[PATCH 2/4] fs: define a firmware security filesystem named fwsecurityfs

Nayna Jain
2022-11-06T21:08:57Z

securityfs is meant for Linux security subsystems to expose policies/logs
or any other information. However, there are various firmware security
features which expose their variables for user management via the kernel.
There is currently no single place to expose these variables. Different
platforms use sysfs/platform specific filesystem(efivarfs)/securityfs
interface as they find it appropriate. Thus, there is a gap in kernel
interfaces to expose variables for security features.

Define a firmware security filesystem (fwsecurityfs) to be used by
security features enabled by the firmware. These variables are platform
specific. This filesystem provides platforms a way to implement their
own underlying semantics by defining own inode and file operations.

Similar to securityfs, the firmware security filesystem is recommended
to be exposed on a well known mount point /sys/firmware/security.
Platforms can define their own directory or file structure under this path.

Example:

# mount -t fwsecurityfs fwsecurityfs /sys/firmware/security

# cd /sys/firmware/security/

Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
---
fs/Kconfig | 1 +
fs/Makefile | 1 +
fs/fwsecurityfs/Kconfig | 14 ++
fs/fwsecurityfs/Makefile | 10 ++
fs/fwsecurityfs/super.c | 263 +++++++++++++++++++++++++++++++++++
include/linux/fwsecurityfs.h | 29 ++++
include/uapi/linux/magic.h | 1 +
7 files changed, 319 insertions(+)
create mode 100644 fs/fwsecurityfs/Kconfig
create mode 100644 fs/fwsecurityfs/Makefile
create mode 100644 fs/fwsecurityfs/super.c
create mode 100644 include/linux/fwsecurityfs.h

diff --git a/fs/Kconfig b/fs/Kconfig
index 2685a4d0d353..2a24f1c779dd 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -275,6 +275,7 @@ config ARCH_HAS_GIGANTIC_PAGE

source "fs/configfs/Kconfig"
source "fs/efivarfs/Kconfig"
+source "fs/fwsecurityfs/Kconfig"

