Add tests to assert that PIDFD_SELF_* correctly refers to the current
thread and process.

This is only practically meaningful to pidfd_send_signal() and
pidfd_getfd(), but also explicitly test that we disallow this feature for
setns() where it would make no sense.

We cannot reasonably wait on ourself using waitid(P_PIDFD, ...) so while in
theory PIDFD_SELF_* would work here, we'd be left blocked if we tried it.

We defer testing of mm-specific functionality which uses pidfd, namely
process_madvise() and process_mrelease() to mm testing (though note the
latter can not be sensibly tested as it would require the testing process
to be dying).

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
 tools/testing/selftests/pidfd/pidfd.h         |   8 +
 .../selftests/pidfd/pidfd_getfd_test.c        | 141 ++++++++++++++++++
 .../selftests/pidfd/pidfd_setns_test.c        |  11 ++
 tools/testing/selftests/pidfd/pidfd_test.c    |  76 ++++++++--
 4 files changed, 224 insertions(+), 12 deletions(-)

diff --git a/tools/testing/selftests/pidfd/pidfd.h b/tools/testing/selftests/pidfd/pidfd.h
index 88d6830ee004..1640b711889b 100644
--- a/tools/testing/selftests/pidfd/pidfd.h
+++ b/tools/testing/selftests/pidfd/pidfd.h
@@ -50,6 +50,14 @@
 #define PIDFD_NONBLOCK O_NONBLOCK
 #endif
 
+/* System header file may not have this available. */
+#ifndef PIDFD_SELF_THREAD
+#define PIDFD_SELF_THREAD -100
+#endif
+#ifndef PIDFD_SELF_THREAD_GROUP
+#define PIDFD_SELF_THREAD_GROUP -200
+#endif
+
 /*
  * The kernel reserves 300 pids via RESERVED_PIDS in kernel/pid.c
  * That means, when it wraps around any pid < 300 will be skipped.
diff --git a/tools/testing/selftests/pidfd/pidfd_getfd_test.c b/tools/testing/selftests/pidfd/pidfd_getfd_test.c
index cd51d547b751..48d224b13c01 100644
--- a/tools/testing/selftests/pidfd/pidfd_getfd_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_getfd_test.c
@@ -6,6 +6,7 @@
 #include <limits.h>
 #include <linux/types.h>
 #include <poll.h>
+#include <pthread.h>
 #include <sched.h>
 #include <signal.h>
 #include <stdio.h>
@@ -15,6 +16,7 @@
 #include <sys/prctl.h>
 #include <sys/wait.h>
 #include <unistd.h>
+#include <sys/mman.h>
 #include <sys/socket.h>
 #include <linux/kcmp.h>
 
@@ -114,6 +116,94 @@ static int child(int sk)
 	return ret;
 }
 
+static int __pidfd_self_thread_worker(unsigned long page_size)
+{
+	int memfd;
+	int newfd;
+	char *ptr;
+	int err = 0;
+
+	/*
+	 * Unshare our FDs so we have our own set. This means
+	 * PIDFD_SELF_THREAD_GROUP will fal.
+	 */
+	if (unshare(CLONE_FILES) < 0) {
+		err = -errno;
+		goto exit;
+	}
+
+	/* Truncate, map in and write to our memfd. */
+	memfd = sys_memfd_create("test_self_child", 0);
+	if (memfd < 0) {
+		err = -errno;
+		goto exit;
+	}
+
+	if (ftruncate(memfd, page_size)) {
+		err = -errno;
+		goto exit_close_memfd;
+	}
+
+	ptr = mmap(NULL, page_size, PROT_READ | PROT_WRITE,
+		   MAP_SHARED, memfd, 0);
+	if (ptr == MAP_FAILED) {
+		err = -errno;
+		goto exit_close_memfd;
+	}
+	ptr[0] = 'y';
+	if (munmap(ptr, page_size)) {
+		err = -errno;
+		goto exit_close_memfd;
+	}
+
+	/* Get a thread-local duplicate of our memfd. */
+	newfd = sys_pidfd_getfd(PIDFD_SELF_THREAD, memfd, 0);
+	if (newfd < 0) {
+		err = -errno;
+		goto exit_close_memfd;
+	}
+
+	if (memfd == newfd) {
+		err = -EINVAL;
+		goto exit_close_fds;
+	}
+
+	/* Map in new fd and make sure that the data is as expected. */
+	ptr = mmap(NULL, page_size, PROT_READ | PROT_WRITE,
+		   MAP_SHARED, newfd, 0);
+	if (ptr == MAP_FAILED) {
+		err = -errno;
+		goto exit_close_fds;
+	}
+
+	if (ptr[0] != 'y') {
+		err = -EINVAL;
+		goto exit_close_fds;
+	}
+
+	if (munmap(ptr, page_size)) {
+		err = -errno;
+		goto exit_close_fds;
+	}
+
+exit_close_fds:
+	close(newfd);
+exit_close_memfd:
+	close(memfd);
+exit:
+	return err;
+}
+
+static void *pidfd_self_thread_worker(void *arg)
+{
+	unsigned long page_size = (unsigned long)arg;
+	int ret;
+
+	/* We forward any errors for the caller to handle. */
+	ret = __pidfd_self_thread_worker(page_size);
+	return (void *)(intptr_t)ret;
+}
+
 FIXTURE(child)
 {
 	/*
@@ -264,6 +354,57 @@ TEST_F(child, no_strange_EBADF)
 	EXPECT_EQ(errno, ESRCH);
 }
 
