1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Copyright (C) 2016 Linaro Ltd <ard.biesheuvel@linaro.org> 4 */ 5 6 #include <linux/cache.h> 7 #include <linux/crc32.h> 8 #include <linux/init.h> 9 #include <linux/libfdt.h> 10 #include <linux/mm_types.h> 11 #include <linux/sched.h> 12 #include <linux/types.h> 13 #include <linux/pgtable.h> 14 #include <linux/random.h> 15 16 #include <asm/cacheflush.h> 17 #include <asm/fixmap.h> 18 #include <asm/kernel-pgtable.h> 19 #include <asm/memory.h> 20 #include <asm/mmu.h> 21 #include <asm/sections.h> 22 #include <asm/setup.h> 23 24 enum kaslr_status { 25 KASLR_ENABLED, 26 KASLR_DISABLED_CMDLINE, 27 KASLR_DISABLED_NO_SEED, 28 KASLR_DISABLED_FDT_REMAP, 29 }; 30 31 static enum kaslr_status __initdata kaslr_status; 32 u64 __ro_after_init module_alloc_base; 33 u16 __initdata memstart_offset_seed; 34 35 static __init u64 get_kaslr_seed(void *fdt) 36 { 37 int node, len; 38 fdt64_t *prop; 39 u64 ret; 40 41 node = fdt_path_offset(fdt, "/chosen"); 42 if (node < 0) 43 return 0; 44 45 prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len); 46 if (!prop || len != sizeof(u64)) 47 return 0; 48 49 ret = fdt64_to_cpu(*prop); 50 *prop = 0; 51 return ret; 52 } 53 54 static __init bool cmdline_contains_nokaslr(const u8 *cmdline) 55 { 56 const u8 *str; 57 58 str = strstr(cmdline, "nokaslr"); 59 return str == cmdline || (str > cmdline && *(str - 1) == ' '); 60 } 61 62 static __init bool is_kaslr_disabled_cmdline(void *fdt) 63 { 64 if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) { 65 int node; 66 const u8 *prop; 67 68 node = fdt_path_offset(fdt, "/chosen"); 69 if (node < 0) 70 goto out; 71 72 prop = fdt_getprop(fdt, node, "bootargs", NULL); 73 if (!prop) 74 goto out; 75 76 if (cmdline_contains_nokaslr(prop)) 77 return true; 78 79 if (IS_ENABLED(CONFIG_CMDLINE_EXTEND)) 80 goto out; 81 82 return false; 83 } 84 out: 85 return cmdline_contains_nokaslr(CONFIG_CMDLINE); 86 } 87 88 /* 89 * This routine will be executed with the kernel mapped at its default virtual 90 * address, and if it returns successfully, the kernel will be remapped, and 91 * start_kernel() will be executed from a randomized virtual offset. The 92 * relocation will result in all absolute references (e.g., static variables 93 * containing function pointers) to be reinitialized, and zero-initialized 94 * .bss variables will be reset to 0. 95 */ 96 u64 __init kaslr_early_init(void) 97 { 98 void *fdt; 99 u64 seed, offset, mask, module_range; 100 unsigned long raw; 101 102 /* 103 * Set a reasonable default for module_alloc_base in case 104 * we end up running with module randomization disabled. 105 */ 106 module_alloc_base = (u64)_etext - MODULES_VSIZE; 107 __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base)); 108 109 /* 110 * Try to map the FDT early. If this fails, we simply bail, 111 * and proceed with KASLR disabled. We will make another 112 * attempt at mapping the FDT in setup_machine() 113 */ 114 fdt = get_early_fdt_ptr(); 115 if (!fdt) { 116 kaslr_status = KASLR_DISABLED_FDT_REMAP; 117 return 0; 118 } 119 120 /* 121 * Retrieve (and wipe) the seed from the FDT 122 */ 123 seed = get_kaslr_seed(fdt); 124 125 /* 126 * Check if 'nokaslr' appears on the command line, and 127 * return 0 if that is the case. 128 */ 129 if (is_kaslr_disabled_cmdline(fdt)) { 130 kaslr_status = KASLR_DISABLED_CMDLINE; 131 return 0; 132 } 133 134 /* 135 * Mix in any entropy obtainable architecturally if enabled 136 * and supported. 