Re: [PATCH] kprobes: Don't call disarm_kprobe() for disabled kprobes.

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

Hi,

On Fri, 12 Aug 2022 19:05:09 -0700
Kuniyuki Iwashima <kuniyu@amazon.com> wrote:

> The assumption in __disable_kprobe() is wrong, and it could try to disarm
> an already disarmed kprobe and fire the WARN_ONCE() below. [0]  We can
> easily reproduce this issue.
> 
> 1. Write 0 to /sys/kernel/debug/kprobes/enabled.
> 
>   # echo 0 > /sys/kernel/debug/kprobes/enabled
> 
> 2. Run execsnoop.  At this time, one kprobe is disabled.
> 
>   # /usr/share/bcc/tools/execsnoop &
>   [1] 2460
>   PCOMM            PID    PPID   RET ARGS
> 
>   # cat /sys/kernel/debug/kprobes/list
>   ffffffff91345650  r  __x64_sys_execve+0x0    [FTRACE]
>   ffffffff91345650  k  __x64_sys_execve+0x0    [DISABLED][FTRACE]
> 
> 3. Write 1 to /sys/kernel/debug/kprobes/enabled, which changes
>    kprobes_all_disarmed to false but does not arm the disabled kprobe.
> 
>   # echo 1 > /sys/kernel/debug/kprobes/enabled
> 
>   # cat /sys/kernel/debug/kprobes/list
>   ffffffff91345650  r  __x64_sys_execve+0x0    [FTRACE]
>   ffffffff91345650  k  __x64_sys_execve+0x0    [DISABLED][FTRACE]
> 
> 4. Kill execsnoop, when __disable_kprobe() calls disarm_kprobe() for the
>    disabled kprobe and hits the WARN_ONCE() in __disarm_kprobe_ftrace().
> 
>   # fg
>   /usr/share/bcc/tools/execsnoop
>   ^C

Good catch! I missed such scenario.
Hmm, actually, ftrace's kprobe events can not be removed when it is enabled.
Thus this was not tested. BPF may remove it without disabling it.

