Date:   Mon, 24 Oct 2016 06:14:02 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Vince Weaver <vincent.weaver@...ne.edu>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: perf: perf_fuzzer triggers vmalloc_fault (then crashes)

On Mon, Oct 24, 2016 at 12:18:02PM +0200, Peter Zijlstra wrote:
> On Fri, Oct 21, 2016 at 11:05:40PM -0400, Vince Weaver wrote:
> > 
> > This is on an AMD a10 system.  With paranoid=1.  Think it's 
> > probably unrelated to the (unreseolved) AMD IBS issues.
> > This is 4.9-rc0 just before rc1 (can't get actual rc1 to boot)
> > 
> > Machine locks hard after this.
> > 
> > [ 8098.085662] BAD LUCK: lost 42 message(s) from NMI context!
> > [ 8098.085663] ------------[ cut here ]------------
> > [ 8098.085664] WARNING: CPU: 0 PID: 21338 at arch/x86/mm/fault.c:435 vmalloc_fault+0x58/0x1f0
> > [ 8098.085668] CPU: 0 PID: 21338 Comm: perf_fuzzer Not tainted 4.8.0+ #37
> > [ 8098.085668] Hardware name: Hewlett-Packard HP Compaq Pro 6305 SFF/1850, BIOS K06 v02.57 08/16/2013
> > [ 8098.085670] Call Trace:
> > [ 8098.085670]  <NMI>  [<ffffffff81263c2f>] ? dump_stack+0x46/0x59
> > [ 8098.085670]  [<ffffffff810499c4>] ? __warn+0xd5/0xee
> > [ 8098.085671]  [<ffffffff8103b4de>] ? vmalloc_fault+0x58/0x1f0
> > [ 8098.085671]  [<ffffffff8103c193>] ? __do_page_fault+0x6d/0x48e
> > [ 8098.085671]  [<ffffffff810eaf5b>] ? perf_log_throttle+0xa4/0xf4
> > [ 8098.085672]  [<ffffffff8145df72>] ? trace_page_fault+0x22/0x30
> > [ 8098.085672]  [<ffffffff8103918d>] ? __unwind_start+0x28/0x42
> > [ 8098.085672]  [<ffffffff81004721>] ? perf_callchain_kernel+0x75/0xac
> > [ 8098.085672]  [<ffffffff810efb0a>] ? get_perf_callchain+0x13a/0x1f0
> > [ 8098.085673]  [<ffffffff810efc2a>] ? perf_callchain+0x6a/0x6c
> > [ 8098.085673]  [<ffffffff810ecf5d>] ? perf_prepare_sample+0x71/0x2eb
> > [ 8098.085673]  [<ffffffff810ed1f1>] ? perf_event_output_forward+0x1a/0x54
> > [ 8098.085674]  [<ffffffff810313bc>] ? __default_send_IPI_shortcut+0x10/0x2d
> > [ 8098.085674]  [<ffffffff810eb247>] ? __perf_event_overflow+0xfb/0x167
> > [ 8098.085674]  [<ffffffff81004247>] ? x86_pmu_handle_irq+0x113/0x150
> > [ 8098.085675]  [<ffffffff81003116>] ? native_read_msr+0x6/0x34
> > [ 8098.085675]  [<ffffffff81002dee>] ? perf_event_nmi_handler+0x22/0x39
> > [ 8098.085675]  [<ffffffff81006621>] ? perf_ibs_nmi_handler+0x4a/0x51
> > [ 8098.085676]  [<ffffffff81002dee>] ? perf_event_nmi_handler+0x22/0x39
> > [ 8098.085676]  [<ffffffff81018493>] ? nmi_handle+0x4d/0xf0
> > [ 8098.085676]  [<ffffffff810065d7>] ? perf_ibs_handle_irq+0x3d1/0x3d1
> > [ 8098.085676]  [<ffffffff810186dd>] ? default_do_nmi+0x3c/0xd5
> > [ 8098.085677]  [<ffffffff81018808>] ? do_nmi+0x92/0x102
> > [ 8098.085677]  [<ffffffff8145e2a7>] ? end_repeat_nmi+0x1a/0x1e
> > [ 8098.085677]  [<ffffffff8145c2d5>] ? entry_SYSCALL_64_after_swapgs+0x12/0x4a
> > [ 8098.085678]  [<ffffffff8145c2d5>] ? entry_SYSCALL_64_after_swapgs+0x12/0x4a
> > [ 8098.085678]  [<ffffffff8145c2d5>] ? entry_SYSCALL_64_after_swapgs+0x12/0x4a
> > [ 8098.085678]  <EOE> ^A4---[ end trace 632723104d47d31a ]---
> 
> So we get an NMI based stack unwind (without frame pointers) overrun the
> actual stack, and tickle the new guard page thing:
> 
> > [ 8098.085679] BUG: stack guard page was hit at ffffc90008500000 (stack is ffffc900084fc000..ffffc900084fffff)
> > [ 8098.085679] kernel stack overflow (page fault): 0000 [#1] SMP
> > [ 8098.085683] CPU: 0 PID: 21338 Comm: perf_fuzzer Tainted: G        W       4.8.0+ #37
> > [ 8098.085683] Hardware name: Hewlett-Packard HP Compaq Pro 6305 SFF/1850, BIOS K06 v02.57 08/16/2013
> > [ 8098.085684] task: ffff8802265d2080 task.stack: ffffc900084fc000
> > [ 8098.085684] RIP: 0010:[<ffffffff8103918d>] ^Ac [<ffffffff8103918d>] __unwind_start+0x28/0x42
