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/crc32.h> 10 #include <linux/init.h> 11 #include <linux/libfdt.h> 12 #include <linux/mm_types.h> 13 #include <linux/sched.h> 14 #include <linux/types.h> 15 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 u64 __read_mostly module_alloc_base; 24 u16 __initdata memstart_offset_seed; 25 26 static __init u64 get_kaslr_seed(void *fdt) 27 { 28 int node, len; 29 u64 *prop; 30 u64 ret; 31 32 node = fdt_path_offset(fdt, "/chosen"); 33 if (node < 0) 34 return 0; 35 36 prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len); 37 if (!prop || len != sizeof(u64)) 38 return 0; 39 40 ret = fdt64_to_cpu(*prop); 41 *prop = 0; 42 return ret; 43 } 44 45 static __init const u8 *get_cmdline(void *fdt) 46 { 47 static __initconst const u8 default_cmdline[] = CONFIG_CMDLINE; 48 49 if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) { 50 int node; 51 const u8 *prop; 52 53 node = fdt_path_offset(fdt, "/chosen"); 54 if (node < 0) 55 goto out; 56 57 prop = fdt_getprop(fdt, node, "bootargs", NULL); 58 if (!prop) 59 goto out; 60 return prop; 61 } 62 out: 63 return default_cmdline; 64 } 65 66 extern void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size, 67 pgprot_t prot); 68 69 /* 70 * This routine will be executed with the kernel mapped at its default virtual 71 * address, and if it returns successfully, the kernel will be remapped, and 72 * start_kernel() will be executed from a randomized virtual offset. The 73 * relocation will result in all absolute references (e.g., static variables 74 * containing function pointers) to be reinitialized, and zero-initialized 75 * .bss variables will be reset to 0. 76 */ 77 u64 __init kaslr_early_init(u64 dt_phys, u64 modulo_offset) 78 { 79 void *fdt; 80 u64 seed, offset, mask, module_range; 81 const u8 *cmdline, *str; 82 int size; 83 84 /* 85 * Set a reasonable default for module_alloc_base in case 86 * we end up running with module randomization disabled. 87 */ 88 module_alloc_base = (u64)_etext - MODULES_VSIZE; 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 = 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 * lower half of the VMALLOC area (VA_BITS - 2). 120 * Even if we could randomize at page granularity for 16k and 64k pages, 121 * let's always round to 2 MB so we don't interfere with the ability to 122 * map using contiguous PTEs 123 */ 124 mask = ((1UL << (VA_BITS - 2)) - 1) & ~(SZ_2M - 1); 125 offset = seed & mask; 126 127 /* use the top 16 bits to randomize the linear region */ 128 memstart_offset_seed = seed >> 48; 129 130 /* 131 * The kernel Image should not extend across a 1GB/32MB/512MB alignment 132 * boundary (for 4KB/16KB/64KB granule kernels, respectively). If this 133 * happens, increase the KASLR offset by the size of the kernel image. 134 */ 135 if ((((u64)_text + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT) != 136 (((u64)_end + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT)) 137 offset = (offset + (u64)(_end - _text)) & mask; 138 139 if (IS_ENABLED(CONFIG_KASAN)) 140 /* 141 * KASAN does not expect the module region to intersect the 142 * vmalloc region, since shadow memory is allocated for each 143 * module at load time, whereas the vmalloc region is shadowed 144 * by KASAN zero pages. So keep modules out of the vmalloc 145 * region if KASAN is enabled. 146 */ 147 return offset; 148 149 if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) { 150 /* 151 * Randomize the module region independently from the core 152 * kernel. This prevents modules from leaking any information 153 * about the address of the kernel itself, but results in 154 * branches between modules and the core kernel that are 155 * resolved via PLTs. (Branches between modules will be 156 * resolved normally.) 157 */ 158 module_range = VMALLOC_END - VMALLOC_START - MODULES_VSIZE; 159 module_alloc_base = VMALLOC_START; 160 } else { 161 /* 162 * Randomize the module region by setting module_alloc_base to 163 * a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE, 164 * _stext) . This guarantees that the resulting region still 165 * covers [_stext, _etext], and that all relative branches can 166 * be resolved without veneers. 167 */ 168 module_range = MODULES_VSIZE - (u64)(_etext - _stext); 169 module_alloc_base = (u64)_etext + offset - MODULES_VSIZE; 170 } 171 172 /* use the lower 21 bits to randomize the base of the module region */ 173 module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21; 174 module_alloc_base &= PAGE_MASK; 175 176 return offset; 177 } 178