++ b/arch/x86/include/asm/shstk.h
@@ -6,6 +6,7 @@
#include <linux/types.h>
struct task_struct;
+struct kernel_clone_args;
struct ksignal;
#ifdef CONFIG_X86_USER_SHADOW_STACK
@@ -16,8 +17,8 @@ struct thread_shstk {
long shstk_prctl(struct task_struct *task, int option, unsigned long arg2);
void reset_thread_features(void);
-unsigned long shstk_alloc_thread_stack(struct task_struct *p, unsigned long clone_flags,
- unsigned long stack_size);
+unsigned long shstk_alloc_thread_stack(struct task_struct *p,
+ const struct kernel_clone_args *args);
void shstk_free(struct task_struct *p);
int setup_signal_shadow_stack(struct ksignal *ksig);
int restore_signal_shadow_stack(void);
@@ -28,8 +29,10 @@ static inline long shstk_prctl(struct task_struct *task, int option,
unsigned long arg2) { return -EINVAL; }
static inline void reset_thread_features(void) {}
static inline unsigned long shstk_alloc_thread_stack(struct task_struct *p,
- unsigned long clone_flags,
- unsigned long stack_size) { return 0; }
+ const struct kernel_clone_args *args)
+{
+ return 0;
+}
static inline void shstk_free(struct task_struct *p) {}
static inline int setup_signal_shadow_stack(struct ksignal *ksig) { return 0; }
static inline int restore_signal_shadow_stack(void) { return 0; }
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 704883c21f3a..56bf3394360a 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -209,7 +209,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
* is disabled, new_ssp will remain 0, and fpu_clone() will know not to
* update it.
*/
- new_ssp = shstk_alloc_thread_stack(p, clone_flags, args->stack_size);
+ new_ssp = shstk_alloc_thread_stack(p, args);
if (IS_ERR_VALUE(new_ssp))
return PTR_ERR((void *)new_ssp);
diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
index 2ddf23387c7e..9d82dd0bed1f 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 = page_address(page);
+ int offset, token;
+ unsigned long ssp;
+ u64 expected;
+
+ if (!features_enabled(ARCH_SHSTK_SHSTK))
+ return 0;
+
+ token = args->shadow_stack_token;
+ ssp = token + 8;
+ expected = (ssp + FRAME_SIZE) | BIT(0);
+ offset = offset_in_page(token);
+
+ if (!cmpxchg_to_user_page(vma, page, token, (unsigned long *)(maddr + offset),
+ expected, 0))
+ return -EINVAL;
+ set_page_dirty_lock(page);
+
+ return 0;
+}
+
+unsigned long shstk_alloc_thread_stack(struct task_struct *tsk,
+ const struct kernel_clone_args *args)
{
struct thread_shstk *shstk = &tsk->thread.shstk;
+ unsigned long clone_flags = args->flags;
unsigned long addr, size;
/*
* If shadow stack is not enabled on the new thread, skip any
- * switch to a new shadow stack.
+ * implicit switch to a new shadow stack and reject attempts to
+ * explicitly specify one.
*/
- if (!features_enabled(ARCH_SHSTK_SHSTK))
+ if (!features_enabled(ARCH_SHSTK_SHSTK)) {
+ if (args->shadow_stack_token)
+ return (unsigned long)ERR_PTR(-EINVAL);
+
return 0;
+ }
+
+ /*
+ * If the user specified a shadow stack then use it, otherwise
+ * fall back to a default allocation strategy. Validation is
+ * done in arch_shstk_validate_clone().
+ */
+ if (args->shadow_stack_token) {
+ shstk->base = 0;
+ shstk->size = 0;
+ return args->shadow_stack_token + 8;
+ }
/*
* For CLONE_VFORK the child will share the parents shadow stack.
@@ -222,7 +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 7ee8a179d103..96cc0c7a5c90 100644
--- a/include/asm-generic/cacheflush.h
+++ b/include/asm-generic/cacheflush.h
@@ -124,4 +124,15 @@ static inline void flush_cache_vunmap(unsigned long start, unsigned long end)
} while (0)
#endif
+#ifndef cmpxchg_to_user_page
+#define cmpxchg_to_user_page(vma, page, vaddr, ptr, old, new) \
+({ \
+ bool ret; \
+ \
+ ret = try_cmpxchg(ptr, &old, new); \
+ flush_icache_user_page(vma, page, vaddr, sizeof(*ptr)); \
+ ret; \
+})
+#endif
+
#endif /* _ASM_GENERIC_CACHEFLUSH_H */
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index ca1db4b92c32..c34f3cb68822 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -16,6 +16,7 @@ struct task_struct;
struct rusage;
union thread_union;
struct css_set;
+struct vm_area_struct;
/* All the bits taken by the old clone syscall. */
#define CLONE_LEGACY_FLAGS 0xffffffffULL
@@ -44,6 +45,7 @@ struct kernel_clone_args {
struct cgroup *cgrp;
struct css_set *cset;
unsigned int kill_seq;
+ unsigned long shadow_stack_token;
};
/*
@@ -237,4 +239,19 @@ static inline void task_unlock(struct task_struct *p)
DEFINE_GUARD(task_lock, struct task_struct *, task_lock(_T), task_unlock(_T))
+#ifdef CONFIG_ARCH_HAS_USER_SHADOW_STACK
+int arch_shstk_validate_clone(struct task_struct *p,
+ struct vm_area_struct *vma,
+ struct page *page,
+ struct kernel_clone_args *args);
+#else
+static inline int arch_shstk_validate_clone(struct task_struct *p,
+ struct vm_area_struct *vma,
+ struct page *page,
+ struct kernel_clone_args *args)
+{
+ return 0;
+}
+#endif
+
#endif /* _LINUX_SCHED_TASK_H */
diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index 359a14cc76a4..9cf5c419e109 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -84,6 +84,7 @@
* kernel's limit of nested PID namespaces.
* @cgroup: If CLONE_INTO_CGROUP is specified set this to
* a file descriptor for the cgroup.
+ * @shadow_stack_token: Pointer to shadow stack token at top of stack.
*
* The structure is versioned by size and thus extensible.
