kprobes: Propagate error from disarm_kprobe_ftrace()

Improve error handling when disarming ftrace-based kprobes. Like with
arm_kprobe_ftrace(), propagate any errors from disarm_kprobe_ftrace() so
that we do not disable/unregister kprobes that are still armed. In other
words, unregister_kprobe() and disable_kprobe() should not report success
if the kprobe could not be disarmed.

disarm_all_kprobes() keeps its current behavior and attempts to
disarm all kprobes. It returns the last encountered error and gives a
warning if not all probes could be disarmed.

This patch is based on Petr Mladek's original patchset (patches 2 and 3)
back in 2015, which improved kprobes error handling, found here:

   https://lkml.org/lkml/2015/2/26/452

However, further work on this had been paused since then and the patches
were not upstreamed.

Based-on-patches-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Jessica Yu <jeyu@kernel.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: David S . Miller <davem@davemloft.net>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Joe Lawrence <joe.lawrence@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/20180109235124.30886-3-jeyu@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 2d98814..102160f 100644 (file)
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1011,23 +1011,27 @@ err_ftrace:
 }
 
 /* Caller must lock kprobe_mutex */
-static void disarm_kprobe_ftrace(struct kprobe *p)
+static int disarm_kprobe_ftrace(struct kprobe *p)
 {
-       int ret;
+       int ret = 0;
 
-       kprobe_ftrace_enabled--;
-       if (kprobe_ftrace_enabled == 0) {
+       if (kprobe_ftrace_enabled == 1) {
                ret = unregister_ftrace_function(&kprobe_ftrace_ops);
-               WARN(ret < 0, "Failed to init kprobe-ftrace (%d)\n", ret);
+               if (WARN(ret < 0, "Failed to unregister kprobe-ftrace (%d)\n", ret))
+                       return ret;
        }
+
+       kprobe_ftrace_enabled--;
+
        ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
                           (unsigned long)p->addr, 1, 0);
        WARN(ret < 0, "Failed to disarm kprobe-ftrace at %p (%d)\n", p->addr, ret);
+       return ret;
 }
 #else  /* !CONFIG_KPROBES_ON_FTRACE */
 #define prepare_kprobe(p)      arch_prepare_kprobe(p)
 #define arm_kprobe_ftrace(p)   (-ENODEV)
-#define disarm_kprobe_ftrace(p)        do {} while (0)
+#define disarm_kprobe_ftrace(p)        (-ENODEV)
 #endif
 
 /* Arm a kprobe with text_mutex */
@@ -1046,18 +1050,18 @@ static int arm_kprobe(struct kprobe *kp)
 }
 
 /* Disarm a kprobe with text_mutex */
-static void disarm_kprobe(struct kprobe *kp, bool reopt)
+static int disarm_kprobe(struct kprobe *kp, bool reopt)
 {
-       if (unlikely(kprobe_ftrace(kp))) {
-               disarm_kprobe_ftrace(kp);
-               return;
-       }
+       if (unlikely(kprobe_ftrace(kp)))
+               return disarm_kprobe_ftrace(kp);
 
        cpus_read_lock();
        mutex_lock(&text_mutex);
        __disarm_kprobe(kp, reopt);
        mutex_unlock(&text_mutex);
        cpus_read_unlock();
+
+       return 0;
 }
 
 /*
@@ -1639,11 +1643,12 @@ static int aggr_kprobe_disabled(struct kprobe *ap)
 static struct kprobe *__disable_kprobe(struct kprobe *p)
 {
        struct kprobe *orig_p;
+       int ret;
 
        /* Get an original kprobe for return */
        orig_p = __get_valid_kprobe(p);
        if (unlikely(orig_p == NULL))
-               return NULL;
+               return ERR_PTR(-EINVAL);
 
        if (!kprobe_disabled(p)) {
                /* Disable probe if it is a child probe */
@@ -1657,8 +1662,13 @@ static struct kprobe *__disable_kprobe(struct kprobe *p)
                         * should have already been disarmed, so
                         * skip unneed disarming process.
                         */
-                       if (!kprobes_all_disarmed)
-                               disarm_kprobe(orig_p, true);
+                       if (!kprobes_all_disarmed) {
+                               ret = disarm_kprobe(orig_p, true);
+                               if (ret) {
+                                       p->flags &= ~KPROBE_FLAG_DISABLED;
+                                       return ERR_PTR(ret);
+                               }
+                       }
                        orig_p->flags |= KPROBE_FLAG_DISABLED;
                }
        }
@@ -1675,8 +1685,8 @@ static int __unregister_kprobe_top(struct kprobe *p)
 
        /* Disable kprobe. This will disarm it if needed. */
        ap = __disable_kprobe(p);
-       if (ap == NULL)
-               return -EINVAL;
+       if (IS_ERR(ap))
+               return PTR_ERR(ap);
 
        if (ap == p)
                /*
@@ -2109,12 +2119,14 @@ static void kill_kprobe(struct kprobe *p)
 int disable_kprobe(struct kprobe *kp)
 {
        int ret = 0;
+       struct kprobe *p;
 
        mutex_lock(&kprobe_mutex);
 
        /* Disable this kprobe */
-       if (__disable_kprobe(kp) == NULL)
-               ret = -EINVAL;
+       p = __disable_kprobe(kp);
+       if (IS_ERR(p))
+               ret = PTR_ERR(p);
 
        mutex_unlock(&kprobe_mutex);
        return ret;
@@ -2486,34 +2498,50 @@ already_enabled:
        return ret;
 }
 
-static void disarm_all_kprobes(void)
+static int disarm_all_kprobes(void)
 {
        struct hlist_head *head;
        struct kprobe *p;
-       unsigned int i;
+       unsigned int i, total = 0, errors = 0;
+       int err, ret = 0;
 
        mutex_lock(&kprobe_mutex);
 
        /* If kprobes are already disarmed, just return */
        if (kprobes_all_disarmed) {
                mutex_unlock(&kprobe_mutex);
-               return;
+               return 0;
        }
 
        kprobes_all_disarmed = true;
-       printk(KERN_INFO "Kprobes globally disabled\n");
 
        for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
                head = &kprobe_table[i];
+               /* Disarm all kprobes on a best-effort basis */
                hlist_for_each_entry_rcu(p, head, hlist) {
-                       if (!arch_trampoline_kprobe(p) && !kprobe_disabled(p))
-                               disarm_kprobe(p, false);
+                       if (!arch_trampoline_kprobe(p) && !kprobe_disabled(p)) {
+                               err = disarm_kprobe(p, false);
+                               if (err) {
+                                       errors++;
+                                       ret = err;
+                               }
+                               total++;
+                       }
                }
        }
+
+       if (errors)
+               pr_warn("Kprobes globally disabled, but failed to disarm %d out of %d probes\n",
+                       errors, total);
+       else
+               pr_info("Kprobes globally disabled\n");
+
        mutex_unlock(&kprobe_mutex);
 
        /* Wait for disarming all kprobes by optimizer */
        wait_for_kprobe_optimizer();
+
+       return ret;
 }
 
 /*
@@ -2556,7 +2584,7 @@ static ssize_t write_enabled_file_bool(struct file *file,
        case 'n':
        case 'N':
        case '0':
-               disarm_all_kprobes();
+               ret = disarm_all_kprobes();
                break;
        default:
                return -EINVAL;