From: Peter Xu peterx@redhat.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@nvidia.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@redhat.com Signed-off-by: John Hubbard jhubbard@nvidia.com Reviewed-by: Claudio Imbrenda imbrenda@linux.ibm.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: Christoph Hellwig hch@lst.de Reviewed-by: Jan Kara jack@suse.cz Cc: Andrea Arcangeli aarcange@redhat.com Cc: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Jason Gunthorpe jgg@ziepe.ca Cc: David Hildenbrand david@redhat.com Cc: Lukas Bulwahn lukas.bulwahn@gmail.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Jason Gunthorpe jgg@nvidia.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.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) {