linux-kernel - Re: [PATCH] x86, powerpc : pkey-mprotect must allow pkey-0

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Message-ID: <ec90ed75-2810-bcc3-8439-8dc85a6b46ac@redhat.com>
Date:   Fri, 9 Mar 2018 12:04:49 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     Ram Pai <linuxram@...ibm.com>, mpe@...erman.id.au,
        mingo@...hat.com, akpm@...ux-foundation.org
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org, x86@...nel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        dave.hansen@...el.com, benh@...nel.crashing.org, paulus@...ba.org,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, hbabu@...ibm.com, mhocko@...nel.org,
        bauerman@...ux.vnet.ibm.com, ebiederm@...ssion.com, corbet@....net,
        arnd@...db.de, msuchanek@...e.com, Ulrich.Weigand@...ibm.com
Subject: Re: [PATCH] x86, powerpc : pkey-mprotect must allow pkey-0

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.

Thanks,
Florian