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SubjectRe: [PATCH] x86, powerpc : pkey-mprotect must allow pkey-0
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On 03/09/2018 09:00 PM, Ram Pai wrote:
> On Fri, Mar 09, 2018 at 12:04:49PM +0100, Florian Weimer wrote:
>> On 03/09/2018 09:12 AM, Ram Pai wrote:
>>> Once an address range is associated with an allocated pkey, it cannot be
>>> reverted back to key-0. There is no valid reason for the above behavior.
>>
>> mprotect without a key does not necessarily use key 0, e.g. if
>> protection keys are used to emulate page protection flag combination
>> which is not directly supported by the hardware.
>>
>> Therefore, it seems to me that filtering out non-allocated keys is
>> the right thing to do.
>
> I am not sure, what you mean. Do you agree with the patch or otherwise?

I think it's inconsistent to make key 0 allocated, but not the key which
is used for PROT_EXEC emulation, which is still reserved. Even if you
change the key 0 behavior, it is still not possible to emulate mprotect
behavior faithfully with an allocated key.

Thanks,
Florian

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