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> 22f80fb3a3SArd Biesheuvel 23294a9dddSMark Brown enum kaslr_status { 24294a9dddSMark Brown KASLR_ENABLED, 25294a9dddSMark Brown KASLR_DISABLED_CMDLINE, 26294a9dddSMark Brown KASLR_DISABLED_NO_SEED, 27294a9dddSMark Brown KASLR_DISABLED_FDT_REMAP, 28294a9dddSMark Brown }; 29294a9dddSMark Brown 302203e1adSMark Brown static enum kaslr_status __initdata kaslr_status; 315a9e3e15SJisheng Zhang u64 __ro_after_init module_alloc_base; 32c031a421SArd Biesheuvel u16 __initdata memstart_offset_seed; 33f80fb3a3SArd Biesheuvel 34f80fb3a3SArd Biesheuvel static __init u64 get_kaslr_seed(void *fdt) 35f80fb3a3SArd Biesheuvel { 36f80fb3a3SArd Biesheuvel int node, len; 3767831edfSLuc Van Oostenryck fdt64_t *prop; 38f80fb3a3SArd Biesheuvel u64 ret; 39f80fb3a3SArd Biesheuvel 40f80fb3a3SArd Biesheuvel node = fdt_path_offset(fdt, "/chosen"); 41f80fb3a3SArd Biesheuvel if (node < 0) 42f80fb3a3SArd Biesheuvel return 0; 43f80fb3a3SArd Biesheuvel 44f80fb3a3SArd Biesheuvel prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len); 45f80fb3a3SArd Biesheuvel if (!prop || len != sizeof(u64)) 46f80fb3a3SArd Biesheuvel return 0; 47f80fb3a3SArd Biesheuvel 48f80fb3a3SArd Biesheuvel ret = fdt64_to_cpu(*prop); 49f80fb3a3SArd Biesheuvel *prop = 0; 50f80fb3a3SArd Biesheuvel return ret; 51f80fb3a3SArd Biesheuvel } 52f80fb3a3SArd Biesheuvel 531598ecdaSArd Biesheuvel static __init const u8 *kaslr_get_cmdline(void *fdt) 54f80fb3a3SArd Biesheuvel { 55f80fb3a3SArd Biesheuvel static __initconst const u8 default_cmdline[] = CONFIG_CMDLINE; 56f80fb3a3SArd Biesheuvel 57f80fb3a3SArd Biesheuvel if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) { 58f80fb3a3SArd Biesheuvel int node; 59f80fb3a3SArd Biesheuvel const u8 *prop; 60f80fb3a3SArd Biesheuvel 61f80fb3a3SArd Biesheuvel node = fdt_path_offset(fdt, "/chosen"); 62f80fb3a3SArd Biesheuvel if (node < 0) 63f80fb3a3SArd Biesheuvel goto out; 64f80fb3a3SArd Biesheuvel 65f80fb3a3SArd Biesheuvel prop = fdt_getprop(fdt, node, "bootargs", NULL); 66f80fb3a3SArd Biesheuvel if (!prop) 67f80fb3a3SArd Biesheuvel goto out; 68f80fb3a3SArd Biesheuvel return prop; 69f80fb3a3SArd Biesheuvel } 70f80fb3a3SArd Biesheuvel out: 71f80fb3a3SArd Biesheuvel return default_cmdline; 72f80fb3a3SArd Biesheuvel } 73f80fb3a3SArd Biesheuvel 74f80fb3a3SArd Biesheuvel /* 75f80fb3a3SArd Biesheuvel * This routine will be executed with the kernel mapped at its default virtual 76f80fb3a3SArd Biesheuvel * address, and if it returns successfully, the kernel will be remapped, and 77f80fb3a3SArd Biesheuvel * start_kernel() will be executed from a randomized virtual offset. The 78f80fb3a3SArd Biesheuvel * relocation will result in all absolute references (e.g., static variables 79f80fb3a3SArd Biesheuvel * containing function pointers) to be reinitialized, and zero-initialized 80f80fb3a3SArd Biesheuvel * .bss variables will be reset to 0. 81f80fb3a3SArd Biesheuvel */ 824a23e56aSArd Biesheuvel u64 __init kaslr_early_init(u64 dt_phys) 83f80fb3a3SArd Biesheuvel { 84f80fb3a3SArd Biesheuvel void *fdt; 85f80fb3a3SArd Biesheuvel u64 seed, offset, mask, module_range; 86f80fb3a3SArd Biesheuvel const u8 *cmdline, *str; 87*9bceb80bSGuenter Roeck unsigned long raw; 88f80fb3a3SArd Biesheuvel int size; 89f80fb3a3SArd Biesheuvel 90f80fb3a3SArd Biesheuvel /* 91f80fb3a3SArd Biesheuvel * Set a reasonable default for module_alloc_base in case 92f80fb3a3SArd Biesheuvel * we end up running with module randomization disabled. 