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Date: Sun, 6 Feb 2022 22:22:09 -0800 From: John Hubbard <jhubbard@...dia.com> To: Andrew Morton <akpm@...ux-foundation.org>, Peter Xu <peterx@...hat.com>, Jason Gunthorpe <jgg@...pe.ca> CC: David Hildenbrand <david@...hat.com>, Lukas Bulwahn <lukas.bulwahn@...il.com>, Claudio Imbrenda <imbrenda@...ux.ibm.com>, Christoph Hellwig <hch@...radead.org>, Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>, "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>, Alex Williamson <alex.williamson@...hat.com>, Andrea Arcangeli <aarcange@...hat.com>, LKML <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>, John Hubbard <jhubbard@...dia.com>, Christoph Hellwig <hch@....de> Subject: [PATCH v5 1/5] mm: Fix invalid page pointer returned with FOLL_PIN gups From: Peter Xu <peterx@...hat.com> 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. Cc: Andrea Arcangeli <aarcange@...hat.com> Cc: Andrew Morton <akpm@...ux-foundation.org> Cc: Jan Kara <jack@...e.cz> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com> Fixes: 3faa52c03f44 ("mm/gup: track FOLL_PIN pages") Reviewed-by: Claudio Imbrenda <imbrenda@...ux.ibm.com> Reviewed-by: Christoph Hellwig <hch@....de> Reviewed-by: Jan Kara <jack@...e.cz> Reported-by: Alex Williamson <alex.williamson@...hat.com> Debugged-by: Alex Williamson <alex.williamson@...hat.com> Tested-by: Alex Williamson <alex.williamson@...hat.com> Signed-off-by: Peter Xu <peterx@...hat.com> [jhubbard: added some tags, removed a reference to an out of tree module, and reflowed to 72 columns.] Signed-off-by: John Hubbard <jhubbard@...dia.com> --- mm/gup.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/gup.c b/mm/gup.c index a9d4d724aef7..80229ecf0114 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) { -- 2.35.1
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