Subject: [PATCH][kprobe] disallow kprobes on emulate_step and branch_taken

From: "Gui,Jian" <[email-masked]>
Date: Wed, 01 Nov 2006 10:50:15 +0800

Probing on emulate_step function will crash 2.6.18.1 when it is
triggered. This problem is powerpc dependent.

When kprobe is triggered, emulate_step() is on its kernel path and
will cause recursive kprobe fault. And branch_taken() is called
in emulate_step(). This patch can disallow kprobes on both of them.

diff -Nur orig/arch/powerpc/lib/sstep.c linux-2.6.18.1/arch/powerpc/lib/sstep.c
--- orig/arch/powerpc/lib/sstep.c       2006-11-01 08:45:06.000000000 -0500
+++ linux-2.6.18.1/arch/powerpc/lib/sstep.c     2006-11-01 08:50:19.000000000 -0500
@@ -9,6 +9,7 @@
   * 2 of the License, or (at your option) any later version.
   */
  #include <linux/kernel.h>
+#include <linux/kprobes.h>
  #include <linux/ptrace.h>
  #include <asm/sstep.h>
  #include <asm/processor.h>
@@ -25,7 +26,7 @@
  /*
   * Determine whether a conditional branch instruction would branch.
   */
-static int branch_taken(unsigned int instr, struct pt_regs *regs)
+static int __kprobes branch_taken(unsigned int instr, struct pt_regs *regs)
  {
         unsigned int bo = (instr >> 21) & 0x1f;
         unsigned int bi;
@@ -51,7 +52,7 @@
   * or -1 if the instruction is one that should not be stepped,
   * such as an rfid, or a mtmsrd that would clear MSR_RI.
   */
-int emulate_step(struct pt_regs *regs, unsigned int instr)
+int __kprobes emulate_step(struct pt_regs *regs, unsigned int instr)
  {
         unsigned int opcode, rd;
         unsigned long int imm;