x86/intel_rdt: Protect against resource group changes during locking

We intend to modify file permissions to make the "tasks", "cpus", and
"cpus_list" not accessible to the user when cache pseudo-locking in
progress. Even so, it is still possible for the user to force the file
permissions (using chmod) to make them writeable. Similarly, directory
permissions will be modified to prevent future monitor group creation but
the user can override these restrictions also.

Add additional checks to the files we intend to restrict to ensure that no
modifications from user space are attempted while setting up a
pseudo-locking or after a pseudo-locked region is set up.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: fenghua.yu@intel.com
Cc: tony.luck@intel.com
Cc: vikas.shivappa@linux.intel.com
Cc: gavin.hindman@intel.com
Cc: jithu.joseph@intel.com
Cc: dave.hansen@intel.com
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/0c5cb006e81ead0b8bfff2df530c5d3017fd31d1.1529706536.git.reinette.chatre@intel.com

arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c

@@ -283,6 +283,16 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,
 	}
 	rdt_last_cmd_clear();
 
+	/*
+	 * No changes to pseudo-locked region allowed. It has to be removed
+	 * and re-created instead.
+	 */
+	if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED) {
+		ret = -EINVAL;
+		rdt_last_cmd_puts("resource group is pseudo-locked\n");
+		goto out;
+	}
+
 	for_each_alloc_enabled_rdt_resource(r) {
 		list_for_each_entry(dom, &r->domains, list)
 			dom->have_new_ctrl = false;

arch/x86/kernel/cpu/intel_rdt_rdtgroup.c

@@ -449,6 +449,13 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of,
 		goto unlock;
 	}
 
+	if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED ||
+	    rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP) {
+		ret = -EINVAL;
+		rdt_last_cmd_puts("pseudo-locking in progress\n");
+		goto unlock;
+	}
+
 	if (is_cpu_list(of))
 		ret = cpulist_parse(buf, newmask);
 	else
@@ -651,13 +658,22 @@ static ssize_t rdtgroup_tasks_write(struct kernfs_open_file *of,
 	if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
 		return -EINVAL;
 	rdtgrp = rdtgroup_kn_lock_live(of->kn);
+	if (!rdtgrp) {
+		rdtgroup_kn_unlock(of->kn);
+		return -ENOENT;
+	}
 	rdt_last_cmd_clear();
 
-	if (rdtgrp)
-		ret = rdtgroup_move_task(pid, rdtgrp, of);
-	else
-		ret = -ENOENT;
+	if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED ||
+	    rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP) {
+		ret = -EINVAL;
+		rdt_last_cmd_puts("pseudo-locking in progress\n");
+		goto unlock;
+	}
+
+	ret = rdtgroup_move_task(pid, rdtgrp, of);
 
+unlock:
 	rdtgroup_kn_unlock(of->kn);
 
 	return ret ?: nbytes;
@@ -2315,6 +2331,14 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
 		goto out_unlock;
 	}
 
+	if (rtype == RDTMON_GROUP &&
+	    (prdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP ||
+	     prdtgrp->mode == RDT_MODE_PSEUDO_LOCKED)) {
+		ret = -EINVAL;
+		rdt_last_cmd_puts("pseudo-locking in progress\n");
+		goto out_unlock;
+	}
+
 	/* allocate the rdtgroup. */
 	rdtgrp = kzalloc(sizeof(*rdtgrp), GFP_KERNEL);
 	if (!rdtgrp) {