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 struct arm64_ftr_override kaslr_feature_override __initdata; 55 56 /* 57 * This routine will be executed with the kernel mapped at its default virtual 58 * address, and if it returns successfully, the kernel will be remapped, and 59 * start_kernel() will be executed from a randomized virtual offset. The 60 * relocation will result in all absolute references (e.g., static variables 61 * containing function pointers) to be reinitialized, and zero-initialized 62 * .bss variables will be reset to 0. 63 */ 64 u64 __init kaslr_early_init(void) 65 { 66 void *fdt; 67 u64 seed, offset, mask, module_range; 68 unsigned long raw; 69 70 /* 71 * Set a reasonable default for module_alloc_base in case 72 * we end up running with module randomization disabled. 73 */ 74 module_alloc_base = (u64)_etext - MODULES_VSIZE; 75 __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base)); 76 77 /* 78 * Try to map the FDT early. If this fails, we simply bail, 79 * and proceed with KASLR disabled. We will make another 80 * attempt at mapping the FDT in setup_machine() 81 */ 82 fdt = get_early_fdt_ptr(); 83 if (!fdt) { 84 kaslr_status = KASLR_DISABLED_FDT_REMAP; 85 return 0; 86 } 87 88 /* 89 * Retrieve (and wipe) the seed from the FDT 90 */ 91 seed = get_kaslr_seed(fdt); 92 93 /* 94 * Check if 'nokaslr' appears on the command line, and 95 * return 0 if that is the case. 96 */ 97 if (kaslr_feature_override.val & kaslr_feature_override.mask & 0xf) { 98 kaslr_status = KASLR_DISABLED_CMDLINE; 99 return 0; 100 } 101 102 /* 103 * Mix in any entropy obtainable architecturally if enabled 104 * and supported. 105 */ 106 107 if (arch_get_random_seed_long_early(&raw)) 108 seed ^= raw; 109 110 if (!seed) { 111 kaslr_status = KASLR_DISABLED_NO_SEED; 112 return 0; 113 } 114 115 /* 116 * OK, so we are proceeding with KASLR enabled. Calculate a suitable 117 * kernel image offset from the seed. Let's place the kernel in the 118 * middle half of the VMALLOC area (VA_BITS_MIN - 2), and stay clear of 119 * the lower and upper quarters to avoid colliding with other 120 * allocations. 121 * Even if we could randomize at page granularity for 16k and 64k pages, 122 * let's always round to 2 MB so we don't interfere with the ability to 123 * map using contiguous PTEs 124 */ 125 mask = ((1UL << (VA_BITS_MIN - 2)) - 1) & ~(SZ_2M - 1); 126 offset = BIT(VA_BITS_MIN - 3) + (seed & mask); 127 128 /* use the top 16 bits to randomize the linear region */ 129 memstart_offset_seed = seed >> 48; 130 131 if (!IS_ENABLED(CONFIG_KASAN_VMALLOC) && 132 (IS_ENABLED(CONFIG_KASAN_GENERIC) || 133 IS_ENABLED(CONFIG_KASAN_SW_TAGS))) 134 /* 135 * KASAN without KASAN_VMALLOC does not expect the module region 136 * to intersect the vmalloc region, since shadow memory is 137 * allocated for each module at load time, whereas the vmalloc 138 * region is shadowed by KASAN zero pages. So keep modules 139 * out of the vmalloc region if KASAN is enabled without 140 * KASAN_VMALLOC, and put the kernel well within 4 GB of the 141 * module region. 142 */ 143 return offset % SZ_2G; 144 145 if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) { 146 /* 147 * Randomize the module region over a 2 GB window covering the 148 * kernel. This reduces the risk of modules leaking information 149 * about the address of the kernel itself, but results in 150 * branches between modules and the core kernel that are 151 * resolved via PLTs. (Branches between modules will be 152 * resolved normally.) 153 */ 154 module_range = SZ_2G - (u64)(_end - _stext); 155 module_alloc_base = max((u64)_end + offset - SZ_2G, 156 (u64)MODULES_VADDR); 157 } else { 158 /* 159 * Randomize the module region by setting module_alloc_base to 160 * a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE, 161 * _stext) . This guarantees that the resulting region still 162 * covers [_stext, _etext], and that all relative branches can 163 * be resolved without veneers. 164 */ 165 module_range = MODULES_VSIZE - (u64)(_etext - _stext); 166 module_alloc_base = (u64)_etext + offset - MODULES_VSIZE; 167 } 168 169 /* use the lower 21 bits to randomize the base of the module region */ 170 module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21; 171 module_alloc_base &= PAGE_MASK; 172 173 __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base)); 174 __flush_dcache_area(&memstart_offset_seed, sizeof(memstart_offset_seed)); 175 176 return offset; 177 } 178 179 static int __init kaslr_init(void) 180 { 181 switch (kaslr_status) { 182 case KASLR_ENABLED: 183 pr_info("KASLR enabled\n"); 184 break; 185 case KASLR_DISABLED_CMDLINE: 186 pr_info("KASLR disabled on command line\n"); 187 break; 188 case KASLR_DISABLED_NO_SEED: 189 pr_warn("KASLR disabled due to lack of seed\n"); 190 break; 191 case KASLR_DISABLED_FDT_REMAP: 192 pr_warn("KASLR disabled due to FDT remapping failure\n"); 193 break; 194 } 195 196 return 0; 197 } 198 core_initcall(kaslr_init) 199