[PATCH] kprobes: Allow multiple kprobes at the same address

Allow registration of multiple kprobes at an address in an architecture
agnostic way.  Corresponding handlers will be invoked in a sequence.  But,
a kprobe and a jprobe can't (yet) co-exist at the same address.

Signed-off-by: Ananth N Mavinakayanahalli <amavin@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 134 insertions, 13 deletions

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index f20c163de4f..99ddba5a4e0 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -43,6 +43,9 @@ typedef int (*kprobe_fault_handler_t) (struct kprobe *, struct pt_regs *,
 struct kprobe {
         struct hlist_node hlist;
 
+        /* list of kprobes for multi-handler support */
+        struct list_head list;
+
         /* location of the probe point */
         kprobe_opcode_t *addr;
 
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index d8903e60c99..037142b72a4 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -44,6 +44,7 @@ static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
 
 unsigned int kprobe_cpu = NR_CPUS;
 static DEFINE_SPINLOCK(kprobe_lock);
+static struct kprobe *curr_kprobe;
 
 /* Locks kprobe: irqs must be disabled */
 void lock_kprobes(void)
@@ -73,22 +74,139 @@ struct kprobe *get_kprobe(void *addr)
         return NULL;
 }
 
+/*
+ * Aggregate handlers for multiple kprobes support - these handlers
+ * take care of invoking the individual kprobe handlers on p->list
+ */
+int aggr_pre_handler(struct kprobe *p, struct pt_regs *regs)
+{
+        struct kprobe *kp;
+
+        list_for_each_entry(kp, &p->list, list) {
+                if (kp->pre_handler) {
+                        curr_kprobe = kp;
+                        kp->pre_handler(kp, regs);
+                        curr_kprobe = NULL;
+                }
+        }
+        return 0;
+}
+
+void aggr_post_handler(struct kprobe *p, struct pt_regs *regs,
+                unsigned long flags)
+{
+        struct kprobe *kp;
+
+        list_for_each_entry(kp, &p->list, list) {
+                if (kp->post_handler) {
+                        curr_kprobe = kp;
+                        kp->post_handler(kp, regs, flags);
+                        curr_kprobe = NULL;
+                }
+        }
+        return;
+}
+
+int aggr_fault_handler(struct kprobe *p, struct pt_regs *regs, int trapnr)
+{
+        /*
+         * if we faulted "during" the execution of a user specified
+         * probe handler, invoke just that probe's fault handler
+         */
+        if (curr_kprobe && curr_kprobe->fault_handler) {
+                if (curr_kprobe->fault_handler(curr_kprobe, regs, trapnr))
+                        return 1;
+        }
+        return 0;
+}
+
+/*
+ * Fill in the required fields of the "manager kprobe". Replace the
+ * earlier kprobe in the hlist with the manager kprobe
+ */
+static inline void add_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
+{
+        ap->addr = p->addr;
+        ap->opcode = p->opcode;
+        memcpy(&ap->ainsn, &p->ainsn, sizeof(struct arch_specific_insn));
+
+        ap->pre_handler = aggr_pre_handler;
+        ap->post_handler = aggr_post_handler;
+        ap->fault_handler = aggr_fault_handler;
+
+        INIT_LIST_HEAD(&ap->list);
+        list_add(&p->list, &ap->list);
+
+        INIT_HLIST_NODE(&ap->hlist);
+        hlist_del(&p->hlist);
+        hlist_add_head(&ap->hlist,
+                &kprobe_table[hash_ptr(ap->addr, KPROBE_HASH_BITS)]);
+}
+
+/*
+ * This is the second or subsequent kprobe at the address - handle
+ * the intricacies
+ * TODO: Move kcalloc outside the spinlock
+ */
+static int register_aggr_kprobe(struct kprobe *old_p, struct kprobe *p)
+{
+        int ret = 0;
+        struct kprobe *ap;
+
+        if (old_p->break_handler || p->break_handler) {
+                ret = -EEXIST;  /* kprobe and jprobe can't (yet) coexist */
+        } else if (old_p->pre_handler == aggr_pre_handler) {
+                list_add(&p->list, &old_p->list);
+        } else {
+                ap = kcalloc(1, sizeof(struct kprobe), GFP_ATOMIC);
+                if (!ap)
+                        return -ENOMEM;
+                add_aggr_kprobe(ap, old_p);
+                list_add(&p->list, &ap->list);
+        }
+        return ret;
+}
+
+/* kprobe removal house-keeping routines */
+static inline void cleanup_kprobe(struct kprobe *p, unsigned long flags)
+{
+        *p->addr = p->opcode;
+        hlist_del(&p->hlist);
+        flush_icache_range((unsigned long) p->addr,
+                   (unsigned long) p->addr + sizeof(kprobe_opcode_t));
+        spin_unlock_irqrestore(&kprobe_lock, flags);
+        arch_remove_kprobe(p);
+}
+
+static inline void cleanup_aggr_kprobe(struct kprobe *old_p,
+                struct kprobe *p, unsigned long flags)
+{
+        list_del(&p->list);
+        if (list_empty(&old_p->list)) {
+                cleanup_kprobe(old_p, flags);
+                kfree(old_p);
+        } else
+                spin_unlock_irqrestore(&kprobe_lock, flags);
+}
+
 int register_kprobe(struct kprobe *p)
 {
         int ret = 0;
         unsigned long flags = 0;
+        struct kprobe *old_p;
 
         if ((ret = arch_prepare_kprobe(p)) != 0) {
                 goto rm_kprobe;
         }
         spin_lock_irqsave(&kprobe_lock, flags);
-        INIT_HLIST_NODE(&p->hlist);
-        if (get_kprobe(p->addr)) {
-                ret = -EEXIST;
+        old_p = get_kprobe(p->addr);
+        if (old_p) {
+                ret = register_aggr_kprobe(old_p, p);
                 goto out;
         }
-        arch_copy_kprobe(p);
 
+        arch_copy_kprobe(p);
+        INIT_HLIST_NODE(&p->hlist);
         hlist_add_head(&p->hlist,
                        &kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);
 
@@ -107,17 +225,17 @@ rm_kprobe:
 void unregister_kprobe(struct kprobe *p)
 {
         unsigned long flags;
+        struct kprobe *old_p;
+
         spin_lock_irqsave(&kprobe_lock, flags);
-        if (!get_kprobe(p->addr)) {
+        old_p = get_kprobe(p->addr);
+        if (old_p) {
+                if (old_p->pre_handler == aggr_pre_handler)
+                        cleanup_aggr_kprobe(old_p, p, flags);
+                else
+                        cleanup_kprobe(p, flags);
+        } else
                 spin_unlock_irqrestore(&kprobe_lock, flags);
-                return;
-        }
-        *p->addr = p->opcode;
-        hlist_del(&p->hlist);
-        flush_icache_range((unsigned long) p->addr,
-                           (unsigned long) p->addr + sizeof(kprobe_opcode_t));
-        spin_unlock_irqrestore(&kprobe_lock, flags);
-        arch_remove_kprobe(p);
 }
 
 static struct notifier_block kprobe_exceptions_nb = {