> > [ 8098.085684] RSP: 0018:ffff88022ec05af0  EFLAGS: 00010006
> > [ 8098.085685] RAX: 00000000ffffffea RBX: ffff88022ec05b08 RCX: ffffc90008500000
> > [ 8098.085685] RDX: ffff88022ec00000 RSI: 0000000000001000 RDI: 000000000000c4d0
> > [ 8098.085685] RBP: ffffc90008500000 R08: ffff88022ec08000 R09: 0000000000000000
> > [ 8098.085686] R10: 0000000000000002 R11: 0000000000000206 R12: ffff88022ec05b70
> > [ 8098.085686] R13: ffff88022ec05ef8 R14: 0000000000000000 R15: 0000000000000001
> > [ 8098.085687] FS:  00007f06e791c700(0000) GS:ffff88022ec00000(0000) knlGS:0000000000000000
> > [ 8098.085687] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [ 8098.085687] CR2: ffffc90008500000 CR3: 0000000223c25000 CR4: 00000000000407f0
> > [ 8098.085688] DR0: 0000000000000000 DR1: 0000000000005fc8 DR2: 0000000000005fc8
> > [ 8098.085688] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
> > [ 8098.085689] Call Trace:
> > [ 8098.085690]  <NMI> ^Ad [<ffffffff81004721>] ? perf_callchain_kernel+0x75/0xac
> > [ 8098.085690]  [<ffffffff8126da5e>] ? vsnprintf+0x380/0x3b4
> > [ 8098.085690]  [<ffffffff8126db7e>] ? sprintf+0x42/0x4a
> > [ 8098.085691]  [<ffffffff810a8982>] ? __sprint_symbol+0x9d/0xd1
> > [ 8098.085691]  [<ffffffff8126be12>] ? symbol_string+0x51/0x5d
> > [ 8098.085691]  [<ffffffff810a8982>] ? __sprint_symbol+0x9d/0xd1
> > [ 8098.085692]  [<ffffffff8126be12>] ? symbol_string+0x51/0x5d
> > [ 8098.085692]  [<ffffffff8126d3ea>] ? pointer+0x85/0x379
> > [ 8098.085692]  [<ffffffff8126d75e>] ? vsnprintf+0x80/0x3b4
> > [ 8098.085692]  [<ffffffff810dbe53>] ? irq_work_queue+0xa/0x66
> > [ 8098.085693]  [<ffffffff81084db5>] ? vprintk_nmi+0x88/0x97
> > [ 8098.085693]  [<ffffffff81084db5>] ? vprintk_nmi+0x88/0x97
> > [ 8098.085693]  [<ffffffff810f19b1>] ? printk+0x43/0x4b
> > [ 8098.085694]  [<ffffffff810a4919>] ? __module_text_address+0x9/0x4f
> > [ 8098.085694]  [<ffffffff810a8346>] ? is_module_text_address+0x5/0xc
> > [ 8098.085694]  [<ffffffff81017eed>] ? show_trace_log_lvl+0x108/0x195
> > [ 8098.085694]  [<ffffffff8103bae3>] ? no_context+0x102/0x36c
> > [ 8098.085695]  [<ffffffff8103bae3>] ? no_context+0x102/0x36c
> > [ 8098.085695]  [<ffffffff8101784a>] ? show_stack_log_lvl+0x15b/0x172
> > [ 8098.085695]  [<ffffffff810178c5>] ? show_regs+0x64/0x136
> > [ 8098.085696]  [<ffffffff81017dad>] ? __die+0x8c/0xc4
> > [ 8098.085696]  [<ffffffff8101802b>] ? die+0x3d/0x56
> > [ 8098.085696]  [<ffffffff810163ed>] ? handle_stack_overflow+0x47/0x51
> > [ 8098.085697]  [<ffffffff8103bae3>] ? no_context+0x102/0x36c
> > [ 8098.085697]  <EOE> ^AdCode: ^A1BUG: unable to handle kernel ^AcNULL pointer dereference^Ac at 0000000000000008
> > [ 8098.085697] IP:^Ac [<0000000000000008>] 0x8
> > [ 8098.085698] PGD 2231d5067 PUD 225162067 PMD 0 
> > [ 8098.085698] Oops: 0010 [#2] SMP
> > [ 8098.085702] 
> > [ 8098.957250] ---[ end trace 632723104d47d31b ]---
> > [ 8098.957250] Kernel panic - not syncing: Fatal exception in interrupt
> > [ 8098.957301] Kernel Offset: disabled
> > [ 8098.973814] ---[ end Kernel panic - not syncing: Fatal exception in interrupt
> > [ 8098.981719] ------------[ cut here ]------------
> > [ 8098.981720] WARNING: CPU: 0 PID: 21338 at arch/x86/kernel/smp.c:127 update_process_times+0x3b/0x45
> 
> And then the machine (understandably) goes off the rails entirely..
> 
> Josh, Andy, any clue on how I should go about fixing this?

This is a bug in the unwinder.  The NMI hit in the entry code right
after setting up the stack pointer from cpu_current_top_of_stack, so the
kernel stack was empty.  __unwind_start() tried to dereference the
pointer (0xffffc90008500000) at the top of the stack.  I'll make a
patch.

-- 
Josh

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