Re: [PATCH] mm/page_alloc: silence a KASAN false positive

[Alexander Potapenko]

On Wed, Jun 10, 2020 at 7:55 AM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>
> On Wed, Jun 10, 2020 at 7:22 AM Qian Cai <cai@xxxxxx> wrote:
> >
> > kernel_init_free_pages() will use memset() on s390 to clear all pages
> > from kmalloc_order() which will override KASAN redzones because a
> > redzone was setup from the end of the allocation size to the end of the
> > last page. Silence it by not reporting it there. An example of the
> > report is,
>
> Interesting. The reason why we did not hit it on x86_64 is because
> clear_page is implemented in asm (arch/x86/lib/clear_page_64.S) and
> thus is not instrumented. Arm64 probably does the same. However, on
> s390 clear_page is defined to memset.

Can we define it to __memset() instead?
__memset() is supposed to be ignored by KASAN, e.g. KASAN runtime uses
it in the places where we don't care about bugs.