linux-kernel - Re: [PATCH] arm64: signal: nofpsimd: Do not allocate fp/simd context when not available

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Message-ID: <YhkYbhxA8+IQxVcb@sirena.org.uk>
Date:   Fri, 25 Feb 2022 17:57:02 +0000
From:   Mark Brown <broonie@...nel.org>
To:     David Engraf <david.engraf@...go.com>
Cc:     suzuki.poulose@....com, catalin.marinas@....com, will@...nel.org,
        mark.rutland@....com, elver@...gle.com, ebiederm@...ssion.com,
        seanjc@...gle.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: signal: nofpsimd: Do not allocate fp/simd context
 when not available

On Fri, Feb 25, 2022 at 11:40:08AM +0100, David Engraf wrote:
> Commit 6d502b6ba1b2 ("arm64: signal: nofpsimd: Handle fp/simd context for
> signal frames") introduced saving the fp/simd context for signal handling
> only when support is available. But setup_sigframe_layout() always
> reserves memory for fp/simd context. The additional memory is not touched
> because preserve_fpsimd_context() is not called and thus the magic is
> invalid.
> 
> This may lead to an error when parse_user_sigframe() checks the fp/simd
> area and does not find a valid magic number.

How did you spot this - do you have a system that can reproduce this?
It'd be good to have coverage if there's testing but there's no easily
obtainable userspace that I'm aware of.

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