Re: MPK: removing a pkey

[Florian Weimer <fweimer@redhat.com>]

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.

Florian

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