xref: /openbmc/linux/mm/kmsan/hooks.c (revision 236bdb88)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * KMSAN hooks for kernel subsystems.
4  *
5  * These functions handle creation of KMSAN metadata for memory allocations.
6  *
7  * Copyright (C) 2018-2022 Google LLC
8  * Author: Alexander Potapenko <glider@google.com>
9  *
10  */
11 
12 #include <linux/cacheflush.h>
13 #include <linux/dma-direction.h>
14 #include <linux/gfp.h>
15 #include <linux/kmsan.h>
16 #include <linux/mm.h>
17 #include <linux/mm_types.h>
18 #include <linux/scatterlist.h>
19 #include <linux/slab.h>
20 #include <linux/uaccess.h>
21 #include <linux/usb.h>
22 
23 #include "../internal.h"
24 #include "../slab.h"
25 #include "kmsan.h"
26 
27 /*
28  * Instrumented functions shouldn't be called under
29  * kmsan_enter_runtime()/kmsan_leave_runtime(), because this will lead to
30  * skipping effects of functions like memset() inside instrumented code.
31  */
32 
33 void kmsan_task_create(struct task_struct *task)
34 {
35 	kmsan_enter_runtime();
36 	kmsan_internal_task_create(task);
37 	kmsan_leave_runtime();
38 }
39 
40 void kmsan_task_exit(struct task_struct *task)
41 {
42 	struct kmsan_ctx *ctx = &task->kmsan_ctx;
43 
44 	if (!kmsan_enabled || kmsan_in_runtime())
45 		return;
46 
47 	ctx->allow_reporting = false;
48 }
49 
50 void kmsan_slab_alloc(struct kmem_cache *s, void *object, gfp_t flags)
51 {
52 	if (unlikely(object == NULL))
53 		return;
54 	if (!kmsan_enabled || kmsan_in_runtime())
55 		return;
56 	/*
57 	 * There's a ctor or this is an RCU cache - do nothing. The memory
58 	 * status hasn't changed since last use.
59 	 */
60 	if (s->ctor || (s->flags & SLAB_TYPESAFE_BY_RCU))
61 		return;
62 
63 	kmsan_enter_runtime();
64 	if (flags & __GFP_ZERO)
65 		kmsan_internal_unpoison_memory(object, s->object_size,
66 					       KMSAN_POISON_CHECK);
67 	else
68 		kmsan_internal_poison_memory(object, s->object_size, flags,
69 					     KMSAN_POISON_CHECK);
70 	kmsan_leave_runtime();
71 }
72 
73 void kmsan_slab_free(struct kmem_cache *s, void *object)
74 {
75 	if (!kmsan_enabled || kmsan_in_runtime())
76 		return;
77 
78 	/* RCU slabs could be legally used after free within the RCU period */
79 	if (unlikely(s->flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)))
80 		return;
81 	/*
82 	 * If there's a constructor, freed memory must remain in the same state
83 	 * until the next allocation. We cannot save its state to detect
84 	 * use-after-free bugs, instead we just keep it unpoisoned.
