[PATCH v2] binfmt_elf: Introduce KUnit test

From: Kees Cook
Date: Thu Mar 03 2022 - 23:48:43 EST

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").

$ ./tools/testing/kunit/kunit.py run --arch x86_64 \
--kconfig_add CONFIG_IA32_EMULATION=y '*binfmt_elf'
...
[19:41:08] ================== binfmt_elf (1 subtest) ==================
[19:41:08] [PASSED] total_mapping_size_test
[19:41:08] =================== [PASSED] binfmt_elf ====================
[19:41:08] ============== compat_binfmt_elf (1 subtest) ===============
[19:41:08] [PASSED] total_mapping_size_test
[19:41:08] ================ [PASSED] compat_binfmt_elf ================
[19:41:08] ============================================================
[19:41:08] Testing complete. Passed: 2, Failed: 0, Crashed: 0, Skipped: 0, Errors: 0

Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
This is now at the top of my for-next/execve tree
v1: https://lore.kernel.org/lkml/20220224054332.1852813-1-keescook@xxxxxxxxxxxx
v2:
- improve commit log
- fix comment URL (Daniel)
- drop redundant KUnit Kconfig help info (Daniel)
- note in Kconfig help that COMPAT builds add a compat test (David)
---
fs/Kconfig.binfmt | 10 +++++++
fs/binfmt_elf.c | 4 +++
fs/binfmt_elf_test.c | 64 ++++++++++++++++++++++++++++++++++++++++++
fs/compat_binfmt_elf.c | 2 ++
4 files changed, 80 insertions(+)
create mode 100644 fs/binfmt_elf_test.c

diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
index 4d5ae61580aa..f7065e825b7f 100644
--- a/fs/Kconfig.binfmt
+++ b/fs/Kconfig.binfmt
@@ -28,6 +28,16 @@ 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, which try to gather
+ prior bug fixes into a regression test collection. This is really
+ only needed for debugging. Note that with CONFIG_COMPAT=y, the
+ compat_binfmt_elf KUnit test is also created.
+
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 4c5a2175f605..eaf39b1bdbbb 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -2346,3 +2346,7 @@ 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..11d734fec366
--- /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/linux-fsdevel/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.
--
2.32.0