On Tue, Nov 15, 2016 at 11:04:45AM -0800, Dmitry Vyukov wrote: > On Tue, Nov 15, 2016 at 10:57 AM, Peter Zijlstra <pet...@infradead.org> wrote: > > On Tue, Nov 15, 2016 at 12:43:56PM -0500, Vince Weaver wrote: > >> > >> Running on my haswell machine with the imc/uncore patch applied, the > >> perf_fuzzer next tripped over this issue. > >> > >> [ 202.034495] BAD LUCK: lost 371 message(s) from NMI context! > >> [ 202.034496] > >> ================================================================== > >> [ 202.048327] BUG: KASAN: stack-out-of-bounds in > >> unwind_get_return_address+0x35/0x80 at addr ffff8800cff0bd90 > >> [ 202.058826] Read of size 8 by task perf_fuzzer/16254 > >> [ 202.064186] page:ffffea00033fc2c0 count:1 mapcount:0 mapping: > >> (null) index:0x0^Ac > >> [ 202.073068] flags: 0x1ffff8000000400(reserved) > >> [ 202.077885] page dumped because: kasan: bad access detected > >> [ 202.083880] CPU: 4 PID: 16254 Comm: perf_fuzzer Not tainted 4.9.0-rc5+ > >> #5 > >> [ 202.091204] Hardware name: LENOVO 10AM000AUS/SHARKBAY, BIOS FBKT72AUS > >> 01/26/2014 > >> [ 202.099181] ffff8800cff0b1d8^Ac ffffffff816bb796^Ac > >> ffff8800cff0b270^Ac ffff8800cff0bd90^Ac > >> [ 202.107896] ffff8800cff0b260^Ac ffffffff812fbe95^Ac > >> 00007ffc9d1ab480^Ac 0000000000000000^Ac > >> [ 202.116638] ffffffff8125117d^Ac 0000000000000092^Ac > >> 0000000000000000^Ac ffff8800cff0b7c0^Ac > >> [ 202.125339] Call Trace: > >> [ 202.127994] <NMI> [<ffffffff816bb796>] dump_stack+0x63/0x8d > >> [ 202.134184] [<ffffffff812fbe95>] kasan_report_error+0x495/0x4c0 > >> [ 202.140680] [<ffffffff8125117d>] ? perf_output_begin+0x28d/0x4c0 > >> [ 202.147228] [<ffffffff812fc319>] kasan_report+0x39/0x40 > >> [ 202.152987] [<ffffffff81095ce5>] ? unwind_get_return_address+0x35/0x80 > >> [ 202.160094] [<ffffffff812fa8fe>] __asan_load8+0x5e/0x70 > >> [ 202.165859] [<ffffffff81095ce5>] unwind_get_return_address+0x35/0x80 > > > > Josh, any ideas? > > I think this is a false positive due to imprecise unwind that hits a > stack redzone. > We probably need to use READ_ONCE_NOCHECK as in get_wchan.
I'm not so sure about that. The unwind should be precise here: it should only be looking at the frame pointers and return addresses on the current task's stack. I can't see any reason why it would be reading into the KASAN stack redzone. -- Josh
