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From: Rik van Riel <riel@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>,
	Hugh Dickins <hughd@google.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>,
	linux-mm <linux-mm@kvack.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	tbsaunde@tbsaunde.org, robert@ocallahan.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm: check VMA flags to avoid invalid PROT_NONE NUMA balancing
Date: Sun, 25 Sep 2016 20:49:20 -0400	[thread overview]
Message-ID: <1474850960.17726.48.camel@redhat.com> (raw)
In-Reply-To: <CA+55aFyL+qFsJpxQufgRKgWeB6Yj0e1oapdu5mdU9_t+zwtBjg@mail.gmail.com>

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On Sun, 2016-09-25 at 15:50 -0700, Linus Torvalds wrote:
> On Sun, Sep 25, 2016 at 3:34 PM, Rik van Riel <riel@redhat.com>
> wrote:
> > 
> > 
> > The patch looks good to me, too.
> > 
> > Acked-by: Rik van Riel <riel@redhat.com>
> 
> Thanks, amended the commit since I hadn't pushed out yet.
> 
> Btw, the only reason this bug could happen is that we do that
> "force=1" for remote vm accesses, which turns into FOLL_FORCE, which
> in turn will turn into us allowing an access even when we technically
> shouldn't.
> 
> I'd really like to re-open the "drop FOLL_FORCE entirely" discussion,
> because the thing really is disgusting.
> 
> I realize that debuggers etc sometimes would want to punch through
> PROT_NONE protections,

Reading the code for a little bit, it looks like get_user_pages
interprets both PROT_NONE and PAGE_NUMA ptes as present, and will
simply return the page to the caller.

Furthermore, if a page in a PROT_NONE VMA is actually not present,
it should be faulted in with PROT_NONE permissions, after which
the page is passed to the debugger.

That is, punching through PROT_NONE permissions should only happen
from outside of the process. Inside the process, PROT_NONE should
be preserved regardless of FOLL_FORCE.

-- 
All Rights Reversed.

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  parent reply	other threads:[~2016-09-26  0:49 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-11 22:54 [PATCH] mm: check VMA flags to avoid invalid PROT_NONE NUMA balancing Lorenzo Stoakes
2016-09-11 22:59 ` Lorenzo Stoakes
2016-09-11 22:59   ` Lorenzo Stoakes
2016-09-25 18:47 ` Lorenzo Stoakes
2016-09-25 18:47   ` Lorenzo Stoakes
2016-09-25 20:52   ` Linus Torvalds
2016-09-25 20:52     ` Linus Torvalds
2016-09-25 22:24     ` Linus Torvalds
2016-09-25 22:24       ` Linus Torvalds
2016-09-25 22:34     ` Rik van Riel
2016-09-25 22:50       ` Linus Torvalds
2016-09-25 22:50         ` Linus Torvalds
2016-09-25 23:28         ` Hugh Dickins
2016-09-25 23:28           ` Hugh Dickins
2016-09-26  0:49         ` Rik van Riel [this message]
2016-09-26  1:05           ` Linus Torvalds
2016-09-26  1:05             ` Linus Torvalds
2016-10-07 10:07         ` Lorenzo Stoakes
2016-10-07 10:07           ` Lorenzo Stoakes
2016-10-07 15:34           ` Linus Torvalds
2016-10-07 15:34             ` Linus Torvalds
2016-10-07 16:22             ` Lorenzo Stoakes
2016-10-07 16:22               ` Lorenzo Stoakes
2016-10-07 18:16               ` Hugh Dickins
2016-10-07 18:16                 ` Hugh Dickins
2016-10-07 18:26                 ` Lorenzo Stoakes
2016-10-07 18:26                   ` Lorenzo Stoakes
2016-10-10  7:47                 ` Jan Kara
2016-10-10  7:47                   ` Jan Kara
2016-10-10  8:28                   ` Lorenzo Stoakes
2016-10-10  8:28                     ` Lorenzo Stoakes
2016-10-10 16:37                     ` Jan Kara
2016-10-10 16:37                       ` Jan Kara
2016-09-26  8:19 ` Mel Gorman

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