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Date:   Fri, 11 Aug 2023 17:38:24 +0100
From:   Catalin Marinas <catalin.marinas@arm.com>
To:     Mark Brown <broonie@kernel.org>
Cc:     Will Deacon <will@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Marc Zyngier <maz@kernel.org>,
        Oliver Upton <oliver.upton@linux.dev>,
        James Morse <james.morse@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
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        Shuah Khan <shuah@kernel.org>,
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Subject: Re: [PATCH v4 21/36] arm64/mm: Implement map_shadow_stack()
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On Mon, Aug 07, 2023 at 11:00:26PM +0100, Mark Brown wrote:
> As discussed extensively in the changelog for the addition of this
> syscall on x86 ("x86/shstk: Introduce map_shadow_stack syscall") the
> existing mmap() and madvise() syscalls do not map entirely well onto the
> security requirements for guarded control stacks since they lead to
> windows where memory is allocated but not yet protected or stacks which
> are not properly and safely initialised. Instead a new syscall
> map_shadow_stack() has been defined which allocates and initialises a
> shadow stack page.

I guess I need to read the x86 discussion after all ;).

Given that we won't have an mmap(PROT_SHADOW_STACK), are we going to
have restrictions on mprotect()? E.g. it would be useful to reject a
PROT_EXEC on the shadow stack.

-- 
Catalin