BUG: KASAN: stack-out-of-bounds

[Andrey Ryabinin]

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.