xref: /kernel/linux/linux-6.6/mm/kmsan/shadow.c (revision 62306a36) 
1// SPDX-License-Identifier: GPL-2.0
2/*
3 * KMSAN shadow implementation.
4 *
5 * Copyright (C) 2017-2022 Google LLC
6 * Author: Alexander Potapenko <glider@google.com>
7 *
8 */
9
10#include <asm/kmsan.h>
11#include <asm/tlbflush.h>
12#include <linux/cacheflush.h>
13#include <linux/memblock.h>
14#include <linux/mm_types.h>
15#include <linux/slab.h>
16#include <linux/smp.h>
17#include <linux/stddef.h>
18
19#include "../internal.h"
20#include "kmsan.h"
21
22#define shadow_page_for(page) ((page)->kmsan_shadow)
23
24#define origin_page_for(page) ((page)->kmsan_origin)
25
26static void *shadow_ptr_for(struct page *page)
27{
28	return page_address(shadow_page_for(page));
29}
30
31static void *origin_ptr_for(struct page *page)
32{
33	return page_address(origin_page_for(page));
34}
35
36static bool page_has_metadata(struct page *page)
37{
38	return shadow_page_for(page) && origin_page_for(page);
39}
40
41static void set_no_shadow_origin_page(struct page *page)
42{
43	shadow_page_for(page) = NULL;
44	origin_page_for(page) = NULL;
45}
46
47/*
48 * Dummy load and store pages to be used when the real metadata is unavailable.
49 * There are separate pages for loads and stores, so that every load returns a
50 * zero, and every store doesn't affect other loads.
51 */
52static char dummy_load_page[PAGE_SIZE] __aligned(PAGE_SIZE);
53static char dummy_store_page[PAGE_SIZE] __aligned(PAGE_SIZE);
54
55static unsigned long vmalloc_meta(void *addr, bool is_origin)
56{
57	unsigned long addr64 = (unsigned long)addr, off;
58
59	KMSAN_WARN_ON(is_origin && !IS_ALIGNED(addr64, KMSAN_ORIGIN_SIZE));
60	if (kmsan_internal_is_vmalloc_addr(addr)) {
61		off = addr64 - VMALLOC_START;
62		return off + (is_origin ? KMSAN_VMALLOC_ORIGIN_START :
63					  KMSAN_VMALLOC_SHADOW_START);
64	}
65	if (kmsan_internal_is_module_addr(addr)) {
66		off = addr64 - MODULES_VADDR;
67		return off + (is_origin ? KMSAN_MODULES_ORIGIN_START :
68					  KMSAN_MODULES_SHADOW_START);
69	}
70	return 0;
71}
72
73static struct page *virt_to_page_or_null(void *vaddr)
74{
75	if (kmsan_virt_addr_valid(vaddr))
76		return virt_to_page(vaddr);
77	else
78		return NULL;
79}
80
81struct shadow_origin_ptr kmsan_get_shadow_origin_ptr(void *address, u64 size,
82						     bool store)
83{
84	struct shadow_origin_ptr ret;
85	void *shadow;
86
87	/*
88	 * Even if we redirect this memory access to the dummy page, it will
89	 * go out of bounds.
90	 */
91	KMSAN_WARN_ON(size > PAGE_SIZE);
92
93	if (!kmsan_enabled)
94		goto return_dummy;
95
96	KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(address, size));
97	shadow = kmsan_get_metadata(address, KMSAN_META_SHADOW);
98	if (!shadow)
99		goto return_dummy;
100
101	ret.shadow = shadow;
102	ret.origin = kmsan_get_metadata(address, KMSAN_META_ORIGIN);
103	return ret;
104
105return_dummy:
106	if (store) {
107		/* Ignore this store. */
108		ret.shadow = dummy_store_page;
109		ret.origin = dummy_store_page;
110	} else {
111		/* This load will return zero. */
112		ret.shadow = dummy_load_page;
113		ret.origin = dummy_load_page;
114	}
115	return ret;
116}
117
118/*
119 * Obtain the shadow or origin pointer for the given address, or NULL if there's
120 * none. The caller must check the return value for being non-NULL if needed.
