aboutsummaryrefslogtreecommitdiff
path: root/kernel/livepatch/patch.c
blob: 4c4f5a776d80807a25175f768074ca00ca6fa9d2 (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
// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * patch.c - livepatch patching functions
 *
 * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
 * Copyright (C) 2014 SUSE
 * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/livepatch.h>
#include <linux/list.h>
#include <linux/ftrace.h>
#include <linux/rculist.h>
#include <linux/slab.h>
#include <linux/bug.h>
#include <linux/printk.h>
#include "core.h"
#include "patch.h"
#include "transition.h"

static LIST_HEAD(klp_ops);

struct klp_ops *klp_find_ops(void *old_func)
{
	struct klp_ops *ops;
	struct klp_func *func;

	list_for_each_entry(ops, &klp_ops, node) {
		func = list_first_entry(&ops->func_stack, struct klp_func,
					stack_node);
		if (func->old_func == old_func)
			return ops;
	}

	return NULL;
}

static void notrace klp_ftrace_handler(unsigned long ip,
				       unsigned long parent_ip,
				       struct ftrace_ops *fops,
				       struct ftrace_regs *fregs)
{
	struct klp_ops *ops;
	struct klp_func *func;
	int patch_state;
	int bit;

	ops = container_of(fops, struct klp_ops, fops);

	/*
	 * The ftrace_test_recursion_trylock() will disable preemption,
	 * which is required for the variant of synchronize_rcu() that is
	 * used to allow patching functions where RCU is not watching.
	 * See klp_synchronize_transition() for more details.
	 */
	bit = ftrace_test_recursion_trylock(ip, parent_ip);
	if (WARN_ON_ONCE(bit < 0))
		return;

	func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
				      stack_node);

	/*
	 * func should never be NULL because preemption should be disabled here
	 * and unregister_ftrace_function() does the equivalent of a
	 * synchronize_rcu() before the func_stack removal.
	 */
	if (WARN_ON_ONCE(!func))
		goto unlock;

	/*
	 * In the enable path, enforce the order of the ops->func_stack and
	 * func->transition reads.  The corresponding write barrier is in
	 * __klp_enable_patch().
	 *
	 * (Note that this barrier technically isn't needed in the disable
	 * path.  In the rare case where klp_update_patch_state() runs before
	 * this handler, its TIF_PATCH_PENDING read and this func->transition
	 * read need to be ordered.  But klp_update_patch_state() already
	 * enforces that.)
	 */
	smp_rmb();

	if (unlikely(func->transition)) {

		/*
		 * Enforce the order of the func->transition and
		 * current->patch_state reads.  Otherwise we could read an
		 * out-of-date task state and pick the wrong function.  The
		 * corresponding write barrier is in klp_init_transition().
		 */
		smp_rmb();

		patch_state = current->patch_state;

		WARN_ON_ONCE(patch_state == KLP_UNDEFINED);

		if (patch_state == KLP_UNPATCHED) {
			/*
			 * Use the previously patched version of the function.
			 * If no previous patches exist, continue with the
			 * original function.
			 */
			func = list_entry_rcu(func->stack_node.next,
					      struct klp_func, stack_node);

			if (&func->stack_node == &ops->func_stack)
				goto unlock;
		}
	}

	/*
	 * NOPs are used to replace existing patches with original code.
	 * Do nothing! Setting pc would cause an infinite loop.
	 */
	if (func->nop)
		goto unlock;

	ftrace_instruction_pointer_set(fregs, (unsigned long)func->new_func);

unlock:
	ftrace_test_recursion_unlock(bit);
}

static void klp_unpatch_func(struct klp_func *func)
{
	struct klp_ops *ops;

	if (WARN_ON(!func->patched))
		return;
	if (WARN_ON(!func->old_func))
		return;

	ops = klp_find_ops(func->old_func);
	if (WARN_ON(!ops))
		return;

	if (list_is_singular(&ops->func_stack)) {
		unsigned long ftrace_loc;

		ftrace_loc = ftrace_location((unsigned long)func->old_func);
		if (WARN_ON(!ftrace_loc))
			return;

		WARN_ON(unregister_ftrace_function(&ops->fops));
		WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0));

		list_del_rcu(&func->stack_node);
		list_del(&ops->node);
		kfree(ops);
	} else {
		list_del_rcu(&func->stack_node);
	}

	func->patched = false;
}

static int klp_patch_func(struct klp_func *func)
{
	struct klp_ops *ops;
	int ret;

	if (WARN_ON(!func->old_func))
		return -EINVAL;

	if (WARN_ON(func->patched))
		return -EINVAL;

	ops = klp_find_ops(func->old_func);
	if (!ops) {
		unsigned long ftrace_loc;

		ftrace_loc = ftrace_location((unsigned long)func->old_func);
		if (!ftrace_loc) {
			pr_err("failed to find location for function '%s'\n",
				func->old_name);
			return -EINVAL;
		}

		ops = kzalloc(sizeof(*ops), GFP_KERNEL);
		if (!ops)
			return -ENOMEM;

		ops->fops.func = klp_ftrace_handler;
		ops->fops.flags = FTRACE_OPS_FL_DYNAMIC |
#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
				  FTRACE_OPS_FL_SAVE_REGS |
#endif
				  FTRACE_OPS_FL_IPMODIFY |
				  FTRACE_OPS_FL_PERMANENT;

		list_add(&ops->node, &klp_ops);

		INIT_LIST_HEAD(&ops->func_stack);
		list_add_rcu(&func->stack_node, &ops->func_stack);

		ret = ftrace_set_filter_ip(&ops->fops, ftrace_loc, 0, 0);
		if (ret) {
			pr_err("failed to set ftrace filter for function '%s' (%d)\n",
			       func->old_name, ret);
			goto err;
		}

		ret = register_ftrace_function(&ops->fops);
		if (ret) {
			pr_err("failed to register ftrace handler for function '%s' (%d)\n",
			       func->old_name, ret);
			ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0);
			goto err;
		}


	} else {
		list_add_rcu(&func->stack_node, &ops->func_stack);
	}

	func->patched = true;

	return 0;

err:
	list_del_rcu(&func->stack_node);
	list_del(&ops->node);
	kfree(ops);
	return ret;
}

static void __klp_unpatch_object(struct klp_object *obj, bool nops_only)
{
	struct klp_func *func;

	klp_for_each_func(obj, func) {
		if (nops_only && !func->nop)
			continue;

		if (func->patched)
			klp_unpatch_func(func);
	}

	if (obj->dynamic || !nops_only)
		obj->patched = false;
}


void klp_unpatch_object(struct klp_object *obj)
{
	__klp_unpatch_object(obj, false);
}

int klp_patch_object(struct klp_object *obj)
{
	struct klp_func *func;
	int ret;

	if (WARN_ON(obj->patched))
		return -EINVAL;

	klp_for_each_func(obj, func) {
		ret = klp_patch_func(func);
		if (ret) {
			klp_unpatch_object(obj);
			return ret;
		}
	}
	obj->patched = true;

	return 0;
}

static void __klp_unpatch_objects(struct klp_patch *patch, bool nops_only)
{
	struct klp_object *obj;

	klp_for_each_object(patch, obj)
		if (obj->patched)
			__klp_unpatch_object(obj, nops_only);
}

void klp_unpatch_objects(struct klp_patch *patch)
{
	__klp_unpatch_objects(patch, false);
}

void klp_unpatch_objects_dynamic(struct klp_patch *patch)
{
	__klp_unpatch_objects(patch, true);
}