1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * arch/arm64/kernel/probes/decode-insn.c
4 *
5 * Copyright (C) 2013 Linaro Limited.
6 */
7
8 #include <linux/kernel.h>
9 #include <linux/kprobes.h>
10 #include <linux/module.h>
11 #include <linux/kallsyms.h>
12 #include <asm/insn.h>
13 #include <asm/sections.h>
14
15 #include "decode-insn.h"
16 #include "simulate-insn.h"
17
18 static bool __kprobes aarch64_insn_is_steppable(u32 insn)
19 {
20 /*
21 * Branch instructions will write a new value into the PC which is
22 * likely to be relative to the XOL address and therefore invalid.
23 * Deliberate generation of an exception during stepping is also not
24 * currently safe. Lastly, MSR instructions can do any number of nasty
25 * things we can't handle during single-stepping.
26 */
27 if (aarch64_get_insn_class(insn) == AARCH64_INSN_CLS_BR_SYS) {
28 if (aarch64_insn_is_branch(insn) ||
29 aarch64_insn_is_msr_imm(insn) ||
30 aarch64_insn_is_msr_reg(insn) ||
31 aarch64_insn_is_exception(insn) ||
32 aarch64_insn_is_eret(insn))
33 return false;
34
35 /*
36 * The MRS instruction may not return a correct value when
37 * executing in the single-stepping environment. We do make one
38 * exception, for reading the DAIF bits.
39 */
40 if (aarch64_insn_is_mrs(insn))
41 return aarch64_insn_extract_system_reg(insn)
42 != AARCH64_INSN_SPCLREG_DAIF;
43
44 /*
45 * The HINT instruction is is problematic when single-stepping,
46 * except for the NOP case.
47 */
48 if (aarch64_insn_is_hint(insn))
49 return aarch64_insn_is_nop(insn);
50
51 return true;
52 }
53
54 /*
55 * Instructions which load PC relative literals are not going to work
56 * when executed from an XOL slot. Instructions doing an exclusive
57 * load/store are not going to complete successfully when single-step
58 * exception handling happens in the middle of the sequence.
59 */
60 if (aarch64_insn_uses_literal(insn) ||
61 aarch64_insn_is_exclusive(insn))
62 return false;
63
64 return true;
65 }
66
67 /* Return:
68 * INSN_REJECTED If instruction is one not allowed to kprobe,
69 * INSN_GOOD If instruction is supported and uses instruction slot,
70 * INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot.
71 */
72 enum probe_insn __kprobes
73 arm_probe_decode_insn(probe_opcode_t insn, struct arch_probe_insn *api)
74 {
75 /*
76 * Instructions reading or modifying the PC won't work from the XOL
77 * slot.
78 */
79 if (aarch64_insn_is_steppable(insn))
80 return INSN_GOOD;
81
82 if (aarch64_insn_is_bcond(insn)) {
83 api->handler = simulate_b_cond;
84 } else if (aarch64_insn_is_cbz(insn) ||
85 aarch64_insn_is_cbnz(insn)) {
86 api->handler = simulate_cbz_cbnz;
87 } else if (aarch64_insn_is_tbz(insn) ||
88 aarch64_insn_is_tbnz(insn)) {
89 api->handler = simulate_tbz_tbnz;
90 } else if (aarch64_insn_is_adr_adrp(insn)) {
91 api->handler = simulate_adr_adrp;
92 } else if (aarch64_insn_is_b(insn) ||
93 aarch64_insn_is_bl(insn)) {
94 api->handler = simulate_b_bl;
95 } else if (aarch64_insn_is_br(insn) ||
96 aarch64_insn_is_blr(insn) ||
97 aarch64_insn_is_ret(insn)) {
98 api->handler = simulate_br_blr_ret;
99 } else if (aarch64_insn_is_ldr_lit(insn)) {
100 api->handler = simulate_ldr_literal;
101 } else if (aarch64_insn_is_ldrsw_lit(insn)) {
102 api->handler = simulate_ldrsw_literal;
103 } else {
104 /*
105 * Instruction cannot be stepped out-of-line and we don't
106 * (yet) simulate it.
107 */
108 return INSN_REJECTED;
109 }
110
111 return INSN_GOOD_NO_SLOT;
112 }
113
114 #ifdef CONFIG_KPROBES
115 static bool __kprobes
116 is_probed_address_atomic(kprobe_opcode_t *scan_start, kprobe_opcode_t *scan_end)
117 {
118 while (scan_start >= scan_end) {
119 /*
120 * atomic region starts from exclusive load and ends with
121 * exclusive store.
122 */
123 if (aarch64_insn_is_store_ex(le32_to_cpu(*scan_start)))
124 return false;
125 else if (aarch64_insn_is_load_ex(le32_to_cpu(*scan_start)))
126 return true;
127 scan_start--;
128 }
129
130 return false;
131 }
132
133 enum probe_insn __kprobes
134 arm_kprobe_decode_insn(kprobe_opcode_t *addr, struct arch_specific_insn *asi)
135 {
136 enum probe_insn decoded;
137 probe_opcode_t insn = le32_to_cpu(*addr);
138 probe_opcode_t *scan_end = NULL;
139 unsigned long size = 0, offset = 0;
140
141 /*
142 * If there's a symbol defined in front of and near enough to
143 * the probe address assume it is the entry point to this
144 * code and use it to further limit how far back we search
145 * when determining if we're in an atomic sequence. If we could
146 * not find any symbol skip the atomic test altogether as we
147 * could otherwise end up searching irrelevant text/literals.
148 * KPROBES depends on KALLSYMS so this last case should never
149 * happen.
150 */
151 if (kallsyms_lookup_size_offset((unsigned long) addr, &size, &offset)) {
152 if (offset < (MAX_ATOMIC_CONTEXT_SIZE*sizeof(kprobe_opcode_t)))
153 scan_end = addr - (offset / sizeof(kprobe_opcode_t));
154 else
155 scan_end = addr - MAX_ATOMIC_CONTEXT_SIZE;
156 }
157 decoded = arm_probe_decode_insn(insn, &asi->api);
158
159 if (decoded != INSN_REJECTED && scan_end)
160 if (is_probed_address_atomic(addr - 1, scan_end))
161 return INSN_REJECTED;
162
163 return decoded;
164 }
165 #endif