On Wed, 8 Jun 2016, Dave Hansen wrote:
> Proposed semantics:
> 1. protection key 0 is special and represents the default,
> unassigned protection key. It is always allocated.
> 2. mprotect() never affects a mapping's pkey_mprotect()-assigned
> protection key. A protection key of 0 (even if set explicitly)
> represents an unassigned protection key.
> 2a. mprotect(PROT_EXEC) on a mapping with an assigned protection
> key may or may not result in a mapping with execute-only
> properties. pkey_mprotect() plus pkey_set() on all threads
> should be used to _guarantee_ execute-only semantics.
> 3. mprotect(PROT_EXEC) may result in an "execute-only" mapping. The
> kernel will internally attempt to allocate and dedicate a
> protection key for the purpose of execute-only mappings. This
> may not be possible in cases where there are no free protection
> keys available.
Shouldn't we just reserve a protection key for PROT_EXEC unconditionally?
Thanks,
tglx
