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Subject: Re: [PATCH 1/9] x86, pkeys: do not special case protection key 0
To:     Shuah Khan <shuah@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        linux-kernel@vger.kernel.org
References: <20180326172721.D5B2CBB4@viggo.jf.intel.com>
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 <9c2de5f6-d9e2-3647-7aa8-86102e9fa6c3@kernel.org>
Cc:     linux-mm@kvack.org, stable@kernel.org, linuxram@us.ibm.com,
        tglx@linutronix.de, mpe@ellerman.id.au, mingo@kernel.org,
        akpm@linux-foundation.org, Shuah Khan <shuahkh@osg.samsung.com>
From:   Dave Hansen <dave.hansen@intel.com>
Message-ID: <b54257c2-138c-7ac9-8176-0dc4868093ef@intel.com>
Date:   Mon, 26 Mar 2018 10:53:35 -0700
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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.