[PATCH v2 2/3] fortify: Add KUnit test for FORTIFY_SOURCE internals

Kees Cook
2022-09-02T20:43:55Z

Add lib/fortify_kunit.c KUnit test for checking the expected behavioral
characteristics of FORTIFY_SOURCE internals.

Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Tom Rix <trix@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: "Steven Rostedt (Google)" <rostedt@goodmis.org>
Cc: David Gow <davidgow@google.com>
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Sander Vanheule <sander@svanheule.net>
Cc: linux-hardening@vger.kernel.org
Cc: llvm@lists.linux.dev
Signed-off-by: Kees Cook <keescook@chromium.org>
---
MAINTAINERS | 1 +
lib/Kconfig.debug | 9 ++++++
lib/Makefile | 1 +
lib/fortify_kunit.c | 77 +++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 88 insertions(+)
create mode 100644 lib/fortify_kunit.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 9d7f64dc0efe..640115472199 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8002,6 +8002,7 @@ L: linux-hardening@vger.kernel.org
S: Supported
T: git git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/hardening
F: include/linux/fortify-string.h
+F: lib/fortify_kunit.c
F: lib/test_fortify/*
F: scripts/test_fortify.sh
K: \b__NO_FORTIFY\b
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 36455953d306..1f267c0ddffd 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2542,6 +2542,15 @@ config STACKINIT_KUNIT_TEST
CONFIG_GCC_PLUGIN_STRUCTLEAK, CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF,
or CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL.

+config FORTIFY_KUNIT_TEST
+ tristate "Test fortified str*() and mem*() function internals at runtime" if !KUNIT_ALL_TESTS
+ depends on KUNIT && FORTIFY_SOURCE
+ default KUNIT_ALL_TESTS
+ help
+ Builds unit tests for checking internals of FORTIFY_SOURCE as used
+ by the str*() and mem*() family of functions. For testing runtime
+ traps of FORTIFY_SOURCE, see LKDTM's "FORTIFY_*" tests.
+
config TEST_UDELAY
tristate "udelay test driver"
help
diff --git a/lib/Makefile b/lib/Makefile
index f545140ed9e7..4ee1ceae945a 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -381,6 +381,7 @@ obj-$(CONFIG_IS_SIGNED_TYPE_KUNIT_TEST) += is_signed_type_kunit.o
obj-$(CONFIG_OVERFLOW_KUNIT_TEST) += overflow_kunit.o
CFLAGS_stackinit_kunit.o += $(call cc-disable-warning, switch-unreachable)
obj-$(CONFIG_STACKINIT_KUNIT_TEST) += stackinit_kunit.o
+obj-$(CONFIG_FORTIFY_KUNIT_TEST) += fortify_kunit.o

obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o

diff --git a/lib/fortify_kunit.c b/lib/fortify_kunit.c
new file mode 100644
index 000000000000..4d7930b65107
--- /dev/null
+++ b/lib/fortify_kunit.c
@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Runtime test cases for CONFIG_FORTIFY_SOURCE that aren't expected to
+ * Oops th kernel on success. (For those, see drivers/misc/lkdtm/fortify.c)
+ *
+ * For corner cases with UBSAN, try testing with:
+ *
+ * ./tools/testing/kunit/kunit.py run --arch=x86_64 \
+ * --kconfig_add CONFIG_FORTIFY_SOURCE=y \
+ * --kconfig_add CONFIG_UBSAN=y \
+ * --kconfig_add CONFIG_UBSAN_TRAP=y \
+ * --kconfig_add CONFIG_UBSAN_BOUNDS=y \
+ * --kconfig_add CONFIG_UBSAN_LOCAL_BOUNDS=y \
+ * --make_options LLVM=1 fortify
+ */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <kunit/test.h>
+#include <linux/string.h>
+#include <linux/init.h>
+
+static const char array_of_10[] = "this is 10";
+static const char *ptr_of_11 = "this is 11!";
+static char array_unknown[] = "compiler thinks I might change";
+
+static void known_sizes_test(struct kunit *test)
+{
+ KUNIT_EXPECT_EQ(test, __compiletime_strlen("88888888"), 8);
+ KUNIT_EXPECT_EQ(test, __compiletime_strlen(array_of_10), 10);
+ KUNIT_EXPECT_EQ(test, __compiletime_strlen(ptr_of_11), 11);
+
+ KUNIT_EXPECT_EQ(test, __compiletime_strlen(array_unknown), SIZE_MAX);
+ /* Externally defined and dynamically sized string pointer: */
+ KUNIT_EXPECT_EQ(test, __compiletime_strlen(saved_command_line), SIZE_MAX);
+}
+
+/* This is volatile so the optimizer can't perform DCE below. */
+static volatile int pick;
+
+/* Not inline to keep optimizer from figuring out which string we want. */
+static noinline size_t want_minus_one(int pick)
+{
+ const char *str;
+
+ switch (pick) {
+ case 1:
+ str = "4444";
+ break;
+ case 2:
+ str = "333";
+ break;
+ default:
+ str = "1";
+ break;
+ }
+ return __compiletime_strlen(str);
+}
+
+static void control_flow_split_test(struct kunit *test)
+{
+ KUNIT_EXPECT_EQ(test, want_minus_one(pick), SIZE_MAX);
+}
+
+static struct kunit_case fortify_test_cases[] = {
+ KUNIT_CASE(known_sizes_test),
+ KUNIT_CASE(control_flow_split_test),
+ {}
+};
+
+static struct kunit_suite fortify_test_suite = {
+ .name = "fortify",
+ .test_cases = fortify_test_cases,
+};
+
+kunit_test_suite(fortify_test_suite);
+
+MODULE_LICENSE("GPL");
--
2.34.1