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Tue, 15 Oct 2019 06:17:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1571120259; bh=nh6Hu+eyt5jL/ceEK128KwBXAqUtFIn8LM1k3NDK07I=; h=From:To:Cc:Subject:Date:From; b=XHBG5pufxoVnNckW5hndEwneiCcNJNTEmeXrRRxIdOsSngBWpKTOyu7V0mmAlBEdR UtlEEJXPzuw2S8MdQ2rTZzPH9N1+A5duLVkV0yeTt+i8BYi1hhaPGS1tTRPJ7oYSIa I467hNAHu6lj3y/aq7hurHWuuLypxbLBGFvwH45I= DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org B7E5360A43 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=prsood@codeaurora.org From: Prateek Sood To: rostedt@goodmis.org, mingo@redhat.com Cc: linux-kernel@vger.kernel.org, kaushalk@codeaurora.org, Prateek Sood Subject: [PATCH] trace: fix race in perf_trace_buf initialization Date: Tue, 15 Oct 2019 11:47:25 +0530 Message-Id: <1571120245-4186-1-git-send-email-prsood@codeaurora.org> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.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. Signed-off-by: Prateek Sood --- 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); } -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc., is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.