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 14 #include <asm/archrandom.h> 15 #include <asm/cacheflush.h> 16 #include <asm/fixmap.h> 17 #include <asm/kernel-pgtable.h> 18 #include <asm/memory.h> 19 #include <asm/mmu.h> 20 #include <asm/pgtable.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 const u8 *kaslr_get_cmdline(void *fdt) 54 { 55 static __initconst const u8 default_cmdline[] = CONFIG_CMDLINE; 56 57 if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) { 58 int node; 59 const u8 *prop; 60 61 node = fdt_path_offset(fdt, "/chosen"); 62 if (node < 0) 63 goto out; 64 65 prop = fdt_getprop(fdt, node, "bootargs", NULL); 66 if (!prop) 67 goto out; 68 return prop; 69 } 70 out: 71 return default_cmdline; 72 } 73 74 /* 75 * This routine will be executed with the kernel mapped at its default virtual 76 * address, and if it returns successfully, the kernel will be remapped, and 77 * start_kernel() will be executed from a randomized virtual offset. The 78 * relocation will result in all absolute references (e.g., static variables 79 * containing function pointers) to be reinitialized, and zero-initialized 80 * .bss variables will be reset to 0. 81 */ 82 u64 __init kaslr_early_init(u64 dt_phys) 83 { 84 void *fdt; 85 u64 seed, offset, mask, module_range; 86 const u8 *cmdline, *str; 87 int size; 88 89 /* 90 * Set a reasonable default for module_alloc_base in case 91 * we end up running with module randomization disabled. 92 */ 93 module_alloc_base = (u64)_etext - MODULES_VSIZE; 94 __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base)); 95 96 /* 97 * Try to map the FDT early. If this fails, we simply bail, 98 * and proceed with KASLR disabled. We will make another 99 * attempt at mapping the FDT in setup_machine() 100 */ 101 early_fixmap_init(); 102 fdt = fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL); 103 if (!fdt) { 104 kaslr_status = KASLR_DISABLED_FDT_REMAP; 105 return 0; 106 } 107 108 /* 109 * Retrieve (and wipe) the seed from the FDT 110 */ 111 seed = get_kaslr_seed(fdt); 112 113 /* 114 * Check if 'nokaslr' appears on the command line, and 115 * return 0 if that is the case. 116 */ 117 cmdline = kaslr_get_cmdline(fdt); 118 str = strstr(cmdline, "nokaslr"); 119 if (str == cmdline || (str > cmdline && *(str - 1) == ' ')) { 120 kaslr_status = KASLR_DISABLED_CMDLINE; 121 return 0; 122 } 123 124 /* 125 * Mix in any entropy obtainable architecturally, open coded 126 * since this runs extremely early. 127 */ 128 if (__early_cpu_has_rndr()) { 129 unsigned long raw; 130 131 if (__arm64_rndr(&raw)) 132 seed ^= raw; 133 } 134 135 if (!seed) { 136 kaslr_status = KASLR_DISABLED_NO_SEED; 137 return 0; 138 } 139 140 /* 141 * OK, so we are proceeding with KASLR enabled. Calculate a suitable 142 * kernel image offset from the seed. Let's place the kernel in the 143 * middle half of the VMALLOC area (VA_BITS_MIN - 2), and stay clear of 144 * the lower and upper quarters to avoid colliding with other 145 * allocations. 146 * Even if we could randomize at page granularity for 16k and 64k pages, 147 * let's always round to 2 MB so we don't interfere with the ability to 148 * map using contiguous PTEs 149 */ 150 mask = ((1UL << (VA_BITS_MIN - 2)) - 1) & ~(SZ_2M - 1); 151 offset = BIT(VA_BITS_MIN - 3) + (seed & mask); 152 153 /* use the top 16 bits to randomize the linear region */ 154 memstart_offset_seed = seed >> 48; 155 156 if (IS_ENABLED(CONFIG_KASAN)) 157 /* 158 * KASAN does not expect the module region to intersect the 159 * vmalloc region, since shadow memory is allocated for each 160 * module at load time, whereas the vmalloc region is shadowed 161 * by KASAN zero pages. So keep modules out of the vmalloc 162 * region if KASAN is enabled, and put the kernel well within 163 * 4 GB of the module region. 164 */ 165 return offset % SZ_2G; 166 167 if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) { 168 /* 169 * Randomize the module region over a 2 GB window covering the 170 * kernel. This reduces the risk of modules leaking information 171 * about the address of the kernel itself, but results in 172 * branches between modules and the core kernel that are 173 * resolved via PLTs. (Branches between modules will be 174 * resolved normally.) 175 */ 176 module_range = SZ_2G - (u64)(_end - _stext); 177 module_alloc_base = max((u64)_end + offset - SZ_2G, 178 (u64)MODULES_VADDR); 179 } else { 180 /* 181 * Randomize the module region by setting module_alloc_base to 182 * a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE, 183 * _stext) . This guarantees that the resulting region still 184 * covers [_stext, _etext], and that all relative branches can 185 * be resolved without veneers. 186 */ 187 module_range = MODULES_VSIZE - (u64)(_etext - _stext); 188 module_alloc_base = (u64)_etext + offset - MODULES_VSIZE; 189 } 190 191 /* use the lower 21 bits to randomize the base of the module region */ 192 module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21; 193 module_alloc_base &= PAGE_MASK; 194 195 __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base)); 196 __flush_dcache_area(&memstart_offset_seed, sizeof(memstart_offset_seed)); 197 198 return offset; 199 } 200 201 static int __init kaslr_init(void) 202 { 203 switch (kaslr_status) { 204 case KASLR_ENABLED: 205 pr_info("KASLR enabled\n"); 206 break; 207 case KASLR_DISABLED_CMDLINE: 208 pr_info("KASLR disabled on command line\n"); 209 break; 210 case KASLR_DISABLED_NO_SEED: 211 pr_warn("KASLR disabled due to lack of seed\n"); 212 break; 213 case KASLR_DISABLED_FDT_REMAP: 214 pr_warn("KASLR disabled due to FDT remapping failure\n"); 215 break; 216 } 217 218 return 0; 219 } 220 core_initcall(kaslr_init) 221