drivers/misc/lkdtm/bugs.c

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This source file includes following definitions.
recursive_loop
lkdtm_bugs_init
lkdtm_PANIC
lkdtm_BUG
lkdtm_WARNING
lkdtm_WARNING_MESSAGE
lkdtm_EXCEPTION
lkdtm_LOOP
lkdtm_EXHAUST_STACK
__lkdtm_CORRUPT_STACK
lkdtm_CORRUPT_STACK
lkdtm_CORRUPT_STACK_STRONG
lkdtm_UNALIGNED_LOAD_STORE_WRITE
lkdtm_SOFTLOCKUP
lkdtm_HARDLOCKUP
lkdtm_SPINLOCKUP
lkdtm_HUNG_TASK
lkdtm_CORRUPT_LIST_ADD
lkdtm_CORRUPT_LIST_DEL
lkdtm_CORRUPT_USER_DS
lkdtm_STACK_GUARD_PAGE_LEADING
lkdtm_STACK_GUARD_PAGE_TRAILING
lkdtm_UNSET_SMEP
   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * This is for all the tests related to logic bugs (e.g. bad dereferences,
   4  * bad alignment, bad loops, bad locking, bad scheduling, deep stacks, and
   5  * lockups) along with other things that don't fit well into existing LKDTM
   6  * test source files.
   7  */
   8 #include "lkdtm.h"
   9 #include <linux/list.h>
  10 #include <linux/sched.h>
  11 #include <linux/sched/signal.h>
  12 #include <linux/sched/task_stack.h>
  13 #include <linux/uaccess.h>
  14 
  15 struct lkdtm_list {
  16         struct list_head node;
  17 };
  18 
  19 /*
  20  * Make sure our attempts to over run the kernel stack doesn't trigger
  21  * a compiler warning when CONFIG_FRAME_WARN is set. Then make sure we
  22  * recurse past the end of THREAD_SIZE by default.
  23  */
  24 #if defined(CONFIG_FRAME_WARN) && (CONFIG_FRAME_WARN > 0)
  25 #define REC_STACK_SIZE (_AC(CONFIG_FRAME_WARN, UL) / 2)
  26 #else
  27 #define REC_STACK_SIZE (THREAD_SIZE / 8)
  28 #endif
  29 #define REC_NUM_DEFAULT ((THREAD_SIZE / REC_STACK_SIZE) * 2)
  30 
  31 static int recur_count = REC_NUM_DEFAULT;
  32 
  33 static DEFINE_SPINLOCK(lock_me_up);
  34 
  35 /*
  36  * Make sure compiler does not optimize this function or stack frame away:
  37  * - function marked noinline
  38  * - stack variables are marked volatile
  39  * - stack variables are written (memset()) and read (pr_info())
  40  * - function has external effects (pr_info())
  41  * */
  42 static int noinline recursive_loop(int remaining)
  43 {
  44         volatile char buf[REC_STACK_SIZE];
  45 
  46         memset((void *)buf, remaining & 0xFF, sizeof(buf));
  47         pr_info("loop %d/%d ...\n", (int)buf[remaining % sizeof(buf)],
  48                 recur_count);
  49         if (!remaining)
  50                 return 0;
  51         else
  52                 return recursive_loop(remaining - 1);
  53 }
  54 
  55 /* If the depth is negative, use the default, otherwise keep parameter. */
  56 void __init lkdtm_bugs_init(int *recur_param)
  57 {
  58         if (*recur_param < 0)
  59                 *recur_param = recur_count;
  60         else
  61                 recur_count = *recur_param;
  62 }
  63 
  64 void lkdtm_PANIC(void)
  65 {
  66         panic("dumptest");
  67 }
  68 
  69 void lkdtm_BUG(void)
  70 {
  71         BUG();
  72 }
  73 
  74 static int warn_counter;
  75 
  76 void lkdtm_WARNING(void)
  77 {
  78         WARN_ON(++warn_counter);
  79 }
  80 
  81 void lkdtm_WARNING_MESSAGE(void)
  82 {
  83         WARN(1, "Warning message trigger count: %d\n", ++warn_counter);
  84 }
  85 
  86 void lkdtm_EXCEPTION(void)
  87 {
  88         *((volatile int *) 0) = 0;
  89 }
  90 
  91 void lkdtm_LOOP(void)
  92 {
  93         for (;;)
