kmemcheck: Test the full object in kmemcheck_is_obj_initialized()

This is a fix for bug #14845 (bugzilla.kernel.org). The update_checksum()
function in mm/kmemleak.c calls kmemcheck_is_obj_initialised() before scanning
an object. When KMEMCHECK_PARTIAL_OK is enabled, this function returns true.
However, the crc32_le() reads smaller intervals (32-bit) for which
kmemleak_is_obj_initialised() may be false leading to a kmemcheck warning.

Note that kmemcheck_is_obj_initialized() is currently only used by
kmemleak before scanning a memory location.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christian Casteyde <casteyde.christian@free.fr>
Cc: Vegard Nossum <vegardno@ifi.uio.no>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

arch/x86/mm/kmemcheck/kmemcheck.c

@@ -337,7 +337,7 @@ bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size)
 	if (!shadow)
 		return true;
 
-	status = kmemcheck_shadow_test(shadow, size);
+	status = kmemcheck_shadow_test_all(shadow, size);
 
 	return status == KMEMCHECK_SHADOW_INITIALIZED;
 }

arch/x86/mm/kmemcheck/shadow.c

@@ -125,12 +125,12 @@ void kmemcheck_mark_initialized_pages(struct page *p, unsigned int n)
 
 enum kmemcheck_shadow kmemcheck_shadow_test(void *shadow, unsigned int size)
 {
+#ifdef CONFIG_KMEMCHECK_PARTIAL_OK
 	uint8_t *x;
 	unsigned int i;
 
 	x = shadow;
 
-#ifdef CONFIG_KMEMCHECK_PARTIAL_OK
 	/*
 	 * Make sure _some_ bytes are initialized. Gcc frequently generates
 	 * code to access neighboring bytes.
@@ -139,13 +139,25 @@ enum kmemcheck_shadow kmemcheck_shadow_test(void *shadow, unsigned int size)
 		if (x[i] == KMEMCHECK_SHADOW_INITIALIZED)
 			return x[i];
 	}
+
+	return x[0];
 #else
+	return kmemcheck_shadow_test_all(shadow, size);
+#endif
+}
+
+enum kmemcheck_shadow kmemcheck_shadow_test_all(void *shadow, unsigned int size)
+{
+	uint8_t *x;
+	unsigned int i;
+
+	x = shadow;
+
 	/* All bytes must be initialized. */
 	for (i = 0; i < size; ++i) {
 		if (x[i] != KMEMCHECK_SHADOW_INITIALIZED)
 			return x[i];
 	}
-#endif
 
 	return x[0];
 }

arch/x86/mm/kmemcheck/shadow.h

@@ -11,6 +11,8 @@ enum kmemcheck_shadow {
 void *kmemcheck_shadow_lookup(unsigned long address);
 
 enum kmemcheck_shadow kmemcheck_shadow_test(void *shadow, unsigned int size);
+enum kmemcheck_shadow kmemcheck_shadow_test_all(void *shadow,
+						unsigned int size);
 void kmemcheck_shadow_set(void *shadow, unsigned int size);
 
 #endif