blob: f8d74e09f8e4de9f5afd8636f1e761d0da147da6 [file] [log] [blame]
Kees Cookf5509cc2016-06-07 11:05:33 -07001/*
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>
Kees Cooka93e0bc2019-09-17 11:00:25 -070018#include <linux/highmem.h>
Kees Cookf5509cc2016-06-07 11:05:33 -070019#include <linux/slab.h>
Ingo Molnar5b825c32017-02-02 17:54:15 +010020#include <linux/sched.h>
Ingo Molnar29930022017-02-08 18:51:36 +010021#include <linux/sched/task.h>
22#include <linux/sched/task_stack.h>
Sahara96dc4f92017-02-16 18:29:15 +000023#include <linux/thread_info.h>
Kees Cookf5509cc2016-06-07 11:05:33 -070024#include <asm/sections.h>
25
Kees Cookf5509cc2016-06-07 11:05:33 -070026/*
27 * Checks if a given pointer and length is contained by the current
28 * stack frame (if possible).
29 *
30 * Returns:
31 * NOT_STACK: not at all on the stack
32 * GOOD_FRAME: fully within a valid stack frame
33 * GOOD_STACK: fully on the stack (when can't do frame-checking)
34 * BAD_STACK: error condition (invalid stack position or bad stack frame)
35 */
36static noinline int check_stack_object(const void *obj, unsigned long len)
37{
38 const void * const stack = task_stack_page(current);
39 const void * const stackend = stack + THREAD_SIZE;
40 int ret;
41
42 /* Object is not on the stack at all. */
43 if (obj + len <= stack || stackend <= obj)
44 return NOT_STACK;
45
46 /*
47 * Reject: object partially overlaps the stack (passing the
48 * the check above means at least one end is within the stack,
49 * so if this check fails, the other end is outside the stack).
50 */
51 if (obj < stack || stackend < obj + len)
52 return BAD_STACK;
53
54 /* Check if object is safely within a valid frame. */
55 ret = arch_within_stack_frames(stack, stackend, obj, len);
56 if (ret)
57 return ret;
58
59 return GOOD_STACK;
60}
61
62static void report_usercopy(const void *ptr, unsigned long len,
63 bool to_user, const char *type)
64{
65 pr_emerg("kernel memory %s attempt detected %s %p (%s) (%lu bytes)\n",
66 to_user ? "exposure" : "overwrite",
67 to_user ? "from" : "to", ptr, type ? : "unknown", len);
68 /*
69 * For greater effect, it would be nice to do do_group_exit(),
70 * but BUG() actually hooks all the lock-breaking and per-arch
71 * Oops code, so that is used here instead.
72 */
73 BUG();
74}
75
76/* Returns true if any portion of [ptr,ptr+n) over laps with [low,high). */
77static bool overlaps(const void *ptr, unsigned long n, unsigned long low,
78 unsigned long high)
79{
80 unsigned long check_low = (uintptr_t)ptr;
81 unsigned long check_high = check_low + n;
82
83 /* Does not overlap if entirely above or entirely below. */
Josh Poimboeuf94cd97a2016-08-22 11:53:59 -050084 if (check_low >= high || check_high <= low)
Kees Cookf5509cc2016-06-07 11:05:33 -070085 return false;
86
87 return true;
88}
89
90/* Is this address range in the kernel text area? */
91static inline const char *check_kernel_text_object(const void *ptr,
92 unsigned long n)
93{
94 unsigned long textlow = (unsigned long)_stext;
95 unsigned long texthigh = (unsigned long)_etext;
96 unsigned long textlow_linear, texthigh_linear;
97
98 if (overlaps(ptr, n, textlow, texthigh))
99 return "<kernel text>";
100
101 /*
102 * Some architectures have virtual memory mappings with a secondary
103 * mapping of the kernel text, i.e. there is more than one virtual
104 * kernel address that points to the kernel image. It is usually
105 * when there is a separate linear physical memory mapping, in that
106 * __pa() is not just the reverse of __va(). This can be detected
107 * and checked:
108 */
Laura Abbott46f62362017-01-10 13:35:45 -0800109 textlow_linear = (unsigned long)lm_alias(textlow);
Kees Cookf5509cc2016-06-07 11:05:33 -0700110 /* No different mapping: we're done. */
111 if (textlow_linear == textlow)
112 return NULL;
113
114 /* Check the secondary mapping... */
Laura Abbott46f62362017-01-10 13:35:45 -0800115 texthigh_linear = (unsigned long)lm_alias(texthigh);
Kees Cookf5509cc2016-06-07 11:05:33 -0700116 if (overlaps(ptr, n, textlow_linear, texthigh_linear))
117 return "<linear kernel text>";
118
119 return NULL;
120}
121
122static inline const char *check_bogus_address(const void *ptr, unsigned long n)
123{
124 /* Reject if object wraps past end of memory. */
Isaac J. Manjarres3e7e8012019-08-13 15:37:37 -0700125 if ((unsigned long)ptr + (n - 1) < (unsigned long)ptr)
Kees Cookf5509cc2016-06-07 11:05:33 -0700126 return "<wrapped address>";
127
128 /* Reject if NULL or ZERO-allocation. */
129 if (ZERO_OR_NULL_PTR(ptr))
130 return "<null>";
131
132 return NULL;
133}
134
Kees Cook8e1f74e2016-09-07 09:54:34 -0700135/* Checks for allocs that are marked in some way as spanning multiple pages. */
136static inline const char *check_page_span(const void *ptr, unsigned long n,
137 struct page *page, bool to_user)
Kees Cookf5509cc2016-06-07 11:05:33 -0700138{
Kees Cook8e1f74e2016-09-07 09:54:34 -0700139#ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN
Kees Cookf5509cc2016-06-07 11:05:33 -0700140 const void *end = ptr + n - 1;
Kees Cook8e1f74e2016-09-07 09:54:34 -0700141 struct page *endpage;
Kees Cookf5509cc2016-06-07 11:05:33 -0700142 bool is_reserved, is_cma;
143
144 /*
Kees Cookf5509cc2016-06-07 11:05:33 -0700145 * Sometimes the kernel data regions are not marked Reserved (see
146 * check below). And sometimes [_sdata,_edata) does not cover
147 * rodata and/or bss, so check each range explicitly.
