[PATCH] binfmt_elf: Introduce KUnit test

[Kees Cook <keescook@chromium.org>]

Adds simple KUnit test for some binfmt_elf internals: specifically a
regression test for the problem fixed by commit 8904d9cd90ee ("ELF:
fix overflow in total mapping size calculation").

Cc: Eric Biederman <ebiederm@xmission.com>
Cc: David Gow <davidgow@google.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: "Magnus Groß" <magnus.gross@rwth-aachen.de>
Cc: kunit-dev@googlegroups.com
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
I'm exploring ways to mock copy_to_user() for more tests in here.
kprobes doesn't seem to let me easily hijack a function...
---
 fs/Kconfig.binfmt      | 17 +++++++++++
 fs/binfmt_elf.c        |  4 +++
 fs/binfmt_elf_test.c   | 64 ++++++++++++++++++++++++++++++++++++++++++
 fs/compat_binfmt_elf.c |  2 ++
 4 files changed, 87 insertions(+)
 create mode 100644 fs/binfmt_elf_test.c

diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
index 4d5ae61580aa..8e14589ee9cc 100644
--- a/fs/Kconfig.binfmt
+++ b/fs/Kconfig.binfmt
@@ -28,6 +28,23 @@ config BINFMT_ELF
 	  ld.so (check the file <file:Documentation/Changes> for location and
 	  latest version).
 
