hugetlb: fix copy_huge_page_from_user contig page struct assumption

page structs are not guaranteed to be contiguous for gigantic pages.  The
routine copy_huge_page_from_user can encounter gigantic pages, yet it
assumes page structs are contiguous when copying pages from user space.

Since page structs for the target gigantic page are not contiguous, the
data copied from user space could overwrite other pages not associated
with the gigantic page and cause data corruption.

Non-contiguous page structs are generally not an issue.  However, they can
exist with a specific kernel configuration and hotplug operations.  For
example: Configure the kernel with CONFIG_SPARSEMEM and
!CONFIG_SPARSEMEM_VMEMMAP.  Then, hotplug add memory for the area where
the gigantic page will be allocated.

Link: https://lkml.kernel.org/r/20210217184926.33567-2-mike.kravetz@oracle.com
Fixes: 8fb5debc5fcd ("userfaultfd: hugetlbfs: add hugetlb_mcopy_atomic_pte for userfaultfd support")
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memory.c b/mm/memory.c
index ef4e10c60b5f3bb54a88678b1bbb2c19bed825b6..784249f3307bd1ad120a6c28af8513b266f69bc8 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5177,17 +5177,19 @@ long copy_huge_page_from_user(struct page *dst_page,
        void *page_kaddr;
        unsigned long i, rc = 0;
        unsigned long ret_val = pages_per_huge_page * PAGE_SIZE;
+       struct page *subpage = dst_page;
 
-       for (i = 0; i < pages_per_huge_page; i++) {
+       for (i = 0; i < pages_per_huge_page;
+            i++, subpage = mem_map_next(subpage, dst_page, i)) {
                if (allow_pagefault)
-                       page_kaddr = kmap(dst_page + i);
+                       page_kaddr = kmap(subpage);
                else
-                       page_kaddr = kmap_atomic(dst_page + i);
+                       page_kaddr = kmap_atomic(subpage);
                rc = copy_from_user(page_kaddr,
                                (const void __user *)(src + i * PAGE_SIZE),
                                PAGE_SIZE);
                if (allow_pagefault)
-                       kunmap(dst_page + i);
+                       kunmap(subpage);
                else
                        kunmap_atomic(page_kaddr);