For memfd_restricted() calls without a userspace mount, the backing
file should be the shmem mount in the kernel, and the size of backing
pages should be as defined by system-wide shmem configuration.

If a userspace mount is provided, the size of backing pages should be
as defined in the mount.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
 tools/testing/selftests/Makefile              |   1 +
 .../selftests/restrictedmem/.gitignore        |   3 +
 .../testing/selftests/restrictedmem/Makefile  |  14 +
 .../testing/selftests/restrictedmem/common.c  |   9 +
 .../testing/selftests/restrictedmem/common.h  |   8 +
 .../restrictedmem_hugepage_test.c             | 344 ++++++++++++++++++
 6 files changed, 379 insertions(+)
 create mode 100644 tools/testing/selftests/restrictedmem/.gitignore
 create mode 100644 tools/testing/selftests/restrictedmem/Makefile
 create mode 100644 tools/testing/selftests/restrictedmem/common.c
 create mode 100644 tools/testing/selftests/restrictedmem/common.h
 create mode 100644 tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index f07aef7c592c..44078eeefb79 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -60,6 +60,7 @@ TARGETS += pstore
 TARGETS += ptrace
 TARGETS += openat2
 TARGETS += resctrl
+TARGETS += restrictedmem
 TARGETS += rlimits
 TARGETS += rseq
 TARGETS += rtc
diff --git a/tools/testing/selftests/restrictedmem/.gitignore b/tools/testing/selftests/restrictedmem/.gitignore
new file mode 100644
index 000000000000..2581bcc8ff29
--- /dev/null
+++ b/tools/testing/selftests/restrictedmem/.gitignore
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+restrictedmem_hugepage_test
diff --git a/tools/testing/selftests/restrictedmem/Makefile b/tools/testing/selftests/restrictedmem/Makefile
new file mode 100644
index 000000000000..da9665718c8a
--- /dev/null
+++ b/tools/testing/selftests/restrictedmem/Makefile
@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: GPL-2.0
+
+CFLAGS = $(KHDR_INCLUDES)
+
+TEST_GEN_PROGS += restrictedmem_hugepage_test
+
+include ../lib.mk
+
+EXTRA_CLEAN = $(OUTPUT)/common.o
+
+$(OUTPUT)/common.o: common.c
+	$(CC) $(CFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c -ffreestanding $< -o $@
+
+$(TEST_GEN_PROGS): $(OUTPUT)/common.o
diff --git a/tools/testing/selftests/restrictedmem/common.c b/tools/testing/selftests/restrictedmem/common.c
new file mode 100644
index 000000000000..79b2ac98cc89
--- /dev/null
+++ b/tools/testing/selftests/restrictedmem/common.c
@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <sys/syscall.h>
+#include <unistd.h>
+
+int memfd_restricted(unsigned int flags, char *mount_path)
+{
+	return syscall(__NR_memfd_restricted, flags, mount_path);
+}
diff --git a/tools/testing/selftests/restrictedmem/common.h b/tools/testing/selftests/restrictedmem/common.h
new file mode 100644
index 000000000000..5d59edc4f23f
--- /dev/null
+++ b/tools/testing/selftests/restrictedmem/common.h
@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef SELFTESTS_RESTRICTEDMEM_COMMON_H
+#define SELFTESTS_RESTRICTEDMEM_COMMON_H
+
+int memfd_restricted(unsigned int flags, char *mount_path);
+
+#endif  // SELFTESTS_RESTRICTEDMEM_COMMON_H
diff --git a/tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c b/tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c
new file mode 100644
index 000000000000..0d9cf2ced754
--- /dev/null
+++ b/tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c
