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
19 #ifdef CONFIG_DYNAMIC_FTRACE
20 /*
21 * Replace a single instruction, which may be a branch or NOP.
22 * If @validate == true, a replaced instruction is checked against 'old'.
23 */
ftrace_modify_code(unsigned long pc,u32 old,u32 new,bool validate)24 static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
25 bool validate)
26 {
27 u32 replaced;
28
29 /*
30 * Note:
31 * We are paranoid about modifying text, as if a bug were to happen, it
32 * could cause us to read or write to someplace that could cause harm.
33 * Carefully read and modify the code with aarch64_insn_*() which uses
34 * probe_kernel_*(), and make sure what we read is what we expected it
35 * to be before modifying it.
36 */
37 if (validate) {
38 if (aarch64_insn_read((void *)pc, &replaced))
39 return -EFAULT;
40
41 if (replaced != old)
42 return -EINVAL;
43 }
44 if (aarch64_insn_patch_text_nosync((void *)pc, new))
45 return -EPERM;
46
47 return 0;
48 }
49
50 /*
51 * Replace tracer function in ftrace_caller()
52 */
ftrace_update_ftrace_func(ftrace_func_t func)53 int ftrace_update_ftrace_func(ftrace_func_t func)
54 {
55 unsigned long pc;
56 u32 new;
57
58 pc = (unsigned long)&ftrace_call;
59 new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func,
60 AARCH64_INSN_BRANCH_LINK);
61
62 return ftrace_modify_code(pc, 0, new, false);
63 }
64
get_ftrace_plt(struct module * mod,unsigned long addr)65 static struct plt_entry *get_ftrace_plt(struct module *mod, unsigned long addr)
66 {
67 #ifdef CONFIG_ARM64_MODULE_PLTS
68 struct plt_entry *plt = mod->arch.ftrace_trampolines;
69
70 if (addr == FTRACE_ADDR)
71 return &plt[FTRACE_PLT_IDX];
72 if (addr == FTRACE_REGS_ADDR &&
73 IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))
74 return &plt[FTRACE_REGS_PLT_IDX];
75 #endif
76 return NULL;
77 }
78
79 /*
80 * Find the address the callsite must branch to in order to reach '*addr'.
81 *
82 * Due to the limited range of 'BL' instructions, modules may be placed too far
83 * away to branch directly and must use a PLT.
84 *
85 * Returns true when '*addr' contains a reachable target address, or has been
86 * modified to contain a PLT address. Returns false otherwise.
87 */
ftrace_find_callable_addr(struct dyn_ftrace * rec,struct module * mod,unsigned long * addr)88 static bool ftrace_find_callable_addr(struct dyn_ftrace *rec,
89 struct module *mod,
90 unsigned long *addr)
91 {
92 unsigned long pc = rec->ip;
93 long offset = (long)*addr - (long)pc;
94 struct plt_entry *plt;
95
96 /*
97 * When the target is within range of the 'BL' instruction, use 'addr'
98 * as-is and branch to that directly.
99 */
100 if (offset >= -SZ_128M && offset < SZ_128M)
101 return true;
102
103 /*
104 * When the target is outside of the range of a 'BL' instruction, we
105 * must use a PLT to reach it. We can only place PLTs for modules, and
106 * only when module PLT support is built-in.
107 */
108 if (!IS_ENABLED(CONFIG_ARM64_MODULE_PLTS))
109 return false;
110
111 /*
112 * 'mod' is only set at module load time, but if we end up
113 * dealing with an out-of-range condition, we can assume it
114 * is due to a module being loaded far away from the kernel.
115 *
116 * NOTE: __module_text_address() must be called with preemption
117 * disabled, but we can rely on ftrace_lock to ensure that 'mod'
118 * retains its validity throughout the remainder of this code.
119 */
120 if (!mod) {
121 preempt_disable();
122 mod = __module_text_address(pc);
123 preempt_enable();
124 }
125
126 if (WARN_ON(!mod))
127 return false;
128
129 plt = get_ftrace_plt(mod, *addr);
130 if (!plt) {
131 pr_err("ftrace: no module PLT for %ps\n", (void *)*addr);
132 return false;
133 }
134
135 *addr = (unsigned long)plt;
136 return true;
137 }
138
139 /*
140 * Turn on the call to ftrace_caller() in instrumented function
141 */
ftrace_make_call(struct dyn_ftrace * rec,unsigned long addr)142 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
143 {
144 unsigned long pc = rec->ip;
145 u32 old, new;
146
147 if (!ftrace_find_callable_addr(rec, NULL, &addr))
148 return -EINVAL;
149
150 old = aarch64_insn_gen_nop();
151 new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
152
153 return ftrace_modify_code(pc, old, new, true);
154 }
155
156 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
ftrace_modify_call(struct dyn_ftrace * rec,unsigned long old_addr,unsigned long addr)157 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
158 unsigned long addr)
159 {
160 unsigned long pc = rec->ip;
161 u32 old, new;
162
163 if (!ftrace_find_callable_addr(rec, NULL, &old_addr))
164 return -EINVAL;
165 if (!ftrace_find_callable_addr(rec, NULL, &addr))
166 return -EINVAL;
167
168 old = aarch64_insn_gen_branch_imm(pc, old_addr,
169 AARCH64_INSN_BRANCH_LINK);
170 new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
171
172 return ftrace_modify_code(pc, old, new, true);
173 }
174
175 /*
176 * The compiler has inserted two NOPs before the regular function prologue.
