[PATCH] kprobes: fix race in recovery of reentrant probe

There is a window where a probe gets removed right after the probe is hit
on some different cpu.  In this case probe handlers can't find a matching
probe instance related to break address.  In this case we need to read the
original instruction at break address to see if that is not a break/int3
instruction and recover safely.

Previous code had a bug where we were not checking for the above race in
case of reentrant probes and the below patch fixes this race.

Tested on IA64, Powerpc, x86_64.

Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/arch/x86_64/kernel/kprobes.c b/arch/x86_64/kernel/kprobes.c
index b7dc1f816d13..8b866a8572cf 100644
--- a/arch/x86_64/kernel/kprobes.c
+++ b/arch/x86_64/kernel/kprobes.c
@@ -334,6 +334,15 @@ int __kprobes kprobe_handler(struct pt_regs *regs)
                                 return 1;
                         }
                 } else {
+                        if (*addr != BREAKPOINT_INSTRUCTION) {
+                        /* The breakpoint instruction was removed by
+                         * another cpu right after we hit, no further
+                         * handling of this interrupt is appropriate
+                         */
+                                regs->rip = (unsigned long)addr;
+                                ret = 1;
+                                goto no_kprobe;
+                        }
                         p = __get_cpu_var(current_kprobe);
                         if (p->break_handler && p->break_handler(p, regs)) {
                                 goto ss_probe;