s390/hypfs: Enable limited access during lockdown

jira KERNEL-216
Rebuild_History Non-Buildable kernel-5.14.0-611.9.1.el9_7
commit-author Peter Oberparleiter <oberpar@linux.ibm.com>
commit 3868f91

When kernel lockdown is active, debugfs_locked_down() blocks access to
hypfs files that register ioctl callbacks, even if the ioctl interface
is not required for a function. This unnecessarily breaks userspace
tools that only rely on read operations.

Resolve this by registering a minimal set of file operations during
lockdown, avoiding ioctl registration and preserving access for affected
tooling.

Note that this change restores hypfs functionality when lockdown is
active from early boot (e.g. via lockdown=integrity kernel parameter),
but does not apply to scenarios where lockdown is enabled dynamically
while Linux is running.

	Tested-by: Mete Durlu <meted@linux.ibm.com>
	Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Fixes: 5496197 ("debugfs: Restrict debugfs when the kernel is locked down")
	Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
	Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
(cherry picked from commit 3868f91)
	Signed-off-by: Jonathan Maple <jmaple@ciq.com>

Author: PlaidCat

arch/s390/hypfs/hypfs_dbfs.c

@@ -6,6 +6,7 @@
  * Author(s): Michael Holzheu <holzheu@linux.vnet.ibm.com>
  */
 
+#include <linux/security.h>
 #include <linux/slab.h>
 #include "hypfs.h"
 
@@ -83,7 +84,7 @@ void hypfs_dbfs_create_file(struct hypfs_dbfs_file *df)
 {
 	const struct file_operations *fops = &dbfs_ops;
 
-	if (df->unlocked_ioctl)
+	if (df->unlocked_ioctl && !security_locked_down(LOCKDOWN_DEBUGFS))
 		fops = &dbfs_ops_ioctl;
 	df->dentry = debugfs_create_file(df->name, 0400, dbfs_dir, df, fops);
 	mutex_init(&df->lock);