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/sched.h>
19 #include <linux/slab.h>
20 #include <asm/sections.h>
30 * Checks if a given pointer and length is contained by the current
31 * stack frame (if possible).
34 * NOT_STACK: not at all on the stack
35 * GOOD_FRAME: fully within a valid stack frame
36 * GOOD_STACK: fully on the stack (when can't do frame-checking)
37 * BAD_STACK: error condition (invalid stack position or bad stack frame)
39 static noinline int check_stack_object(const void *obj, unsigned long len)
41 const void * const stack = task_stack_page(current);
42 const void * const stackend = stack + THREAD_SIZE;
45 /* Object is not on the stack at all. */
46 if (obj + len <= stack || stackend <= obj)
50 * Reject: object partially overlaps the stack (passing the
51 * the check above means at least one end is within the stack,
52 * so if this check fails, the other end is outside the stack).
54 if (obj < stack || stackend < obj + len)
57 /* Check if object is safely within a valid frame. */
58 ret = arch_within_stack_frames(stack, stackend, obj, len);
65 static void report_usercopy(const void *ptr, unsigned long len,
66 bool to_user, const char *type)
68 pr_emerg("kernel memory %s attempt detected %s %p (%s) (%lu bytes)\n",
69 to_user ? "exposure" : "overwrite",
70 to_user ? "from" : "to", ptr, type ? : "unknown", len);
72 * For greater effect, it would be nice to do do_group_exit(),
73 * but BUG() actually hooks all the lock-breaking and per-arch
74 * Oops code, so that is used here instead.
79 /* Returns true if any portion of [ptr,ptr+n) over laps with [low,high). */
80 static bool overlaps(const void *ptr, unsigned long n, unsigned long low,
83 unsigned long check_low = (uintptr_t)ptr;
84 unsigned long check_high = check_low + n;
86 /* Does not overlap if entirely above or entirely below. */
87 if (check_low >= high || check_high <= low)
93 /* Is this address range in the kernel text area? */
94 static inline const char *check_kernel_text_object(const void *ptr,
97 unsigned long textlow = (unsigned long)_stext;
98 unsigned long texthigh = (unsigned long)_etext;
99 unsigned long textlow_linear, texthigh_linear;
101 if (overlaps(ptr, n, textlow, texthigh))
102 return "<kernel text>";
105 * Some architectures have virtual memory mappings with a secondary
106 * mapping of the kernel text, i.e. there is more than one virtual
107 * kernel address that points to the kernel image. It is usually
108 * when there is a separate linear physical memory mapping, in that
109 * __pa() is not just the reverse of __va(). This can be detected
112 textlow_linear = (unsigned long)__va(__pa(textlow));
113 /* No different mapping: we're done. */
114 if (textlow_linear == textlow)
117 /* Check the secondary mapping... */
118 texthigh_linear = (unsigned long)__va(__pa(texthigh));
119 if (overlaps(ptr, n, textlow_linear, texthigh_linear))
120 return "<linear kernel text>";
125 static inline const char *check_bogus_address(const void *ptr, unsigned long n)
127 /* Reject if object wraps past end of memory. */
128 if ((unsigned long)ptr + n < (unsigned long)ptr)
129 return "<wrapped address>";
131 /* Reject if NULL or ZERO-allocation. */
132 if (ZERO_OR_NULL_PTR(ptr))
138 /* Checks for allocs that are marked in some way as spanning multiple pages. */
139 static inline const char *check_page_span(const void *ptr, unsigned long n,
140 struct page *page, bool to_user)
142 #ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN
143 const void *end = ptr + n - 1;
144 struct page *endpage;
145 bool is_reserved, is_cma;
148 * Sometimes the kernel data regions are not marked Reserved (see
149 * check below). And sometimes [_sdata,_edata) does not cover
150 * rodata and/or bss, so check each range explicitly.
153 /* Allow reads of kernel rodata region (if not marked as Reserved). */
154 if (ptr >= (const void *)__start_rodata &&
155 end <= (const void *)__end_rodata) {
161 /* Allow kernel data region (if not marked as Reserved). */
162 if (ptr >= (const void *)_sdata && end <= (const void *)_edata)
165 /* Allow kernel bss region (if not marked as Reserved). */
166 if (ptr >= (const void *)__bss_start &&
167 end <= (const void *)__bss_stop)
170 /* Is the object wholly within one base page? */
171 if (likely(((unsigned long)ptr & (unsigned long)PAGE_MASK) ==
172 ((unsigned long)end & (unsigned long)PAGE_MASK)))
175 /* Allow if fully inside the same compound (__GFP_COMP) page. */
176 endpage = virt_to_head_page(end);
177 if (likely(endpage == page))
181 * Reject if range is entirely either Reserved (i.e. special or
182 * device memory), or CMA. Otherwise, reject since the object spans
183 * several independently allocated pages.
185 is_reserved = PageReserved(page);
186 is_cma = is_migrate_cma_page(page);
187 if (!is_reserved && !is_cma)
188 return "<spans multiple pages>";
190 for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) {
191 page = virt_to_head_page(ptr);
192 if (is_reserved && !PageReserved(page))
193 return "<spans Reserved and non-Reserved pages>";
194 if (is_cma && !is_migrate_cma_page(page))
195 return "<spans CMA and non-CMA pages>";
202 static inline const char *check_heap_object(const void *ptr, unsigned long n,
208 * Some architectures (arm64) return true for virt_addr_valid() on
209 * vmalloced addresses. Work around this by checking for vmalloc
212 if (is_vmalloc_addr(ptr))
215 if (!virt_addr_valid(ptr))
218 page = virt_to_head_page(ptr);
220 /* Check slab allocator for flags and size. */
222 return __check_heap_object(ptr, n, page);
224 /* Verify object does not incorrectly span multiple pages. */
225 return check_page_span(ptr, n, page, to_user);
229 * Validates that the given object is:
230 * - not bogus address
231 * - known-safe heap or stack object
232 * - not in kernel text
234 void __check_object_size(const void *ptr, unsigned long n, bool to_user)
238 /* Skip all tests if size is zero. */
242 /* Check for invalid addresses. */
243 err = check_bogus_address(ptr, n);
247 /* Check for bad heap object. */
248 err = check_heap_object(ptr, n, to_user);
252 /* Check for bad stack object. */
253 switch (check_stack_object(ptr, n)) {
255 /* Object is not touching the current process stack. */
260 * Object is either in the correct frame (when it
261 * is possible to check) or just generally on the
262 * process stack (when frame checking not available).
266 err = "<process stack>";
270 /* Check for object in kernel to avoid text exposure. */
271 err = check_kernel_text_object(ptr, n);
276 report_usercopy(ptr, n, to_user, err);
278 EXPORT_SYMBOL(__check_object_size);