[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>

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index f20c163..99ddba5 100644 (file)
--- 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 d8903e6..037142b 100644 (file)
--- 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 = {