1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * Dynamic Ftrace based Kprobes Optimization
4  *
5  * Copyright (C) Hitachi Ltd., 2012
6  * Copyright 2016 Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
7  *		  IBM Corporation
8  */
9 #include <linux/kprobes.h>
10 #include <linux/ptrace.h>
11 #include <linux/hardirq.h>
12 #include <linux/preempt.h>
13 #include <linux/ftrace.h>
14 
15 /* Ftrace callback handler for kprobes */
16 void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip,
17 			   struct ftrace_ops *ops, struct ftrace_regs *fregs)
18 {
19 	struct kprobe *p;
20 	struct kprobe_ctlblk *kcb;
21 	struct pt_regs *regs;
22 	int bit;
23 
24 	bit = ftrace_test_recursion_trylock(nip, parent_nip);
25 	if (bit < 0)
26 		return;
27 
28 	regs = ftrace_get_regs(fregs);
29 	preempt_disable_notrace();
30 	p = get_kprobe((kprobe_opcode_t *)nip);
31 	if (unlikely(!p) || kprobe_disabled(p))
32 		goto out;
33 
34 	kcb = get_kprobe_ctlblk();
35 	if (kprobe_running()) {
36 		kprobes_inc_nmissed_count(p);
37 	} else {
38 		/*
39 		 * On powerpc, NIP is *before* this instruction for the
40 		 * pre handler
41 		 */
42 		regs_add_return_ip(regs, -MCOUNT_INSN_SIZE);
43 
44 		__this_cpu_write(current_kprobe, p);
45 		kcb->kprobe_status = KPROBE_HIT_ACTIVE;
46 		if (!p->pre_handler || !p->pre_handler(p, regs)) {
47 			/*
48 			 * Emulate singlestep (and also recover regs->nip)
49 			 * as if there is a nop
50 			 */
51 			regs_add_return_ip(regs, MCOUNT_INSN_SIZE);
52 			if (unlikely(p->post_handler)) {
53 				kcb->kprobe_status = KPROBE_HIT_SSDONE;
54 				p->post_handler(p, regs, 0);
55 			}
56 		}
57 		/*
58 		 * If pre_handler returns !0, it changes regs->nip. We have to
59 		 * skip emulating post_handler.
60 		 */
61 		__this_cpu_write(current_kprobe, NULL);
62 	}
63 out:
64 	preempt_enable_notrace();
65 	ftrace_test_recursion_unlock(bit);
66 }
67 NOKPROBE_SYMBOL(kprobe_ftrace_handler);
68 
69 int arch_prepare_kprobe_ftrace(struct kprobe *p)
70 {
71 	p->ainsn.insn = NULL;
72 	p->ainsn.boostable = -1;
73 	return 0;
74 }
75