[PATCH] kprobes: Fix to handle forcibly unoptimized kprobes on freeing_list

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

Sinec forcibly unoptimized kprobes will be put on the freeing_list directly
in the unoptimize_kprobe(), do_unoptimize_kprobes() must continue to check
the freeing_list even if unoptimizing_list is empty.

This bug can be happen if a kprobe is put in an instruction which is in the
middle of the jump-replaced instruction sequence of an optprobe, *and* the
optprobe is recently unregistered and queued on unoptimizing_list.
In this case, the optprobe will be unoptimized forcibly (means immediately)
and put it into the freeing_list, expecting the optprobe will be handled in
do_unoptimize_kprobe().
But if there is no other optprobes on the unoptimizing_list, current code
returns from the do_unoptimize_kprobe() soon and do not handle the optprobe
which is on the freeing_list, and it will hit the WARN_ON_ONCE() in the
do_free_cleaned_kprobes(), because it is not handled in the latter loop of
the do_unoptimize_kprobe().

To solve this issue, do not return from do_unoptimize_kprobes() immediately
even if unoptimizing_list is empty.

Moreover, this change affects another case. kill_optimized_kprobes() expects
kprobe_optimizer() will just free the optprobe on freeing_list.
So I changed it to just do list_move() to freeing_list if optprobes are on
unoptimizing list. And the do_unoptimize_kprobe() will skip
arch_disarm_kprobe() if the probe on freeing_list has gone flag.

Link: https://lore.kernel.org/all/Y8URdIfVr3pq2X8w@xxxxxxxxxxxxxxxx/

Fixes: e4add247789e ("kprobes: Fix optimize_kprobe()/unoptimize_kprobe() cancellation logic")
Reported-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
---
 kernel/kprobes.c |   23 ++++++++++-------------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 1c18ecf9f98b..73b150fad936 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -555,17 +555,15 @@ static void do_unoptimize_kprobes(void)
 	/* See comment in do_optimize_kprobes() */
 	lockdep_assert_cpus_held();
 
-	/* Unoptimization must be done anytime */
-	if (list_empty(&unoptimizing_list))
-		return;
+	if (!list_empty(&unoptimizing_list))
+		arch_unoptimize_kprobes(&unoptimizing_list, &freeing_list);
 
-	arch_unoptimize_kprobes(&unoptimizing_list, &freeing_list);
-	/* Loop on 'freeing_list' for disarming */
+	/* Loop on 'freeing_list' for disarming and removing from kprobe hash list */
 	list_for_each_entry_safe(op, tmp, &freeing_list, list) {
 		/* Switching from detour code to origin */
 		op->kp.flags &= ~KPROBE_FLAG_OPTIMIZED;
-		/* Disarm probes if marked disabled */
-		if (kprobe_disabled(&op->kp))
+		/* Disarm probes if marked disabled and not gone */
+		if (kprobe_disabled(&op->kp) && !kprobe_gone(&op->kp))
 			arch_disarm_kprobe(&op->kp);
 		if (kprobe_unused(&op->kp)) {
 			/*
@@ -797,14 +795,13 @@ static void kill_optimized_kprobe(struct kprobe *p)
 	op->kp.flags &= ~KPROBE_FLAG_OPTIMIZED;
 
 	if (kprobe_unused(p)) {
-		/* Enqueue if it is unused */
-		list_add(&op->list, &freeing_list);
 		/*
-		 * Remove unused probes from the hash list. After waiting
-		 * for synchronization, this probe is reclaimed.
-		 * (reclaiming is done by do_free_cleaned_kprobes().)
+		 * Unused kprobe is on unoptimizing or freeing list. We move it
+		 * to freeing_list and let the kprobe_optimizer() removes it from
+		 * the kprobe hash list and frees it.
 		 */
-		hlist_del_rcu(&op->kp.hlist);
+		if (optprobe_queued_unopt(op))
+			list_move(&op->list, &freeing_list);
 	}
 
 	/* Don't touch the code, because it is already freed. */