  94                 ;
  95 }
  96 
  97 void lkdtm_EXHAUST_STACK(void)
  98 {
  99         pr_info("Calling function with %lu frame size to depth %d ...\n",
 100                 REC_STACK_SIZE, recur_count);
 101         recursive_loop(recur_count);
 102         pr_info("FAIL: survived without exhausting stack?!\n");
 103 }
 104 
 105 static noinline void __lkdtm_CORRUPT_STACK(void *stack)
 106 {
 107         memset(stack, '\xff', 64);
 108 }
 109 
 110 /* This should trip the stack canary, not corrupt the return address. */
 111 noinline void lkdtm_CORRUPT_STACK(void)
 112 {
 113         /* Use default char array length that triggers stack protection. */
 114         char data[8] __aligned(sizeof(void *));
 115 
 116         __lkdtm_CORRUPT_STACK(&data);
 117 
 118         pr_info("Corrupted stack containing char array ...\n");
 119 }
 120 
 121 /* Same as above but will only get a canary with -fstack-protector-strong */
 122 noinline void lkdtm_CORRUPT_STACK_STRONG(void)
 123 {
 124         union {
 125                 unsigned short shorts[4];
 126                 unsigned long *ptr;
 127         } data __aligned(sizeof(void *));
 128 
 129         __lkdtm_CORRUPT_STACK(&data);
 130 
 131         pr_info("Corrupted stack containing union ...\n");
 132 }
 133 
 134 void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void)
 135 {
 136         static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5};
 137         u32 *p;
 138         u32 val = 0x12345678;
 139 
 140         p = (u32 *)(data + 1);
 141         if (*p == 0)
 142                 val = 0x87654321;
 143         *p = val;
 144 }
 145 
 146 void lkdtm_SOFTLOCKUP(void)
 147 {
 148         preempt_disable();
 149         for (;;)
 150                 cpu_relax();
 151 }
 152 
 153 void lkdtm_HARDLOCKUP(void)
 154 {
 155         local_irq_disable();
 156         for (;;)
 157                 cpu_relax();
 158 }
 159 
 160 void lkdtm_SPINLOCKUP(void)
 161 {
 162         /* Must be called twice to trigger. */
 163         spin_lock(&lock_me_up);
 164         /* Let sparse know we intended to exit holding the lock. */
 165         __release(&lock_me_up);
 166 }
 167 
 168 void lkdtm_HUNG_TASK(void)
 169 {
 170         set_current_state(TASK_UNINTERRUPTIBLE);
 171         schedule();
 172 }
 173 
 174 void lkdtm_CORRUPT_LIST_ADD(void)
 175 {
 176         /*
 177          * Initially, an empty list via LIST_HEAD:
 178          *      test_head.next = &test_head
 179          *      test_head.prev = &test_head
 180          */
 181         LIST_HEAD(test_head);
 182         struct lkdtm_list good, bad;
 183         void *target[2] = { };
 184         void *redirection = &target;
 185 
 186         pr_info("attempting good list addition\n");
 187 
 188         /*
 189          * Adding to the list performs these actions:
 190          *      test_head.next->prev = &good.node
 191          *      good.node.next = test_head.next
 192          *      good.node.prev = test_head
 193          *      test_head.next = good.node
 194          */
 195         list_add(&good.node, &test_head);
 196 
 197         pr_info("attempting corrupted list addition\n");
 198         /*
 199          * In simulating this "write what where" primitive, the "what" is
 200          * the address of &bad.node, and the "where" is the address held
 201          * by "redirection".