@@ -0,0 +1,344 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include "linux/limits.h"
+#include <errno.h>
+#include <limits.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+
+#include "linux/restrictedmem.h"
+
+#include "common.h"
+#include "../kselftest_harness.h"
+
+static int get_hpage_pmd_size(void)
+{
+	FILE *fp;
+	char buf[100];
+	char *ret;
+	int size;
+
+	fp = fopen("/sys/kernel/mm/transparent_hugepage/hpage_pmd_size", "r");
+	if (!fp)
+		return -1;
+
+	ret = fgets(buf, 100, fp);
+	if (ret != buf) {
+		size = -1;
+		goto out;
+	}
+
+	if (sscanf(buf, "%d\n", &size) != 1)
+		size = -1;
+
+out:
+	fclose(fp);
+
+	return size;
+}
+
+static bool is_valid_shmem_thp_policy(char *policy)
+{
+	if (strcmp(policy, "always") == 0)
+		return true;
+	if (strcmp(policy, "within_size") == 0)
+		return true;
+	if (strcmp(policy, "advise") == 0)
+		return true;
+	if (strcmp(policy, "never") == 0)
+		return true;
+	if (strcmp(policy, "deny") == 0)
+		return true;
+	if (strcmp(policy, "force") == 0)
+		return true;
+
+	return false;
+}
+
+static int get_shmem_thp_policy(char *policy)
+{
+	FILE *fp;
+	char buf[100];
+	char *left = NULL;
+	char *right = NULL;
+	int ret = -1;
+
+	fp = fopen("/sys/kernel/mm/transparent_hugepage/shmem_enabled", "r");
+	if (!fp)
+		return -1;
+
+	if (fgets(buf, 100, fp) != buf)
+		goto out;
+
+	/*
+	 * Expect shmem_enabled to be of format like "always within_size advise
+	 * [never] deny force"
+	 */
+	left = memchr(buf, '[', 100);
+	if (!left)
+		goto out;
+
+	right = memchr(buf, ']', 100);
+	if (!right)
+		goto out;
+
+	memcpy(policy, left + 1, right - left - 1);
+
+	ret = !is_valid_shmem_thp_policy(policy);
+
+out:
+	fclose(fp);
+	return ret;
+}
+
+static int set_shmem_thp_policy(char *policy)
+{
+	FILE *fp;
+	size_t len = strlen(policy);
+	int ret = -1;
+
+	if (!is_valid_shmem_thp_policy(policy))
+		return ret;
+
+	fp = fopen("/sys/kernel/mm/transparent_hugepage/shmem_enabled", "w");
+	if (!fp)
+		return ret;
+
+	if (fwrite(policy, 1, len, fp) != len)
+		goto out;
+
+	if (fwrite("\n", 1, 1, fp) != 1)
+		goto out;
+
+	ret = 0;
+
+out:
+	fclose(fp);
+	return ret;
+}
+
+FIXTURE(reset_shmem_enabled)
+{
+	/*
+	 * Expect shmem_enabled to be one of always, within_size, advise, never,
+	 * deny, force
+	 */
+	char shmem_enabled[12];
+};
+
+FIXTURE_SETUP(reset_shmem_enabled)
+{
+	memset(self->shmem_enabled, 0, 12);
+	ASSERT_EQ(0, get_shmem_thp_policy(self->shmem_enabled));
+}
+
+FIXTURE_TEARDOWN(reset_shmem_enabled)
+{
+	ASSERT_EQ(0, set_shmem_thp_policy(self->shmem_enabled));
+}
+
+TEST_F(reset_shmem_enabled, restrictedmem_fstat_shmem_enabled_never)
+{
+	int mfd = -1;
+	struct stat stat;
+	char *orig_shmem_enabled;
+
+	ASSERT_EQ(0, set_shmem_thp_policy("never"));
+
+	mfd = memfd_restricted(0, NULL);
+	ASSERT_NE(-1, mfd);
+
+	ASSERT_EQ(0, fstat(mfd, &stat));
+
+	/*
+	 * st_blksize is set based on the superblock's s_blocksize_bits. For
+	 * shmem, this is set to PAGE_SHIFT
+	 */
+	ASSERT_EQ(stat.st_blksize, getpagesize());
+
+	close(mfd);
+}
+
+TEST_F(reset_shmem_enabled, restrictedmem_fstat_shmem_enabled_always)
+{
+	int mfd = -1;
+	struct stat stat;
+	char *orig_shmem_enabled;
+
+	ASSERT_EQ(0, set_shmem_thp_policy("always"));
+
+	mfd = memfd_restricted(0, NULL);
+	ASSERT_NE(-1, mfd);
+
+	ASSERT_EQ(0, fstat(mfd, &stat));
+
+	ASSERT_EQ(stat.st_blksize, get_hpage_pmd_size());
+
+	close(mfd);
+}
+
+TEST(restrictedmem_tmpfile_no_mount_path)
+{
+	int mfd = memfd_restricted(RMFD_TMPFILE, NULL);
+
+	ASSERT_EQ(-1, mfd);