177 * All instrumented functions follow the AAPCS, so x0-x8 and x19-x30 are live,
178 * and x9-x18 are free for our use.
179 *
180 * At runtime we want to be able to swing a single NOP <-> BL to enable or
181 * disable the ftrace call. The BL requires us to save the original LR value,
182 * so here we insert a <MOV X9, LR> over the first NOP so the instructions
183 * before the regular prologue are:
184 *
185 * | Compiled | Disabled | Enabled |
186 * +----------+------------+------------+
187 * | NOP | MOV X9, LR | MOV X9, LR |
188 * | NOP | NOP | BL <entry> |
189 *
190 * The LR value will be recovered by ftrace_regs_entry, and restored into LR
191 * before returning to the regular function prologue. When a function is not
192 * being traced, the MOV is not harmful given x9 is not live per the AAPCS.
193 *
194 * Note: ftrace_process_locs() has pre-adjusted rec->ip to be the address of
195 * the BL.
196 */
ftrace_init_nop(struct module * mod,struct dyn_ftrace * rec)197 int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
198 {
199 unsigned long pc = rec->ip - AARCH64_INSN_SIZE;
200 u32 old, new;
201
202 old = aarch64_insn_gen_nop();
203 new = aarch64_insn_gen_move_reg(AARCH64_INSN_REG_9,
204 AARCH64_INSN_REG_LR,
205 AARCH64_INSN_VARIANT_64BIT);
206 return ftrace_modify_code(pc, old, new, true);
207 }
208 #endif
209
210 /*
211 * Turn off the call to ftrace_caller() in instrumented function
212 */
ftrace_make_nop(struct module * mod,struct dyn_ftrace * rec,unsigned long addr)213 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
214 unsigned long addr)
215 {
216 unsigned long pc = rec->ip;
217 u32 old = 0, new;
218
219 new = aarch64_insn_gen_nop();
220
221 /*
222 * When using mcount, callsites in modules may have been initalized to
223 * call an arbitrary module PLT (which redirects to the _mcount stub)
224 * rather than the ftrace PLT we'll use at runtime (which redirects to
225 * the ftrace trampoline). We can ignore the old PLT when initializing
226 * the callsite.
227 *
228 * Note: 'mod' is only set at module load time.
229 */
230 if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS) &&
231 IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) && mod) {
232 return aarch64_insn_patch_text_nosync((void *)pc, new);
233 }
234
235 if (!ftrace_find_callable_addr(rec, mod, &addr))
236 return -EINVAL;
237
238 old = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
239
240 return ftrace_modify_code(pc, old, new, true);
241 }
242
arch_ftrace_update_code(int command)243 void arch_ftrace_update_code(int command)
244 {
245 command |= FTRACE_MAY_SLEEP;
246 ftrace_modify_all_code(command);
247 }
248
ftrace_dyn_arch_init(void)249 int __init ftrace_dyn_arch_init(void)
250 {
251 return 0;
252 }
253 #endif /* CONFIG_DYNAMIC_FTRACE */
254
255 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
256 /*
257 * function_graph tracer expects ftrace_return_to_handler() to be called
258 * on the way back to parent. For this purpose, this function is called
259 * in _mcount() or ftrace_caller() to replace return address (*parent) on
260 * the call stack to return_to_handler.
261 *
262 * Note that @frame_pointer is used only for sanity check later.
263 */
prepare_ftrace_return(unsigned long self_addr,unsigned long * parent,unsigned long frame_pointer)264 void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
265 unsigned long frame_pointer)
266 {
267 unsigned long return_hooker = (unsigned long)&return_to_handler;
268 unsigned long old;
269
270 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
271 return;
272
273 /*
274 * Note:
275 * No protection against faulting at *parent, which may be seen
276 * on other archs. It's unlikely on AArch64.
277 */
278 old = *parent;
279
280 if (!function_graph_enter(old, self_addr, frame_pointer, NULL))
281 *parent = return_hooker;
282 }
283
284 #ifdef CONFIG_DYNAMIC_FTRACE
285 /*
286 * Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
287 * depending on @enable.
288 */
ftrace_modify_graph_caller(bool enable)289 static int ftrace_modify_graph_caller(bool enable)
290 {
291 unsigned long pc = (unsigned long)&ftrace_graph_call;
292 u32 branch, nop;
293
294 branch = aarch64_insn_gen_branch_imm(pc,
295 (unsigned long)ftrace_graph_caller,
296 AARCH64_INSN_BRANCH_NOLINK);
297 nop = aarch64_insn_gen_nop();
298
299 if (enable)
300 return ftrace_modify_code(pc, nop, branch, true);
301 else
302 return ftrace_modify_code(pc, branch, nop, true);
303 }
304
ftrace_enable_ftrace_graph_caller(void)305 int ftrace_enable_ftrace_graph_caller(void)
306 {
307 return ftrace_modify_graph_caller(true);
308 }
309
ftrace_disable_ftrace_graph_caller(void)310 int ftrace_disable_ftrace_graph_caller(void)
311 {
312 return ftrace_modify_graph_caller(false);
313 }
314 #endif /* CONFIG_DYNAMIC_FTRACE */
315 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
316