85 	 */
86 	if (s->ctor)
87 		return;
88 	kmsan_enter_runtime();
89 	kmsan_internal_poison_memory(object, s->object_size, GFP_KERNEL,
90 				     KMSAN_POISON_CHECK | KMSAN_POISON_FREE);
91 	kmsan_leave_runtime();
92 }
93 
94 void kmsan_kmalloc_large(const void *ptr, size_t size, gfp_t flags)
95 {
96 	if (unlikely(ptr == NULL))
97 		return;
98 	if (!kmsan_enabled || kmsan_in_runtime())
99 		return;
100 	kmsan_enter_runtime();
101 	if (flags & __GFP_ZERO)
102 		kmsan_internal_unpoison_memory((void *)ptr, size,
103 					       /*checked*/ true);
104 	else
105 		kmsan_internal_poison_memory((void *)ptr, size, flags,
106 					     KMSAN_POISON_CHECK);
107 	kmsan_leave_runtime();
108 }
109 
110 void kmsan_kfree_large(const void *ptr)
111 {
112 	struct page *page;
113 
114 	if (!kmsan_enabled || kmsan_in_runtime())
115 		return;
116 	kmsan_enter_runtime();
117 	page = virt_to_head_page((void *)ptr);
118 	KMSAN_WARN_ON(ptr != page_address(page));
119 	kmsan_internal_poison_memory((void *)ptr,
120 				     PAGE_SIZE << compound_order(page),
121 				     GFP_KERNEL,
122 				     KMSAN_POISON_CHECK | KMSAN_POISON_FREE);
123 	kmsan_leave_runtime();
124 }
125 
126 static unsigned long vmalloc_shadow(unsigned long addr)
127 {
128 	return (unsigned long)kmsan_get_metadata((void *)addr,
129 						 KMSAN_META_SHADOW);
130 }
131 
132 static unsigned long vmalloc_origin(unsigned long addr)
133 {
134 	return (unsigned long)kmsan_get_metadata((void *)addr,
135 						 KMSAN_META_ORIGIN);
136 }
137 
138 void kmsan_vunmap_range_noflush(unsigned long start, unsigned long end)
139 {
140 	__vunmap_range_noflush(vmalloc_shadow(start), vmalloc_shadow(end));
141 	__vunmap_range_noflush(vmalloc_origin(start), vmalloc_origin(end));
142 	flush_cache_vmap(vmalloc_shadow(start), vmalloc_shadow(end));
143 	flush_cache_vmap(vmalloc_origin(start), vmalloc_origin(end));
144 }
145 
146 /*
147  * This function creates new shadow/origin pages for the physical pages mapped
148  * into the virtual memory. If those physical pages already had shadow/origin,
149  * those are ignored.
150  */
151 void kmsan_ioremap_page_range(unsigned long start, unsigned long end,
152 			      phys_addr_t phys_addr, pgprot_t prot,
153 			      unsigned int page_shift)
154 {
155 	gfp_t gfp_mask = GFP_KERNEL | __GFP_ZERO;
156 	struct page *shadow, *origin;
157 	unsigned long off = 0;
158 	int nr;
159 
160 	if (!kmsan_enabled || kmsan_in_runtime())
161 		return;
162 
163 	nr = (end - start) / PAGE_SIZE;
164 	kmsan_enter_runtime();
165 	for (int i = 0; i < nr; i++, off += PAGE_SIZE) {
166 		shadow = alloc_pages(gfp_mask, 1);
167 		origin = alloc_pages(gfp_mask, 1);
168 		__vmap_pages_range_noflush(
169 			vmalloc_shadow(start + off),
170 			vmalloc_shadow(start + off + PAGE_SIZE), prot, &shadow,
171 			PAGE_SHIFT);
172 		__vmap_pages_range_noflush(
173 			vmalloc_origin(start + off),
174 			vmalloc_origin(start + off + PAGE_SIZE), prot, &origin,
175 			PAGE_SHIFT);
176 	}
177 	flush_cache_vmap(vmalloc_shadow(start), vmalloc_shadow(end));
178 	flush_cache_vmap(vmalloc_origin(start), vmalloc_origin(end));
179 	kmsan_leave_runtime();
180 }
181 
182 void kmsan_iounmap_page_range(unsigned long start, unsigned long end)
183 {
184 	unsigned long v_shadow, v_origin;
185 	struct page *shadow, *origin;
186 	int nr;
187 
188 	if (!kmsan_enabled || kmsan_in_runtime())
189 		return;
190 
191 	nr = (end - start) / PAGE_SIZE;
192 	kmsan_enter_runtime();
193 	v_shadow = (unsigned long)vmalloc_shadow(start);
194 	v_origin = (unsigned long)vmalloc_origin(start);
