Re: [RFC] security: replace indirect calls with static calls

[Mathieu Desnoyers]

----- On Feb 5, 2021, at 10:40 AM, Peter Zijlstra peterz@xxxxxxxxxxxxx wrote:

> On Fri, Feb 05, 2021 at 10:09:26AM -0500, Mathieu Desnoyers wrote:
>> Then we should be able to generate the following using static keys as a
>> jump table and N static calls:
>> 
>>   jump <static key label target>
>> label_N:
>>   stack setup
>>   call
>> label_N-1:
>>   stack setup
>>   call
>> label_N-2:
>>   stack setup
>>   call
>>   ...
>> label_0:
>>   jump end
>> label_fallback:
>>   <iteration and indirect calls>
>> end:
>> 
>> So the static keys would be used to jump to the appropriate label (using
>> a static branch, which has pretty much 0 overhead). Static calls would
>> be used to implement each of the calls.
>> 
>> Thoughts ?
> 
> At some point I tried to extend the static_branch infra to do multiple
> targets and while the low level plumbing is trivial, I ran into trouble
> trying to get a sane C level API for it.

Did you try doing an API for a variable number of targets, or was it for
a specific number of targets ? It might be easier to just duplicate some
of the API code for number of targets between 2 and 12, and let the
users code choose the maximum number of targets they want to accelerate.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com