drivers/misc/lkdtm_usercopy.c

   1 /*
   2  * This is for all the tests related to copy_to_user() and copy_from_user()
   3  * hardening.
   4  */
   5 #include "lkdtm.h"
   6 #include <linux/slab.h>
   7 #include <linux/vmalloc.h>
   8 #include <linux/sched/task_stack.h>
   9 #include <linux/mman.h>
  10 #include <linux/uaccess.h>
  11 #include <asm/cacheflush.h>
  12
  13 /*
  14  * Many of the tests here end up using const sizes, but those would
  15  * normally be ignored by hardened usercopy, so force the compiler
  16  * into choosing the non-const path to make sure we trigger the
  17  * hardened usercopy checks by added "unconst" to all the const copies,
  18  * and making sure "cache_size" isn't optimized into a const.
  19  */
  20 static volatile size_t unconst = 0;
  21 static volatile size_t cache_size = 1024;
  22 static struct kmem_cache *bad_cache;
  23
  24 static const unsigned char test_text[] = "This is a test.\n";
  25
  26 /*
  27  * Instead of adding -Wno-return-local-addr, just pass the stack address
  28  * through a function to obfuscate it from the compiler.
  29  */
  30 static noinline unsigned char *trick_compiler(unsigned char *stack)
  31 {
  32         return stack + 0;
  33 }
  34
  35 static noinline unsigned char *do_usercopy_stack_callee(int value)
  36 {
  37         unsigned char buf[32];
  38         int i;
  39
  40         /* Exercise stack to avoid everything living in registers. */
  41         for (i = 0; i < sizeof(buf); i++) {
  42                 buf[i] = value & 0xff;
  43         }
  44
  45         return trick_compiler(buf);
  46 }
  47
  48 static noinline void do_usercopy_stack(bool to_user, bool bad_frame)
  49 {
  50         unsigned long user_addr;
  51         unsigned char good_stack[32];
  52         unsigned char *bad_stack;
  53         int i;
  54
  55         /* Exercise stack to avoid everything living in registers. */
  56         for (i = 0; i < sizeof(good_stack); i++)
  57                 good_stack[i] = test_text[i % sizeof(test_text)];
  58
  59         /* This is a pointer to outside our current stack frame. */
  60         if (bad_frame) {
  61                 bad_stack = do_usercopy_stack_callee((uintptr_t)&bad_stack);
  62         } else {
  63                 /* Put start address just inside stack. */
  64                 bad_stack = task_stack_page(current) + THREAD_SIZE;
  65                 bad_stack -= sizeof(unsigned long);
  66         }
  67
  68         user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
  69                             PROT_READ | PROT_WRITE | PROT_EXEC,
  70                             MAP_ANONYMOUS | MAP_PRIVATE, 0);
  71         if (user_addr >= TASK_SIZE) {
  72                 pr_warn("Failed to allocate user memory\n");
  73                 return;
  74         }
  75
  76         if (to_user) {
  77                 pr_info("attempting good copy_to_user of local stack\n");
  78                 if (copy_to_user((void __user *)user_addr, good_stack,
  79                                  unconst + sizeof(good_stack))) {
  80                         pr_warn("copy_to_user failed unexpectedly?!\n");
  81                         goto free_user;
  82                 }
  83
  84                 pr_info("attempting bad copy_to_user of distant stack\n");
  85                 if (copy_to_user((void __user *)user_addr, bad_stack,
  86                                  unconst + sizeof(good_stack))) {
  87                         pr_warn("copy_to_user failed, but lacked Oops\n");
  88                         goto free_user;
  89                 }
  90         } else {
  91                 /*
  92                  * There isn't a safe way to not be protected by usercopy
  93                  * if we're going to write to another thread's stack.
