Re: [PATCH 3/5] Kprobes: Temporary disarming of reentrant probe for x86_64

[Prasanna S Panchamukhi <prasanna at in dot ibm dot com>]

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>



---

 linux-2.6.12-rc4-mm2-prasanna/arch/x86_64/kernel/kprobes.c |   73 ++++++++++---
 1 files changed, 60 insertions(+), 13 deletions(-)

diff -puN arch/x86_64/kernel/kprobes.c~kprobes-temporarily-disarm-x86_64 arch/x86_64/kernel/kprobes.c
--- linux-2.6.12-rc4-mm2/arch/x86_64/kernel/kprobes.c~kprobes-temporarily-disarm-x86_64	2005-05-19 15:42:57.000000000 +0530
+++ linux-2.6.12-rc4-mm2-prasanna/arch/x86_64/kernel/kprobes.c	2005-05-19 15:42:57.000000000 +0530
@@ -43,12 +43,10 @@
 
 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);
@@ -238,6 +236,31 @@ 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;
@@ -273,10 +296,30 @@ 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->count_disarm++;
+				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)) {
@@ -306,11 +349,7 @@ 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 */
@@ -411,13 +450,21 @@ int post_kprobe_handler(struct pt_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);
+	}
 
 	resume_execution(current_kprobe, regs);
 	regs->eflags |= kprobe_saved_rflags;
 
+	/*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();
 
 	/*

_
-- 

Prasanna S Panchamukhi
Linux Technology Center
India Software Labs, IBM Bangalore
Ph: 91-80-25044636
<prasanna@in.ibm.com>