summaryrefslogtreecommitdiff
path: root/arch/arm64/kernel/ftrace.c
blob: b30b955a892113413bc394b383630285f191f2ae (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
// SPDX-License-Identifier: GPL-2.0-only
/*
 * arch/arm64/kernel/ftrace.c
 *
 * Copyright (C) 2013 Linaro Limited
 * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
 */

#include <linux/ftrace.h>
#include <linux/module.h>
#include <linux/swab.h>
#include <linux/uaccess.h>

#include <asm/cacheflush.h>
#include <asm/debug-monitors.h>
#include <asm/ftrace.h>
#include <asm/insn.h>
#include <asm/patching.h>

#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
struct fregs_offset {
	const char *name;
	int offset;
};

#define FREGS_OFFSET(n, field)				\
{							\
	.name = n,					\
	.offset = offsetof(struct ftrace_regs, field),	\
}

static const struct fregs_offset fregs_offsets[] = {
	FREGS_OFFSET("x0", regs[0]),
	FREGS_OFFSET("x1", regs[1]),
	FREGS_OFFSET("x2", regs[2]),
	FREGS_OFFSET("x3", regs[3]),
	FREGS_OFFSET("x4", regs[4]),
	FREGS_OFFSET("x5", regs[5]),
	FREGS_OFFSET("x6", regs[6]),
	FREGS_OFFSET("x7", regs[7]),
	FREGS_OFFSET("x8", regs[8]),

	FREGS_OFFSET("x29", fp),
	FREGS_OFFSET("x30", lr),
	FREGS_OFFSET("lr", lr),

	FREGS_OFFSET("sp", sp),
	FREGS_OFFSET("pc", pc),
};

int ftrace_regs_query_register_offset(const char *name)
{
	for (int i = 0; i < ARRAY_SIZE(fregs_offsets); i++) {
		const struct fregs_offset *roff = &fregs_offsets[i];
		if (!strcmp(roff->name, name))
			return roff->offset;
	}

	return -EINVAL;
}
#endif

/*
 * Replace a single instruction, which may be a branch or NOP.
 * If @validate == true, a replaced instruction is checked against 'old'.
 */
static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
			      bool validate)
{
	u32 replaced;

	/*
	 * Note:
	 * We are paranoid about modifying text, as if a bug were to happen, it
	 * could cause us to read or write to someplace that could cause harm.
	 * Carefully read and modify the code with aarch64_insn_*() which uses
	 * probe_kernel_*(), and make sure what we read is what we expected it
	 * to be before modifying it.
	 */
	if (validate) {
		if (aarch64_insn_read((void *)pc, &replaced))
			return -EFAULT;

		if (replaced != old)
			return -EINVAL;
	}
	if (aarch64_insn_patch_text_nosync((void *)pc, new))
		return -EPERM;

	return 0;
}

/*
 * Replace tracer function in ftrace_caller()
 */
int ftrace_update_ftrace_func(ftrace_func_t func)
{
	unsigned long pc;
	u32 new;

	pc = (unsigned long)ftrace_call;
	new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func,
					  AARCH64_INSN_BRANCH_LINK);

	return ftrace_modify_code(pc, 0, new, false);
}

static struct plt_entry *get_ftrace_plt(struct module *mod, unsigned long addr)
{
#ifdef CONFIG_ARM64_MODULE_PLTS
	struct plt_entry *plt = mod->arch.ftrace_trampolines;

	if (addr == FTRACE_ADDR)
		return &plt[FTRACE_PLT_IDX];
#endif
	return NULL;
}

/*
 * Find the address the callsite must branch to in order to reach '*addr'.
 *
 * Due to the limited range of 'BL' instructions, modules may be placed too far
 * away to branch directly and must use a PLT.
 *
 * Returns true when '*addr' contains a reachable target address, or has been
 * modified to contain a PLT address. Returns false otherwise.
 */
static bool ftrace_find_callable_addr(struct dyn_ftrace *rec,
				      struct module *mod,
				      unsigned long *addr)
{
	unsigned long pc = rec->ip;
	long offset = (long)*addr - (long)pc;
	struct plt_entry *plt;

	/*
	 * When the target is within range of the 'BL' instruction, use 'addr'
	 * as-is and branch to that directly.
	 */
	if (offset >= -SZ_128M && offset < SZ_128M)
		return true;

	/*
	 * When the target is outside of the range of a 'BL' instruction, we
	 * must use a PLT to reach it. We can only place PLTs for modules, and
	 * only when module PLT support is built-in.
	 */
	if (!IS_ENABLED(CONFIG_ARM64_MODULE_PLTS))
		return false;

	/*
	 * 'mod' is only set at module load time, but if we end up
	 * dealing with an out-of-range condition, we can assume it
	 * is due to a module being loaded far away from the kernel.
	 *
	 * NOTE: __module_text_address() must be called with preemption
	 * disabled, but we can rely on ftrace_lock to ensure that 'mod'
	 * retains its validity throughout the remainder of this code.
	 */
	if (!mod) {
		preempt_disable();
		mod = __module_text_address(pc);
		preempt_enable();
	}

	if (WARN_ON(!mod))
		return false;

	plt = get_ftrace_plt(mod, *addr);
	if (!plt) {
		pr_err("ftrace: no module PLT for %ps\n", (void *)*addr);
		return false;
	}