195 	for (int i = 0; i < nr;
196 	     i++, v_shadow += PAGE_SIZE, v_origin += PAGE_SIZE) {
197 		shadow = kmsan_vmalloc_to_page_or_null((void *)v_shadow);
198 		origin = kmsan_vmalloc_to_page_or_null((void *)v_origin);
199 		__vunmap_range_noflush(v_shadow, vmalloc_shadow(end));
200 		__vunmap_range_noflush(v_origin, vmalloc_origin(end));
201 		if (shadow)
202 			__free_pages(shadow, 1);
203 		if (origin)
204 			__free_pages(origin, 1);
205 	}
206 	flush_cache_vmap(vmalloc_shadow(start), vmalloc_shadow(end));
207 	flush_cache_vmap(vmalloc_origin(start), vmalloc_origin(end));
208 	kmsan_leave_runtime();
209 }
210 
211 void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy,
212 			size_t left)
213 {
214 	unsigned long ua_flags;
215 
216 	if (!kmsan_enabled || kmsan_in_runtime())
217 		return;
218 	/*
219 	 * At this point we've copied the memory already. It's hard to check it
220 	 * before copying, as the size of actually copied buffer is unknown.
221 	 */
222 
223 	/* copy_to_user() may copy zero bytes. No need to check. */
224 	if (!to_copy)
225 		return;
226 	/* Or maybe copy_to_user() failed to copy anything. */
227 	if (to_copy <= left)
228 		return;
229 
230 	ua_flags = user_access_save();
231 	if ((u64)to < TASK_SIZE) {
232 		/* This is a user memory access, check it. */
233 		kmsan_internal_check_memory((void *)from, to_copy - left, to,
234 					    REASON_COPY_TO_USER);
235 	} else {
236 		/* Otherwise this is a kernel memory access. This happens when a
237 		 * compat syscall passes an argument allocated on the kernel
238 		 * stack to a real syscall.
239 		 * Don't check anything, just copy the shadow of the copied
240 		 * bytes.
241 		 */
242 		kmsan_internal_memmove_metadata((void *)to, (void *)from,
243 						to_copy - left);
244 	}
245 	user_access_restore(ua_flags);
246 }
247 EXPORT_SYMBOL(kmsan_copy_to_user);
248 
249 /* Helper function to check an URB. */
250 void kmsan_handle_urb(const struct urb *urb, bool is_out)
251 {
252 	if (!urb)
253 		return;
254 	if (is_out)
255 		kmsan_internal_check_memory(urb->transfer_buffer,
256 					    urb->transfer_buffer_length,
257 					    /*user_addr*/ 0, REASON_SUBMIT_URB);
258 	else
259 		kmsan_internal_unpoison_memory(urb->transfer_buffer,
260 					       urb->transfer_buffer_length,
261 					       /*checked*/ false);
262 }
263 EXPORT_SYMBOL_GPL(kmsan_handle_urb);
264 
265 static void kmsan_handle_dma_page(const void *addr, size_t size,
266 				  enum dma_data_direction dir)
267 {
268 	switch (dir) {
269 	case DMA_BIDIRECTIONAL:
270 		kmsan_internal_check_memory((void *)addr, size, /*user_addr*/ 0,
271 					    REASON_ANY);
272 		kmsan_internal_unpoison_memory((void *)addr, size,
273 					       /*checked*/ false);
274 		break;
275 	case DMA_TO_DEVICE:
276 		kmsan_internal_check_memory((void *)addr, size, /*user_addr*/ 0,
277 					    REASON_ANY);
278 		break;
279 	case DMA_FROM_DEVICE:
280 		kmsan_internal_unpoison_memory((void *)addr, size,
281 					       /*checked*/ false);
282 		break;
283 	case DMA_NONE:
284 		break;
285 	}
286 }
287 
288 /* Helper function to handle DMA data transfers. */
289 void kmsan_handle_dma(struct page *page, size_t offset, size_t size,
290 		      enum dma_data_direction dir)
291 {
292 	u64 page_offset, to_go, addr;
293 
294 	if (PageHighMem(page))
295 		return;
296 	addr = (u64)page_address(page) + offset;
297 	/*
298 	 * The kernel may occasionally give us adjacent DMA pages not belonging
299 	 * to the same allocation. Process them separately to avoid triggering
300 	 * internal KMSAN checks.
