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Message-ID: <Zv_PFVffwIkKevzE@arm.com>
Date: Fri, 4 Oct 2024 14:18:45 +0300
From: Catalin Marinas <catalin.marinas@....com>
To: Mark Brown <broonie@...nel.org>
Cc: Will Deacon <will@...nel.org>, Jonathan Corbet <corbet@....net>,
Andrew Morton <akpm@...ux-foundation.org>,
Marc Zyngier <maz@...nel.org>,
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Subject: Re: [PATCH v13 22/40] arm64/gcs: Ensure that new threads have a GCS
On Tue, Oct 01, 2024 at 11:59:01PM +0100, Mark Brown wrote:
> When a new thread is created by a thread with GCS enabled the GCS needs
> to be specified along with the regular stack.
>
> Unfortunately plain clone() is not extensible and existing clone3()
> users will not specify a stack so all existing code would be broken if
> we mandated specifying the stack explicitly. For compatibility with
> these cases and also x86 (which did not initially implement clone3()
> support for shadow stacks) if no GCS is specified we will allocate one
> so when a thread is created which has GCS enabled allocate one for it.
> We follow the extensively discussed x86 implementation and allocate
> min(RLIMIT_STACK/2, 2G). Since the GCS only stores the call stack and not
> any variables this should be more than sufficient for most applications.
>
> GCSs allocated via this mechanism will be freed when the thread exits.
I think Szabolcs mentioned a GCS leak with v12:
https://lore.kernel.org/r/ZtrihWQFyb2/XrQV@arm.com
(and in some private messages IIRC)
Has this been identified? The changelog only mentions a leak in v8.
--
Catalin
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