+config BINFMT_ELF_KUNIT_TEST
+	bool "Build KUnit tests for ELF binary support" if !KUNIT_ALL_TESTS
+	depends on KUNIT=y && BINFMT_ELF=y
+	default KUNIT_ALL_TESTS
+	help
+	  This builds the ELF loader KUnit tests.
+
+	  KUnit tests run during boot and output the results to the debug log
+	  in TAP format (https://testanything.org/). Only useful for kernel devs
+	  running KUnit test harness and are not for inclusion into a
+	  production build.
+
+	  For more information on KUnit and unit tests in general please refer
+	  to the KUnit documentation in Documentation/dev-tools/kunit/.
+
+	  If unsure, say N.
+
 config COMPAT_BINFMT_ELF
 	def_bool y
 	depends on COMPAT && BINFMT_ELF
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 76ff2af15ba5..9bea703ed1c2 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -2335,3 +2335,7 @@ static void __exit exit_elf_binfmt(void)
 core_initcall(init_elf_binfmt);
 module_exit(exit_elf_binfmt);
 MODULE_LICENSE("GPL");
+
+#ifdef CONFIG_BINFMT_ELF_KUNIT_TEST
+#include "binfmt_elf_test.c"
+#endif
diff --git a/fs/binfmt_elf_test.c b/fs/binfmt_elf_test.c
new file mode 100644
index 000000000000..486ad419f763
--- /dev/null
+++ b/fs/binfmt_elf_test.c
@@ -0,0 +1,64 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <kunit/test.h>
+
+static void total_mapping_size_test(struct kunit *test)
+{
+	struct elf_phdr empty[] = {
+		{ .p_type = PT_LOAD, .p_vaddr = 0, .p_memsz = 0, },
+		{ .p_type = PT_INTERP, .p_vaddr = 10, .p_memsz = 999999, },
+	};
+	/*
+	 * readelf -lW /bin/mount | grep '^  .*0x0' | awk '{print "\t\t{ .p_type = PT_" \
+	 *				$1 ", .p_vaddr = " $3 ", .p_memsz = " $6 ", },"}'
+	 */
+	struct elf_phdr mount[] = {
+		{ .p_type = PT_PHDR, .p_vaddr = 0x00000040, .p_memsz = 0x0002d8, },
+		{ .p_type = PT_INTERP, .p_vaddr = 0x00000318, .p_memsz = 0x00001c, },
+		{ .p_type = PT_LOAD, .p_vaddr = 0x00000000, .p_memsz = 0x0033a8, },
+		{ .p_type = PT_LOAD, .p_vaddr = 0x00004000, .p_memsz = 0x005c91, },
+		{ .p_type = PT_LOAD, .p_vaddr = 0x0000a000, .p_memsz = 0x0022f8, },
+		{ .p_type = PT_LOAD, .p_vaddr = 0x0000d330, .p_memsz = 0x000d40, },
+		{ .p_type = PT_DYNAMIC, .p_vaddr = 0x0000d928, .p_memsz = 0x000200, },
+		{ .p_type = PT_NOTE, .p_vaddr = 0x00000338, .p_memsz = 0x000030, },
+		{ .p_type = PT_NOTE, .p_vaddr = 0x00000368, .p_memsz = 0x000044, },
+		{ .p_type = PT_GNU_PROPERTY, .p_vaddr = 0x00000338, .p_memsz = 0x000030, },
+		{ .p_type = PT_GNU_EH_FRAME, .p_vaddr = 0x0000b490, .p_memsz = 0x0001ec, },
+		{ .p_type = PT_GNU_STACK, .p_vaddr = 0x00000000, .p_memsz = 0x000000, },
+		{ .p_type = PT_GNU_RELRO, .p_vaddr = 0x0000d330, .p_memsz = 0x000cd0, },
+	};
+	size_t mount_size = 0xE070;
+	/* https://lore.kernel.org/lkml/YfF18Dy85mCntXrx@fractal.localdomain */
+	struct elf_phdr unordered[] = {
+		{ .p_type = PT_LOAD, .p_vaddr = 0x00000000, .p_memsz = 0x0033a8, },
+		{ .p_type = PT_LOAD, .p_vaddr = 0x0000d330, .p_memsz = 0x000d40, },
+		{ .p_type = PT_LOAD, .p_vaddr = 0x00004000, .p_memsz = 0x005c91, },
+		{ .p_type = PT_LOAD, .p_vaddr = 0x0000a000, .p_memsz = 0x0022f8, },
+	};
+
+	/* No headers, no size. */
+	KUNIT_EXPECT_EQ(test, total_mapping_size(NULL, 0), 0);
+	KUNIT_EXPECT_EQ(test, total_mapping_size(empty, 0), 0);
+	/* Empty headers, no size. */
+	KUNIT_EXPECT_EQ(test, total_mapping_size(empty, 1), 0);
+	/* No PT_LOAD headers, no size. */
+	KUNIT_EXPECT_EQ(test, total_mapping_size(&empty[1], 1), 0);
+	/* Empty PT_LOAD and non-PT_LOAD headers, no size. */
+	KUNIT_EXPECT_EQ(test, total_mapping_size(empty, 2), 0);
+
+	/* Normal set of PT_LOADS, and expected size. */
+	KUNIT_EXPECT_EQ(test, total_mapping_size(mount, ARRAY_SIZE(mount)), mount_size);
+	/* Unordered PT_LOADs result in same size. */
+	KUNIT_EXPECT_EQ(test, total_mapping_size(unordered, ARRAY_SIZE(unordered)), mount_size);
+}
+
+static struct kunit_case binfmt_elf_test_cases[] = {
+	KUNIT_CASE(total_mapping_size_test),
+	{},
+};
+
+static struct kunit_suite binfmt_elf_test_suite = {
+	.name = KBUILD_MODNAME,
+	.test_cases = binfmt_elf_test_cases,
+};
+
+kunit_test_suite(binfmt_elf_test_suite);
diff --git a/fs/compat_binfmt_elf.c b/fs/compat_binfmt_elf.c
index 95e72d271b95..8f0af4f62631 100644
--- a/fs/compat_binfmt_elf.c
+++ b/fs/compat_binfmt_elf.c
@@ -135,6 +135,8 @@
 #define elf_format		compat_elf_format
 #define init_elf_binfmt		init_compat_elf_binfmt
 #define exit_elf_binfmt		exit_compat_elf_binfmt
+#define binfmt_elf_test_cases	compat_binfmt_elf_test_cases
+#define binfmt_elf_test_suite	compat_binfmt_elf_test_suite
 
 /*
  * We share all the actual code with the native (64-bit) version.
-- 
2.30.2