kunit: memcpy: Split slow memcpy tests into MEMCPY_SLOW_KUNIT_TEST

Since the long memcpy tests may stall a system for tens of seconds
in virtualized architecture environments, split those tests off under
CONFIG_MEMCPY_SLOW_KUNIT_TEST so they can be separately disabled.
Reported-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/lkml/20221226195206.GA2626419@roeck-us.netReviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-and-tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: David Gow <davidgow@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>

lib/Kconfig.debug

@@ -2566,6 +2566,15 @@ config MEMCPY_KUNIT_TEST
 
 	  If unsure, say N.
 
+config MEMCPY_SLOW_KUNIT_TEST
+	bool "Include exhaustive memcpy tests"
+	depends on MEMCPY_KUNIT_TEST
+	default y
+	help
+	  Some memcpy tests are quite exhaustive in checking for overlaps
+	  and bit ranges. These can be very slow, so they are split out
+	  as a separate config, in case they need to be disabled.
+
 config IS_SIGNED_TYPE_KUNIT_TEST
 	tristate "Test is_signed_type() macro" if !KUNIT_ALL_TESTS
 	depends on KUNIT

lib/memcpy_kunit.c

@@ -309,6 +309,8 @@ static void set_random_nonzero(struct kunit *test, u8 *byte)
 
 static void init_large(struct kunit *test)
 {
+	if (!IS_ENABLED(CONFIG_MEMCPY_SLOW_KUNIT_TEST))
+		kunit_skip(test, "Slow test skipped. Enable with CONFIG_MEMCPY_SLOW_KUNIT_TEST=y");
 
 	/* Get many bit patterns. */
 	get_random_bytes(large_src, ARRAY_SIZE(large_src));