[PATCH 3.16 098/157] x86/kprobes: Avoid kretprobe recursion bug

From: Ben Hutchings
Date: Sat Aug 10 2019 - 16:48:11 EST


3.16.72-rc1 review patch. If anyone has any objections, please let me know.

------------------

From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

commit b191fa96ea6dc00d331dcc28c1f7db5e075693a0 upstream.

Avoid kretprobe recursion loop bg by setting a dummy
kprobes to current_kprobe per-CPU variable.

This bug has been introduced with the asm-coded trampoline
code, since previously it used another kprobe for hooking
the function return placeholder (which only has a nop) and
trampoline handler was called from that kprobe.

This revives the old lost kprobe again.

With this fix, we don't see deadlock anymore.

And you can see that all inner-called kretprobe are skipped.

event_1 235 0
event_2 19375 19612

The 1st column is recorded count and the 2nd is missed count.
Above shows (event_1 rec) + (event_2 rec) ~= (event_2 missed)
(some difference are here because the counter is racy)

Reported-by: Andrea Righi <righi.andrea@xxxxxxxxx>
Tested-by: Andrea Righi <righi.andrea@xxxxxxxxx>
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Fixes: c9becf58d935 ("[PATCH] kretprobe: kretprobe-booster")
Link: http://lkml.kernel.org/r/155094064889.6137.972160690963039.stgit@devbox
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
arch/x86/kernel/kprobes/core.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)

--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -686,11 +686,16 @@ static void __used kretprobe_trampoline_
NOKPROBE_SYMBOL(kretprobe_trampoline_holder);
NOKPROBE_SYMBOL(kretprobe_trampoline);

+static struct kprobe kretprobe_kprobe = {
+ .addr = (void *)kretprobe_trampoline,
+};
+
/*
* Called from kretprobe_trampoline
*/
__visible __used void *trampoline_handler(struct pt_regs *regs)
{
+ struct kprobe_ctlblk *kcb;
struct kretprobe_instance *ri = NULL;
struct hlist_head *head, empty_rp;
struct hlist_node *tmp;
@@ -700,6 +705,17 @@ __visible __used void *trampoline_handle
void *frame_pointer;
bool skipped = false;

+ preempt_disable();
+
+ /*
+ * Set a dummy kprobe for avoiding kretprobe recursion.
+ * Since kretprobe never run in kprobe handler, kprobe must not
+ * be running at this point.
+ */
+ kcb = get_kprobe_ctlblk();
+ __this_cpu_write(current_kprobe, &kretprobe_kprobe);
+ kcb->kprobe_status = KPROBE_HIT_ACTIVE;
+
INIT_HLIST_HEAD(&empty_rp);
kretprobe_hash_lock(current, &head, &flags);
/* fixup registers */
@@ -775,10 +791,9 @@ __visible __used void *trampoline_handle
orig_ret_address = (unsigned long)ri->ret_addr;
if (ri->rp && ri->rp->handler) {
__this_cpu_write(current_kprobe, &ri->rp->kp);
- get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
ri->ret_addr = correct_ret_addr;
ri->rp->handler(ri, regs);
- __this_cpu_write(current_kprobe, NULL);
+ __this_cpu_write(current_kprobe, &kretprobe_kprobe);
}

recycle_rp_inst(ri, &empty_rp);
@@ -794,6 +809,9 @@ __visible __used void *trampoline_handle

kretprobe_hash_unlock(current, &flags);

+ __this_cpu_write(current_kprobe, NULL);
+ preempt_enable();
+
hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
hlist_del(&ri->hlist);
kfree(ri);