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f5509cc1 KC |
1 | /* |
2 | * This implements the various checks for CONFIG_HARDENED_USERCOPY*, | |
3 | * which are designed to protect kernel memory from needless exposure | |
4 | * and overwrite under many unintended conditions. This code is based | |
5 | * on PAX_USERCOPY, which is: | |
6 | * | |
7 | * Copyright (C) 2001-2016 PaX Team, Bradley Spengler, Open Source | |
8 | * Security Inc. | |
9 | * | |
10 | * This program is free software; you can redistribute it and/or modify | |
11 | * it under the terms of the GNU General Public License version 2 as | |
12 | * published by the Free Software Foundation. | |
13 | * | |
14 | */ | |
15 | #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt | |
16 | ||
17 | #include <linux/mm.h> | |
18 | #include <linux/slab.h> | |
5b825c3a | 19 | #include <linux/sched.h> |
f5509cc1 KC |
20 | #include <asm/sections.h> |
21 | ||
22 | enum { | |
23 | BAD_STACK = -1, | |
24 | NOT_STACK = 0, | |
25 | GOOD_FRAME, | |
26 | GOOD_STACK, | |
27 | }; | |
28 | ||
29 | /* | |
30 | * Checks if a given pointer and length is contained by the current | |
31 | * stack frame (if possible). | |
32 | * | |
33 | * Returns: | |
34 | * NOT_STACK: not at all on the stack | |
35 | * GOOD_FRAME: fully within a valid stack frame | |
36 | * GOOD_STACK: fully on the stack (when can't do frame-checking) | |
37 | * BAD_STACK: error condition (invalid stack position or bad stack frame) | |
38 | */ | |
39 | static noinline int check_stack_object(const void *obj, unsigned long len) | |
40 | { | |
41 | const void * const stack = task_stack_page(current); | |
42 | const void * const stackend = stack + THREAD_SIZE; | |
43 | int ret; | |
44 | ||
45 | /* Object is not on the stack at all. */ | |
46 | if (obj + len <= stack || stackend <= obj) | |
47 | return NOT_STACK; | |
48 | ||
49 | /* | |
50 | * Reject: object partially overlaps the stack (passing the | |
51 | * the check above means at least one end is within the stack, | |
52 | * so if this check fails, the other end is outside the stack). | |
53 | */ | |
54 | if (obj < stack || stackend < obj + len) | |
55 | return BAD_STACK; | |
56 | ||
57 | /* Check if object is safely within a valid frame. */ | |
58 | ret = arch_within_stack_frames(stack, stackend, obj, len); | |
59 | if (ret) | |
60 | return ret; | |
61 | ||
62 | return GOOD_STACK; | |
63 | } | |
64 | ||
65 | static void report_usercopy(const void *ptr, unsigned long len, | |
66 | bool to_user, const char *type) | |
67 | { | |
68 | pr_emerg("kernel memory %s attempt detected %s %p (%s) (%lu bytes)\n", | |
69 | to_user ? "exposure" : "overwrite", | |
70 | to_user ? "from" : "to", ptr, type ? : "unknown", len); | |
71 | /* | |
72 | * For greater effect, it would be nice to do do_group_exit(), | |
73 | * but BUG() actually hooks all the lock-breaking and per-arch | |
74 | * Oops code, so that is used here instead. | |
75 | */ | |
76 | BUG(); | |
77 | } | |
78 | ||
79 | /* Returns true if any portion of [ptr,ptr+n) over laps with [low,high). */ | |
80 | static bool overlaps(const void *ptr, unsigned long n, unsigned long low, | |
81 | unsigned long high) | |
82 | { | |
83 | unsigned long check_low = (uintptr_t)ptr; | |
84 | unsigned long check_high = check_low + n; | |
85 | ||
86 | /* Does not overlap if entirely above or entirely below. */ | |
94cd97af | 87 | if (check_low >= high || check_high <= low) |
f5509cc1 KC |
88 | return false; |
89 | ||
90 | return true; | |
91 | } | |
92 | ||
93 | /* Is this address range in the kernel text area? */ | |
