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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>,
	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 18:05:56 -0700	[thread overview]
Message-ID: <CA+55aFyP2Aw7ET5oNX9fB644PGKrguk-mhXdcEN_aHvnVVsUjg@mail.gmail.com> (raw)
In-Reply-To: <1474850960.17726.48.camel@redhat.com>

On Sun, Sep 25, 2016 at 5:49 PM, Rik van Riel <riel@redhat.com> wrote:
>
> 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.

So the thing is, I don't think the code should even get that far.

It should just fail in check_vma_flags() (possibly after doing the
fast-lookup of the page tables, but that would fail with PROT_NONE).

But thanks to FOLL_FORCE, it doesn't. So things that actually use the
page array and prot_none can get access to the underlying data.

                 Linus

WARNING: multiple messages have this Message-ID (diff)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>,
	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 18:05:56 -0700	[thread overview]
Message-ID: <CA+55aFyP2Aw7ET5oNX9fB644PGKrguk-mhXdcEN_aHvnVVsUjg@mail.gmail.com> (raw)
In-Reply-To: <1474850960.17726.48.camel@redhat.com>

On Sun, Sep 25, 2016 at 5:49 PM, Rik van Riel <riel@redhat.com> wrote:
>
> 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.

So the thing is, I don't think the code should even get that far.

It should just fail in check_vma_flags() (possibly after doing the
fast-lookup of the page tables, but that would fail with PROT_NONE).

But thanks to FOLL_FORCE, it doesn't. So things that actually use the
page array and prot_none can get access to the underlying data.

                 Linus

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  reply	other threads:[~2016-09-26  1:05 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
2016-09-26  1:05           ` Linus Torvalds [this message]
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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