blob: a9852b24715d25598a7603560ffc042ca0153a2b [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>
18#include <linux/slab.h>
Ingo Molnar5b825c32017-02-02 17:54:15 +010019#include <linux/sched.h>
Ingo Molnar29930022017-02-08 18:51:36 +010020#include <linux/sched/task.h>
21#include <linux/sched/task_stack.h>
Sahara96dc4f92017-02-16 18:29:15 +000022#include <linux/thread_info.h>
Kees Cookf5509cc2016-06-07 11:05:33 -070023#include <asm/sections.h>
24
Kees Cookf5509cc2016-06-07 11:05:33 -070025/*
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
61static void report_usercopy(const void *ptr, unsigned long len,
62 bool to_user, const char *type)
63{
64 pr_emerg("kernel memory %s attempt detected %s %p (%s) (%lu bytes)\n",
65 to_user ? "exposure" : "overwrite",
66 to_user ? "from" : "to", ptr, type ? : "unknown", len);
67 /*
68 * For greater effect, it would be nice to do do_group_exit(),
69 * but BUG() actually hooks all the lock-breaking and per-arch
70 * Oops code, so that is used here instead.
71 */
72 BUG();
73}
74
75/* Returns true if any portion of [ptr,ptr+n) over laps with [low,high). */
76static bool overlaps(const void *ptr, unsigned long n, unsigned long low,
77 unsigned long high)
78{
79 unsigned long check_low = (uintptr_t)ptr;
80 unsigned long check_high = check_low + n;
81
82 /* Does not overlap if entirely above or entirely below. */
Josh Poimboeuf94cd97a2016-08-22 11:53:59 -050083 if (check_low >= high || check_high <= low)
Kees Cookf5509cc2016-06-07 11:05:33 -070084 return false;
85
86 return true;
87}
88
89/* Is this address range in the kernel text area? */
90static inline const char *check_kernel_text_object(const void *ptr,
91 unsigned long n)
92{
93 unsigned long textlow = (unsigned long)_stext;
94 unsigned long texthigh = (unsigned long)_etext;
95 unsigned long textlow_linear, texthigh_linear;
96
97 if (overlaps(ptr, n, textlow, texthigh))
98 return "<kernel text>";
99
100 /*
101 * Some architectures have virtual memory mappings with a secondary
102 * mapping of the kernel text, i.e. there is more than one virtual
103 * kernel address that points to the kernel image. It is usually
104 * when there is a separate linear physical memory mapping, in that
105 * __pa() is not just the reverse of __va(). This can be detected
106 * and checked:
107 */
Laura Abbott46f62362017-01-10 13:35:45 -0800108 textlow_linear = (unsigned long)lm_alias(textlow);
Kees Cookf5509cc2016-06-07 11:05:33 -0700109 /* No different mapping: we're done. */
110 if (textlow_linear == textlow)
111 return NULL;
112
113 /* Check the secondary mapping... */
Laura Abbott46f62362017-01-10 13:35:45 -0800114 texthigh_linear = (unsigned long)lm_alias(texthigh);
Kees Cookf5509cc2016-06-07 11:05:33 -0700115 if (overlaps(ptr, n, textlow_linear, texthigh_linear))
116 return "<linear kernel text>";
117
118 return NULL;
119}
120
121static inline const char *check_bogus_address(const void *ptr, unsigned long n)
122{
123 /* Reject if object wraps past end of memory. */
Eric Biggers7329a652016-08-19 12:15:22 -0700124 if ((unsigned long)ptr + n < (unsigned long)ptr)
Kees Cookf5509cc2016-06-07 11:05:33 -0700125 return "<wrapped address>";
126
127 /* Reject if NULL or ZERO-allocation. */
128 if (ZERO_OR_NULL_PTR(ptr))
129 return "<null>";
130
131 return NULL;
132}
133
Kees Cook8e1f74e2016-09-07 09:54:34 -0700134/* Checks for allocs that are marked in some way as spanning multiple pages. */
135static inline const char *check_page_span(const void *ptr, unsigned long n,
136 struct page *page, bool to_user)
Kees Cookf5509cc2016-06-07 11:05:33 -0700137{
Kees Cook8e1f74e2016-09-07 09:54:34 -0700138#ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN
Kees Cookf5509cc2016-06-07 11:05:33 -0700139 const void *end = ptr + n - 1;
Kees Cook8e1f74e2016-09-07 09:54:34 -0700140 struct page *endpage;
Kees Cookf5509cc2016-06-07 11:05:33 -0700141 bool is_reserved, is_cma;
142
143 /*
Kees Cookf5509cc2016-06-07 11:05:33 -0700144 * Sometimes the kernel data regions are not marked Reserved (see
145 * check below). And sometimes [_sdata,_edata) does not cover
146 * rodata and/or bss, so check each range explicitly.
