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Date: Fri, 18 Oct 2019 17:12:16 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Prateek Sood <prsood@...eaurora.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
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);
> }
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