mm/kasan: don't use kasan shadow pointer in generic functions

We can't use generic functions like print_hex_dump to access kasan shadow
region.  This require us to setup another kasan shadow region for the
address passed (kasan shadow address).  Some architectures won't be able
to do that.  Hence make a copy of the shadow region row and pass that to
generic functions.
Signed-off-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Reviewed-by: NAndrey Ryabinin <ryabinin.a.a@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/kasan/report.c

@@ -164,14 +164,20 @@ static void print_shadow_for_address(const void *addr)
 	for (i = -SHADOW_ROWS_AROUND_ADDR; i <= SHADOW_ROWS_AROUND_ADDR; i++) {
 		const void *kaddr = kasan_shadow_to_mem(shadow_row);
 		char buffer[4 + (BITS_PER_LONG/8)*2];
+		char shadow_buf[SHADOW_BYTES_PER_ROW];
 
 		snprintf(buffer, sizeof(buffer),
 			(i == 0) ? ">%p: " : " %p: ", kaddr);
-
+		/*
+		 * We should not pass a shadow pointer to generic
+		 * function, because generic functions may try to
+		 * access kasan mapping for the passed address.
+		 */
 		kasan_disable_current();
+		memcpy(shadow_buf, shadow_row, SHADOW_BYTES_PER_ROW);
 		print_hex_dump(KERN_ERR, buffer,
 			DUMP_PREFIX_NONE, SHADOW_BYTES_PER_ROW, 1,
-			shadow_row, SHADOW_BYTES_PER_ROW, 0);
+			shadow_buf, SHADOW_BYTES_PER_ROW, 0);
 		kasan_enable_current();
 
 		if (row_is_guilty(shadow_row, shadow))