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Message-Id: <1571120245-4186-1-git-send-email-prsood@codeaurora.org>
Date: Tue, 15 Oct 2019 11:47:25 +0530
From: Prateek Sood <prsood@...eaurora.org>
To: rostedt@...dmis.org, mingo@...hat.com
Cc: linux-kernel@...r.kernel.org, kaushalk@...eaurora.org,
Prateek Sood <prsood@...eaurora.org>
Subject: [PATCH] trace: fix race in perf_trace_buf initialization
[ 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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is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
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