* New struct members must go at the end of the struct and
@@ -101,12 +102,14 @@ struct clone_args {
__aligned_u64 set_tid;
__aligned_u64 set_tid_size;
__aligned_u64 cgroup;
+ __aligned_u64 shadow_stack_token;
};
#endif
-#define CLONE_ARGS_SIZE_VER0 64 /* sizeof first published struct */
-#define CLONE_ARGS_SIZE_VER1 80 /* sizeof second published struct */
-#define CLONE_ARGS_SIZE_VER2 88 /* sizeof third published struct */
+#define CLONE_ARGS_SIZE_VER0 64 /* sizeof first published struct */
+#define CLONE_ARGS_SIZE_VER1 80 /* sizeof second published struct */
+#define CLONE_ARGS_SIZE_VER2 88 /* sizeof third published struct */
+#define CLONE_ARGS_SIZE_VER3 96 /* sizeof fourth published struct */
/*
* Scheduling policies
diff --git a/kernel/fork.c b/kernel/fork.c
index 1ee8eb11f38b..89c19996235d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1902,6 +1902,51 @@ static bool need_futex_hash_allocate_default(u64 clone_flags)
return true;
}
+static int shstk_validate_clone(struct task_struct *p,
+ struct kernel_clone_args *args)
+{
+ struct mm_struct *mm;
+ struct vm_area_struct *vma;
+ struct page *page;
+ unsigned long addr;
+ int ret;
+
+ if (!IS_ENABLED(CONFIG_ARCH_HAS_USER_SHADOW_STACK))
+ return 0;
+
+ if (!args->shadow_stack_token)
+ return 0;
+
+ mm = get_task_mm(p);
+ if (!mm)
+ return -EFAULT;
+
+ mmap_read_lock(mm);
+
+ addr = untagged_addr_remote(mm, args->shadow_stack_token);
+ page = get_user_page_vma_remote(mm, addr, FOLL_FORCE | FOLL_WRITE,
+ &vma);
+ if (IS_ERR(page)) {
+ ret = -EFAULT;
+ goto out;
+ }
+
+ if (!(vma->vm_flags & VM_SHADOW_STACK) ||
+ !(vma->vm_flags & VM_WRITE)) {
+ ret = -EFAULT;
+ goto out_page;
+ }
+
+ ret = arch_shstk_validate_clone(p, vma, page, args);
+
+out_page:
+ put_page(page);
+out:
+ mmap_read_unlock(mm);
+ mmput(mm);
+ return ret;
+}
+
/*
* This creates a new process as a copy of the old one,
* but does not actually start it yet.
@@ -2176,6 +2221,9 @@ __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;
@@ -2757,7 +2805,9 @@ 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_token) !=
+ CLONE_ARGS_SIZE_VER3);
+ BUILD_BUG_ON(sizeof(struct clone_args) != CLONE_ARGS_SIZE_VER3);
if (unlikely(usize > PAGE_SIZE))
return -E2BIG;
@@ -2790,16 +2840,17 @@ 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_token = args.shadow_stack_token,
};
if (args.set_tid &&
@@ -2840,6 +2891,27 @@ 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_token)
+ return true;
+
+ if (!IS_ALIGNED(kargs->shadow_stack_token, 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. */
@@ -2862,7 +2934,7 @@ 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 v17 5/8] selftests/clone3: Remove redundant flushes of output streams
From: Mark Brown @ 2025-06-09 12:54 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: <20250609-clone3-shadow-stack-v17-0-8840ed97ff6f@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 eeca8005723f..939b26c86d42 100644
--- a/tools/testing/selftests/clone3/clone3_selftests.h
+++ b/tools/testing/selftests/clone3/clone3_selftests.h
@@ -35,8 +35,6 @@ struct __clone_args {
static pid_t sys_clone3(struct __clone_args *args, size_t size)
{
- fflush(stdout);
- fflush(stderr);
return syscall(__NR_clone3, args, size);
}
--
2.39.5
^ permalink raw reply related
* [PATCH RFT v17 6/8] selftests/clone3: Factor more of main loop into test_clone3()
From: Mark Brown @ 2025-06-09 12:54 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: <20250609-clone3-shadow-stack-v17-0-8840ed97ff6f@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 e61f07973ce5..e066b201fa64 100644
--- a/tools/testing/selftests/clone3/clone3.c
+++ b/tools/testing/selftests/clone3/clone3.c
@@ -30,6 +30,19 @@ enum test_mode {
CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG,
};
+typedef bool (*filter_function)(void);
+typedef size_t (*size_function)(void);
+
+struct test {
+ const char *name;
+ uint64_t flags;
+ size_t size;
+ size_function size_function;
+ int expected;
+ enum test_mode test_mode;
+ filter_function filter;
+};
+
static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
{
struct __clone_args args = {
@@ -109,30 +122,40 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
return 0;
}
-static bool test_clone3(uint64_t flags, size_t size, int expected,
- enum test_mode test_mode)
+static void test_clone3(const struct test *test)
{
+ size_t size;
int ret;
+ if (test->filter && test->filter()) {
+ ksft_test_result_skip("%s\n", test->name);
+ return;
+ }
+
+ if (test->size_function)
+ size = test->size_function();
+ else
+ size = test->size;
+
+ ksft_print_msg("Running test '%s'\n", test->name);
+
ksft_print_msg(
"[%d] Trying clone3() with flags %#" PRIx64 " (size %zu)\n",
- getpid(), flags, size);
- ret = call_clone3(flags, size, test_mode);
+ getpid(), test->flags, size);
+ ret = call_clone3(test->flags, size, test->test_mode);
ksft_print_msg("[%d] clone3() with flags says: %d expected %d\n",
- getpid(), ret, expected);
- if (ret != expected) {
+ getpid(), ret, test->expected);
+ if (ret != test->expected) {
ksft_print_msg(
"[%d] Result (%d) is different than expected (%d)\n",
- getpid(), ret, expected);
- return false;
+ getpid(), ret, test->expected);
+ ksft_test_result_fail("%s\n", test->name);
+ return;
}
- return true;
+ ksft_test_result_pass("%s\n", test->name);
}
-typedef bool (*filter_function)(void);
-typedef size_t (*size_function)(void);
-
static bool not_root(void)
{
if (getuid() != 0) {
@@ -160,16 +183,6 @@ static size_t page_size_plus_8(void)
return getpagesize() + 8;
}
-struct test {
- const char *name;
- uint64_t flags;
- size_t size;
- size_function size_function;
- int expected;
- enum test_mode test_mode;
- filter_function filter;
-};
-
static const struct test tests[] = {
{
