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 static struct kmem_cache *double_free_cache; 11 static struct kmem_cache *a_cache; 12 static struct kmem_cache *b_cache; 13 14 /* 15 * This tries to stay within the next largest power-of-2 kmalloc cache 16 * to avoid actually overwriting anything important if it's not detected 17 * correctly. 18 */ 19 void lkdtm_OVERWRITE_ALLOCATION(void) 20 { 21 size_t len = 1020; 22 u32 *data = kmalloc(len, GFP_KERNEL); 23 if (!data) 24 return; 25 26 data[1024 / sizeof(u32)] = 0x12345678; 27 kfree(data); 28 } 29 30 void lkdtm_WRITE_AFTER_FREE(void) 31 { 32 int *base, *again; 33 size_t len = 1024; 34 /* 35 * The slub allocator uses the first word to store the free 36 * pointer in some configurations. Use the middle of the 37 * allocation to avoid running into the freelist 38 */ 39 size_t offset = (len / sizeof(*base)) / 2; 40 41 base = kmalloc(len, GFP_KERNEL); 42 if (!base) 43 return; 44 pr_info("Allocated memory %p-%p\n", base, &base[offset * 2]); 45 pr_info("Attempting bad write to freed memory at %p\n", 46 &base[offset]); 47 kfree(base); 48 base[offset] = 0x0abcdef0; 49 /* Attempt to notice the overwrite. */ 50 again = kmalloc(len, GFP_KERNEL); 51 kfree(again); 52 if (again != base) 53 pr_info("Hmm, didn't get the same memory range.\n"); 54 } 55 56 void lkdtm_READ_AFTER_FREE(void) 57 { 58 int *base, *val, saw; 59 size_t len = 1024; 60 /* 61 * The slub allocator uses the first word to store the free 62 * pointer in some configurations. Use the middle of the 63 * allocation to avoid running into the freelist 64 */ 65 size_t offset = (len / sizeof(*base)) / 2; 66 67 base = kmalloc(len, GFP_KERNEL); 68 if (!base) { 69 pr_info("Unable to allocate base memory.\n"); 70 return; 71 } 72 73 val = kmalloc(len, GFP_KERNEL); 74 if (!val) { 75 pr_info("Unable to allocate val memory.\n"); 76 kfree(base); 77 return; 78 } 79 80 *val = 0x12345678; 81 base[offset] = *val; 82 pr_info("Value in memory before free: %x\n", base[offset]); 83 84 kfree(base); 85 86 pr_info("Attempting bad read from freed memory\n"); 87 saw = base[offset]; 88 if (saw != *val) { 89 /* Good! Poisoning happened, so declare a win. */ 90 pr_info("Memory correctly poisoned (%x)\n", saw); 91 BUG(); 92 } 93 pr_info("Memory was not poisoned\n"); 94 95 kfree(val); 96 } 97 98 void lkdtm_WRITE_BUDDY_AFTER_FREE(void) 99 { 100 unsigned long p = __get_free_page(GFP_KERNEL); 101 if (!p) { 102 pr_info("Unable to allocate free page\n"); 103 return; 104 } 105 106 pr_info("Writing to the buddy page before free\n"); 107 memset((void *)p, 0x3, PAGE_SIZE); 108 free_page(p); 109 schedule(); 110 pr_info("Attempting bad write to the buddy page after free\n"); 111 memset((void *)p, 0x78, PAGE_SIZE); 112 /* Attempt to notice the overwrite. */ 113 p = __get_free_page(GFP_KERNEL); 114 free_page(p); 115 schedule(); 116 } 117 118 void lkdtm_READ_BUDDY_AFTER_FREE(void) 119 { 120 unsigned long p = __get_free_page(GFP_KERNEL); 121 int saw, *val; 122 int *base; 123 124 if (!p) { 125 pr_info("Unable to allocate free page\n"); 126 return; 127 } 128 129 val = kmalloc(1024, GFP_KERNEL); 130 if (!val) { 131 pr_info("Unable to allocate val memory.\n"); 132 free_page(p); 133 return; 134 } 135 136 base = (int *)p; 137 138 *val = 0x12345678; 139 base[0] = *val; 140 pr_info("Value in memory before free: %x\n", base[0]); 141 free_page(p); 142 pr_info("Attempting to read from freed memory\n"); 143 saw = base[0]; 144 if (saw != *val) { 145 /* Good! Poisoning happened, so declare a win. */ 146 pr_info("Memory correctly poisoned (%x)\n", saw); 147 BUG(); 148 } 149 pr_info("Buddy page was not poisoned\n"); 150 151 kfree(val); 152 } 153 154 void lkdtm_SLAB_FREE_DOUBLE(void) 155 { 156 int *val; 157 158 val = kmem_cache_alloc(double_free_cache, GFP_KERNEL); 159 if (!val) { 160 pr_info("Unable to allocate double_free_cache memory.\n"); 161 return; 162 } 163 164 /* Just make sure we got real memory. */ 165 *val = 0x12345678; 166 pr_info("Attempting double slab free ...\n"); 167 kmem_cache_free(double_free_cache, val); 168 kmem_cache_free(double_free_cache, val); 169 } 170 171 void lkdtm_SLAB_FREE_CROSS(void) 172 { 173 int *val; 174 175 val = kmem_cache_alloc(a_cache, GFP_KERNEL); 176 if (!val) { 177 pr_info("Unable to allocate a_cache memory.\n"); 178 return; 179 } 180 181 /* Just make sure we got real memory. */ 182 *val = 0x12345679; 183 pr_info("Attempting cross-cache slab free ...\n"); 184 kmem_cache_free(b_cache, val); 185 } 186 187 void lkdtm_SLAB_FREE_PAGE(void) 188 { 189 unsigned long p = __get_free_page(GFP_KERNEL); 190 191 pr_info("Attempting non-Slab slab free ...\n"); 192 kmem_cache_free(NULL, (void *)p); 193 free_page(p); 194 } 195 196 /* 197 * We have constructors to keep the caches distinctly separated without 198 * needing to boot with "slab_nomerge". 199 */ 200 static void ctor_double_free(void *region) 201 { } 202 static void ctor_a(void *region) 203 { } 204 static void ctor_b(void *region) 205 { } 206 207 void __init lkdtm_heap_init(void) 208 { 209 double_free_cache = kmem_cache_create("lkdtm-heap-double_free", 210 64, 0, 0, ctor_double_free); 211 a_cache = kmem_cache_create("lkdtm-heap-a", 64, 0, 0, ctor_a); 212 b_cache = kmem_cache_create("lkdtm-heap-b", 64, 0, 0, ctor_b); 213 } 214 215 void __exit lkdtm_heap_exit(void) 216 { 217 kmem_cache_destroy(double_free_cache); 218 kmem_cache_destroy(a_cache); 219 kmem_cache_destroy(b_cache); 220 } 221