drivers/misc/lkdtm_heap.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * This is for all the tests relating directly to heap memory, including
   4  * page allocation and slab allocations.
   5  */
   6 #include "lkdtm.h"
   7 #include <linux/slab.h>
   8 #include <linux/sched.h>
   9
  10 /*
  11  * This tries to stay within the next largest power-of-2 kmalloc cache
  12  * to avoid actually overwriting anything important if it's not detected
  13  * correctly.
  14  */
  15 void lkdtm_OVERWRITE_ALLOCATION(void)
  16 {
  17         size_t len = 1020;
  18         u32 *data = kmalloc(len, GFP_KERNEL);
  19         if (!data)
  20                 return;
  21
  22         data[1024 / sizeof(u32)] = 0x12345678;
  23         kfree(data);
  24 }
  25
  26 void lkdtm_WRITE_AFTER_FREE(void)
  27 {
  28         int *base, *again;
  29         size_t len = 1024;
  30         /*
  31          * The slub allocator uses the first word to store the free
  32          * pointer in some configurations. Use the middle of the
  33          * allocation to avoid running into the freelist
  34          */
  35         size_t offset = (len / sizeof(*base)) / 2;
  36
  37         base = kmalloc(len, GFP_KERNEL);
  38         if (!base)
  39                 return;
  40         pr_info("Allocated memory %p-%p\n", base, &base[offset * 2]);
  41         pr_info("Attempting bad write to freed memory at %p\n",
  42                 &base[offset]);
  43         kfree(base);
  44         base[offset] = 0x0abcdef0;
  45         /* Attempt to notice the overwrite. */
  46         again = kmalloc(len, GFP_KERNEL);
  47         kfree(again);
  48         if (again != base)
  49                 pr_info("Hmm, didn't get the same memory range.\n");
  50 }
  51
  52 void lkdtm_READ_AFTER_FREE(void)
  53 {
  54         int *base, *val, saw;
  55         size_t len = 1024;
  56         /*
  57          * The slub allocator uses the first word to store the free
  58          * pointer in some configurations. Use the middle of the
  59          * allocation to avoid running into the freelist
  60          */
  61         size_t offset = (len / sizeof(*base)) / 2;
  62
  63         base = kmalloc(len, GFP_KERNEL);
  64         if (!base) {
  65                 pr_info("Unable to allocate base memory.\n");
  66                 return;
  67         }
  68
  69         val = kmalloc(len, GFP_KERNEL);
  70         if (!val) {
  71                 pr_info("Unable to allocate val memory.\n");
  72                 kfree(base);
  73                 return;
  74         }
  75
  76         *val = 0x12345678;
  77         base[offset] = *val;
  78         pr_info("Value in memory before free: %x\n", base[offset]);
  79
  80         kfree(base);
  81
  82         pr_info("Attempting bad read from freed memory\n");
  83         saw = base[offset];
  84         if (saw != *val) {
  85                 /* Good! Poisoning happened, so declare a win. */
  86                 pr_info("Memory correctly poisoned (%x)\n", saw);
  87                 BUG();
  88         }
  89         pr_info("Memory was not poisoned\n");
  90
  91         kfree(val);
  92 }
  93
  94 void lkdtm_WRITE_BUDDY_AFTER_FREE(void)
  95 {
  96         unsigned long p = __get_free_page(GFP_KERNEL);
  97         if (!p) {
  98                 pr_info("Unable to allocate free page\n");
  99                 return;
 100         }
 101
 102         pr_info("Writing to the buddy page before free\n");
 103         memset((void *)p, 0x3, PAGE_SIZE);
 104         free_page(p);
 105         schedule();
 106         pr_info("Attempting bad write to the buddy page after free\n");
 107         memset((void *)p, 0x78, PAGE_SIZE);
 108         /* Attempt to notice the overwrite. */
 109         p = __get_free_page(GFP_KERNEL);
 110         free_page(p);
 111         schedule();
 112 }
 113
 114 void lkdtm_READ_BUDDY_AFTER_FREE(void)
 115 {
 116         unsigned long p = __get_free_page(GFP_KERNEL);
 117         int saw, *val;
 118         int *base;
 119
 120         if (!p) {
 121                 pr_info("Unable to allocate free page\n");
 122                 return;
 123         }
 124
 125         val = kmalloc(1024, GFP_KERNEL);
 126         if (!val) {
 127                 pr_info("Unable to allocate val memory.\n");
 128                 free_page(p);
 129                 return;
 130         }
 131
 132         base = (int *)p;
 133
 134         *val = 0x12345678;
 135         base[0] = *val;
 136         pr_info("Value in memory before free: %x\n", base[0]);
 137         free_page(p);
 138         pr_info("Attempting to read from freed memory\n");
 139         saw = base[0];
 140         if (saw != *val) {
 141                 /* Good! Poisoning happened, so declare a win. */
 142                 pr_info("Memory correctly poisoned (%x)\n", saw);
 143                 BUG();
 144         }
 145         pr_info("Buddy page was not poisoned\n");
 146
 147         kfree(val);
 148 }