.name = "simple clone3()",
@@ -319,24 +332,8 @@ int main(int argc, char *argv[])
ksft_set_plan(ARRAY_SIZE(tests));
test_clone3_supported();
- for (i = 0; i < ARRAY_SIZE(tests); i++) {
- if (tests[i].filter && tests[i].filter()) {
- ksft_test_result_skip("%s\n", tests[i].name);
- continue;
- }
-
- if (tests[i].size_function)
- size = tests[i].size_function();
- else
- size = tests[i].size;
-
- ksft_print_msg("Running test '%s'\n", tests[i].name);
-
- ksft_test_result(test_clone3(tests[i].flags, size,
- tests[i].expected,
- tests[i].test_mode),
- "%s\n", tests[i].name);
- }
+ for (i = 0; i < ARRAY_SIZE(tests); i++)
+ test_clone3(&tests[i]);
ksft_finished();
}
--
2.39.5
^ permalink raw reply related
* [PATCH RFT v17 7/8] selftests/clone3: Allow tests to flag if -E2BIG is a valid error code
From: Mark Brown @ 2025-06-09 12:54 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: <20250609-clone3-shadow-stack-v17-0-8840ed97ff6f@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 e066b201fa64..5b8b7d640e70 100644
--- a/tools/testing/selftests/clone3/clone3.c
+++ b/tools/testing/selftests/clone3/clone3.c
@@ -39,6 +39,7 @@ struct test {
size_t size;
size_function size_function;
int expected;
+ bool e2big_valid;
enum test_mode test_mode;
filter_function filter;
};
@@ -146,6 +147,11 @@ static void test_clone3(const struct test *test)
ksft_print_msg("[%d] clone3() with flags says: %d expected %d\n",
getpid(), ret, test->expected);
if (ret != test->expected) {
+ if (test->e2big_valid && ret == -E2BIG) {
+ ksft_print_msg("Test reported -E2BIG\n");
+ ksft_test_result_skip("%s\n", test->name);
+ return;
+ }
ksft_print_msg(
"[%d] Result (%d) is different than expected (%d)\n",
getpid(), ret, test->expected);
--
2.39.5
^ permalink raw reply related
* [PATCH RFT v17 8/8] selftests/clone3: Test shadow stack support
From: Mark Brown @ 2025-06-09 12:54 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: <20250609-clone3-shadow-stack-v17-0-8840ed97ff6f@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 5b8b7d640e70..6fd2b3238e2c 100644
--- a/tools/testing/selftests/clone3/clone3.c
+++ b/tools/testing/selftests/clone3/clone3.c
@@ -3,6 +3,7 @@
/* Based on Christian Brauner's clone3() example */
#define _GNU_SOURCE
+#include <asm/mman.h>
#include <errno.h>
#include <inttypes.h>
#include <linux/types.h>
@@ -11,6 +12,7 @@
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
+#include <sys/mman.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/un.h>
@@ -19,8 +21,12 @@
#include <sched.h>
#include "../kselftest.h"
+#include "../ksft_shstk.h"
#include "clone3_selftests.h"
+static bool shadow_stack_supported;
+static size_t max_supported_args_size;
+
enum test_mode {
CLONE3_ARGS_NO_TEST,
CLONE3_ARGS_ALL_0,
@@ -28,6 +34,10 @@ enum test_mode {
CLONE3_ARGS_INVAL_EXIT_SIGNAL_NEG,
CLONE3_ARGS_INVAL_EXIT_SIGNAL_CSIG,
CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG,
+ CLONE3_ARGS_SHADOW_STACK,
+ CLONE3_ARGS_SHADOW_STACK_MISALIGNED,
+ CLONE3_ARGS_SHADOW_STACK_NO_TOKEN,
+ CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY,
};
typedef bool (*filter_function)(void);
@@ -44,6 +54,44 @@ struct test {
filter_function filter;
};
+
+/*
+ * We check for shadow stack support by attempting to use
+ * map_shadow_stack() since features may have been locked by the
+ * dynamic linker resulting in spurious errors when we attempt to
+ * enable on startup. We warn if the enable failed.
+ */
+static void test_shadow_stack_supported(void)
+{
+ long ret;
+
+ ret = syscall(__NR_map_shadow_stack, 0, getpagesize(), 0);
+ if (ret == -1) {
+ ksft_print_msg("map_shadow_stack() not supported\n");
+ } else if ((void *)ret == MAP_FAILED) {
+ ksft_print_msg("Failed to map shadow stack\n");
+ } else {
+ ksft_print_msg("Shadow stack supportd\n");
+ shadow_stack_supported = true;
+
+ if (!shadow_stack_enabled)
+ ksft_print_msg("Mapped but did not enable shadow stack\n");
+ }
+}
+
+static void *get_shadow_stack_page(unsigned long flags)
+{
+ unsigned long long page;
+
+ page = syscall(__NR_map_shadow_stack, 0, getpagesize(), flags);
+ if ((void *)page == MAP_FAILED) {
+ ksft_print_msg("map_shadow_stack() failed: %d\n", errno);
+ return 0;
+ }
+
+ return (void *)page;
+}
+
static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
{
struct __clone_args args = {
@@ -57,6 +105,7 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
} args_ext;
pid_t pid = -1;
+ void *p;
int status;
memset(&args_ext, 0, sizeof(args_ext));
@@ -89,6 +138,26 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
case CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG:
args.exit_signal = 0x00000000000000f0ULL;
break;
+ case CLONE3_ARGS_SHADOW_STACK:
+ p = get_shadow_stack_page(SHADOW_STACK_SET_TOKEN);
+ p += getpagesize() - sizeof(void *);
+ args.shadow_stack_token = (unsigned long long)p;
+ break;
+ case CLONE3_ARGS_SHADOW_STACK_MISALIGNED:
+ p = get_shadow_stack_page(SHADOW_STACK_SET_TOKEN);
+ p += getpagesize() - sizeof(void *) - 1;
+ args.shadow_stack_token = (unsigned long long)p;
+ break;
+ case CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY:
+ p = malloc(getpagesize());
+ p += getpagesize() - sizeof(void *);
+ args.shadow_stack_token = (unsigned long long)p;
+ break;
+ case CLONE3_ARGS_SHADOW_STACK_NO_TOKEN:
+ p = get_shadow_stack_page(0);
+ p += getpagesize() - sizeof(void *);
+ args.shadow_stack_token = (unsigned long long)p;
+ break;
}
memcpy(&args_ext.args, &args, sizeof(struct __clone_args));
@@ -102,7 +171,12 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
if (pid == 0) {
ksft_print_msg("I am the child, my PID is %d\n", getpid());
- _exit(EXIT_SUCCESS);
+ /*
+ * Use a raw syscall to ensure we don't get issues
+ * with manually specified shadow stack and exit handlers.
