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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * arch/arm64/kernel/ftrace.c
4 *
5 * Copyright (C) 2013 Linaro Limited
6 * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
7 */
8
9#include <linux/ftrace.h>
10#include <linux/module.h>
11#include <linux/swab.h>
12#include <linux/uaccess.h>
13
14#include <asm/cacheflush.h>
15#include <asm/debug-monitors.h>
16#include <asm/ftrace.h>
17#include <asm/insn.h>
18#include <asm/patching.h>
19
20#ifdef CONFIG_DYNAMIC_FTRACE
21/*
22 * Replace a single instruction, which may be a branch or NOP.
23 * If @validate == true, a replaced instruction is checked against 'old'.
24 */
25static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
26 bool validate)
27{
28 u32 replaced;
29
30 /*
31 * Note:
32 * We are paranoid about modifying text, as if a bug were to happen, it
33 * could cause us to read or write to someplace that could cause harm.
34 * Carefully read and modify the code with aarch64_insn_*() which uses
35 * probe_kernel_*(), and make sure what we read is what we expected it
36 * to be before modifying it.
37 */
38 if (validate) {
39 if (aarch64_insn_read((void *)pc, &replaced))
40 return -EFAULT;
41
42 if (replaced != old)
43 return -EINVAL;
44 }
45 if (aarch64_insn_patch_text_nosync((void *)pc, new))
46 return -EPERM;
47
48 return 0;
49}
50
51/*
52 * Replace tracer function in ftrace_caller()
53 */
54int ftrace_update_ftrace_func(ftrace_func_t func)
55{
56 unsigned long pc;
57 u32 new;
58
59 pc = (unsigned long)function_nocfi(ftrace_call);
60 new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func,
61 AARCH64_INSN_BRANCH_LINK);
62
63 return ftrace_modify_code(pc, 0, new, false);
64}
65
66static struct plt_entry *get_ftrace_plt(struct module *mod, unsigned long addr)
67{
68#ifdef CONFIG_ARM64_MODULE_PLTS
69 struct plt_entry *plt = mod->arch.ftrace_trampolines;
70
71 if (addr == FTRACE_ADDR)
72 return &plt[FTRACE_PLT_IDX];
73 if (addr == FTRACE_REGS_ADDR &&
74 IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))
75 return &plt[FTRACE_REGS_PLT_IDX];
76#endif
77 return NULL;
78}
79
80/*
81 * Turn on the call to ftrace_caller() in instrumented function
82 */
83int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
84{
85 unsigned long pc = rec->ip;
86 u32 old, new;
87 long offset = (long)pc - (long)addr;
88
89 if (offset < -SZ_128M || offset >= SZ_128M) {
90 struct module *mod;
91 struct plt_entry *plt;
92
93 if (!IS_ENABLED(CONFIG_ARM64_MODULE_PLTS))
94 return -EINVAL;
95
96 /*
97 * On kernels that support module PLTs, the offset between the
98 * branch instruction and its target may legally exceed the
99 * range of an ordinary relative 'bl' opcode. In this case, we
100 * need to branch via a trampoline in the module.
101 *
102 * NOTE: __module_text_address() must be called with preemption
103 * disabled, but we can rely on ftrace_lock to ensure that 'mod'
104 * retains its validity throughout the remainder of this code.
105 */
106 preempt_disable();
107 mod = __module_text_address(pc);
108 preempt_enable();
109
110 if (WARN_ON(!mod))
111 return -EINVAL;
112
113 plt = get_ftrace_plt(mod, addr);
114 if (!plt) {
115 pr_err("ftrace: no module PLT for %ps\n", (void *)addr);
116 return -EINVAL;
117 }
118
119 addr = (unsigned long)plt;
120 }
121
122 old = aarch64_insn_gen_nop();
123 new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
124
125 return ftrace_modify_code(pc, old, new, true);
126}
127
128#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
129int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
130 unsigned long addr)
131{
132 unsigned long pc = rec->ip;
133 u32 old, new;
134
135 old = aarch64_insn_gen_branch_imm(pc, old_addr,
136 AARCH64_INSN_BRANCH_LINK);
137 new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
138
139 return ftrace_modify_code(pc, old, new, true);
140}
141
142/*
143 * The compiler has inserted two NOPs before the regular function prologue.
144 * All instrumented functions follow the AAPCS, so x0-x8 and x19-x30 are live,
145 * and x9-x18 are free for our use.
146 *
147 * At runtime we want to be able to swing a single NOP <-> BL to enable or
148 * disable the ftrace call. The BL requires us to save the original LR value,
149 * so here we insert a <MOV X9, LR> over the first NOP so the instructions
150 * before the regular prologue are:
151 *
152 * | Compiled | Disabled | Enabled |
153 * +----------+------------+------------+
154 * | NOP | MOV X9, LR | MOV X9, LR |
155 * | NOP | NOP | BL <entry> |
156 *
157 * The LR value will be recovered by ftrace_regs_entry, and restored into LR
158 * before returning to the regular function prologue. When a function is not
159 * being traced, the MOV is not harmful given x9 is not live per the AAPCS.
