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

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Message-ID: <CA+zEjCsQPVYSV7CdhKnvjujXkMXuRQd=VPok1awb20xifYmidw@mail.gmail.com>
Date:   Fri, 25 Feb 2022 15:15:29 +0100
From:   Alexandre Ghiti <alexandre.ghiti@...onical.com>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     Marco Elver <elver@...gle.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andrey Ryabinin <ryabinin.a.a@...il.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,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH -fixes v3 0/6] Fixes KASAN and other along the way

On Fri, Feb 25, 2022 at 3:10 PM Alexander Potapenko <glider@...gle.com> wrote:
>
>
>
> On Fri, Feb 25, 2022 at 3:04 PM Alexandre Ghiti <alexandre.ghiti@...onical.com> wrote:
>>
>> 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!
>>
>
> The problem does not reproduce for me with GCC 11.2.0: kernels built with both [1] and [2] are bootable.

Do you mean you reach userspace? Because my image boots too, and fails
at some point:

[    0.000150] sched_clock: 64 bits at 10MHz, resolution 100ns, wraps
every 4398046511100ns
[    0.015847] Console: colour dummy device 80x25
[    0.016899] printk: console [tty0] enabled
[    0.020326] printk: bootconsole [ns16550a0] disabled

It traps here.

> FWIW here is how I run them:
>
> qemu-system-riscv64 -m 2048 -smp 1 -nographic -no-reboot \
>   -device virtio-rng-pci -machine virt -device \
>   virtio-net-pci,netdev=net0 -netdev \
>   user,id=net0,restrict=on,hostfwd=tcp:127.0.0.1:12529-:22 -device \
>   virtio-blk-device,drive=hd0 -drive \
>   file=${IMAGE},if=none,format=raw,id=hd0 -snapshot \
>   -kernel ${KERNEL_SRC_DIR}/arch/riscv/boot/Image -append "root=/dev/vda
>   console=ttyS0 earlyprintk=serial"
>
>
>>
>> Thanks for the tips,
>>
>> Alex
>
>
>
> --
> Alexander Potapenko
> Software Engineer
>
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