+ */
+ syscall(__NR_exit, EXIT_SUCCESS);
+ ksft_print_msg("CHILD FAILED TO EXIT PID is %d\n", getpid());
}
ksft_print_msg("I am the parent (%d). My child's pid is %d\n",
@@ -184,6 +258,26 @@ static bool no_timenamespace(void)
return true;
}
+static bool have_shadow_stack(void)
+{
+ if (shadow_stack_supported) {
+ ksft_print_msg("Shadow stack supported\n");
+ return true;
+ }
+
+ return false;
+}
+
+static bool no_shadow_stack(void)
+{
+ if (!shadow_stack_supported) {
+ ksft_print_msg("Shadow stack not supported\n");
+ return true;
+ }
+
+ return false;
+}
+
static size_t page_size_plus_8(void)
{
return getpagesize() + 8;
@@ -327,6 +421,50 @@ static const struct test tests[] = {
.expected = -EINVAL,
.test_mode = CLONE3_ARGS_NO_TEST,
},
+ {
+ .name = "Shadow stack on system with shadow stack",
+ .size = 0,
+ .expected = 0,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK,
+ .filter = no_shadow_stack,
+ },
+ {
+ .name = "Shadow stack with misaligned address",
+ .flags = CLONE_VM,
+ .size = 0,
+ .expected = -EINVAL,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK_MISALIGNED,
+ .filter = no_shadow_stack,
+ },
+ {
+ .name = "Shadow stack with normal memory",
+ .flags = CLONE_VM,
+ .size = 0,
+ .expected = -EFAULT,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY,
+ .filter = no_shadow_stack,
+ },
+ {
+ .name = "Shadow stack with no token",
+ .flags = CLONE_VM,
+ .size = 0,
+ .expected = -EINVAL,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK_NO_TOKEN,
+ .filter = no_shadow_stack,
+ },
+ {
+ .name = "Shadow stack on system without shadow stack",
+ .flags = CLONE_VM,
+ .size = 0,
+ .expected = -EFAULT,
+ .e2big_valid = true,
+ .test_mode = CLONE3_ARGS_SHADOW_STACK_NORMAL_MEMORY,
+ .filter = have_shadow_stack,
+ },
};
int main(int argc, char *argv[])
@@ -334,9 +472,12 @@ int main(int argc, char *argv[])
size_t size;
int i;
+ enable_shadow_stack();
+
ksft_print_header();
ksft_set_plan(ARRAY_SIZE(tests));
test_clone3_supported();
+ test_shadow_stack_supported();
for (i = 0; i < ARRAY_SIZE(tests); i++)
test_clone3(&tests[i]);
diff --git a/tools/testing/selftests/clone3/clone3_selftests.h b/tools/testing/selftests/clone3/clone3_selftests.h
index 939b26c86d42..8151c4fc971a 100644
--- a/tools/testing/selftests/clone3/clone3_selftests.h
+++ b/tools/testing/selftests/clone3/clone3_selftests.h
@@ -31,12 +31,75 @@ struct __clone_args {
__aligned_u64 set_tid;
__aligned_u64 set_tid_size;
__aligned_u64 cgroup;
+#ifndef CLONE_ARGS_SIZE_VER2
+#define CLONE_ARGS_SIZE_VER2 88 /* sizeof third published struct */
+#endif
+ __aligned_u64 shadow_stack_token;
+#ifndef CLONE_ARGS_SIZE_VER3
+#define CLONE_ARGS_SIZE_VER3 96 /* sizeof fourth published struct */
+#endif
};
+/*
+ * For architectures with shadow stack support we need to be
+ * absolutely sure that the clone3() syscall will be inline and not a
+ * function call so we open code.
+ */
+#ifdef __x86_64__
+static __always_inline pid_t sys_clone3(struct __clone_args *args, size_t size)
+{
+ register long _num __asm__ ("rax") = __NR_clone3;
+ register long _args __asm__ ("rdi") = (long)(args);
+ register long _size __asm__ ("rsi") = (long)(size);
+ long ret;
+
+ __asm__ volatile (
+ "syscall\n"
+ : "=a"(ret)
+ : "r"(_args), "r"(_size),
+ "0"(_num)
+ : "rcx", "r11", "memory", "cc"
+ );
+
+ if (ret < 0) {
+ errno = -ret;
+ return -1;
+ }
+
+ return ret;
+}
+#elif defined(__aarch64__)
+static __always_inline pid_t sys_clone3(struct __clone_args *args, size_t size)
+{
+ register long _num __asm__ ("x8") = __NR_clone3;
+ register long _args __asm__ ("x0") = (long)(args);
+ register long _size __asm__ ("x1") = (long)(size);
+ register long arg2 __asm__ ("x2") = 0;
+ register long arg3 __asm__ ("x3") = 0;
+ register long arg4 __asm__ ("x4") = 0;
+
+ __asm__ volatile (
+ "svc #0\n"
+ : "=r"(_args)
+ : "r"(_args), "r"(_size),
+ "r"(_num), "r"(arg2),
+ "r"(arg3), "r"(arg4)
+ : "memory", "cc"
+ );
+
+ if ((int)_args < 0) {
+ errno = -((int)_args);
+ return -1;
+ }
+
+ return _args;
+}
+#else
static pid_t sys_clone3(struct __clone_args *args, size_t size)
{
return syscall(__NR_clone3, args, size);
}
+#endif
static inline void test_clone3_supported(void)
{
--
2.39.5
^ permalink raw reply related
* [PATCH net-next v3 0/6] tcp: support preloading data on a listening socket
From: Jeremy Harris @ 2025-06-09 15:56 UTC (permalink / raw)
To: netdev; +Cc: linux-api, edumazet, ncardwell, Jeremy Harris
I didn't get any comments on v2 apart from the kernel test robot
so I'm repeating the same resposes to v1 comment here.
I figured I should do a v3 to fix the compiler warnings the robot
pointed out.
v2 changes:
- Split out the preload operation to a separate routine from
tcp_sendmsg_locked() and restrict from looping over the supplied
iovec
v3 changes:
- Fix compiler warnings
------
Support write to a listen TCP socket, for immediate
transmission on all later passive connection establishments
parented by the listen socket.
On a normal connection transmission of the data is triggered by the receipt
of the 3rd-ack. On a fastopen (with accepted cookie) connection the data
is sent in the synack packet.
The data preload is done using a sendmsg with a newly-defined flag
(MSG_PRELOAD); the amount of data limited to a single linear sk_buff.
Note that this definition is the last-but-two bit available if "int"
is 32 bits.
Intent: lower latency for server-first protocols using TCP.
Known cases of this use are SMTP and MySQL.
