1d2912cb1SThomas Gleixner // SPDX-License-Identifier: GPL-2.0-only 2f80fb3a3SArd Biesheuvel /* 3f80fb3a3SArd Biesheuvel * Copyright (C) 2016 Linaro Ltd <ard.biesheuvel@linaro.org> 4f80fb3a3SArd Biesheuvel */ 5f80fb3a3SArd Biesheuvel 65a9e3e15SJisheng Zhang #include <linux/cache.h> 7f80fb3a3SArd Biesheuvel #include <linux/crc32.h> 8f80fb3a3SArd Biesheuvel #include <linux/init.h> 9f80fb3a3SArd Biesheuvel #include <linux/libfdt.h> 10f80fb3a3SArd Biesheuvel #include <linux/mm_types.h> 11f80fb3a3SArd Biesheuvel #include <linux/sched.h> 12f80fb3a3SArd Biesheuvel #include <linux/types.h> 1365fddcfcSMike Rapoport #include <linux/pgtable.h> 1458552408SLinus Torvalds #include <linux/random.h> 15f80fb3a3SArd Biesheuvel 161598ecdaSArd Biesheuvel #include <asm/cacheflush.h> 17f80fb3a3SArd Biesheuvel #include <asm/fixmap.h> 18f80fb3a3SArd Biesheuvel #include <asm/kernel-pgtable.h> 19f80fb3a3SArd Biesheuvel #include <asm/memory.h> 20f80fb3a3SArd Biesheuvel #include <asm/mmu.h> 21f80fb3a3SArd Biesheuvel #include <asm/sections.h> 22f6f0c436SMarc Zyngier #include <asm/setup.h> 23f80fb3a3SArd Biesheuvel 24294a9dddSMark Brown enum kaslr_status { 25294a9dddSMark Brown KASLR_ENABLED, 26294a9dddSMark Brown KASLR_DISABLED_CMDLINE, 27294a9dddSMark Brown KASLR_DISABLED_NO_SEED, 28294a9dddSMark Brown KASLR_DISABLED_FDT_REMAP, 29294a9dddSMark Brown }; 30294a9dddSMark Brown 312203e1adSMark Brown static enum kaslr_status __initdata kaslr_status; 325a9e3e15SJisheng Zhang u64 __ro_after_init module_alloc_base; 33c031a421SArd Biesheuvel u16 __initdata memstart_offset_seed; 34f80fb3a3SArd Biesheuvel 35f80fb3a3SArd Biesheuvel static __init u64 get_kaslr_seed(void *fdt) 36f80fb3a3SArd Biesheuvel { 37f80fb3a3SArd Biesheuvel int node, len; 3867831edfSLuc Van Oostenryck fdt64_t *prop; 39f80fb3a3SArd Biesheuvel u64 ret; 40f80fb3a3SArd Biesheuvel 41f80fb3a3SArd Biesheuvel node = fdt_path_offset(fdt, "/chosen"); 42f80fb3a3SArd Biesheuvel if (node < 0) 43f80fb3a3SArd Biesheuvel return 0; 44f80fb3a3SArd Biesheuvel 45f80fb3a3SArd Biesheuvel prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len); 46f80fb3a3SArd Biesheuvel if (!prop || len != sizeof(u64)) 47f80fb3a3SArd Biesheuvel return 0; 48f80fb3a3SArd Biesheuvel 49f80fb3a3SArd Biesheuvel ret = fdt64_to_cpu(*prop); 50f80fb3a3SArd Biesheuvel *prop = 0; 51f80fb3a3SArd Biesheuvel return ret; 52f80fb3a3SArd Biesheuvel } 53f80fb3a3SArd Biesheuvel 54a762f4ffSMarc Zyngier struct arm64_ftr_override kaslr_feature_override __initdata; 55f80fb3a3SArd Biesheuvel 56f80fb3a3SArd Biesheuvel /* 57f80fb3a3SArd Biesheuvel * This routine will be executed with the kernel mapped at its default virtual 58f80fb3a3SArd Biesheuvel * address, and if it returns successfully, the kernel will be remapped, and 59f80fb3a3SArd Biesheuvel * start_kernel() will be executed from a randomized virtual offset. The 60f80fb3a3SArd Biesheuvel * relocation will result in all absolute references (e.g., static variables 61f80fb3a3SArd Biesheuvel * containing function pointers) to be reinitialized, and zero-initialized 62f80fb3a3SArd Biesheuvel * .bss variables will be reset to 0. 63f80fb3a3SArd Biesheuvel */ 64f6f0c436SMarc Zyngier u64 __init kaslr_early_init(void) 65f80fb3a3SArd Biesheuvel { 66f80fb3a3SArd Biesheuvel void *fdt; 67f80fb3a3SArd Biesheuvel u64 seed, offset, mask, module_range; 689bceb80bSGuenter Roeck unsigned long raw; 69f80fb3a3SArd Biesheuvel 70f80fb3a3SArd Biesheuvel /* 71f80fb3a3SArd Biesheuvel * Set a reasonable default for module_alloc_base in case 72f80fb3a3SArd Biesheuvel * we end up running with module randomization disabled. 