Re: BUG: KASAN: stack-out-of-bounds

[Christophe Leroy <christophe.leroy@c-s.fr>]

Le 27/02/2019 à 10:19, Andrey Ryabinin a écrit :
> 
> 
> On 2/27/19 11:25 AM, Christophe Leroy wrote:
>> With version v8 of the series implementing KASAN on 32 bits powerpc (https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=94309), I'm now able to activate KASAN on a mac99 is QEMU.
>>
>> Then I get the following reports at startup. Which of the two reports I get seems to depend on the option used to build the kernel, but for a given kernel I always get the same report.
>>
>> Is that a real bug, in which case how could I spot it ? Or is it something wrong in my implementation of KASAN ?
>>
>> I checked that after kasan_init(), the entire shadow memory is full of 0 only.
>>
>> I also made a try with the strong STACK_PROTECTOR compiled in, but no difference and nothing detected by the stack protector.
>>
>> ==================================================================
>> BUG: KASAN: stack-out-of-bounds in memchr+0x24/0x74
>> Read of size 1 at addr c0ecdd40 by task swapper/0
>>
>> CPU: 0 PID: 0 Comm: swapper Not tainted 5.0.0-rc7+ #1133
>> Call Trace:
>> [c0e9dca0] [c01c42a0] print_address_description+0x64/0x2bc (unreliable)
>> [c0e9dcd0] [c01c4684] kasan_report+0xfc/0x180
>> [c0e9dd10] [c089579c] memchr+0x24/0x74
>> [c0e9dd30] [c00a9e38] msg_print_text+0x124/0x574
>> [c0e9dde0] [c00ab710] console_unlock+0x114/0x4f8
>> [c0e9de40] [c00adc60] vprintk_emit+0x188/0x1c4
>> --- interrupt: c0e9df00 at 0x400f330
>>      LR = init_stack+0x1f00/0x2000
>> [c0e9de80] [c00ae3c4] printk+0xa8/0xcc (unreliable)
>> [c0e9df20] [c0c28e44] early_irq_init+0x38/0x108
>> [c0e9df50] [c0c16434] start_kernel+0x310/0x488
>> [c0e9dff0] [00003484] 0x3484
>>
>> The buggy address belongs to the variable:
>>   __log_buf+0xec0/0x4020
>> The buggy address belongs to the page:
>> page:c6eac9a0 count:1 mapcount:0 mapping:00000000 index:0x0
>> flags: 0x1000(reserved)
>> raw: 00001000 c6eac9a4 c6eac9a4 00000000 00000000 00000000 ffffffff 00000001
>> page dumped because: kasan: bad access detected
>>
>> Memory state around the buggy address:
>>   c0ecdc00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>   c0ecdc80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>> c0ecdd00: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 00 00 00
>>                                     ^
>>   c0ecdd80: f3 f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
>>   c0ecde00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> ==================================================================
>>
> 
> This one doesn't look good. Notice that it says stack-out-of-bounds, but at the same time there is
> 	"The buggy address belongs to the variable:  __log_buf+0xec0/0x4020"
>   which is printed by following code:
> 	if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
> 		pr_err("The buggy address belongs to the variable:\n");
> 		pr_err(" %pS\n", addr);
> 	}
> 
> So the stack unrelated address got stack-related poisoning. This could be a stack overflow, did you increase THREAD_SHIFT?
> KASAN with stack instrumentation significantly increases stack usage.
> 

I get the above with THREAD_SHIFT set to 13 (default value).
If increasing it to 14, I get the following instead. That means that in 
that case the problem arises a lot earlier in the boot process (but 
still after the final kasan shadow setup).

==================================================================
BUG: KASAN: stack-out-of-bounds in pmac_nvram_init+0x1f8/0x5d0
Read of size 1 at addr f6f37de0 by task swapper/0

CPU: 0 PID: 0 Comm: swapper Not tainted 5.0.0-rc7+ #1143
Call Trace:
[c0e9fd60] [c01c43c0] print_address_description+0x164/0x2bc (unreliable)
[c0e9fd90] [c01c46a4] kasan_report+0xfc/0x180
[c0e9fdd0] [c0c226d4] pmac_nvram_init+0x1f8/0x5d0
[c0e9fef0] [c0c1f73c] pmac_setup_arch+0x298/0x314
[c0e9ff20] [c0c1ac40] setup_arch+0x250/0x268
[c0e9ff50] [c0c151dc] start_kernel+0xb8/0x488
[c0e9fff0] [00003484] 0x3484


Memory state around the buggy address:
  f6f37c80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  f6f37d00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 >f6f37d80: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
                                                ^
  f6f37e00: 00 00 01 f4 f2 f2 f2 f2 00 00 00 00 f2 f2 f2 f2
  f6f37e80: 00 00 00 00 f3 f3 f3 f3 00 00 00 00 00 00 00 00
==================================================================

Christophe