[PATCH v4 00/10] Fix Kselftest's vfork() side effects

[PATCH v4 00/10] Fix Kselftest's vfork() side effects

[Mickaël Salaün]

Hi,

As reported by Kernel Test Robot [1], some pidfd tests fail.  This is
due to the use of vfork() which introduced some side effects.
Similarly, while making it more generic, a previous commit made some
Landlock file system tests flaky, and subject to the host's file system
mount configuration.

This series fixes all these side effects by replacing vfork() with
clone3() and CLONE_VFORK, which is cleaner (no arbitrary shared memory)
and makes the Kselftest framework more robust.

I tried different approaches and I found this one to be the cleaner and
less invasive for current test cases.

This fourth series add a patch from Sean Christopherson that fixes KVM
tests.

I successfully ran the following tests (using TEST_F and
fork/clone/clone3) with this series:
- landlock:fs_test
- landlock:net_test
- landlock:ptrace_test
- move_mount_set_group:move_mount_set_group_test
- net/af_unix:scm_pidfd
- perf_events:remove_on_exec
- pidfd:pidfd_getfd_test
- pidfd:pidfd_setns_test
- seccomp:seccomp_bpf
- user_events:abi_test

[1] https://lore.kernel.org/oe-lkp/202403291015.1fcfa957-oliver.sang@intel.com

Previous versions:
v1: https://lore.kernel.org/r/20240426172252.1862930-1-mic@digikod.net
v2: https://lore.kernel.org/r/20240429130931.2394118-1-mic@digikod.net
v3: https://lore.kernel.org/r/20240429191911.2552580-1-mic@digikod.net

Regards,

Mickaël Salaün (10):
  selftests/pidfd: Fix config for pidfd_setns_test
  selftests/landlock: Fix FS tests when run on a private mount point
  selftests/harness: Fix fixture teardown
  selftests/harness: Fix interleaved scheduling leading to race
    conditions
  selftests/landlock: Do not allocate memory in fixture data
  selftests/harness: Constify fixture variants
  selftests/pidfd: Fix wrong expectation
  selftests/harness: Share _metadata between forked processes
  selftests/harness: Fix vfork() side effects
  selftests/harness: Fix TEST_F()'s exit codes

 tools/testing/selftests/kselftest_harness.h   | 123 +++++++++++++-----
 tools/testing/selftests/landlock/fs_test.c    |  83 +++++++-----
 tools/testing/selftests/pidfd/config          |   2 +
 .../selftests/pidfd/pidfd_setns_test.c        |   2 +-
 4 files changed, 141 insertions(+), 69 deletions(-)


base-commit: e67572cd2204894179d89bd7b984072f19313b03
-- 
2.45.0

[PATCH v4 01/10] selftests/pidfd: Fix config for pidfd_setns_test

[Mickaël Salaün]

Required by switch_timens() to open /proc/self/ns/time_for_children.

CONFIG_GENERIC_VDSO_TIME_NS is not available on UML, so pidfd_setns_test
cannot be run successfully on this architecture.

Cc: Shuah Khan <skhan@linuxfoundation.org>
Fixes: 2b40c5db73e2 ("selftests/pidfd: add pidfd setns tests")
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240502210926.145539-2-mic@digikod.net
---
 tools/testing/selftests/pidfd/config | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/testing/selftests/pidfd/config b/tools/testing/selftests/pidfd/config
index f6f2965e17af..6133524710f7 100644
--- a/tools/testing/selftests/pidfd/config
+++ b/tools/testing/selftests/pidfd/config
@@ -3,5 +3,7 @@ CONFIG_IPC_NS=y
 CONFIG_USER_NS=y
 CONFIG_PID_NS=y
 CONFIG_NET_NS=y
+CONFIG_TIME_NS=y
+CONFIG_GENERIC_VDSO_TIME_NS=y
 CONFIG_CGROUPS=y
 CONFIG_CHECKPOINT_RESTORE=y
-- 
2.45.0

[PATCH v4 02/10] selftests/landlock: Fix FS tests when run on a private mount point

[Mickaël Salaün]

According to the test environment, the mount point of the test's working
directory may be shared or not, which changes the visibility of the
nested "tmp" mount point for the test's parent process calling
umount("tmp").

This was spotted while running tests in containers [1], where mount
points are private.

