[syzbot] riscv/fixes boot error: can't ssh into the instance

Alexandre Ghiti alexandre.ghiti at canonical.com
Fri Feb 18 05:45:04 PST 2022 

Hi Aleksandr,

On Thu, Feb 17, 2022 at 6:08 PM Aleksandr Nogikh <nogikh at google.com> wrote:
>
> Hi Alex,
>
> On Thu, Feb 17, 2022 at 5:53 PM Alexandre Ghiti
> <alexandre.ghiti at canonical.com> wrote:
> >
> > Aleksandr,
> >
> > On Wed, Feb 16, 2022 at 5:58 PM Alexandre Ghiti
> > <alexandre.ghiti at canonical.com> wrote:
> > >
> > > First, thank you for working on this.
> > >
> > > On Wed, Feb 16, 2022 at 5:17 PM Aleksandr Nogikh <nogikh at google.com> wrote:
> > > >
> > > > If I use just defconfig + DEBUG_VIRTUAL, without any KASAN, it begins
> > > > to boot, but overwhelms me with tons of `virt_to_phys used for
> > > > non-linear address:` errors.
> > > >
> > > > Like that
> > > >
> > > > [    2.701271] virt_to_phys used for non-linear address:
> > > > 00000000b59e31b6 (0xffffffff806c2000)
> > > > [    2.701727] WARNING: CPU: 0 PID: 1 at arch/riscv/mm/physaddr.c:16
> > > > __virt_to_phys+0x7e/0x86
> > > > [    2.702207] Modules linked in:
> > > > [    2.702393] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G        W
> > > >   5.17.0-rc1 #1
> > > > [    2.702806] Hardware name: riscv-virtio,qemu (DT)
> > > > [    2.703051] epc : __virt_to_phys+0x7e/0x86
> > > > [    2.703298]  ra : __virt_to_phys+0x7e/0x86
> > > > [    2.703547] epc : ffffffff80008448 ra : ffffffff80008448 sp :
> > > > ffff8f800021bde0
> > > > [    2.703977]  gp : ffffffff80ed9b30 tp : ffffaf8001230000 t0 :
> > > > ffffffff80eea56f
> > > > [    2.704704]  t1 : ffffffff80eea560 t2 : 0000000000000000 s0 :
> > > > ffff8f800021be00
> > > > [    2.705153]  s1 : ffffffff806c2000 a0 : 000000000000004f a1 :
> > > > ffffffff80e723d8
> > > > [    2.705555]  a2 : 0000000000000010 a3 : fffffffffffffffe a4 :
> > > > 0000000000000000
> > > > [    2.706027]  a5 : 0000000000000000 a6 : 0000000000000005 a7 :
> > > > ffffffffffffffff
> > > > [    2.706474]  s2 : ffffffff80b80b08 s3 : 00000000000000c2 s4 :
> > > > ffffffff806c2000
> > > > [    2.706891]  s5 : ffffffff80edba10 s6 : ffffffff80edb960 s7 :
> > > > 0000000000000001
> > > > [    2.707290]  s8 : 00000000000000ff s9 : ffffffff80b80b40 s10:
> > > > 00000000000000cc
> > > > [    2.707689]  s11: ffffaf807e1fcf00 t3 : 0000000000000076 t4 :
> > > > ffffffffffffffff
> > > > [    2.708092]  t5 : 00000000000001f2 t6 : ffff8f800021bb48
> > > > [    2.708433] status: 0000000000000120 badaddr: 0000000000000000
> > > > cause: 0000000000000003
> > > > [    2.708919] [<ffffffff8011416a>] free_reserved_area+0x72/0x19a
> > > > [    2.709296] [<ffffffff80003a5a>] free_initmem+0x6c/0x7c
> > > > [    2.709648] [<ffffffff805f60c8>] kernel_init+0x3a/0x10a
> > > > [    2.709993] [<ffffffff80002fda>] ret_from_exception+0x0/0xc
> > > > [    2.710310] ---[ end trace 0000000000000000 ]---
> > > >
> > >
> > > I was able to reproduce this: the first one regarding init_zero_pfn is
> > > legit but not wrong, I have to check when it was introduced and how to
> > > fix this.
> > > Regarding the huge batch that follows, at first sight, I would say
> > > this is linked to my sv48 patchset but that does not seem important as
> > > the address is a kernel mapping address so the use of virt_to_phys is
> > > right.
> > >
> > > > On Wed, Feb 16, 2022 at 5:09 PM Aleksandr Nogikh <nogikh at google.com> wrote:
> > > > >
> > > > > On Wed, Feb 16, 2022 at 12:56 PM Dmitry Vyukov <dvyukov at google.com> wrote:
> > > > > >
> > > > > > On Wed, 16 Feb 2022 at 12:47, Aleksandr Nogikh <nogikh at google.com> wrote:
> > > > > > >
> > > > > > > On Wed, Feb 16, 2022 at 11:37 AM Aleksandr Nogikh <nogikh at google.com> wrote:
> > > > > > > >
> > > > > > > > Hi Alex,
> > > > > > > >
> > > > > > > > On Wed, Feb 16, 2022 at 5:14 AM Alexandre Ghiti <alex at 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 at canonical.com> wrote:
> > > > > > > > > >> Hi Aleksandr,
> > > > > > > > > >>
> > > > > > > > > >> On Wed, Feb 2, 2022 at 12:08 PM Aleksandr Nogikh <nogikh at 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 at 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 took a quick glance and it traps on a KASAN address that is not
> > > mapped, either because it is too soon or because the mapping failed
> > > somehow.
> > >
> > > I'll definitely dive into that tomorrow, sorry for being slow here and
> > > thanks again for all your work, that helps a lot.
> > >
> > > Thanks,
> > >
> > > Alex
> > >
> > > > >
> > > > > 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.
> >
> > I fixed a few things today: KASAN + SPARSE_VMEMMAP, DEBUG_VIRTUAL and
> > maybe KASAN  + KCOV.
> >
> > With those small fixes, I was able to boot your large dotconfig with
> > KASAN_OUTLINE, the inline version still fails, this is my next target
> > :)
> > I'll push that tomorrow!
>
> Awesome, thank you very much!
> Looking forward to finally seeing the instance run :)

I sent a patchset which should fix your config with *outline* instrumentation.

However, as you'll see in the cover letter, I have an issue with
another KASAN config and if you can take a look at the stacktrace and
see if that rings a bell, that would be great.

Don't hesitate next time to ping me when the riscv syzbot instance fails :)

Alex


>
> --
> Best Regards,
> Aleksandr
>
> >
> > Thanks again,
> >
> > Alex

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