121 * The return value of this function should not depend on whether we're in the
122 * runtime or not.
123 */
124void *kmsan_get_metadata(void *address, bool is_origin)
125{
126	u64 addr = (u64)address, pad, off;
127	struct page *page;
128	void *ret;
129
130	if (is_origin && !IS_ALIGNED(addr, KMSAN_ORIGIN_SIZE)) {
131		pad = addr % KMSAN_ORIGIN_SIZE;
132		addr -= pad;
133	}
134	address = (void *)addr;
135	if (kmsan_internal_is_vmalloc_addr(address) ||
136	    kmsan_internal_is_module_addr(address))
137		return (void *)vmalloc_meta(address, is_origin);
138
139	ret = arch_kmsan_get_meta_or_null(address, is_origin);
140	if (ret)
141		return ret;
142
143	page = virt_to_page_or_null(address);
144	if (!page)
145		return NULL;
146	if (!page_has_metadata(page))
147		return NULL;
148	off = offset_in_page(addr);
149
150	return (is_origin ? origin_ptr_for(page) : shadow_ptr_for(page)) + off;
151}
152
153void kmsan_copy_page_meta(struct page *dst, struct page *src)
154{
155	if (!kmsan_enabled || kmsan_in_runtime())
156		return;
157	if (!dst || !page_has_metadata(dst))
158		return;
159	if (!src || !page_has_metadata(src)) {
160		kmsan_internal_unpoison_memory(page_address(dst), PAGE_SIZE,
161					       /*checked*/ false);
162		return;
163	}
164
165	kmsan_enter_runtime();
166	__memcpy(shadow_ptr_for(dst), shadow_ptr_for(src), PAGE_SIZE);
167	__memcpy(origin_ptr_for(dst), origin_ptr_for(src), PAGE_SIZE);
168	kmsan_leave_runtime();
169}
170EXPORT_SYMBOL(kmsan_copy_page_meta);
171
172void kmsan_alloc_page(struct page *page, unsigned int order, gfp_t flags)
173{
174	bool initialized = (flags & __GFP_ZERO) || !kmsan_enabled;
175	struct page *shadow, *origin;
176	depot_stack_handle_t handle;
177	int pages = 1 << order;
178
179	if (!page)
180		return;
181
182	shadow = shadow_page_for(page);
183	origin = origin_page_for(page);
184
185	if (initialized) {
186		__memset(page_address(shadow), 0, PAGE_SIZE * pages);
187		__memset(page_address(origin), 0, PAGE_SIZE * pages);
188		return;
189	}
190
191	/* Zero pages allocated by the runtime should also be initialized. */
192	if (kmsan_in_runtime())
193		return;
194
195	__memset(page_address(shadow), -1, PAGE_SIZE * pages);
196	kmsan_enter_runtime();
197	handle = kmsan_save_stack_with_flags(flags, /*extra_bits*/ 0);
198	kmsan_leave_runtime();
199	/*
200	 * Addresses are page-aligned, pages are contiguous, so it's ok
201	 * to just fill the origin pages with @handle.