> 
> Actually, WARN_ONCE() is fired twice, and __unregister_kprobe_top() misses
> some cleanups and leaves the aggregated kprobe in the hash table.  Then,
> __unregister_trace_kprobe() initialises tk->rp.kp.list and creates an
> infinite loop like this.
> 
>   aggregated kprobe.list -> kprobe.list -.
>                                      ^    |
>                                      '.__.'
> 
> In this situation, these commands fall into the infinite loop and result
> in RCU stall or soft lockup.
> 
>   cat /sys/kernel/debug/kprobes/list : show_kprobe_addr() enters into the
>                                        infinite loop with RCU.
> 
>   /usr/share/bcc/tools/execsnoop : warn_kprobe_rereg() holds kprobe_mutex,
>                                    and __get_valid_kprobe() is stuck in
> 				   the loop.
> 
> To avoid the issue, make sure we don't call disarm_kprobe() for disabled
> kprobes.
> 
> [0]
> Failed to disarm kprobe-ftrace at __x64_sys_execve+0x0/0x40 (error -2)
> WARNING: CPU: 6 PID: 2460 at kernel/kprobes.c:1130 __disarm_kprobe_ftrace.isra.19 (kernel/kprobes.c:1129)
> Modules linked in: ena
> CPU: 6 PID: 2460 Comm: execsnoop Not tainted 5.19.0+ #28
> Hardware name: Amazon EC2 c5.2xlarge/, BIOS 1.0 10/16/2017
> RIP: 0010:__disarm_kprobe_ftrace.isra.19 (kernel/kprobes.c:1129)
> Code: 24 8b 02 eb c1 80 3d c4 83 f2 01 00 75 d4 48 8b 75 00 89 c2 48 c7 c7 90 fa 0f 92 89 04 24 c6 05 ab 83 01 e8 e4 94 f0 ff <0f> 0b 8b 04 24 eb b1 89 c6 48 c7 c7 60 fa 0f 92 89 04 24 e8 cc 94
> RSP: 0018:ffff9e6ec154bd98 EFLAGS: 00010282
> RAX: 0000000000000000 RBX: ffffffff930f7b00 RCX: 0000000000000001
> RDX: 0000000080000001 RSI: ffffffff921461c5 RDI: 00000000ffffffff
> RBP: ffff89c504286da8 R08: 0000000000000000 R09: c0000000fffeffff
> R10: 0000000000000000 R11: ffff9e6ec154bc28 R12: ffff89c502394e40
> R13: ffff89c502394c00 R14: ffff9e6ec154bc00 R15: 0000000000000000
> FS:  00007fe800398740(0000) GS:ffff89c812d80000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000c00057f010 CR3: 0000000103b54006 CR4: 00000000007706e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> PKRU: 55555554
> Call Trace:
> <TASK>
>  __disable_kprobe (kernel/kprobes.c:1716)
>  disable_kprobe (kernel/kprobes.c:2392)
>  __disable_trace_kprobe (kernel/trace/trace_kprobe.c:340)
>  disable_trace_kprobe (kernel/trace/trace_kprobe.c:429)
>  perf_trace_event_unreg.isra.2 (./include/linux/tracepoint.h:93 kernel/trace/trace_event_perf.c:168)
>  perf_kprobe_destroy (kernel/trace/trace_event_perf.c:295)
>  _free_event (kernel/events/core.c:4971)
>  perf_event_release_kernel (kernel/events/core.c:5176)
>  perf_release (kernel/events/core.c:5186)
>  __fput (fs/file_table.c:321)
>  task_work_run (./include/linux/sched.h:2056 (discriminator 1) kernel/task_work.c:179 (discriminator 1))
>  exit_to_user_mode_prepare (./include/linux/resume_user_mode.h:49 kernel/entry/common.c:169 kernel/entry/common.c:201)
>  syscall_exit_to_user_mode (./arch/x86/include/asm/jump_label.h:55 ./arch/x86/include/asm/nospec-branch.h:384 ./arch/x86/include/asm/entry-common.h:94 kernel/entry/common.c:133 kernel/entry/common.c:296)
>  do_syscall_64 (arch/x86/entry/common.c:87)
>  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120)
> RIP: 0033:0x7fe7ff210654
> Code: 15 79 89 20 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb be 0f 1f 00 8b 05 9a cd 20 00 48 63 ff 85 c0 75 11 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 3a f3 c3 48 83 ec 18 48 89 7c 24 08 e8 34 fc
> RSP: 002b:00007ffdbd1d3538 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
> RAX: 0000000000000000 RBX: 0000000000000008 RCX: 00007fe7ff210654
> RDX: 0000000000000000 RSI: 0000000000002401 RDI: 0000000000000008
> RBP: 0000000000000000 R08: 94ae31d6fda838a4 R0900007fe8001c9d30
> R10: 00007ffdbd1d34b0 R11: 0000000000000246 R12: 00007ffdbd1d3600
> R13: 0000000000000000 R14: fffffffffffffffc R15: 00007ffdbd1d3560
> </TASK>
> 
> Fixes: 69d54b916d83 ("kprobes: makes kprobes/enabled works correctly for optimized kprobes.")
> Reported-by: Ayushman Dutta <ayudutta@amazon.com>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>


Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: stable@vger.kernel.org


> ---
>  kernel/kprobes.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 80697e5e03e4..08350e35aba2 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1707,11 +1707,12 @@ static struct kprobe *__disable_kprobe(struct kprobe *p)
>  		/* Try to disarm and disable this/parent probe */
>  		if (p == orig_p || aggr_kprobe_disabled(orig_p)) {

OK, I checked 
 - p is not disabled
 - orig_p's child probes are disbled (this may includes p)
But forgot to check
 - orig_p is not disabled

>  			/*
> -			 * If 'kprobes_all_disarmed' is set, 'orig_p'
> -			 * should have already been disarmed, so
> -			 * skip unneed disarming process.
> +			 * Don't be lazy here.  Even if 'kprobes_all_disarmed'
> +			 * is false, 'orig_p' might not have been armed yet.
> +			 * Note arm_all_kprobes() __tries__ to arm all kprobes
> +			 * on the best effort basis.
>  			 */
> -			if (!kprobes_all_disarmed) {
> +			if (!kprobes_all_disarmed && !kprobe_disabled(orig_p)) {
>  				ret = disarm_kprobe(orig_p, true);
>  				if (ret) {
>  					p->flags &= ~KPROBE_FLAG_DISABLED;

Thank you,


> -- 
> 2.30.2
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>