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