Messages in this thread | | | Subject | Re: BUG: unable to handle kernel paging request in do_futex | From | Andrey Ryabinin <> | Date | Thu, 14 Dec 2017 19:39:35 +0300 |
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On 12/14/2017 06:31 PM, Thomas Gleixner wrote: > On Thu, 30 Nov 2017, syzbot wrote: >> Hello, >> >> syzkaller hit the following crash on 11fed7829beff10184503fd65e5919926464601a >> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master >> compiler: gcc (GCC) 7.1.1 20170620 >> .config is attached >> Raw console output is attached. >> >> Unfortunately, I don't have any reproducer for this bug yet. >> >> >> BUG: unable to handle kernel paging request at 00000000c314149f > > That's a user space address which is nowhere in the registers. Is that > perhaps pre commit: 328b4ed93b69a ?
Seems so. Kernel version is 4.15.0-rc1-next-20171130+ it shouldn't have that commit.
>> IP: arch_futex_atomic_op_inuser arch/x86/include/asm/futex.h:67 [inline] >> IP: futex_atomic_op_inuser kernel/futex.c:1588 [inline] >> IP: futex_wake_op kernel/futex.c:1637 [inline] >> IP: do_futex+0x14c8/0x2280 kernel/futex.c:3483 >> PGD 5e28067 P4D 5e28067 PUD 5e2a067 PMD 0 >> Oops: 0002 [#1] SMP KASAN > > ^^^^ X86_PF_WRITE > >> Dumping ftrace buffer: >> (ftrace buffer empty) >> Modules linked in: >> CPU: 0 PID: 14626 Comm: syz-executor6 Not tainted 4.15.0-rc1-next-20171130+ >> #56 >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google >> 01/01/2011 >> task: 000000005f17dad6 task.stack: 000000005af7607c >> RIP: 0010:arch_futex_atomic_op_inuser arch/x86/include/asm/futex.h:67 [inline] >> RIP: 0010:futex_atomic_op_inuser kernel/futex.c:1588 [inline] >> RIP: 0010:futex_wake_op kernel/futex.c:1637 [inline] >> RIP: 0010:do_futex+0x14c8/0x2280 kernel/futex.c:3483 >> RSP: 0018:ffff8801cffafa18 EFLAGS: 00010246 >> RAX: 000000007fffffff RBX: 0000000040000002 RCX: ffffffff8164e3d9 >> RDX: 0000000000000000 RSI: ffffc900034e8000 RDI: 0000000000000000 >> RBP: ffff8801cffafe38 R08: 1ffffffff0d31367 R09: 0000000000000004 >> R10: 0000000000000000 R11: ffffffff8748cd60 R12: ffff8801d0f30180 >> R13: 0000000020000000 R14: dffffc0000000000 R15: ffff8801cffafe10 >> FS: 00007f66305e0700(0000) GS:ffff8801db400000(0000) knlGS:0000000000000000 >> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> CR2: fffffffffffffff8 CR3: 00000001ccc2e000 CR4: 00000000001426f0 > > ^^^^^^^^^^^^^^^^ is a totally different address so its either > completely bogus or the above address is a hashed pointer because > that printk used to be %p and was changed to %px in 328b4ed93b69a > >> DR0: 0000000020000000 DR1: 0000000020000000 DR2: 0000000000000000 >> DR3: 0000000000000000 DR6: 00000000ffff0ff3 DR7: 0000000000bb060a >> Call Trace: >> SYSC_futex kernel/futex.c:3533 [inline] >> SyS_futex+0x260/0x390 kernel/futex.c:3501 >> entry_SYSCALL_64_fastpath+0x1f/0x96 >> RIP: 0033:0x4529d9 >> RSP: 002b:00007f66305dfc58 EFLAGS: 00000212 ORIG_RAX: 00000000000000ca >> RAX: ffffffffffffffda RBX: 00007f66305e0700 RCX: 00000000004529d9 >> RDX: 0000000000000007 RSI: 0000000000000085 RDI: 0000000020062000 >> RBP: 0000000000000000 R08: 0000000020000000 R09: 0000000040000002 >> R10: 000000002085fff0 R11: 0000000000000212 R12: 0000000000000000 >> R13: 0000000000a6f7ff R14: 00007f66305e09c0 R15: 0000000000000000 > > The arguments are: > > RDI uaddr 0000000020062000 > RSI op 0000000000000085 > RDX val 0000000000000007 > RCX utime 00000000004529d9 > R8 uaddr2 0000000020000000 > R9 val2 0000000040000002 > >> Code: 31 d2 0f 1f 00 45 87 65 00 0f 1f 00 89 95 30 fc ff ff e9 1d ff ff ff e8 >> 67 56 0b 00 31 d2 8b bd 00 fc ff ff 0f 1f 00 41 8b 45 00 <89> c1 31 f9 f0 41 >> 0f b1 4d 00 75 f0 0f 1f 00 41 89 c4 89 95 30 > > and the code is: > > 27: 41 8b 45 00 mov 0x0(%r13),%eax > 2b:* 89 c1 mov %eax,%ecx <-- trapping instruction > 2d: 31 f9 xor %edi,%ecx > 2f: f0 41 0f b1 4d 00 lock cmpxchg %ecx,0x0(%r13) > 35: 75 f0 jne 0x27 > > The trapping instruction cannot trap :). Assumed it's the move before that, > then the accessed location is R13 + 0 = 0000000020000000, which is uaddr2 > and entirely correct. >
But fault address must be 0xfffffffffffffff8 as per CR2, so it can't be 'mov 0x0(%r13),%eax' either. Right?
> And what I completely fail to understand why this triggers at all. That > code section is guarded by an extable fixup so this should never come in. > > Is this a KASAN artifact? >
I don't see any evidence for KASAN being involved here.
> Thanks, > > tglx >
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