Cc: Günther Noack <gnoack@google.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Link: https://github.com/landlock-lsm/landlock-test-tools/pull/4 [1]
Fixes: 41cca0542d7c ("selftests/harness: Fix TEST_F()'s vfork handling")
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240502210926.145539-3-mic@digikod.net
---

Changes since v1:
* Update commit description.
---
 tools/testing/selftests/landlock/fs_test.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index 9a6036fbf289..46b9effd53e4 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -293,7 +293,15 @@ static void prepare_layout(struct __test_metadata *const _metadata)
 static void cleanup_layout(struct __test_metadata *const _metadata)
 {
 	set_cap(_metadata, CAP_SYS_ADMIN);
-	EXPECT_EQ(0, umount(TMP_DIR));
+	if (umount(TMP_DIR)) {
+		/*
+		 * According to the test environment, the mount point of the
+		 * current directory may be shared or not, which changes the
+		 * visibility of the nested TMP_DIR mount point for the test's
+		 * parent process doing this cleanup.
+		 */
+		ASSERT_EQ(EINVAL, errno);
+	}
 	clear_cap(_metadata, CAP_SYS_ADMIN);
 	EXPECT_EQ(0, remove_path(TMP_DIR));
 }
-- 
2.45.0

[PATCH v4 03/10] selftests/harness: Fix fixture teardown

[Mickaël Salaün]

Make sure fixture teardowns are run when test cases failed, including
when _metadata->teardown_parent is set to true.

Make sure only one fixture teardown is run per test case, handling the
case where the test child forks.

Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Shengyu Li <shengyu.li.evgeny@gmail.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Fixes: 72d7cb5c190b ("selftests/harness: Prevent infinite loop due to Assert in FIXTURE_TEARDOWN")
Fixes: 0710a1a73fb4 ("selftests/harness: Merge TEST_F_FORK() into TEST_F()")
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240502210926.145539-4-mic@digikod.net
---
 tools/testing/selftests/kselftest_harness.h | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index d98702b6955d..55699a762c45 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -382,7 +382,10 @@
 		FIXTURE_DATA(fixture_name) self; \
 		pid_t child = 1; \
 		int status = 0; \
-		bool jmp = false; \
+		/* Makes sure there is only one teardown, even when child forks again. */ \
+		bool *teardown = mmap(NULL, sizeof(*teardown), \
+			PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0); \
+		*teardown = false; \
 		memset(&self, 0, sizeof(FIXTURE_DATA(fixture_name))); \
 		if (setjmp(_metadata->env) == 0) { \
 			/* Use the same _metadata. */ \
@@ -399,15 +402,16 @@
 				_metadata->exit_code = KSFT_FAIL; \
 			} \
 		} \
-		else \
-			jmp = true; \
 		if (child == 0) { \
-			if (_metadata->setup_completed && !_metadata->teardown_parent && !jmp) \
+			if (_metadata->setup_completed && !_metadata->teardown_parent && \
+					__sync_bool_compare_and_swap(teardown, false, true)) \
 				fixture_name##_teardown(_metadata, &self, variant->data); \
 			_exit(0); \
 		} \
-		if (_metadata->setup_completed && _metadata->teardown_parent) \
+		if (_metadata->setup_completed && _metadata->teardown_parent && \
+				__sync_bool_compare_and_swap(teardown, false, true)) \
 			fixture_name##_teardown(_metadata, &self, variant->data); \
+		munmap(teardown, sizeof(*teardown)); \
 		if (!WIFEXITED(status) && WIFSIGNALED(status)) \
 			/* Forward signal to __wait_for_test(). */ \
 			kill(getpid(), WTERMSIG(status)); \
-- 
2.45.0

[PATCH v4 04/10] selftests/harness: Fix interleaved scheduling leading to race conditions

[Mickaël Salaün]

Fix a race condition when running several FIXTURE_TEARDOWN() managing
the same resource.  This fixes a race condition in the Landlock file
system tests when creating or unmounting the same directory.

Using clone3() with CLONE_VFORK guarantees that the child and grandchild
test processes are sequentially scheduled.  This is implemented with a
new clone3_vfork() helper replacing the fork() call.

This avoids triggering this error in __wait_for_test():
  Test ended in some other way [127]

Cc: Christian Brauner <brauner@kernel.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Günther Noack <gnoack@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Will Drewry <wad@chromium.org>
Fixes: 41cca0542d7c ("selftests/harness: Fix TEST_F()'s vfork handling")
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240502210926.145539-5-mic@digikod.net
---

Changes since v2:
* Replace __attribute__((__unused__)) with inline for clone3_vfork()
  (suggested by Kees and Jakub)
---
 tools/testing/selftests/kselftest_harness.h | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index 55699a762c45..9d7178a71c2c 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -66,6 +66,8 @@
 #include <sys/wait.h>
 #include <unistd.h>
 #include <setjmp.h>
+#include <syscall.h>
+#include <linux/sched.h>
 
 #include "kselftest.h"
 
