[tip:x86/asm] x86_32: Return actual stack when requesting sp from regs

[tip-bot for Steven Rostedt]

Commit-ID:  6c8d8b3c69cef1330e0c5cbc2a8b9268024927a0
Gitweb:     http://git.kernel.org/tip/6c8d8b3c69cef1330e0c5cbc2a8b9268024927a0
Author:     Steven Rostedt <rostedt@xxxxxxxxxxx>
AuthorDate: Fri, 13 Jul 2012 15:44:14 -0400
Committer:  Steven Rostedt <rostedt@xxxxxxxxxxx>
CommitDate: Mon, 19 Nov 2012 05:31:37 -0500

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@xxxxxxxxxxxxxxxxxxx

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 arch/x86/include/asm/ptrace.h | 9 +++++++++
 1 file changed, 9 insertions(+)

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);
 }
 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/