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