Re: [PATCH] x86: kmsan: Fix hook for unaligned accesses

[Alexander Potapenko]

On Thu, May 23, 2024 at 11:50 PM Brian Johannesmeyer
<bjohannesmeyer@xxxxxxxxx> 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@xxxxxxxxx>
Reviewed-by: Alexander Potapenko <glider@xxxxxxxxxx>