[PATCH] kprobes: Temporary disarming of reentrant probe for i386

This patch includes i386 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, 49 insertions, 13 deletions

diff --git a/arch/i386/kernel/kprobes.c b/arch/i386/kernel/kprobes.c
index b8e2bae0ab4..3762f6b35ab 100644
--- a/arch/i386/kernel/kprobes.c
+++ b/arch/i386/kernel/kprobes.c
@@ -37,12 +37,10 @@
 #include <asm/kdebug.h>
 #include <asm/desc.h>
 
-/* 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_eflags, kprobe_saved_eflags;
+static struct kprobe *kprobe_prev;
+static unsigned long kprobe_status_prev, kprobe_old_eflags_prev, kprobe_saved_eflags_prev;
 static struct pt_regs jprobe_saved_regs;
 static long *jprobe_saved_esp;
 /* copy of the kernel stack at the probe fire time */
@@ -93,6 +91,31 @@ void arch_remove_kprobe(struct kprobe *p)
 {
 }
 
+static inline void save_previous_kprobe(void)
+{
+        kprobe_prev = current_kprobe;
+        kprobe_status_prev = kprobe_status;
+        kprobe_old_eflags_prev = kprobe_old_eflags;
+        kprobe_saved_eflags_prev = kprobe_saved_eflags;
+}
+
+static inline void restore_previous_kprobe(void)
+{
+        current_kprobe = kprobe_prev;
+        kprobe_status = kprobe_status_prev;
+        kprobe_old_eflags = kprobe_old_eflags_prev;
+        kprobe_saved_eflags = kprobe_saved_eflags_prev;
+}
+
+static inline void set_current_kprobe(struct kprobe *p, struct pt_regs *regs)
+{
+        current_kprobe = p;
+        kprobe_saved_eflags = kprobe_old_eflags
+                = (regs->eflags & (TF_MASK | IF_MASK));
+        if (is_IF_modifier(p->opcode))
+                kprobe_saved_eflags &= ~IF_MASK;
+}
+
 static inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 {
         regs->eflags |= TF_MASK;
@@ -184,9 +207,18 @@ static int kprobe_handler(struct pt_regs *regs)
                                 unlock_kprobes();
                                 goto no_kprobe;
                         }
-                        arch_disarm_kprobe(p);
-                        regs->eip = (unsigned long)p->addr;
-                        ret = 1;
+                        /* We have reentered the kprobe_handler(), since
+                         * another probe was hit while within the handler.
+                         * We here save the original kprobes variables and
+                         * just single step on the 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;
                 } else {
                         p = current_kprobe;
                         if (p->break_handler && p->break_handler(p, regs)) {
@@ -221,11 +253,7 @@ static int kprobe_handler(struct pt_regs *regs)
         }
 
         kprobe_status = KPROBE_HIT_ACTIVE;
-        current_kprobe = p;
-        kprobe_saved_eflags = kprobe_old_eflags
-            = (regs->eflags & (TF_MASK | IF_MASK));
-        if (is_IF_modifier(p->opcode))
-                kprobe_saved_eflags &= ~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 */
@@ -370,14 +398,22 @@ static inline 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_eflags;
 
+        /*Restore back the original saved kprobes variables and continue. */
+        if (kprobe_status == KPROBE_REENTER) {
+                restore_previous_kprobe();
+                goto out;
+        }
         unlock_kprobes();
+out:
         preempt_enable_no_resched();
 
         /*