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

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Date:	Tue, 20 Nov 2012 14:56:27 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH][GIT PULL] x86_32: Return actual stack when requesting sp
 from regs


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);
 }
 


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