@@ -80,6 +82,17 @@
 #  define TH_LOG_ENABLED 1
 #endif
 
+/* Wait for the child process to end but without sharing memory mapping. */
+static inline pid_t clone3_vfork(void)
+{
+	struct clone_args args = {
+		.flags = CLONE_VFORK,
+		.exit_signal = SIGCHLD,
+	};
+
+	return syscall(__NR_clone3, &args, sizeof(args));
+}
+
 /**
  * TH_LOG()
  *
@@ -1183,7 +1196,7 @@ void __run_test(struct __fixture_metadata *f,
 	fflush(stdout);
 	fflush(stderr);
 
-	t->pid = fork();
+	t->pid = clone3_vfork();
 	if (t->pid < 0) {
 		ksft_print_msg("ERROR SPAWNING TEST CHILD\n");
 		t->exit_code = KSFT_FAIL;
-- 
2.45.0

[PATCH v4 05/10] selftests/landlock: Do not allocate memory in fixture data

[Mickaël Salaün]

Do not allocate self->dir_path in the test process because this would
not be visible in the FIXTURE_TEARDOWN() process when relying on
fork()/clone3() instead of vfork().

This change is required for a following commit removing vfork() call to
not break the layout3_fs.* test cases.

Cc: Günther Noack <gnoack@google.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240502210926.145539-6-mic@digikod.net
---

Changes since v1:
* Extract change from a bigger patch (suggested by Kees).
---
 tools/testing/selftests/landlock/fs_test.c | 57 +++++++++++++---------
 1 file changed, 35 insertions(+), 22 deletions(-)

diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index 46b9effd53e4..1e2cffde02b5 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -9,6 +9,7 @@
 
 #define _GNU_SOURCE
 #include <fcntl.h>
+#include <libgen.h>
 #include <linux/landlock.h>
 #include <linux/magic.h>
 #include <sched.h>
@@ -4624,7 +4625,6 @@ FIXTURE(layout3_fs)
 {
 	bool has_created_dir;
 	bool has_created_file;
-	char *dir_path;
 	bool skip_test;
 };
 
@@ -4683,11 +4683,24 @@ FIXTURE_VARIANT_ADD(layout3_fs, hostfs) {
 	.cwd_fs_magic = HOSTFS_SUPER_MAGIC,
 };
 
+static char *dirname_alloc(const char *path)
+{
+	char *dup;
+
+	if (!path)
+		return NULL;
+
+	dup = strdup(path);
+	if (!dup)
+		return NULL;
+
+	return dirname(dup);
+}
+
 FIXTURE_SETUP(layout3_fs)
 {
 	struct stat statbuf;
-	const char *slash;
-	size_t dir_len;
+	char *dir_path = dirname_alloc(variant->file_path);
 
 	if (!supports_filesystem(variant->mnt.type) ||
 	    !cwd_matches_fs(variant->cwd_fs_magic)) {
@@ -4697,25 +4710,15 @@ FIXTURE_SETUP(layout3_fs)
 
 	_metadata->teardown_parent = true;
 
-	slash = strrchr(variant->file_path, '/');
-	ASSERT_NE(slash, NULL);
-	dir_len = (size_t)slash - (size_t)variant->file_path;
-	ASSERT_LT(0, dir_len);
-	self->dir_path = malloc(dir_len + 1);
-	self->dir_path[dir_len] = '\0';
-	strncpy(self->dir_path, variant->file_path, dir_len);
-
 	prepare_layout_opt(_metadata, &variant->mnt);
 
 	/* Creates directory when required. */
-	if (stat(self->dir_path, &statbuf)) {
+	if (stat(dir_path, &statbuf)) {
 		set_cap(_metadata, CAP_DAC_OVERRIDE);
-		EXPECT_EQ(0, mkdir(self->dir_path, 0700))
+		EXPECT_EQ(0, mkdir(dir_path, 0700))
 		{
 			TH_LOG("Failed to create directory \"%s\": %s",
-			       self->dir_path, strerror(errno));
-			free(self->dir_path);
-			self->dir_path = NULL;
+			       dir_path, strerror(errno));
 		}
 		self->has_created_dir = true;
 		clear_cap(_metadata, CAP_DAC_OVERRIDE);
@@ -4736,6 +4739,8 @@ FIXTURE_SETUP(layout3_fs)
 		self->has_created_file = true;
 		clear_cap(_metadata, CAP_DAC_OVERRIDE);
 	}
+
+	free(dir_path);
 }
 
