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 22294a9dddSMark Brown enum kaslr_status { 23294a9dddSMark Brown KASLR_ENABLED, 24294a9dddSMark Brown KASLR_DISABLED_CMDLINE, 25294a9dddSMark Brown KASLR_DISABLED_NO_SEED, 26294a9dddSMark Brown KASLR_DISABLED_FDT_REMAP, 27294a9dddSMark Brown }; 28294a9dddSMark Brown 29294a9dddSMark Brown enum kaslr_status __ro_after_init kaslr_status; 305a9e3e15SJisheng Zhang u64 __ro_after_init module_alloc_base; 31c031a421SArd Biesheuvel u16 __initdata memstart_offset_seed; 32f80fb3a3SArd Biesheuvel 33f80fb3a3SArd Biesheuvel static __init u64 get_kaslr_seed(void *fdt) 34f80fb3a3SArd Biesheuvel { 35f80fb3a3SArd Biesheuvel int node, len; 3667831edfSLuc Van Oostenryck fdt64_t *prop; 37f80fb3a3SArd Biesheuvel u64 ret; 38f80fb3a3SArd Biesheuvel 39f80fb3a3SArd Biesheuvel node = fdt_path_offset(fdt, "/chosen"); 40f80fb3a3SArd Biesheuvel if (node < 0) 41f80fb3a3SArd Biesheuvel return 0; 42f80fb3a3SArd Biesheuvel 43f80fb3a3SArd Biesheuvel prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len); 44f80fb3a3SArd Biesheuvel if (!prop || len != sizeof(u64)) 45f80fb3a3SArd Biesheuvel return 0; 46f80fb3a3SArd Biesheuvel 47f80fb3a3SArd Biesheuvel ret = fdt64_to_cpu(*prop); 48f80fb3a3SArd Biesheuvel *prop = 0; 49f80fb3a3SArd Biesheuvel return ret; 50f80fb3a3SArd Biesheuvel } 51f80fb3a3SArd Biesheuvel 521598ecdaSArd Biesheuvel static __init const u8 *kaslr_get_cmdline(void *fdt) 53f80fb3a3SArd Biesheuvel { 54f80fb3a3SArd Biesheuvel static __initconst const u8 default_cmdline[] = CONFIG_CMDLINE; 55f80fb3a3SArd Biesheuvel 56f80fb3a3SArd Biesheuvel if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) { 57f80fb3a3SArd Biesheuvel int node; 58f80fb3a3SArd Biesheuvel const u8 *prop; 59f80fb3a3SArd Biesheuvel 60f80fb3a3SArd Biesheuvel node = fdt_path_offset(fdt, "/chosen"); 61f80fb3a3SArd Biesheuvel if (node < 0) 62f80fb3a3SArd Biesheuvel goto out; 63f80fb3a3SArd Biesheuvel 64f80fb3a3SArd Biesheuvel prop = fdt_getprop(fdt, node, "bootargs", NULL); 65f80fb3a3SArd Biesheuvel if (!prop) 66f80fb3a3SArd Biesheuvel goto out; 67f80fb3a3SArd Biesheuvel return prop; 68f80fb3a3SArd Biesheuvel } 69f80fb3a3SArd Biesheuvel out: 70f80fb3a3SArd Biesheuvel return default_cmdline; 71f80fb3a3SArd Biesheuvel } 72f80fb3a3SArd Biesheuvel 73f80fb3a3SArd Biesheuvel /* 74f80fb3a3SArd Biesheuvel * This routine will be executed with the kernel mapped at its default virtual 75f80fb3a3SArd Biesheuvel * address, and if it returns successfully, the kernel will be remapped, and 76f80fb3a3SArd Biesheuvel * start_kernel() will be executed from a randomized virtual offset. The 77f80fb3a3SArd Biesheuvel * relocation will result in all absolute references (e.g., static variables 78f80fb3a3SArd Biesheuvel * containing function pointers) to be reinitialized, and zero-initialized 79f80fb3a3SArd Biesheuvel * .bss variables will be reset to 0. 80f80fb3a3SArd Biesheuvel */ 814a23e56aSArd Biesheuvel u64 __init kaslr_early_init(u64 dt_phys) 82f80fb3a3SArd Biesheuvel { 83f80fb3a3SArd Biesheuvel void *fdt; 84f80fb3a3SArd Biesheuvel u64 seed, offset, mask, module_range; 85f80fb3a3SArd Biesheuvel const u8 *cmdline, *str; 86f80fb3a3SArd Biesheuvel int size; 87f80fb3a3SArd Biesheuvel 88f80fb3a3SArd Biesheuvel /* 89f80fb3a3SArd Biesheuvel * Set a reasonable default for module_alloc_base in case 90f80fb3a3SArd Biesheuvel * we end up running with module randomization disabled. 