Re: [PATCH v2 11/11] uprobes/x86: Make arch_uretprobe_is_alive(RP_CHECK_CALL) more clever

[Srikar Dronamraju]

> If you ret-probe func_1() and func_2() prepare_uretprobe() hits the
> MAX_URETPROBE_DEPTH limit and "return" from func_2() is not reported.
> 
> When we know that the new call is not chained, we can do the more
> strict check. In this case "sp" points to the new ret-addr, so every
> frame which uses the same "sp" must be dead. The only complication is
> that arch_uretprobe_is_alive() needs to know was it chained or not, so
> we add the new RP_CHECK_CHAIN_CALL enum and change prepare_uretprobe()
> to pass RP_CHECK_CALL only if !chained.
> 
> Note: arch_uretprobe_is_alive() could also re-read *sp and check if
> this word is still trampoline_vaddr. This could obviously improve the
> logic, but I would like to avoid another copy_from_user() especially
> in the case when we can't avoid the false "alive == T" positives.
> 
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>

Looks good to me.

Acked-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>

-- 
Thanks and Regards
Srikar Dronamraju

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