linux-kernel - Re: keys: GPF in request

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Date:   Wed, 01 Feb 2017 13:11:32 +0000
From:   David Howells <dhowells@...hat.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     dhowells@...hat.com, james.l.morris@...cle.com, serge@...lyn.com,
        keyrings@...r.kernel.org, linux-security-module@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: keys: GPF in request_key

Dmitry Vyukov <dvyukov@...gle.com> wrote:

> Code: 41 54 49 89 f4 53 49 89 d7 48 89 fb 48 83 ec 08 e8 d1 50 67 ff
> 49 8d 7c 24 10 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80>
> 3c 02 00 0f 85 35 02 00 00 49 83 7c 24 10 00 0f 84 bb 01 00

This disassembles to:

   0:   41 54                   push   %r12
   2:   49 89 f4                mov    %rsi,%r12
   5:   53                      push   %rbx
   6:   49 89 d7                mov    %rdx,%r15
   9:   48 89 fb                mov    %rdi,%rbx
   c:   48 83 ec 08             sub    $0x8,%rsp
  10:   e8 d1 50 67 ff          callq  0xffffffffff6750e6
  15:   49 8d 7c 24 10          lea    0x10(%r12),%rdi
  1a:   48 b8 00 00 00 00 00    movabs $0xdffffc0000000000,%rax
  21:   fc ff df 
  24:   48 89 fa                mov    %rdi,%rdx
  27:   48 c1 ea 03             shr    $0x3,%rdx
  2b:*  80 3c 02 00             cmpb   $0x0,(%rdx,%rax,1)               <-- trapping instruction
  2f:   0f 85 35 02 00 00       jne    0x26a
  35:   49 83 7c 24 10 00       cmpq   $0x0,0x10(%r12)
  3b:   0f                      .byte 0xf
  3c:   84                      .byte 0x84
  3d:   bb                      .byte 0xbb
  3e:   01 00                   add    %eax,(%rax)

I can see that RAX got loaded from the instruction at 0x1a, but the code
doesn't look very much like what I get out of the compiler (your compiled
function is also at least double the size of what I get, presumably due to
kasan?).

Can you disassemble __key_link_begin() for me and send me your config?

In particular, 0xdffffc0000000000 looks very weird.  Is this code validating
the pointer in R12?

David