91f80fb3a3SArd Biesheuvel */ 92f80fb3a3SArd Biesheuvel module_alloc_base = (u64)_etext - MODULES_VSIZE; 938ea23593SArd Biesheuvel __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base)); 94f80fb3a3SArd Biesheuvel 95f80fb3a3SArd Biesheuvel /* 96f80fb3a3SArd Biesheuvel * Try to map the FDT early. If this fails, we simply bail, 97f80fb3a3SArd Biesheuvel * and proceed with KASLR disabled. We will make another 98f80fb3a3SArd Biesheuvel * attempt at mapping the FDT in setup_machine() 99f80fb3a3SArd Biesheuvel */ 100f80fb3a3SArd Biesheuvel early_fixmap_init(); 101e112b032SHsin-Yi Wang fdt = fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL); 102294a9dddSMark Brown if (!fdt) { 103294a9dddSMark Brown kaslr_status = KASLR_DISABLED_FDT_REMAP; 104f80fb3a3SArd Biesheuvel return 0; 105294a9dddSMark Brown } 106f80fb3a3SArd Biesheuvel 107f80fb3a3SArd Biesheuvel /* 108f80fb3a3SArd Biesheuvel * Retrieve (and wipe) the seed from the FDT 109f80fb3a3SArd Biesheuvel */ 110f80fb3a3SArd Biesheuvel seed = get_kaslr_seed(fdt); 111294a9dddSMark Brown if (!seed) { 112294a9dddSMark Brown kaslr_status = KASLR_DISABLED_NO_SEED; 113f80fb3a3SArd Biesheuvel return 0; 114294a9dddSMark Brown } 115f80fb3a3SArd Biesheuvel 116f80fb3a3SArd Biesheuvel /* 117f80fb3a3SArd Biesheuvel * Check if 'nokaslr' appears on the command line, and 118f80fb3a3SArd Biesheuvel * return 0 if that is the case. 119f80fb3a3SArd Biesheuvel */ 1201598ecdaSArd Biesheuvel cmdline = kaslr_get_cmdline(fdt); 121f80fb3a3SArd Biesheuvel str = strstr(cmdline, "nokaslr"); 122294a9dddSMark Brown if (str == cmdline || (str > cmdline && *(str - 1) == ' ')) { 123294a9dddSMark Brown kaslr_status = KASLR_DISABLED_CMDLINE; 124f80fb3a3SArd Biesheuvel return 0; 125294a9dddSMark Brown } 126f80fb3a3SArd Biesheuvel 127f80fb3a3SArd Biesheuvel /* 128f80fb3a3SArd Biesheuvel * OK, so we are proceeding with KASLR enabled. Calculate a suitable 129f80fb3a3SArd Biesheuvel * kernel image offset from the seed. Let's place the kernel in the 13090ec95cdSSteve Capper * middle half of the VMALLOC area (VA_BITS_MIN - 2), and stay clear of 131f2b9ba87SArd Biesheuvel * the lower and upper quarters to avoid colliding with other 132f2b9ba87SArd Biesheuvel * allocations. 133f80fb3a3SArd Biesheuvel * Even if we could randomize at page granularity for 16k and 64k pages, 134f80fb3a3SArd Biesheuvel * let's always round to 2 MB so we don't interfere with the ability to 135f80fb3a3SArd Biesheuvel * map using contiguous PTEs 136f80fb3a3SArd Biesheuvel */ 13790ec95cdSSteve Capper mask = ((1UL << (VA_BITS_MIN - 2)) - 1) & ~(SZ_2M - 1); 13890ec95cdSSteve Capper offset = BIT(VA_BITS_MIN - 3) + (seed & mask); 139f80fb3a3SArd Biesheuvel 140c031a421SArd Biesheuvel /* use the top 16 bits to randomize the linear region */ 141c031a421SArd Biesheuvel memstart_offset_seed = seed >> 48; 142c031a421SArd Biesheuvel 143f80fb3a3SArd Biesheuvel if (IS_ENABLED(CONFIG_KASAN)) 144f80fb3a3SArd Biesheuvel /* 145f80fb3a3SArd Biesheuvel * KASAN does not expect the module region to intersect the 146f80fb3a3SArd Biesheuvel * vmalloc region, since shadow memory is allocated for each 147f80fb3a3SArd Biesheuvel * module at load time, whereas the vmalloc region is shadowed 148f80fb3a3SArd Biesheuvel * by KASAN zero pages. So keep modules out of the vmalloc 149f2b9ba87SArd Biesheuvel * region if KASAN is enabled, and put the kernel well within 150f2b9ba87SArd Biesheuvel * 4 GB of the module region. 