[PATCH] kprobes: fix single-step out of line - take2

Now that PPC64 has no-execute support, here is a second try to fix the
single step out of line during kprobe execution.  Kprobes on x86_64 already
solved this problem by allocating an executable page and using it as the
scratch area for stepping out of line.  Reuse that.

Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 22 insertions, 4 deletions

diff --git a/arch/ppc64/kernel/kprobes.c b/arch/ppc64/kernel/kprobes.c
index 782ce3efa2c1..86cc5496db9f 100644
--- a/arch/ppc64/kernel/kprobes.c
+++ b/arch/ppc64/kernel/kprobes.c
@@ -36,6 +36,8 @@
 #include <asm/kdebug.h>
 #include <asm/sstep.h>
 
+static DECLARE_MUTEX(kprobe_mutex);
+
 static struct kprobe *current_kprobe;
 static unsigned long kprobe_status, kprobe_saved_msr;
 static struct kprobe *kprobe_prev;
@@ -54,6 +56,15 @@ int arch_prepare_kprobe(struct kprobe *p)
                 printk("Cannot register a kprobe on rfid or mtmsrd\n");
                 ret = -EINVAL;
         }
+
+        /* insn must be on a special executable page on ppc64 */
+        if (!ret) {
+                up(&kprobe_mutex);
+                p->ainsn.insn = get_insn_slot();
+                down(&kprobe_mutex);
+                if (!p->ainsn.insn)
+                        ret = -ENOMEM;
+        }
         return ret;
 }
 
@@ -79,16 +90,22 @@ void arch_disarm_kprobe(struct kprobe *p)
 
 void arch_remove_kprobe(struct kprobe *p)
 {
+        up(&kprobe_mutex);
+        free_insn_slot(p->ainsn.insn);
+        down(&kprobe_mutex);
 }
 
 static inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 {
+        kprobe_opcode_t insn = *p->ainsn.insn;
+
         regs->msr |= MSR_SE;
-        /*single step inline if it a breakpoint instruction*/
-        if (p->opcode == BREAKPOINT_INSTRUCTION)
+
+        /* single step inline if it is a trap variant */
+        if (IS_TW(insn) || IS_TD(insn) || IS_TWI(insn) || IS_TDI(insn))
                 regs->nip = (unsigned long)p->addr;
         else
-                regs->nip = (unsigned long)&p->ainsn.insn;
+                regs->nip = (unsigned long)p->ainsn.insn;
 }
 
 static inline void save_previous_kprobe(void)
@@ -205,9 +222,10 @@ no_kprobe:
 static void resume_execution(struct kprobe *p, struct pt_regs *regs)
 {
         int ret;
+        unsigned int insn = *p->ainsn.insn;
 
         regs->nip = (unsigned long)p->addr;
-        ret = emulate_step(regs, p->ainsn.insn[0]);
+        ret = emulate_step(regs, insn);
         if (ret == 0)
                 regs->nip = (unsigned long)p->addr + 4;
 }