[PATCH 2/4] parisc: Implement kretprobes

[Sven Schnelle <svens@stackframe.org>]

Implement kretprobes on parisc, parts stolen from powerpc.

Signed-off-by: Sven Schnelle <svens@stackframe.org>
---
 arch/parisc/Kconfig          |   1 +
 arch/parisc/kernel/kprobes.c | 110 ++++++++++++++++++++++++++++++++++-
 2 files changed, 110 insertions(+), 1 deletion(-)

diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
index 7712688608f4..c8038165b81f 100644
--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -56,6 +56,7 @@ config PARISC
 	select NEED_SG_DMA_LENGTH
 	select HAVE_ARCH_KGDB
 	select HAVE_KPROBES
+	select HAVE_KRETPROBES
 
 	help
 	  The PA-RISC microprocessor is designed by Hewlett-Packard and used
diff --git a/arch/parisc/kernel/kprobes.c b/arch/parisc/kernel/kprobes.c
index 8b1977cd3eb9..d58960b33bda 100644
--- a/arch/parisc/kernel/kprobes.c
+++ b/arch/parisc/kernel/kprobes.c
@@ -172,6 +172,112 @@ int __kprobes parisc_kprobe_ss_handler(struct pt_regs *regs)
 	return 1;
 }
 
+static inline void kretprobe_trampoline(void)
+{
+	asm volatile("nop");
+	asm volatile("nop");
+}
+
+static int __kprobes trampoline_probe_handler(struct kprobe *p,
+					      struct pt_regs *regs);
+
+static struct kprobe trampoline_p = {
+	.pre_handler = trampoline_probe_handler
+};
+
+static int __kprobes trampoline_probe_handler(struct kprobe *p,
+					      struct pt_regs *regs)
+{
+	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)trampoline_p.addr;
+	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
+	 * a return probe installed on them, and/or more than one 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, 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);
+	}
+	instruction_pointer_set(regs, orig_ret_address);
+	return 1;
+}
+
+void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
+				      struct pt_regs *regs)
+{
+	ri->ret_addr = (kprobe_opcode_t *)regs->gr[2];
+
+	/* Replace the return addr with trampoline addr. */
+	regs->gr[2] = (unsigned long)trampoline_p.addr;
+}
+
+int __kprobes arch_trampoline_kprobe(struct kprobe *p)
+{
+	return p->addr == trampoline_p.addr;
+}
 bool arch_kprobe_on_func_entry(unsigned long offset)
 {
 	return !offset;
@@ -179,5 +285,7 @@ bool arch_kprobe_on_func_entry(unsigned long offset)
 
 int __init arch_init_kprobes(void)
 {
-	return 0;
+	trampoline_p.addr = (kprobe_opcode_t *)
+		dereference_function_descriptor(kretprobe_trampoline);
+	return register_kprobe(&trampoline_p);
 }
-- 
2.20.1