73f80fb3a3SArd Biesheuvel */ 74f80fb3a3SArd Biesheuvel module_alloc_base = (u64)_etext - MODULES_VSIZE; 75fade9c2cSFuad Tabba dcache_clean_inval_poc((unsigned long)&module_alloc_base, 76814b1860SFuad Tabba (unsigned long)&module_alloc_base + 77814b1860SFuad Tabba sizeof(module_alloc_base)); 78f80fb3a3SArd Biesheuvel 79f80fb3a3SArd Biesheuvel /* 80f80fb3a3SArd Biesheuvel * Try to map the FDT early. If this fails, we simply bail, 81f80fb3a3SArd Biesheuvel * and proceed with KASLR disabled. We will make another 82f80fb3a3SArd Biesheuvel * attempt at mapping the FDT in setup_machine() 83f80fb3a3SArd Biesheuvel */ 84f6f0c436SMarc Zyngier fdt = get_early_fdt_ptr(); 85294a9dddSMark Brown if (!fdt) { 86294a9dddSMark Brown kaslr_status = KASLR_DISABLED_FDT_REMAP; 87f80fb3a3SArd Biesheuvel return 0; 88294a9dddSMark Brown } 89f80fb3a3SArd Biesheuvel 90f80fb3a3SArd Biesheuvel /* 91f80fb3a3SArd Biesheuvel * Retrieve (and wipe) the seed from the FDT 92f80fb3a3SArd Biesheuvel */ 93f80fb3a3SArd Biesheuvel seed = get_kaslr_seed(fdt); 94f80fb3a3SArd Biesheuvel 95f80fb3a3SArd Biesheuvel /* 96f80fb3a3SArd Biesheuvel * Check if 'nokaslr' appears on the command line, and 97f80fb3a3SArd Biesheuvel * return 0 if that is the case. 98f80fb3a3SArd Biesheuvel */ 99a762f4ffSMarc Zyngier if (kaslr_feature_override.val & kaslr_feature_override.mask & 0xf) { 100294a9dddSMark Brown kaslr_status = KASLR_DISABLED_CMDLINE; 101f80fb3a3SArd Biesheuvel return 0; 102294a9dddSMark Brown } 103f80fb3a3SArd Biesheuvel 1042e8e1ea8SMark Brown /* 1059bceb80bSGuenter Roeck * Mix in any entropy obtainable architecturally if enabled 1069bceb80bSGuenter Roeck * and supported. 1072e8e1ea8SMark Brown */ 1082e8e1ea8SMark Brown 1099bceb80bSGuenter Roeck if (arch_get_random_seed_long_early(&raw)) 1102e8e1ea8SMark Brown seed ^= raw; 1112e8e1ea8SMark Brown 1122203e1adSMark Brown if (!seed) { 1132203e1adSMark Brown kaslr_status = KASLR_DISABLED_NO_SEED; 1142203e1adSMark Brown return 0; 1152203e1adSMark Brown } 1162203e1adSMark Brown 117f80fb3a3SArd Biesheuvel /* 118f80fb3a3SArd Biesheuvel * OK, so we are proceeding with KASLR enabled. Calculate a suitable 119f80fb3a3SArd Biesheuvel * kernel image offset from the seed. Let's place the kernel in the 12090ec95cdSSteve Capper * middle half of the VMALLOC area (VA_BITS_MIN - 2), and stay clear of 121f2b9ba87SArd Biesheuvel * the lower and upper quarters to avoid colliding with other 122f2b9ba87SArd Biesheuvel * allocations. 123f80fb3a3SArd Biesheuvel * Even if we could randomize at page granularity for 16k and 64k pages, 124f80fb3a3SArd Biesheuvel * let's always round to 2 MB so we don't interfere with the ability to 125f80fb3a3SArd Biesheuvel * map using contiguous PTEs 126f80fb3a3SArd Biesheuvel */ 12790ec95cdSSteve Capper mask = ((1UL << (VA_BITS_MIN - 2)) - 1) & ~(SZ_2M - 1); 12890ec95cdSSteve Capper offset = BIT(VA_BITS_MIN - 3) + (seed & mask); 129f80fb3a3SArd Biesheuvel 130c031a421SArd Biesheuvel /* use the top 16 bits to randomize the linear region */ 131c031a421SArd Biesheuvel memstart_offset_seed = seed >> 48; 132c031a421SArd Biesheuvel 13331d02e7aSLecopzer Chen if (!IS_ENABLED(CONFIG_KASAN_VMALLOC) && 13431d02e7aSLecopzer Chen (IS_ENABLED(CONFIG_KASAN_GENERIC) || 13531d02e7aSLecopzer Chen IS_ENABLED(CONFIG_KASAN_SW_TAGS))) 136f80fb3a3SArd Biesheuvel /* 13731d02e7aSLecopzer Chen * KASAN without KASAN_VMALLOC does not expect the module region 13831d02e7aSLecopzer Chen * to intersect the vmalloc region, since shadow memory is 13931d02e7aSLecopzer Chen * allocated for each module at load time, whereas the vmalloc 14031d02e7aSLecopzer Chen * region is shadowed by KASAN zero pages. So keep modules 14131d02e7aSLecopzer Chen * out of the vmalloc region if KASAN is enabled without 14231d02e7aSLecopzer Chen * KASAN_VMALLOC, and put the kernel well within 4 GB of the 14331d02e7aSLecopzer Chen * module region. 