Measurements:
Packet capture (laptop, loopback, TFO requeste) for initial SYN to first
client data packet (5 samples):
- baseline TFO-C 1064 1470 1455 1547 1595 usec
- patched non-TFO 140 150 159 144 153 usec
- patched TFO-C 142 149 149 125 125 usec
Out of scope:
- Client-first protocols
- TLS-on-connect
Testing:
A) packetdrill scripts for
- normal non-TFO
- normal TFO
- synack lost
- 3rd-ack acks only the SYN
- 3rd-ack acks partial data
(NB: packetdrill can only check the data size, not actual content)
B) Application use, running the application testsuite
and manual check of specific cases via packet capture
C) Daily-driver laptop use (not expected to trigger the feature;
only regression-test)
D) KASAN/syzkaller
- enable_syscalls: "socket$inet_tcp", "listen", "sendmsg", "accept",
"read", "write", "close", "syz_emit_ethernet", "syz_extract_tcp_res"
- the coverage seems rather limited; the sendmsg onto a listen socket
is there, but I am not convinced actual TCP connections are being
excercised. tcp_input.c only 2%; tcp_minisocks.c is entirely uncovered.
- A need for limiting iteration in the sendmesg handling was found (RCU
timeouts), hence v2, but no hint of locking problems.
Eric: could you expand on your previous comment "I do not see any
locking"? If it referred to the syscall write operation on the listening
socket, tcp_sendmsg_locked() is called with the sk locked - so I'm
unsure where you're looking.
Jeremy Harris (6):
tcp: support writing to a socket in listening state
tcp: copy write-data from listen socket to accept child socket
tcp: fastopen: add write-data to fastopen synack packet
tcp: transmit any pending data on receipt of 3rd-ack
tcp: fastopen: retransmit data when only the SYN of a synack-with-data
is acked
tcp: fastopen: extend retransmit-queue trimming to handle linear
sk_buff
include/linux/socket.h | 1 +
net/ipv4/tcp.c | 112 ++++++++++++++++++
net/ipv4/tcp_fastopen.c | 3 +-
net/ipv4/tcp_input.c | 15 ++-
net/ipv4/tcp_ipv4.c | 4 +-
net/ipv4/tcp_minisocks.c | 58 ++++++++-
net/ipv4/tcp_output.c | 50 +++++++-
.../perf/trace/beauty/include/linux/socket.h | 1 +
tools/perf/trace/beauty/msg_flags.c | 3 +
9 files changed, 234 insertions(+), 13 deletions(-)
base-commit: 2c7e4a2663a1ab5a740c59c31991579b6b865a26
--
2.49.0
^ permalink raw reply
* [PATCH net-next v3 1/6] tcp: support writing to a socket in listening state
From: Jeremy Harris @ 2025-06-09 16:05 UTC (permalink / raw)
To: netdev; +Cc: linux-api, edumazet, ncardwell, Jeremy Harris
In-Reply-To: <cover.1749466540.git.jgh@exim.org>
In the tcp sendmsg handler, permit a write in LISTENING state if
a MSG_PRELOAD flag is used. Copy from iovec to a linear sk_buff
for placement on the socket write queue.
Signed-off-by: Jeremy Harris <jgh@exim.org>
---
include/linux/socket.h | 1 +
net/ipv4/tcp.c | 112 ++++++++++++++++++
.../perf/trace/beauty/include/linux/socket.h | 1 +
tools/perf/trace/beauty/msg_flags.c | 3 +
4 files changed, 117 insertions(+)
diff --git a/include/linux/socket.h b/include/linux/socket.h
index 3b262487ec06..b41f4cd4dc97 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -330,6 +330,7 @@ struct ucred {
#define MSG_SOCK_DEVMEM 0x2000000 /* Receive devmem skbs as cmsg */
#define MSG_ZEROCOPY 0x4000000 /* Use user data in kernel path */
#define MSG_SPLICE_PAGES 0x8000000 /* Splice the pages from the iterator in sendmsg() */
+#define MSG_PRELOAD 0x10000000 /* Preload tx data while listening */
#define MSG_FASTOPEN 0x20000000 /* Send data in TCP SYN */
#define MSG_CMSG_CLOEXEC 0x40000000 /* Set close_on_exec for file
descriptor received through
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index f64f8276a73c..c0a787c1649d 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1057,6 +1057,115 @@ int tcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg, int *copied,
return err;
}
+/* Cut-down version of tcp_sendmsg_locked(), for writing on a listen socket
+ */
+static int tcp_sendmsg_preload(struct sock *sk, struct msghdr *msg)
+{
+ struct sk_buff *skb;
+ int flags, err, copied = 0;
+ int size_goal;
+ int process_backlog = 0;
+ long timeo;
+
+ if (sk->sk_state != TCP_LISTEN)
+ return -EINVAL;
+
+ flags = msg->msg_flags;
+
+ timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);
+
+ /* Ok commence sending. */
+restart:
+ /* Use a arbitrary "mss" value */
+ size_goal = 1000;
+
+ err = -EPIPE;
+ if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))
+ goto do_error;
+
+ while (msg_data_left(msg)) {
+ ssize_t copy = 0;
+
+ skb = tcp_write_queue_tail(sk);
+ if (skb)
+ copy = size_goal - skb->len;
+
+ trace_tcp_sendmsg_locked(sk, msg, skb, size_goal);
+
+ if (copy <= 0 || !tcp_skb_can_collapse_to(skb)) {
+ bool first_skb = !skb;
+
+ /* Limit to only one skb on the sk write queue */
+
+ if (!first_skb)
+ goto out_nopush;
+
+ if (!sk_stream_memory_free(sk))
+ goto wait_for_space;
+
+ if (unlikely(process_backlog >= 16)) {
+ process_backlog = 0;
+ if (sk_flush_backlog(sk))
+ goto restart;
+ }
+
+ skb = tcp_stream_alloc_skb(sk, sk->sk_allocation,
+ first_skb);
+ if (!skb)
+ goto wait_for_space;
+
+ process_backlog++;
+
+#ifdef CONFIG_SKB_DECRYPTED
+ skb->decrypted = !!(flags & MSG_SENDPAGE_DECRYPTED);
+#endif
+ tcp_skb_entail(sk, skb);
+ copy = size_goal;
+ }
+
+ /* Try to append data to the end of skb. */
+ if (copy > msg_data_left(msg))
+ copy = msg_data_left(msg);
+
+ copy = min_t(int, copy, skb_tailroom(skb));
+ err = skb_add_data_nocache(sk, skb, &msg->msg_iter, copy);
+ if (err)
+ goto do_error;
+
+ TCP_SKB_CB(skb)->end_seq += copy;
+ tcp_skb_pcount_set(skb, 0);
+
+ copied += copy;
+ goto out_nopush;
+
+wait_for_space:
+ set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
+ tcp_remove_empty_skb(sk);
+
+ err = sk_stream_wait_memory(sk, &timeo);
+ if (err != 0)
+ goto do_error;
+ }
+
+out_nopush:
+ return copied;
+
+do_error:
+ tcp_remove_empty_skb(sk);
+
+ if (copied)
+ goto out_nopush;
+
+ err = sk_stream_error(sk, flags, err);
+ /* make sure we wake any epoll edge trigger waiter */
+ if (unlikely(tcp_rtx_and_write_queues_empty(sk) && err == -EAGAIN)) {
+ sk->sk_write_space(sk);
+ tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
+ }
+
+ return err;
+}
+
