linux-kernel - Re: [PATCH 1/9] x86, pkeys: do not special case protection key 0

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Message-ID: <b54257c2-138c-7ac9-8176-0dc4868093ef@intel.com>
Date:   Mon, 26 Mar 2018 10:53:35 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Shuah Khan <shuah@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, stable@...nel.org, linuxram@...ibm.com,
        tglx@...utronix.de, mpe@...erman.id.au, mingo@...nel.org,
        akpm@...ux-foundation.org, Shuah Khan <shuahkh@....samsung.com>
Subject: Re: [PATCH 1/9] x86, pkeys: do not special case protection key 0

On 03/26/2018 10:47 AM, Shuah Khan wrote:
> 
> Also what happens "pkey_free() pkey-0" - can you elaborate more on that
> "silliness consequences"

It's just what happens if you free any other pkey that is in use: it
might get reallocated later.  The most likely scenario is that you will
get pkey-0 back from pkey_alloc(), you will set an access-disable or
write-disable bit in PKRU for it, and your next stack access will SIGSEGV.