Re: UBSAN: array-index-out-of-bounds in kernel/bpf/arraymap.c:177

[Qian Cai]

On Mon, May 18, 2020 at 7:55 PM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Sun, May 17, 2020 at 7:45 PM Qian Cai <cai@xxxxxx> wrote:
> >
> > With Clang 9.0.1,
> >
> > return array->value + array->elem_size * (index & array->index_mask);
> >
> > but array->value is,
> >
> > char value[0] __aligned(8);
>
> This, and ptrs and pptrs, should be flexible arrays. But they are in a
> union, and unions don't support flexible arrays. Putting each of them
> into anonymous struct field also doesn't work:
>
> /data/users/andriin/linux/include/linux/bpf.h:820:18: error: flexible
> array member in a struct with no named members
>    struct { void *ptrs[] __aligned(8); };
>
> So it probably has to stay this way. Is there a way to silence UBSAN
> for this particular case?

I am not aware of any way to disable a particular function in UBSAN
except for the whole file in kernel/bpf/Makefile,

UBSAN_SANITIZE_arraymap.o := n

If there is no better way to do it, I'll send a patch for it.