Re: x86: bad pte in pageattr_test

[Andrey Ryabinin]

On 04/11/2016 12:03 PM, Dmitry Vyukov wrote:
> On Mon, Apr 11, 2016 at 10:52 AM, Andrey Ryabinin
> <ryabinin.a.a@xxxxxxxxx> wrote:
>>
>>
>> On 04/11/2016 11:28 AM, Dmitry Vyukov wrote:
>>> Hello,
>>>
>>> I've got the following WARNING while running syzkaller fuzzer:
>>>
>>> CPA ffff880054118000: bad pte after revert 8000000054118363
>>> ------------[ cut here ]------------
>>> WARNING: CPU: 2 PID: 1503 at arch/x86/mm/pageattr-test.c:226
>>> pageattr_test+0xa6c/0xd10
>>> NOT PASSED. Please report.
>>> Modules linked in:
>>> CPU: 2 PID: 1503 Comm: pageattr-test Not tainted 4.6.0-rc2+ #346
>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>>>  ffffffff87eb25c0 ffff88003b627a70 ffffffff82c8b17f ffffffff81490b58
>>>  fffffbfff0fd64b8 ffff88003b627ae8 0000000000000000 ffffffff86a77e00
>>>  ffffffff8129487c 0000000000000009 ffff88003b627ab8 ffffffff8136639f
>>> Call Trace:
>>>  [<     inline     >] __dump_stack lib/dump_stack.c:15
>>>  [<ffffffff82c8b17f>] dump_stack+0x12e/0x18f lib/dump_stack.c:51
>>>  [<ffffffff8136639f>] __warn+0x19f/0x1e0 kernel/panic.c:512
>>>  [<ffffffff8136648c>] warn_slowpath_fmt+0xac/0xd0 kernel/panic.c:527
>>>  [<ffffffff8129487c>] pageattr_test+0xa6c/0xd10 arch/x86/mm/pageattr-test.c:226
>>>  [<ffffffff81294b3b>] do_pageattr_test+0x1b/0x60 arch/x86/mm/pageattr-test.c:240
>>>  [<ffffffff813cde7f>] kthread+0x23f/0x2d0 drivers/block/aoe/aoecmd.c:1303
>>
>> It seems, that your script is buggy. It should be kthread() from kernel/kthread.c here.
> 
> 
> I probably used a non-matching vmlinux for symbolization. 

No, it's a bug in your script. To find out source location, it uses 'function_name + offset' instead of absolute address.
We have 2 kthread() functions in kernel and this confuses you script.


E.g. my vmlinux :
 $ addr2line -i -e vmlinux ffffffff811b5290
	/home/andrew/linux/kernel/kthread.c:178
 $ addr2line -i -e kasan_conf/vmlinux ffffffff825c7240
	/home/andrew/linux/drivers/block/aoe/aoecmd.c:1289


 $ echo '[<ffffffff811b5290>] kthread+0x00/0x00' | python kasan_symbolize.py vmlinux
	[<ffffffff811b5290>] kthread+0x00/0x00 drivers/block/aoe/aoecmd.c:462
 $ echo '[<ffffffff825c7240>] kthread+0x00/0x00' | python kasan_symbolize.py vmlinux
	[<ffffffff825c7240>] kthread+0x00/0x00 drivers/block/aoe/aoecmd.c:462

> Please
> check the raw report below if the symbolized one does not make sense.
> 
> \/\/\/\/\/\/\/\/
> 
>>> For the repcord, full syzkaller log:
>>> https://gist.githubusercontent.com/dvyukov/323ff7275c5ac38156cb40caeacac057/raw/0836f8dd81024e441f81caebdcb73ca1221aef97/gistfile1.txt