 FIXTURE_TEARDOWN(layout3_fs)
@@ -4754,16 +4759,17 @@ FIXTURE_TEARDOWN(layout3_fs)
 	}
 
 	if (self->has_created_dir) {
+		char *dir_path = dirname_alloc(variant->file_path);
+
 		set_cap(_metadata, CAP_DAC_OVERRIDE);
 		/*
 		 * Don't check for error because the directory might already
 		 * have been removed (cf. release_inode test).
 		 */
-		rmdir(self->dir_path);
+		rmdir(dir_path);
 		clear_cap(_metadata, CAP_DAC_OVERRIDE);
+		free(dir_path);
 	}
-	free(self->dir_path);
-	self->dir_path = NULL;
 
 	cleanup_layout(_metadata);
 }
@@ -4830,7 +4836,10 @@ TEST_F_FORK(layout3_fs, tag_inode_dir_mnt)
 
 TEST_F_FORK(layout3_fs, tag_inode_dir_child)
 {
-	layer3_fs_tag_inode(_metadata, self, variant, self->dir_path);
+	char *dir_path = dirname_alloc(variant->file_path);
+
+	layer3_fs_tag_inode(_metadata, self, variant, dir_path);
+	free(dir_path);
 }
 
 TEST_F_FORK(layout3_fs, tag_inode_file)
@@ -4857,9 +4866,13 @@ TEST_F_FORK(layout3_fs, release_inodes)
 	if (self->has_created_file)
 		EXPECT_EQ(0, remove_path(variant->file_path));
 
-	if (self->has_created_dir)
+	if (self->has_created_dir) {
+		char *dir_path = dirname_alloc(variant->file_path);
+
 		/* Don't check for error because of cgroup specificities. */
-		remove_path(self->dir_path);
+		remove_path(dir_path);
+		free(dir_path);
+	}
 
 	ruleset_fd =
 		create_ruleset(_metadata, LANDLOCK_ACCESS_FS_READ_DIR, layer1);
-- 
2.45.0

[PATCH v4 06/10] selftests/harness: Constify fixture variants

[Mickaël Salaün]

FIXTURE_VARIANT_ADD() types are passed as const pointers to
FIXTURE_TEARDOWN().  Make that explicit by constifying the variants
declarations.

Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Will Drewry <wad@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240502210926.145539-7-mic@digikod.net
---

Changes since v1:
* Extract change from a bigger patch (suggested by Kees).
---
 tools/testing/selftests/kselftest_harness.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index 9d7178a71c2c..201040207c85 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -338,7 +338,7 @@ static inline pid_t clone3_vfork(void)
  * variant.
  */
 #define FIXTURE_VARIANT_ADD(fixture_name, variant_name) \
-	extern FIXTURE_VARIANT(fixture_name) \
+	extern const FIXTURE_VARIANT(fixture_name) \
 		_##fixture_name##_##variant_name##_variant; \
 	static struct __fixture_variant_metadata \
 		_##fixture_name##_##variant_name##_object = \
@@ -350,7 +350,7 @@ static inline pid_t clone3_vfork(void)
 		__register_fixture_variant(&_##fixture_name##_fixture_object, \
 			&_##fixture_name##_##variant_name##_object);	\
 	} \
-	FIXTURE_VARIANT(fixture_name) \
+	const FIXTURE_VARIANT(fixture_name) \
 		_##fixture_name##_##variant_name##_variant =
 
 /**
-- 
2.45.0

[PATCH v4 07/10] selftests/pidfd: Fix wrong expectation

[Mickaël Salaün]

Replace a wrong EXPECT_GT(self->child_pid_exited, 0) with EXPECT_GE(),
which will be actually tested on the parent and child sides with a
following commit.

Cc: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240502210926.145539-8-mic@digikod.net
---

Changes since v1:
* Extract change from a bigger patch (suggested by Kees).
---
 tools/testing/selftests/pidfd/pidfd_setns_test.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/pidfd/pidfd_setns_test.c b/tools/testing/selftests/pidfd/pidfd_setns_test.c
index 6e2f2cd400ca..47746b0c6acd 100644
--- a/tools/testing/selftests/pidfd/pidfd_setns_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_setns_test.c
@@ -158,7 +158,7 @@ FIXTURE_SETUP(current_nsset)
 	/* Create task that exits right away. */
 	self->child_pid_exited = create_child(&self->child_pidfd_exited,
 					      CLONE_NEWUSER | CLONE_NEWNET);
-	EXPECT_GT(self->child_pid_exited, 0);
+	EXPECT_GE(self->child_pid_exited, 0);
 
 	if (self->child_pid_exited == 0)
 		_exit(EXIT_SUCCESS);
-- 
2.45.0

[PATCH v4 08/10] selftests/harness: Share _metadata between forked processes

[Mickaël Salaün]

Unconditionally share _metadata between all forked processes, which
enables to actually catch errors which were previously ignored.

