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))
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
