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

[David Gow]

On Sat, Sep 3, 2022 at 4:43 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> Add lib/fortify_kunit.c KUnit test for checking the expected behavioral
> characteristics of FORTIFY_SOURCE internals.
>
> Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
> Cc: Tom Rix <trix@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>
> Cc: David Gow <davidgow@xxxxxxxxxx>
> Cc: Yury Norov <yury.norov@xxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Cc: Sander Vanheule <sander@xxxxxxxxxxxxx>
> Cc: linux-hardening@xxxxxxxxxxxxxxx
> Cc: llvm@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---

Overall, this looks good. It's a bit of a shame FORTIFY_SOURCE doesn't
work under UML, but I tested it on everything else I had to hand and
it looked good.

One tiny typo in a comment below, but otherwise this is:

Reviewed-by: David Gow <davidgow@xxxxxxxxxx>

Cheers,
-- David

>  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@xxxxxxxxxxxxxxx
>  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)

Nit: Oops _the_ kernel

> + *
> + * 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
>