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 */
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 *)®s->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(). */
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
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
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