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  */
22 asm(
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 );
62 NOKPROBE_SYMBOL(arch_rethook_trampoline);
63 
64 /*
65  * Called from arch_rethook_trampoline
66  */
arch_rethook_trampoline_callback(struct pt_regs * regs)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 }
94 NOKPROBE_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  */
104 STACK_FRAME_NON_STANDARD_FP(arch_rethook_trampoline);
105 
106 /* This is called from rethook_trampoline_handler(). */
arch_rethook_fixup_return(struct pt_regs * regs,unsigned long correct_ret_addr)107 void 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 }
115 NOKPROBE_SYMBOL(arch_rethook_fixup_return);
116 
arch_rethook_prepare(struct rethook_node * rh,struct pt_regs * regs,bool mcount)117 void 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 }
127 NOKPROBE_SYMBOL(arch_rethook_prepare);
128