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 23 enum kaslr_status { 24 KASLR_ENABLED, 25 KASLR_DISABLED_CMDLINE, 26 KASLR_DISABLED_NO_SEED, 27 KASLR_DISABLED_FDT_REMAP, 28 }; 29 30 static enum kaslr_status __initdata kaslr_status; 31 u64 __ro_after_init module_alloc_base; 32 u16 __initdata memstart_offset_seed; 33 34 static __init u64 get_kaslr_seed(void *fdt) 35 { 36 int node, len; 37 fdt64_t *prop; 38 u64 ret; 39 40 node = fdt_path_offset(fdt, "/chosen"); 41 if (node < 0) 42 return 0; 43 44 prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len); 45 if (!prop || len != sizeof(u64)) 46 return 0; 47 48 ret = fdt64_to_cpu(*prop); 49 *prop = 0; 50 return ret; 51 } 52 53 static __init bool cmdline_contains_nokaslr(const u8 *cmdline) 54 { 55 const u8 *str; 56 57 str = strstr(cmdline, "nokaslr"); 58 return str == cmdline || (str > cmdline && *(str - 1) == ' '); 59 } 60 61 static __init bool is_kaslr_disabled_cmdline(void *fdt) 62 { 63 if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) { 64 int node; 65 const u8 *prop; 66 67 node = fdt_path_offset(fdt, "/chosen"); 68 if (node < 0) 69 goto out; 70 71 prop = fdt_getprop(fdt, node, "bootargs", NULL); 72 if (!prop) 73 goto out; 74 75 if (cmdline_contains_nokaslr(prop)) 76 return true; 77 78 if (IS_ENABLED(CONFIG_CMDLINE_EXTEND)) 79 goto out; 80 81 return false; 82 } 83 out: 84 return cmdline_contains_nokaslr(CONFIG_CMDLINE); 85 } 86 87 /* 88 * This routine will be executed with the kernel mapped at its default virtual 89 * address, and if it returns successfully, the kernel will be remapped, and 90 * start_kernel() will be executed from a randomized virtual offset. The 91 * relocation will result in all absolute references (e.g., static variables 92 * containing function pointers) to be reinitialized, and zero-initialized 93 * .bss variables will be reset to 0. 94 */ 95 u64 __init kaslr_early_init(u64 dt_phys) 96 { 97 void *fdt; 98 u64 seed, offset, mask, module_range; 99 unsigned long raw; 100 int size; 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 early_fixmap_init(); 115 fdt = fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL); 116 if (!fdt) { 117 kaslr_status = KASLR_DISABLED_FDT_REMAP; 118 return 0; 119 } 120 121 /* 122 * Retrieve (and wipe) the seed from the FDT 123 */ 124 seed = get_kaslr_seed(fdt); 125 126 /* 127 * Check if 'nokaslr' appears on the command line, and 128 * return 0 if that is the case. 129 */ 130 if (is_kaslr_disabled_cmdline(fdt)) { 131 kaslr_status = KASLR_DISABLED_CMDLINE; 132 return 0; 133 } 134 135 /* 136 * Mix in any entropy obtainable architecturally if enabled 137 * and supported. 138 */ 139 140 if (arch_get_random_seed_long_early(&raw)) 141 seed ^= raw; 142 143 if (!seed) { 144 kaslr_status = KASLR_DISABLED_NO_SEED; 145 return 0; 146 } 147 148 /* 149 * OK, so we are proceeding with KASLR enabled. Calculate a suitable 150 * kernel image offset from the seed. Let's place the kernel in the 151 * middle half of the VMALLOC area (VA_BITS_MIN - 2), and stay clear of 152 * the lower and upper quarters to avoid colliding with other 153 * allocations. 154 * Even if we could randomize at page granularity for 16k and 64k pages, 155 * let's always round to 2 MB so we don't interfere with the ability to 156 * map using contiguous PTEs 157 */ 158 mask = ((1UL << (VA_BITS_MIN - 2)) - 1) & ~(SZ_2M - 1); 159 offset = BIT(VA_BITS_MIN - 3) + (seed & mask); 160 161 /* use the top 16 bits to randomize the linear region */ 162 memstart_offset_seed = seed >> 48; 163 164 if (IS_ENABLED(CONFIG_KASAN)) 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