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