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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>,
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	Eric Biederman <ebiederm@xmission.com>,
	Kees Cook <keescook@chromium.org>, Shuah Khan <shuah@kernel.org>,
	"Rick P. Edgecombe" <rick.p.edgecombe@intel.com>,
	Deepak Gupta <debug@rivosinc.com>, Ard Biesheuvel <ardb@kernel.org>,
	Szabolcs Nagy <Szabolcs.Nagy@arm.com>,
	"H.J. Lu" <hjl.tools@gmail.com>,
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Subject: Re: [PATCH v4 21/36] arm64/mm: Implement map_shadow_stack()
Message-ID: <ZNZkADhSnodXuH5F@arm.com>
References: <20230807-arm64-gcs-v4-0-68cfa37f9069@kernel.org>
 <20230807-arm64-gcs-v4-21-68cfa37f9069@kernel.org>
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In-Reply-To: <20230807-arm64-gcs-v4-21-68cfa37f9069@kernel.org>

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