[PATCH] kprobes: Temporary disarming of reentrant probe for x86_64

This patch includes x86_64 architecture specific changes to support temporary
disarming on reentrancy of probes.

Signed-of-by: Prasanna S Panchamukhi <prasanna@in.ibm.com>

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 62 insertions, 14 deletions

diff --git a/arch/x86_64/kernel/kprobes.c b/arch/x86_64/kernel/kprobes.c
index 324bf57925a9..4e680f87a75f 100644
--- a/arch/x86_64/kernel/kprobes.c
+++ b/arch/x86_64/kernel/kprobes.c
@@ -45,12 +45,10 @@
 
 static DECLARE_MUTEX(kprobe_mutex);
 
-/* kprobe_status settings */
-#define KPROBE_HIT_ACTIVE       0x00000001
-#define KPROBE_HIT_SS           0x00000002
-
 static struct kprobe *current_kprobe;
 static unsigned long kprobe_status, kprobe_old_rflags, kprobe_saved_rflags;
+static struct kprobe *kprobe_prev;
+static unsigned long kprobe_status_prev, kprobe_old_rflags_prev, kprobe_saved_rflags_prev;
 static struct pt_regs jprobe_saved_regs;
 static long *jprobe_saved_rsp;
 static kprobe_opcode_t *get_insn_slot(void);
@@ -240,6 +238,31 @@ void arch_remove_kprobe(struct kprobe *p)
         down(&kprobe_mutex);
 }
 
+static inline void save_previous_kprobe(void)
+{
+        kprobe_prev = current_kprobe;
+        kprobe_status_prev = kprobe_status;
+        kprobe_old_rflags_prev = kprobe_old_rflags;
+        kprobe_saved_rflags_prev = kprobe_saved_rflags;
+}
+
+static inline void restore_previous_kprobe(void)
+{
+        current_kprobe = kprobe_prev;
+        kprobe_status = kprobe_status_prev;
+        kprobe_old_rflags = kprobe_old_rflags_prev;
+        kprobe_saved_rflags = kprobe_saved_rflags_prev;
+}
+
+static inline void set_current_kprobe(struct kprobe *p, struct pt_regs *regs)
+{
+        current_kprobe = p;
+        kprobe_saved_rflags = kprobe_old_rflags
+                = (regs->eflags & (TF_MASK | IF_MASK));
+        if (is_IF_modifier(p->ainsn.insn))
+                kprobe_saved_rflags &= ~IF_MASK;
+}
+
 static void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 {
         regs->eflags |= TF_MASK;
@@ -319,10 +342,30 @@ int kprobe_handler(struct pt_regs *regs)
                                 regs->eflags |= kprobe_saved_rflags;
                                 unlock_kprobes();
                                 goto no_kprobe;
+                        } else if (kprobe_status == KPROBE_HIT_SSDONE) {
+                                /* TODO: Provide re-entrancy from
+                                 * post_kprobes_handler() and avoid exception
+                                 * stack corruption while single-stepping on
+                                 * the instruction of the new probe.
+                                 */
+                                arch_disarm_kprobe(p);
+                                regs->rip = (unsigned long)p->addr;
+                                ret = 1;
+                        } else {
+                                /* We have reentered the kprobe_handler(), since
+                                 * another probe was hit while within the
+                                 * handler. We here save the original kprobe
+                                 * variables and just single step on instruction
+                                 * of the new probe without calling any user
+                                 * handlers.
+                                 */
+                                save_previous_kprobe();
+                                set_current_kprobe(p, regs);
+                                p->nmissed++;
+                                prepare_singlestep(p, regs);
+                                kprobe_status = KPROBE_REENTER;
+                                return 1;
                         }
-                        arch_disarm_kprobe(p);
-                        regs->rip = (unsigned long)p->addr;
-                        ret = 1;
                 } else {
                         p = current_kprobe;
                         if (p->break_handler && p->break_handler(p, regs)) {
@@ -352,11 +395,7 @@ int kprobe_handler(struct pt_regs *regs)
         }
 
         kprobe_status = KPROBE_HIT_ACTIVE;
-        current_kprobe = p;
-        kprobe_saved_rflags = kprobe_old_rflags
-            = (regs->eflags & (TF_MASK | IF_MASK));
-        if (is_IF_modifier(p->ainsn.insn))
-                kprobe_saved_rflags &= ~IF_MASK;
+        set_current_kprobe(p, regs);
 
         if (p->pre_handler && p->pre_handler(p, regs))
                 /* handler has already set things up, so skip ss setup */
@@ -506,14 +545,23 @@ int post_kprobe_handler(struct pt_regs *regs)
         if (!kprobe_running())
                 return 0;
 
-        if (current_kprobe->post_handler)
+        if ((kprobe_status != KPROBE_REENTER) && current_kprobe->post_handler) {
+                kprobe_status = KPROBE_HIT_SSDONE;
                 current_kprobe->post_handler(current_kprobe, regs, 0);
+        }
 
         if (current_kprobe->post_handler != trampoline_post_handler)
                 resume_execution(current_kprobe, regs);
         regs->eflags |= kprobe_saved_rflags;
 
-        unlock_kprobes();
+        /* Restore the original saved kprobes variables and continue. */
+        if (kprobe_status == KPROBE_REENTER) {
+                restore_previous_kprobe();
+                goto out;
+        } else {
+                unlock_kprobes();
+        }
+out:
         preempt_enable_no_resched();
 
         /*