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 */
15 asm(".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 */
25 static int trampoline_rethook_handler(struct kprobe *p, struct pt_regs *regs)
26 {
27 return !rethook_trampoline_handler(regs, regs->gpr[1]);
28 }
29 NOKPROBE_SYMBOL(trampoline_rethook_handler);
30
31 void 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 }
39 NOKPROBE_SYMBOL(arch_rethook_prepare);
40
41 /* This is called from rethook_trampoline_handler(). */
42 void 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 }
62 NOKPROBE_SYMBOL(arch_rethook_fixup_return);
63
64 static struct kprobe trampoline_p = {
65 .addr = (kprobe_opcode_t *) &arch_rethook_trampoline,
66 .pre_handler = trampoline_rethook_handler
67 };
68
69 /* rethook initializer */
70 int __init arch_init_kprobes(void)
71 {
72 return register_kprobe(&trampoline_p);
73 }
74
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