blob: 3c8da0af96959387e9bb1d2c0bfe272334344e26 [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>
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. */
Josh Poimboeuf94cd97a2016-08-22 11:53:59 -050086 if (check_low >= high || check_high <= low)
Kees Cookf5509cc2016-06-07 11:05:33 -070087 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. */
Eric Biggers7329a652016-08-19 12:15:22 -0700127 if ((unsigned long)ptr + n < (unsigned long)ptr)
Kees Cookf5509cc2016-06-07 11:05:33 -0700128 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
Kees Cook8e1f74e2016-09-07 09:54:34 -0700137/* 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)
Kees Cookf5509cc2016-06-07 11:05:33 -0700140{
Kees Cook8e1f74e2016-09-07 09:54:34 -0700141#ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN
Kees Cookf5509cc2016-06-07 11:05:33 -0700142 const void *end = ptr + n - 1;
Kees Cook8e1f74e2016-09-07 09:54:34 -0700143 struct page *endpage;
Kees Cookf5509cc2016-06-07 11:05:33 -0700144 bool is_reserved, is_cma;
145
146 /*
Kees Cookf5509cc2016-06-07 11:05:33 -0700147 * 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
Kees Cook8e1f74e2016-09-07 09:54:34 -0700174 /* Allow if fully inside the same compound (__GFP_COMP) page. */
Kees Cookf5509cc2016-06-07 11:05:33 -0700175 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)
Kees Cook8e1f74e2016-09-07 09:54:34 -0700187 return "<spans multiple pages>";
Kees Cookf5509cc2016-06-07 11:05:33 -0700188
189 for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) {
190 page = virt_to_head_page(ptr);
191 if (is_reserved && !PageReserved(page))
Kees Cook8e1f74e2016-09-07 09:54:34 -0700192 return "<spans Reserved and non-Reserved pages>";
Kees Cookf5509cc2016-06-07 11:05:33 -0700193 if (is_cma && !is_migrate_cma_page(page))
Kees Cook8e1f74e2016-09-07 09:54:34 -0700194 return "<spans CMA and non-CMA pages>";
Kees Cookf5509cc2016-06-07 11:05:33 -0700195 }
Kees Cook8e1f74e2016-09-07 09:54:34 -0700196#endif
Kees Cookf5509cc2016-06-07 11:05:33 -0700197
198 return NULL;
Kees Cook8e1f74e2016-09-07 09:54:34 -0700199}
Kees Cookf5509cc2016-06-07 11:05:33 -0700200
Kees Cook8e1f74e2016-09-07 09:54:34 -0700201static 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.
Laura Abbottaa4f0602016-09-20 08:56:36 -0700210 *
211 * We also need to check for module addresses explicitly since we
212 * may copy static data from modules to userspace
Kees Cook8e1f74e2016-09-07 09:54:34 -0700213 */
Laura Abbottaa4f0602016-09-20 08:56:36 -0700214 if (is_vmalloc_or_module_addr(ptr))
Kees Cook8e1f74e2016-09-07 09:54:34 -0700215 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);
Kees Cookf5509cc2016-06-07 11:05:33 -0700228}
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);