arm64: Add kernel return probes support (kretprobes)

The pre-handler of this special 'trampoline' kprobe executes the return
probe handler functions and restores original return address in ELR_EL1.
This way the saved pt_regs still hold the original register context to be
carried back to the probed kernel function.

Signed-off-by: Sandeepa Prabhu <sandeepa.s.prabhu@gmail.com>
Signed-off-by: David A. Long <dave.long@linaro.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 1f7d644..6af0e2e 100644 (file)
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -89,6 +89,7 @@ config ARM64
        select HAVE_RCU_TABLE_FREE
        select HAVE_SYSCALL_TRACEPOINTS
        select HAVE_KPROBES
+       select HAVE_KRETPROBES if HAVE_KPROBES
        select IOMMU_DMA if IOMMU_SUPPORT
        select IRQ_DOMAIN
        select IRQ_FORCED_THREADING

diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index be1f074..9c70e88 100644 (file)
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -578,7 +578,95 @@ bool arch_within_kprobe_blacklist(unsigned long addr)
 
 void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
 {
-       return NULL;
+       struct kretprobe_instance *ri = NULL;
+       struct hlist_head *head, empty_rp;
+       struct hlist_node *tmp;
+       unsigned long flags, orig_ret_address = 0;
+       unsigned long trampoline_address =
+               (unsigned long)&kretprobe_trampoline;
+       kprobe_opcode_t *correct_ret_addr = NULL;
+
+       INIT_HLIST_HEAD(&empty_rp);
+       kretprobe_hash_lock(current, &head, &flags);
+
+       /*
+        * It is possible to have multiple instances associated with a given
+        * task either because multiple functions in the call path have
+        * return probes installed on them, and/or more than one
+        * return probe was registered for a target function.
+        *
+        * We can handle this because:
+        *     - instances are always pushed into the head of the list
+        *     - when multiple return probes are registered for the same
+        *       function, the (chronologically) first instance's ret_addr
+        *       will be the real return address, and all the rest will
+        *       point to kretprobe_trampoline.
+        */
+       hlist_for_each_entry_safe(ri, tmp, head, hlist) {
+               if (ri->task != current)
+                       /* another task is sharing our hash bucket */
+                       continue;
+
+               orig_ret_address = (unsigned long)ri->ret_addr;
+
+               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;
+       }
+
+       kretprobe_assert(ri, orig_ret_address, trampoline_address);
+
+       correct_ret_addr = ri->ret_addr;
+       hlist_for_each_entry_safe(ri, tmp, head, hlist) {
+               if (ri->task != current)
+                       /* another task is sharing our hash bucket */
+                       continue;
+
+               orig_ret_address = (unsigned long)ri->ret_addr;
+               if (ri->rp && ri->rp->handler) {
+                       __this_cpu_write(current_kprobe, &ri->rp->kp);
+                       get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
+                       ri->ret_addr = correct_ret_addr;
+                       ri->rp->handler(ri, regs);
+                       __this_cpu_write(current_kprobe, NULL);
+               }
+
+               recycle_rp_inst(ri, &empty_rp);
+
+               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;
+       }
+
+       kretprobe_hash_unlock(current, &flags);
+
+       hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
+               hlist_del(&ri->hlist);
+               kfree(ri);
+       }
+       return (void *)orig_ret_address;
+}
+
+void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
+                                     struct pt_regs *regs)
+{
+       ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
+
+       /* replace return addr (x30) with trampoline */
+       regs->regs[30] = (long)&kretprobe_trampoline;
+}
+
+int __kprobes arch_trampoline_kprobe(struct kprobe *p)
+{
+       return 0;
 }
 
 int __init arch_init_kprobes(void)