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1// SPDX-License-Identifier: GPL-2.0-only
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.
10 */
11#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
12
13#include <linux/mm.h>
14#include <linux/highmem.h>
15#include <linux/kstrtox.h>
16#include <linux/slab.h>
17#include <linux/sched.h>
18#include <linux/sched/task.h>
19#include <linux/sched/task_stack.h>
20#include <linux/thread_info.h>
21#include <linux/vmalloc.h>
22#include <linux/atomic.h>
23#include <linux/jump_label.h>
24#include <asm/sections.h>
25#include "slab.h"
26
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
34 * GOOD_STACK: within the current stack (when can't frame-check exactly)
35 * BAD_STACK: error condition (invalid stack position or bad stack frame)
36 */
37static 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
49 * check above means at least one end is within the stack,
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
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
71 return GOOD_STACK;
72}
73
74/*
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.
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.
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).
85 */
86void __noreturn usercopy_abort(const char *name, const char *detail,
87 bool to_user, unsigned long offset,
88 unsigned long len)
89{
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
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). */
106static bool overlaps(const unsigned long ptr, unsigned long n,
107 unsigned long low, unsigned long high)
108{
109 const unsigned long check_low = ptr;
110 unsigned long check_high = check_low + n;
111
112 /* Does not overlap if entirely above or entirely below. */
113 if (check_low >= high || check_high <= low)
114 return false;
115
116 return true;
117}
118
119/* Is this address range in the kernel text area? */
120static inline void check_kernel_text_object(const unsigned long ptr,
121 unsigned long n, bool to_user)
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))
128 usercopy_abort("kernel text", NULL, to_user, ptr - textlow, n);
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 */
138 textlow_linear = (unsigned long)lm_alias(textlow);
139 /* No different mapping: we're done. */
140 if (textlow_linear == textlow)
141 return;
142
143 /* Check the secondary mapping... */
144 texthigh_linear = (unsigned long)lm_alias(texthigh);
145 if (overlaps(ptr, n, textlow_linear, texthigh_linear))
146 usercopy_abort("linear kernel text", NULL, to_user,
147 ptr - textlow_linear, n);
148}
149
150static inline void check_bogus_address(const unsigned long ptr, unsigned long n,
151 bool to_user)
152{
153 /* Reject if object wraps past end of memory. */
154 if (ptr + (n - 1) < ptr)
155 usercopy_abort("wrapped address", NULL, to_user, 0, ptr + n);
156
157 /* Reject if NULL or ZERO-allocation. */
158 if (ZERO_OR_NULL_PTR(ptr))
159 usercopy_abort("null address", NULL, to_user, ptr, n);
160}
161
162static inline void check_heap_object(const void *ptr, unsigned long n,
163 bool to_user)
164{
165 unsigned long addr = (unsigned long)ptr;
166 unsigned long offset;
167 struct folio *folio;
168
169 if (is_kmap_addr(ptr)) {
170 offset = offset_in_page(ptr);
171 if (n > PAGE_SIZE - offset)
172 usercopy_abort("kmap", NULL, to_user, offset, n);
173 return;
174 }
175
176 if (is_vmalloc_addr(ptr)) {
177 struct vmap_area *area = find_vmap_area(addr);
178
179 if (!area)
180 usercopy_abort("vmalloc", "no area", to_user, 0, n);
181
182 if (n > area->va_end - addr) {
183 offset = addr - area->va_start;
184 usercopy_abort("vmalloc", NULL, to_user, offset, n);
185 }
186 return;
187 }
188
189 if (!virt_addr_valid(ptr))
190 return;
191
192 folio = virt_to_folio(ptr);
193
194 if (folio_test_slab(folio)) {
195 /* Check slab allocator for flags and size. */
196 __check_heap_object(ptr, n, folio_slab(folio), to_user);
197 } else if (folio_test_large(folio)) {
198 offset = ptr - folio_address(folio);
199 if (n > folio_size(folio) - offset)
200 usercopy_abort("page alloc", NULL, to_user, offset, n);
201 }
202}
203
204static DEFINE_STATIC_KEY_FALSE_RO(bypass_usercopy_checks);
205
206/*
207 * Validates that the given object is:
208 * - not bogus address
209 * - fully contained by stack (or stack frame, when available)
210 * - fully within SLAB object (or object whitelist area, when available)
211 * - not in kernel text
212 */
213void __check_object_size(const void *ptr, unsigned long n, bool to_user)
214{
215 if (static_branch_unlikely(&bypass_usercopy_checks))
216 return;
217
218 /* Skip all tests if size is zero. */
219 if (!n)
220 return;
221
222 /* Check for invalid addresses. */
223 check_bogus_address((const unsigned long)ptr, n, to_user);
224
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:
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);
248 }
249
250 /* Check for bad heap object. */
251 check_heap_object(ptr, n, to_user);
252
253 /* Check for object in kernel to avoid text exposure. */
254 check_kernel_text_object((const unsigned long)ptr, n, to_user);
255}
256EXPORT_SYMBOL(__check_object_size);
257
258static bool enable_checks __initdata = true;
259
260static int __init parse_hardened_usercopy(char *str)
261{
262 if (kstrtobool(str, &enable_checks))
263 pr_warn("Invalid option string for hardened_usercopy: '%s'\n",
264 str);
265 return 1;
266}
267
268__setup("hardened_usercopy=", parse_hardened_usercopy);
269
270static int __init set_hardened_usercopy(void)
271{
272 if (enable_checks == false)
273 static_branch_enable(&bypass_usercopy_checks);
274 return 1;
275}
276
277late_initcall(set_hardened_usercopy);
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);