[syzbot] [arm?] upstream test error: KASAN: invalid-access Write in setup_arch

[Alexander Potapenko]

On Mon, Sep 2, 2024 at 12:03 PM 'Aleksandr Nogikh' via kasan-dev
<kasan-dev at googlegroups.com> wrote:
>
> +kasan-dev
>
> On Sat, Aug 31, 2024 at 7:53 PM 'Marc Zyngier' via syzkaller-bugs
> <syzkaller-bugs at googlegroups.com> wrote:
> >
> > On Fri, 30 Aug 2024 10:52:54 +0100,
> > Will Deacon <will at kernel.org> wrote:
> > >
> > > On Fri, Aug 30, 2024 at 01:35:24AM -0700, syzbot wrote:
> > > > Hello,
> > > >
> > > > syzbot found the following issue on:
> > > >
> > > > HEAD commit:    33faa93bc856 Merge branch kvmarm-master/next into kvmarm-m..
> > > > git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm.git fuzzme
> > >
> > > +Marc, as this is his branch.
> > >
> > > > console output: https://syzkaller.appspot.com/x/log.txt?x=1398420b980000
> > > > kernel config:  https://syzkaller.appspot.com/x/.config?x=2b7b31c9aa1397ca
> > > > dashboard link: https://syzkaller.appspot.com/bug?extid=908886656a02769af987
> > > > compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> > > > userspace arch: arm64
> >
> > As it turns out, this isn't specific to this branch. I can reproduce
> > it with this config on a vanilla 6.10 as a KVM guest. Even worse,
> > compiling with clang results in an unbootable kernel (without any
> > output at all).
> >
> > Mind you, the binary is absolutely massive (130MB with gcc, 156MB with
> > clang), and I wouldn't be surprised if we were hitting some kind of
> > odd limit.
> >
> > > >
> > > > Downloadable assets:
> > > > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/384ffdcca292/non_bootable_disk-33faa93b.raw.xz
> > > > vmlinux: https://storage.googleapis.com/syzbot-assets/9093742fcee9/vmlinux-33faa93b.xz
> > > > kernel image: https://storage.googleapis.com/syzbot-assets/b1f599907931/Image-33faa93b.gz.xz
> > > >
> > > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > > Reported-by: syzbot+908886656a02769af987 at syzkaller.appspotmail.com
> > > >
> > > > Booting Linux on physical CPU 0x0000000000 [0x000f0510]
> > > > Linux version 6.11.0-rc5-syzkaller-g33faa93bc856 (syzkaller at syzkaller) (gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40) #0 SMP PREEMPT now
> > > > random: crng init done
> > > > Machine model: linux,dummy-virt
> > > > efi: UEFI not found.
> > > > NUMA: No NUMA configuration found
> > > > NUMA: Faking a node at [mem 0x0000000040000000-0x00000000bfffffff]
> > > > NUMA: NODE_DATA [mem 0xbfc1d340-0xbfc20fff]
> > > > Zone ranges:
> > > >   DMA      [mem 0x0000000040000000-0x00000000bfffffff]
> > > >   DMA32    empty
> > > >   Normal   empty
> > > >   Device   empty
> > > > Movable zone start for each node
> > > > Early memory node ranges
> > > >   node   0: [mem 0x0000000040000000-0x00000000bfffffff]
> > > > Initmem setup node 0 [mem 0x0000000040000000-0x00000000bfffffff]
> > > > cma: Reserved 32 MiB at 0x00000000bba00000 on node -1
> > > > psci: probing for conduit method from DT.
> > > > psci: PSCIv1.1 detected in firmware.
> > > > psci: Using standard PSCI v0.2 function IDs
> > > > psci: Trusted OS migration not required
> > > > psci: SMC Calling Convention v1.0
> > > > ==================================================================
> > > > BUG: KASAN: invalid-access in smp_build_mpidr_hash arch/arm64/kernel/setup.c:133 [inline]
> > > > BUG: KASAN: invalid-access in setup_arch+0x984/0xd60 arch/arm64/kernel/setup.c:356
> > > > Write of size 4 at addr 03ff800086867e00 by task swapper/0
> > > > Pointer tag: [03], memory tag: [fe]
> > > >
> > > > CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.11.0-rc5-syzkaller-g33faa93bc856 #0
> > > > Hardware name: linux,dummy-virt (DT)
> > > > Call trace:
> > > >  dump_backtrace+0x204/0x3b8 arch/arm64/kernel/stacktrace.c:317
> > > >  show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:324
> > > >  __dump_stack lib/dump_stack.c:93 [inline]
> > > >  dump_stack_lvl+0x260/0x3b4 lib/dump_stack.c:119
> > > >  print_address_description mm/kasan/report.c:377 [inline]
> > > >  print_report+0x118/0x5ac mm/kasan/report.c:488
> > > >  kasan_report+0xc8/0x108 mm/kasan/report.c:601
> > > >  kasan_check_range+0x94/0xb8 mm/kasan/sw_tags.c:84
> > > >  __hwasan_store4_noabort+0x20/0x2c mm/kasan/sw_tags.c:149
> > > >  smp_build_mpidr_hash arch/arm64/kernel/setup.c:133 [inline]
> > > >  setup_arch+0x984/0xd60 arch/arm64/kernel/setup.c:356
> > > >  start_kernel+0xe0/0xff0 init/main.c:926
> > > >  __primary_switched+0x84/0x8c arch/arm64/kernel/head.S:243
> > > >
> > > > The buggy address belongs to stack of task swapper/0
> > > >
> > > > Memory state around the buggy address:
> > > >  ffff800086867c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > > >  ffff800086867d00: 00 fe fe 00 00 00 fe fe fe fe fe fe fe fe fe fe
> > > > >ffff800086867e00: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
> > > >                    ^
> > > >  ffff800086867f00: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
> > > >  ffff800086868000: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
> > > > ==================================================================
> > >
> > > I can't spot the issue here. We have a couple of fixed-length
> > > (4 element) arrays on the stack and they're indexed by a simple loop
> > > counter that runs from 0-3.
> >
> > Having trimmed the config to the extreme, I can only trigger the
> > warning with CONFIG_KASAN_SW_TAGS (CONFIG_KASAN_GENERIC does not
> > scream). Same thing if I use gcc 14.2.0.
> >
> > However, compiling with clang 14 (Debian clang version 14.0.6) does
> > *not* result in a screaming kernel, even with KASAN_SW_TAGS.
> >
> > So I can see two possibilities here:
> >
> > - either gcc is incompatible with KASAN_SW_TAGS and the generic
> >   version is the only one that works
> >
> > - or we have a compiler bug on our hands.
> >
> > Frankly, I can't believe the later, as the code is so daft that I
> > can't imagine gcc getting it *that* wrong.
> >
> > Who knows enough about KASAN to dig into this?

This looks related to Samuel's "arm64: Fix KASAN random tag seed
initialization" patch that landed in August.

I am a bit surprised the bug is reported before the
"KernelAddressSanitizer initialized" banner is printed - I thought we
shouldn't be reporting anything until the tool is fully initialized.