commit e03b4a084ea6b0a18b0e874baec439e69090c168 upstream.
The in_nmi() check in pre_handler_kretprobe() is meant to avoid
recursion, and blindly assumes that anything NMI is recursive.
However, since commit:
9b38cc704e84 ("kretprobe: Prevent triggering kretprobe from within kprobe_flush_task")
there is a better way to detect and avoid actual recursion.
By setting a dummy kprobe, any actual exceptions will terminate early
(by trying to handle the dummy kprobe), and recursion will not happen.
Employ this to avoid the kretprobe_table_lock() recursion, replacing
the over-eager in_nmi() check.
Cc: stable@xxxxxxxxxxxxxxx # 5.9.x
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/159870615628.1229682.6087311596892125907.stgit@devnote2
---
kernel/kprobes.c | 16 ++++------------
1 file changed, 4 insertions(+), 12 deletions(-)
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index e995541d277d..b885d884603d 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1359,7 +1359,8 @@ static void cleanup_rp_inst(struct kretprobe *rp)
struct hlist_node *next;
struct hlist_head *head;
- /* No race here */
+ /* To avoid recursive kretprobe by NMI, set kprobe busy here */
+ kprobe_busy_begin();
for (hash = 0; hash < KPROBE_TABLE_SIZE; hash++) {
kretprobe_table_lock(hash, &flags);
head = &kretprobe_inst_table[hash];
@@ -1369,6 +1370,8 @@ static void cleanup_rp_inst(struct kretprobe *rp)
}
kretprobe_table_unlock(hash, &flags);
}
+ kprobe_busy_end();
+
free_rp_inst(rp);
}
NOKPROBE_SYMBOL(cleanup_rp_inst);
@@ -1937,17 +1940,6 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
unsigned long hash, flags = 0;
struct kretprobe_instance *ri;
- /*
- * To avoid deadlocks, prohibit return probing in NMI contexts,
- * just skip the probe and increase the (inexact) 'nmissed'
- * statistical counter, so that the user is informed that
- * something happened:
- */
- if (unlikely(in_nmi())) {
- rp->nmissed++;
- return 0;
- }
-
/* TODO: consider to only swap the RA after the last pre_handler fired */
hash = hash_ptr(current, KPROBE_HASH_BITS);
raw_spin_lock_irqsave(&rp->lock, flags);
