Re: BUG: KASAN: stack-out-of-bounds in unwind_next_frame+0x1df5/0x2650

[Ivan Babrou <ivan@cloudflare.com>]

On Wed, Feb 3, 2021 at 7:10 PM Josh Poimboeuf <jpoimboe@redhat.com> wrote:

> This line gives a big clue:
>
>   [160676.608966][    C4] RIP: 0010:0xffffffffc17d814c
>
> That address, without a function name, most likely means that it was
> running in some generated code (mostly likely BPF) when it got
> interrupted.

We do have eBPF/XDP in our environment.

> Right now, the ORC unwinder tries to fall back to frame pointers when it
> encounters generated code:
>
>         orc = orc_find(state->signal ? state->ip : state->ip - 1);
>         if (!orc)
>                 /*
>                  * As a fallback, try to assume this code uses a frame pointer.
>                  * This is useful for generated code, like BPF, which ORC
>                  * doesn't know about.  This is just a guess, so the rest of
>                  * the unwind is no longer considered reliable.
>                  */
>                 orc = &orc_fp_entry;
>                 state->error = true;
>         }
>
> Because the ORC unwinder is guessing from that point onward, it's
> possible for it to read the KASAN stack redzone, if the generated code
> hasn't set up frame pointers.  So the best fix may be for the unwinder
> to just always bypass KASAN when reading the stack.
>
> The unwinder has a mechanism for detecting and warning about
> out-of-bounds, and KASAN is short-circuiting that.
>
> This should hopefully get rid of *all* the KASAN unwinder warnings, both
> crypto and networking.

It definitely worked on my dm-crypt case, and I've tried it without
your previous AVX related patch. I will apply it to our tree and
deploy to the staging KASAN environment to see how it fares with
respect to networking stacks. Feel free to ping me if I don't get back
to you with the results on Monday.

Thanks for looking into this!