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References: <20240523215029.4160518-1-bjohannesmeyer@gmail.com>
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From: Alexander Potapenko <glider@google.com>
Date: Fri, 24 May 2024 10:28:05 +0200
Message-ID: <CAG_fn=XR6KVQ=DbKZW3kNXsCHgULm2J7i6GCm8CZUjpjuk-d2A@mail.gmail.com>
Subject: Re: [PATCH] x86: kmsan: Fix hook for unaligned accesses
To: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
Cc: Marco Elver <elver@google.com>, Dmitry Vyukov <dvyukov@google.com>, 
	Andrew Morton <akpm@linux-foundation.org>, kasan-dev@googlegroups.com, linux-mm@kvack.org, 
	linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>, 
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, 
	Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org, 
	"H . Peter Anvin" <hpa@zytor.com>
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On Thu, May 23, 2024 at 11:50=E2=80=AFPM Brian Johannesmeyer
<bjohannesmeyer@gmail.com> wrote:
>
> When called with a 'from' that is not 4-byte-aligned,
> string_memcpy_fromio() calls the movs() macro to copy the first few bytes=
,
> so that 'from' becomes 4-byte-aligned before calling rep_movs(). This
> movs() macro modifies 'to', and the subsequent line modifies 'n'.
>
> As a result, on unaligned accesses, kmsan_unpoison_memory() uses the
> updated (aligned) values of 'to' and 'n'. Hence, it does not unpoison the
> entire region.
>
> This patch saves the original values of 'to' and 'n', and passes those to
> kmsan_unpoison_memory(), so that the entire region is unpoisoned.

Nice catch! Does it fix any known bugs?

> Signed-off-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
Reviewed-by: Alexander Potapenko <glider@google.com>