lib/test_overflow.c: avoid tainting the kernel and fix wrap size

This adds __GFP_NOWARN to the kmalloc()-portions of the overflow test to
avoid tainting the kernel.  Additionally fixes up the math on wrap size
to be architecture and page size agnostic.

Link: http://lkml.kernel.org/r/201905282012.0A8767E24@keescook
Fixes: ca90800a91 ("test_overflow: Add memory allocation overflow tests")
Signed-off-by: Kees Cook <keescook@chromium.org>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/test_overflow.c

@@ -486,16 +486,17 @@ static int __init test_overflow_shift(void)
  * Deal with the various forms of allocator arguments. See comments above
  * the DEFINE_TEST_ALLOC() instances for mapping of the "bits".
  */
-#define alloc010(alloc, arg, sz) alloc(sz, GFP_KERNEL)
-#define alloc011(alloc, arg, sz) alloc(sz, GFP_KERNEL, NUMA_NO_NODE)
+#define alloc_GFP		 (GFP_KERNEL | __GFP_NOWARN)
+#define alloc010(alloc, arg, sz) alloc(sz, alloc_GFP)
+#define alloc011(alloc, arg, sz) alloc(sz, alloc_GFP, NUMA_NO_NODE)
 #define alloc000(alloc, arg, sz) alloc(sz)
 #define alloc001(alloc, arg, sz) alloc(sz, NUMA_NO_NODE)
-#define alloc110(alloc, arg, sz) alloc(arg, sz, GFP_KERNEL)
+#define alloc110(alloc, arg, sz) alloc(arg, sz, alloc_GFP)
 #define free0(free, arg, ptr)	 free(ptr)
 #define free1(free, arg, ptr)	 free(arg, ptr)
 
-/* Wrap around to 8K */
-#define TEST_SIZE		(9 << PAGE_SHIFT)
+/* Wrap around to 16K */
+#define TEST_SIZE		(5 * 4096)
 
 #define DEFINE_TEST_ALLOC(func, free_func, want_arg, want_gfp, want_node)\
 static int __init test_ ## func (void *arg)				\