1 /* 2 * Copyright (C) 2016 Linaro Ltd <ard.biesheuvel@linaro.org> 3 * 4 * This program is free software; you can redistribute it and/or modify 5 * it under the terms of the GNU General Public License version 2 as 6 * published by the Free Software Foundation. 7 */ 8 9 #include <linux/cache.h> 10 #include <linux/crc32.h> 11 #include <linux/init.h> 12 #include <linux/libfdt.h> 13 #include <linux/mm_types.h> 14 #include <linux/sched.h> 15 #include <linux/types.h> 16 17 #include <asm/fixmap.h> 18 #include <asm/kernel-pgtable.h> 19 #include <asm/memory.h> 20 #include <asm/mmu.h> 21 #include <asm/pgtable.h> 22 #include <asm/sections.h> 23 24 u64 __ro_after_init module_alloc_base; 25 u16 __initdata memstart_offset_seed; 26 27 static __init u64 get_kaslr_seed(void *fdt) 28 { 29 int node, len; 30 u64 *prop; 31 u64 ret; 32 33 node = fdt_path_offset(fdt, "/chosen"); 34 if (node < 0) 35 return 0; 36 37 prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len); 38 if (!prop || len != sizeof(u64)) 39 return 0; 40 41 ret = fdt64_to_cpu(*prop); 42 *prop = 0; 43 return ret; 44 } 45 46 static __init const u8 *get_cmdline(void *fdt) 47 { 48 static __initconst const u8 default_cmdline[] = CONFIG_CMDLINE; 49 50 if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) { 51 int node; 52 const u8 *prop; 53 54 node = fdt_path_offset(fdt, "/chosen"); 55 if (node < 0) 56 goto out; 57 58 prop = fdt_getprop(fdt, node, "bootargs", NULL); 59 if (!prop) 60 goto out; 61 return prop; 62 } 63 out: 64 return default_cmdline; 65 } 66 67 extern void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size, 68 pgprot_t prot); 69 70 /* 71 * This routine will be executed with the kernel mapped at its default virtual 72 * address, and if it returns successfully, the kernel will be remapped, and 73 * start_kernel() will be executed from a randomized virtual offset. The 74 * relocation will result in all absolute references (e.g., static variables 75 * containing function pointers) to be reinitialized, and zero-initialized 76 * .bss variables will be reset to 0. 77 */ 78 u64 __init kaslr_early_init(u64 dt_phys, u64 modulo_offset) 79 { 80 void *fdt; 81 u64 seed, offset, mask, module_range; 82 const u8 *cmdline, *str; 83 int size; 84 85 /* 86 * Set a reasonable default for module_alloc_base in case 87 * we end up running with module randomization disabled. 88 */ 89 module_alloc_base = (u64)_etext - MODULES_VSIZE; 90 91 /* 92 * Try to map the FDT early. If this fails, we simply bail, 93 * and proceed with KASLR disabled. We will make another 94 * attempt at mapping the FDT in setup_machine() 95 */ 96 early_fixmap_init(); 97 fdt = __fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL); 98 if (!fdt) 99 return 0; 100 101 /* 102 * Retrieve (and wipe) the seed from the FDT 103 */ 104 seed = get_kaslr_seed(fdt); 105 if (!seed) 106 return 0; 107 108 /* 109 * Check if 'nokaslr' appears on the command line, and 110 * return 0 if that is the case. 111 */ 112 cmdline = get_cmdline(fdt); 113 str = strstr(cmdline, "nokaslr"); 114 if (str == cmdline || (str > cmdline && *(str - 1) == ' ')) 115 return 0; 116 117 /* 118 * OK, so we are proceeding with KASLR enabled. Calculate a suitable 119 * kernel image offset from the seed. Let's place the kernel in the 120 * lower half of the VMALLOC area (VA_BITS - 2). 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 - 2)) - 1) & ~(SZ_2M - 1); 126 offset = seed & mask; 127 128 /* use the top 16 bits to randomize the linear region */ 129 memstart_offset_seed = seed >> 48; 130 131 /* 132 * The kernel Image should not extend across a 1GB/32MB/512MB alignment 133 * boundary (for 4KB/16KB/64KB granule kernels, respectively). If this 134 * happens, increase the KASLR offset by the size of the kernel image. 135 */ 136 if ((((u64)_text + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT) != 137 (((u64)_end + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT)) 138 offset = (offset + (u64)(_end - _text)) & mask; 139 140 if (IS_ENABLED(CONFIG_KASAN)) 141 /* 142 * KASAN does not expect the module region to intersect the 143 * vmalloc region, since shadow memory is allocated for each 144 * module at load time, whereas the vmalloc region is shadowed 145 * by KASAN zero pages. So keep modules out of the vmalloc 146 * region if KASAN is enabled. 147 */ 148 return offset; 149 150 if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) { 151 /* 152 * Randomize the module region independently from the core 153 * kernel. This prevents modules from leaking any information 154 * about the address of the kernel itself, but results in 155 * branches between modules and the core kernel that are 156 * resolved via PLTs. (Branches between modules will be 157 * resolved normally.) 158 */ 159 module_range = VMALLOC_END - VMALLOC_START - MODULES_VSIZE; 160 module_alloc_base = VMALLOC_START; 161 } else { 162 /* 163 * Randomize the module region by setting module_alloc_base to 164 * a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE, 165 * _stext) . This guarantees that the resulting region still 166 * covers [_stext, _etext], and that all relative branches can 167 * be resolved without veneers. 168 */ 169 module_range = MODULES_VSIZE - (u64)(_etext - _stext); 170 module_alloc_base = (u64)_etext + offset - MODULES_VSIZE; 171 } 172 173 /* use the lower 21 bits to randomize the base of the module region */ 174 module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21; 175 module_alloc_base &= PAGE_MASK; 176 177 return offset; 178 } 179