151f80fb3a3SArd Biesheuvel */ 152f2b9ba87SArd Biesheuvel return offset % SZ_2G; 153f80fb3a3SArd Biesheuvel 154f80fb3a3SArd Biesheuvel if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) { 155f80fb3a3SArd Biesheuvel /* 156b2eed9b5SArd Biesheuvel * Randomize the module region over a 2 GB window covering the 157f2b9ba87SArd Biesheuvel * kernel. This reduces the risk of modules leaking information 158f80fb3a3SArd Biesheuvel * about the address of the kernel itself, but results in 159f80fb3a3SArd Biesheuvel * branches between modules and the core kernel that are 160f80fb3a3SArd Biesheuvel * resolved via PLTs. (Branches between modules will be 161f80fb3a3SArd Biesheuvel * resolved normally.) 162f80fb3a3SArd Biesheuvel */ 163b2eed9b5SArd Biesheuvel module_range = SZ_2G - (u64)(_end - _stext); 164b2eed9b5SArd Biesheuvel module_alloc_base = max((u64)_end + offset - SZ_2G, 165f2b9ba87SArd Biesheuvel (u64)MODULES_VADDR); 166f80fb3a3SArd Biesheuvel } else { 167f80fb3a3SArd Biesheuvel /* 168f80fb3a3SArd Biesheuvel * Randomize the module region by setting module_alloc_base to 169f80fb3a3SArd Biesheuvel * a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE, 170f80fb3a3SArd Biesheuvel * _stext) . This guarantees that the resulting region still 171f80fb3a3SArd Biesheuvel * covers [_stext, _etext], and that all relative branches can 172f80fb3a3SArd Biesheuvel * be resolved without veneers. 173f80fb3a3SArd Biesheuvel */ 174f80fb3a3SArd Biesheuvel module_range = MODULES_VSIZE - (u64)(_etext - _stext); 175f80fb3a3SArd Biesheuvel module_alloc_base = (u64)_etext + offset - MODULES_VSIZE; 176f80fb3a3SArd Biesheuvel } 177f80fb3a3SArd Biesheuvel 178f80fb3a3SArd Biesheuvel /* use the lower 21 bits to randomize the base of the module region */ 179f80fb3a3SArd Biesheuvel module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21; 180f80fb3a3SArd Biesheuvel module_alloc_base &= PAGE_MASK; 181f80fb3a3SArd Biesheuvel 1821598ecdaSArd Biesheuvel __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base)); 1831598ecdaSArd Biesheuvel __flush_dcache_area(&memstart_offset_seed, sizeof(memstart_offset_seed)); 1841598ecdaSArd Biesheuvel 185f80fb3a3SArd Biesheuvel return offset; 186f80fb3a3SArd Biesheuvel } 187294a9dddSMark Brown 188294a9dddSMark Brown static int __init kaslr_init(void) 189294a9dddSMark Brown { 190294a9dddSMark Brown switch (kaslr_status) { 191294a9dddSMark Brown case KASLR_ENABLED: 192294a9dddSMark Brown pr_info("KASLR enabled\n"); 193294a9dddSMark Brown break; 194294a9dddSMark Brown case KASLR_DISABLED_CMDLINE: 195294a9dddSMark Brown pr_info("KASLR disabled on command line\n"); 196294a9dddSMark Brown break; 197294a9dddSMark Brown case KASLR_DISABLED_NO_SEED: 198294a9dddSMark Brown pr_warn("KASLR disabled due to lack of seed\n"); 199294a9dddSMark Brown break; 200294a9dddSMark Brown case KASLR_DISABLED_FDT_REMAP: 201294a9dddSMark Brown pr_warn("KASLR disabled due to FDT remapping failure\n"); 202294a9dddSMark Brown break; 203294a9dddSMark Brown } 204294a9dddSMark Brown 205294a9dddSMark Brown return 0; 206294a9dddSMark Brown } 207294a9dddSMark Brown core_initcall(kaslr_init) 208