[PATCH v4 17/29] arm64: implement PKEYS support

[Florian Weimer]

* Szabolcs Nagy:

>> A user can still set it by interacting with the register directly, but I guess
>> we want something for the glibc interface..
>> 
>> Dave, any thoughts here?
>
> adding Florian too, since i found an old thread of his that tried
> to add separate PKEY_DISABLE_READ and PKEY_DISABLE_EXECUTE, but
> it did not seem to end up upstream. (this makes more sense to me
> as libc api than the weird disable access semantics)

I still think it makes sense to have a full complenent of PKEY_* flags
complementing the PROT_* flags, in a somewhat abstract fashion for
pkey_alloc only.  The internal protection mask register encoding will
differ from architecture to architecture, but the abstract glibc
functions pkey_set and pkey_get could use them (if we are a bit
careful).

Thanks,
Florian