xref: /linux/mm/kmsan/init.c (revision a1ff5a7d78a036d6c2178ee5acd6ba4946243800)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * KMSAN initialization routines.
4  *
5  * Copyright (C) 2017-2021 Google LLC
6  * Author: Alexander Potapenko <glider@google.com>
7  *
8  */
9 
10 #include "kmsan.h"
11 
12 #include <asm/sections.h>
13 #include <linux/mm.h>
14 #include <linux/memblock.h>
15 
16 #include "../internal.h"
17 
18 #define NUM_FUTURE_RANGES 128
19 struct start_end_pair {
20 	u64 start, end;
21 };
22 
23 static struct start_end_pair start_end_pairs[NUM_FUTURE_RANGES] __initdata;
24 static int future_index __initdata;
25 
26 /*
27  * Record a range of memory for which the metadata pages will be created once
28  * the page allocator becomes available.
29  */
kmsan_record_future_shadow_range(void * start,void * end)30 static void __init kmsan_record_future_shadow_range(void *start, void *end)
31 {
32 	u64 nstart = (u64)start, nend = (u64)end, cstart, cend;
33 	bool merged = false;
34 
35 	KMSAN_WARN_ON(future_index == NUM_FUTURE_RANGES);
36 	KMSAN_WARN_ON((nstart >= nend) ||
37 		      /* Virtual address 0 is valid on s390. */
38 		      (!IS_ENABLED(CONFIG_S390) && !nstart) ||
39 		      !nend);
40 	nstart = ALIGN_DOWN(nstart, PAGE_SIZE);
41 	nend = ALIGN(nend, PAGE_SIZE);
42 
43 	/*
44 	 * Scan the existing ranges to see if any of them overlaps with
45 	 * [start, end). In that case, merge the two ranges instead of
46 	 * creating a new one.
47 	 * The number of ranges is less than 20, so there is no need to organize
48 	 * them into a more intelligent data structure.
49 	 */
50 	for (int i = 0; i < future_index; i++) {
51 		cstart = start_end_pairs[i].start;
52 		cend = start_end_pairs[i].end;
53 		if ((cstart < nstart && cend < nstart) ||
54 		    (cstart > nend && cend > nend))
55 			/* ranges are disjoint - do not merge */
56 			continue;
57 		start_end_pairs[i].start = min(nstart, cstart);
58 		start_end_pairs[i].end = max(nend, cend);
59 		merged = true;
60 		break;
61 	}
62 	if (merged)
63 		return;
64 	start_end_pairs[future_index].start = nstart;
65 	start_end_pairs[future_index].end = nend;
66 	future_index++;
67 }
68 
69 /*
70  * Initialize the shadow for existing mappings during kernel initialization.
71  * These include kernel text/data sections, NODE_DATA and future ranges
72  * registered while creating other data (e.g. percpu).
73  *
74  * Allocations via memblock can be only done before slab is initialized.
75  */
kmsan_init_shadow(void)76 void __init kmsan_init_shadow(void)
77 {
78 	const size_t nd_size = sizeof(pg_data_t);
79 	phys_addr_t p_start, p_end;
80 	u64 loop;
81 	int nid;
82 
83 	for_each_reserved_mem_range(loop, &p_start, &p_end)
84 		kmsan_record_future_shadow_range(phys_to_virt(p_start),
85 						 phys_to_virt(p_end));
86 	/* Allocate shadow for .data */
87 	kmsan_record_future_shadow_range(_sdata, _edata);
88 
89 	for_each_online_node(nid)
90 		kmsan_record_future_shadow_range(
91 			NODE_DATA(nid), (char *)NODE_DATA(nid) + nd_size);
92 
93 	for (int i = 0; i < future_index; i++)
94 		kmsan_init_alloc_meta_for_range(
95 			(void *)start_end_pairs[i].start,
96 			(void *)start_end_pairs[i].end);
97 }
98 
99 struct metadata_page_pair {
100 	struct page *shadow, *origin;
101 };
102 static struct metadata_page_pair held_back[NR_PAGE_ORDERS] __initdata;
103 
104 /*
105  * Eager metadata allocation. When the memblock allocator is freeing pages to
106  * pagealloc, we use 2/3 of them as metadata for the remaining 1/3.
107  * We store the pointers to the returned blocks of pages in held_back[] grouped
108  * by their order: when kmsan_memblock_free_pages() is called for the first
109  * time with a certain order, it is reserved as a shadow block, for the second
110  * time - as an origin block. On the third time the incoming block receives its
111  * shadow and origin ranges from the previously saved shadow and origin blocks,
112  * after which held_back[order] can be used again.
