linux-kernel - Re: [PATCH 1/3] x86, pkeys: do not special case protection key 0

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Date:   Sat, 17 Mar 2018 10:12:15 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linuxram@...ibm.com, dave.hansen@...el.com, mpe@...erman.id.au,
        mingo@...nel.org, akpm@...ux-foundation.org, shuah@...nel.org
Subject: Re: [PATCH 1/3] x86, pkeys: do not special case protection key 0

On Fri, 16 Mar 2018, Dave Hansen wrote:

> 
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> mm_pkey_is_allocated() treats pkey 0 as unallocated.  That is
> inconsistent with the manpages, and also inconsistent with
> mm->context.pkey_allocation_map.  Stop special casing it and only
> disallow values that are actually bad (< 0).
> 
> The end-user visible effect of this is that you can now use
> mprotect_pkey() to set pkey=0.
> 
> This is a bit nicer than what Ram proposed because it is simpler
> and removes special-casing for pkey 0.  On the other hand, it does
> allow applciations to pkey_free() pkey-0, but that's just a silly
> thing to do, so we are not going to protect against it.

What's the consequence of that? Application crashing and burning itself or
something more subtle?

Thanks,

	tglx