| Message ID | 20220128061918.20121-1-peterx@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] mm: Fix invalid page pointer returned with FOLL_PIN gups | expand |
On 1/27/22 22:19, Peter Xu wrote: > 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. > > Attaching the Fixes to the FOLL_PIN rework commit, as it happened later than > 1027e4436b6a. > Reviewed-by: John Hubbard <jhubbard@nvidia.com> thanks,
diff --git a/mm/gup.c b/mm/gup.c index f0af462ac1e2..65575ae3602f 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -440,7 +440,7 @@ 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) {
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. Attaching the Fixes to the FOLL_PIN rework commit, as it happened later than 1027e4436b6a. Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Jan Kara <jack@suse.cz> Cc: Jérôme Glisse <jglisse@redhat.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Fixes: 3faa52c03f44 ("mm/gup: track FOLL_PIN pages") Reported-by: Alex Williamson <alex.williamson@redhat.com> Debugged-by: Alex Williamson <alex.williamson@redhat.com> Tested-by: Alex Williamson <alex.williamson@redhat.com> Signed-off-by: Peter Xu <peterx@redhat.com> --- v2: - Drop the WARN_ON_ONCE() [Jason, John] - Add Alex's Tested-by too, as after dropping the WARN_ON_ONCE() then the patch is exactly the one that Alex helped on bug verification, hence very safe to grant the credit alongside. --- mm/gup.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)