This is required for a following commit replacing vfork() with clone3()
and CLONE_VFORK (i.e. not sharing the full memory) .  It should also be
useful to share _metadata to extend expectations to test process's
forks.  For instance, this change identified a wrong expectation in
pidfd_setns_test.

Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Will Drewry <wad@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240502210926.145539-9-mic@digikod.net
---

Changes since v1:
* Extract change from a bigger patch (suggested by Kees).
---
 tools/testing/selftests/kselftest_harness.h | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index 201040207c85..abf2ffd2094f 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -430,19 +430,17 @@ static inline pid_t clone3_vfork(void)
 			kill(getpid(), WTERMSIG(status)); \
 		__test_check_assert(_metadata); \
 	} \
-	static struct __test_metadata \
-		      _##fixture_name##_##test_name##_object = { \
-		.name = #test_name, \
-		.fn = &wrapper_##fixture_name##_##test_name, \
-		.fixture = &_##fixture_name##_fixture_object, \
-		.termsig = signal, \
-		.timeout = tmout, \
-		.teardown_parent = false, \
-	 }; \
 	static void __attribute__((constructor)) \
 			_register_##fixture_name##_##test_name(void) \
 	{ \
-		__register_test(&_##fixture_name##_##test_name##_object); \
+		struct __test_metadata *object = mmap(NULL, sizeof(*object), \
+			PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0); \
+		object->name = #test_name; \
+		object->fn = &wrapper_##fixture_name##_##test_name; \
+		object->fixture = &_##fixture_name##_fixture_object; \
+		object->termsig = signal; \
+		object->timeout = tmout; \
+		__register_test(object); \
 	} \
 	static void fixture_name##_##test_name( \
 		struct __test_metadata __attribute__((unused)) *_metadata, \
-- 
2.45.0

[PATCH v4 09/10] selftests/harness: Fix vfork() side effects

[Mickaël Salaün]

Setting the time namespace with CLONE_NEWTIME returns -EUSERS if the
calling thread shares memory with another thread (because of the shared
vDSO), which is the case when it is created with vfork().

Fix pidfd_setns_test by replacing test harness's vfork() call with a
clone3() call with CLONE_VFORK, and an explicit sharing of the
_metadata and self objects.

Replace _metadata->teardown_parent with a new FIXTURE_TEARDOWN_PARENT()
helper that can replace FIXTURE_TEARDOWN().  This is a cleaner approach
and it enables to selectively share the fixture data between the child
process running tests and the parent process running the fixture
teardown.  This also avoids updating several tests to not rely on the
self object's copy-on-write property (e.g. storing the returned value of
a fork() call).

Cc: Christian Brauner <brauner@kernel.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Günther Noack <gnoack@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Will Drewry <wad@chromium.org>
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202403291015.1fcfa957-oliver.sang@intel.com
Fixes: 0710a1a73fb4 ("selftests/harness: Merge TEST_F_FORK() into TEST_F()")
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240502210926.145539-10-mic@digikod.net
---

Changes since v1:
* Split changes (suggested by Kees).
* Improve documentation.
* Remove the static fixture_name##_teardown_parent initialisation to
  false (as suggested by checkpatch.pl).
---
 tools/testing/selftests/kselftest_harness.h | 66 ++++++++++++++++-----
 tools/testing/selftests/landlock/fs_test.c  | 16 ++---
 2 files changed, 57 insertions(+), 25 deletions(-)

diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index abf2ffd2094f..d3837a3a584e 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -294,6 +294,32 @@ static inline pid_t clone3_vfork(void)
  * A bare "return;" statement may be used to return early.
  */
 #define FIXTURE_TEARDOWN(fixture_name) \
+	static const bool fixture_name##_teardown_parent; \
+	__FIXTURE_TEARDOWN(fixture_name)
+
+/**
+ * FIXTURE_TEARDOWN_PARENT()
+ * *_metadata* is included so that EXPECT_*, ASSERT_* etc. work correctly.
+ *
+ * @fixture_name: fixture name
+ *
+ * .. code-block:: c
+ *
+ *     FIXTURE_TEARDOWN_PARENT(fixture_name) { implementation }
+ *
+ * Same as FIXTURE_TEARDOWN() but run this code in a parent process.  This
+ * enables the test process to drop its privileges without impacting the
+ * related FIXTURE_TEARDOWN_PARENT() (e.g. to remove files from a directory
+ * where write access was dropped).
+ *
+ * To make it possible for the parent process to use *self*, share (MAP_SHARED)
+ * the fixture data between all forked processes.
+ */
+#define FIXTURE_TEARDOWN_PARENT(fixture_name) \
+	static const bool fixture_name##_teardown_parent = true; \
+	__FIXTURE_TEARDOWN(fixture_name)
+
+#define __FIXTURE_TEARDOWN(fixture_name) \
 	void fixture_name##_teardown( \
 		struct __test_metadata __attribute__((unused)) *_metadata, \
 		FIXTURE_DATA(fixture_name) __attribute__((unused)) *self, \
@@ -368,10 +394,11 @@ static inline pid_t clone3_vfork(void)
  * Very similar to TEST() except that *self* is the setup instance of fixture's
  * datatype exposed for use by the implementation.
  *
- * The @test_name code is run in a separate process sharing the same memory
- * (i.e. vfork), which means that the test process can update its privileges
- * without impacting the related FIXTURE_TEARDOWN() (e.g. to remove files from
- * a directory where write access was dropped).
+ * The _metadata object is shared (MAP_SHARED) with all the potential forked
+ * processes, which enables them to use EXCEPT_*() and ASSERT_*().
+ *
+ * The *self* object is only shared with the potential forked processes if
+ * FIXTURE_TEARDOWN_PARENT() is used instead of FIXTURE_TEARDOWN().
  */
 #define TEST_F(fixture_name, test_name) \
 	__TEST_F_IMPL(fixture_name, test_name, -1, TEST_TIMEOUT_DEFAULT)
@@ -392,39 +419,49 @@ static inline pid_t clone3_vfork(void)
 		struct __fixture_variant_metadata *variant) \
 	{ \
 		/* fixture data is alloced, setup, and torn down per call. */ \
-		FIXTURE_DATA(fixture_name) self; \
+		FIXTURE_DATA(fixture_name) self_private, *self = NULL; \
 		pid_t child = 1; \
 		int status = 0; \
 		/* Makes sure there is only one teardown, even when child forks again. */ \
 		bool *teardown = mmap(NULL, sizeof(*teardown), \
 			PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0); \
 		*teardown = false; \
-		memset(&self, 0, sizeof(FIXTURE_DATA(fixture_name))); \
+		if (sizeof(*self) > 0) { \
+			if (fixture_name##_teardown_parent) { \
+				self = mmap(NULL, sizeof(*self), PROT_READ | PROT_WRITE, \
+					MAP_SHARED | MAP_ANONYMOUS, -1, 0); \
+			} else { \
+				memset(&self_private, 0, sizeof(self_private)); \
+				self = &self_private; \
+			} \
+		} \
 		if (setjmp(_metadata->env) == 0) { \
-			/* Use the same _metadata. */ \
-			child = vfork(); \
+			/* _metadata and potentially self are shared with all forks. */ \
+			child = clone3_vfork(); \
 			if (child == 0) { \
-				fixture_name##_setup(_metadata, &self, variant->data); \
+				fixture_name##_setup(_metadata, self, variant->data); \
 				/* Let setup failure terminate early. */ \
 				if (_metadata->exit_code) \
 					_exit(0); \
 				_metadata->setup_completed = true; \
-				fixture_name##_##test_name(_metadata, &self, variant->data); \
+				fixture_name##_##test_name(_metadata, self, variant->data); \
 			} else if (child < 0 || child != waitpid(child, &status, 0)) { \
 				ksft_print_msg("ERROR SPAWNING TEST GRANDCHILD\n"); \
 				_metadata->exit_code = KSFT_FAIL; \
 			} \
 		} \
 		if (child == 0) { \
-			if (_metadata->setup_completed && !_metadata->teardown_parent && \
+			if (_metadata->setup_completed && !fixture_name##_teardown_parent && \
 					__sync_bool_compare_and_swap(teardown, false, true)) \
-				fixture_name##_teardown(_metadata, &self, variant->data); \
+				fixture_name##_teardown(_metadata, self, variant->data); \
 			_exit(0); \
 		} \
-		if (_metadata->setup_completed && _metadata->teardown_parent && \
+		if (_metadata->setup_completed && fixture_name##_teardown_parent && \
 				__sync_bool_compare_and_swap(teardown, false, true)) \
-			fixture_name##_teardown(_metadata, &self, variant->data); \
+			fixture_name##_teardown(_metadata, self, variant->data); \
 		munmap(teardown, sizeof(*teardown)); \
+		if (self && fixture_name##_teardown_parent) \
+			munmap(self, sizeof(*self)); \
 		if (!WIFEXITED(status) && WIFSIGNALED(status)) \
 			/* Forward signal to __wait_for_test(). */ \
 			kill(getpid(), WTERMSIG(status)); \
@@ -895,7 +932,6 @@ struct __test_metadata {
 	bool timed_out;	/* did this test timeout instead of exiting? */
 	bool aborted;	/* stopped test due to failed ASSERT */
 	bool setup_completed; /* did setup finish? */
-	bool teardown_parent; /* run teardown in a parent process */
 	jmp_buf env;	/* for exiting out of test early */
 	struct __test_results *results;
 	struct __test_metadata *prev, *next;
diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index 1e2cffde02b5..27744524df51 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -286,8 +286,6 @@ static void prepare_layout_opt(struct __test_metadata *const _metadata,
 
