linux-kernel - Re: [PATCH] mm: check VMA flags to avoid invalid PROT

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Date:   Sun, 25 Sep 2016 18:05:56 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Rik van Riel <riel@...hat.com>
Cc:     Hugh Dickins <hughd@...gle.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        linux-mm <linux-mm@...ck.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        tbsaunde@...aunde.org, robert@...llahan.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm: check VMA flags to avoid invalid PROT_NONE NUMA balancing

On Sun, Sep 25, 2016 at 5:49 PM, Rik van Riel <riel@...hat.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