x86/intel_rdt: Prevent pseudo-locking from using stale pointers

When the last CPU in an rdt_domain goes offline, its rdt_domain struct gets
freed. Current pseudo-locking code is unaware of this scenario and tries to
dereference the freed structure in a few places.

Add checks to prevent pseudo-locking code from doing this.

While further work is needed to seamlessly restore resource groups (not
just pseudo-locking) to their configuration when the domain is brought back
online, the immediate issue of invalid pointers is addressed here.

Fixes: f4e80d67a5274 ("x86/intel_rdt: Resctrl files reflect pseudo-locked information")
Fixes: 443810fe61605 ("x86/intel_rdt: Create debugfs files for pseudo-locking testing")
Fixes: 746e08590b864 ("x86/intel_rdt: Create character device exposing pseudo-locked region")
Fixes: 33dc3e410a0d9 ("x86/intel_rdt: Make CPU information accessible for pseudo-locked regions")
Signed-off-by: Jithu Joseph <jithu.joseph@intel.com>
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: gavin.hindman@intel.com
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/231f742dbb7b00a31cc104416860e27dba6b072d.1539384145.git.reinette.chatre@intel.com

4 files changed, 55 insertions, 12 deletions

diff --git a/arch/x86/kernel/cpu/intel_rdt.c b/arch/x86/kernel/cpu/intel_rdt.c
index 1214f3f7ec6d..44272b7107ad 100644
--- a/arch/x86/kernel/cpu/intel_rdt.c
+++ b/arch/x86/kernel/cpu/intel_rdt.c
@@ -608,6 +608,13 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
                         cancel_delayed_work(&d->cqm_limbo);
                 }
 
+                /*
+                 * rdt_domain "d" is going to be freed below, so clear
+                 * its pointer from pseudo_lock_region struct.
+                 */
+                if (d->plr)
+                        d->plr->d = NULL;
+
                 kfree(d->ctrl_val);
                 kfree(d->mbps_val);
                 bitmap_free(d->rmid_busy_llc);
diff --git a/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c b/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c
index 0f53049719cd..27937458c231 100644
--- a/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c
+++ b/arch/x86/kernel/cpu/intel_rdt_ctrlmondata.c
@@ -404,8 +404,16 @@ int rdtgroup_schemata_show(struct kernfs_open_file *of,
                         for_each_alloc_enabled_rdt_resource(r)
                                 seq_printf(s, "%s:uninitialized\n", r->name);
                 } else if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED) {
-                        seq_printf(s, "%s:%d=%x\n", rdtgrp->plr->r->name,
-                                   rdtgrp->plr->d->id, rdtgrp->plr->cbm);
+                        if (!rdtgrp->plr->d) {
+                                rdt_last_cmd_clear();
+                                rdt_last_cmd_puts("Cache domain offline\n");
+                                ret = -ENODEV;
+                        } else {
+                                seq_printf(s, "%s:%d=%x\n",
+                                           rdtgrp->plr->r->name,
+                                           rdtgrp->plr->d->id,
+                                           rdtgrp->plr->cbm);
+                        }
                 } else {
                         closid = rdtgrp->closid;
                         for_each_alloc_enabled_rdt_resource(r) {
diff --git a/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c b/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
index 41aeb431e834..966ac0c20d67 100644
--- a/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
+++ b/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
@@ -1174,6 +1174,11 @@ static int pseudo_lock_measure_cycles(struct rdtgroup *rdtgrp, int sel)
                 goto out;
         }
 
+        if (!plr->d) {
+                ret = -ENODEV;
+                goto out;
+        }
+
         plr->thread_done = 0;
         cpu = cpumask_first(&plr->d->cpu_mask);
         if (!cpu_online(cpu)) {
@@ -1494,6 +1499,11 @@ static int pseudo_lock_dev_mmap(struct file *filp, struct vm_area_struct *vma)
 
         plr = rdtgrp->plr;
 
+        if (!plr->d) {
+                mutex_unlock(&rdtgroup_mutex);
+                return -ENODEV;
+        }
+
         /*
          * Task is required to run with affinity to the cpus associated
          * with the pseudo-locked region. If this is not the case the task
diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index dbc7fc98b60a..f27b8115ffa2 100644
--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
+++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
@@ -268,17 +268,27 @@ static int rdtgroup_cpus_show(struct kernfs_open_file *of,
                               struct seq_file *s, void *v)
 {
         struct rdtgroup *rdtgrp;
+        struct cpumask *mask;
         int ret = 0;
 
         rdtgrp = rdtgroup_kn_lock_live(of->kn);
 
         if (rdtgrp) {
-                if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED)
-                        seq_printf(s, is_cpu_list(of) ? "%*pbl\n" : "%*pb\n",
-                                   cpumask_pr_args(&rdtgrp->plr->d->cpu_mask));
-                else
+                if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED) {
+                        if (!rdtgrp->plr->d) {
+                                rdt_last_cmd_clear();
+                                rdt_last_cmd_puts("Cache domain offline\n");
+                                ret = -ENODEV;
+                        } else {
+                                mask = &rdtgrp->plr->d->cpu_mask;
+                                seq_printf(s, is_cpu_list(of) ?
+                                           "%*pbl\n" : "%*pb\n",
+                                           cpumask_pr_args(mask));
+                        }
+                } else {
                         seq_printf(s, is_cpu_list(of) ? "%*pbl\n" : "%*pb\n",
                                    cpumask_pr_args(&rdtgrp->cpu_mask));
+                }
         } else {
                 ret = -ENOENT;
         }
@@ -1282,6 +1292,7 @@ static int rdtgroup_size_show(struct kernfs_open_file *of,
         struct rdt_resource *r;
         struct rdt_domain *d;
         unsigned int size;
+        int ret = 0;
         bool sep;
         u32 ctrl;
 
@@ -1292,11 +1303,18 @@ static int rdtgroup_size_show(struct kernfs_open_file *of,
         }
 
         if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED) {
-                seq_printf(s, "%*s:", max_name_width, rdtgrp->plr->r->name);
-                size = rdtgroup_cbm_to_size(rdtgrp->plr->r,
-                                            rdtgrp->plr->d,
-                                            rdtgrp->plr->cbm);
-                seq_printf(s, "%d=%u\n", rdtgrp->plr->d->id, size);
+                if (!rdtgrp->plr->d) {
+                        rdt_last_cmd_clear();
+                        rdt_last_cmd_puts("Cache domain offline\n");
+                        ret = -ENODEV;
+                } else {
+                        seq_printf(s, "%*s:", max_name_width,
+                                   rdtgrp->plr->r->name);
+                        size = rdtgroup_cbm_to_size(rdtgrp->plr->r,
+                                                    rdtgrp->plr->d,
+                                                    rdtgrp->plr->cbm);
+                        seq_printf(s, "%d=%u\n", rdtgrp->plr->d->id, size);
+                }
                 goto out;
         }
 
@@ -1326,7 +1344,7 @@ static int rdtgroup_size_show(struct kernfs_open_file *of,
 out:
         rdtgroup_kn_unlock(of->kn);
 
-        return 0;
+        return ret;
 }
 
 /* rdtgroup information files for one cache resource. */