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authorTiejun Chen <tiejun.chen@windriver.com>2012-09-17 03:54:31 +0400
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2012-09-18 09:32:45 +0400
commit8e9f69371536981a2a8c9ee4a49dbe3aa4946df4 (patch)
tree8785a164fdaa422a146fdda4b21100189858f90d /arch/powerpc/lib
parenta9c4e541ea9b22944da356f2a9258b4eddcc953b (diff)
downloadlinux-8e9f69371536981a2a8c9ee4a49dbe3aa4946df4.tar.xz
powerpc/kprobe: Don't emulate store when kprobe stwu r1
We don't do the real store operation for kprobing 'stwu Rx,(y)R1' since this may corrupt the exception frame, now we will do this operation safely in exception return code after migrate current exception frame below the kprobed function stack. So we only update gpr[1] here and trigger a thread flag to mask this. Note we should make sure if we trigger kernel stack over flow. Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'arch/powerpc/lib')
-rw-r--r--arch/powerpc/lib/sstep.c36
1 files changed, 34 insertions, 2 deletions
diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index 9a52349874ee..e15c521846ca 100644
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -566,7 +566,7 @@ int __kprobes emulate_step(struct pt_regs *regs, unsigned int instr)
unsigned long int ea;
unsigned int cr, mb, me, sh;
int err;
- unsigned long old_ra;
+ unsigned long old_ra, val3;
long ival;
opcode = instr >> 26;
@@ -1486,11 +1486,43 @@ int __kprobes emulate_step(struct pt_regs *regs, unsigned int instr)
goto ldst_done;
case 36: /* stw */
- case 37: /* stwu */
val = regs->gpr[rd];
err = write_mem(val, dform_ea(instr, regs), 4, regs);
goto ldst_done;
+ case 37: /* stwu */
+ val = regs->gpr[rd];
+ val3 = dform_ea(instr, regs);
+ /*
+ * For PPC32 we always use stwu to change stack point with r1. So
+ * this emulated store may corrupt the exception frame, now we
+ * have to provide the exception frame trampoline, which is pushed
+ * below the kprobed function stack. So we only update gpr[1] but
+ * don't emulate the real store operation. We will do real store
+ * operation safely in exception return code by checking this flag.
+ */
+ if ((ra == 1) && !(regs->msr & MSR_PR) \
+ && (val3 >= (regs->gpr[1] - STACK_INT_FRAME_SIZE))) {
+ /*
+ * Check if we will touch kernel sack overflow
+ */
+ if (val3 - STACK_INT_FRAME_SIZE <= current->thread.ksp_limit) {
+ printk(KERN_CRIT "Can't kprobe this since Kernel stack overflow.\n");
+ err = -EINVAL;
+ break;
+ }
+
+ /*
+ * Check if we already set since that means we'll
+ * lose the previous value.
+ */
+ WARN_ON(test_thread_flag(TIF_EMULATE_STACK_STORE));
+ set_thread_flag(TIF_EMULATE_STACK_STORE);
+ err = 0;
+ } else
+ err = write_mem(val, val3, 4, regs);
+ goto ldst_done;
+
case 38: /* stb */
case 39: /* stbu */
val = regs->gpr[rd];