137 */ 138 139 if (arch_get_random_seed_long_early(&raw)) 140 seed ^= raw; 141 142 if (!seed) { 143 kaslr_status = KASLR_DISABLED_NO_SEED; 144 return 0; 145 } 146 147 /* 148 * OK, so we are proceeding with KASLR enabled. Calculate a suitable 149 * kernel image offset from the seed. Let's place the kernel in the 150 * middle half of the VMALLOC area (VA_BITS_MIN - 2), and stay clear of 151 * the lower and upper quarters to avoid colliding with other 152 * allocations. 153 * Even if we could randomize at page granularity for 16k and 64k pages, 154 * let's always round to 2 MB so we don't interfere with the ability to 155 * map using contiguous PTEs 156 */ 157 mask = ((1UL << (VA_BITS_MIN - 2)) - 1) & ~(SZ_2M - 1); 158 offset = BIT(VA_BITS_MIN - 3) + (seed & mask); 159 160 /* use the top 16 bits to randomize the linear region */ 161 memstart_offset_seed = seed >> 48; 162 163 if (IS_ENABLED(CONFIG_KASAN_GENERIC) || 164 IS_ENABLED(CONFIG_KASAN_SW_TAGS)) 165 /* 166 * KASAN does not expect the module region to intersect the 167 * vmalloc region, since shadow memory is allocated for each 168 * module at load time, whereas the vmalloc region is shadowed 169 * by KASAN zero pages. So keep modules out of the vmalloc 170 * region if KASAN is enabled, and put the kernel well within 171 * 4 GB of the module region. 172 */ 173 return offset % SZ_2G; 174 175 if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) { 176 /* 177 * Randomize the module region over a 2 GB window covering the 178 * kernel. This reduces the risk of modules leaking information 179 * about the address of the kernel itself, but results in 180 * branches between modules and the core kernel that are 181 * resolved via PLTs. (Branches between modules will be 182 * resolved normally.) 183 */ 184 module_range = SZ_2G - (u64)(_end - _stext); 185 module_alloc_base = max((u64)_end + offset - SZ_2G, 186 (u64)MODULES_VADDR); 187 } else { 188 /* 189 * Randomize the module region by setting module_alloc_base to 190 * a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE, 191 * _stext) . This guarantees that the resulting region still 192 * covers [_stext, _etext], and that all relative branches can 193 * be resolved without veneers. 194 */ 195 module_range = MODULES_VSIZE - (u64)(_etext - _stext); 196 module_alloc_base = (u64)_etext + offset - MODULES_VSIZE; 197 } 198 199 /* use the lower 21 bits to randomize the base of the module region */ 200 module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21; 201 module_alloc_base &= PAGE_MASK; 202 203 __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base)); 204 __flush_dcache_area(&memstart_offset_seed, sizeof(memstart_offset_seed)); 205 206 return offset; 207 } 208 209 static int __init kaslr_init(void) 210 { 211 switch (kaslr_status) { 212 case KASLR_ENABLED: 213 pr_info("KASLR enabled\n"); 214 break; 215 case KASLR_DISABLED_CMDLINE: 216 pr_info("KASLR disabled on command line\n"); 217 break; 218 case KASLR_DISABLED_NO_SEED: 219 pr_warn("KASLR disabled due to lack of seed\n"); 220 break; 221 case KASLR_DISABLED_FDT_REMAP: 222 pr_warn("KASLR disabled due to FDT remapping failure\n"); 223 break; 224 } 225 226 return 0; 227 } 228 core_initcall(kaslr_init) 229