On 4/17/18 2:25 PM, Kees Cook wrote:
> On Tue, Apr 17, 2018 at 1:20 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>> On Tue, Apr 17, 2018 at 1:03 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>>> The above bfq_dispatch_request+0x99/0xad0 is still
>>> __bfq_dispatch_request at block/bfq-iosched.c:3902, just with KASAN
>>> removed. 0x99 is 153 decimal:
>>>
>>> (gdb) disass bfq_dispatch_request
>>> Dump of assembler code for function bfq_dispatch_request:
>>> ...
>>> 0xffffffff8134b2ad <+141>: test %rax,%rax
>>> 0xffffffff8134b2b0 <+144>: je 0xffffffff8134b2bd
>>> <bfq_dispatch_request+157>
>>> 0xffffffff8134b2b2 <+146>: addl $0x1,0x100(%rax)
>>> 0xffffffff8134b2b9 <+153>: addl $0x1,0x3c(%rbx)
>>> 0xffffffff8134b2bd <+157>: orl $0x2,0x18(%r12)
>>> 0xffffffff8134b2c3 <+163>: test %ebp,%ebp
>>> 0xffffffff8134b2c5 <+165>: je 0xffffffff8134b2ce
>>> <bfq_dispatch_request+174>
>>> 0xffffffff8134b2c7 <+167>: mov 0x108(%r14),%rax
>>> 0xffffffff8134b2ce <+174>: mov %r15,%rdi
>>> 0xffffffff8134b2d1 <+177>: callq 0xffffffff81706f90 <_raw_spin_unlock_irq>
>>>
>>> Just as a sanity-check, at +157 %r12 should be rq, rq_flags is 0x18
>>> offset from, $0x2 is RQF_STARTED, so that maps to "rq->rq_flags |=
>>> RQF_STARTED", the next C statement. I don't know what +146 is, though?
>>> An increment of something 256 bytes offset? There's a lot of inline
>>> fun and reordering happening here, so I'm ignoring that for the
>>> moment.
>>
>> No -- I'm reading this wrong. The RIP is the IP _after_ the trap, so
>> +146 is the offender.
>>
>> [ 29.284746] watchpoint @ ffff95d41a0fe580 triggered
>> [ 29.285349] sense before:ffff95d41f45f700 after:ffff95d41f45f701 (@ffff95d41a
>> 0fe580)
>> [ 29.286176] elevator before:ffff95d419419c00 after:ffff95d419419c00
>> [ 29.286847] elevator_data before:ffff95d419418c00 after:ffff95d419418c00
>> ...
>> [ 29.295069] RIP: 0010:bfq_dispatch_request+0x99/0xbb0
>> [ 29.295622] RSP: 0018:ffffb26e01707a40 EFLAGS: 00000002
>> [ 29.296181] RAX: ffff95d41a0fe480 RBX: ffff95d419418c00 RCX: ffff95d419418c08
>>
>> RAX is ffff95d41a0fe480 and sense is stored at ffff95d41a0fe580,
>> exactly 0x100 away.
>>
>> WTF is this addl?
>
> What are the chances? :P Two ++ statements in a row separate by a
> collapsed goto. FML. :)
>
> ...
> bfqq->dispatched++;
> goto inc_in_driver_start_rq;
> ...
> inc_in_driver_start_rq:
> bfqd->rq_in_driver++;
> ...
>
> And there's the 0x100 (256):
>
> struct bfq_queue {
> ...
> int dispatched; /* 256 4 */
>
> So bfqq is corrupted somewhere... I'll keep digging. I hope you're all
> enjoying my live debugging transcript. ;)
It has to be the latter bfqq->dispatched increment, as those are
transient (and bfqd is not).
Adding Paolo.
--
Jens Axboe
