Re: MPK: removing a pkey

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On 11/23/2017 04:00 PM, Dave Hansen wrote:
> On 11/23/2017 12:11 AM, Vlastimil Babka wrote:
>>> 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.
>> So, just to be sure, if we call pkey_mprotect() with 0, will it blindly
>> set 0, or the result of arch_override_mprotect_pkey() (thus equivalent
>> to call with -1) ? I assume the latter?
> 
> It's supposed to set 0.
> 
> -1 was, as far as I remember, an internal-to-the-kernel-only thing to
> tell us that a key came from *mprotect()* instead of pkey_mprotect().

So, pkey_mprotect(..., 0) will set it to 0, regardless of PROT_EXEC.
pkey_mprotect(..., -1) or mprotect() will set it to 0-or-PROT_EXEC-pkey.

Can't shake the feeling that it's somewhat weird, but I guess it's
flexible at least. So just has to be well documented.

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