From: Prateek Sood prsood@codeaurora.org

[ 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.

Link: http://lkml.kernel.org/r/1571120245-4186-1-git-send-email-prsood@codeaurora....

Cc: stable@vger.kernel.org Fixes: e12f03d7031a9 ("perf/core: Implement the 'perf_kprobe' PMU") Acked-by: Song Liu songliubraving@fb.com Signed-off-by: Prateek Sood prsood@codeaurora.org Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.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 0892e38ed6fb..a9dfa04ffa44 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); }