1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Support for Kernel relocation at boot time
4 *
5 * Copyright (C) 2023 Loongson Technology Corporation Limited
6 */
7
8 #include <linux/elf.h>
9 #include <linux/kernel.h>
10 #include <linux/printk.h>
11 #include <linux/panic_notifier.h>
12 #include <linux/start_kernel.h>
13 #include <asm/bootinfo.h>
14 #include <asm/early_ioremap.h>
15 #include <asm/inst.h>
16 #include <asm/sections.h>
17 #include <asm/setup.h>
18
19 #define RELOCATED(x) ((void *)((long)x + reloc_offset))
20 #define RELOCATED_KASLR(x) ((void *)((long)x + random_offset))
21
22 static unsigned long reloc_offset;
23
relocate_relative(void)24 static inline void __init relocate_relative(void)
25 {
26 Elf64_Rela *rela, *rela_end;
27 rela = (Elf64_Rela *)&__rela_dyn_begin;
28 rela_end = (Elf64_Rela *)&__rela_dyn_end;
29
30 for ( ; rela < rela_end; rela++) {
31 Elf64_Addr addr = rela->r_offset;
32 Elf64_Addr relocated_addr = rela->r_addend;
33
34 if (rela->r_info != R_LARCH_RELATIVE)
35 continue;
36
37 if (relocated_addr >= VMLINUX_LOAD_ADDRESS)
38 relocated_addr = (Elf64_Addr)RELOCATED(relocated_addr);
39
40 *(Elf64_Addr *)RELOCATED(addr) = relocated_addr;
41 }
42 }
43
relocate_absolute(long random_offset)44 static inline void __init relocate_absolute(long random_offset)
45 {
46 void *begin, *end;
47 struct rela_la_abs *p;
48
49 begin = RELOCATED_KASLR(&__la_abs_begin);
50 end = RELOCATED_KASLR(&__la_abs_end);
51
52 for (p = begin; (void *)p < end; p++) {
53 long v = p->symvalue;
54 uint32_t lu12iw, ori, lu32id, lu52id;
55 union loongarch_instruction *insn = (void *)p->pc;
56
57 lu12iw = (v >> 12) & 0xfffff;
58 ori = v & 0xfff;
59 lu32id = (v >> 32) & 0xfffff;
60 lu52id = v >> 52;
61
62 insn[0].reg1i20_format.immediate = lu12iw;
63 insn[1].reg2i12_format.immediate = ori;
64 insn[2].reg1i20_format.immediate = lu32id;
65 insn[3].reg2i12_format.immediate = lu52id;
66 }
67 }
68
69 #ifdef CONFIG_RANDOMIZE_BASE
rotate_xor(unsigned long hash,const void * area,size_t size)70 static inline __init unsigned long rotate_xor(unsigned long hash,
71 const void *area, size_t size)
72 {
73 size_t i, diff;
74 const typeof(hash) *ptr = PTR_ALIGN(area, sizeof(hash));
75
76 diff = (void *)ptr - area;
77 if (size < diff + sizeof(hash))
78 return hash;
79
80 size = ALIGN_DOWN(size - diff, sizeof(hash));
81
82 for (i = 0; i < size / sizeof(hash); i++) {
83 /* Rotate by odd number of bits and XOR. */
84 hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7);
85 hash ^= ptr[i];
86 }
87
88 return hash;
89 }
90
get_random_boot(void)91 static inline __init unsigned long get_random_boot(void)
92 {
93 unsigned long hash = 0;
94 unsigned long entropy = random_get_entropy();
95
96 /* Attempt to create a simple but unpredictable starting entropy. */
97 hash = rotate_xor(hash, linux_banner, strlen(linux_banner));
98
99 /* Add in any runtime entropy we can get */
100 hash = rotate_xor(hash, &entropy, sizeof(entropy));
101
102 return hash;
103 }
104
nokaslr(char * p)105 static int __init nokaslr(char *p)
106 {
107 pr_info("KASLR is disabled.\n");
108
109 return 0; /* Print a notice and silence the boot warning */
110 }
111 early_param("nokaslr", nokaslr);
112
kaslr_disabled(void)113 static inline __init bool kaslr_disabled(void)
114 {
115 char *str;
116 const char *builtin_cmdline = CONFIG_CMDLINE;
117
118 str = strstr(builtin_cmdline, "nokaslr");
119 if (str == builtin_cmdline || (str > builtin_cmdline && *(str - 1) == ' '))
120 return true;
121
122 str = strstr(boot_command_line, "nokaslr");
123 if (str == boot_command_line || (str > boot_command_line && *(str - 1) == ' '))
124 return true;
125
126 return false;
127 }
128
129 /* Choose a new address for the kernel */