144f80fb3a3SArd Biesheuvel */ 145f2b9ba87SArd Biesheuvel return offset % SZ_2G; 146f80fb3a3SArd Biesheuvel 147f80fb3a3SArd Biesheuvel if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) { 148f80fb3a3SArd Biesheuvel /* 149b2eed9b5SArd Biesheuvel * Randomize the module region over a 2 GB window covering the 150f2b9ba87SArd Biesheuvel * kernel. This reduces the risk of modules leaking information 151f80fb3a3SArd Biesheuvel * about the address of the kernel itself, but results in 152f80fb3a3SArd Biesheuvel * branches between modules and the core kernel that are 153f80fb3a3SArd Biesheuvel * resolved via PLTs. (Branches between modules will be 154f80fb3a3SArd Biesheuvel * resolved normally.) 155f80fb3a3SArd Biesheuvel */ 156b2eed9b5SArd Biesheuvel module_range = SZ_2G - (u64)(_end - _stext); 157b2eed9b5SArd Biesheuvel module_alloc_base = max((u64)_end + offset - SZ_2G, 158f2b9ba87SArd Biesheuvel (u64)MODULES_VADDR); 159f80fb3a3SArd Biesheuvel } else { 160f80fb3a3SArd Biesheuvel /* 161f80fb3a3SArd Biesheuvel * Randomize the module region by setting module_alloc_base to 162f80fb3a3SArd Biesheuvel * a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE, 163f80fb3a3SArd Biesheuvel * _stext) . This guarantees that the resulting region still 164f80fb3a3SArd Biesheuvel * covers [_stext, _etext], and that all relative branches can 165*f9c4ff2aSBarry Song * be resolved without veneers unless this region is exhausted 166*f9c4ff2aSBarry Song * and we fall back to a larger 2GB window in module_alloc() 167*f9c4ff2aSBarry Song * when ARM64_MODULE_PLTS is enabled. 168f80fb3a3SArd Biesheuvel */ 169f80fb3a3SArd Biesheuvel module_range = MODULES_VSIZE - (u64)(_etext - _stext); 170f80fb3a3SArd Biesheuvel module_alloc_base = (u64)_etext + offset - MODULES_VSIZE; 171f80fb3a3SArd Biesheuvel } 172f80fb3a3SArd Biesheuvel 173f80fb3a3SArd Biesheuvel /* use the lower 21 bits to randomize the base of the module region */ 174f80fb3a3SArd Biesheuvel module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21; 175f80fb3a3SArd Biesheuvel module_alloc_base &= PAGE_MASK; 176f80fb3a3SArd Biesheuvel 177fade9c2cSFuad Tabba dcache_clean_inval_poc((unsigned long)&module_alloc_base, 178814b1860SFuad Tabba (unsigned long)&module_alloc_base + 179814b1860SFuad Tabba sizeof(module_alloc_base)); 180fade9c2cSFuad Tabba dcache_clean_inval_poc((unsigned long)&memstart_offset_seed, 181814b1860SFuad Tabba (unsigned long)&memstart_offset_seed + 182814b1860SFuad Tabba sizeof(memstart_offset_seed)); 1831598ecdaSArd Biesheuvel 184f80fb3a3SArd Biesheuvel return offset; 185f80fb3a3SArd Biesheuvel } 186294a9dddSMark Brown 187294a9dddSMark Brown static int __init kaslr_init(void) 188294a9dddSMark Brown { 189294a9dddSMark Brown switch (kaslr_status) { 190294a9dddSMark Brown case KASLR_ENABLED: 191294a9dddSMark Brown pr_info("KASLR enabled\n"); 192294a9dddSMark Brown break; 193294a9dddSMark Brown case KASLR_DISABLED_CMDLINE: 194294a9dddSMark Brown pr_info("KASLR disabled on command line\n"); 195294a9dddSMark Brown break; 196294a9dddSMark Brown case KASLR_DISABLED_NO_SEED: 197294a9dddSMark Brown pr_warn("KASLR disabled due to lack of seed\n"); 198294a9dddSMark Brown break; 199294a9dddSMark Brown case KASLR_DISABLED_FDT_REMAP: 200294a9dddSMark Brown pr_warn("KASLR disabled due to FDT remapping failure\n"); 201294a9dddSMark Brown break; 202294a9dddSMark Brown } 203294a9dddSMark Brown 204294a9dddSMark Brown return 0; 205294a9dddSMark Brown } 206294a9dddSMark Brown core_initcall(kaslr_init) 207