linux-kernel - Re: [PATCH][GIT PULL] x86_32: Return actual stack when requesting sp from regs

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Date:	Sat, 8 Dec 2012 16:07:34 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Subject: Re: [PATCH][GIT PULL] x86_32: Return actual stack when requesting sp
 from regs


* Steven Rostedt <rostedt@...dmis.org> wrote:

> Ingo, Peter,
> 
> I posted this back in July as an RFC and did get Masami's reviewed-by
> tag. I'm currently cleaning out my inbox and realized I didn't push this
> further. I didn't know which branch to base this on, so I just picked
> the tip/x86/asm branch where I did my last x86 work in.
> 
> https://lkml.org/lkml/2012/7/13/351
> 
> Please pull the latest tip/x86/asm tree, which can be found at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
> tip/x86/asm
> 
> Head SHA1: 6c8d8b3c69cef1330e0c5cbc2a8b9268024927a0
> 
> 
> Steven Rostedt (1):
>       x86_32: Return actual stack when requesting sp from regs
> 
> ----
>  arch/x86/include/asm/ptrace.h |    9 +++++++++
>  1 file changed, 9 insertions(+)
> ---------------------------
> commit 6c8d8b3c69cef1330e0c5cbc2a8b9268024927a0
> Author: Steven Rostedt <rostedt@...dmis.org>
> Date:   Fri Jul 13 15:44:14 2012 -0400
> 
>     x86_32: Return actual stack when requesting sp from regs
>     
>     As x86_32 traps do not save sp when taken in kernel mode, we need to
>     accommodate the sp when requesting to get the register.
>     
>     This affects kprobes.
>     
>     Before:
>     
>      # echo 'p:ftrace sys_read+4 s=%sp' > /debug/tracing/kprobe_events
>      # echo 1 > /debug/tracing/events/kprobes/enable
>      # cat trace
>                 sshd-1345  [000] d...   489.117168: ftrace: (sys_read+0x4/0x70) s=b7e96768
>                 sshd-1345  [000] d...   489.117191: ftrace: (sys_read+0x4/0x70) s=b7e96768
>                  cat-1447  [000] d...   489.117392: ftrace: (sys_read+0x4/0x70) s=5a7
>                  cat-1447  [001] d...   489.118023: ftrace: (sys_read+0x4/0x70) s=b77ad05f
>                 less-1448  [000] d...   489.118079: ftrace: (sys_read+0x4/0x70) s=b7762e06
>                 less-1448  [000] d...   489.118117: ftrace: (sys_read+0x4/0x70) s=b7764970
>     
>     After:
>                 sshd-1352  [000] d...   362.348016: ftrace: (sys_read+0x4/0x70) s=f3febfa8
>                 sshd-1352  [000] d...   362.348048: ftrace: (sys_read+0x4/0x70) s=f3febfa8
>                 bash-1355  [001] d...   362.348081: ftrace: (sys_read+0x4/0x70) s=f5075fa8
>                 sshd-1352  [000] d...   362.348082: ftrace: (sys_read+0x4/0x70) s=f3febfa8
>                 sshd-1352  [000] d...   362.690950: ftrace: (sys_read+0x4/0x70) s=f3febfa8
>                 bash-1355  [001] d...   362.691033: ftrace: (sys_read+0x4/0x70) s=f5075fa8
>     
>     Link: http://lkml.kernel.org/r/1342208654.30075.22.camel@gandalf.stny.rr.com
>     
>     Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
>     Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> 
> diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
> index dcfde52..2233713 100644
> --- a/arch/x86/include/asm/ptrace.h
> +++ b/arch/x86/include/asm/ptrace.h
> @@ -246,6 +246,15 @@ static inline unsigned long regs_get_register(struct pt_regs *regs,
>  {
>  	if (unlikely(offset > MAX_REG_OFFSET))
>  		return 0;
> +#ifdef CONFIG_X86_32
> +	/*
> +	 * Traps from the kernel do not save sp and ss.
> +	 * Use the helper function to retrieve sp.
> +	 */
> +	if (offset == offsetof(struct pt_regs, sp) &&
> +	    regs->cs == __KERNEL_CS)
> +		return kernel_stack_pointer(regs);
> +#endif
>  	return *(unsigned long *)((unsigned long)regs + offset);
>  }

Pulled, thanks Steve!

	Ingo
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