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Date: Tue, 13 Sep 2022 07:05:16 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>,
Tom Rix <trix@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Vlastimil Babka <vbabka@...e.cz>,
"Steven Rostedt (Google)" <rostedt@...dmis.org>,
David Gow <davidgow@...gle.com>,
Yury Norov <yury.norov@...il.com>,
Masami Hiramatsu <mhiramat@...nel.org>,
Sander Vanheule <sander@...nheule.net>,
linux-hardening@...r.kernel.org, llvm@...ts.linux.dev,
Peter Zijlstra <peterz@...radead.org>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Dan Williams <dan.j.williams@...el.com>,
Isabella Basso <isabbasso@...eup.net>,
Eric Dumazet <edumazet@...gle.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
Eric Biggers <ebiggers@...gle.com>,
Hannes Reinecke <hare@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] fortify: Add KUnit test for FORTIFY_SOURCE
internals
Hi Kees,
On Fri, Sep 02, 2022 at 01:43:50PM -0700, Kees Cook wrote:
> Add lib/fortify_kunit.c KUnit test for checking the expected behavioral
> characteristics of FORTIFY_SOURCE internals.
>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Cc: Nathan Chancellor <nathan@...nel.org>
> Cc: Tom Rix <trix@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> Cc: David Gow <davidgow@...gle.com>
> Cc: Yury Norov <yury.norov@...il.com>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Sander Vanheule <sander@...nheule.net>
> Cc: linux-hardening@...r.kernel.org
> Cc: llvm@...ts.linux.dev
> Signed-off-by: Kees Cook <keescook@...omium.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@...r.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);
> +}
I noticed that my allmodconfig + ThinLTO builds broke with this change:
$ make -skj"$(nproc)" ARCH=arm64 KCONFIG_ALLCONFIG=<(printf "CONFIG_%s=n\nCONFIG_%s=n\nCONFIG_%s=y\nCONFIG_%s=n\n" GCOV_KERNEL KASAN LTO_CLANG_THIN WERROR) LLVM=1 mrproper allmodconfig all
...
ERROR: modpost: "saved_command_line" [lib/fortify_kunit.ko] undefined!
...
saved_command_line is not exported to modules. This appears to be
related to the fact that CONFIG_KCSAN gets enabled due to the way
KCONFIG_ALLCONFIG works, as the issue does not show up in our CI, which
uses merge_config.sh.
A smaller reproducer on top of defconfig:
$ make -skj"$(nproc)" ARCH=arm64 LLVM=1 defconfig
$ scripts/config \
-d LTO_NONE \
-e EXPERT \
-e FORTIFY_SOURCE \
-e KCSAN \
-e LTO_CLANG_THIN \
-m FORTIFY_KUNIT_TEST \
-m KUNIT
$ make -skj"$(nproc)" ARCH=arm64 LLVM=1 olddefconfig all
...
ERROR: modpost: "saved_command_line" [lib/fortify_kunit.ko] undefined!
...
I don't see this without LTO. Is this a compiler problem?
Small note, Marco's patch is needed to avoid a separate linking error
with ToT LLVM:
https://lore.kernel.org/20220912094541.929856-1-elver@google.com/
Cheers,
Nathan
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