linux-kernel - Re: [PATCH -fixes v3 0/6] Fixes KASAN and other along the way

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Date:   Fri, 25 Feb 2022 15:04:18 +0100
From:   Alexandre Ghiti <alexandre.ghiti@...onical.com>
To:     Marco Elver <elver@...gle.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Aleksandr Nogikh <nogikh@...gle.com>,
        Nick Hu <nickhu@...estech.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com
Subject: Re: [PATCH -fixes v3 0/6] Fixes KASAN and other along the way

On Fri, Feb 25, 2022 at 2:06 PM Marco Elver <elver@...gle.com> wrote:
>
> On Fri, 25 Feb 2022 at 13:40, Alexandre Ghiti
> <alexandre.ghiti@...onical.com> wrote:
> >
> > As reported by Aleksandr, syzbot riscv is broken since commit
> > 54c5639d8f50 ("riscv: Fix asan-stack clang build"). This commit actually
> > breaks KASAN_INLINE which is not fixed in this series, that will come later
> > when found.
> >
> > Nevertheless, this series fixes small things that made the syzbot
> > configuration + KASAN_OUTLINE fail to boot.
> >
> > Note that even though the config at [1] boots fine with this series, I
> > was not able to boot the small config at [2] which fails because
> > kasan_poison receives a really weird address 0x4075706301000000 (maybe a
> > kasan person could provide some hint about what happens below in
> > do_ctors -> __asan_register_globals):
>
> asan_register_globals is responsible for poisoning redzones around
> globals. As hinted by 'do_ctors', it calls constructors, and in this
> case a compiler-generated constructor that calls
> __asan_register_globals with metadata generated by the compiler. That
> metadata contains information about global variables. Note, these
> constructors are called on initial boot, but also every time a kernel
> module (that has globals) is loaded.
>
> It may also be a toolchain issue, but it's hard to say. If you're
> using GCC to test, try Clang (11 or later), and vice-versa.

I tried 3 different gcc toolchains already, but that did not fix the
issue. The only thing that worked was setting asan-globals=0 in
scripts/Makefile.kasan, but ok, that's not a fix.
I tried to bisect this issue but our kasan implementation has been
broken quite a few times, so it failed.

I keep digging!

Thanks for the tips,

Alex