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d2912cb1 | 1 | // SPDX-License-Identifier: GPL-2.0-only |
f5509cc1 KC |
2 | /* |
3 | * This implements the various checks for CONFIG_HARDENED_USERCOPY*, | |
4 | * which are designed to protect kernel memory from needless exposure | |
5 | * and overwrite under many unintended conditions. This code is based | |
6 | * on PAX_USERCOPY, which is: | |
7 | * | |
8 | * Copyright (C) 2001-2016 PaX Team, Bradley Spengler, Open Source | |
9 | * Security Inc. | |
f5509cc1 KC |
10 | */ |
11 | #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt | |
12 | ||
13 | #include <linux/mm.h> | |
314eed30 | 14 | #include <linux/highmem.h> |
f15be1b8 | 15 | #include <linux/kstrtox.h> |
f5509cc1 | 16 | #include <linux/slab.h> |
5b825c3a | 17 | #include <linux/sched.h> |
29930025 IM |
18 | #include <linux/sched/task.h> |
19 | #include <linux/sched/task_stack.h> | |
96dc4f9f | 20 | #include <linux/thread_info.h> |
0aef499f | 21 | #include <linux/vmalloc.h> |
b5cb15d9 CR |
22 | #include <linux/atomic.h> |
23 | #include <linux/jump_label.h> | |
f5509cc1 | 24 | #include <asm/sections.h> |
0b3eb091 | 25 | #include "slab.h" |
f5509cc1 | 26 | |
f5509cc1 KC |
27 | /* |
28 | * Checks if a given pointer and length is contained by the current | |
29 | * stack frame (if possible). | |
30 | * | |
31 | * Returns: | |
32 | * NOT_STACK: not at all on the stack | |
33 | * GOOD_FRAME: fully within a valid stack frame | |
2792d84e | 34 | * GOOD_STACK: within the current stack (when can't frame-check exactly) |
f5509cc1 KC |
35 | * BAD_STACK: error condition (invalid stack position or bad stack frame) |
36 | */ | |
37 | static noinline int check_stack_object(const void *obj, unsigned long len) | |
38 | { | |
39 | const void * const stack = task_stack_page(current); | |
40 | const void * const stackend = stack + THREAD_SIZE; | |
41 | int ret; | |
42 | ||
43 | /* Object is not on the stack at all. */ | |
44 | if (obj + len <= stack || stackend <= obj) | |
45 | return NOT_STACK; | |
46 | ||
47 | /* | |
48 | * Reject: object partially overlaps the stack (passing the | |
5ce1be0e | 49 | * check above means at least one end is within the stack, |
f5509cc1 KC |
50 | * so if this check fails, the other end is outside the stack). |
51 | */ | |
52 | if (obj < stack || stackend < obj + len) | |
53 | return BAD_STACK; | |
54 | ||
55 | /* Check if object is safely within a valid frame. */ | |
56 | ret = arch_within_stack_frames(stack, stackend, obj, len); | |
57 | if (ret) | |
58 | return ret; | |
59 | ||
2792d84e KC |
60 | /* Finally, check stack depth if possible. */ |
61 | #ifdef CONFIG_ARCH_HAS_CURRENT_STACK_POINTER | |
62 | if (IS_ENABLED(CONFIG_STACK_GROWSUP)) { | |
63 | if ((void *)current_stack_pointer < obj + len) | |
64 | return BAD_STACK; | |
65 | } else { | |
66 | if (obj < (void *)current_stack_pointer) | |
67 | return BAD_STACK; | |
68 | } | |
69 | #endif | |
70 | ||
f5509cc1 KC |
71 | return GOOD_STACK; |
72 | } | |
73 | ||
b394d468 | 74 | /* |
afcc90f8 KC |
75 | * If these functions are reached, then CONFIG_HARDENED_USERCOPY has found |
76 | * an unexpected state during a copy_from_user() or copy_to_user() call. | |
b394d468 KC |
77 | * There are several checks being performed on the buffer by the |
78 | * __check_object_size() function. Normal stack buffer usage should never | |
79 | * trip the checks, and kernel text addressing will always trip the check. | |
afcc90f8 KC |
80 | * For cache objects, it is checking that only the whitelisted range of |
81 | * bytes for a given cache is being accessed (via the cache's usersize and | |
82 | * useroffset fields). To adjust a cache whitelist, use the usercopy-aware | |
83 | * kmem_cache_create_usercopy() function to create the cache (and | |
84 | * carefully audit the whitelist range). | |
b394d468 KC |
85 | */ |
86 | void __noreturn usercopy_abort(const char *name, const char *detail, | |
