arch/mips/kernel/relocate.c

   1 /*
   2  * This file is subject to the terms and conditions of the GNU General Public
   3  * License.  See the file "COPYING" in the main directory of this archive
   4  * for more details.
   5  *
   6  * Support for Kernel relocation at boot time
   7  *
   8  * Copyright (C) 2015, Imagination Technologies Ltd.
   9  * Authors: Matt Redfearn (matt.redfearn@imgtec.com)
  10  */
  11 #include <asm/bootinfo.h>
  12 #include <asm/cacheflush.h>
  13 #include <asm/fw/fw.h>
  14 #include <asm/sections.h>
  15 #include <asm/setup.h>
  16 #include <asm/timex.h>
  17 #include <linux/elf.h>
  18 #include <linux/kernel.h>
  19 #include <linux/libfdt.h>
  20 #include <linux/of_fdt.h>
  21 #include <linux/sched.h>
  22 #include <linux/start_kernel.h>
  23 #include <linux/string.h>
  24 #include <linux/printk.h>
  25
  26 #define RELOCATED(x) ((void *)((long)x + offset))
  27
  28 extern u32 _relocation_start[]; /* End kernel image / start relocation table */
  29 extern u32 _relocation_end[];   /* End relocation table */
  30
  31 extern long __start___ex_table; /* Start exception table */
  32 extern long __stop___ex_table;  /* End exception table */
  33
  34 static inline u32 __init get_synci_step(void)
  35 {
  36         u32 res;
  37
  38         __asm__("rdhwr  %0, $1" : "=r" (res));
  39
  40         return res;
  41 }
  42
  43 static void __init sync_icache(void *kbase, unsigned long kernel_length)
  44 {
  45         void *kend = kbase + kernel_length;
  46         u32 step = get_synci_step();
  47
  48         do {
  49                 __asm__ __volatile__(
  50                         "synci  0(%0)"
  51                         : /* no output */
  52                         : "r" (kbase));
  53
  54                 kbase += step;
  55         } while (kbase < kend);
  56
  57         /* Completion barrier */
  58         __sync();
  59 }
  60
  61 static int __init apply_r_mips_64_rel(u32 *loc_orig, u32 *loc_new, long offset)
  62 {
  63         *(u64 *)loc_new += offset;
  64
  65         return 0;
  66 }
  67
  68 static int __init apply_r_mips_32_rel(u32 *loc_orig, u32 *loc_new, long offset)
  69 {
  70         *loc_new += offset;
  71
  72         return 0;
  73 }
  74
  75 static int __init apply_r_mips_26_rel(u32 *loc_orig, u32 *loc_new, long offset)
  76 {
  77         unsigned long target_addr = (*loc_orig) & 0x03ffffff;
  78
  79         if (offset % 4) {
  80                 pr_err("Dangerous R_MIPS_26 REL relocation\n");
  81                 return -ENOEXEC;
  82         }
  83
  84         /* Original target address */
  85         target_addr <<= 2;
  86         target_addr += (unsigned long)loc_orig & ~0x03ffffff;
  87
  88         /* Get the new target address */
  89         target_addr += offset;
  90
  91         if ((target_addr & 0xf0000000) != ((unsigned long)loc_new & 0xf0000000)) {
  92                 pr_err("R_MIPS_26 REL relocation overflow\n");
  93                 return -ENOEXEC;
  94         }
  95
  96         target_addr -= (unsigned long)loc_new & ~0x03ffffff;
  97         target_addr >>= 2;
  98
  99         *loc_new = (*loc_new & ~0x03ffffff) | (target_addr & 0x03ffffff);
 100
 101         return 0;
 102 }
 103
 104
 105 static int __init apply_r_mips_hi16_rel(u32 *loc_orig, u32 *loc_new, long offset)
 106 {
 107         unsigned long insn = *loc_orig;
 108         unsigned long target = (insn & 0xffff) << 16; /* high 16bits of target */
 109
 110         target += offset;
 111
 112         *loc_new = (insn & ~0xffff) | ((target >> 16) & 0xffff);
 113         return 0;
 114 }
 115
 116 static int (*reloc_handlers_rel[]) (u32 *, u32 *, long) __initdata = {
 117         [R_MIPS_64]             = apply_r_mips_64_rel,
