Messages in this thread |  | | Date | Thu, 27 Feb 2014 17:06:36 -0500 (EST) | From | Vince Weaver <> | Subject | Re: perf_fuzzer compiled for x32 causes reboot |
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I spent some more time on this. I managed to get a trace that exhibited the bug practically right away, but still unable to generate a reproducible trace :(
So instead I'm adding WARN's and trace_printks to see what I can find out.
Here's a summary of what I think is happneing. Please let me know if I'm wildly wrong in analyzing this.
Userspace accesses the perf ring-buffer-user-page of an event for the first time (in this trace it's a SW_CPU_CLOCK event).
This triggers a page_fault to bring in the page.
This triggers a TRACEPOINT event (task/task_newtask) which has PERF_SAMPLE_IP|PERF_SAMPLE_TID|PERF_SAMPLE_TIME|PERF_SAMPLE_CALLCHAIN|PERF_SAMPLE_ID|PERF_SAMPLE_CPU|PERF_SAMPLE_PERIOD|PERF_SAMPLE_STREAM_ID|PERF_SAMPLE_WEIGHT|PERF_SAMPLE_DATA_SRC|PERF_SAMPLE_TRANSACTION; and exclude_callchain_kernel=1, triggering a perf_callchain().
Here is a dump of the stack right after we enter perf_callchain()
vince@core2:~$ [ 202.320444] ------------[ cut here ]------------ [ 202.324001] WARNING: CPU: 1 PID: 2873 at kernel/events/callchain.c:168 perf_callchain+0x67/0x211() hermal_sys ehci_pci ehci_hcd sg sd_mod usbcore usb_common [ 202.324001] CPU: 1 PID: 2873 Comm: perf_fuzzer Not tainted 3.14.0-rc3+ #24 [ 202.324001] Hardware name: AOpen DE7000/nMCP7ALPx-DE R1.06 Oct.19.2012, BIOS 080015 10/19/2012 [ 202.324001] 00000000000000a8 ffff880119ec1b48 ffffffff81531dc1 00000000000000a8 [ 202.324001] 0000000000000000 ffff880119ec1b88 ffffffff81040ce4 ffff880119ec1b88 [ 202.324001] ffffffff810d416f ffff880119ec1e38 ffff8800cba67800 0000000000000000 [ 202.324001] Call Trace: [ 202.324001] [<ffffffff81531dc1>] dump_stack+0x49/0x60 [ 202.324001] [<ffffffff81040ce4>] warn_slowpath_common+0x81/0x9b [ 202.324001] [<ffffffff810d416f>] ? perf_callchain+0x67/0x211 [ 202.324001] [<ffffffff81040d18>] warn_slowpath_null+0x1a/0x1c [ 202.324001] [<ffffffff810d416f>] perf_callchain+0x67/0x211 [ 202.324001] [<ffffffff8106b0ab>] ? local_clock+0x1b/0x24 [ 202.324001] [<ffffffff810d0872>] perf_prepare_sample+0x7b/0x304 [ 202.324001] [<ffffffff810d1079>] __perf_event_overflow+0x156/0x1c1 [ 202.324001] [<ffffffff810f4613>] ? free_pgtables+0xa7/0xc9 [ 202.324001] [<ffffffff810d125e>] perf_swevent_overflow+0x41/0x5b [ 202.324001] [<ffffffff810d12ea>] perf_swevent_event+0x72/0x74 [ 202.324001] [<ffffffff810d1478>] perf_tp_event+0xea/0x1ef [ 202.324001] [<ffffffff8103515a>] ? perf_trace_x86_exceptions+0x4c/0xba [ 202.324001] [<ffffffff810351b6>] perf_trace_x86_exceptions+0xa8/0xba [ 202.324001] [<ffffffff8103515a>] ? perf_trace_x86_exceptions+0x4c/0xba [ 202.324001] [<ffffffff81538439>] trace_do_page_fault+0x48/0x99 [ 202.324001] [<ffffffff815354b2>] trace_page_fault+0x22/0x30 [ 202.324001] ---[ end trace 31ccd31b4e82cb42 ]---
This triggers a kernel pagefault because the BP register is not valid and copy_from_user_nmi() tries to copy the user stack area from there.
This *should* be OK? And it maybe looks like it works, but then
copy_user_handle_tail()
causes another page fault again at the invaid BP register.
But then the code continues to perf_output_begin()
237.265689: page_fault_kernel: address=0x17a0 ip=copy_user_handle_tail error_code=0x0 237.265689: function: __do_page_fault 237.265689: function: bad_area_nosemaphore 237.265690: function: __bad_area_nosemaphore 237.265690: function: no_context 237.265690: function: fixup_exception 237.265690: function: search_exception_tables 237.265690: function: search_extable 237.265691: function: perf_output_begin 237.265692: bprint: perf_output_begin: VMW: event type 2 config 2a st: 2c3e7
how are we back in __do_page_fault again here?
237.265692: function: __do_page_fault 237.265692: function: down_read_trylock 237.265692: function: _cond_resched 237.265693: function: find_vma 237.265693: function: bad_area 237.265693: function: up_read 237.265693: function: __bad_area_nosemaphore 237.265694: function: is_prefetch 237.265694: function: convert_ip_to_linear 237.265695: function: unhandled_signal 237.265695: function: __printk_ratelimit 237.265695: function: _raw_spin_trylock 237.265695: function: _raw_spin_unlock_irqrestore 237.265696: function: printk 237.265696: function: vprintk_emit
[ 202.877004] perf_fuzzer[2873]: segfault at 17a0 ip 00000000004017fd sp 00000000ffd19d10 error 6 in perf_fuzzer[400000+d1000]
Vince
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