mm/usercopy: Detect large folio overruns

Move the compound page overrun detection out of
CONFIG_HARDENED_USERCOPY_PAGESPAN and convert it to use folios so it's
enabled for more people.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220110231530.665970-4-willy@infradead.org

diff --git a/mm/usercopy.c b/mm/usercopy.c
index e1e856dca124614c545f0ac07ba6a4f1af4cfeb0..9458c2b24b027a13f966fa28c1f30205510d5d65 100644 (file)
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -164,7 +164,6 @@ static inline void check_page_span(const void *ptr, unsigned long n,
 {
 #ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN
        const void *end = ptr + n - 1;
-       struct page *endpage;
        bool is_reserved, is_cma;
 
        /*
@@ -195,11 +194,6 @@ static inline void check_page_span(const void *ptr, unsigned long n,
                   ((unsigned long)end & (unsigned long)PAGE_MASK)))
                return;
 
-       /* Allow if fully inside the same compound (__GFP_COMP) page. */
-       endpage = virt_to_head_page(end);
-       if (likely(endpage == page))
-               return;
-
        /*
         * Reject if range is entirely either Reserved (i.e. special or
         * device memory), or CMA. Otherwise, reject since the object spans
@@ -259,6 +253,10 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
        if (folio_test_slab(folio)) {
                /* Check slab allocator for flags and size. */
                __check_heap_object(ptr, n, folio_slab(folio), to_user);
+       } else if (folio_test_large(folio)) {
+               unsigned long offset = ptr - folio_address(folio);
+               if (offset + n > folio_size(folio))
+                       usercopy_abort("page alloc", NULL, to_user, offset, n);
        } else {
                /* Verify object does not incorrectly span multiple pages. */
                check_page_span(ptr, n, folio_page(folio, 0), to_user);