This is a note to let you know that I've just added the patch titled
s390/kprobes: fix current_kprobe never cleared after kprobes reenter
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
s390-kprobes-fix-current_kprobe-never-cleared-after-kprobes-reenter.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From cd57953936f2213dfaccce10d20f396956222c7d Mon Sep 17 00:00:00 2001
From: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Date: Wed, 1 Mar 2023 17:58:06 +0100
Subject: s390/kprobes: fix current_kprobe never cleared after kprobes reenter
From: Vasily Gorbik <gor@xxxxxxxxxxxxx>
commit cd57953936f2213dfaccce10d20f396956222c7d upstream.
Recent test_kprobe_missed kprobes kunit test uncovers the following
problem. Once kprobe is triggered from another kprobe (kprobe reenter),
all future kprobes on this cpu are considered as kprobe reenter, thus
pre_handler and post_handler are not being called and kprobes are counted
as "missed".
Commit b9599798f953 ("[S390] kprobes: activation and deactivation")
introduced a simpler scheme for kprobes (de)activation and status
tracking by using push_kprobe/pop_kprobe, which supposed to work for
both initial kprobe entry as well as kprobe reentry and helps to avoid
handling those two cases differently. The problem is that a sequence of
calls in case of kprobes reenter:
push_kprobe() <- NULL (current_kprobe)
push_kprobe() <- kprobe1 (current_kprobe)
pop_kprobe() -> kprobe1 (current_kprobe)
pop_kprobe() -> kprobe1 (current_kprobe)
leaves "kprobe1" as "current_kprobe" on this cpu, instead of setting it
to NULL. In fact push_kprobe/pop_kprobe can only store a single state
(there is just one prev_kprobe in kprobe_ctlblk). Which is a hack but
sufficient, there is no need to have another prev_kprobe just to store
NULL. To make a simple and backportable fix simply reset "prev_kprobe"
when kprobe is poped from this "stack". No need to worry about
"kprobe_status" in this case, because its value is only checked when
current_kprobe != NULL.
Cc: stable@xxxxxxxxxxxxxxx
Fixes: b9599798f953 ("[S390] kprobes: activation and deactivation")
Reviewed-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Signed-off-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/s390/kernel/kprobes.c | 1 +
1 file changed, 1 insertion(+)
--- a/arch/s390/kernel/kprobes.c
+++ b/arch/s390/kernel/kprobes.c
@@ -241,6 +241,7 @@ static void pop_kprobe(struct kprobe_ctl
{
__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
kcb->kprobe_status = kcb->prev_kprobe.status;
+ kcb->prev_kprobe.kp = NULL;
}
NOKPROBE_SYMBOL(pop_kprobe);
Patches currently in stable-queue which might be from gor@xxxxxxxxxxxxx are
queue-5.10/s390-vmem-fix-empty-page-tables-cleanup-under-kasan.patch
queue-5.10/s390-kprobes-fix-irq-mask-clobbering-on-kprobe-reenter-from-post_handler.patch
queue-5.10/s390-kprobes-fix-current_kprobe-never-cleared-after-kprobes-reenter.patch
