[PATCH] x86: kprobes: fix swapped segment registers in kretprobe

[PATCH] x86: kprobes: fix swapped segment registers in kretprobe

[Roland McGrath]

The following changes since commit bea9a6d239cb2aa2ced4dcb0a05e1827ce61fa3d:

  Merge branch 'upstream-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jlbec/ocfs2 (2010-07-18 10:09:25 -0700)

are available in the git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/frob/linux-2.6-roland.git x86/kprobes

Roland McGrath (1):
      x86: kprobes: fix swapped segment registers in kretprobe

 arch/x86/kernel/kprobes.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)


Thanks,
Roland
---
[PATCH] x86: kprobes: fix swapped segment registers in kretprobe

In commit f007ea26, the order of the %es and %ds segment registers
got accidentally swapped, so synthesized 'struct pt_regs' frames
have the two values inverted.  It's almost sure that these values
never matter, and that they also never differ.  But wrong is wrong.

Signed-off-by: Roland McGrath <roland@redhat.com>
---
 arch/x86/kernel/kprobes.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 345a4b1..675879b 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -640,8 +640,8 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
 	/* Skip cs, ip, orig_ax and gs. */	\
 	"	subl $16, %esp\n"	\
 	"	pushl %fs\n"		\
-	"	pushl %ds\n"		\
 	"	pushl %es\n"		\
+	"	pushl %ds\n"		\
 	"	pushl %eax\n"		\
 	"	pushl %ebp\n"		\
 	"	pushl %edi\n"		\

Re: [PATCH] x86: kprobes: fix swapped segment registers in kretprobe

[Linus Torvalds]

On Sun, Jul 18, 2010 at 3:11 PM, Roland McGrath <roland@redhat.com> wrote:
>
> [PATCH] x86: kprobes: fix swapped segment registers in kretprobe
>
> In commit f007ea26, the order of the %es and %ds segment registers
> got accidentally swapped, so synthesized 'struct pt_regs' frames
> have the two values inverted.  It's almost sure that these values
> never matter, and that they also never differ.  But wrong is wrong.

Heh, yes. ES and DS are almost guaranteed to be the same, or string
instructions act oddly. But I could imagine that some wine usage could
trigger this. Of course, you'd also have to have probes etc.

Regardless - pulled,

                  Linus

Re: [PATCH] x86: kprobes: fix swapped segment registers in kretprobe

[Masami Hiramatsu]

Roland McGrath wrote:
> The following changes since commit bea9a6d239cb2aa2ced4dcb0a05e1827ce61fa3d:
> 
>   Merge branch 'upstream-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jlbec/ocfs2 (2010-07-18 10:09:25 -0700)
> 
> are available in the git repository at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/frob/linux-2.6-roland.git x86/kprobes
> 
> Roland McGrath (1):
>       x86: kprobes: fix swapped segment registers in kretprobe
> 
>  arch/x86/kernel/kprobes.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> 
> Thanks,
> Roland
> ---
> [PATCH] x86: kprobes: fix swapped segment registers in kretprobe
> 
> In commit f007ea26, the order of the %es and %ds segment registers
> got accidentally swapped, so synthesized 'struct pt_regs' frames
> have the two values inverted.  It's almost sure that these values
> never matter, and that they also never differ.  But wrong is wrong.

Oops, thanks Roland for finding it.

Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>


> 
> Signed-off-by: Roland McGrath <roland@redhat.com>
> ---
>  arch/x86/kernel/kprobes.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
> index 345a4b1..675879b 100644
> --- a/arch/x86/kernel/kprobes.c
> +++ b/arch/x86/kernel/kprobes.c
> @@ -640,8 +640,8 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
>  	/* Skip cs, ip, orig_ax and gs. */	\
>  	"	subl $16, %esp\n"	\
>  	"	pushl %fs\n"		\
> -	"	pushl %ds\n"		\
>  	"	pushl %es\n"		\
> +	"	pushl %ds\n"		\
>  	"	pushl %eax\n"		\
>  	"	pushl %ebp\n"		\
>  	"	pushl %edi\n"		\
> --
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