[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <24bc512a-b5c2-b7ea-fa83-5752cec7455b@redhat.com>
Date: Wed, 14 Jun 2023 17:31:36 +0200
From: David Hildenbrand <david@...hat.com>
To: Peter Xu <peterx@...hat.com>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Cc: Matthew Wilcox <willy@...radead.org>,
Andrea Arcangeli <aarcange@...hat.com>,
John Hubbard <jhubbard@...dia.com>,
Mike Rapoport <rppt@...nel.org>,
Vlastimil Babka <vbabka@...e.cz>,
"Kirill A . Shutemov" <kirill@...temov.name>,
Andrew Morton <akpm@...ux-foundation.org>,
Mike Kravetz <mike.kravetz@...cle.com>,
James Houghton <jthoughton@...gle.com>,
Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH 2/7] mm/hugetlb: Fix hugetlb_follow_page_mask() on
permission checks
On 13.06.23 23:53, Peter Xu wrote:
> It seems hugetlb_follow_page_mask() was missing permission checks. For
> example, one follow_page() can get the hugetlb page with FOLL_WRITE even if
> the page is read-only.
I'm curious if there even is a follow_page() user that operates on
hugetlb ...
s390x secure storage does not apply to hugetlb IIRC.
ksm.c? no.
huge_memory.c ? no
So what remains is most probably mm/migrate.c, which never sets FOLL_WRITE.
Or am I missing something a user?
> > And it wasn't there even in the old follow_page_mask(), where we can
> reference from before commit 57a196a58421 ("hugetlb: simplify hugetlb
> handling in follow_page_mask").
>
> Let's add them, namely, either the need to CoW due to missing write bit, or
> proper CoR on !AnonExclusive pages over R/O pins to reject the follow page.
> That brings this function closer to follow_hugetlb_page().
>
> I just doubt how many of us care for that, for FOLL_PIN follow_page doesn't
> really happen at all. But we'll care, and care more if we switch over
> slow-gup to use hugetlb_follow_page_mask(). We'll also care when to return
> -EMLINK then, as that's the gup internal api to mean "we should do CoR".
>
> When at it, switching the try_grab_page() to use WARN_ON_ONCE(), to be
> clear that it just should never fail.
>
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
> mm/hugetlb.c | 22 ++++++++++++++++------
> 1 file changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 82dfdd96db4c..9c261921b2cf 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6481,8 +6481,21 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
> ptl = huge_pte_lock(h, mm, pte);
> entry = huge_ptep_get(pte);
> if (pte_present(entry)) {
> - page = pte_page(entry) +
> - ((address & ~huge_page_mask(h)) >> PAGE_SHIFT);
> + page = pte_page(entry);
> +
> + if (gup_must_unshare(vma, flags, page)) {
> + /* Tell the caller to do Copy-On-Read */
> + page = ERR_PTR(-EMLINK);
> + goto out;
> + }
> +
> + if ((flags & FOLL_WRITE) && !pte_write(entry)) {
> + page = NULL;
> + goto out;
> + }
> +
> + page += ((address & ~huge_page_mask(h)) >> PAGE_SHIFT);
> +
> /*
> * Note that page may be a sub-page, and with vmemmap
> * optimizations the page struct may be read only.
> @@ -6492,10 +6505,7 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
> * try_grab_page() should always be able to get the page here,
> * because we hold the ptl lock and have verified pte_present().
> */
> - if (try_grab_page(page, flags)) {
> - page = NULL;
> - goto out;
> - }
> + WARN_ON_ONCE(try_grab_page(page, flags));
> }
> out:
> spin_unlock(ptl);
--
Cheers,
David / dhildenb
Powered by blists - more mailing lists