87 | bool to_user, unsigned long offset, | |
88 | unsigned long len) | |
f5509cc1 | 89 | { |
b394d468 KC |
90 | pr_emerg("Kernel memory %s attempt detected %s %s%s%s%s (offset %lu, size %lu)!\n", |
91 | to_user ? "exposure" : "overwrite", | |
92 | to_user ? "from" : "to", | |
93 | name ? : "unknown?!", | |
94 | detail ? " '" : "", detail ? : "", detail ? "'" : "", | |
95 | offset, len); | |
96 | ||
f5509cc1 KC |
97 | /* |
98 | * For greater effect, it would be nice to do do_group_exit(), | |
99 | * but BUG() actually hooks all the lock-breaking and per-arch | |
100 | * Oops code, so that is used here instead. | |
101 | */ | |
102 | BUG(); | |
103 | } | |
104 | ||
105 | /* Returns true if any portion of [ptr,ptr+n) over laps with [low,high). */ | |
f4e6e289 KC |
106 | static bool overlaps(const unsigned long ptr, unsigned long n, |
107 | unsigned long low, unsigned long high) | |
f5509cc1 | 108 | { |
f4e6e289 | 109 | const unsigned long check_low = ptr; |
f5509cc1 KC |
110 | unsigned long check_high = check_low + n; |
111 | ||
112 | /* Does not overlap if entirely above or entirely below. */ | |
94cd97af | 113 | if (check_low >= high || check_high <= low) |
f5509cc1 KC |
114 | return false; |
115 | ||
116 | return true; | |
117 | } | |
118 | ||
119 | /* Is this address range in the kernel text area? */ | |
f4e6e289 KC |
120 | static inline void check_kernel_text_object(const unsigned long ptr, |
121 | unsigned long n, bool to_user) | |
f5509cc1 KC |
122 | { |
123 | unsigned long textlow = (unsigned long)_stext; | |
124 | unsigned long texthigh = (unsigned long)_etext; | |
125 | unsigned long textlow_linear, texthigh_linear; | |
126 | ||
127 | if (overlaps(ptr, n, textlow, texthigh)) | |
f4e6e289 | 128 | usercopy_abort("kernel text", NULL, to_user, ptr - textlow, n); |
f5509cc1 KC |
129 | |
130 | /* | |
131 | * Some architectures have virtual memory mappings with a secondary | |
132 | * mapping of the kernel text, i.e. there is more than one virtual | |
133 | * kernel address that points to the kernel image. It is usually | |
134 | * when there is a separate linear physical memory mapping, in that | |
135 | * __pa() is not just the reverse of __va(). This can be detected | |
136 | * and checked: | |
137 | */ | |
46f6236a | 138 | textlow_linear = (unsigned long)lm_alias(textlow); |
f5509cc1 KC |
139 | /* No different mapping: we're done. */ |
140 | if (textlow_linear == textlow) | |
f4e6e289 | 141 | return; |
f5509cc1 KC |
142 | |
143 | /* Check the secondary mapping... */ | |
46f6236a | 144 | texthigh_linear = (unsigned long)lm_alias(texthigh); |
f5509cc1 | 145 | if (overlaps(ptr, n, textlow_linear, texthigh_linear)) |
f4e6e289 KC |
146 | usercopy_abort("linear kernel text", NULL, to_user, |
147 | ptr - textlow_linear, n); | |
f5509cc1 KC |
148 | } |
149 | ||
f4e6e289 KC |
150 | static inline void check_bogus_address(const unsigned long ptr, unsigned long n, |
151 | bool to_user) | |
f5509cc1 KC |
152 | { |
153 | /* Reject if object wraps past end of memory. */ | |
95153169 | 154 | if (ptr + (n - 1) < ptr) |
f4e6e289 | 155 | usercopy_abort("wrapped address", NULL, to_user, 0, ptr + n); |
f5509cc1 KC |
156 | |
157 | /* Reject if NULL or ZERO-allocation. */ | |
158 | if (ZERO_OR_NULL_PTR(ptr)) | |
f4e6e289 | 159 | usercopy_abort("null address", NULL, to_user, ptr, n); |
f5509cc1 KC |
160 | } |
161 | ||
f4e6e289 KC |
162 | static inline void check_heap_object(const void *ptr, unsigned long n, |
163 | bool to_user) | |
8e1f74ea | 164 | { |
170b2c35 | 165 | unsigned long addr = (unsigned long)ptr; |
1dfbe9fc | 166 | unsigned long offset; |
0b3eb091 | 167 | struct folio *folio; |
8e1f74ea | 168 | |
4e140f59 | 169 | if (is_kmap_addr(ptr)) { |
1dfbe9fc MWO |
170 | offset = offset_in_page(ptr); |
171 | if (n > PAGE_SIZE - offset) | |
172 | usercopy_abort("kmap", NULL, to_user, offset, n); | |
4e140f59 MWO |
173 | return; |
174 | } | |
175 | ||
