tracing/kprobes: Dump the culprit kprobe in case of kprobe recursion

Kprobes can enter into a probing recursion, ie: a kprobe that does an
endless loop because one of its core mechanism function used during
probing is also probed itself.

This patch helps pinpointing the kprobe that raised such recursion
by dumping it and raising a BUG instead of a warning (we also disarm
the kprobe to try avoiding recursion in BUG itself). Having a BUG
instead of a warning stops the stacktrace in the right place and
doesn't pollute the logs with hundreds of traces that eventually end
up in a stack overflow.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 16ae9610f6ffb51b1d47180360da71c0ba0fd33a..ecee3d23fef8d622d52165fd1dffe26d3af6459f 100644 (file)
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -490,9 +490,13 @@ static int __kprobes reenter_kprobe(struct kprobe *p, struct pt_regs *regs,
                        /* A probe has been hit in the codepath leading up
                         * to, or just after, single-stepping of a probed
                         * instruction. This entire codepath should strictly
-                        * reside in .kprobes.text section. Raise a warning
-                        * to highlight this peculiar case.
+                        * reside in .kprobes.text section.
+                        * Raise a BUG or we'll continue in an endless
+                        * reentering loop and eventually a stack overflow.
                         */
+                       arch_disarm_kprobe(p);
+                       dump_kprobe(p);
+                       BUG();
                }
        default:
                /* impossible cases */

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index bcd9c07848bef0c4fa9eb8042add0ad59faeb374..87eb79c9dd6074a3e4708c84393418beb7a9c39b 100644 (file)
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -296,6 +296,8 @@ void recycle_rp_inst(struct kretprobe_instance *ri, struct hlist_head *head);
 int disable_kprobe(struct kprobe *kp);
 int enable_kprobe(struct kprobe *kp);
 
+void dump_kprobe(struct kprobe *kp);
+
 #else /* !CONFIG_KPROBES: */
 
 static inline int kprobes_built_in(void)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index ef177d653b2cb791b11f98723d3afe5ada5ac586..f72e96c25a3899ef8aabf909458e2399afca773b 100644 (file)
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1141,6 +1141,13 @@ static void __kprobes kill_kprobe(struct kprobe *p)
        arch_remove_kprobe(p);
 }
 
+void __kprobes dump_kprobe(struct kprobe *kp)
+{
+       printk(KERN_WARNING "Dumping kprobe:\n");
+       printk(KERN_WARNING "Name: %s\nAddress: %p\nOffset: %x\n",
+              kp->symbol_name, kp->addr, kp->offset);
+}
+
 /* Module notifier call back, checking kprobes on the module */
 static int __kprobes kprobes_module_callback(struct notifier_block *nb,
                                             unsigned long val, void *data)