On 11/22/2017 08:21 AM, Florian Weimer wrote: > On 11/22/2017 05:10 PM, Dave Hansen wrote: >> On 11/22/2017 04:15 AM, Florian Weimer wrote: >>> On 11/22/2017 09:18 AM, Vlastimil Babka wrote: >>>> And, was the pkey == -1 internal wiring supposed to be exposed to the >>>> pkey_mprotect() signal, or should there have been a pre-check returning >>>> EINVAL in SYSCALL_DEFINE4(pkey_mprotect), before calling >>>> do_mprotect_pkey())? I assume it's too late to change it now anyway (or >>>> not?), so should we also document it? >>> >>> I think the -1 case to the set the default key is useful because it >>> allows you to use a key value of -1 to mean “MPK is not supported”, and >>> still call pkey_mprotect. >> >> The behavior to not allow 0 to be set was unintentional and is a bug. >> We should fix that. > > On the other hand, x86-64 has no single default protection key due to > the PROT_EXEC emulation. No, the default is clearly 0 and documented to be so. The PROT_EXEC emulation one should be inaccessible in all the APIs so does not even show up as *being* a key in the API. The fact that it's implemented with pkeys should be pretty immaterial other than the fact that you can't touch the high bits in PKRU.
