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f80fb3a3 AB |
1 | /* |
2 | * Copyright (C) 2016 Linaro Ltd <ard.biesheuvel@linaro.org> | |
3 | * | |
4 | * This program is free software; you can redistribute it and/or modify | |
5 | * it under the terms of the GNU General Public License version 2 as | |
6 | * published by the Free Software Foundation. | |
7 | */ | |
8 | ||
5a9e3e15 | 9 | #include <linux/cache.h> |
f80fb3a3 AB |
10 | #include <linux/crc32.h> |
11 | #include <linux/init.h> | |
12 | #include <linux/libfdt.h> | |
13 | #include <linux/mm_types.h> | |
14 | #include <linux/sched.h> | |
15 | #include <linux/types.h> | |
16 | ||
17 | #include <asm/fixmap.h> | |
18 | #include <asm/kernel-pgtable.h> | |
19 | #include <asm/memory.h> | |
20 | #include <asm/mmu.h> | |
21 | #include <asm/pgtable.h> | |
22 | #include <asm/sections.h> | |
23 | ||
5a9e3e15 | 24 | u64 __ro_after_init module_alloc_base; |
c031a421 | 25 | u16 __initdata memstart_offset_seed; |
f80fb3a3 AB |
26 | |
27 | static __init u64 get_kaslr_seed(void *fdt) | |
28 | { | |
29 | int node, len; | |
30 | u64 *prop; | |
31 | u64 ret; | |
32 | ||
33 | node = fdt_path_offset(fdt, "/chosen"); | |
34 | if (node < 0) | |
35 | return 0; | |
36 | ||
37 | prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len); | |
38 | if (!prop || len != sizeof(u64)) | |
39 | return 0; | |
40 | ||
41 | ret = fdt64_to_cpu(*prop); | |
42 | *prop = 0; | |
43 | return ret; | |
44 | } | |
45 | ||
46 | static __init const u8 *get_cmdline(void *fdt) | |
47 | { | |
48 | static __initconst const u8 default_cmdline[] = CONFIG_CMDLINE; | |
49 | ||
50 | if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) { | |
51 | int node; | |
52 | const u8 *prop; | |
53 | ||
54 | node = fdt_path_offset(fdt, "/chosen"); | |
55 | if (node < 0) | |
56 | goto out; | |
57 | ||
58 | prop = fdt_getprop(fdt, node, "bootargs", NULL); | |
59 | if (!prop) | |
60 | goto out; | |
61 | return prop; | |
62 | } | |
63 | out: | |
64 | return default_cmdline; | |
65 | } | |
66 | ||
67 | extern void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size, | |
68 | pgprot_t prot); | |
69 | ||
70 | /* | |
71 | * This routine will be executed with the kernel mapped at its default virtual | |
72 | * address, and if it returns successfully, the kernel will be remapped, and | |
73 | * start_kernel() will be executed from a randomized virtual offset. The | |
74 | * relocation will result in all absolute references (e.g., static variables | |
75 | * containing function pointers) to be reinitialized, and zero-initialized | |
76 | * .bss variables will be reset to 0. | |
77 | */ | |
08cdac61 | 78 | u64 __init kaslr_early_init(u64 dt_phys, u64 modulo_offset) |
f80fb3a3 AB |
79 | { |
80 | void *fdt; | |
81 | u64 seed, offset, mask, module_range; | |
82 | const u8 *cmdline, *str; | |
83 | int size; | |
84 | ||
85 | /* | |
86 | * Set a reasonable default for module_alloc_base in case | |
87 | * we end up running with module randomization disabled. | |
88 | */ | |
89 | module_alloc_base = (u64)_etext - MODULES_VSIZE; | |
90 | ||
91 | /* | |
92 | * Try to map the FDT early. If this fails, we simply bail, | |
93 | * and proceed with KASLR disabled. We will make another | |
94 | * attempt at mapping the FDT in setup_machine() | |
95 | */ | |
96 | early_fixmap_init(); | |
97 | fdt = __fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL); | |
98 | if (!fdt) | |
99 | return 0; | |
100 | ||