int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
{
struct net_devmem_dmabuf_binding *binding = NULL;
@@ -1129,6 +1238,9 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
goto out_err;
}
+ if (unlikely(flags & MSG_PRELOAD))
+ return tcp_sendmsg_preload(sk, msg);
+
timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);
tcp_rate_check_app_limited(sk); /* is sending application-limited? */
diff --git a/tools/perf/trace/beauty/include/linux/socket.h b/tools/perf/trace/beauty/include/linux/socket.h
index c3322eb3d686..e9ea498169f3 100644
--- a/tools/perf/trace/beauty/include/linux/socket.h
+++ b/tools/perf/trace/beauty/include/linux/socket.h
@@ -330,6 +330,7 @@ struct ucred {
#define MSG_SOCK_DEVMEM 0x2000000 /* Receive devmem skbs as cmsg */
#define MSG_ZEROCOPY 0x4000000 /* Use user data in kernel path */
#define MSG_SPLICE_PAGES 0x8000000 /* Splice the pages from the iterator in sendmsg() */
+#define MSG_PRELOAD 0x10000000 /* Preload tx data while listening */
#define MSG_FASTOPEN 0x20000000 /* Send data in TCP SYN */
#define MSG_CMSG_CLOEXEC 0x40000000 /* Set close_on_exec for file
descriptor received through
diff --git a/tools/perf/trace/beauty/msg_flags.c b/tools/perf/trace/beauty/msg_flags.c
index 2da581ff0c80..27e40da9b02d 100644
--- a/tools/perf/trace/beauty/msg_flags.c
+++ b/tools/perf/trace/beauty/msg_flags.c
@@ -20,6 +20,9 @@
#ifndef MSG_SPLICE_PAGES
#define MSG_SPLICE_PAGES 0x8000000
#endif
+#ifndef MSG_PRELOAD
+#define MSG_PRELOAD 0x10000000
+#endif
#ifndef MSG_FASTOPEN
#define MSG_FASTOPEN 0x20000000
#endif
--
2.49.0
^ permalink raw reply related
* [PATCH net-next v3 2/6] tcp: copy write-data from listen socket to accept child socket
From: Jeremy Harris @ 2025-06-09 16:05 UTC (permalink / raw)
To: netdev; +Cc: linux-api, edumazet, ncardwell, Jeremy Harris
In-Reply-To: <cover.1749466540.git.jgh@exim.org>
Set the request_sock flag for fastopen earlier, making it available
to the af_ops SYN-handler function.
In that function copy data from the listen socket write queue into an
sk_buff, allocating if needed and adding to the write queue of the
newly-created child socket.
Set sequence number values depending on the fastopen status.
Signed-off-by: Jeremy Harris <jgh@exim.org>
---
net/ipv4/tcp_fastopen.c | 3 ++-
net/ipv4/tcp_ipv4.c | 4 +--
net/ipv4/tcp_minisocks.c | 58 ++++++++++++++++++++++++++++++++++++----
3 files changed, 57 insertions(+), 8 deletions(-)
diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index 9b83d639b5ac..03a86d0b87ba 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -245,6 +245,8 @@ static struct sock *tcp_fastopen_create_child(struct sock *sk,
struct sock *child;
bool own_req;
+ tcp_rsk(req)->tfo_listener = true;
+
child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
NULL, &own_req);
if (!child)
@@ -261,7 +263,6 @@ static struct sock *tcp_fastopen_create_child(struct sock *sk,
tp = tcp_sk(child);
rcu_assign_pointer(tp->fastopen_rsk, req);
- tcp_rsk(req)->tfo_listener = true;
/* RFC1323: The window in SYN & SYN/ACK segments is never
* scaled. So correct it appropriately.
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 6a14f9e6fef6..e488effdbdb2 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1747,8 +1747,8 @@ EXPORT_IPV6_MOD(tcp_v4_conn_request);
/*
- * The three way handshake has completed - we got a valid synack -
- * now create the new socket.
+ * The three way handshake has completed - we got a valid synack
+ * (or a FASTOPEN syn) - now create the new socket.
*/
struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
struct request_sock *req,
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 43d7852ce07e..d471531b4a78 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -529,7 +529,7 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
struct inet_connection_sock *newicsk;
const struct tcp_sock *oldtp;
struct tcp_sock *newtp;
- u32 seq;
+ u32 seq, a_seq, n_seq;
if (!newsk)
return NULL;
@@ -550,9 +550,55 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
newtp->segs_in = 1;
seq = treq->snt_isn + 1;
- newtp->snd_sml = newtp->snd_una = seq;
- WRITE_ONCE(newtp->snd_nxt, seq);
- newtp->snd_up = seq;
+ n_seq = seq;
+ a_seq = seq;
+ newtp->write_seq = seq;
+ newtp->snd_una = seq;
+
+ /* If there is write-data sitting on the listen socket, copy it to
+ * the accept socket. If FASTOPEN we will send it on the synack,
+ * otherwise it sits there until 3rd-ack arrives.
+ */
+
+ if (unlikely(!skb_queue_empty(&sk->sk_write_queue))) {
+ struct sk_buff *l_skb = tcp_send_head(sk),
+ *a_skb = tcp_write_queue_tail(newsk);
+ ssize_t copy = 0;
+
+ if (a_skb)
+ copy = l_skb->len - a_skb->len;
+
+ if (copy <= 0 || !tcp_skb_can_collapse_to(a_skb)) {
+ bool first_skb = tcp_rtx_and_write_queues_empty(newsk);
+
+ a_skb = tcp_stream_alloc_skb(newsk,
+ newsk->sk_allocation,
+ first_skb);
+ if (!a_skb) {
+ /* is this the correct free? */
+ bh_unlock_sock(newsk);
+ sk_free(newsk);
+ return NULL;
+ }
+
+ tcp_skb_entail(newsk, a_skb);
+ }
+ copy = min_t(int, l_skb->len, skb_tailroom(a_skb));
+ skb_put_data(a_skb, l_skb->data, copy);
+
+ TCP_SKB_CB(a_skb)->end_seq += copy;
+
+ a_seq += l_skb->len;
+
+ if (treq->tfo_listener)
+ seq = a_seq;
+
+ /* assumes only one skb on the listen write queue */
+ }
+
+ newtp->snd_sml = seq;
+ WRITE_ONCE(newtp->snd_nxt, a_seq);
+ newtp->snd_up = n_seq;
INIT_LIST_HEAD(&newtp->tsq_node);
INIT_LIST_HEAD(&newtp->tsorted_sent_queue);
@@ -567,7 +613,9 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
newtp->total_retrans = req->num_retrans;
tcp_init_xmit_timers(newsk);
- WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1);
+
+ newtp->pushed_seq = n_seq;
+ WRITE_ONCE(newtp->write_seq, a_seq);
if (sock_flag(newsk, SOCK_KEEPOPEN))
tcp_reset_keepalive_timer(newsk, keepalive_time_when(newtp));
--
2.49.0
^ permalink raw reply related
* [PATCH net-next v3 3/6] tcp: fastopen: add write-data to fastopen synack packet
From: Jeremy Harris @ 2025-06-09 16:05 UTC (permalink / raw)
To: netdev; +Cc: linux-api, edumazet, ncardwell, Jeremy Harris
In-Reply-To: <cover.1749466540.git.jgh@exim.org>
While building the synack packet, for a fastopen socket
copy data from write queue to the packet.