 202          */
 203         test_head.next = redirection;
 204         list_add(&bad.node, &test_head);
 205 
 206         if (target[0] == NULL && target[1] == NULL)
 207                 pr_err("Overwrite did not happen, but no BUG?!\n");
 208         else
 209                 pr_err("list_add() corruption not detected!\n");
 210 }
 211 
 212 void lkdtm_CORRUPT_LIST_DEL(void)
 213 {
 214         LIST_HEAD(test_head);
 215         struct lkdtm_list item;
 216         void *target[2] = { };
 217         void *redirection = &target;
 218 
 219         list_add(&item.node, &test_head);
 220 
 221         pr_info("attempting good list removal\n");
 222         list_del(&item.node);
 223 
 224         pr_info("attempting corrupted list removal\n");
 225         list_add(&item.node, &test_head);
 226 
 227         /* As with the list_add() test above, this corrupts "next". */
 228         item.node.next = redirection;
 229         list_del(&item.node);
 230 
 231         if (target[0] == NULL && target[1] == NULL)
 232                 pr_err("Overwrite did not happen, but no BUG?!\n");
 233         else
 234                 pr_err("list_del() corruption not detected!\n");
 235 }
 236 
 237 /* Test if unbalanced set_fs(KERNEL_DS)/set_fs(USER_DS) check exists. */
 238 void lkdtm_CORRUPT_USER_DS(void)
 239 {
 240         pr_info("setting bad task size limit\n");
 241         set_fs(KERNEL_DS);
 242 
 243         /* Make sure we do not keep running with a KERNEL_DS! */
 244         force_sig(SIGKILL);
 245 }
 246 
 247 /* Test that VMAP_STACK is actually allocating with a leading guard page */
 248 void lkdtm_STACK_GUARD_PAGE_LEADING(void)
 249 {
 250         const unsigned char *stack = task_stack_page(current);
 251         const unsigned char *ptr = stack - 1;
 252         volatile unsigned char byte;
 253 
 254         pr_info("attempting bad read from page below current stack\n");
 255 
 256         byte = *ptr;
 257 
 258         pr_err("FAIL: accessed page before stack!\n");
 259 }
 260 
 261 /* Test that VMAP_STACK is actually allocating with a trailing guard page */
 262 void lkdtm_STACK_GUARD_PAGE_TRAILING(void)
 263 {
 264         const unsigned char *stack = task_stack_page(current);
 265         const unsigned char *ptr = stack + THREAD_SIZE;
 266         volatile unsigned char byte;
 267 
 268         pr_info("attempting bad read from page above current stack\n");
 269 
 270         byte = *ptr;
 271 
 272         pr_err("FAIL: accessed page after stack!\n");
 273 }
 274 
 275 void lkdtm_UNSET_SMEP(void)
 276 {
 277 #if IS_ENABLED(CONFIG_X86_64) && !IS_ENABLED(CONFIG_UML)
 278 #define MOV_CR4_DEPTH   64
 279         void (*direct_write_cr4)(unsigned long val);
 280         unsigned char *insn;
 281         unsigned long cr4;
 282         int i;
 283 
 284         cr4 = native_read_cr4();
 285 
 286         if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) {
 287                 pr_err("FAIL: SMEP not in use\n");
 288                 return;
 289         }
 290         cr4 &= ~(X86_CR4_SMEP);
 291 
 292         pr_info("trying to clear SMEP normally\n");
 293         native_write_cr4(cr4);
 294         if (cr4 == native_read_cr4()) {
 295                 pr_err("FAIL: pinning SMEP failed!\n");
 296                 cr4 |= X86_CR4_SMEP;
 297                 pr_info("restoring SMEP\n");
 298                 native_write_cr4(cr4);
 299                 return;
 300         }
 301         pr_info("ok: SMEP did not get cleared\n");
 302 
 303         /*
 304          * To test the post-write pinning verification we need to call
 305          * directly into the middle of native_write_cr4() where the
 306          * cr4 write happens, skipping any pinning. This searches for
 307          * the cr4 writing instruction.
 308          */
 309         insn = (unsigned char *)native_write_cr4;
 310         for (i = 0; i < MOV_CR4_DEPTH; i++) {
 311                 /* mov %rdi, %cr4 */
 312                 if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7)
 313                         break;
 314                 /* mov %rdi,%rax; mov %rax, %cr4 */
 315                 if (insn[i]   == 0x48 && insn[i+1] == 0x89 &&
 316                     insn[i+2] == 0xf8 && insn[i+3] == 0x0f &&
 317                     insn[i+4] == 0x22 && insn[i+5] == 0xe0)
 318                         break;
 319         }
 320         if (i >= MOV_CR4_DEPTH) {
 321                 pr_info("ok: cannot locate cr4 writing call gadget\n");
 322                 return;
 323         }
 324         direct_write_cr4 = (void *)(insn + i);
 325 
 326         pr_info("trying to clear SMEP with call gadget\n");
 327         direct_write_cr4(cr4);
 328         if (native_read_cr4() & X86_CR4_SMEP) {
 329                 pr_info("ok: SMEP removal was reverted\n");
 330         } else {
 331                 pr_err("FAIL: cleared SMEP not detected!\n");
 332                 cr4 |= X86_CR4_SMEP;
 333                 pr_info("restoring SMEP\n");
 334                 native_write_cr4(cr4);
 335         }
 336 #else
 337         pr_err("FAIL: this test is x86_64-only\n");
 338 #endif
 339 }
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root/drivers/misc/lkdtm/bugs.c

DEFINITIONS
