linux-kernel - Re: [PATCH 26/34] mm: implement new mprotect

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Message-ID: <566B2E83.4070002@gmail.com>
Date:	Fri, 11 Dec 2015 21:13:55 +0100
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Dave Hansen <dave@...1.net>
CC:	mtk.manpages@...il.com, lkml <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"x86@...nel.org" <x86@...nel.org>, dave.hansen@...ux.intel.com,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH 26/34] mm: implement new mprotect_key() system call

On 12/09/2015 06:05 PM, Dave Hansen wrote:
> On 12/09/2015 08:45 AM, Michael Kerrisk (man-pages) wrote:
>>>>>> * Explanation of what a protection domain is.
>>>>
>>>> A protection domain is a unique view of memory and is represented by the
>>>> value in the PKRU register.
>> Out something about this in pkey(7), but explain what you mean by a
>> "unique view of memory".
> 
> Let's say there are only two protection keys: 0 and 1.  There are two
> disable bits per protection key (Access and Write Disable), so a two-key
> PKRU looks like:
> 
> |   PKEY0   |   PKEY1   |
> | AD0 | WD0 | AD1 | WD1 |
> 
> In this example, there are 16 possible protection domains, one for each
> possible combination of the 4 rights-disable bits.
> 
> "Changing a protection domain" would mean changing (setting or clearing)
> the value of any of those 4 bits.  Each unique value of PKRU represents
> a view of memory, or unique protection domain.

Again, some of this could make its way into pkey(7). And I guess there
are useful nuggets for that page to be found in Jon's article at
https://lwn.net/Articles/667156/

Thanks,

Michael




-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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