+TEST(pidfd_self)
+{
+	int memfd = sys_memfd_create("test_self", 0);
+	unsigned long page_size = sysconf(_SC_PAGESIZE);
+	int newfd;
+	char *ptr;
+	pthread_t thread;
+	void *res;
+	int err;
+
+	ASSERT_GE(memfd, 0);
+	ASSERT_EQ(ftruncate(memfd, page_size), 0);
+
+	/*
+	 * Map so we can assert that the duplicated fd references the same
+	 * memory.
+	 */
+	ptr = mmap(NULL, page_size, PROT_READ | PROT_WRITE,
+		   MAP_SHARED, memfd, 0);
+	ASSERT_NE(ptr, MAP_FAILED);
+	ptr[0] = 'x';
+	ASSERT_EQ(munmap(ptr, page_size), 0);
+
+	/* Now get a duplicate of our memfd. */
+	newfd = sys_pidfd_getfd(PIDFD_SELF_THREAD_GROUP, memfd, 0);
+	ASSERT_GE(newfd, 0);
+	ASSERT_NE(memfd, newfd);
+
+	/* Now map duplicate fd and make sure it references the same memory. */
+	ptr = mmap(NULL, page_size, PROT_READ | PROT_WRITE,
+		   MAP_SHARED, newfd, 0);
+	ASSERT_NE(ptr, MAP_FAILED);
+	ASSERT_EQ(ptr[0], 'x');
+	ASSERT_EQ(munmap(ptr, page_size), 0);
+
+	/* Cleanup. */
+	close(memfd);
+	close(newfd);
+
+	/*
+	 * Fire up the thread and assert that we can lookup the thread-specific
+	 * PIDFD_SELF_THREAD (also aliased by PIDFD_SELF).
+	 */
+	ASSERT_EQ(pthread_create(&thread, NULL, pidfd_self_thread_worker,
+				 (void *)page_size), 0);
+	ASSERT_EQ(pthread_join(thread, &res), 0);
+	err = (int)(intptr_t)res;
+
+	ASSERT_EQ(err, 0);
+}
+
 #if __NR_pidfd_getfd == -1
 int main(void)
 {
diff --git a/tools/testing/selftests/pidfd/pidfd_setns_test.c b/tools/testing/selftests/pidfd/pidfd_setns_test.c
index 7c2a4349170a..bbd39dc5ceb7 100644
--- a/tools/testing/selftests/pidfd/pidfd_setns_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_setns_test.c
@@ -752,4 +752,15 @@ TEST(setns_einval)
 	close(fd);
 }
 
