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> 13f80fb3a3SArd Biesheuvel 141598ecdaSArd Biesheuvel #include <asm/cacheflush.h> 15f80fb3a3SArd Biesheuvel #include <asm/fixmap.h> 16f80fb3a3SArd Biesheuvel #include <asm/kernel-pgtable.h> 17f80fb3a3SArd Biesheuvel #include <asm/memory.h> 18f80fb3a3SArd Biesheuvel #include <asm/mmu.h> 19f80fb3a3SArd Biesheuvel #include <asm/pgtable.h> 20f80fb3a3SArd Biesheuvel #include <asm/sections.h> 21f80fb3a3SArd Biesheuvel 225a9e3e15SJisheng Zhang u64 __ro_after_init module_alloc_base; 23c031a421SArd Biesheuvel u16 __initdata memstart_offset_seed; 24f80fb3a3SArd Biesheuvel 25f80fb3a3SArd Biesheuvel static __init u64 get_kaslr_seed(void *fdt) 26f80fb3a3SArd Biesheuvel { 27f80fb3a3SArd Biesheuvel int node, len; 2867831edfSLuc Van Oostenryck fdt64_t *prop; 29f80fb3a3SArd Biesheuvel u64 ret; 30f80fb3a3SArd Biesheuvel 31f80fb3a3SArd Biesheuvel node = fdt_path_offset(fdt, "/chosen"); 32f80fb3a3SArd Biesheuvel if (node < 0) 33f80fb3a3SArd Biesheuvel return 0; 34f80fb3a3SArd Biesheuvel 35f80fb3a3SArd Biesheuvel prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len); 36f80fb3a3SArd Biesheuvel if (!prop || len != sizeof(u64)) 37f80fb3a3SArd Biesheuvel return 0; 38f80fb3a3SArd Biesheuvel 39f80fb3a3SArd Biesheuvel ret = fdt64_to_cpu(*prop); 40f80fb3a3SArd Biesheuvel *prop = 0; 41f80fb3a3SArd Biesheuvel return ret; 42f80fb3a3SArd Biesheuvel } 43f80fb3a3SArd Biesheuvel 441598ecdaSArd Biesheuvel static __init const u8 *kaslr_get_cmdline(void *fdt) 45f80fb3a3SArd Biesheuvel { 46f80fb3a3SArd Biesheuvel static __initconst const u8 default_cmdline[] = CONFIG_CMDLINE; 47f80fb3a3SArd Biesheuvel 48f80fb3a3SArd Biesheuvel if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) { 49f80fb3a3SArd Biesheuvel int node; 50f80fb3a3SArd Biesheuvel const u8 *prop; 51f80fb3a3SArd Biesheuvel 52f80fb3a3SArd Biesheuvel node = fdt_path_offset(fdt, "/chosen"); 53f80fb3a3SArd Biesheuvel if (node < 0) 54f80fb3a3SArd Biesheuvel goto out; 55f80fb3a3SArd Biesheuvel 56f80fb3a3SArd Biesheuvel prop = fdt_getprop(fdt, node, "bootargs", NULL); 57f80fb3a3SArd Biesheuvel if (!prop) 58f80fb3a3SArd Biesheuvel goto out; 59f80fb3a3SArd Biesheuvel return prop; 60f80fb3a3SArd Biesheuvel } 61f80fb3a3SArd Biesheuvel out: 62f80fb3a3SArd Biesheuvel return default_cmdline; 63f80fb3a3SArd Biesheuvel } 64f80fb3a3SArd Biesheuvel 65f80fb3a3SArd Biesheuvel /* 66f80fb3a3SArd Biesheuvel * This routine will be executed with the kernel mapped at its default virtual 67f80fb3a3SArd Biesheuvel * address, and if it returns successfully, the kernel will be remapped, and 68f80fb3a3SArd Biesheuvel * start_kernel() will be executed from a randomized virtual offset. The 69f80fb3a3SArd Biesheuvel * relocation will result in all absolute references (e.g., static variables 70f80fb3a3SArd Biesheuvel * containing function pointers) to be reinitialized, and zero-initialized 71f80fb3a3SArd Biesheuvel * .bss variables will be reset to 0. 