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 #include <linux/pgtable.h> 14 #include <linux/random.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/sections.h> 21 #include <asm/setup.h> 22 23 u64 __ro_after_init module_alloc_base; 24 u16 __initdata memstart_offset_seed; 25 26 struct arm64_ftr_override kaslr_feature_override __initdata; 27 28 static int __init kaslr_init(void) 29 { 30 u64 module_range; 31 u32 seed; 32 33 /* 34 * Set a reasonable default for module_alloc_base in case 35 * we end up running with module randomization disabled. 36 */ 37 module_alloc_base = (u64)_etext - MODULES_VSIZE; 38 39 if (kaslr_feature_override.val & kaslr_feature_override.mask & 0xf) { 40 pr_info("KASLR disabled on command line\n"); 41 return 0; 42 } 43 44 if (!kaslr_offset()) { 45 pr_warn("KASLR disabled due to lack of seed\n"); 46 return 0; 47 } 48 49 pr_info("KASLR enabled\n"); 50 51 /* 52 * KASAN without KASAN_VMALLOC does not expect the module region to 53 * intersect the vmalloc region, since shadow memory is allocated for 54 * each module at load time, whereas the vmalloc region will already be 55 * shadowed by KASAN zero pages. 56 */ 57 BUILD_BUG_ON((IS_ENABLED(CONFIG_KASAN_GENERIC) || 58 IS_ENABLED(CONFIG_KASAN_SW_TAGS)) && 59 !IS_ENABLED(CONFIG_KASAN_VMALLOC)); 60 61 seed = get_random_u32(); 62 63 if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) { 64 /* 65 * Randomize the module region over a 2 GB window covering the 66 * kernel. This reduces the risk of modules leaking information 67 * about the address of the kernel itself, but results in 68 * branches between modules and the core kernel that are 69 * resolved via PLTs. (Branches between modules will be 70 * resolved normally.) 71 */ 72 module_range = SZ_2G - (u64)(_end - _stext); 73 module_alloc_base = max((u64)_end - SZ_2G, (u64)MODULES_VADDR); 74 } else { 75 /* 76 * Randomize the module region by setting module_alloc_base to 77 * a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE, 78 * _stext) . This guarantees that the resulting region still 79 * covers [_stext, _etext], and that all relative branches can 80 * be resolved without veneers unless this region is exhausted 81 * and we fall back to a larger 2GB window in module_alloc() 82 * when ARM64_MODULE_PLTS is enabled. 83 */ 84 module_range = MODULES_VSIZE - (u64)(_etext - _stext); 85 } 86 87 /* use the lower 21 bits to randomize the base of the module region */ 88 module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21; 89 module_alloc_base &= PAGE_MASK; 90 91 return 0; 92 } 93 subsys_initcall(kaslr_init) 94