init.c

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