[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>

diff --git a/arch/x86_64/kernel/kprobes.c b/arch/x86_64/kernel/kprobes.c
index 324bf57..4e680f8 100644 (file)
--- 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();
 
        /*