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Subject[tip:perf/urgent] kprobes: Fix error check when reusing optimized probes
Commit-ID:  5f843ed415581cfad4ef8fefe31c138a8346ca8a
Gitweb: https://git.kernel.org/tip/5f843ed415581cfad4ef8fefe31c138a8346ca8a
Author: Masami Hiramatsu <mhiramat@kernel.org>
AuthorDate: Mon, 15 Apr 2019 15:01:25 +0900
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 16 Apr 2019 09:38:16 +0200

kprobes: Fix error check when reusing optimized probes

The following commit introduced a bug in one of our error paths:

819319fc9346 ("kprobes: Return error if we fail to reuse kprobe instead of BUG_ON()")

it missed to handle the return value of kprobe_optready() as
error-value. In reality, the kprobe_optready() returns a bool
result, so "true" case must be passed instead of 0.

This causes some errors on kprobe boot-time selftests on ARM:

[ ] Beginning kprobe tests...
[ ] Probe ARM code
[ ] kprobe
[ ] kretprobe
[ ] ARM instruction simulation
[ ] Check decoding tables
[ ] Run test cases
[ ] FAIL: test_case_handler not run
[ ] FAIL: Test andge r10, r11, r14, asr r7
[ ] FAIL: Scenario 11
...
[ ] FAIL: Scenario 7
[ ] Total instruction simulation tests=1631, pass=1433 fail=198
[ ] kprobe tests failed

This can happen if an optimized probe is unregistered and next
kprobe is registered on same address until the previous probe
is not reclaimed.

If this happens, a hidden aggregated probe may be kept in memory,
and no new kprobe can probe same address. Also, in that case
register_kprobe() will return "1" instead of minus error value,
which can mislead caller logic.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: David S . Miller <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Naveen N . Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org # v5.0+
Fixes: 819319fc9346 ("kprobes: Return error if we fail to reuse kprobe instead of BUG_ON()")
Link: http://lkml.kernel.org/r/155530808559.32517.539898325433642204.stgit@devnote2
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/kprobes.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index c83e54727131..b1ea30a5540e 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -709,7 +709,6 @@ static void unoptimize_kprobe(struct kprobe *p, bool force)
static int reuse_unused_kprobe(struct kprobe *ap)
{
struct optimized_kprobe *op;
- int ret;

/*
* Unused kprobe MUST be on the way of delayed unoptimizing (means
@@ -720,9 +719,8 @@ static int reuse_unused_kprobe(struct kprobe *ap)
/* Enable the probe again */
ap->flags &= ~KPROBE_FLAG_DISABLED;
/* Optimize it again (remove from op->list) */
- ret = kprobe_optready(ap);
- if (ret)
- return ret;
+ if (!kprobe_optready(ap))
+ return -EINVAL;

optimize_kprobe(ap);
return 0;
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