d319f344 | 176 | if (is_vmalloc_addr(ptr) && !pagefault_disabled()) { |
35fb9ae4 | 177 | struct vmap_area *area = find_vmap_area(addr); |
0aef499f | 178 | |
993d0b28 | 179 | if (!area) |
0aef499f | 180 | usercopy_abort("vmalloc", "no area", to_user, 0, n); |
0aef499f | 181 | |
1dfbe9fc MWO |
182 | if (n > area->va_end - addr) { |
183 | offset = addr - area->va_start; | |
0aef499f | 184 | usercopy_abort("vmalloc", NULL, to_user, offset, n); |
1dfbe9fc | 185 | } |
0aef499f MWO |
186 | return; |
187 | } | |
188 | ||
a5f4d9df YS |
189 | if (!virt_addr_valid(ptr)) |
190 | return; | |
191 | ||
4e140f59 | 192 | folio = virt_to_folio(ptr); |
8e1f74ea | 193 | |
0b3eb091 | 194 | if (folio_test_slab(folio)) { |
f4e6e289 | 195 | /* Check slab allocator for flags and size. */ |
0b3eb091 | 196 | __check_heap_object(ptr, n, folio_slab(folio), to_user); |
ab502103 | 197 | } else if (folio_test_large(folio)) { |
1dfbe9fc MWO |
198 | offset = ptr - folio_address(folio); |
199 | if (n > folio_size(folio) - offset) | |
ab502103 | 200 | usercopy_abort("page alloc", NULL, to_user, offset, n); |
f4e6e289 | 201 | } |
f5509cc1 KC |
202 | } |
203 | ||
b5cb15d9 CR |
204 | static DEFINE_STATIC_KEY_FALSE_RO(bypass_usercopy_checks); |
205 | ||
f5509cc1 KC |
206 | /* |
207 | * Validates that the given object is: | |
208 | * - not bogus address | |
7bff3c06 QC |
209 | * - fully contained by stack (or stack frame, when available) |
210 | * - fully within SLAB object (or object whitelist area, when available) | |
f5509cc1 KC |
211 | * - not in kernel text |
212 | */ | |
213 | void __check_object_size(const void *ptr, unsigned long n, bool to_user) | |
214 | { | |
b5cb15d9 CR |
215 | if (static_branch_unlikely(&bypass_usercopy_checks)) |
216 | return; | |
217 | ||
f5509cc1 KC |
218 | /* Skip all tests if size is zero. */ |
219 | if (!n) | |
220 | return; | |
221 | ||
222 | /* Check for invalid addresses. */ | |
f4e6e289 | 223 | check_bogus_address((const unsigned long)ptr, n, to_user); |
f5509cc1 | 224 | |
f5509cc1 KC |
225 | /* Check for bad stack object. */ |
226 | switch (check_stack_object(ptr, n)) { | |
227 | case NOT_STACK: | |
228 | /* Object is not touching the current process stack. */ | |
229 | break; | |
230 | case GOOD_FRAME: | |
231 | case GOOD_STACK: | |
232 | /* | |
233 | * Object is either in the correct frame (when it | |
234 | * is possible to check) or just generally on the | |
235 | * process stack (when frame checking not available). | |
236 | */ | |
237 | return; | |
238 | default: | |
2792d84e KC |
239 | usercopy_abort("process stack", NULL, to_user, |
240 | #ifdef CONFIG_ARCH_HAS_CURRENT_STACK_POINTER | |
241 | IS_ENABLED(CONFIG_STACK_GROWSUP) ? | |
242 | ptr - (void *)current_stack_pointer : | |
243 | (void *)current_stack_pointer - ptr, | |
244 | #else | |
245 | 0, | |
246 | #endif | |
247 | n); | |
f5509cc1 KC |
248 | } |
249 | ||
7bff3c06 QC |
250 | /* Check for bad heap object. */ |
251 | check_heap_object(ptr, n, to_user); | |
252 | ||
f5509cc1 | 253 | /* Check for object in kernel to avoid text exposure. */ |
f4e6e289 | 254 | check_kernel_text_object((const unsigned long)ptr, n, to_user); |
f5509cc1 KC |
255 | } |
256 | EXPORT_SYMBOL(__check_object_size); | |
b5cb15d9 CR |
257 | |
258 | static bool enable_checks __initdata = true; | |
259 | ||
260 | static int __init parse_hardened_usercopy(char *str) | |
261 | { | |
f15be1b8 | 262 | if (kstrtobool(str, &enable_checks)) |
05fe3c10 RD |
263 | pr_warn("Invalid option string for hardened_usercopy: '%s'\n", |
264 | str); | |
265 | return 1; | |
b5cb15d9 CR |
266 | } |
267 | ||
268 | __setup("hardened_usercopy=", parse_hardened_usercopy); | |
269 | ||
270 | static int __init set_hardened_usercopy(void) | |
271 | { | |
272 | if (enable_checks == false) | |
273 | static_branch_enable(&bypass_usercopy_checks); | |
274 | return 1; | |
275 | } | |
276 | ||
277 | late_initcall(set_hardened_usercopy); |