  94                  */
  95                 if (!bad_frame)
  96                         goto free_user;
  97
  98                 pr_info("attempting good copy_from_user of local stack\n");
  99                 if (copy_from_user(good_stack, (void __user *)user_addr,
 100                                    unconst + sizeof(good_stack))) {
 101                         pr_warn("copy_from_user failed unexpectedly?!\n");
 102                         goto free_user;
 103                 }
 104
 105                 pr_info("attempting bad copy_from_user of distant stack\n");
 106                 if (copy_from_user(bad_stack, (void __user *)user_addr,
 107                                    unconst + sizeof(good_stack))) {
 108                         pr_warn("copy_from_user failed, but lacked Oops\n");
 109                         goto free_user;
 110                 }
 111         }
 112
 113 free_user:
 114         vm_munmap(user_addr, PAGE_SIZE);
 115 }
 116
 117 static void do_usercopy_heap_size(bool to_user)
 118 {
 119         unsigned long user_addr;
 120         unsigned char *one, *two;
 121         size_t size = unconst + 1024;
 122
 123         one = kmalloc(size, GFP_KERNEL);
 124         two = kmalloc(size, GFP_KERNEL);
 125         if (!one || !two) {
 126                 pr_warn("Failed to allocate kernel memory\n");
 127                 goto free_kernel;
 128         }
 129
 130         user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
 131                             PROT_READ | PROT_WRITE | PROT_EXEC,
 132                             MAP_ANONYMOUS | MAP_PRIVATE, 0);
 133         if (user_addr >= TASK_SIZE) {
 134                 pr_warn("Failed to allocate user memory\n");
 135                 goto free_kernel;
 136         }
 137
 138         memset(one, 'A', size);
 139         memset(two, 'B', size);
 140
 141         if (to_user) {
 142                 pr_info("attempting good copy_to_user of correct size\n");
 143                 if (copy_to_user((void __user *)user_addr, one, size)) {
 144                         pr_warn("copy_to_user failed unexpectedly?!\n");
 145                         goto free_user;
 146                 }
 147
 148                 pr_info("attempting bad copy_to_user of too large size\n");
 149                 if (copy_to_user((void __user *)user_addr, one, 2 * size)) {
 150                         pr_warn("copy_to_user failed, but lacked Oops\n");
 151                         goto free_user;
 152                 }
 153         } else {
 154                 pr_info("attempting good copy_from_user of correct size\n");
 155                 if (copy_from_user(one, (void __user *)user_addr, size)) {
 156                         pr_warn("copy_from_user failed unexpectedly?!\n");
 157                         goto free_user;
 158                 }
 159
 160                 pr_info("attempting bad copy_from_user of too large size\n");
 161                 if (copy_from_user(one, (void __user *)user_addr, 2 * size)) {
 162                         pr_warn("copy_from_user failed, but lacked Oops\n");
 163                         goto free_user;
 164                 }
 165         }
 166
 167 free_user:
 168         vm_munmap(user_addr, PAGE_SIZE);
 169 free_kernel:
 170         kfree(one);
 171         kfree(two);
 172 }
 173
 174 static void do_usercopy_heap_flag(bool to_user)
 175 {
 176         unsigned long user_addr;
 177         unsigned char *good_buf = NULL;
 178         unsigned char *bad_buf = NULL;
 179
 180         /* Make sure cache was prepared. */
 181         if (!bad_cache) {
 182                 pr_warn("Failed to allocate kernel cache\n");
 183                 return;
 184         }
 185
 186         /*
 187          * Allocate one buffer from each cache (kmalloc will have the
 188          * SLAB_USERCOPY flag already, but "bad_cache" won't).