endmenu

diff --git a/fs/Makefile b/fs/Makefile
index 4dea17840761..b945019a9bbe 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -134,6 +134,7 @@ obj-$(CONFIG_F2FS_FS) += f2fs/
obj-$(CONFIG_CEPH_FS) += ceph/
obj-$(CONFIG_PSTORE) += pstore/
obj-$(CONFIG_EFIVAR_FS) += efivarfs/
+obj-$(CONFIG_FWSECURITYFS) += fwsecurityfs/
obj-$(CONFIG_EROFS_FS) += erofs/
obj-$(CONFIG_VBOXSF_FS) += vboxsf/
obj-$(CONFIG_ZONEFS_FS) += zonefs/
diff --git a/fs/fwsecurityfs/Kconfig b/fs/fwsecurityfs/Kconfig
new file mode 100644
index 000000000000..1dc2ee831eda
--- /dev/null
+++ b/fs/fwsecurityfs/Kconfig
@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Copyright (C) 2022 IBM Corporation
+# Author: Nayna Jain <nayna@linux.ibm.com>
+#
+
+config FWSECURITYFS
+ bool "Enable the fwsecurityfs filesystem"
+ help
+ This will build fwsecurityfs filesystem which should be mounted
+ on /sys/firmware/security. This filesystem can be used by
+ platform to expose firmware-managed variables.
+
+ If you are unsure how to answer this question, answer N.
diff --git a/fs/fwsecurityfs/Makefile b/fs/fwsecurityfs/Makefile
new file mode 100644
index 000000000000..5c7b76228ebb
--- /dev/null
+++ b/fs/fwsecurityfs/Makefile
@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Copyright (C) 2022 IBM Corporation
+# Author: Nayna Jain <nayna@linux.ibm.com>
+#
+# Makefile for the firmware security filesystem
+
+obj-$(CONFIG_FWSECURITYFS) += fwsecurityfs.o
+
+fwsecurityfs-objs := super.o
diff --git a/fs/fwsecurityfs/super.c b/fs/fwsecurityfs/super.c
new file mode 100644
index 000000000000..99ca4da4ab63
--- /dev/null
+++ b/fs/fwsecurityfs/super.c
@@ -0,0 +1,263 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2022 IBM Corporation
+ * Author: Nayna Jain <nayna@linux.ibm.com>
+ */
+
+#include <linux/fs.h>
+#include <linux/fs_context.h>
+#include <linux/pagemap.h>
+#include <linux/init.h>
+#include <linux/namei.h>
+#include <linux/magic.h>
+#include <linux/fwsecurityfs.h>
+
+static struct super_block *fwsecsb;
+static struct vfsmount *mount;
+static int mount_count;
+static bool fwsecurityfs_initialized;
+
+static void fwsecurityfs_free_inode(struct inode *inode)
+{
+ free_inode_nonrcu(inode);
+}
+
+static const struct super_operations fwsecurityfs_super_operations = {
+ .statfs = simple_statfs,
+ .free_inode = fwsecurityfs_free_inode,
+};
+
+static int fwsecurityfs_fill_super(struct super_block *sb,
+ struct fs_context *fc)
+{
+ static const struct tree_descr files[] = {{""}};
+ int rc;
+
+ rc = simple_fill_super(sb, FWSECURITYFS_MAGIC, files);
+ if (rc)
+ return rc;
+
+ sb->s_op = &fwsecurityfs_super_operations;
+
+ fwsecsb = sb;
+
+ rc = arch_fwsecurityfs_init();
+
+ if (!rc)
+ fwsecurityfs_initialized = true;
+
+ return rc;
+}
+
+static int fwsecurityfs_get_tree(struct fs_context *fc)
+{
+ return get_tree_single(fc, fwsecurityfs_fill_super);
+}
+
+static const struct fs_context_operations fwsecurityfs_context_ops = {
+ .get_tree = fwsecurityfs_get_tree,
+};
+
+static int fwsecurityfs_init_fs_context(struct fs_context *fc)
+{
+ fc->ops = &fwsecurityfs_context_ops;
+
+ return 0;
+}
+
+static void fwsecurityfs_kill_sb(struct super_block *sb)
+{
+ kill_litter_super(sb);
+
+ fwsecurityfs_initialized = false;
+}
+
+static struct file_system_type fs_type = {
+ .owner = THIS_MODULE,
+ .name = "fwsecurityfs",
+ .init_fs_context = fwsecurityfs_init_fs_context,
+ .kill_sb = fwsecurityfs_kill_sb,
+};
+
+static struct dentry *fwsecurityfs_create_dentry(const char *name, umode_t mode,
+ u16 filesize,
+ struct dentry *parent,
+ struct dentry *dentry, void *data,
+ const struct file_operations *fops,
+ const struct inode_operations *iops)
+{
+ struct inode *inode;
+ int rc;
+ struct inode *dir;
+ struct dentry *ldentry = dentry;
+
+ /* Calling simple_pin_fs() while initial mount in progress results in recursive
+ * call to mount.
+ */
+ if (fwsecurityfs_initialized) {
+ rc = simple_pin_fs(&fs_type, &mount, &mount_count);
+ if (rc)
+ return ERR_PTR(rc);
+ }
+
+ dir = d_inode(parent);
+
+ /* For userspace created files, lock is already taken. */
+ if (!dentry)
+ inode_lock(dir);
+
+ if (!dentry) {
+ ldentry = lookup_one_len(name, parent, strlen(name));
+ if (IS_ERR(ldentry))
+ goto out;
+
+ if (d_really_is_positive(ldentry)) {
+ rc = -EEXIST;
+ goto out1;
+ }
+ }
+
+ inode = new_inode(dir->i_sb);
+ if (!inode) {
+ rc = -ENOMEM;
+ goto out1;
+ }
+
+ inode->i_ino = get_next_ino();
+ inode->i_mode = mode;
