linux-kernel - Re: [PATCH v21 4/8] fork: Add shadow stack support to clone3()

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aMv9XRq_sAQbQwjI@willie-the-truck>
Date: Thu, 18 Sep 2025 13:38:53 +0100
From: Will Deacon <will@...nel.org>
To: Mark Brown <broonie@...nel.org>, brauner@...nel.org
Cc: "Rick P. Edgecombe" <rick.p.edgecombe@...el.com>,
	Deepak Gupta <debug@...osinc.com>,
	Szabolcs Nagy <Szabolcs.Nagy@....com>,
	"H.J. Lu" <hjl.tools@...il.com>,
	Florian Weimer <fweimer@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>, jannh@...gle.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Yury Khrustalev <yury.khrustalev@....com>,
	Wilco Dijkstra <wilco.dijkstra@....com>,
	linux-kselftest@...r.kernel.org, linux-api@...r.kernel.org,
	Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v21 4/8] fork: Add shadow stack support to clone3()

On Tue, Sep 16, 2025 at 12:12:09AM +0100, Mark Brown wrote:
> Unlike with the normal stack there is no API for configuring the shadow
> stack for a new thread, instead the kernel will dynamically allocate a
> new shadow stack with the same size as the normal stack. This appears to
> be due to the shadow stack series having been in development since
> before the more extensible clone3() was added rather than anything more
> deliberate.
> 
> Add a parameter to clone3() specifying a shadow stack pointer to use
> for the new thread, this is inconsistent with the way we specify the
> normal stack but during review concerns were expressed about having to
> identify where the shadow stack pointer should be placed especially in
> cases where the shadow stack has been previously active.  If no shadow
> stack is specified then the existing implicit allocation behaviour is
> maintained.
> 
> If a shadow stack pointer is specified then it is required to have an
> architecture defined token placed on the stack, this will be consumed by
> the new task, the shadow stack is specified by pointing to this token.  If
> no valid token is present then this will be reported with -EINVAL.  This
> token prevents new threads being created pointing at the shadow stack of
> an existing running thread.  On architectures with support for userspace
> pivoting of shadow stacks it is expected that the same format and placement
> of tokens will be used, this is the case for arm64 and x86.
> 
> If the architecture does not support shadow stacks the shadow stack
> pointer must be not be specified, architectures that do support the
> feature are expected to enforce the same requirement on individual
> systems that lack shadow stack support.
> 
> Update the existing arm64 and x86 implementations to pay attention to
> the newly added arguments, in order to maintain compatibility we use the
> existing behaviour if no shadow stack is specified. Since we are now
> using more fields from the kernel_clone_args we pass that into the
> shadow stack code rather than individual fields.
> 
> Portions of the x86 architecture code were written by Rick Edgecombe.
> 
> Acked-by: Yury Khrustalev <yury.khrustalev@....com>
> Reviewed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> Signed-off-by: Mark Brown <broonie@...nel.org>
> ---
>  arch/arm64/mm/gcs.c              | 47 +++++++++++++++++++-
>  arch/x86/include/asm/shstk.h     | 11 +++--
>  arch/x86/kernel/process.c        |  2 +-
>  arch/x86/kernel/shstk.c          | 53 ++++++++++++++++++++---
>  include/asm-generic/cacheflush.h | 11 +++++
>  include/linux/sched/task.h       | 17 ++++++++
>  include/uapi/linux/sched.h       |  9 ++--
>  kernel/fork.c                    | 93 ++++++++++++++++++++++++++++++++++------
>  8 files changed, 217 insertions(+), 26 deletions(-)

It would be great if Christian could give this the thumbs up, given that
it changes clone3(). I think the architecture parts are all ready at this
point.

Will