94 | static inline const char *check_kernel_text_object(const void *ptr, | |
95 | unsigned long n) | |
96 | { | |
97 | unsigned long textlow = (unsigned long)_stext; | |
98 | unsigned long texthigh = (unsigned long)_etext; | |
99 | unsigned long textlow_linear, texthigh_linear; | |
100 | ||
101 | if (overlaps(ptr, n, textlow, texthigh)) | |
102 | return "<kernel text>"; | |
103 | ||
104 | /* | |
105 | * Some architectures have virtual memory mappings with a secondary | |
106 | * mapping of the kernel text, i.e. there is more than one virtual | |
107 | * kernel address that points to the kernel image. It is usually | |
108 | * when there is a separate linear physical memory mapping, in that | |
109 | * __pa() is not just the reverse of __va(). This can be detected | |
110 | * and checked: | |
111 | */ | |
46f6236a | 112 | textlow_linear = (unsigned long)lm_alias(textlow); |
f5509cc1 KC |
113 | /* No different mapping: we're done. */ |
114 | if (textlow_linear == textlow) | |
115 | return NULL; | |
116 | ||
117 | /* Check the secondary mapping... */ | |
46f6236a | 118 | texthigh_linear = (unsigned long)lm_alias(texthigh); |
f5509cc1 KC |
119 | if (overlaps(ptr, n, textlow_linear, texthigh_linear)) |
120 | return "<linear kernel text>"; | |
121 | ||
122 | return NULL; | |
123 | } | |
124 | ||
125 | static inline const char *check_bogus_address(const void *ptr, unsigned long n) | |
126 | { | |
127 | /* Reject if object wraps past end of memory. */ | |
7329a655 | 128 | if ((unsigned long)ptr + n < (unsigned long)ptr) |
f5509cc1 KC |
129 | return "<wrapped address>"; |
130 | ||
131 | /* Reject if NULL or ZERO-allocation. */ | |
132 | if (ZERO_OR_NULL_PTR(ptr)) | |
133 | return "<null>"; | |
134 | ||
135 | return NULL; | |
136 | } | |
137 | ||
8e1f74ea KC |
138 | /* Checks for allocs that are marked in some way as spanning multiple pages. */ |
139 | static inline const char *check_page_span(const void *ptr, unsigned long n, | |
140 | struct page *page, bool to_user) | |
f5509cc1 | 141 | { |
8e1f74ea | 142 | #ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN |
f5509cc1 | 143 | const void *end = ptr + n - 1; |
8e1f74ea | 144 | struct page *endpage; |
f5509cc1 KC |
145 | bool is_reserved, is_cma; |
146 | ||
f5509cc1 KC |
147 | /* |
148 | * Sometimes the kernel data regions are not marked Reserved (see | |
149 | * check below). And sometimes [_sdata,_edata) does not cover | |
150 | * rodata and/or bss, so check each range explicitly. | |
151 | */ | |
152 | ||
153 | /* Allow reads of kernel rodata region (if not marked as Reserved). */ | |
154 | if (ptr >= (const void *)__start_rodata && | |
155 | end <= (const void *)__end_rodata) { | |
156 | if (!to_user) | |
157 | return "<rodata>"; | |
158 | return NULL; | |
159 | } | |
160 | ||
161 | /* Allow kernel data region (if not marked as Reserved). */ | |
162 | if (ptr >= (const void *)_sdata && end <= (const void *)_edata) | |
163 | return NULL; | |
164 | ||
165 | /* Allow kernel bss region (if not marked as Reserved). */ | |
166 | if (ptr >= (const void *)__bss_start && | |
167 | end <= (const void *)__bss_stop) | |
168 | return NULL; | |
169 | ||
170 | /* Is the object wholly within one base page? */ | |
171 | if (likely(((unsigned long)ptr & (unsigned long)PAGE_MASK) == | |
172 | ((unsigned long)end & (unsigned long)PAGE_MASK))) | |
173 | return NULL; | |
174 | ||
8e1f74ea | 175 | /* Allow if fully inside the same compound (__GFP_COMP) page. */ |
f5509cc1 KC |
176 | endpage = virt_to_head_page(end); |
177 | if (likely(endpage == page)) | |
