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
9 #include <linux/crc32.h>
10 #include <linux/init.h>
11 #include <linux/libfdt.h>
12 #include <linux/mm_types.h>
13 #include <linux/sched.h>
14 #include <linux/types.h>
15
16 #include <asm/cacheflush.h>
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
24 u64 __read_mostly module_alloc_base;
25 u16 __initdata memstart_offset_seed;
26
get_kaslr_seed(void * fdt)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
kaslr_get_cmdline(void * fdt)46 static __init const u8 *kaslr_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 */
kaslr_early_init(u64 dt_phys,u64 modulo_offset)78 u64 __init kaslr_early_init(u64 dt_phys, u64 modulo_offset)
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 __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base));
91
92 /*
93 * Try to map the FDT early. If this fails, we simply bail,
94 * and proceed with KASLR disabled. We will make another
95 * attempt at mapping the FDT in setup_machine()
96 */
97 early_fixmap_init();
98 fdt = __fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL);
99 if (!fdt)
100 return 0;
101
102 /*
103 * Retrieve (and wipe) the seed from the FDT
104 */
105 seed = get_kaslr_seed(fdt);
106 if (!seed)
107 return 0;
108
109 /*
110 * Check if 'nokaslr' appears on the command line, and
111 * return 0 if that is the case.
112 */
113 cmdline = kaslr_get_cmdline(fdt);
114 str = strstr(cmdline, "nokaslr");
115 if (str == cmdline || (str > cmdline && *(str - 1) == ' '))
116 return 0;
117
118 /*
119 * OK, so we are proceeding with KASLR enabled. Calculate a suitable
120 * kernel image offset from the seed. Let's place the kernel in the
121 * lower half of the VMALLOC area (VA_BITS - 2).
122 * Even if we could randomize at page granularity for 16k and 64k pages,
123 * let's always round to 2 MB so we don't interfere with the ability to
124 * map using contiguous PTEs
125 */
126 mask = ((1UL << (VA_BITS - 2)) - 1) & ~(SZ_2M - 1);
127 offset = seed & mask;
128
129 /* use the top 16 bits to randomize the linear region */
130 memstart_offset_seed = seed >> 48;
131
132 /*
133 * The kernel Image should not extend across a 1GB/32MB/512MB alignment
134 * boundary (for 4KB/16KB/64KB granule kernels, respectively). If this
135 * happens, increase the KASLR offset by the size of the kernel image
136 * rounded up by SWAPPER_BLOCK_SIZE.
137 */
138 if ((((u64)_text + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT) !=
139 (((u64)_end + offset + modulo_offset) >> SWAPPER_TABLE_SHIFT)) {
140 u64 kimg_sz = _end - _text;
141 offset = (offset + round_up(kimg_sz, SWAPPER_BLOCK_SIZE))
142 & mask;
143 }
144
145 if (IS_ENABLED(CONFIG_KASAN))
146 /*
147 * KASAN does not expect the module region to intersect the
148 * vmalloc region, since shadow memory is allocated for each
149 * module at load time, whereas the vmalloc region is shadowed
150 * by KASAN zero pages. So keep modules out of the vmalloc
151 * region if KASAN is enabled.
152 */
153 return offset;
154
155 if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) {
156 /*
157 * Randomize the module region independently from the core
158 * kernel. This prevents modules from leaking any information
159 * about the address of the kernel itself, but results in
160 * branches between modules and the core kernel that are
161 * resolved via PLTs. (Branches between modules will be
162 * resolved normally.)
163 */
164 module_range = VMALLOC_END - VMALLOC_START - MODULES_VSIZE;
165 module_alloc_base = VMALLOC_START;
166 } else {
167 /*
168 * Randomize the module region by setting module_alloc_base to
169 * a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE,
170 * _stext) . This guarantees that the resulting region still
171 * covers [_stext, _etext], and that all relative branches can
172 * be resolved without veneers.
173 */
174 module_range = MODULES_VSIZE - (u64)(_etext - _stext);
175 module_alloc_base = (u64)_etext + offset - MODULES_VSIZE;
176 }
177
178 /* use the lower 21 bits to randomize the base of the module region */
179 module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21;
180 module_alloc_base &= PAGE_MASK;
181
182 __flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base));
183 __flush_dcache_area(&memstart_offset_seed, sizeof(memstart_offset_seed));
184
185 return offset;
186 }
187