Move the data from write queue to retransmit queue.
Signed-off-by: Jeremy Harris <jgh@exim.org>
---
net/ipv4/tcp_output.c | 32 ++++++++++++++++++++++++++++++--
1 file changed, 30 insertions(+), 2 deletions(-)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 3ac8d2d17e1f..c50553c1c795 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3702,7 +3702,7 @@ int tcp_send_synack(struct sock *sk)
/**
* tcp_make_synack - Allocate one skb and build a SYNACK packet.
- * @sk: listener socket
+ * @sk: listener socket (or child socket for fastopen)
* @dst: dst entry attached to the SYNACK. It is consumed and caller
* should not use it again.
* @req: request_sock pointer
@@ -3719,6 +3719,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
struct inet_request_sock *ireq = inet_rsk(req);
const struct tcp_sock *tp = tcp_sk(sk);
struct tcp_out_options opts;
+ struct sock *fastopen_sk = (struct sock *)sk;
struct tcp_key key = {};
struct sk_buff *skb;
int tcp_header_size;
@@ -3748,7 +3749,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
* cpu might call us concurrently.
* sk->sk_wmem_alloc in an atomic, we can promote to rw.
*/
- skb_set_owner_w(skb, (struct sock *)sk);
+ skb_set_owner_w(skb, fastopen_sk);
break;
}
skb_dst_set(skb, dst);
@@ -3831,6 +3832,33 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
th->window = htons(min(req->rsk_rcv_wnd, 65535U));
tcp_options_write(th, NULL, tcp_rsk(req), &opts, &key);
th->doff = (tcp_header_size >> 2);
+
+ /* If this is a FASTOPEN, and there is write-data on the accept socket,
+ * re-copy it to the synack segment. If not FASTOPEN. any data waits
+ * until 3rd-ack arrival.
+ */
+
+ if (synack_type == TCP_SYNACK_FASTOPEN &&
+ !skb_queue_empty(&sk->sk_write_queue)) {
+ struct sk_buff *a_skb = tcp_write_queue_tail(sk);
+ int copy = min_t(int, a_skb->len, skb_tailroom(skb));
+
+ skb_put_data(skb, a_skb->data, copy);
+ TCP_SKB_CB(skb)->end_seq += copy;
+
+ tcp_skb_pcount_set(a_skb, 1);
+ WRITE_ONCE(tcp_sk(fastopen_sk)->write_seq,
+ TCP_SKB_CB(a_skb)->end_seq);
+
+ skb_set_delivery_time(a_skb, now, SKB_CLOCK_MONOTONIC);
+
+ /* Move the data to the retransmit queue.
+ * Code elsewhere implies this is a full child socket and
+ * can be treated as writeable - permitting the cast.
+ */
+ tcp_event_new_data_sent(fastopen_sk, a_skb);
+ }
+
TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
/* Okay, we have all we need - do the md5 hash if needed */
--
2.49.0
^ permalink raw reply related
* [PATCH net-next v3 4/6] tcp: transmit any pending data on receipt of 3rd-ack
From: Jeremy Harris @ 2025-06-09 16:05 UTC (permalink / raw)
To: netdev; +Cc: linux-api, edumazet, ncardwell, Jeremy Harris
In-Reply-To: <cover.1749466540.git.jgh@exim.org>
For the non-fastopen case of prelaod, when the 3rd-ack arrives there
will be data on the write queue. Transmit it immediately
by allowing the SYN_RECV state to run the xmit-recovery code.
Signed-off-by: Jeremy Harris <jgh@exim.org>
---
net/ipv4/tcp_input.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 8ec92dec321a..345a08baaf02 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3900,7 +3900,8 @@ static void tcp_xmit_recovery(struct sock *sk, int rexmit)
{
struct tcp_sock *tp = tcp_sk(sk);
- if (rexmit == REXMIT_NONE || sk->sk_state == TCP_SYN_SENT)
+ if ((rexmit == REXMIT_NONE && sk->sk_state != TCP_SYN_RECV) ||
+ sk->sk_state == TCP_SYN_SENT)
return;
if (unlikely(rexmit == REXMIT_NEW)) {
--
2.49.0
^ permalink raw reply related
* [PATCH net-next v3 5/6] tcp: fastopen: retransmit data when only the SYN of a synack-with-data is acked
From: Jeremy Harris @ 2025-06-09 16:05 UTC (permalink / raw)
To: netdev; +Cc: linux-api, edumazet, ncardwell, Jeremy Harris
In-Reply-To: <cover.1749466540.git.jgh@exim.org>
A corner-case for the 3rd-ack after a data-on-synack is for only
the SYN to be acked. Handle this by, in ack processing, when in
SYN_RECV state (the state is not yet updated to ESTABLISHED)
marking the retransmit-queue sk_buff as having been lost.
Signed-off-by: Jeremy Harris <jgh@exim.org>
---
net/ipv4/tcp_input.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 345a08baaf02..a53021edddd5 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4069,6 +4069,18 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
&rexmit);
}
+ /* On receiving a 3rd-ack, if we never sent a packet via
+ * the normal means (which counts them), yet there is data
+ * remaining for retransmit, it was data-on-synack not acked;
+ * mark the skb for retransmission.