determine_relocation_address(void)130 static inline void __init *determine_relocation_address(void)
131 {
132 unsigned long kernel_length;
133 unsigned long random_offset;
134 void *destination = _text;
135
136 if (kaslr_disabled())
137 return destination;
138
139 kernel_length = (long)_end - (long)_text;
140
141 random_offset = get_random_boot() << 16;
142 random_offset &= (CONFIG_RANDOMIZE_BASE_MAX_OFFSET - 1);
143 if (random_offset < kernel_length)
144 random_offset += ALIGN(kernel_length, 0xffff);
145
146 return RELOCATED_KASLR(destination);
147 }
148
relocation_addr_valid(void * location_new)149 static inline int __init relocation_addr_valid(void *location_new)
150 {
151 if ((unsigned long)location_new & 0x00000ffff)
152 return 0; /* Inappropriately aligned new location */
153
154 if ((unsigned long)location_new < (unsigned long)_end)
155 return 0; /* New location overlaps original kernel */
156
157 return 1;
158 }
159 #endif
160
update_reloc_offset(unsigned long * addr,long random_offset)161 static inline void __init update_reloc_offset(unsigned long *addr, long random_offset)
162 {
163 unsigned long *new_addr = (unsigned long *)RELOCATED_KASLR(addr);
164
165 *new_addr = (unsigned long)reloc_offset;
166 }
167
relocate_kernel(void)168 unsigned long __init relocate_kernel(void)
169 {
170 unsigned long kernel_length;
171 unsigned long random_offset = 0;
172 void *location_new = _text; /* Default to original kernel start */
173 char *cmdline = early_ioremap(fw_arg1, COMMAND_LINE_SIZE); /* Boot command line is passed in fw_arg1 */
174
175 strscpy(boot_command_line, cmdline, COMMAND_LINE_SIZE);
176
177 #ifdef CONFIG_RANDOMIZE_BASE
178 location_new = determine_relocation_address();
179
180 /* Sanity check relocation address */
181 if (relocation_addr_valid(location_new))
182 random_offset = (unsigned long)location_new - (unsigned long)(_text);
183 #endif
184 reloc_offset = (unsigned long)_text - VMLINUX_LOAD_ADDRESS;
185
186 if (random_offset) {
187 kernel_length = (long)(_end) - (long)(_text);
188
189 /* Copy the kernel to it's new location */
190 memcpy(location_new, _text, kernel_length);
191
192 /* Sync the caches ready for execution of new kernel */
193 __asm__ __volatile__ (
194 "ibar 0 \t\n"
195 "dbar 0 \t\n"
196 ::: "memory");
197
198 reloc_offset += random_offset;
199
200 /* The current thread is now within the relocated kernel */
201 __current_thread_info = RELOCATED_KASLR(__current_thread_info);
202
203 update_reloc_offset(&reloc_offset, random_offset);
204 }
205
206 if (reloc_offset)
207 relocate_relative();
208
209 relocate_absolute(random_offset);
210
211 return random_offset;
212 }
213
214 /*
215 * Show relocation information on panic.
216 */
show_kernel_relocation(const char * level)217 static void show_kernel_relocation(const char *level)
218 {
219 if (reloc_offset > 0) {
220 printk(level);
221 pr_cont("Kernel relocated by 0x%lx\n", reloc_offset);
222 pr_cont(" .text @ 0x%px\n", _text);
223 pr_cont(" .data @ 0x%px\n", _sdata);
224 pr_cont(" .bss @ 0x%px\n", __bss_start);
225 }
226 }
227
kernel_location_notifier_fn(struct notifier_block * self,unsigned long v,void * p)228 static int kernel_location_notifier_fn(struct notifier_block *self,
229 unsigned long v, void *p)
230 {
231 show_kernel_relocation(KERN_EMERG);
232 return NOTIFY_DONE;
233 }
234
235 static struct notifier_block kernel_location_notifier = {
236 .notifier_call = kernel_location_notifier_fn
237 };
238
register_kernel_offset_dumper(void)239 static int __init register_kernel_offset_dumper(void)
240 {
241 atomic_notifier_chain_register(&panic_notifier_list,
242 &kernel_location_notifier);
243 return 0;
244 }
245
246 arch_initcall(register_kernel_offset_dumper);
247