301 	 */
302 	while (size > 0) {
303 		page_offset = addr % PAGE_SIZE;
304 		to_go = min(PAGE_SIZE - page_offset, (u64)size);
305 		kmsan_handle_dma_page((void *)addr, to_go, dir);
306 		addr += to_go;
307 		size -= to_go;
308 	}
309 }
310 
311 void kmsan_handle_dma_sg(struct scatterlist *sg, int nents,
312 			 enum dma_data_direction dir)
313 {
314 	struct scatterlist *item;
315 	int i;
316 
317 	for_each_sg(sg, item, nents, i)
318 		kmsan_handle_dma(sg_page(item), item->offset, item->length,
319 				 dir);
320 }
321 
322 /* Functions from kmsan-checks.h follow. */
323 void kmsan_poison_memory(const void *address, size_t size, gfp_t flags)
324 {
325 	if (!kmsan_enabled || kmsan_in_runtime())
326 		return;
327 	kmsan_enter_runtime();
328 	/* The users may want to poison/unpoison random memory. */
329 	kmsan_internal_poison_memory((void *)address, size, flags,
330 				     KMSAN_POISON_NOCHECK);
331 	kmsan_leave_runtime();
332 }
333 EXPORT_SYMBOL(kmsan_poison_memory);
334 
335 void kmsan_unpoison_memory(const void *address, size_t size)
336 {
337 	unsigned long ua_flags;
338 
339 	if (!kmsan_enabled || kmsan_in_runtime())
340 		return;
341 
342 	ua_flags = user_access_save();
343 	kmsan_enter_runtime();
344 	/* The users may want to poison/unpoison random memory. */
345 	kmsan_internal_unpoison_memory((void *)address, size,
346 				       KMSAN_POISON_NOCHECK);
347 	kmsan_leave_runtime();
348 	user_access_restore(ua_flags);
349 }
350 EXPORT_SYMBOL(kmsan_unpoison_memory);
351 
352 /*
353  * Version of kmsan_unpoison_memory() that can be called from within the KMSAN
354  * runtime.
355  *
356  * Non-instrumented IRQ entry functions receive struct pt_regs from assembly
357  * code. Those regs need to be unpoisoned, otherwise using them will result in
358  * false positives.
359  * Using kmsan_unpoison_memory() is not an option in entry code, because the
360  * return value of in_task() is inconsistent - as a result, certain calls to
361  * kmsan_unpoison_memory() are ignored. kmsan_unpoison_entry_regs() ensures that
362  * the registers are unpoisoned even if kmsan_in_runtime() is true in the early
363  * entry code.
364  */
365 void kmsan_unpoison_entry_regs(const struct pt_regs *regs)
366 {
367 	unsigned long ua_flags;
368 
369 	if (!kmsan_enabled)
370 		return;
371 
372 	ua_flags = user_access_save();
373 	kmsan_internal_unpoison_memory((void *)regs, sizeof(*regs),
374 				       KMSAN_POISON_NOCHECK);
375 	user_access_restore(ua_flags);
376 }
377 
378 void kmsan_check_memory(const void *addr, size_t size)
379 {
380 	if (!kmsan_enabled)
381 		return;
382 	return kmsan_internal_check_memory((void *)addr, size, /*user_addr*/ 0,
383 					   REASON_ANY);
384 }
385 EXPORT_SYMBOL(kmsan_check_memory);
386