From: Vasily Gorbik gor@linux.ibm.com
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@vger.kernel.org Fixes: b9599798f953 ("[S390] kprobes: activation and deactivation") Reviewed-by: Heiko Carstens hca@linux.ibm.com Signed-off-by: Vasily Gorbik gor@linux.ibm.com Signed-off-by: Heiko Carstens hca@linux.ibm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/s390/kernel/kprobes.c | 1 + 1 file changed, 1 insertion(+)
--- a/arch/s390/kernel/kprobes.c +++ b/arch/s390/kernel/kprobes.c @@ -272,6 +272,7 @@ 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);