linux-kernel - Re: [x86.git#mm] stack protector fixes, vmsplice exploit

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Date:	Thu, 14 Feb 2008 23:43:47 +0200
From:	pageexec@...email.hu
To:	Ingo Molnar <mingo@...e.hu>, Jakub Jelinek <jakub@...hat.com>
CC:	Sam Ravnborg <sam@...nborg.org>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [x86.git#mm] stack protector fixes, vmsplice exploit

On 14 Feb 2008 at 17:35, Jakub Jelinek wrote:

> Where do you see a mispredicted branch?

try it with -Os (gentoo gcc 4.2.2):

0000000000000000 <foo>:
   0:   48 83 ec 58             sub    $0x58,%rsp
   4:   65 48 8b 04 25 28 00 00 00      mov    %gs:0x28,%rax
   d:   48 89 44 24 48          mov    %rax,0x48(%rsp)
  12:   31 c0                   xor    %eax,%eax
  14:   48 89 e7                mov    %rsp,%rdi
  17:   e8 00 00 00 00          callq  1c <foo+0x1c>    18: R_X86_64_PC32       
bar+0xfffffffffffffffc
  1c:   48 8b 54 24 48          mov    0x48(%rsp),%rdx
  21:   65 48 33 14 25 28 00 00 00      xor    %gs:0x28,%rdx
  2a:   b8 06 00 00 00          mov    $0x6,%eax
  2f:   74 05                   je     36 <foo+0x36>
  31:   e8 00 00 00 00          callq  36 <foo+0x36>    32: R_X86_64_PC32       
__stack_chk_fail+0xfffffffffffffffc
  36:   48 83 c4 58             add    $0x58,%rsp
  3a:   c3                      retq

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