 189          */
 190         good_buf = kmalloc(cache_size, GFP_KERNEL);
 191         bad_buf = kmem_cache_alloc(bad_cache, GFP_KERNEL);
 192         if (!good_buf || !bad_buf) {
 193                 pr_warn("Failed to allocate buffers from caches\n");
 194                 goto free_alloc;
 195         }
 196
 197         /* Allocate user memory we'll poke at. */
 198         user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
 199                             PROT_READ | PROT_WRITE | PROT_EXEC,
 200                             MAP_ANONYMOUS | MAP_PRIVATE, 0);
 201         if (user_addr >= TASK_SIZE) {
 202                 pr_warn("Failed to allocate user memory\n");
 203                 goto free_alloc;
 204         }
 205
 206         memset(good_buf, 'A', cache_size);
 207         memset(bad_buf, 'B', cache_size);
 208
 209         if (to_user) {
 210                 pr_info("attempting good copy_to_user with SLAB_USERCOPY\n");
 211                 if (copy_to_user((void __user *)user_addr, good_buf,
 212                                  cache_size)) {
 213                         pr_warn("copy_to_user failed unexpectedly?!\n");
 214                         goto free_user;
 215                 }
 216
 217                 pr_info("attempting bad copy_to_user w/o SLAB_USERCOPY\n");
 218                 if (copy_to_user((void __user *)user_addr, bad_buf,
 219                                  cache_size)) {
 220                         pr_warn("copy_to_user failed, but lacked Oops\n");
 221                         goto free_user;
 222                 }
 223         } else {
 224                 pr_info("attempting good copy_from_user with SLAB_USERCOPY\n");
 225                 if (copy_from_user(good_buf, (void __user *)user_addr,
 226                                    cache_size)) {
 227                         pr_warn("copy_from_user failed unexpectedly?!\n");
 228                         goto free_user;
 229                 }
 230
 231                 pr_info("attempting bad copy_from_user w/o SLAB_USERCOPY\n");
 232                 if (copy_from_user(bad_buf, (void __user *)user_addr,
 233                                    cache_size)) {
 234                         pr_warn("copy_from_user failed, but lacked Oops\n");
 235                         goto free_user;
 236                 }
 237         }
 238
 239 free_user:
 240         vm_munmap(user_addr, PAGE_SIZE);
 241 free_alloc:
 242         if (bad_buf)
 243                 kmem_cache_free(bad_cache, bad_buf);
 244         kfree(good_buf);
 245 }
 246
 247 /* Callable tests. */
 248 void lkdtm_USERCOPY_HEAP_SIZE_TO(void)
 249 {
 250         do_usercopy_heap_size(true);
 251 }
 252
 253 void lkdtm_USERCOPY_HEAP_SIZE_FROM(void)
 254 {
 255         do_usercopy_heap_size(false);
 256 }
 257
 258 void lkdtm_USERCOPY_HEAP_FLAG_TO(void)
 259 {
 260         do_usercopy_heap_flag(true);
 261 }
 262
 263 void lkdtm_USERCOPY_HEAP_FLAG_FROM(void)
 264 {
 265         do_usercopy_heap_flag(false);
 266 }
 267
 268 void lkdtm_USERCOPY_STACK_FRAME_TO(void)
 269 {
 270         do_usercopy_stack(true, true);
 271 }
 272
 273 void lkdtm_USERCOPY_STACK_FRAME_FROM(void)
 274 {
 275         do_usercopy_stack(false, true);
 276 }
 277
 278 void lkdtm_USERCOPY_STACK_BEYOND(void)
 279 {
 280         do_usercopy_stack(true, false);
 281 }
 282
 283 void lkdtm_USERCOPY_KERNEL(void)
 284 {
 285         unsigned long user_addr;
 286
 287         user_addr = vm_mmap(NULL, 0, PAGE_SIZE,
 288                             PROT_READ | PROT_WRITE | PROT_EXEC,
 289                             MAP_ANONYMOUS | MAP_PRIVATE, 0);
 290         if (user_addr >= TASK_SIZE) {
 291                 pr_warn("Failed to allocate user memory\n");
 292                 return;
 293         }
 294
 295         pr_info("attempting good copy_to_user from kernel rodata\n");
 296         if (copy_to_user((void __user *)user_addr, test_text,
 297                          unconst + sizeof(test_text))) {
 298                 pr_warn("copy_to_user failed unexpectedly?!\n");
 299                 goto free_user;
 300         }
 301
 302         pr_info("attempting bad copy_to_user from kernel text\n");
 303         if (copy_to_user((void __user *)user_addr, vm_mmap,
 304                          unconst + PAGE_SIZE)) {
 305                 pr_warn("copy_to_user failed, but lacked Oops\n");
 306                 goto free_user;
 307         }
 308
 309 free_user:
 310         vm_munmap(user_addr, PAGE_SIZE);
 311 }
 312
 313 void __init lkdtm_usercopy_init(void)
 314 {
 315         /* Prepare cache that lacks SLAB_USERCOPY flag. */
 316         bad_cache = kmem_cache_create("lkdtm-no-usercopy", cache_size, 0,
 317                                       0, NULL);
 318 }
 319
 320 void __exit lkdtm_usercopy_exit(void)
 321 {
 322         kmem_cache_destroy(bad_cache);
 323 }