[PATCH v5 1/2] string: Add load_unaligned_zeropad() code path to sized_strscpy()

[Catalin Marinas]

On Wed, Apr 02, 2025 at 05:06:59PM -0700, Peter Collingbourne wrote:
> The call to read_word_at_a_time() in sized_strscpy() is problematic
> with MTE because it may trigger a tag check fault when reading
> across a tag granule (16 bytes) boundary. To make this code
> MTE compatible, let's start using load_unaligned_zeropad()
> on architectures where it is available (i.e. architectures that
> define CONFIG_DCACHE_WORD_ACCESS). Because load_unaligned_zeropad()
> takes care of page boundaries as well as tag granule boundaries,
> also disable the code preventing crossing page boundaries when using
> load_unaligned_zeropad().
> 
> Signed-off-by: Peter Collingbourne <pcc at google.com>
> Link: https://linux-review.googlesource.com/id/If4b22e43b5a4ca49726b4bf98ada827fdf755548
> Fixes: 94ab5b61ee16 ("kasan, arm64: enable CONFIG_KASAN_HW_TAGS")
> Cc: stable at vger.kernel.org

Up to you if you want to keep the panic behaviour on unmapped pages.
Either way:

Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>