On x86, an optkprobe at A replaces five bytes with a jump. If a disabled
probe B is at A+2, get_optimized_kprobe() stops at B when arming a new
probe C at A+4. It leaves A optimized:
A A+1 A+2 A+3 A+4
A's jump | e9 | d0 | d1 | d2 | d3 |
after C | e9 | d0 | d1 | d2 | cc |
The INT3 for C overwrites the last byte of A's jump displacement, so
execution can jump to the wrong address. B can have prepared optinsns
while disarmed, but has no jump to unoptimize.
Continue past disarmed and unprepared probes to find the active optimized
probe before arming a probe in its jump.
Fixes: afd66255b9a4 ("kprobes: Introduce kprobes jump optimization")
Cc: [email protected]
Signed-off-by: Leon Hwang <[email protected]>
---
kernel/kprobes.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 6337da5cab9e..e6f6e18fa1b5 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -495,14 +495,16 @@ static bool kprobe_queued(struct kprobe *p)
static struct kprobe *get_optimized_kprobe(kprobe_opcode_t *addr)
{
int i;
- struct kprobe *p = NULL;
+ struct kprobe *p;
struct optimized_kprobe *op;
/* Don't check i == 0, since that is a breakpoint case. */
- for (i = 1; !p && i < MAX_OPTIMIZED_LENGTH / sizeof(kprobe_opcode_t);
i++)
+ for (i = 1; i < MAX_OPTIMIZED_LENGTH / sizeof(kprobe_opcode_t); i++) {
p = get_kprobe(addr - i);
+ /* A disabled probe can have prepared, but inactive, optinsns.
*/
+ if (!p || !kprobe_optready(p) || kprobe_disarmed(p))
+ continue;
- if (p && kprobe_optready(p)) {
op = container_of(p, struct optimized_kprobe, kp);
if (arch_within_optimized_kprobe(op, addr))
return p;
--
2.55.0
