linux-kernel - [PATCH 5.17 12/12] mm: fix invalid page pointer returned with FOLL

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Date:   Fri, 13 May 2022 16:24:12 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Peter Xu <peterx@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Christoph Hellwig <hch@....de>, Jan Kara <jack@...e.cz>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        David Hildenbrand <david@...hat.com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.17 12/12] mm: fix invalid page pointer returned with FOLL_PIN gups

From: Peter Xu <peterx@...hat.com>

commit 7196040e19ad634293acd3eff7083149d7669031 upstream.

Patch series "mm/gup: some cleanups", v5.

This patch (of 5):

Alex reported invalid page pointer returned with pin_user_pages_remote()
from vfio after upstream commit 4b6c33b32296 ("vfio/type1: Prepare for
batched pinning with struct vfio_batch").

It turns out that it's not the fault of the vfio commit; however after
vfio switches to a full page buffer to store the page pointers it starts
to expose the problem easier.

The problem is for VM_PFNMAP vmas we should normally fail with an
-EFAULT then vfio will carry on to handle the MMIO regions.  However
when the bug triggered, follow_page_mask() returned -EEXIST for such a
page, which will jump over the current page, leaving that entry in
**pages untouched.  However the caller is not aware of it, hence the
caller will reference the page as usual even if the pointer data can be
anything.

We had that -EEXIST logic since commit 1027e4436b6a ("mm: make GUP
handle pfn mapping unless FOLL_GET is requested") which seems very
reasonable.  It could be that when we reworked GUP with FOLL_PIN we
could have overlooked that special path in commit 3faa52c03f44 ("mm/gup:
track FOLL_PIN pages"), even if that commit rightfully touched up
follow_devmap_pud() on checking FOLL_PIN when it needs to return an
-EEXIST.

Attaching the Fixes to the FOLL_PIN rework commit, as it happened later
than 1027e4436b6a.

[jhubbard@...dia.com: added some tags, removed a reference to an out of tree module.]

Link: https://lkml.kernel.org/r/20220207062213.235127-1-jhubbard@nvidia.com
Link: https://lkml.kernel.org/r/20220204020010.68930-1-jhubbard@nvidia.com
Link: https://lkml.kernel.org/r/20220204020010.68930-2-jhubbard@nvidia.com
Fixes: 3faa52c03f44 ("mm/gup: track FOLL_PIN pages")
Signed-off-by: Peter Xu <peterx@...hat.com>
Signed-off-by: John Hubbard <jhubbard@...dia.com>
Reviewed-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
Reported-by: Alex Williamson <alex.williamson@...hat.com>
Debugged-by: Alex Williamson <alex.williamson@...hat.com>
Tested-by: Alex Williamson <alex.williamson@...hat.com>
Reviewed-by: Christoph Hellwig <hch@....de>
Reviewed-by: Jan Kara <jack@...e.cz>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Jason Gunthorpe <jgg@...pe.ca>
Cc: David Hildenbrand <david@...hat.com>
Cc: Lukas Bulwahn <lukas.bulwahn@...il.com>
Cc: Matthew Wilcox (Oracle) <willy@...radead.org>
Cc: Jason Gunthorpe <jgg@...dia.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/gup.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/gup.c
+++ b/mm/gup.c
@@ -465,7 +465,7 @@ static int follow_pfn_pte(struct vm_area
 		pte_t *pte, unsigned int flags)
 {
 	/* No page to get reference */
-	if (flags & FOLL_GET)
+	if (flags & (FOLL_GET | FOLL_PIN))
 		return -EFAULT;
 
 	if (flags & FOLL_TOUCH) {