Messages in this thread | | | From | Aleksandr Nogikh <> | Date | Wed, 16 Feb 2022 17:09:03 +0100 | Subject | Re: [syzbot] riscv/fixes boot error: can't ssh into the instance |
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On Wed, Feb 16, 2022 at 12:56 PM Dmitry Vyukov <dvyukov@google.com> wrote: > > On Wed, 16 Feb 2022 at 12:47, Aleksandr Nogikh <nogikh@google.com> wrote: > > > > On Wed, Feb 16, 2022 at 11:37 AM Aleksandr Nogikh <nogikh@google.com> wrote: > > > > > > Hi Alex, > > > > > > On Wed, Feb 16, 2022 at 5:14 AM Alexandre Ghiti <alex@ghiti.fr> wrote: > > > > > > > > Hi Dmitry, > > > > > > > > On 2/15/22 18:12, Dmitry Vyukov wrote: > > > > > On Wed, 2 Feb 2022 at 14:18, Alexandre Ghiti > > > > > <alexandre.ghiti@canonical.com> wrote: > > > > >> Hi Aleksandr, > > > > >> > > > > >> On Wed, Feb 2, 2022 at 12:08 PM Aleksandr Nogikh <nogikh@google.com> wrote: > > > > >>> Hello, > > > > >>> > > > > >>> syzbot has already not been able to fuzz its RISC-V instance for 97 > > > > >> That's a longtime, I'll take a look more regularly. > > > > >> > > > > >>> days now because the compiled kernel cannot boot. I bisected the issue > > > > >>> to the following commit: > > > > >>> > > > > >>> commit 54c5639d8f507ebefa814f574cb6f763033a72a5 > > > > >>> Author: Alexandre Ghiti <alexandre.ghiti@canonical.com> > > > > >>> Date: Fri Oct 29 06:59:27 2021 +0200 > > > > >>> > > > > >>> riscv: Fix asan-stack clang build > > > > >>> > > > > >>> Apparently, the problem appears on GCC-built RISC-V kernels with KASAN > > > > >>> enabled. In the previous message syzbot mentions > > > > >>> "riscv64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU > > > > >>> Binutils for Debian) 2.35.2", but the issue also reproduces finely on > > > > >>> a newer GCC compiler: "riscv64-linux-gnu-gcc (Debian 11.2.0-10) > > > > >>> 11.2.0, GNU ld (GNU Binutils for Debian) 2.37". > > > > >>> For convenience, I also duplicate the .config file from the bot's > > > > >>> message: https://syzkaller.appspot.com/x/.config?x=522544a2e0ef2a7d > > > > >>> > > > > >>> Can someone with KASAN and RISC-V expertise please take a look? > > > > >> I'll take a look at that today. > > > > >> > > > > >> Thanks for reporting the issue, > > > > > > > > > > > > > I took a quick look, not enough to fix it but I know the issue comes > > > > from the inline instrumentation, I have no problem with the outline > > > > instrumentation. I need to find some cycles to work on this, my goal is > > > > to fix this for 5.17. > > > > > > Thanks for the update! > > > > > > Can you please share the .config with which you tested the outline > > > instrumentation? > > > I updated the syzbot config to use KASAN_OUTLINE instead of KASAN_INLINE, > > > but it still does not boot :( > > > > > > Here's what I used: > > > https://gist.github.com/a-nogikh/279c85c2d24f47efcc3e865c08844138 > > > > Update: it doesn't boot with that big config, but boots if I generate > > a simple one with KASAN_OUTLINE: > > > > make defconfig ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- > > ./scripts/config -e KASAN -e KASAN_OUTLINE > > make olddefconfig ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- > > > > And it indeed doesn't work if I use KASAN_INLINE. > > It may be an issue with code size. Full syzbot config + KASAN + KCOV > produce hugely massive .text. It may be hitting some limitation in the > bootloader/kernel bootstrap code.
I bisected the difference between the config we use on syzbot and the simple one that was generated like I described above. Turns out that it's the DEBUG_VIRTUAL config that makes the difference.
make defconfig ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- ./scripts/config -e KASAN -e KASAN_OUTLINE -e DEBUG_VIRTUAL make olddefconfig ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu-
And the resulting kernel does not boot. My env: the `riscv/fixes` branch, commit 6df2a016c0c8a3d0933ef33dd192ea6606b115e3, qemu 6.2.0.
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