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

[Mark Brown]

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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