summaryrefslogtreecommitdiff
path: root/arch/arm64/kernel/ftrace.c
blob: 50986e388d2b27e92f6984914af4ce756ea0ee46 (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
/*
 * arch/arm64/kernel/ftrace.c
 *
 * Copyright (C) 2013 Linaro Limited
 * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#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>

#ifdef CONFIG_DYNAMIC_FTRACE
/*
 * 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);
}

/*
 * 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;
	long offset = (long)pc - (long)addr;

	if (offset < -SZ_128M || offset >= SZ_128M) {
#ifdef CONFIG_ARM64_MODULE_PLTS
		struct plt_entry trampoline;
		struct module *mod;

		/*
		 * On kernels that support module PLTs, the offset between the
		 * branch instruction and its target may legally exceed the
		 * range of an ordinary relative 'bl' opcode. In this case, we
		 * need to branch via a trampoline in the module.
		 *
		 * 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.
		 */
		preempt_disable();
		mod = __module_text_address(pc);
		preempt_enable();

		if (WARN_ON(!mod))
			return -EINVAL;

		/*
		 * There is only one ftrace trampoline per module. For now,
		 * this is not a problem since on arm64, all dynamic ftrace
		 * invocations are routed via ftrace_caller(). This will need
		 * to be revisited if support for multiple ftrace entry points
		 * is added in the future, but for now, the pr_err() below
		 * deals with a theoretical issue only.
		 */
		trampoline = get_plt_entry(addr);
		if (!plt_entries_equal(mod->arch.ftrace_trampoline,
				       &trampoline)) {
			if (!plt_entries_equal(mod->arch.ftrace_trampoline,
					       &(struct plt_entry){})) {
				pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n");
				return -EINVAL;
			}

			/* point the trampoline to our ftrace entry point */
			module_disable_ro(mod);
			*mod->arch.ftrace_trampoline = trampoline;
			module_enable_ro(mod, true);

			/* update trampoline before patching in the branch */
			smp_wmb();
		}
		addr = (unsigned long)(void *)mod->arch.ftrace_trampoline;
#else /* CONFIG_ARM64_MODULE_PLTS */
		return -EINVAL;
#endif /* CONFIG_ARM64_MODULE_PLTS */
	}

	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);
}

/*
 * 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;
	bool validate = true;
	u32 old = 0, new;
	long offset = (long)pc - (long)addr;

	if (offset < -SZ_128M || offset >= SZ_128M) {
#ifdef CONFIG_ARM64_MODULE_PLTS
		u32 replaced;

		/*
		 * '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.
		 */
		if (!mod) {
			preempt_disable();
			mod = __module_text_address(pc);
			preempt_enable();

			if (WARN_ON(!mod))
				return -EINVAL;
		}

		/*
		 * The instruction we are about to patch may be a branch and
		 * link instruction that was redirected via a PLT entry. In
		 * this case, the normal validation will fail, but we can at
		 * least check that we are dealing with a branch and link
		 * instruction that points into the right module.
		 */
		if (aarch64_insn_read((void *)pc, &replaced))
			return -EFAULT;

		if (!aarch64_insn_is_bl(replaced) ||
		    !within_module(pc + aarch64_get_branch_offset(replaced),
				   mod))
			return -EINVAL;

		validate = false;
#else /* CONFIG_ARM64_MODULE_PLTS */
		return -EINVAL;
#endif /* CONFIG_ARM64_MODULE_PLTS */
	} else {
		old = aarch64_insn_gen_branch_imm(pc, addr,
						  AARCH64_INSN_BRANCH_LINK);
	}

	new = aarch64_insn_gen_nop();

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

void arch_ftrace_update_code(int command)
{
	ftrace_modify_all_code(command);
}

int __init ftrace_dyn_arch_init(void)
{
	return 0;
}
#endif /* CONFIG_DYNAMIC_FTRACE */

#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.
 *
 * Note that @frame_pointer is used only for sanity check later.
 */
void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
			   unsigned long frame_pointer)
{
	unsigned long return_hooker = (unsigned long)&return_to_handler;
	unsigned long old;
	struct ftrace_graph_ent trace;
	int err;

	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;

	trace.func = self_addr;
	trace.depth = current->curr_ret_stack + 1;

	/* Only trace if the calling function expects to */
	if (!ftrace_graph_entry(&trace))
		return;

	err = ftrace_push_return_trace(old, self_addr, &trace.depth,
				       frame_pointer, NULL);
	if (err == -EBUSY)
		return;
	else
		*parent = return_hooker;
}

#ifdef CONFIG_DYNAMIC_FTRACE
/*
 * 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 */
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */