Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
In-Reply-To: <CAGXu5jJTMqbXia7TmN2yEW11SM+XC3pkMt=bb+xBrY7-OOf=tw@mail.gmail.com>
References: <10360653.ov98egbaqx@natalenko.name> <CAGXu5j+-PNYxSc3v+QtQLK0S3wdtFthFSxNM_69kFDnPQX0Gaw@mail.gmail.com>
 <CAGXu5j+_UH0h9qeYCKKjhC7jw-mi_=fg4ASHi2=pCF9xGTpA4Q@mail.gmail.com>
 <2864697.7uzmEJovl2@natalenko.name> <CAGXu5jLSmJv9AstzsgSscrv-wA7FwfrxAKRxj-FVBmihQvnj1g@mail.gmail.com>
 <CAGXu5j+dh1zm32iBjRVh0s+3gLJYgjwt+z1aBJmrK2Cr8XPWnA@mail.gmail.com>
 <CAGXu5jLhnWnUiscP9B=kTEFNyRw9jgFn7Zr5FxhZrO20553+1Q@mail.gmail.com>
 <CAGXu5jKuZwicyyXH2gB3vp-OjtS+MkG+hqxV1cq1jaG9vAAO=g@mail.gmail.com>
 <CAGXu5jLQuzpjFcfjpT=MvgOxBizFNMjnfmY+E7eCHkDAV5swHg@mail.gmail.com> <CAGXu5jJTMqbXia7TmN2yEW11SM+XC3pkMt=bb+xBrY7-OOf=tw@mail.gmail.com>
From:   Kees Cook <keescook@chromium.org>
Date:   Tue, 17 Apr 2018 13:20:14 -0700
Message-ID: <CAGXu5j+xX3kDDS_sPY44hPVb=8isMX-evYzPx3ur=rge1rL5JQ@mail.gmail.com>
Subject: Re: usercopy whitelist woe in scsi_sense_cache
To:     Oleksandr Natalenko <oleksandr@natalenko.name>,
        Jens Axboe <axboe@kernel.dk>,
        Bart Van Assche <bart.vanassche@wdc.com>,
        Paolo Valente <paolo.valente@linaro.org>
Cc:     David Windsor <dave@nullcore.net>,
        "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        linux-scsi@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Hannes Reinecke <hare@suse.com>,
        Johannes Thumshirn <jthumshirn@suse.de>,
        linux-block@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Apr 17, 2018 at 1:03 PM, Kees Cook <keescook@chromium.org> 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?

-Kees

-- 
Kees Cook
Pixel Security