178 | return NULL; | |
179 | ||
180 | /* | |
181 | * Reject if range is entirely either Reserved (i.e. special or | |
182 | * device memory), or CMA. Otherwise, reject since the object spans | |
183 | * several independently allocated pages. | |
184 | */ | |
185 | is_reserved = PageReserved(page); | |
186 | is_cma = is_migrate_cma_page(page); | |
187 | if (!is_reserved && !is_cma) | |
8e1f74ea | 188 | return "<spans multiple pages>"; |
f5509cc1 KC |
189 | |
190 | for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) { | |
191 | page = virt_to_head_page(ptr); | |
192 | if (is_reserved && !PageReserved(page)) | |
8e1f74ea | 193 | return "<spans Reserved and non-Reserved pages>"; |
f5509cc1 | 194 | if (is_cma && !is_migrate_cma_page(page)) |
8e1f74ea | 195 | return "<spans CMA and non-CMA pages>"; |
f5509cc1 | 196 | } |
8e1f74ea | 197 | #endif |
f5509cc1 KC |
198 | |
199 | return NULL; | |
8e1f74ea KC |
200 | } |
201 | ||
202 | static inline const char *check_heap_object(const void *ptr, unsigned long n, | |
203 | bool to_user) | |
204 | { | |
205 | struct page *page; | |
206 | ||
207 | /* | |
208 | * Some architectures (arm64) return true for virt_addr_valid() on | |
209 | * vmalloced addresses. Work around this by checking for vmalloc | |
210 | * first. | |
aa4f0601 LA |
211 | * |
212 | * We also need to check for module addresses explicitly since we | |
213 | * may copy static data from modules to userspace | |
8e1f74ea | 214 | */ |
aa4f0601 | 215 | if (is_vmalloc_or_module_addr(ptr)) |
8e1f74ea KC |
216 | return NULL; |
217 | ||
218 | if (!virt_addr_valid(ptr)) | |
219 | return NULL; | |
220 | ||
221 | page = virt_to_head_page(ptr); | |
222 | ||
223 | /* Check slab allocator for flags and size. */ | |
224 | if (PageSlab(page)) | |
225 | return __check_heap_object(ptr, n, page); | |
f5509cc1 | 226 | |
8e1f74ea KC |
227 | /* Verify object does not incorrectly span multiple pages. */ |
228 | return check_page_span(ptr, n, page, to_user); | |
f5509cc1 KC |
229 | } |
230 | ||
231 | /* | |
232 | * Validates that the given object is: | |
233 | * - not bogus address | |
234 | * - known-safe heap or stack object | |
235 | * - not in kernel text | |
236 | */ | |
237 | void __check_object_size(const void *ptr, unsigned long n, bool to_user) | |
238 | { | |
239 | const char *err; | |
240 | ||
241 | /* Skip all tests if size is zero. */ | |
242 | if (!n) | |
243 | return; | |
244 | ||
245 | /* Check for invalid addresses. */ | |
246 | err = check_bogus_address(ptr, n); | |
247 | if (err) | |
248 | goto report; | |
249 | ||
250 | /* Check for bad heap object. */ | |
251 | err = check_heap_object(ptr, n, to_user); | |
252 | if (err) | |
253 | goto report; | |
254 | ||
255 | /* Check for bad stack object. */ | |
256 | switch (check_stack_object(ptr, n)) { | |
257 | case NOT_STACK: | |
258 | /* Object is not touching the current process stack. */ | |
259 | break; | |
260 | case GOOD_FRAME: | |
261 | case GOOD_STACK: | |
262 | /* | |
263 | * Object is either in the correct frame (when it | |
264 | * is possible to check) or just generally on the | |
265 | * process stack (when frame checking not available). | |
266 | */ | |
267 | return; | |
268 | default: | |
269 | err = "<process stack>"; | |
270 | goto report; | |
271 | } | |
272 | ||
273 | /* Check for object in kernel to avoid text exposure. */ | |
274 | err = check_kernel_text_object(ptr, n); | |
275 | if (!err) | |
276 | return; | |
277 | ||
278 | report: | |
279 | report_usercopy(ptr, n, to_user, err); | |
280 | } | |
281 | EXPORT_SYMBOL(__check_object_size); |