160 *
161 * Note: ftrace_process_locs() has pre-adjusted rec->ip to be the address of
162 * the BL.
163 */
164int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
165{
166 unsigned long pc = rec->ip - AARCH64_INSN_SIZE;
167 u32 old, new;
168
169 old = aarch64_insn_gen_nop();
170 new = aarch64_insn_gen_move_reg(AARCH64_INSN_REG_9,
171 AARCH64_INSN_REG_LR,
172 AARCH64_INSN_VARIANT_64BIT);
173 return ftrace_modify_code(pc, old, new, true);
174}
175#endif
176
177/*
178 * Turn off the call to ftrace_caller() in instrumented function
179 */
180int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
181 unsigned long addr)
182{
183 unsigned long pc = rec->ip;
184 bool validate = true;
185 u32 old = 0, new;
186 long offset = (long)pc - (long)addr;
187
188 if (offset < -SZ_128M || offset >= SZ_128M) {
189 u32 replaced;
190
191 if (!IS_ENABLED(CONFIG_ARM64_MODULE_PLTS))
192 return -EINVAL;
193
194 /*
195 * 'mod' is only set at module load time, but if we end up
196 * dealing with an out-of-range condition, we can assume it
197 * is due to a module being loaded far away from the kernel.
198 */
199 if (!mod) {
200 preempt_disable();
201 mod = __module_text_address(pc);
202 preempt_enable();
203
204 if (WARN_ON(!mod))
205 return -EINVAL;
206 }
207
208 /*
209 * The instruction we are about to patch may be a branch and
210 * link instruction that was redirected via a PLT entry. In
211 * this case, the normal validation will fail, but we can at
212 * least check that we are dealing with a branch and link
213 * instruction that points into the right module.
214 */
215 if (aarch64_insn_read((void *)pc, &replaced))
216 return -EFAULT;
217
218 if (!aarch64_insn_is_bl(replaced) ||
219 !within_module(pc + aarch64_get_branch_offset(replaced),
220 mod))
221 return -EINVAL;
222
223 validate = false;
224 } else {
225 old = aarch64_insn_gen_branch_imm(pc, addr,
226 AARCH64_INSN_BRANCH_LINK);
227 }
228
229 new = aarch64_insn_gen_nop();
230
231 return ftrace_modify_code(pc, old, new, validate);
232}
233
234void arch_ftrace_update_code(int command)
235{
236 command |= FTRACE_MAY_SLEEP;
237 ftrace_modify_all_code(command);
238}
239
240int __init ftrace_dyn_arch_init(void)
241{
242 return 0;
243}
244#endif /* CONFIG_DYNAMIC_FTRACE */
245
246#ifdef CONFIG_FUNCTION_GRAPH_TRACER
247/*
248 * function_graph tracer expects ftrace_return_to_handler() to be called
249 * on the way back to parent. For this purpose, this function is called
250 * in _mcount() or ftrace_caller() to replace return address (*parent) on
251 * the call stack to return_to_handler.
252 *
253 * Note that @frame_pointer is used only for sanity check later.
254 */
255void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
256 unsigned long frame_pointer)
257{
258 unsigned long return_hooker = (unsigned long)&return_to_handler;
259 unsigned long old;
260
261 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
262 return;
263
264 /*
265 * Note:
266 * No protection against faulting at *parent, which may be seen
267 * on other archs. It's unlikely on AArch64.
268 */
269 old = *parent;
270
271 if (!function_graph_enter(old, self_addr, frame_pointer, NULL))
272 *parent = return_hooker;
273}
274
275#ifdef CONFIG_DYNAMIC_FTRACE
276/*
277 * Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
278 * depending on @enable.
279 */
280static int ftrace_modify_graph_caller(bool enable)
281{
282 unsigned long pc = (unsigned long)&ftrace_graph_call;
283 u32 branch, nop;
284
285 branch = aarch64_insn_gen_branch_imm(pc,
286 (unsigned long)ftrace_graph_caller,
287 AARCH64_INSN_BRANCH_NOLINK);
288 nop = aarch64_insn_gen_nop();
289
290 if (enable)
291 return ftrace_modify_code(pc, nop, branch, true);
292 else
293 return ftrace_modify_code(pc, branch, nop, true);
294}
295
296int ftrace_enable_ftrace_graph_caller(void)
297{
298 return ftrace_modify_graph_caller(true);
299}
300
301int ftrace_disable_ftrace_graph_caller(void)
302{
303 return ftrace_modify_graph_caller(false);
304}
305#endif /* CONFIG_DYNAMIC_FTRACE */
306#endif /* CONFIG_FUNCTION_GRAPH_TRACER */