147 */
148
149 /* Allow reads of kernel rodata region (if not marked as Reserved). */
150 if (ptr >= (const void *)__start_rodata &&
151 end <= (const void *)__end_rodata) {
152 if (!to_user)
153 return "<rodata>";
154 return NULL;
155 }
156
157 /* Allow kernel data region (if not marked as Reserved). */
158 if (ptr >= (const void *)_sdata && end <= (const void *)_edata)
159 return NULL;
160
161 /* Allow kernel bss region (if not marked as Reserved). */
162 if (ptr >= (const void *)__bss_start &&
163 end <= (const void *)__bss_stop)
164 return NULL;
165
166 /* Is the object wholly within one base page? */
167 if (likely(((unsigned long)ptr & (unsigned long)PAGE_MASK) ==
168 ((unsigned long)end & (unsigned long)PAGE_MASK)))
169 return NULL;
170
Kees Cook8e1f74e2016-09-07 09:54:34 -0700171 /* Allow if fully inside the same compound (__GFP_COMP) page. */
Kees Cookf5509cc2016-06-07 11:05:33 -0700172 endpage = virt_to_head_page(end);
173 if (likely(endpage == page))
174 return NULL;
175
176 /*
177 * Reject if range is entirely either Reserved (i.e. special or
178 * device memory), or CMA. Otherwise, reject since the object spans
179 * several independently allocated pages.
180 */
181 is_reserved = PageReserved(page);
182 is_cma = is_migrate_cma_page(page);
183 if (!is_reserved && !is_cma)
Kees Cook8e1f74e2016-09-07 09:54:34 -0700184 return "<spans multiple pages>";
Kees Cookf5509cc2016-06-07 11:05:33 -0700185
186 for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) {
187 page = virt_to_head_page(ptr);
188 if (is_reserved && !PageReserved(page))
Kees Cook8e1f74e2016-09-07 09:54:34 -0700189 return "<spans Reserved and non-Reserved pages>";
Kees Cookf5509cc2016-06-07 11:05:33 -0700190 if (is_cma && !is_migrate_cma_page(page))
Kees Cook8e1f74e2016-09-07 09:54:34 -0700191 return "<spans CMA and non-CMA pages>";
Kees Cookf5509cc2016-06-07 11:05:33 -0700192 }
Kees Cook8e1f74e2016-09-07 09:54:34 -0700193#endif
Kees Cookf5509cc2016-06-07 11:05:33 -0700194
195 return NULL;
Kees Cook8e1f74e2016-09-07 09:54:34 -0700196}
Kees Cookf5509cc2016-06-07 11:05:33 -0700197
Kees Cook8e1f74e2016-09-07 09:54:34 -0700198static inline const char *check_heap_object(const void *ptr, unsigned long n,
199 bool to_user)
200{
201 struct page *page;
202
Kees Cook8e1f74e2016-09-07 09:54:34 -0700203 if (!virt_addr_valid(ptr))
204 return NULL;
205
206 page = virt_to_head_page(ptr);
207
208 /* Check slab allocator for flags and size. */
209 if (PageSlab(page))
210 return __check_heap_object(ptr, n, page);
211
212 /* Verify object does not incorrectly span multiple pages. */
213 return check_page_span(ptr, n, page, to_user);
Kees Cookf5509cc2016-06-07 11:05:33 -0700214}
215
216/*
217 * Validates that the given object is:
218 * - not bogus address
219 * - known-safe heap or stack object
220 * - not in kernel text
221 */
222void __check_object_size(const void *ptr, unsigned long n, bool to_user)
223{
224 const char *err;
225
226 /* Skip all tests if size is zero. */
227 if (!n)
228 return;
229
230 /* Check for invalid addresses. */
231 err = check_bogus_address(ptr, n);
232 if (err)
233 goto report;
234
235 /* Check for bad heap object. */
236 err = check_heap_object(ptr, n, to_user);
237 if (err)
238 goto report;
239
240 /* Check for bad stack object. */
241 switch (check_stack_object(ptr, n)) {
242 case NOT_STACK:
243 /* Object is not touching the current process stack. */
244 break;
245 case GOOD_FRAME:
246 case GOOD_STACK:
247 /*
248 * Object is either in the correct frame (when it
249 * is possible to check) or just generally on the
250 * process stack (when frame checking not available).
251 */
252 return;
253 default:
254 err = "<process stack>";
255 goto report;
256 }
257
258 /* Check for object in kernel to avoid text exposure. */
259 err = check_kernel_text_object(ptr, n);
260 if (!err)
261 return;
262
263report:
264 report_usercopy(ptr, n, to_user, err);
265}
266EXPORT_SYMBOL(__check_object_size);