+TEST(setns_pidfd_self_disallowed)
+{
+	ASSERT_EQ(setns(PIDFD_SELF_THREAD, 0), -1);
+	EXPECT_EQ(errno, EBADF);
+
+	errno = 0;
+
+	ASSERT_EQ(setns(PIDFD_SELF_THREAD_GROUP, 0), -1);
+	EXPECT_EQ(errno, EBADF);
+}
+
 TEST_HARNESS_MAIN
diff --git a/tools/testing/selftests/pidfd/pidfd_test.c b/tools/testing/selftests/pidfd/pidfd_test.c
index 9faa686f90e4..440447cf89ba 100644
--- a/tools/testing/selftests/pidfd/pidfd_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_test.c
@@ -42,12 +42,41 @@ static pid_t pidfd_clone(int flags, int *pidfd, int (*fn)(void *))
 #endif
 }
 
-static int signal_received;
+static pthread_t signal_received;
 
 static void set_signal_received_on_sigusr1(int sig)
 {
 	if (sig == SIGUSR1)
-		signal_received = 1;
+		signal_received = pthread_self();
+}
+
+static int send_signal(int pidfd)
+{
+	int ret = 0;
+
+	if (sys_pidfd_send_signal(pidfd, SIGUSR1, NULL, 0) < 0) {
+		ret = -EINVAL;
+		goto exit;
+	}
+
+	if (signal_received != pthread_self()) {
+		ret = -EINVAL;
+		goto exit;
+	}
+
+exit:
+	signal_received = 0;
+	return ret;
+}
+
+static void *send_signal_worker(void *arg)
+{
+	int pidfd = (int)(intptr_t)arg;
+	int ret;
+
+	/* We forward any errors for the caller to handle. */
+	ret = send_signal(pidfd);
+	return (void *)(intptr_t)ret;
 }
 
 /*
@@ -56,8 +85,11 @@ static void set_signal_received_on_sigusr1(int sig)
  */
 static int test_pidfd_send_signal_simple_success(void)
 {
-	int pidfd, ret;
+	int pidfd;
 	const char *test_name = "pidfd_send_signal send SIGUSR1";
+	pthread_t thread;
+	void *thread_res;
+	int err;
 
 	if (!have_pidfd_send_signal) {
 		ksft_test_result_skip(
@@ -66,25 +98,45 @@ static int test_pidfd_send_signal_simple_success(void)
 		return 0;
 	}
 
+	signal(SIGUSR1, set_signal_received_on_sigusr1);
+
+	/* Try sending a signal to ourselves via /proc/self. */
 	pidfd = open("/proc/self", O_DIRECTORY | O_CLOEXEC);
 	if (pidfd < 0)
 		ksft_exit_fail_msg(
 			"%s test: Failed to open process file descriptor\n",
 			test_name);
+	err = send_signal(pidfd);
+	if (err)
+		ksft_exit_fail_msg(
+			"%s test: Error %d on sending pidfd signal\n",
+			test_name, err);
+	close(pidfd);
 
-	signal(SIGUSR1, set_signal_received_on_sigusr1);
+	/* Now try the same thing only using PIDFD_SELF_THREAD_GROUP. */
+	err = send_signal(PIDFD_SELF_THREAD_GROUP);
+	if (err)
+		ksft_exit_fail_msg(
+			"%s test: Error %d on PIDFD_SELF_THREAD_GROUP signal\n",
+			test_name, err);
 
-	ret = sys_pidfd_send_signal(pidfd, SIGUSR1, NULL, 0);
-	close(pidfd);
-	if (ret < 0)
-		ksft_exit_fail_msg("%s test: Failed to send signal\n",
+	/*
+	 * Now try the same thing in a thread and assert thread ID is equal to
+	 * worker thread ID.
+	 */
+	if (pthread_create(&thread, NULL, send_signal_worker,
+			   (void *)(intptr_t)PIDFD_SELF_THREAD))
+		ksft_exit_fail_msg("%s test: Failed to create thread\n",
 				   test_name);
-
-	if (signal_received != 1)
-		ksft_exit_fail_msg("%s test: Failed to receive signal\n",
+	if (pthread_join(thread, &thread_res))
+		ksft_exit_fail_msg("%s test: Failed to join thread\n",
 				   test_name);
+	err = (int)(intptr_t)thread_res;
+	if (err)
+		ksft_exit_fail_msg(
+			"%s test: Error %d on PIDFD_SELF_THREAD signal\n",
+			test_name, err);
 
-	signal_received = 0;
 	ksft_test_result_pass("%s test: Sent signal\n", test_name);
 	return 0;
 }
-- 
2.46.2