101 | /* | |
102 | * Retrieve (and wipe) the seed from the FDT | |
103 | */ | |
104 | seed = get_kaslr_seed(fdt); | |
105 | if (!seed) | |
106 | return 0; | |
107 | ||
108 | /* | |
109 | * Check if 'nokaslr' appears on the command line, and | |
110 | * return 0 if that is the case. | |
111 | */ | |
112 | cmdline = get_cmdline(fdt); | |
113 | str = strstr(cmdline, "nokaslr"); | |
114 | if (str == cmdline || (str > cmdline && *(str - 1) == ' ')) | |
115 | return 0; | |
116 | ||
117 | /* | |
118 | * OK, so we are proceeding with KASLR enabled. Calculate a suitable | |
119 | * kernel image offset from the seed. Let's place the kernel in the | |
120 | * lower half of the VMALLOC area (VA_BITS - 2). | |
121 | * Even if we could randomize at page granularity for 16k and 64k pages, | |
122 | * let's always round to 2 MB so we don't interfere with the ability to | |
123 | * map using contiguous PTEs | |
124 | */ | |
125 | mask = ((1UL << (VA_BITS - 2)) - 1) & ~(SZ_2M - 1); | |
126 | offset = seed & mask; | |
127 | ||
c031a421 AB |
128 | /* use the top 16 bits to randomize the linear region */ |
129 | memstart_offset_seed = seed >> 48; | |
130 | ||
f80fb3a3 AB |
131 | /* |
132 | * The kernel Image should not extend across a 1GB/32MB/512MB alignment | |
133 | * boundary (for 4KB/16KB/64KB granule kernels, respectively). If this | |
134 | * happens, increase the KASLR offset by the size of the kernel image. | |
135 | */ | |
08cdac61 AB |
136 | if ((((u64)_text + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT) != |
137 | (((u64)_end + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT)) | |
f80fb3a3 AB |
138 | offset = (offset + (u64)(_end - _text)) & mask; |
139 | ||
140 | if (IS_ENABLED(CONFIG_KASAN)) | |
141 | /* | |
142 | * KASAN does not expect the module region to intersect the | |
143 | * vmalloc region, since shadow memory is allocated for each | |
144 | * module at load time, whereas the vmalloc region is shadowed | |
145 | * by KASAN zero pages. So keep modules out of the vmalloc | |
146 | * region if KASAN is enabled. | |
147 | */ | |
148 | return offset; | |
149 | ||
150 | if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) { | |
151 | /* | |
152 | * Randomize the module region independently from the core | |
153 | * kernel. This prevents modules from leaking any information | |
154 | * about the address of the kernel itself, but results in | |
155 | * branches between modules and the core kernel that are | |
156 | * resolved via PLTs. (Branches between modules will be | |
157 | * resolved normally.) | |
158 | */ | |
159 | module_range = VMALLOC_END - VMALLOC_START - MODULES_VSIZE; | |
160 | module_alloc_base = VMALLOC_START; | |
161 | } else { | |
162 | /* | |
163 | * Randomize the module region by setting module_alloc_base to | |
164 | * a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE, | |
165 | * _stext) . This guarantees that the resulting region still | |
166 | * covers [_stext, _etext], and that all relative branches can | |
167 | * be resolved without veneers. | |
168 | */ | |
169 | module_range = MODULES_VSIZE - (u64)(_etext - _stext); | |
170 | module_alloc_base = (u64)_etext + offset - MODULES_VSIZE; | |
171 | } | |
172 | ||
173 | /* use the lower 21 bits to randomize the base of the module region */ | |
174 | module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21; | |
175 | module_alloc_base &= PAGE_MASK; | |
176 | ||
177 | return offset; | |
178 | } |