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