72f80fb3a3SArd Biesheuvel */ 734a23e56aSArd Biesheuvel u64 __init kaslr_early_init(u64 dt_phys) 74f80fb3a3SArd Biesheuvel { 75f80fb3a3SArd Biesheuvel void *fdt; 76f80fb3a3SArd Biesheuvel u64 seed, offset, mask, module_range; 77f80fb3a3SArd Biesheuvel const u8 *cmdline, *str; 78f80fb3a3SArd Biesheuvel int size; 79f80fb3a3SArd Biesheuvel 80f80fb3a3SArd Biesheuvel /* 81f80fb3a3SArd Biesheuvel * Set a reasonable default for module_alloc_base in case 82f80fb3a3SArd Biesheuvel * we end up running with module randomization disabled. 83f80fb3a3SArd Biesheuvel */ 84f80fb3a3SArd Biesheuvel module_alloc_base = (u64)_etext - MODULES_VSIZE; 858ea23593SArd Biesheuvel __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base)); 86f80fb3a3SArd Biesheuvel 87f80fb3a3SArd Biesheuvel /* 88f80fb3a3SArd Biesheuvel * Try to map the FDT early. If this fails, we simply bail, 89f80fb3a3SArd Biesheuvel * and proceed with KASLR disabled. We will make another 90f80fb3a3SArd Biesheuvel * attempt at mapping the FDT in setup_machine() 91f80fb3a3SArd Biesheuvel */ 92f80fb3a3SArd Biesheuvel early_fixmap_init(); 93e112b032SHsin-Yi Wang fdt = fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL); 94f80fb3a3SArd Biesheuvel if (!fdt) 95f80fb3a3SArd Biesheuvel return 0; 96f80fb3a3SArd Biesheuvel 97f80fb3a3SArd Biesheuvel /* 98f80fb3a3SArd Biesheuvel * Retrieve (and wipe) the seed from the FDT 99f80fb3a3SArd Biesheuvel */ 100f80fb3a3SArd Biesheuvel seed = get_kaslr_seed(fdt); 101f80fb3a3SArd Biesheuvel if (!seed) 102f80fb3a3SArd Biesheuvel return 0; 103f80fb3a3SArd Biesheuvel 104f80fb3a3SArd Biesheuvel /* 105f80fb3a3SArd Biesheuvel * Check if 'nokaslr' appears on the command line, and 106f80fb3a3SArd Biesheuvel * return 0 if that is the case. 107f80fb3a3SArd Biesheuvel */ 1081598ecdaSArd Biesheuvel cmdline = kaslr_get_cmdline(fdt); 109f80fb3a3SArd Biesheuvel str = strstr(cmdline, "nokaslr"); 110f80fb3a3SArd Biesheuvel if (str == cmdline || (str > cmdline && *(str - 1) == ' ')) 111f80fb3a3SArd Biesheuvel return 0; 112f80fb3a3SArd Biesheuvel 113f80fb3a3SArd Biesheuvel /* 114f80fb3a3SArd Biesheuvel * OK, so we are proceeding with KASLR enabled. Calculate a suitable 115f80fb3a3SArd Biesheuvel * kernel image offset from the seed. Let's place the kernel in the 116f2b9ba87SArd Biesheuvel * middle half of the VMALLOC area (VA_BITS - 2), and stay clear of 117f2b9ba87SArd Biesheuvel * the lower and upper quarters to avoid colliding with other 118f2b9ba87SArd Biesheuvel * allocations. 119f80fb3a3SArd Biesheuvel * Even if we could randomize at page granularity for 16k and 64k pages, 120f80fb3a3SArd Biesheuvel * let's always round to 2 MB so we don't interfere with the ability to 121f80fb3a3SArd Biesheuvel * map using contiguous PTEs 122f80fb3a3SArd Biesheuvel */ 123f80fb3a3SArd Biesheuvel mask = ((1UL << (VA_BITS - 2)) - 1) & ~(SZ_2M - 1); 124f2b9ba87SArd Biesheuvel offset = BIT(VA_BITS - 3) + (seed & mask); 125f80fb3a3SArd Biesheuvel 126c031a421SArd