[PATCH AUTOSEL 01/14] mm: fix invalid page pointer returned with FOLL_PIN gups

[Greg Kroah-Hartman]

From: Peter Xu <peterx@xxxxxxxxxx>

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@xxxxxxxxxx: added some tags, removed a reference to an out of tree module.]

Link: https://lkml.kernel.org/r/20220207062213.235127-1-jhubbard@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20220204020010.68930-1-jhubbard@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20220204020010.68930-2-jhubbard@xxxxxxxxxx
Fixes: 3faa52c03f44 ("mm/gup: track FOLL_PIN pages")
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
Reviewed-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
Reported-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
Debugged-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
Tested-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Lukas Bulwahn <lukas.bulwahn@xxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 mm/gup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/gup.c b/mm/gup.c
index 7bc1ba9ce440..41da0bd61bec 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -465,7 +465,7 @@ static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
 		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) {
-- 
2.36.0