[PATCH] Return probe redesign: x86_64 specific changes

The following patch contains the x86_64 specific changes for the new
return probe design.  Changes include:
 * Removing the architecture specific functions for querying a return probe
   instance off a stack address
 * Complete rework onf arch_prepare_kretprobe() and trampoline_probe_handler()
 * Removing trampoline_post_handler()
 * Adding arch_init() so that now we handle registering the return probe
   trampoline instead of kernel/kprobes.c doing it

NOTE:
Note that with this new design, the dependency on calculating a pointer to
the task off the stack pointer no longer exist (resolving the problem of
interruption stacks as pointed out in the original feedback to this port.)

Signed-off-by: Rusty Lynch <rusty.lynch@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 70 insertions, 63 deletions

diff --git a/arch/x86_64/kernel/kprobes.c b/arch/x86_64/kernel/kprobes.c
index 6a1c88376bef..acd2a778ebe6 100644
--- a/arch/x86_64/kernel/kprobes.c
+++ b/arch/x86_64/kernel/kprobes.c
@@ -272,48 +272,23 @@ static void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
                 regs->rip = (unsigned long)p->ainsn.insn;
 }
 
-struct task_struct  *arch_get_kprobe_task(void *ptr)
-{
-        return ((struct thread_info *) (((unsigned long) ptr) &
-                                        (~(THREAD_SIZE -1))))->task;
-}
-
 void arch_prepare_kretprobe(struct kretprobe *rp, struct pt_regs *regs)
 {
         unsigned long *sara = (unsigned long *)regs->rsp;
-        struct kretprobe_instance *ri;
-        static void *orig_ret_addr;
+        struct kretprobe_instance *ri;
+
+        if ((ri = get_free_rp_inst(rp)) != NULL) {
+                ri->rp = rp;
+                ri->task = current;
+                ri->ret_addr = (kprobe_opcode_t *) *sara;
 
-        /*
-         * Save the return address when the return probe hits
-         * the first time, and use it to populate the (krprobe
-         * instance)->ret_addr for subsequent return probes at
-         * the same addrress since stack address would have
-         * the kretprobe_trampoline by then.
-         */
-        if (((void*) *sara) != kretprobe_trampoline)
-                orig_ret_addr = (void*) *sara;
-
-        if ((ri = get_free_rp_inst(rp)) != NULL) {
-                ri->rp = rp;
-                ri->stack_addr = sara;
-                ri->ret_addr = orig_ret_addr;
-                add_rp_inst(ri);
                 /* Replace the return addr with trampoline addr */
                 *sara = (unsigned long) &kretprobe_trampoline;
-        } else {
-                rp->nmissed++;
-        }
-}
 
-void arch_kprobe_flush_task(struct task_struct *tk)
-{
-        struct kretprobe_instance *ri;
-        while ((ri = get_rp_inst_tsk(tk)) != NULL) {
-                *((unsigned long *)(ri->stack_addr)) =
-                                        (unsigned long) ri->ret_addr;
-                recycle_rp_inst(ri);
-        }
+                add_rp_inst(ri);
+        } else {
+                rp->nmissed++;
+        }
 }
 
 /*
@@ -426,36 +401,59 @@ no_kprobe:
  */
 int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
 {
-        struct task_struct *tsk;
-        struct kretprobe_instance *ri;
-        struct hlist_head *head;
-        struct hlist_node *node;
-        unsigned long *sara = (unsigned long *)regs->rsp - 1;
-
-        tsk = arch_get_kprobe_task(sara);
-        head = kretprobe_inst_table_head(tsk);
-
-        hlist_for_each_entry(ri, node, head, hlist) {
-                if (ri->stack_addr == sara && ri->rp) {
-                        if (ri->rp->handler)
-                                ri->rp->handler(ri, regs);
-                }
-        }
-        return 0;
-}
+        struct kretprobe_instance *ri = NULL;
+        struct hlist_head *head;
+        struct hlist_node *node, *tmp;
+        unsigned long orig_ret_address = 0;
+        unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
 
-void trampoline_post_handler(struct kprobe *p, struct pt_regs *regs,
-                                                unsigned long flags)
-{
-        struct kretprobe_instance *ri;
-        /* RA already popped */
-        unsigned long *sara = ((unsigned long *)regs->rsp) - 1;
+        head = kretprobe_inst_table_head(current);
 
-        while ((ri = get_rp_inst(sara))) {
-                regs->rip = (unsigned long)ri->ret_addr;
+        /*
+         * It is possible to have multiple instances associated with a given
+         * task either because an multiple functions in the call path
+         * have a return probe installed on them, and/or more then one return
+         * return probe was registered for a target function.
+         *
+         * We can handle this because:
+         *     - instances are always inserted at the head of the list
+         *     - when multiple return probes are registered for the same
+         *       function, the first instance's ret_addr will point to the
+         *       real return address, and all the rest will point to
+         *       kretprobe_trampoline
+         */
+        hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
+                if (ri->task != current)
+                        /* another task is sharing our hash bucket */
+                        continue;
+
+                if (ri->rp && ri->rp->handler)
+                        ri->rp->handler(ri, regs);
+
+                orig_ret_address = (unsigned long)ri->ret_addr;
                 recycle_rp_inst(ri);
+
+                if (orig_ret_address != trampoline_address)
+                        /*
+                         * This is the real return address. Any other
+                         * instances associated with this task are for
+                         * other calls deeper on the call stack
+                         */
+                        break;
         }
-        regs->eflags &= ~TF_MASK;
+
+        BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
+        regs->rip = orig_ret_address;
+
+        unlock_kprobes();
+        preempt_enable_no_resched();
+
+        /*
+         * By returning a non-zero value, we are telling
+         * kprobe_handler() that we have handled unlocking
+         * and re-enabling preemption.
+         */
+        return 1;
 }
 
 /*
@@ -548,8 +546,7 @@ int post_kprobe_handler(struct pt_regs *regs)
                 current_kprobe->post_handler(current_kprobe, regs, 0);
         }
 
-        if (current_kprobe->post_handler != trampoline_post_handler)
-                resume_execution(current_kprobe, regs);
+        resume_execution(current_kprobe, regs);
         regs->eflags |= kprobe_saved_rflags;
 
         /* Restore the original saved kprobes variables and continue. */
@@ -679,3 +676,13 @@ int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
         }
         return 0;
 }
+
+static struct kprobe trampoline_p = {
+        .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
+        .pre_handler = trampoline_probe_handler
+};
+
+int __init arch_init(void)
+{
+        return register_kprobe(&trampoline_p);
+}