202	 */
203	for (int i = 0; i < PAGE_SIZE * pages / sizeof(handle); i++)
204		((depot_stack_handle_t *)page_address(origin))[i] = handle;
205}
206
207void kmsan_free_page(struct page *page, unsigned int order)
208{
209	if (!kmsan_enabled || kmsan_in_runtime())
210		return;
211	kmsan_enter_runtime();
212	kmsan_internal_poison_memory(page_address(page),
213				     page_size(page),
214				     GFP_KERNEL,
215				     KMSAN_POISON_CHECK | KMSAN_POISON_FREE);
216	kmsan_leave_runtime();
217}
218
219int kmsan_vmap_pages_range_noflush(unsigned long start, unsigned long end,
220				   pgprot_t prot, struct page **pages,
221				   unsigned int page_shift)
222{
223	unsigned long shadow_start, origin_start, shadow_end, origin_end;
224	struct page **s_pages, **o_pages;
225	int nr, mapped, err = 0;
226
227	if (!kmsan_enabled)
228		return 0;
229
230	shadow_start = vmalloc_meta((void *)start, KMSAN_META_SHADOW);
231	shadow_end = vmalloc_meta((void *)end, KMSAN_META_SHADOW);
232	if (!shadow_start)
233		return 0;
234
235	nr = (end - start) / PAGE_SIZE;
236	s_pages = kcalloc(nr, sizeof(*s_pages), GFP_KERNEL);
237	o_pages = kcalloc(nr, sizeof(*o_pages), GFP_KERNEL);
238	if (!s_pages || !o_pages) {
239		err = -ENOMEM;
240		goto ret;
241	}
242	for (int i = 0; i < nr; i++) {
243		s_pages[i] = shadow_page_for(pages[i]);
244		o_pages[i] = origin_page_for(pages[i]);
245	}
246	prot = __pgprot(pgprot_val(prot) | _PAGE_NX);
247	prot = PAGE_KERNEL;
248
249	origin_start = vmalloc_meta((void *)start, KMSAN_META_ORIGIN);
250	origin_end = vmalloc_meta((void *)end, KMSAN_META_ORIGIN);
251	kmsan_enter_runtime();
252	mapped = __vmap_pages_range_noflush(shadow_start, shadow_end, prot,
253					    s_pages, page_shift);
254	if (mapped) {
255		err = mapped;
256		goto ret;
257	}
258	mapped = __vmap_pages_range_noflush(origin_start, origin_end, prot,
259					    o_pages, page_shift);
260	if (mapped) {
261		err = mapped;
262		goto ret;
263	}
264	kmsan_leave_runtime();
265	flush_tlb_kernel_range(shadow_start, shadow_end);
266	flush_tlb_kernel_range(origin_start, origin_end);
267	flush_cache_vmap(shadow_start, shadow_end);
268	flush_cache_vmap(origin_start, origin_end);
269
270ret:
271	kfree(s_pages);
272	kfree(o_pages);
273	return err;
274}
275
276/* Allocate metadata for pages allocated at boot time. */
277void __init kmsan_init_alloc_meta_for_range(void *start, void *end)
278{
279	struct page *shadow_p, *origin_p;
280	void *shadow, *origin;
281	struct page *page;
282	u64 size;
283
284	start = (void *)PAGE_ALIGN_DOWN((u64)start);
285	size = PAGE_ALIGN((u64)end - (u64)start);
286	shadow = memblock_alloc(size, PAGE_SIZE);
287	origin = memblock_alloc(size, PAGE_SIZE);
288	for (u64 addr = 0; addr < size; addr += PAGE_SIZE) {
289		page = virt_to_page_or_null((char *)start + addr);
290		shadow_p = virt_to_page_or_null((char *)shadow + addr);
291		set_no_shadow_origin_page(shadow_p);
292		shadow_page_for(page) = shadow_p;
293		origin_p = virt_to_page_or_null((char *)origin + addr);
294		set_no_shadow_origin_page(origin_p);
295		origin_page_for(page) = origin_p;
296	}
297}
298
299void kmsan_setup_meta(struct page *page, struct page *shadow,
300		      struct page *origin, int order)
301{
302	for (int i = 0; i < (1 << order); i++) {
303		set_no_shadow_origin_page(&shadow[i]);
304		set_no_shadow_origin_page(&origin[i]);
305		shadow_page_for(&page[i]) = &shadow[i];
306		origin_page_for(&page[i]) = &origin[i];
307	}
308}
309