 static void prepare_layout(struct __test_metadata *const _metadata)
 {
-	_metadata->teardown_parent = true;
-
 	prepare_layout_opt(_metadata, &mnt_tmp);
 }
 
@@ -316,7 +314,7 @@ FIXTURE_SETUP(layout0)
 	prepare_layout(_metadata);
 }
 
-FIXTURE_TEARDOWN(layout0)
+FIXTURE_TEARDOWN_PARENT(layout0)
 {
 	cleanup_layout(_metadata);
 }
@@ -379,7 +377,7 @@ FIXTURE_SETUP(layout1)
 	create_layout1(_metadata);
 }
 
-FIXTURE_TEARDOWN(layout1)
+FIXTURE_TEARDOWN_PARENT(layout1)
 {
 	remove_layout1(_metadata);
 
@@ -3692,7 +3690,7 @@ FIXTURE_SETUP(ftruncate)
 	create_file(_metadata, file1_s1d1);
 }
 
-FIXTURE_TEARDOWN(ftruncate)
+FIXTURE_TEARDOWN_PARENT(ftruncate)
 {
 	EXPECT_EQ(0, remove_path(file1_s1d1));
 	cleanup_layout(_metadata);
@@ -3870,7 +3868,7 @@ FIXTURE_SETUP(layout1_bind)
 	clear_cap(_metadata, CAP_SYS_ADMIN);
 }
 
-FIXTURE_TEARDOWN(layout1_bind)
+FIXTURE_TEARDOWN_PARENT(layout1_bind)
 {
 	/* umount(dir_s2d2)) is handled by namespace lifetime. */
 
@@ -4275,7 +4273,7 @@ FIXTURE_SETUP(layout2_overlay)
 	clear_cap(_metadata, CAP_SYS_ADMIN);
 }
 
-FIXTURE_TEARDOWN(layout2_overlay)
+FIXTURE_TEARDOWN_PARENT(layout2_overlay)
 {
 	if (self->skip_test)
 		SKIP(return, "overlayfs is not supported (teardown)");
@@ -4708,8 +4706,6 @@ FIXTURE_SETUP(layout3_fs)
 		SKIP(return, "this filesystem is not supported (setup)");
 	}
 
-	_metadata->teardown_parent = true;
-
 	prepare_layout_opt(_metadata, &variant->mnt);
 
 	/* Creates directory when required. */
@@ -4743,7 +4739,7 @@ FIXTURE_SETUP(layout3_fs)
 	free(dir_path);
 }
 
-FIXTURE_TEARDOWN(layout3_fs)
+FIXTURE_TEARDOWN_PARENT(layout3_fs)
 {
 	if (self->skip_test)
 		SKIP(return, "this filesystem is not supported (teardown)");
-- 
2.45.0

[PATCH v4 10/10] selftests/harness: Fix TEST_F()'s exit codes

[Mickaël Salaün]

Always forward grandchild's exit codes to its parent.  This fixes
KVM_ONE_VCPU_TEST().

Initial patch written by Sean Christopherson [1].

Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Will Drewry <wad@chromium.org>
Link: https://lore.kernel.org/r/ZjPelW6-AbtYvslu@google.com [1]
Fixes: 0710a1a73fb4 ("selftests/harness: Merge TEST_F_FORK() into TEST_F()")
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240502210926.145539-11-mic@digikod.net
---

