drivers/misc/lkdtm_heap.c

   1 /*
   2  * This is for all the tests relating directly to heap memory, including
   3  * page allocation and slab allocations.
   4  */
   5 #include "lkdtm.h"
   6 #include <linux/slab.h>
   7
   8 /*
   9  * This tries to stay within the next largest power-of-2 kmalloc cache
  10  * to avoid actually overwriting anything important if it's not detected
  11  * correctly.
  12  */
  13 void lkdtm_OVERWRITE_ALLOCATION(void)
  14 {
  15         size_t len = 1020;
  16         u32 *data = kmalloc(len, GFP_KERNEL);
  17
  18         data[1024 / sizeof(u32)] = 0x12345678;
  19         kfree(data);
  20 }
  21
  22 void lkdtm_WRITE_AFTER_FREE(void)
  23 {
  24         int *base, *again;
  25         size_t len = 1024;
  26         /*
  27          * The slub allocator uses the first word to store the free
  28          * pointer in some configurations. Use the middle of the
  29          * allocation to avoid running into the freelist
  30          */
  31         size_t offset = (len / sizeof(*base)) / 2;
  32
  33         base = kmalloc(len, GFP_KERNEL);
  34         pr_info("Allocated memory %p-%p\n", base, &base[offset * 2]);
  35         pr_info("Attempting bad write to freed memory at %p\n",
  36                 &base[offset]);
  37         kfree(base);
  38         base[offset] = 0x0abcdef0;
  39         /* Attempt to notice the overwrite. */
  40         again = kmalloc(len, GFP_KERNEL);
  41         kfree(again);
  42         if (again != base)
  43                 pr_info("Hmm, didn't get the same memory range.\n");
  44 }
  45
  46 void lkdtm_READ_AFTER_FREE(void)
  47 {
  48         int *base, *val, saw;
  49         size_t len = 1024;
  50         /*
  51          * The slub allocator uses the first word to store the free
  52          * pointer in some configurations. Use the middle of the
  53          * allocation to avoid running into the freelist
  54          */
  55         size_t offset = (len / sizeof(*base)) / 2;
  56
  57         base = kmalloc(len, GFP_KERNEL);
  58         if (!base) {
  59                 pr_info("Unable to allocate base memory.\n");
  60                 return;
  61         }
  62
  63         val = kmalloc(len, GFP_KERNEL);
  64         if (!val) {
  65                 pr_info("Unable to allocate val memory.\n");
  66                 kfree(base);
  67                 return;
  68         }
  69
  70         *val = 0x12345678;
  71         base[offset] = *val;
  72         pr_info("Value in memory before free: %x\n", base[offset]);
  73
  74         kfree(base);
  75
  76         pr_info("Attempting bad read from freed memory\n");
  77         saw = base[offset];
  78         if (saw != *val) {
  79                 /* Good! Poisoning happened, so declare a win. */
  80                 pr_info("Memory correctly poisoned (%x)\n", saw);
  81                 BUG();
  82         }
  83         pr_info("Memory was not poisoned\n");
  84
  85         kfree(val);
  86 }
  87
  88 void lkdtm_WRITE_BUDDY_AFTER_FREE(void)
  89 {
  90         unsigned long p = __get_free_page(GFP_KERNEL);
  91         if (!p) {
  92                 pr_info("Unable to allocate free page\n");
  93                 return;
  94         }
  95
  96         pr_info("Writing to the buddy page before free\n");
  97         memset((void *)p, 0x3, PAGE_SIZE);
  98         free_page(p);
  99         schedule();
 100         pr_info("Attempting bad write to the buddy page after free\n");
 101         memset((void *)p, 0x78, PAGE_SIZE);
 102         /* Attempt to notice the overwrite. */
 103         p = __get_free_page(GFP_KERNEL);
 104         free_page(p);
 105         schedule();
 106 }
 107
 108 void lkdtm_READ_BUDDY_AFTER_FREE(void)
 109 {
 110         unsigned long p = __get_free_page(GFP_KERNEL);
 111         int saw, *val;
 112         int *base;
 113
 114         if (!p) {
 115                 pr_info("Unable to allocate free page\n");
 116                 return;
 117         }
 118
 119         val = kmalloc(1024, GFP_KERNEL);
 120         if (!val) {
 121                 pr_info("Unable to allocate val memory.\n");
 122                 free_page(p);
 123                 return;
 124         }
 125
 126         base = (int *)p;
 127
 128         *val = 0x12345678;
 129         base[0] = *val;
 130         pr_info("Value in memory before free: %x\n", base[0]);
 131         free_page(p);
 132         pr_info("Attempting to read from freed memory\n");
 133         saw = base[0];
 134         if (saw != *val) {
 135                 /* Good! Poisoning happened, so declare a win. */
 136                 pr_info("Memory correctly poisoned (%x)\n", saw);
 137                 BUG();
 138         }
 139         pr_info("Buddy page was not poisoned\n");
 140
 141         kfree(val);
 142 }