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:
7 * Copyright (C) 2001-2016 PaX Team, Bradley Spengler, Open Source
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.
15 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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>
26 * Checks if a given pointer and length is contained by the current
27 * stack frame (if possible).
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)
35 static noinline int check_stack_object(const void *obj, unsigned long len)
37 const void * const stack = task_stack_page(current);
38 const void * const stackend = stack + THREAD_SIZE;
41 /* Object is not on the stack at all. */
42 if (obj + len <= stack || stackend <= obj)
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).
50 if (obj < stack || stackend < obj + len)
53 /* Check if object is safely within a valid frame. */
54 ret = arch_within_stack_frames(stack, stackend, obj, len);
61 static void report_usercopy(unsigned long len, bool to_user, const char *type)
63 pr_emerg("kernel memory %s attempt detected %s '%s' (%lu bytes)\n",
64 to_user ? "exposure" : "overwrite",
65 to_user ? "from" : "to", type ? : "unknown", len);
67 * For greater effect, it would be nice to do do_group_exit(),
68 * but BUG() actually hooks all the lock-breaking and per-arch
69 * Oops code, so that is used here instead.
74 /* Returns true if any portion of [ptr,ptr+n) over laps with [low,high). */
75 static bool overlaps(const void *ptr, unsigned long n, unsigned long low,
78 unsigned long check_low = (uintptr_t)ptr;
79 unsigned long check_high = check_low + n;
81 /* Does not overlap if entirely above or entirely below. */
82 if (check_low >= high || check_high <= low)
88 /* Is this address range in the kernel text area? */
89 static inline const char *check_kernel_text_object(const void *ptr,
92 unsigned long textlow = (unsigned long)_stext;
93 unsigned long texthigh = (unsigned long)_etext;
94 unsigned long textlow_linear, texthigh_linear;
96 if (overlaps(ptr, n, textlow, texthigh))
97 return "<kernel text>";
100 * Some architectures have virtual memory mappings with a secondary
101 * mapping of the kernel text, i.e. there is more than one virtual
102 * kernel address that points to the kernel image. It is usually
103 * when there is a separate linear physical memory mapping, in that
104 * __pa() is not just the reverse of __va(). This can be detected
107 textlow_linear = (unsigned long)lm_alias(textlow);
108 /* No different mapping: we're done. */
109 if (textlow_linear == textlow)
112 /* Check the secondary mapping... */
113 texthigh_linear = (unsigned long)lm_alias(texthigh);
114 if (overlaps(ptr, n, textlow_linear, texthigh_linear))
115 return "<linear kernel text>";
120 static inline const char *check_bogus_address(const void *ptr, unsigned long n)
122 /* Reject if object wraps past end of memory. */
123 if ((unsigned long)ptr + n < (unsigned long)ptr)
124 return "<wrapped address>";
126 /* Reject if NULL or ZERO-allocation. */
127 if (ZERO_OR_NULL_PTR(ptr))
133 /* Checks for allocs that are marked in some way as spanning multiple pages. */
134 static inline const char *check_page_span(const void *ptr, unsigned long n,
135 struct page *page, bool to_user)
137 #ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN
138 const void *end = ptr + n - 1;
139 struct page *endpage;
140 bool is_reserved, is_cma;
143 * Sometimes the kernel data regions are not marked Reserved (see
144 * check below). And sometimes [_sdata,_edata) does not cover
145 * rodata and/or bss, so check each range explicitly.
148 /* Allow reads of kernel rodata region (if not marked as Reserved). */
149 if (ptr >= (const void *)__start_rodata &&
150 end <= (const void *)__end_rodata) {
156 /* Allow kernel data region (if not marked as Reserved). */
157 if (ptr >= (const void *)_sdata && end <= (const void *)_edata)
160 /* Allow kernel bss region (if not marked as Reserved). */
161 if (ptr >= (const void *)__bss_start &&
162 end <= (const void *)__bss_stop)
165 /* Is the object wholly within one base page? */
166 if (likely(((unsigned long)ptr & (unsigned long)PAGE_MASK) ==
167 ((unsigned long)end & (unsigned long)PAGE_MASK)))
170 /* Allow if fully inside the same compound (__GFP_COMP) page. */
171 endpage = virt_to_head_page(end);
172 if (likely(endpage == page))
176 * Reject if range is entirely either Reserved (i.e. special or
177 * device memory), or CMA. Otherwise, reject since the object spans
178 * several independently allocated pages.
180 is_reserved = PageReserved(page);
181 is_cma = is_migrate_cma_page(page);
182 if (!is_reserved && !is_cma)
183 return "<spans multiple pages>";
185 for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) {
186 page = virt_to_head_page(ptr);
187 if (is_reserved && !PageReserved(page))
188 return "<spans Reserved and non-Reserved pages>";
189 if (is_cma && !is_migrate_cma_page(page))
190 return "<spans CMA and non-CMA pages>";
197 static inline const char *check_heap_object(const void *ptr, unsigned long n,
202 if (!virt_addr_valid(ptr))
205 page = virt_to_head_page(ptr);
207 /* Check slab allocator for flags and size. */
209 return __check_heap_object(ptr, n, page);
211 /* Verify object does not incorrectly span multiple pages. */
212 return check_page_span(ptr, n, page, to_user);
216 * Validates that the given object is:
217 * - not bogus address
218 * - known-safe heap or stack object
219 * - not in kernel text
221 void __check_object_size(const void *ptr, unsigned long n, bool to_user)
225 /* Skip all tests if size is zero. */
229 /* Check for invalid addresses. */
230 err = check_bogus_address(ptr, n);
234 /* Check for bad heap object. */
235 err = check_heap_object(ptr, n, to_user);
239 /* Check for bad stack object. */
240 switch (check_stack_object(ptr, n)) {
242 /* Object is not touching the current process stack. */
247 * Object is either in the correct frame (when it
248 * is possible to check) or just generally on the
249 * process stack (when frame checking not available).
253 err = "<process stack>";
257 /* Check for object in kernel to avoid text exposure. */
258 err = check_kernel_text_object(ptr, n);
263 report_usercopy(n, to_user, err);
265 EXPORT_SYMBOL(__check_object_size);