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Subject: Re: [PATCH 26/26] x86, pkeys: Documentation
To: Ingo Molnar <mingo@kernel.org>
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Cc: x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
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From: Dave Hansen <dave@sr71.net>
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Date: Wed, 7 Oct 2015 13:24:00 -0700
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On 10/03/2015 01:17 AM, Ingo Molnar wrote:
> Right now the native x86 PTE format allows two protection related bits for 
> user-space pages:
> 
>   _PAGE_BIT_RW:                   if 0 the page is read-only,  if 1 then it's read-write
>   _PAGE_BIT_NX:                   if 0 the page is executable, if 1 then it's not executable
> 
> As discussed previously, pkeys allows 'true execute only (--x)' mappings.
> 
> Another possibility would be 'true write-only (-w-)' mappings.

How would those work?

Protection Keys has a Write-Disable and an Access-Disable bit.  But,
Access-Disable denies _all_ data access to the region.  There's no way
to allow only writes.

Or am I missing something?