1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * x86 implementation of rethook. Mostly copied from arch/x86/kernel/kprobes/core.c.
4 */
5#include <linux/bug.h>
6#include <linux/rethook.h>
7#include <linux/kprobes.h>
8#include <linux/objtool.h>
9
10#include "kprobes/common.h"
11
12__visible void arch_rethook_trampoline_callback(struct pt_regs *regs);
13
14#ifndef ANNOTATE_NOENDBR
15#define ANNOTATE_NOENDBR
16#endif
17
18/*
19 * When a target function returns, this code saves registers and calls
20 * arch_rethook_trampoline_callback(), which calls the rethook handler.
21 */
22asm(
23 ".text\n"
24 ".global arch_rethook_trampoline\n"
25 ".type arch_rethook_trampoline, @function\n"
26 "arch_rethook_trampoline:\n"
27#ifdef CONFIG_X86_64
28 ANNOTATE_NOENDBR /* This is only jumped from ret instruction */
29 /* Push a fake return address to tell the unwinder it's a rethook. */
30 " pushq $arch_rethook_trampoline\n"
31 UNWIND_HINT_FUNC
32 " pushq $" __stringify(__KERNEL_DS) "\n"
33 /* Save the 'sp - 16', this will be fixed later. */
34 " pushq %rsp\n"
35 " pushfq\n"
36 SAVE_REGS_STRING
37 " movq %rsp, %rdi\n"
38 " call arch_rethook_trampoline_callback\n"
39 RESTORE_REGS_STRING
40 /* In the callback function, 'regs->flags' is copied to 'regs->ss'. */
41 " addq $16, %rsp\n"
42 " popfq\n"
43#else
44 /* Push a fake return address to tell the unwinder it's a rethook. */
45 " pushl $arch_rethook_trampoline\n"
46 UNWIND_HINT_FUNC
47 " pushl %ss\n"
48 /* Save the 'sp - 8', this will be fixed later. */
49 " pushl %esp\n"
50 " pushfl\n"
51 SAVE_REGS_STRING
52 " movl %esp, %eax\n"
53 " call arch_rethook_trampoline_callback\n"
54 RESTORE_REGS_STRING
55 /* In the callback function, 'regs->flags' is copied to 'regs->ss'. */
56 " addl $8, %esp\n"
57 " popfl\n"
58#endif
59 ASM_RET
60 ".size arch_rethook_trampoline, .-arch_rethook_trampoline\n"
61);
62NOKPROBE_SYMBOL(arch_rethook_trampoline);
63
64/*
65 * Called from arch_rethook_trampoline
66 */
67__used __visible void arch_rethook_trampoline_callback(struct pt_regs *regs)
68{
69 unsigned long *frame_pointer;
70
71 /* fixup registers */
72 regs->cs = __KERNEL_CS;
73#ifdef CONFIG_X86_32
74 regs->gs = 0;
75#endif
76 regs->ip = (unsigned long)&arch_rethook_trampoline;
77 regs->orig_ax = ~0UL;
78 regs->sp += 2*sizeof(long);
79 frame_pointer = (long *)(regs + 1);
80
81 /*
82 * The return address at 'frame_pointer' is recovered by the
83 * arch_rethook_fixup_return() which called from this
84 * rethook_trampoline_handler().
85 */
86 rethook_trampoline_handler(regs, frame: (unsigned long)frame_pointer);
87
88 /*
89 * Copy FLAGS to 'pt_regs::ss' so that arch_rethook_trapmoline()
90 * can do RET right after POPF.
91 */
92 *(unsigned long *)&regs->ss = regs->flags;
93}
94NOKPROBE_SYMBOL(arch_rethook_trampoline_callback);
95
96/*
97 * arch_rethook_trampoline() skips updating frame pointer. The frame pointer
98 * saved in arch_rethook_trampoline_callback() points to the real caller
99 * function's frame pointer. Thus the arch_rethook_trampoline() doesn't have
100 * a standard stack frame with CONFIG_FRAME_POINTER=y.
101 * Let's mark it non-standard function. Anyway, FP unwinder can correctly
102 * unwind without the hint.
103 */
104STACK_FRAME_NON_STANDARD_FP(arch_rethook_trampoline);
105
106/* This is called from rethook_trampoline_handler(). */
107void arch_rethook_fixup_return(struct pt_regs *regs,
108 unsigned long correct_ret_addr)
109{
110 unsigned long *frame_pointer = (void *)(regs + 1);
111
112 /* Replace fake return address with real one. */
113 *frame_pointer = correct_ret_addr;
114}
115NOKPROBE_SYMBOL(arch_rethook_fixup_return);
116
117void arch_rethook_prepare(struct rethook_node *rh, struct pt_regs *regs, bool mcount)
118{
119 unsigned long *stack = (unsigned long *)regs->sp;
120
121 rh->ret_addr = stack[0];
122 rh->frame = regs->sp;
123
124 /* Replace the return addr with trampoline addr */
125 stack[0] = (unsigned long) arch_rethook_trampoline;
126}
127NOKPROBE_SYMBOL(arch_rethook_prepare);
128