On Mon, Sep 21, 2020 at 7:54 AM Dmitry Vyukov <dvyu...@google.com> wrote: > > On Sat, Sep 19, 2020 at 1:08 PM Borislav Petkov <b...@alien8.de> wrote: > > > > On Sat, Sep 19, 2020 at 01:32:14AM -0700, syzbot wrote: > > > Hello, > > > > > > syzbot found the following issue on: > > > > > > HEAD commit: 92ab97ad Merge tag 'sh-for-5.9-part2' of > > > git://git.libc.or.. > > > git tree: upstream > > > console output: https://syzkaller.appspot.com/x/log.txt?x=1069669b900000 > > > kernel config: https://syzkaller.appspot.com/x/.config?x=cd992d74d6c7e62 > > > dashboard link: > > > https://syzkaller.appspot.com/bug?extid=ce179bc99e64377c24bc > > > compiler: clang version 10.0.0 > > > (https://github.com/llvm/llvm-project/ > > > c2443155a0fb245c8f17f2c1c72b6ea391e86e81) > > > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the > > > commit: > > > Reported-by: syzbot+ce179bc99e64377c2...@syzkaller.appspotmail.com > > > > > > general protection fault, probably for non-canonical address > > > 0xffff518084501e28: 0000 [#1] PREEMPT SMP KASAN > > > KASAN: maybe wild-memory-access in range > > > [0xfffaac042280f140-0xfffaac042280f147] > > > CPU: 0 PID: 17449 Comm: syz-executor.5 Not tainted 5.9.0-rc5-syzkaller #0 > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > > > Google 01/01/2011 > > > RIP: 0010:perf_misc_flags+0x125/0x150 arch/x86/events/core.c:2638 > > > Code: e4 48 83 e6 03 41 0f 94 c4 31 ff e8 95 fa 73 00 bb 02 00 00 00 4c > > > 29 e3 49 81 c6 90 00 00 00 4c 89 f0 48 c1 e8 00 00 00 00 38 <00> 74 08 4c > > > 89 f7 e8 40 c0 b3 00 41 8b 06 83 e0 08 48 c1 e0 0b 48 > > > > Hmm, so converting this back to opcodes with decodecode gives: > > > > Code: e4 48 83 e6 03 41 0f 94 c4 31 ff e8 95 fa 73 00 bb 02 00 00 00 4c 29 > > e3 49 81 c6 90 00 00 00 4c 89 f0 48 c1 e8 00 00 00 00 38 <00> 74 08 4c 89 > > f7 e8 40 c0 b3 00 41 8b 06 83 e0 08 48 c1 e0 0b 48 > > All code > > ======== > > 0: e4 48 in $0x48,%al > > 2: 83 e6 03 and $0x3,%esi > > 5: 41 0f 94 c4 sete %r12b > > 9: 31 ff xor %edi,%edi > > b: e8 95 fa 73 00 callq 0x73faa5 > > 10: bb 02 00 00 00 mov $0x2,%ebx > > 15: 4c 29 e3 sub %r12,%rbx > > 18: 49 81 c6 90 00 00 00 add $0x90,%r14 > > 1f: 4c 89 f0 mov %r14,%rax > > 22: 48 c1 e8 00 shr $0x0,%rax > > 26: 00 00 add %al,(%rax) > > 28: 00 38 add %bh,(%rax) > > 2a:* 00 74 08 4c add %dh,0x4c(%rax,%rcx,1) <-- > > trapping instruction > > 2e: 89 f7 mov %esi,%edi > > 30: e8 40 c0 b3 00 callq 0xb3c075 > > 35: 41 8b 06 mov (%r14),%eax > > 38: 83 e0 08 and $0x8,%eax > > 3b: 48 c1 e0 0b shl $0xb,%rax > > 3f: 48 rex.W > > > > and those ADDs before the rIP look real strange. Just as if something > > wrote 4 bytes of 0s there. And building your config with clang-10 gives > > around that area: > > > > ffffffff8101177c: 48 83 e6 03 and $0x3,%rsi > > ffffffff81011780: 41 0f 94 c4 sete %r12b > > ffffffff81011784: 31 ff xor %edi,%edi > > ffffffff81011786: e8 05 c9 73 00 callq ffffffff8174e090 > > <__sanitizer_cov_trace_const_cmp8> > > ffffffff8101178b: bb 02 00 00 00 mov $0x2,%ebx > > ffffffff81011790: 4c 29 e3 sub %r12,%rbx > > ffffffff81011793: 49 81 c6 90 00 00 00 add $0x90,%r14 > > ffffffff8101179a: 4c 89 f0 mov %r14,%rax > > ffffffff8101179d: 48 c1 e8 03 shr $0x3,%rax > > ffffffff810117a1: 42 80 3c 38 00 cmpb $0x0,(%rax,%r15,1) > > ffffffff810117a6: 74 08 je ffffffff810117b0 > > <perf_misc_flags+0x130> > > ffffffff810117a8: 4c 89 f7 mov %r14,%rdi > > ffffffff810117ab: e8 20 75 b3 00 callq ffffffff81b48cd0 > > <__asan_report_load8_noabort> > > ffffffff810117b0: 41 8b 06 mov (%r14),%eax > > ffffffff810117b3: 83 e0 08 and $0x8,%eax > > ffffffff810117b6: 48 c1 e0 0b shl $0xb,%rax > > > > and I can pretty much follow it instruction by instruction until I reach > > that SHR. Your SHR is doing a shift by 0 bytes and that already looks > > suspicious. > > > > After it, your output has a bunch of suspicious ADDs and mine has a CMP; > > JE instead. And that looks really strange too. > > > > Could it be that something has scribbled in guest memory and corrupted > > that area, leading to that strange discrepancy in the opcodes? > > Hi Boris, > > Memory corruption is definitely possible. There are hundreds of known > bugs that can potentially lead to silent memory corruptions, and some > observed to lead to silent memory corruptions. > > However, these tend to produce crash signatures with 1-2 crashes. > While this has 6 and they look similar and all happened on the only > instance that uses clang. So my bet would be on > something-clang-related rather than a silent memory corruption. > +clang-built-linux
general protection fault in pvclock_gtod_notify (2) looks somewhat similar: - only clang - gpf in systems code - happened few times https://syzkaller.appspot.com/bug?extid=1dccfcb049726389379c https://groups.google.com/g/syzkaller-bugs/c/0eUUkjFKrBg/m/nGfTjIfCBAAJ