+	ASSERT_EQ(EINVAL, errno);
+}
+
+TEST(restrictedmem_tmpfile_nonexistent_mount_path)
+{
+	int mfd = memfd_restricted(RMFD_TMPFILE,
+				   "/nonexistent/nonexistent/nonexistent");
+
+	ASSERT_EQ(-1, mfd);
+	ASSERT_EQ(ENOENT, errno);
+}
+
+TEST(restrictedmem_tmpfile_not_tmpfs_mount)
+{
+	int mfd = memfd_restricted(RMFD_TMPFILE, "/proc");
+
+	ASSERT_EQ(-1, mfd);
+	ASSERT_EQ(EINVAL, errno);
+}
+
+static bool directory_exists(const char *path)
+{
+	struct stat sb;
+
+	return stat(path, &sb) == 0 && S_ISDIR(sb.st_mode);
+}
+
+FIXTURE(tmpfs_hugepage_mount_path)
+{
+	char *mount_path;
+};
+
+FIXTURE_SETUP(tmpfs_hugepage_mount_path)
+{
+	int ret = -1;
+
+	/* /tmp is an FHS-mandated world-writable directory */
+	self->mount_path = "/tmp/restrictedmem-selftest-mnt";
+
+	if (!directory_exists(self->mount_path)) {
+		ret = mkdir(self->mount_path, 0777);
+		ASSERT_EQ(0, ret);
+	}
+}
+
+FIXTURE_TEARDOWN(tmpfs_hugepage_mount_path)
+{
+	int ret = -1;
+
+	if (!directory_exists(self->mount_path))
+		return;
+
+	ret = umount2(self->mount_path, MNT_FORCE);
+	EXPECT_EQ(0, ret);
+	if (ret == -1 && errno == EINVAL)
+		fprintf(stderr, "%s was not mounted\n", self->mount_path);
+
+	ret = rmdir(self->mount_path);
+	ASSERT_EQ(0, ret);
+}
+
+TEST_F(tmpfs_hugepage_mount_path, restrictedmem_fstat_tmpfs_huge_always)
+{
+	int ret = -1;
+	int mfd = -1;
+	struct stat stat;
+
+	ret = mount("name", self->mount_path, "tmpfs", 0, "huge=always");
+	ASSERT_EQ(0, ret);
+
+	mfd = memfd_restricted(RMFD_TMPFILE, self->mount_path);
+	ASSERT_NE(-1, mfd);
+
+	ret = fstat(mfd, &stat);
+	ASSERT_EQ(0, ret);
+	ASSERT_EQ(stat.st_blksize, get_hpage_pmd_size());
+
+	close(mfd);
+}
+
+TEST_F(tmpfs_hugepage_mount_path, restrictedmem_fstat_tmpfs_huge_never)
+{
+	int ret = -1;
+	int mfd = -1;
+	struct stat stat;
+
+	ret = mount("name", self->mount_path, "tmpfs", 0, "huge=never");
+	ASSERT_EQ(0, ret);
+
+	mfd = memfd_restricted(RMFD_TMPFILE, self->mount_path);
+	ASSERT_NE(-1, mfd);
+
+	ret = fstat(mfd, &stat);
+	ASSERT_EQ(0, ret);
+	ASSERT_EQ(stat.st_blksize, getpagesize());
+
+	close(mfd);
+}
+
+TEST_F(tmpfs_hugepage_mount_path, restrictedmem_umount_rmdir_while_file_open)
+{
+	int ret = -1;
+	int mfd = -1;
+
+	ret = mount("name", self->mount_path, "tmpfs", 0, "huge=always");
+	ASSERT_EQ(0, ret);
+
+	mfd = memfd_restricted(RMFD_TMPFILE, self->mount_path);
+	ASSERT_NE(-1, mfd);
+
+	ret = umount2(self->mount_path, MNT_FORCE);
+	ASSERT_EQ(-1, ret);
+	ASSERT_EQ(EBUSY, errno);
+
+	ret = rmdir(self->mount_path);
+	ASSERT_EQ(-1, ret);
+	ASSERT_EQ(EBUSY, errno);
+
+	close(mfd);
+}
+
+TEST_F(tmpfs_hugepage_mount_path, restrictedmem_provide_mount_subdir)
+{
+	int ret = -1;
+	int mfd = -1;
+	struct stat stat;
+	char subdir_path[PATH_MAX] = {0};
+
+	ret = mount("name", self->mount_path, "tmpfs", 0, "huge=always");
+	ASSERT_EQ(0, ret);
+
+	snprintf(subdir_path, PATH_MAX, "%s/%s", self->mount_path, "subdir");
+	ret = mkdir(subdir_path, 0777);
+	ASSERT_EQ(0, ret);
+
+	/*
+	 * Any subdirectory of a tmpfs mount can be provided to memfd_restricted
+	 * as a reference to a mount
+	 */
+	mfd = memfd_restricted(RMFD_TMPFILE, subdir_path);
+	ASSERT_NE(-1, mfd);
+
+	ret = fstat(mfd, &stat);
+	ASSERT_EQ(0, ret);
+	ASSERT_EQ(stat.st_blksize, get_hpage_pmd_size());
+
+	/*
+	 * shmem file is created at the mount, so the subdirectory can be
+	 * removed without issues.
+	 */
+	ret = rmdir(subdir_path);
+	ASSERT_EQ(0, ret);
+
+	close(mfd);
+}
+
+TEST_HARNESS_MAIN
-- 
2.39.1.637.g21b0678d19-goog