@@ -440,7 +440,7 @@ 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) {
@@ -1181,7 +1181,13 @@ retry:
/*
* Proper page table entry exists, but no corresponding
* struct page.
+ *
+ * Warn if we jumped over even with a valid **pages.
+ * It shouldn't trigger in practise, but when there's
+ * buggy returns on -EEXIST we'll warn before returning
+ * an invalid page pointer in the array.
*/
+ WARN_ON_ONCE(pages);
goto next_page;
} else if (IS_ERR(page)) {
ret = PTR_ERR(page);
The patch titled Subject: mm/gup.c: fix invalid page pointer returned with FOLL_PIN gups has been removed from the -mm tree. Its filename was mm-fix-invalid-page-pointer-returned-with-foll_pin-gups.patch This patch was dropped because an updated version will be merged ------------------------------------------------------ From: Peter Xu <peterx@redhat.com> Subject: mm/gup.c: fix invalid page pointer returned with FOLL_PIN gups 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"). This problem breaks NVIDIA vfio mdev. 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. Since at it, add another WARN_ON_ONCE() at the -EEXIST handling to make sure we mustn't have **pages set when reaching there, because otherwise it means the caller will try to read a garbage right after __get_user_pages() returns. Attaching the Fixes to the FOLL_PIN rework commit, as it happened later than 1027e4436b6a. Link: https://lkml.kernel.org/r/20220125033700.69705-1-peterx@redhat.com Fixes: 3faa52c03f44 ("mm/gup: track FOLL_PIN pages") Signed-off-by: Peter Xu <peterx@redhat.com> Signed-off-by: John Hubbard <jhubbard@nvidia.com> Reported-by: Alex Williamson <alex.williamson@redhat.com> Debugged-by: Alex Williamson <alex.williamson@redhat.com> Tested-by: Alex Williamson <alex.williamson@redhat.com> Reviewed-by: John Hubbard <jhubbard@nvidia.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Jan Kara <jack@suse.cz> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> --- mm/gup.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)