113  *
114  * At the very end there may be leftover blocks in held_back[]. They are
115  * collected later by kmsan_memblock_discard().
116  */
kmsan_memblock_free_pages(struct page * page,unsigned int order)117 bool kmsan_memblock_free_pages(struct page *page, unsigned int order)
118 {
119 	struct page *shadow, *origin;
120 
121 	if (!held_back[order].shadow) {
122 		held_back[order].shadow = page;
123 		return false;
124 	}
125 	if (!held_back[order].origin) {
126 		held_back[order].origin = page;
127 		return false;
128 	}
129 	shadow = held_back[order].shadow;
130 	origin = held_back[order].origin;
131 	kmsan_setup_meta(page, shadow, origin, order);
132 
133 	held_back[order].shadow = NULL;
134 	held_back[order].origin = NULL;
135 	return true;
136 }
137 
138 #define MAX_BLOCKS 8
139 struct smallstack {
140 	struct page *items[MAX_BLOCKS];
141 	int index;
142 	int order;
143 };
144 
145 static struct smallstack collect = {
146 	.index = 0,
147 	.order = MAX_PAGE_ORDER,
148 };
149 
smallstack_push(struct smallstack * stack,struct page * pages)150 static void smallstack_push(struct smallstack *stack, struct page *pages)
151 {
152 	KMSAN_WARN_ON(stack->index == MAX_BLOCKS);
153 	stack->items[stack->index] = pages;
154 	stack->index++;
155 }
156 #undef MAX_BLOCKS
157 
smallstack_pop(struct smallstack * stack)158 static struct page *smallstack_pop(struct smallstack *stack)
159 {
160 	struct page *ret;
161 
162 	KMSAN_WARN_ON(stack->index == 0);
163 	stack->index--;
164 	ret = stack->items[stack->index];
165 	stack->items[stack->index] = NULL;
166 	return ret;
167 }
168 
do_collection(void)169 static void do_collection(void)
170 {
171 	struct page *page, *shadow, *origin;
172 
173 	while (collect.index >= 3) {
174 		page = smallstack_pop(&collect);
175 		shadow = smallstack_pop(&collect);
176 		origin = smallstack_pop(&collect);
177 		kmsan_setup_meta(page, shadow, origin, collect.order);
178 		__free_pages_core(page, collect.order, MEMINIT_EARLY);
179 	}
180 }
181 
collect_split(void)182 static void collect_split(void)
183 {
184 	struct smallstack tmp = {
185 		.order = collect.order - 1,
186 		.index = 0,
187 	};
188 	struct page *page;
189 
190 	if (!collect.order)
191 		return;
192 	while (collect.index) {
193 		page = smallstack_pop(&collect);
194 		smallstack_push(&tmp, &page[0]);
195 		smallstack_push(&tmp, &page[1 << tmp.order]);
196 	}
197 	__memcpy(&collect, &tmp, sizeof(tmp));
198 }
199 
200 /*
201  * Memblock is about to go away. Split the page blocks left over in held_back[]
202  * and return 1/3 of that memory to the system.
203  */
kmsan_memblock_discard(void)204 static void kmsan_memblock_discard(void)
205 {
206 	/*
207 	 * For each order=N:
208 	 *  - push held_back[N].shadow and .origin to @collect;
209 	 *  - while there are >= 3 elements in @collect, do garbage collection:
210 	 *    - pop 3 ranges from @collect;
211 	 *    - use two of them as shadow and origin for the third one;
212 	 *    - repeat;
213 	 *  - split each remaining element from @collect into 2 ranges of
214 	 *    order=N-1,
215 	 *  - repeat.
216 	 */
217 	collect.order = MAX_PAGE_ORDER;
218 	for (int i = MAX_PAGE_ORDER; i >= 0; i--) {
219 		if (held_back[i].shadow)
220 			smallstack_push(&collect, held_back[i].shadow);
221 		if (held_back[i].origin)
222 			smallstack_push(&collect, held_back[i].origin);
223 		held_back[i].shadow = NULL;
224 		held_back[i].origin = NULL;
225 		do_collection();
226 		collect_split();
227 	}
228 }
229 
kmsan_init_runtime(void)230 void __init kmsan_init_runtime(void)
231 {
232 	/* Assuming current is init_task */
233 	kmsan_internal_task_create(current);
234 	kmsan_memblock_discard();
235 	pr_info("Starting KernelMemorySanitizer\n");
236 	pr_info("ATTENTION: KMSAN is a debugging tool! Do not use it on production machines!\n");
237 	kmsan_enabled = true;
238 }
239