rethook.c

 1// SPDX-License-Identifier: GPL-2.0-only
 2/*
 3 * PowerPC implementation of rethook. This depends on kprobes.
 4 */
 5
 6#include <linux/kprobes.h>
 7#include <linux/rethook.h>
 8
 9/*
10 * Function return trampoline:
11 *     - init_kprobes() establishes a probepoint here
12 *     - When the probed function returns, this probe
13 *         causes the handlers to fire
14 */
15asm(".global arch_rethook_trampoline\n"
16	".type arch_rethook_trampoline, @function\n"
17	"arch_rethook_trampoline:\n"
18	"nop\n"
19	"blr\n"
20	".size arch_rethook_trampoline, .-arch_rethook_trampoline\n");
21
22/*
23 * Called when the probe at kretprobe trampoline is hit
24 */
25static int trampoline_rethook_handler(struct kprobe *p, struct pt_regs *regs)
26{
27	return !rethook_trampoline_handler(regs, regs->gpr[1]);
28}
29NOKPROBE_SYMBOL(trampoline_rethook_handler);
30
31void arch_rethook_prepare(struct rethook_node *rh, struct pt_regs *regs, bool mcount)
32{
33	rh->ret_addr = regs->link;
34	rh->frame = regs->gpr[1];
35
36	/* Replace the return addr with trampoline addr */
37	regs->link = (unsigned long)arch_rethook_trampoline;
38}
39NOKPROBE_SYMBOL(arch_rethook_prepare);
40
41/* This is called from rethook_trampoline_handler(). */
42void arch_rethook_fixup_return(struct pt_regs *regs, unsigned long orig_ret_address)
43{
44	/*
45	 * We get here through one of two paths:
46	 * 1. by taking a trap -> kprobe_handler() -> here
47	 * 2. by optprobe branch -> optimized_callback() -> opt_pre_handler() -> here
48	 *
49	 * When going back through (1), we need regs->nip to be setup properly
50	 * as it is used to determine the return address from the trap.
51	 * For (2), since nip is not honoured with optprobes, we instead setup
52	 * the link register properly so that the subsequent 'blr' in
53	 * arch_rethook_trampoline jumps back to the right instruction.
54	 *
55	 * For nip, we should set the address to the previous instruction since
56	 * we end up emulating it in kprobe_handler(), which increments the nip
57	 * again.
58	 */
59	regs_set_return_ip(regs, orig_ret_address - 4);
60	regs->link = orig_ret_address;
61}
62NOKPROBE_SYMBOL(arch_rethook_fixup_return);
63
64static struct kprobe trampoline_p = {
65	.addr = (kprobe_opcode_t *) &arch_rethook_trampoline,
66	.pre_handler = trampoline_rethook_handler
67};
68
69/* rethook initializer */
70int __init arch_init_kprobes(void)
71{
72	return register_kprobe(&trampoline_p);
73}