+ inode->i_atime = current_time(inode);
+ inode->i_mtime = current_time(inode);
+ inode->i_ctime = current_time(inode);
+ inode->i_private = data;
+
+ if (S_ISDIR(mode)) {
+ inode->i_op = iops ? iops : &simple_dir_inode_operations;
+ inode->i_fop = &simple_dir_operations;
+ inc_nlink(inode);
+ inc_nlink(dir);
+ } else {
+ inode->i_fop = fops ? fops : &simple_dir_operations;
+ }
+
+ if (S_ISREG(mode)) {
+ inode_lock(inode);
+ i_size_write(inode, filesize);
+ inode_unlock(inode);
+ }
+ d_instantiate(ldentry, inode);
+
+ /* dget() here is required for userspace created files. */
+ if (dentry)
+ dget(ldentry);
+
+ if (!dentry)
+ inode_unlock(dir);
+
+ return ldentry;
+
+out1:
+ ldentry = ERR_PTR(rc);
+
+out:
+ if (fwsecurityfs_initialized)
+ simple_release_fs(&mount, &mount_count);
+
+ if (!dentry)
+ inode_unlock(dir);
+
+ return ldentry;
+}
+
+struct dentry *fwsecurityfs_create_file(const char *name, umode_t mode,
+ u16 filesize, struct dentry *parent,
+ struct dentry *dentry, void *data,
+ const struct file_operations *fops)
+{
+ if (!parent)
+ return ERR_PTR(-EINVAL);
+
+ return fwsecurityfs_create_dentry(name, mode, filesize, parent,
+ dentry, data, fops, NULL);
+}
+EXPORT_SYMBOL_GPL(fwsecurityfs_create_file);
+
+struct dentry *fwsecurityfs_create_dir(const char *name, umode_t mode,
+ struct dentry *parent,
+ const struct inode_operations *iops)
+{
+ if (!parent) {
+ if (!fwsecsb)
+ return ERR_PTR(-EIO);
+ parent = fwsecsb->s_root;
+ }
+
+ return fwsecurityfs_create_dentry(name, mode, 0, parent, NULL, NULL,
+ NULL, iops);
+}
+EXPORT_SYMBOL_GPL(fwsecurityfs_create_dir);
+
+static int fwsecurityfs_remove_dentry(struct dentry *dentry)
+{
+ struct inode *dir;
+
+ if (!dentry || IS_ERR(dentry))
+ return -EINVAL;
+
+ dir = d_inode(dentry->d_parent);
+ inode_lock(dir);
+ if (simple_positive(dentry)) {
+ dget(dentry);
+ if (d_is_dir(dentry))
+ simple_rmdir(dir, dentry);
+ else
+ simple_unlink(dir, dentry);
+ d_delete(dentry);
+ dput(dentry);
+ }
+ inode_unlock(dir);
+
+ /* Once fwsecurityfs_initialized is set to true, calling this for
+ * removing files created during initial mount might result in
+ * imbalance of simple_pin_fs() and simple_release_fs() calls.
+ */
+ if (fwsecurityfs_initialized)
+ simple_release_fs(&mount, &mount_count);
+
+ return 0;
+}
+
+int fwsecurityfs_remove_dir(struct dentry *dentry)
+{
+ if (!d_is_dir(dentry))
+ return -EPERM;
+
+ return fwsecurityfs_remove_dentry(dentry);
+}
+EXPORT_SYMBOL_GPL(fwsecurityfs_remove_dir);
+
+int fwsecurityfs_remove_file(struct dentry *dentry)
+{
+ return fwsecurityfs_remove_dentry(dentry);
+};
+EXPORT_SYMBOL_GPL(fwsecurityfs_remove_file);
+
+static int __init fwsecurityfs_init(void)
+{
+ int rc;
+
+ rc = sysfs_create_mount_point(firmware_kobj, "security");
+ if (rc)
+ return rc;
+
+ rc = register_filesystem(&fs_type);
+ if (rc) {
+ sysfs_remove_mount_point(firmware_kobj, "security");
+ return rc;
+ }
+
+ return 0;
+}
+core_initcall(fwsecurityfs_init);
+MODULE_DESCRIPTION("Firmware Security Filesystem");
+MODULE_AUTHOR("Nayna Jain");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/fwsecurityfs.h b/include/linux/fwsecurityfs.h
new file mode 100644
index 000000000000..ed8f328f3133
--- /dev/null
+++ b/include/linux/fwsecurityfs.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2022 IBM Corporation
+ * Author: Nayna Jain <nayna@linux.ibm.com>
+ */
+
+#ifndef _FWSECURITYFS_H_
+#define _FWSECURITYFS_H_
+
+#include <linux/ctype.h>
+#include <linux/fs.h>
+
+struct dentry *fwsecurityfs_create_file(const char *name, umode_t mode,
+ u16 filesize, struct dentry *parent,
+ struct dentry *dentry, void *data,
+ const struct file_operations *fops);
+
+int fwsecurityfs_remove_file(struct dentry *dentry);
+struct dentry *fwsecurityfs_create_dir(const char *name, umode_t mode,
+ struct dentry *parent,
+ const struct inode_operations *iops);
+int fwsecurityfs_remove_dir(struct dentry *dentry);
+
+static int arch_fwsecurityfs_init(void)
+{
+ return 0;
+}
+
+#endif /* _FWSECURITYFS_H_ */
diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
index 6325d1d0e90f..553a5fdfabce 100644
--- a/include/uapi/linux/magic.h
+++ b/include/uapi/linux/magic.h
@@ -53,6 +53,7 @@
#define QNX4_SUPER_MAGIC 0x002f /* qnx4 fs detection */
#define QNX6_SUPER_MAGIC 0x68191122 /* qnx6 fs detection */
#define AFS_FS_MAGIC 0x6B414653
+#define FWSECURITYFS_MAGIC 0x5345434e /* "SECM" */

#define REISERFS_SUPER_MAGIC 0x52654973 /* used by gcc */
--
2.31.1