Messages in this thread Patch in this message | | | From | Masami Hiramatsu <> | Subject | [PATCH -tip 2/2] kprobes: Set unoptimized flag after unoptimizing code | Date | Wed, 27 Nov 2019 14:57:04 +0900 |
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Fix to set unoptimized flag after confirming the code is completely unoptimized. Without this fix, when a kprobe hits the intermediate modified instruction (the first byte is replaced by int3, but latter bytes still be a jump address operand) while unoptimizing, it can return to the middle byte of the modified code. And it causes an invalid instruction exception in the kernel.
Usually, this is a rare case, but if we put a probe on the function called while text patching, it always causes a kernel panic as below. (text_poke() is used for patching the code in optprobe)
# echo p text_poke+5 > kprobe_events # echo 1 > events/kprobes/enable # echo 0 > events/kprobes/enable invalid opcode: 0000 [#1] PREEMPT SMP PTI CPU: 7 PID: 137 Comm: kworker/7:1 Not tainted 5.4.0-rc8+ #29 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014 Workqueue: events kprobe_optimizer RIP: 0010:text_poke+0x9/0x50 Code: 01 00 00 5b 5d 41 5c 41 5d c3 89 c0 0f b7 4c 02 fe 66 89 4c 05 fe e9 31 ff ff ff e8 71 ac 03 00 90 55 48 89 f5 53 cc 30 cb fd <1e> ec 08 8b 05 72 98 31 01 85 c0 75 11 48 83 c4 08 48 89 ee 48 89 RSP: 0018:ffffc90000343df0 EFLAGS: 00010686 RAX: 0000000000000000 RBX: ffffffff81025796 RCX: 0000000000000000 RDX: 0000000000000004 RSI: ffff88807c983148 RDI: ffffffff81025796 RBP: ffff88807c983148 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff82284fe0 R13: ffff88807c983138 R14: ffffffff82284ff0 R15: 0ffff88807d9eee0 FS: 0000000000000000(0000) GS:ffff88807d9c0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000000058158b CR3: 000000007b372000 CR4: 00000000000006a0 Call Trace: arch_unoptimize_kprobe+0x22/0x28 arch_unoptimize_kprobes+0x39/0x87 kprobe_optimizer+0x6e/0x290 process_one_work+0x2a0/0x610 worker_thread+0x28/0x3d0 ? process_one_work+0x610/0x610 kthread+0x10d/0x130 ? kthread_park+0x80/0x80 ret_from_fork+0x3a/0x50 Modules linked in: ---[ end trace 83b34b22a228711b ]---
This can happen even if we blacklist text_poke() and other functions, because there is a small time window which showing the intermediate code to other CPUs.
Fixes: 6274de4984a6 ("kprobes: Support delayed unoptimizing") Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> --- kernel/kprobes.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/kprobes.c b/kernel/kprobes.c index 53534aa258a6..34e28b236d68 100644 --- a/kernel/kprobes.c +++ b/kernel/kprobes.c @@ -510,6 +510,8 @@ static void do_unoptimize_kprobes(void) arch_unoptimize_kprobes(&unoptimizing_list, &freeing_list); /* Loop free_list for disarming */ 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)) arch_disarm_kprobe(&op->kp); @@ -649,6 +651,7 @@ static void force_unoptimize_kprobe(struct optimized_kprobe *op) { lockdep_assert_cpus_held(); arch_unoptimize_kprobe(op); + op->kp.flags &= ~KPROBE_FLAG_OPTIMIZED; if (kprobe_disabled(&op->kp)) arch_disarm_kprobe(&op->kp); } @@ -676,7 +679,6 @@ static void unoptimize_kprobe(struct kprobe *p, bool force) return; } - op->kp.flags &= ~KPROBE_FLAG_OPTIMIZED; if (!list_empty(&op->list)) { /* Dequeue from the optimization queue */ list_del_init(&op->list);
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