+ */
+ if (sk->sk_state == TCP_SYN_RECV && tp->segs_out == 0) {
+ struct sk_buff *skb = tcp_rtx_queue_head(sk);
+
+ if (skb)
+ tcp_mark_skb_lost(sk, skb);
+ }
+
/* If needed, reset TLP/RTO timer when RACK doesn't set. */
if (flag & FLAG_SET_XMIT_TIMER)
tcp_set_xmit_timer(sk);
--
2.49.0
^ permalink raw reply related
* [PATCH net-next v3 6/6] tcp: fastopen: extend retransmit-queue trimming to handle linear sk_buff
From: Jeremy Harris @ 2025-06-09 16:05 UTC (permalink / raw)
To: netdev; +Cc: linux-api, edumazet, ncardwell, Jeremy Harris
In-Reply-To: <cover.1749466540.git.jgh@exim.org>
A corner-case for the 3rd-ack after a data-on-synack is for
some but not all of the data to be acked. Support this by
adding to the retransmit-queue trim routine to handle a
linear sk_buff.
Signed-off-by: Jeremy Harris <jgh@exim.org>
---
net/ipv4/tcp_output.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c50553c1c795..bff5934ff04b 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1708,8 +1708,22 @@ static int __pskb_trim_head(struct sk_buff *skb, int len)
struct skb_shared_info *shinfo;
int i, k, eat;
- DEBUG_NET_WARN_ON_ONCE(skb_headlen(skb));
- eat = len;
+ eat = skb_headlen(skb);
+ if (unlikely(eat)) {
+ if (len < eat)
+ eat = len;
+ skb->head += eat;
+ skb->len -= eat;
+ if (skb->data_len)
+ skb->data_len -= eat;
+
+ eat = len - eat;
+ if (eat == 0)
+ return len;
+ } else {
+ eat = len;
+ }
+
k = 0;
shinfo = skb_shinfo(skb);
for (i = 0; i < shinfo->nr_frags; i++) {
--
2.49.0
^ permalink raw reply related
* Re: [PATCH net-next v3 2/6] tcp: copy write-data from listen socket to accept child socket
From: Eric Dumazet @ 2025-06-09 16:26 UTC (permalink / raw)
To: Jeremy Harris; +Cc: netdev, linux-api, ncardwell
In-Reply-To: <838b683c8a47d7df158c6a5da440f38b38096068.1749466540.git.jgh@exim.org>
On Mon, Jun 9, 2025 at 9:05 AM Jeremy Harris <jgh@exim.org> wrote:
>
> Set the request_sock flag for fastopen earlier, making it available
> to the af_ops SYN-handler function.
>
> In that function copy data from the listen socket write queue into an
> sk_buff, allocating if needed and adding to the write queue of the
> newly-created child socket.
> Set sequence number values depending on the fastopen status.
>
> Signed-off-by: Jeremy Harris <jgh@exim.org>
> ---
> net/ipv4/tcp_fastopen.c | 3 ++-
> net/ipv4/tcp_ipv4.c | 4 +--
> net/ipv4/tcp_minisocks.c | 58 ++++++++++++++++++++++++++++++++++++----
> 3 files changed, 57 insertions(+), 8 deletions(-)
>
> diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
> index 9b83d639b5ac..03a86d0b87ba 100644
> --- a/net/ipv4/tcp_fastopen.c
> +++ b/net/ipv4/tcp_fastopen.c
> @@ -245,6 +245,8 @@ static struct sock *tcp_fastopen_create_child(struct sock *sk,
> struct sock *child;
> bool own_req;
>
> + tcp_rsk(req)->tfo_listener = true;
> +
> child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
> NULL, &own_req);
> if (!child)
> @@ -261,7 +263,6 @@ static struct sock *tcp_fastopen_create_child(struct sock *sk,
> tp = tcp_sk(child);
>
> rcu_assign_pointer(tp->fastopen_rsk, req);
> - tcp_rsk(req)->tfo_listener = true;
>
> /* RFC1323: The window in SYN & SYN/ACK segments is never
> * scaled. So correct it appropriately.
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index 6a14f9e6fef6..e488effdbdb2 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1747,8 +1747,8 @@ EXPORT_IPV6_MOD(tcp_v4_conn_request);
>
>
> /*
> - * The three way handshake has completed - we got a valid synack -
> - * now create the new socket.
> + * The three way handshake has completed - we got a valid synack
> + * (or a FASTOPEN syn) - now create the new socket.
> */
> struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
> struct request_sock *req,
> diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
> index 43d7852ce07e..d471531b4a78 100644
> --- a/net/ipv4/tcp_minisocks.c
> +++ b/net/ipv4/tcp_minisocks.c
> @@ -529,7 +529,7 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
> struct inet_connection_sock *newicsk;
> const struct tcp_sock *oldtp;
> struct tcp_sock *newtp;
> - u32 seq;
> + u32 seq, a_seq, n_seq;
>
> if (!newsk)
> return NULL;
> @@ -550,9 +550,55 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
> newtp->segs_in = 1;
>
> seq = treq->snt_isn + 1;
> - newtp->snd_sml = newtp->snd_una = seq;
> - WRITE_ONCE(newtp->snd_nxt, seq);
> - newtp->snd_up = seq;
> + n_seq = seq;
> + a_seq = seq;
> + newtp->write_seq = seq;
> + newtp->snd_una = seq;
> +
> + /* If there is write-data sitting on the listen socket, copy it to
> + * the accept socket. If FASTOPEN we will send it on the synack,
> + * otherwise it sits there until 3rd-ack arrives.
> + */
> +
> + if (unlikely(!skb_queue_empty(&sk->sk_write_queue))) {
> + struct sk_buff *l_skb = tcp_send_head(sk),
> + *a_skb = tcp_write_queue_tail(newsk);
> + ssize_t copy = 0;
> +
> + if (a_skb)
> + copy = l_skb->len - a_skb->len;
> +
> + if (copy <= 0 || !tcp_skb_can_collapse_to(a_skb)) {
> + bool first_skb = tcp_rtx_and_write_queues_empty(newsk);
> +
> + a_skb = tcp_stream_alloc_skb(newsk,
> + newsk->sk_allocation,
> + first_skb);
> + if (!a_skb) {
> + /* is this the correct free? */
> + bh_unlock_sock(newsk);
> + sk_free(newsk);
> + return NULL;
> + }
> +
> + tcp_skb_entail(newsk, a_skb);
> + }
> + copy = min_t(int, l_skb->len, skb_tailroom(a_skb));
> + skb_put_data(a_skb, l_skb->data, copy);
TCP stack no longer puts payload in skb->head. This caused many
issues, trust me.
Please do not try to bring this back.
Also I see no locking there, this is racy with another thread trying
to sendmsg() data to the listener.
Honestly, I do not like this series at all adding cost in TCP fast
path for a very narrow use-case.
^ permalink raw reply
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