Re: [PATCH -next v2] x86: Prevent KASAN false positive warnings in __show_regs

[Tengda Wu]

On 2025/8/30 5:01, Josh Poimboeuf wrote:
> On Fri, Aug 29, 2025 at 09:47:44AM +0000, Tengda Wu wrote:
>>  static void show_regs_if_on_stack(struct stack_info *info, struct pt_regs *regs,
>>  				  bool partial, const char *log_lvl)
>>  {
>> +	bool kasan_disabled = false;
>> +
>> +	/*
>> +	 * When 'regs' resides in another task's stack space, KASAN should be
>> +	 * disabled to prevent false positives during 'regs->' operation, as
>> +	 * the 'regs' contents may change concurrently with task execution.
>> +	 */
>> +	if (!object_is_on_stack(regs)) {
>> +		kasan_disable_current();
>> +		kasan_disabled = true;
>> +	}
> 
> I don't think this is right.  object_is_on_stack() only checks current's
> *task* stack.  However the regs might be on a different stack used by
> current (e.g., exception stack).  In which case there's no need to
> disable KASAN.
> 
> What really determines the KASAN-safety is whether it's the current task
> or not.
> 

I see.

Since operations walking other tasks' regs-> only occur in show_regs_if_on_stack,
to cover a more accurate range and targets, it seems we have no choice but to add
a task parameter to show_regs_if_on_stack and then perform the check, right?