On 5/5/21 1:48 PM, Madhavan T. Venkataraman wrote:
>
>
> On 5/5/21 11:46 AM, Mark Brown wrote:
>> On Tue, May 04, 2021 at 02:32:35PM -0500, Madhavan T. Venkataraman wrote:
>>
>>> If you prefer, I could do something like this:
>>>
>>> check_pc:
>>> if (!__kernel_text_address(frame->pc))
>>> frame->reliable = false;
>>>
>>> range = lookup_range(frame->pc);
>>>
>>> #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>>> if (tsk->ret_stack &&
>>> frame->pc == (unsigned long)return_to_handler) {
>>> ...
>>> frame->pc = ret_stack->ret;
>>> frame->pc = ptrauth_strip_insn_pac(frame->pc);
>>> goto check_pc;
>>> }
>>> #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
>>
>>> Is that acceptable?
>>
>> I think that works even if it's hard to love the goto, might want some
>> defensiveness to ensure we can't somehow end up in an infinite loop with
>> a sufficiently badly formed stack.
>>
>
> I could do something like this:
>
> - Move all frame->pc checking code into a function called check_frame_pc().
>
> bool check_frame_pc(frame)
> {
> Do all the checks including function graph
> return frame->pc changed
> }
>
> - Then, in unwind_frame()
>
> unwind_frame()
> {
> int i;
> ...
>
> for (i = 0; i < MAX_CHECKS; i++) {
> if (!check_frame(tsk, frame))
Small typo in the last statement - It should be check_frame_pc().
Sorry.
Madhavan
> break;
> }
>
> if (i == MAX_CHECKS)
> frame->reliable = false;
> return 0;
> }
>
> The above would take care of future cases like kretprobe_trampoline().
>
> If this is acceptable, then the only question is - what should be the value of
> MAX_CHECKS (I will rename it to something more appropriate)?
>
> Madhavan
>