93f80fb3a3SArd Biesheuvel */ 94f80fb3a3SArd Biesheuvel module_alloc_base = (u64)_etext - MODULES_VSIZE; 958ea23593SArd Biesheuvel __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base)); 96f80fb3a3SArd Biesheuvel 97f80fb3a3SArd Biesheuvel /* 98f80fb3a3SArd Biesheuvel * Try to map the FDT early. If this fails, we simply bail, 99f80fb3a3SArd Biesheuvel * and proceed with KASLR disabled. We will make another 100f80fb3a3SArd Biesheuvel * attempt at mapping the FDT in setup_machine() 101f80fb3a3SArd Biesheuvel */ 102f80fb3a3SArd Biesheuvel early_fixmap_init(); 103e112b032SHsin-Yi Wang fdt = fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL); 104294a9dddSMark Brown if (!fdt) { 105294a9dddSMark Brown kaslr_status = KASLR_DISABLED_FDT_REMAP; 106f80fb3a3SArd Biesheuvel return 0; 107294a9dddSMark Brown } 108f80fb3a3SArd Biesheuvel 109f80fb3a3SArd Biesheuvel /* 110f80fb3a3SArd Biesheuvel * Retrieve (and wipe) the seed from the FDT 111f80fb3a3SArd Biesheuvel */ 112f80fb3a3SArd Biesheuvel seed = get_kaslr_seed(fdt); 113f80fb3a3SArd Biesheuvel 114f80fb3a3SArd Biesheuvel /* 115f80fb3a3SArd Biesheuvel * Check if 'nokaslr' appears on the command line, and 116f80fb3a3SArd Biesheuvel * return 0 if that is the case. 117f80fb3a3SArd Biesheuvel */ 1181598ecdaSArd Biesheuvel cmdline = kaslr_get_cmdline(fdt); 119f80fb3a3SArd Biesheuvel str = strstr(cmdline, "nokaslr"); 120294a9dddSMark Brown if (str == cmdline || (str > cmdline && *(str - 1) == ' ')) { 121294a9dddSMark Brown kaslr_status = KASLR_DISABLED_CMDLINE; 122f80fb3a3SArd Biesheuvel return 0; 123294a9dddSMark Brown } 124f80fb3a3SArd Biesheuvel 1252e8e1ea8SMark Brown /* 126*9bceb80bSGuenter Roeck * Mix in any entropy obtainable architecturally if enabled 127*9bceb80bSGuenter Roeck * and supported. 1282e8e1ea8SMark Brown */ 1292e8e1ea8SMark Brown 130*9bceb80bSGuenter Roeck if (arch_get_random_seed_long_early(&raw)) 1312e8e1ea8SMark Brown seed ^= raw; 1322e8e1ea8SMark Brown 1332203e1adSMark Brown if (!seed) { 1342203e1adSMark Brown kaslr_status = KASLR_DISABLED_NO_SEED; 1352203e1adSMark Brown return 0; 1362203e1adSMark Brown } 1372203e1adSMark Brown 138f80fb3a3SArd Biesheuvel /* 139f80fb3a3SArd Biesheuvel * OK, so we are proceeding with KASLR enabled. Calculate a suitable 140f80fb3a3SArd Biesheuvel * kernel image offset from the seed. Let's place the kernel in the 14190ec95cdSSteve Capper * middle half of the VMALLOC area (VA_BITS_MIN - 2), and stay clear of 142f2b9ba87SArd Biesheuvel * the lower and upper quarters to avoid colliding with other 143f2b9ba87SArd Biesheuvel * allocations. 144f80fb3a3SArd Biesheuvel * Even if we could randomize at page granularity for 16k and 64k pages, 145f80fb3a3SArd Biesheuvel * let's always round to 2 MB so we don't interfere with the ability to 146f80fb3a3SArd Biesheuvel * map using contiguous PTEs 147f80fb3a3SArd Biesheuvel */ 14890ec95cdSSteve Capper mask = ((1UL << (VA_BITS_MIN - 2)) - 1) & ~(SZ_2M - 1); 14990ec95cdSSteve Capper offset = BIT(VA_BITS_MIN - 3) + (seed & mask); 150f80fb3a3SArd Biesheuvel 151c031a421SArd Biesheuvel /* use the top 16 bits to randomize the linear region */ 152c031a421SArd Biesheuvel memstart_offset_seed = seed >> 48; 153c031a421SArd Biesheuvel 154f80fb3a3SArd Biesheuvel if (IS_ENABLED(CONFIG_KASAN)) 155f80fb3a3SArd Biesheuvel /* 156f80fb3a3SArd Biesheuvel * KASAN does not expect the module region to intersect the 157f80fb3a3SArd Biesheuvel * vmalloc region, since shadow memory is allocated for each 158f80fb3a3SArd Biesheuvel * module at load time, whereas the vmalloc region is shadowed 159f80fb3a3SArd Biesheuvel * by KASAN zero pages. So keep modules out of the vmalloc 160f2b9ba87SArd Biesheuvel * region if KASAN is enabled, and put the kernel well within 161f2b9ba87SArd Biesheuvel * 4 GB of the module region. 