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Date: Mon, 21 Oct 2019 10:12:43 +0530
From: Prateek Sood <prsood@...eaurora.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: mingo@...hat.com, linux-kernel@...r.kernel.org,
kaushalk@...eaurora.org, Peter Zijlstra <peterz@...radead.org>,
Song Liu <songliubraving@...com>
Subject: Re: [PATCH] trace: fix race in perf_trace_buf initialization
On 10/19/19 2:42 AM, Steven Rostedt wrote:
>
> Peter told me it was fine, but I'm also adding Song who is the author
> of the code.
>
> Also needs the tags (which I'll add)
>
> Cc: stable@...r.kernel.org
> Fixes: e12f03d7031a9 ("perf/core: Implement the 'perf_kprobe' PMU")
>
> -- Steve
>
>
> On Tue, 15 Oct 2019 11:47:25 +0530
> Prateek Sood <prsood@...eaurora.org> wrote:
>
>> [ 943.034988] Unable to handle kernel paging request at virtual address 0000003106f2003c
>> [ 943.043653] Mem abort info:
>> [ 943.046679] ESR = 0x96000045
>> [ 943.050428] Exception class = DABT (current EL), IL = 32 bits
>> [ 943.056643] SET = 0, FnV = 0
>> [ 943.060168] EA = 0, S1PTW = 0
>> [ 943.063449] Data abort info:
>> [ 943.066474] ISV = 0, ISS = 0x00000045
>> [ 943.070856] CM = 0, WnR = 1
>> [ 943.074016] user pgtable: 4k pages, 39-bit VAs, pgdp = ffffffc034b9b000
>> [ 943.081446] [0000003106f2003c] pgd=0000000000000000, pud=0000000000000000
>> [ 943.088862] Internal error: Oops: 96000045 [#1] PREEMPT SMP
>> [ 943.141700] Process syz-executor (pid: 18393, stack limit = 0xffffffc093190000)
>> [ 943.164146] pstate: 80400005 (Nzcv daif +PAN -UAO)
>> [ 943.169119] pc : __memset+0x20/0x1ac
>> [ 943.172831] lr : memset+0x3c/0x50
>> [ 943.176269] sp : ffffffc09319fc50
>>
>> [ 943.557593] __memset+0x20/0x1ac
>> [ 943.560953] perf_trace_buf_alloc+0x140/0x1a0
>> [ 943.565472] perf_trace_sys_enter+0x158/0x310
>> [ 943.569985] syscall_trace_enter+0x348/0x7c0
>> [ 943.574413] el0_svc_common+0x11c/0x368
>> [ 943.578394] el0_svc_handler+0x12c/0x198
>> [ 943.582459] el0_svc+0x8/0xc
>>
>> In Ramdumps:
>> total_ref_count = 3
>> perf_trace_buf = (
>> 0x0 -> NULL,
>> 0x0 -> NULL,
>> 0x0 -> NULL,
>> 0x0 -> NULL)
>>
>> event_call in perf_trace_sys_enter()
>> event_call = 0xFFFFFF900CB511D8 -> (
>> list = (next = 0xFFFFFF900CB4E2E0, prev = 0xFFFFFF900CB512B0),
>> class = 0xFFFFFF900CDC8308,
>> name = 0xFFFFFF900CDDA1D8,
>> tp = 0xFFFFFF900CDDA1D8,
>> event = (
>> node = (next = 0x0, pprev = 0xFFFFFF900CB80210),
>> list = (next = 0xFFFFFF900CB512E0, prev = 0xFFFFFF900CB4E310),
>> type = 21,
>> funcs = 0xFFFFFF900CB51130),
>> print_fmt = 0xFFFFFF900CB51150,
>> filter = 0x0,
>> mod = 0x0,
>> data = 0x0,
>> flags = 18,
>> perf_refcount = 1,
>> perf_events = 0xFFFFFF8DB8E54158,
>> prog_array = 0x0,
>> perf_perm = 0x0)
>>
>> perf_events added on CPU0
>> (struct hlist_head *)(0xFFFFFF8DB8E54158+__per_cpu_offset[0]) -> (
>> first = 0xFFFFFFC0980FD0E0 -> (
>> next = 0x0,
>> pprev = 0xFFFFFFBEBFD74158))
>>
>> Could you please confirm:
>> 1) the race mentioned below exists or not.
>> 2) if following patch fixes it.
>>
>>
>>> 8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8
>>
>> A race condition exists while initialiazing perf_trace_buf from
>> perf_trace_init() and perf_kprobe_init().
>>
>> CPU0 CPU1
>> perf_trace_init()
>> mutex_lock(&event_mutex)
>> perf_trace_event_init()
>> perf_trace_event_reg()
>> total_ref_count == 0
>> buf = alloc_percpu()
>> perf_trace_buf[i] = buf
>> tp_event->class->reg() //fails perf_kprobe_init()
>> goto fail perf_trace_event_init()
>> perf_trace_event_reg()
>> fail:
>> total_ref_count == 0
>>
>> total_ref_count == 0
>> buf = alloc_percpu()
>> perf_trace_buf[i] = buf
>> tp_event->class->reg()
>> total_ref_count++
>>
>> free_percpu(perf_trace_buf[i])
>> perf_trace_buf[i] = NULL
>>
>> Any subsequent call to perf_trace_event_reg() will observe total_ref_count > 0,
>> causing the perf_trace_buf to be NULL always. This can result in perf_trace_buf
>> getting accessed from perf_trace_buf_alloc() without being initialized. Acquiring
>> event_mutex in perf_kprobe_init() before calling perf_trace_event_init() should
>> fix this race.
>>
>> Signed-off-by: Prateek Sood <prsood@...eaurora.org>
>> ---
>> kernel/trace/trace_event_perf.c | 4 ++++
>> 1 file changed, 4 insertions(+)
>>
>> diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
>> index 4629a61..48ee92c 100644
>> --- a/kernel/trace/trace_event_perf.c
>> +++ b/kernel/trace/trace_event_perf.c
>> @@ -272,9 +272,11 @@ int perf_kprobe_init(struct perf_event *p_event, bool is_retprobe)
>> goto out;
>> }
>>
>> + mutex_lock(&event_mutex);
>> ret = perf_trace_event_init(tp_event, p_event);
>> if (ret)
>> destroy_local_trace_kprobe(tp_event);
>> + mutex_unlock(&event_mutex);
>> out:
>> kfree(func);
>> return ret;
>> @@ -282,8 +284,10 @@ int perf_kprobe_init(struct perf_event *p_event, bool is_retprobe)
>>
>> void perf_kprobe_destroy(struct perf_event *p_event)
>> {
>> + mutex_lock(&event_mutex);
>> perf_trace_event_close(p_event);
>> perf_trace_event_unreg(p_event);
>> + mutex_unlock(&event_mutex);
>>
>> destroy_local_trace_kprobe(p_event->tp_event);
>> }
>
Hi Song,
Could you please help in this query.
Thanks
Prateek
--
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