148 */
149
150 /* Allow reads of kernel rodata region (if not marked as Reserved). */
151 if (ptr >= (const void *)__start_rodata &&
152 end <= (const void *)__end_rodata) {
153 if (!to_user)
154 return "<rodata>";
155 return NULL;
156 }
157
158 /* Allow kernel data region (if not marked as Reserved). */
159 if (ptr >= (const void *)_sdata && end <= (const void *)_edata)
160 return NULL;
161
162 /* Allow kernel bss region (if not marked as Reserved). */
163 if (ptr >= (const void *)__bss_start &&
164 end <= (const void *)__bss_stop)
165 return NULL;
166
167 /* Is the object wholly within one base page? */
168 if (likely(((unsigned long)ptr & (unsigned long)PAGE_MASK) ==
169 ((unsigned long)end & (unsigned long)PAGE_MASK)))
170 return NULL;
171
Kees Cook8e1f74e2016-09-07 09:54:34 -0700172 /* Allow if fully inside the same compound (__GFP_COMP) page. */
Kees Cookf5509cc2016-06-07 11:05:33 -0700173 endpage = virt_to_head_page(end);
174 if (likely(endpage == page))
175 return NULL;
176
177 /*
178 * Reject if range is entirely either Reserved (i.e. special or
179 * device memory), or CMA. Otherwise, reject since the object spans
180 * several independently allocated pages.
181 */
182 is_reserved = PageReserved(page);
183 is_cma = is_migrate_cma_page(page);
184 if (!is_reserved && !is_cma)
Kees Cook8e1f74e2016-09-07 09:54:34 -0700185 return "<spans multiple pages>";
Kees Cookf5509cc2016-06-07 11:05:33 -0700186
187 for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) {
188 page = virt_to_head_page(ptr);
189 if (is_reserved && !PageReserved(page))
Kees Cook8e1f74e2016-09-07 09:54:34 -0700190 return "<spans Reserved and non-Reserved pages>";
Kees Cookf5509cc2016-06-07 11:05:33 -0700191 if (is_cma && !is_migrate_cma_page(page))
Kees Cook8e1f74e2016-09-07 09:54:34 -0700192 return "<spans CMA and non-CMA pages>";
Kees Cookf5509cc2016-06-07 11:05:33 -0700193 }
Kees Cook8e1f74e2016-09-07 09:54:34 -0700194#endif
Kees Cookf5509cc2016-06-07 11:05:33 -0700195
196 return NULL;
Kees Cook8e1f74e2016-09-07 09:54:34 -0700197}
Kees Cookf5509cc2016-06-07 11:05:33 -0700198
Kees Cook8e1f74e2016-09-07 09:54:34 -0700199static inline const char *check_heap_object(const void *ptr, unsigned long n,
200 bool to_user)
201{
202 struct page *page;
203
Kees Cook8e1f74e2016-09-07 09:54:34 -0700204 if (!virt_addr_valid(ptr))
205 return NULL;
206
Kees Cooka93e0bc2019-09-17 11:00:25 -0700207 /*
208 * When CONFIG_HIGHMEM=y, kmap_to_page() will give either the
209 * highmem page or fallback to virt_to_page(). The following
210 * is effectively a highmem-aware virt_to_head_page().
211 */
212 page = compound_head(kmap_to_page((void *)ptr));
Kees Cook8e1f74e2016-09-07 09:54:34 -0700213
214 /* Check slab allocator for flags and size. */
215 if (PageSlab(page))
216 return __check_heap_object(ptr, n, page);
217
218 /* Verify object does not incorrectly span multiple pages. */
219 return check_page_span(ptr, n, page, to_user);
Kees Cookf5509cc2016-06-07 11:05:33 -0700220}
221
222/*
223 * Validates that the given object is:
224 * - not bogus address
225 * - known-safe heap or stack object
226 * - not in kernel text
227 */
228void __check_object_size(const void *ptr, unsigned long n, bool to_user)
229{
230 const char *err;
231
232 /* Skip all tests if size is zero. */
233 if (!n)
234 return;
235
236 /* Check for invalid addresses. */
237 err = check_bogus_address(ptr, n);
238 if (err)
239 goto report;
240
241 /* Check for bad heap object. */
242 err = check_heap_object(ptr, n, to_user);
243 if (err)
244 goto report;
245
246 /* Check for bad stack object. */
247 switch (check_stack_object(ptr, n)) {
248 case NOT_STACK:
249 /* Object is not touching the current process stack. */
250 break;
251 case GOOD_FRAME:
252 case GOOD_STACK:
253 /*
254 * Object is either in the correct frame (when it
255 * is possible to check) or just generally on the
256 * process stack (when frame checking not available).
257 */
258 return;
259 default:
260 err = "<process stack>";
261 goto report;
262 }
263
264 /* Check for object in kernel to avoid text exposure. */
265 err = check_kernel_text_object(ptr, n);
266 if (!err)
267 return;
268
269report:
270 report_usercopy(ptr, n, to_user, err);
271}
272EXPORT_SYMBOL(__check_object_size);