162f80fb3a3SArd Biesheuvel */ 163f2b9ba87SArd Biesheuvel return offset % SZ_2G; 164f80fb3a3SArd Biesheuvel 165f80fb3a3SArd Biesheuvel if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) { 166f80fb3a3SArd Biesheuvel /* 167b2eed9b5SArd Biesheuvel * Randomize the module region over a 2 GB window covering the 168f2b9ba87SArd Biesheuvel * kernel. This reduces the risk of modules leaking information 169f80fb3a3SArd Biesheuvel * about the address of the kernel itself, but results in 170f80fb3a3SArd Biesheuvel * branches between modules and the core kernel that are 171f80fb3a3SArd Biesheuvel * resolved via PLTs. (Branches between modules will be 172f80fb3a3SArd Biesheuvel * resolved normally.) 173f80fb3a3SArd Biesheuvel */ 174b2eed9b5SArd Biesheuvel module_range = SZ_2G - (u64)(_end - _stext); 175b2eed9b5SArd Biesheuvel module_alloc_base = max((u64)_end + offset - SZ_2G, 176f2b9ba87SArd Biesheuvel (u64)MODULES_VADDR); 177f80fb3a3SArd Biesheuvel } else { 178f80fb3a3SArd Biesheuvel /* 179f80fb3a3SArd Biesheuvel * Randomize the module region by setting module_alloc_base to 180f80fb3a3SArd Biesheuvel * a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE, 181f80fb3a3SArd Biesheuvel * _stext) . This guarantees that the resulting region still 182f80fb3a3SArd Biesheuvel * covers [_stext, _etext], and that all relative branches can 183f80fb3a3SArd Biesheuvel * be resolved without veneers. 184f80fb3a3SArd Biesheuvel */ 185f80fb3a3SArd Biesheuvel module_range = MODULES_VSIZE - (u64)(_etext - _stext); 186f80fb3a3SArd Biesheuvel module_alloc_base = (u64)_etext + offset - MODULES_VSIZE; 187f80fb3a3SArd Biesheuvel } 188f80fb3a3SArd Biesheuvel 189f80fb3a3SArd Biesheuvel /* use the lower 21 bits to randomize the base of the module region */ 190f80fb3a3SArd Biesheuvel module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21; 191f80fb3a3SArd Biesheuvel module_alloc_base &= PAGE_MASK; 192f80fb3a3SArd Biesheuvel 1931598ecdaSArd Biesheuvel __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base)); 1941598ecdaSArd Biesheuvel __flush_dcache_area(&memstart_offset_seed, sizeof(memstart_offset_seed)); 1951598ecdaSArd Biesheuvel 196f80fb3a3SArd Biesheuvel return offset; 197f80fb3a3SArd Biesheuvel } 198294a9dddSMark Brown 199294a9dddSMark Brown static int __init kaslr_init(void) 200294a9dddSMark Brown { 201294a9dddSMark Brown switch (kaslr_status) { 202294a9dddSMark Brown case KASLR_ENABLED: 203294a9dddSMark Brown pr_info("KASLR enabled\n"); 204294a9dddSMark Brown break; 205294a9dddSMark Brown case KASLR_DISABLED_CMDLINE: 206294a9dddSMark Brown pr_info("KASLR disabled on command line\n"); 207294a9dddSMark Brown break; 208294a9dddSMark Brown case KASLR_DISABLED_NO_SEED: 209294a9dddSMark Brown pr_warn("KASLR disabled due to lack of seed\n"); 210294a9dddSMark Brown break; 211294a9dddSMark Brown case KASLR_DISABLED_FDT_REMAP: 212294a9dddSMark Brown pr_warn("KASLR disabled due to FDT remapping failure\n"); 213294a9dddSMark Brown break; 214294a9dddSMark Brown } 215294a9dddSMark Brown 216294a9dddSMark Brown return 0; 217294a9dddSMark Brown } 218294a9dddSMark Brown core_initcall(kaslr_init) 219