lkml.org 
[lkml]   [2014]   [Dec]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: fs: proc: gpf in find_entry
Andrey Ryabinin <ryabinin.a.a@gmail.com> writes:

> 2014-12-22 17:37 GMT+03:00 Sasha Levin <sasha.levin@oracle.com>:
>> Hi all,
>>
>> While fuzzing with trinity inside a KVM tools guest running the latest -next
>> kernel, I've stumbled on the following spew:
>>
>> [ 2015.960381] general protection fault: 0000 [#1] PREEMPT SMP KASAN
>
> Actually this is NULL-ptr dereference. Since you are using kasan with
> inline instrumentation
> NULL-ptr deref transforms into GPF.
>
>
>> [ 2015.970534] RAX: 0000000000000000 RBX: ffff88000003a960 RCX: 0000000000000073
>> [ 2015.970534] RDX: 1ffff10101c8f3c4 RSI: 0000000000000000 RDI: ffff88080e479e20
>> [ 2015.970534] RBP: ffff88080e477a28 R08: 0000000000000066 R09: 0000000000000073
>> [ 2015.970534] R10: ffffda0017d55630 R11: dfffe90000000000 R12: ffff88005fc644b8
>> [ 2015.970534] R13: dfffe90000000000 R14: ffffffff92464884 R15: 0000000000000000
>
> [...]
>
>> All code
>> ========
>> 0: e8 03 42 80 3c callq 0x3c804208
>> 5: 28 00 sub %al,(%rax)
>> 7: 0f 85 ff 01 00 00 jne 0x20c
>> d: 4c 8b 7b 18 mov 0x18(%rbx),%r15
>> 11: 4d 85 ff test %r15,%r15
>> 14: 0f 84 de 01 00 00 je 0x1f8
>> 1a: 41 f6 c7 07 test $0x7,%r15b
>> 1e: 0f 85 d4 01 00 00 jne 0x1f8
>> 24: 4c 89 f8 mov %r15,%rax
>> 27: 48 c1 e8 03 shr $0x3,%rax
>> 2b:* 42 80 3c 28 00 cmpb $0x0,(%rax,%r13,1) <-- trapping instruction
>
> Three commands above are result of KASAN's instrumentation.
> They check shadow for address in %r15:
> if (*((%r15 >> 3) + kasan_shadow_offset)
>
>
>> 30: 0f 85 b5 01 00 00 jne 0x1eb
>> 36: 4d 8b 37 mov (%r15),%r14
>
> And here is memory access, that KASAN checking.

Then frankly I suspect this is a KASAN bug.

These two instructions:
>> 11: 4d 85 ff test %r15,%r15
>> 14: 0f 84 de 01 00 00 je 0x1f8

Should prevent a NULL %r15 value from ever reaching the trapping
instruction.

What other horrible things does KASAN do to the machine code?

Eric


\
 
 \ /
  Last update: 2014-12-22 17:21    [W:0.032 / U:0.576 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site