Changes since v3:
* New patch mainly from Sean Christopherson.
---
 tools/testing/selftests/kselftest_harness.h | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index d3837a3a584e..77d4fac8d0c0 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -442,7 +442,7 @@ static inline pid_t clone3_vfork(void)
 				fixture_name##_setup(_metadata, self, variant->data); \
 				/* Let setup failure terminate early. */ \
 				if (_metadata->exit_code) \
-					_exit(0); \
+					_exit(_metadata->exit_code); \
 				_metadata->setup_completed = true; \
 				fixture_name##_##test_name(_metadata, self, variant->data); \
 			} else if (child < 0 || child != waitpid(child, &status, 0)) { \
@@ -454,7 +454,7 @@ static inline pid_t clone3_vfork(void)
 			if (_metadata->setup_completed && !fixture_name##_teardown_parent && \
 					__sync_bool_compare_and_swap(teardown, false, true)) \
 				fixture_name##_teardown(_metadata, self, variant->data); \
-			_exit(0); \
+			_exit(_metadata->exit_code); \
 		} \
 		if (_metadata->setup_completed && fixture_name##_teardown_parent && \
 				__sync_bool_compare_and_swap(teardown, false, true)) \
@@ -462,8 +462,10 @@ static inline pid_t clone3_vfork(void)
 		munmap(teardown, sizeof(*teardown)); \
 		if (self && fixture_name##_teardown_parent) \
 			munmap(self, sizeof(*self)); \
-		if (!WIFEXITED(status) && WIFSIGNALED(status)) \
-			/* Forward signal to __wait_for_test(). */ \
+		/* Forward exit codes and signals to __wait_for_test(). */ \
+		if (WIFEXITED(status)) \
+			_exit(_metadata->exit_code); \
+		if (WIFSIGNALED(status)) \
 			kill(getpid(), WTERMSIG(status)); \
 		__test_check_assert(_metadata); \
 	} \
-- 
2.45.0

Re: [PATCH v4 10/10] selftests/harness: Fix TEST_F()'s exit codes

[Sean Christopherson]

On Thu, May 02, 2024, Mickaël Salaün wrote:
> @@ -462,8 +462,10 @@ static inline pid_t clone3_vfork(void)
>  		munmap(teardown, sizeof(*teardown)); \
>  		if (self && fixture_name##_teardown_parent) \
>  			munmap(self, sizeof(*self)); \
> -		if (!WIFEXITED(status) && WIFSIGNALED(status)) \
> -			/* Forward signal to __wait_for_test(). */ \
> +		/* Forward exit codes and signals to __wait_for_test(). */ \
> +		if (WIFEXITED(status)) \
> +			_exit(_metadata->exit_code); \

This needs to be:

		if (WIFEXITED(status)) \
			_exit(WEXITSTATUS(status)); \

otherwise existing tests that communicate FAIL/SKIP via exit() continue to yield
exit(0) and thus false passes.

If that conflicts with tests that want to communicate via _metadata->exit_code,
then maybe this?

		if (WIFEXITED(status)) \
			_exit(WEXITSTATUS(status) ?: _metadata->exit_code); \

Or I suppose _metadata->exit_code could have priority, but that seems weird to
me, e.g. if a test sets exit_code and then explodes, it seems like the explosion
should be reported.

> +		if (WIFSIGNALED(status)) \
>  			kill(getpid(), WTERMSIG(status)); \
>  		__test_check_assert(_metadata); \
>  	} \
> -- 
> 2.45.0
> 

Re: [PATCH v4 10/10] selftests/harness: Fix TEST_F()'s exit codes

[Mickaël Salaün]

On Thu, May 02, 2024 at 03:45:22PM GMT, Sean Christopherson wrote:
> On Thu, May 02, 2024, Mickaël Salaün wrote:
> > @@ -462,8 +462,10 @@ static inline pid_t clone3_vfork(void)
> >  		munmap(teardown, sizeof(*teardown)); \
> >  		if (self && fixture_name##_teardown_parent) \
> >  			munmap(self, sizeof(*self)); \
> > -		if (!WIFEXITED(status) && WIFSIGNALED(status)) \
> > -			/* Forward signal to __wait_for_test(). */ \
> > +		/* Forward exit codes and signals to __wait_for_test(). */ \
> > +		if (WIFEXITED(status)) \
> > +			_exit(_metadata->exit_code); \
> 
> This needs to be:
> 
> 		if (WIFEXITED(status)) \
> 			_exit(WEXITSTATUS(status)); \
> 
> otherwise existing tests that communicate FAIL/SKIP via exit() continue to yield
> exit(0) and thus false passes.

Yes of course.

> 
> If that conflicts with tests that want to communicate via _metadata->exit_code,
> then maybe this?
> 
> 		if (WIFEXITED(status)) \
> 			_exit(WEXITSTATUS(status) ?: _metadata->exit_code); \

I prefer this approach handling failed expectations in the fixture
teardown too.

However, the direct call to _exit() doesn't handle failed asserts.  I'll
fix that.


> 
> Or I suppose _metadata->exit_code could have priority, but that seems weird to
> me, e.g. if a test sets exit_code and then explodes, it seems like the explosion
> should be reported.
> 
> > +		if (WIFSIGNALED(status)) \
> >  			kill(getpid(), WTERMSIG(status)); \
> >  		__test_check_assert(_metadata); \
> >  	} \
> > -- 
> > 2.45.0
> > 
>