	*addr = (unsigned long)plt;
	return true;
}

/*
 * Turn on the call to ftrace_caller() in instrumented function
 */
int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
	unsigned long pc = rec->ip;
	u32 old, new;

	if (!ftrace_find_callable_addr(rec, NULL, &addr))
		return -EINVAL;

	old = aarch64_insn_gen_nop();
	new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);

	return ftrace_modify_code(pc, old, new, true);
}

#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
/*
 * The compiler has inserted two NOPs before the regular function prologue.
 * All instrumented functions follow the AAPCS, so x0-x8 and x19-x30 are live,
 * and x9-x18 are free for our use.
 *
 * At runtime we want to be able to swing a single NOP <-> BL to enable or
 * disable the ftrace call. The BL requires us to save the original LR value,
 * so here we insert a <MOV X9, LR> over the first NOP so the instructions
 * before the regular prologue are:
 *
 * | Compiled | Disabled   | Enabled    |
 * +----------+------------+------------+
 * | NOP      | MOV X9, LR | MOV X9, LR |
 * | NOP      | NOP        | BL <entry> |
 *
 * The LR value will be recovered by ftrace_regs_entry, and restored into LR
 * before returning to the regular function prologue. When a function is not
 * being traced, the MOV is not harmful given x9 is not live per the AAPCS.
 *
 * Note: ftrace_process_locs() has pre-adjusted rec->ip to be the address of
 * the BL.
 */
int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
{
	unsigned long pc = rec->ip - AARCH64_INSN_SIZE;
	u32 old, new;

	old = aarch64_insn_gen_nop();
	new = aarch64_insn_gen_move_reg(AARCH64_INSN_REG_9,
					AARCH64_INSN_REG_LR,
					AARCH64_INSN_VARIANT_64BIT);
	return ftrace_modify_code(pc, old, new, true);
}
#endif

/*
 * Turn off the call to ftrace_caller() in instrumented function
 */
int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
		    unsigned long addr)
{
	unsigned long pc = rec->ip;
	u32 old = 0, new;

	new = aarch64_insn_gen_nop();

	/*
	 * When using mcount, callsites in modules may have been initalized to
	 * call an arbitrary module PLT (which redirects to the _mcount stub)
	 * rather than the ftrace PLT we'll use at runtime (which redirects to
	 * the ftrace trampoline). We can ignore the old PLT when initializing
	 * the callsite.
	 *
	 * Note: 'mod' is only set at module load time.
	 */
	if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_ARGS) &&
	    IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) && mod) {
		return aarch64_insn_patch_text_nosync((void *)pc, new);
	}

	if (!ftrace_find_callable_addr(rec, mod, &addr))
		return -EINVAL;

	old = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);

	return ftrace_modify_code(pc, old, new, true);
}

void arch_ftrace_update_code(int command)
{
	command |= FTRACE_MAY_SLEEP;
	ftrace_modify_all_code(command);
}

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
/*
 * function_graph tracer expects ftrace_return_to_handler() to be called
 * on the way back to parent. For this purpose, this function is called
 * in _mcount() or ftrace_caller() to replace return address (*parent) on
 * the call stack to return_to_handler.
 */
void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
			   unsigned long frame_pointer)
{
	unsigned long return_hooker = (unsigned long)&return_to_handler;
	unsigned long old;

	if (unlikely(atomic_read(&current->tracing_graph_pause)))
		return;

	/*
	 * Note:
	 * No protection against faulting at *parent, which may be seen
	 * on other archs. It's unlikely on AArch64.
	 */
	old = *parent;

	if (!function_graph_enter(old, self_addr, frame_pointer,
	    (void *)frame_pointer)) {
		*parent = return_hooker;
	}
}

#ifdef CONFIG_DYNAMIC_FTRACE_WITH_ARGS
void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
		       struct ftrace_ops *op, struct ftrace_regs *fregs)
{
	prepare_ftrace_return(ip, &fregs->lr, fregs->fp);
}
#else
/*
 * Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
 * depending on @enable.
 */
static int ftrace_modify_graph_caller(bool enable)
{
	unsigned long pc = (unsigned long)&ftrace_graph_call;
	u32 branch, nop;

	branch = aarch64_insn_gen_branch_imm(pc,
					     (unsigned long)ftrace_graph_caller,
					     AARCH64_INSN_BRANCH_NOLINK);
	nop = aarch64_insn_gen_nop();

	if (enable)
		return ftrace_modify_code(pc, nop, branch, true);
	else
		return ftrace_modify_code(pc, branch, nop, true);
}

int ftrace_enable_ftrace_graph_caller(void)
{
	return ftrace_modify_graph_caller(true);
}

int ftrace_disable_ftrace_graph_caller(void)
{
	return ftrace_modify_graph_caller(false);
}
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_ARGS */
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */