[RFC PATCH v19 1/5] exec: Add a new AT_CHECK flag to execveat(2)

[Florian Weimer]

* Mickaël Salaün:

>> > If we want to avoid that, we could have an agreed-upon error code which
>> > the LSM can signal that it'll never fail AT_CHECK checks, so we only
>> > have to perform the extra system call once.
>
> I'm not sure to follow.  Either we check executable code or we don't,
> but it doesn't make sense to only check some parts (except for migration
> of user space code in a system, which is one purpose of the securebits
> added with the next patch).
>
> The idea with AT_CHECK is to unconditionnaly check executable right the
> same way it is checked when a file is executed.  User space can decide
> to check that or not according to its policy (i.e. securebits).

I meant it purely as a performance optimization, to skip future system
calls if we know they won't provide any useful information for this
process.  In the grand scheme of things, the extra system call probably
does not matter because we already have to do costly things like mmap.

Thanks,
Florian