kprobes/x86: Fix the return address of multiple kretprobes

Fix the return address of subsequent kretprobes when multiple
kretprobes are set on the same function.

For example:

 # cd /sys/kernel/debug/tracing
 # echo "r:event1 sys_symlink" > kprobe_events
 # echo "r:event2 sys_symlink" >> kprobe_events
 # echo 1 > events/kprobes/enable
 # ln -s /tmp/foo /tmp/bar

(without this patch)

 # cat trace
              ln-897   [000] 20404.133727: event1: (kretprobe_trampoline+0x0/0x4c <- sys_symlink)
              ln-897   [000] 20404.133747: event2: (system_call_fastpath+0x16/0x1b <- sys_symlink)

(with this patch)

 # cat trace
              ln-740   [000] 13799.491076: event1: (system_call_fastpath+0x16/0x1b <- sys_symlink)
              ln-740   [000] 13799.491096: event2: (system_call_fastpath+0x16/0x1b <- sys_symlink)

Signed-off-by: KUMANO Syuhei <kumano.prog@gmail.com>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
LKML-Reference: <1281853084.3254.11.camel@camp10-laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 22 insertions, 3 deletions

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 1bfb6cf4dd5..770ebfb349e 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -709,6 +709,7 @@ static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
         struct hlist_node *node, *tmp;
         unsigned long flags, orig_ret_address = 0;
         unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
+        kprobe_opcode_t *correct_ret_addr = NULL;
 
         INIT_HLIST_HEAD(&empty_rp);
         kretprobe_hash_lock(current, &head, &flags);
@@ -740,14 +741,34 @@ static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
                         /* another task is sharing our hash bucket */
                         continue;
 
+                orig_ret_address = (unsigned long)ri->ret_addr;
+
+                if (orig_ret_address != trampoline_address)
+                        /*
+                         * This is the real return address. Any other
+                         * instances associated with this task are for
+                         * other calls deeper on the call stack
+                         */
+                        break;
+        }
+
+        kretprobe_assert(ri, orig_ret_address, trampoline_address);
+
+        correct_ret_addr = ri->ret_addr;
+        hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
+                if (ri->task != current)
+                        /* another task is sharing our hash bucket */
+                        continue;
+
+                orig_ret_address = (unsigned long)ri->ret_addr;
                 if (ri->rp && ri->rp->handler) {
                         __get_cpu_var(current_kprobe) = &ri->rp->kp;
                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
+                        ri->ret_addr = correct_ret_addr;
                         ri->rp->handler(ri, regs);
                         __get_cpu_var(current_kprobe) = NULL;
                 }
 
-                orig_ret_address = (unsigned long)ri->ret_addr;
                 recycle_rp_inst(ri, &empty_rp);
 
                 if (orig_ret_address != trampoline_address)
@@ -759,8 +780,6 @@ static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
                         break;
         }
 
-        kretprobe_assert(ri, orig_ret_address, trampoline_address);
-
         kretprobe_hash_unlock(current, &flags);
 
         hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {