Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 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> |
Kees Cook | a93e0bc | 2019-09-17 11:00:25 -0700 | [diff] [blame] | 18 | #include <linux/highmem.h> |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 19 | #include <linux/slab.h> |
Ingo Molnar | 5b825c3 | 2017-02-02 17:54:15 +0100 | [diff] [blame] | 20 | #include <linux/sched.h> |
Ingo Molnar | 2993002 | 2017-02-08 18:51:36 +0100 | [diff] [blame] | 21 | #include <linux/sched/task.h> |
| 22 | #include <linux/sched/task_stack.h> |
Sahara | 96dc4f9 | 2017-02-16 18:29:15 +0000 | [diff] [blame] | 23 | #include <linux/thread_info.h> |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 24 | #include <asm/sections.h> |
| 25 | |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 26 | /* |
| 27 | * Checks if a given pointer and length is contained by the current |
| 28 | * stack frame (if possible). |
| 29 | * |
| 30 | * Returns: |
| 31 | * NOT_STACK: not at all on the stack |
| 32 | * GOOD_FRAME: fully within a valid stack frame |
| 33 | * GOOD_STACK: fully on the stack (when can't do frame-checking) |
| 34 | * BAD_STACK: error condition (invalid stack position or bad stack frame) |
| 35 | */ |
| 36 | static noinline int check_stack_object(const void *obj, unsigned long len) |
| 37 | { |
| 38 | const void * const stack = task_stack_page(current); |
| 39 | const void * const stackend = stack + THREAD_SIZE; |
| 40 | int ret; |
| 41 | |
| 42 | /* Object is not on the stack at all. */ |
| 43 | if (obj + len <= stack || stackend <= obj) |
| 44 | return NOT_STACK; |
| 45 | |
| 46 | /* |
| 47 | * Reject: object partially overlaps the stack (passing the |
| 48 | * the check above means at least one end is within the stack, |
| 49 | * so if this check fails, the other end is outside the stack). |
| 50 | */ |
| 51 | if (obj < stack || stackend < obj + len) |
| 52 | return BAD_STACK; |
| 53 | |
| 54 | /* Check if object is safely within a valid frame. */ |
| 55 | ret = arch_within_stack_frames(stack, stackend, obj, len); |
| 56 | if (ret) |
| 57 | return ret; |
| 58 | |
| 59 | return GOOD_STACK; |
| 60 | } |
| 61 | |
| 62 | static void report_usercopy(const void *ptr, unsigned long len, |
| 63 | bool to_user, const char *type) |
| 64 | { |
| 65 | pr_emerg("kernel memory %s attempt detected %s %p (%s) (%lu bytes)\n", |
| 66 | to_user ? "exposure" : "overwrite", |
| 67 | to_user ? "from" : "to", ptr, type ? : "unknown", len); |
| 68 | /* |
| 69 | * For greater effect, it would be nice to do do_group_exit(), |
| 70 | * but BUG() actually hooks all the lock-breaking and per-arch |
| 71 | * Oops code, so that is used here instead. |
| 72 | */ |
| 73 | BUG(); |
| 74 | } |
| 75 | |
| 76 | /* Returns true if any portion of [ptr,ptr+n) over laps with [low,high). */ |
| 77 | static bool overlaps(const void *ptr, unsigned long n, unsigned long low, |
| 78 | unsigned long high) |
| 79 | { |
| 80 | unsigned long check_low = (uintptr_t)ptr; |
| 81 | unsigned long check_high = check_low + n; |
| 82 | |
| 83 | /* Does not overlap if entirely above or entirely below. */ |
Josh Poimboeuf | 94cd97a | 2016-08-22 11:53:59 -0500 | [diff] [blame] | 84 | if (check_low >= high || check_high <= low) |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 85 | return false; |
| 86 | |
| 87 | return true; |
| 88 | } |
| 89 | |
| 90 | /* Is this address range in the kernel text area? */ |
| 91 | static inline const char *check_kernel_text_object(const void *ptr, |
| 92 | unsigned long n) |
| 93 | { |
| 94 | unsigned long textlow = (unsigned long)_stext; |
| 95 | unsigned long texthigh = (unsigned long)_etext; |
| 96 | unsigned long textlow_linear, texthigh_linear; |
| 97 | |
| 98 | if (overlaps(ptr, n, textlow, texthigh)) |
| 99 | return "<kernel text>"; |
| 100 | |
| 101 | /* |
| 102 | * Some architectures have virtual memory mappings with a secondary |
| 103 | * mapping of the kernel text, i.e. there is more than one virtual |
| 104 | * kernel address that points to the kernel image. It is usually |
| 105 | * when there is a separate linear physical memory mapping, in that |
| 106 | * __pa() is not just the reverse of __va(). This can be detected |
| 107 | * and checked: |
| 108 | */ |
Laura Abbott | 46f6236 | 2017-01-10 13:35:45 -0800 | [diff] [blame] | 109 | textlow_linear = (unsigned long)lm_alias(textlow); |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 110 | /* No different mapping: we're done. */ |
| 111 | if (textlow_linear == textlow) |
| 112 | return NULL; |
| 113 | |
| 114 | /* Check the secondary mapping... */ |
Laura Abbott | 46f6236 | 2017-01-10 13:35:45 -0800 | [diff] [blame] | 115 | texthigh_linear = (unsigned long)lm_alias(texthigh); |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 116 | if (overlaps(ptr, n, textlow_linear, texthigh_linear)) |
| 117 | return "<linear kernel text>"; |
| 118 | |
| 119 | return NULL; |
| 120 | } |
| 121 | |
| 122 | static inline const char *check_bogus_address(const void *ptr, unsigned long n) |
| 123 | { |
| 124 | /* Reject if object wraps past end of memory. */ |
Isaac J. Manjarres | 3e7e801 | 2019-08-13 15:37:37 -0700 | [diff] [blame] | 125 | if ((unsigned long)ptr + (n - 1) < (unsigned long)ptr) |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 126 | return "<wrapped address>"; |
| 127 | |
| 128 | /* Reject if NULL or ZERO-allocation. */ |
| 129 | if (ZERO_OR_NULL_PTR(ptr)) |
| 130 | return "<null>"; |
| 131 | |
| 132 | return NULL; |
| 133 | } |
| 134 | |
Kees Cook | 8e1f74e | 2016-09-07 09:54:34 -0700 | [diff] [blame] | 135 | /* Checks for allocs that are marked in some way as spanning multiple pages. */ |
| 136 | static inline const char *check_page_span(const void *ptr, unsigned long n, |
| 137 | struct page *page, bool to_user) |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 138 | { |
Kees Cook | 8e1f74e | 2016-09-07 09:54:34 -0700 | [diff] [blame] | 139 | #ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 140 | const void *end = ptr + n - 1; |
Kees Cook | 8e1f74e | 2016-09-07 09:54:34 -0700 | [diff] [blame] | 141 | struct page *endpage; |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 142 | bool is_reserved, is_cma; |
| 143 | |
| 144 | /* |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 145 | * Sometimes the kernel data regions are not marked Reserved (see |
| 146 | * check below). And sometimes [_sdata,_edata) does not cover |
| 147 | * rodata and/or bss, so check each range explicitly. |
| 148 | */ |
| 149 | |
| 150 | /* Allow reads of kernel rodata region (if not marked as Reserved). */ |
| 151 | if (ptr >= (const void *)__start_rodata && |
| 152 | end <= (const void *)__end_rodata) { |
| 153 | if (!to_user) |
| 154 | return "<rodata>"; |
| 155 | return NULL; |
| 156 | } |
| 157 | |
| 158 | /* Allow kernel data region (if not marked as Reserved). */ |
| 159 | if (ptr >= (const void *)_sdata && end <= (const void *)_edata) |
| 160 | return NULL; |
| 161 | |
| 162 | /* Allow kernel bss region (if not marked as Reserved). */ |
| 163 | if (ptr >= (const void *)__bss_start && |
| 164 | end <= (const void *)__bss_stop) |
| 165 | return NULL; |
| 166 | |
| 167 | /* Is the object wholly within one base page? */ |
| 168 | if (likely(((unsigned long)ptr & (unsigned long)PAGE_MASK) == |
| 169 | ((unsigned long)end & (unsigned long)PAGE_MASK))) |
| 170 | return NULL; |
| 171 | |
Kees Cook | 8e1f74e | 2016-09-07 09:54:34 -0700 | [diff] [blame] | 172 | /* Allow if fully inside the same compound (__GFP_COMP) page. */ |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 173 | endpage = virt_to_head_page(end); |
| 174 | if (likely(endpage == page)) |
| 175 | return NULL; |
| 176 | |
| 177 | /* |
| 178 | * Reject if range is entirely either Reserved (i.e. special or |
| 179 | * device memory), or CMA. Otherwise, reject since the object spans |
| 180 | * several independently allocated pages. |
| 181 | */ |
| 182 | is_reserved = PageReserved(page); |
| 183 | is_cma = is_migrate_cma_page(page); |
| 184 | if (!is_reserved && !is_cma) |
Kees Cook | 8e1f74e | 2016-09-07 09:54:34 -0700 | [diff] [blame] | 185 | return "<spans multiple pages>"; |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 186 | |
| 187 | for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) { |
| 188 | page = virt_to_head_page(ptr); |
| 189 | if (is_reserved && !PageReserved(page)) |
Kees Cook | 8e1f74e | 2016-09-07 09:54:34 -0700 | [diff] [blame] | 190 | return "<spans Reserved and non-Reserved pages>"; |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 191 | if (is_cma && !is_migrate_cma_page(page)) |
Kees Cook | 8e1f74e | 2016-09-07 09:54:34 -0700 | [diff] [blame] | 192 | return "<spans CMA and non-CMA pages>"; |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 193 | } |
Kees Cook | 8e1f74e | 2016-09-07 09:54:34 -0700 | [diff] [blame] | 194 | #endif |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 195 | |
| 196 | return NULL; |
Kees Cook | 8e1f74e | 2016-09-07 09:54:34 -0700 | [diff] [blame] | 197 | } |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 198 | |
Kees Cook | 8e1f74e | 2016-09-07 09:54:34 -0700 | [diff] [blame] | 199 | static inline const char *check_heap_object(const void *ptr, unsigned long n, |
| 200 | bool to_user) |
| 201 | { |
| 202 | struct page *page; |
| 203 | |
Kees Cook | 8e1f74e | 2016-09-07 09:54:34 -0700 | [diff] [blame] | 204 | if (!virt_addr_valid(ptr)) |
| 205 | return NULL; |
| 206 | |
Kees Cook | a93e0bc | 2019-09-17 11:00:25 -0700 | [diff] [blame] | 207 | /* |
| 208 | * When CONFIG_HIGHMEM=y, kmap_to_page() will give either the |
| 209 | * highmem page or fallback to virt_to_page(). The following |
| 210 | * is effectively a highmem-aware virt_to_head_page(). |
| 211 | */ |
| 212 | page = compound_head(kmap_to_page((void *)ptr)); |
Kees Cook | 8e1f74e | 2016-09-07 09:54:34 -0700 | [diff] [blame] | 213 | |
| 214 | /* Check slab allocator for flags and size. */ |
| 215 | if (PageSlab(page)) |
| 216 | return __check_heap_object(ptr, n, page); |
| 217 | |
| 218 | /* Verify object does not incorrectly span multiple pages. */ |
| 219 | return check_page_span(ptr, n, page, to_user); |
Kees Cook | f5509cc | 2016-06-07 11:05:33 -0700 | [diff] [blame] | 220 | } |
| 221 | |
| 222 | /* |
| 223 | * Validates that the given object is: |
| 224 | * - not bogus address |
| 225 | * - known-safe heap or stack object |
| 226 | * - not in kernel text |
| 227 | */ |
| 228 | void __check_object_size(const void *ptr, unsigned long n, bool to_user) |
| 229 | { |
| 230 | const char *err; |
| 231 | |
| 232 | /* Skip all tests if size is zero. */ |
| 233 | if (!n) |
| 234 | return; |
| 235 | |
| 236 | /* Check for invalid addresses. */ |
| 237 | err = check_bogus_address(ptr, n); |
| 238 | if (err) |
| 239 | goto report; |
| 240 | |
| 241 | /* Check for bad heap object. */ |
| 242 | err = check_heap_object(ptr, n, to_user); |
| 243 | if (err) |
| 244 | goto report; |
| 245 | |
| 246 | /* Check for bad stack object. */ |
| 247 | switch (check_stack_object(ptr, n)) { |
| 248 | case NOT_STACK: |
| 249 | /* Object is not touching the current process stack. */ |
| 250 | break; |
| 251 | case GOOD_FRAME: |
| 252 | case GOOD_STACK: |
| 253 | /* |
| 254 | * Object is either in the correct frame (when it |
| 255 | * is possible to check) or just generally on the |
| 256 | * process stack (when frame checking not available). |
| 257 | */ |
| 258 | return; |
| 259 | default: |
| 260 | err = "<process stack>"; |
| 261 | goto report; |
| 262 | } |
| 263 | |
| 264 | /* Check for object in kernel to avoid text exposure. */ |
| 265 | err = check_kernel_text_object(ptr, n); |
| 266 | if (!err) |
| 267 | return; |
| 268 | |
| 269 | report: |
| 270 | report_usercopy(ptr, n, to_user, err); |
| 271 | } |
| 272 | EXPORT_SYMBOL(__check_object_size); |