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 unsigned long orig_ret_address; 28 29 orig_ret_address = rethook_trampoline_handler(regs, 0); 30 /* 31 * We get here through one of two paths: 32 * 1. by taking a trap -> kprobe_handler() -> here 33 * 2. by optprobe branch -> optimized_callback() -> opt_pre_handler() -> here 34 * 35 * When going back through (1), we need regs->nip to be setup properly 36 * as it is used to determine the return address from the trap. 37 * For (2), since nip is not honoured with optprobes, we instead setup 38 * the link register properly so that the subsequent 'blr' in 39 * __kretprobe_trampoline jumps back to the right instruction. 40 * 41 * For nip, we should set the address to the previous instruction since 42 * we end up emulating it in kprobe_handler(), which increments the nip 43 * again. 44 */ 45 regs_set_return_ip(regs, orig_ret_address - 4); 46 regs->link = orig_ret_address; 47 48 return 0; 49 } 50 NOKPROBE_SYMBOL(trampoline_rethook_handler); 51 52 void arch_rethook_prepare(struct rethook_node *rh, struct pt_regs *regs, bool mcount) 53 { 54 rh->ret_addr = regs->link; 55 rh->frame = 0; 56 57 /* Replace the return addr with trampoline addr */ 58 regs->link = (unsigned long)arch_rethook_trampoline; 59 } 60 NOKPROBE_SYMBOL(arch_prepare_kretprobe); 61 62 static struct kprobe trampoline_p = { 63 .addr = (kprobe_opcode_t *) &arch_rethook_trampoline, 64 .pre_handler = trampoline_rethook_handler 65 }; 66 67 static int init_arch_rethook(void) 68 { 69 return register_kprobe(&trampoline_p); 70 } 71 72 core_initcall(init_arch_rethook); 73