Biesheuvel /* use the top 16 bits to randomize the linear region */ 127c031a421SArd Biesheuvel memstart_offset_seed = seed >> 48; 128c031a421SArd Biesheuvel 129f80fb3a3SArd Biesheuvel if (IS_ENABLED(CONFIG_KASAN)) 130f80fb3a3SArd Biesheuvel /* 131f80fb3a3SArd Biesheuvel * KASAN does not expect the module region to intersect the 132f80fb3a3SArd Biesheuvel * vmalloc region, since shadow memory is allocated for each 133f80fb3a3SArd Biesheuvel * module at load time, whereas the vmalloc region is shadowed 134f80fb3a3SArd Biesheuvel * by KASAN zero pages. So keep modules out of the vmalloc 135f2b9ba87SArd Biesheuvel * region if KASAN is enabled, and put the kernel well within 136f2b9ba87SArd Biesheuvel * 4 GB of the module region. 137f80fb3a3SArd Biesheuvel */ 138f2b9ba87SArd Biesheuvel return offset % SZ_2G; 139f80fb3a3SArd Biesheuvel 140f80fb3a3SArd Biesheuvel if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) { 141f80fb3a3SArd Biesheuvel /* 142b2eed9b5SArd Biesheuvel * Randomize the module region over a 2 GB window covering the 143f2b9ba87SArd Biesheuvel * kernel. This reduces the risk of modules leaking information 144f80fb3a3SArd Biesheuvel * about the address of the kernel itself, but results in 145f80fb3a3SArd Biesheuvel * branches between modules and the core kernel that are 146f80fb3a3SArd Biesheuvel * resolved via PLTs. (Branches between modules will be 147f80fb3a3SArd Biesheuvel * resolved normally.) 148f80fb3a3SArd Biesheuvel */ 149b2eed9b5SArd Biesheuvel module_range = SZ_2G - (u64)(_end - _stext); 150b2eed9b5SArd Biesheuvel module_alloc_base = max((u64)_end + offset - SZ_2G, 151f2b9ba87SArd Biesheuvel (u64)MODULES_VADDR); 152f80fb3a3SArd Biesheuvel } else { 153f80fb3a3SArd Biesheuvel /* 154f80fb3a3SArd Biesheuvel * Randomize the module region by setting module_alloc_base to 155f80fb3a3SArd Biesheuvel * a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE, 156f80fb3a3SArd Biesheuvel * _stext) . This guarantees that the resulting region still 157f80fb3a3SArd Biesheuvel * covers [_stext, _etext], and that all relative branches can 158f80fb3a3SArd Biesheuvel * be resolved without veneers. 159f80fb3a3SArd Biesheuvel */ 160f80fb3a3SArd Biesheuvel module_range = MODULES_VSIZE - (u64)(_etext - _stext); 161f80fb3a3SArd Biesheuvel module_alloc_base = (u64)_etext + offset - MODULES_VSIZE; 162f80fb3a3SArd Biesheuvel } 163f80fb3a3SArd Biesheuvel 164f80fb3a3SArd Biesheuvel /* use the lower 21 bits to randomize the base of the module region */ 165f80fb3a3SArd Biesheuvel module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21; 166f80fb3a3SArd Biesheuvel module_alloc_base &= PAGE_MASK; 167f80fb3a3SArd Biesheuvel 1681598ecdaSArd Biesheuvel __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base)); 1691598ecdaSArd Biesheuvel __flush_dcache_area(&memstart_offset_seed, sizeof(memstart_offset_seed)); 1701598ecdaSArd Biesheuvel 171f80fb3a3SArd Biesheuvel return offset; 172f80fb3a3SArd Biesheuvel } 173