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, (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