 118         [R_MIPS_32]             = apply_r_mips_32_rel,
 119         [R_MIPS_26]             = apply_r_mips_26_rel,
 120         [R_MIPS_HI16]           = apply_r_mips_hi16_rel,
 121 };
 122
 123 int __init do_relocations(void *kbase_old, void *kbase_new, long offset)
 124 {
 125         u32 *r;
 126         u32 *loc_orig;
 127         u32 *loc_new;
 128         int type;
 129         int res;
 130
 131         for (r = _relocation_start; r < _relocation_end; r++) {
 132                 /* Sentinel for last relocation */
 133                 if (*r == 0)
 134                         break;
 135
 136                 type = (*r >> 24) & 0xff;
 137                 loc_orig = (void *)(kbase_old + ((*r & 0x00ffffff) << 2));
 138                 loc_new = RELOCATED(loc_orig);
 139
 140                 if (reloc_handlers_rel[type] == NULL) {
 141                         /* Unsupported relocation */
 142                         pr_err("Unhandled relocation type %d at 0x%pK\n",
 143                                type, loc_orig);
 144                         return -ENOEXEC;
 145                 }
 146
 147                 res = reloc_handlers_rel[type](loc_orig, loc_new, offset);
 148                 if (res)
 149                         return res;
 150         }
 151
 152         return 0;
 153 }
 154
 155 /*
 156  * The exception table is filled in by the relocs tool after vmlinux is linked.
 157  * It must be relocated separately since there will not be any relocation
 158  * information for it filled in by the linker.
 159  */
 160 static int __init relocate_exception_table(long offset)
 161 {
 162         unsigned long *etable_start, *etable_end, *e;
 163
 164         etable_start = RELOCATED(&__start___ex_table);
 165         etable_end = RELOCATED(&__stop___ex_table);
 166
 167         for (e = etable_start; e < etable_end; e++)
 168                 *e += offset;
 169
 170         return 0;
 171 }
 172
 173 #ifdef CONFIG_RANDOMIZE_BASE
 174
 175 static inline __init unsigned long rotate_xor(unsigned long hash,
 176                                               const void *area, size_t size)
 177 {
 178         size_t i;
 179         unsigned long *ptr = (unsigned long *)area;
 180
 181         for (i = 0; i < size / sizeof(hash); i++) {
 182                 /* Rotate by odd number of bits and XOR. */
 183                 hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7);
 184                 hash ^= ptr[i];
 185         }
 186
 187         return hash;
 188 }
 189
 190 static inline __init unsigned long get_random_boot(void)
 191 {
 192         unsigned long entropy = random_get_entropy();
 193         unsigned long hash = 0;
 194
 195         /* Attempt to create a simple but unpredictable starting entropy. */
 196         hash = rotate_xor(hash, linux_banner, strlen(linux_banner));
 197
 198         /* Add in any runtime entropy we can get */
 199         hash = rotate_xor(hash, &entropy, sizeof(entropy));
 200
 201 #if defined(CONFIG_USE_OF)
 202         /* Get any additional entropy passed in device tree */
 203         {
 204                 int node, len;
 205                 u64 *prop;
 206
 207                 node = fdt_path_offset(initial_boot_params, "/chosen");
 208                 if (node >= 0) {
 209                         prop = fdt_getprop_w(initial_boot_params, node,
 210                                              "kaslr-seed", &len);
 211                         if (prop && (len == sizeof(u64)))
 212                                 hash = rotate_xor(hash, prop, sizeof(*prop));
 213                 }
 214         }
 215 #endif /* CONFIG_USE_OF */
 216
 217         return hash;
 218 }
 219
 220 static inline __init bool kaslr_disabled(void)
 221 {
 222         char *str;
 223
 224 #if defined(CONFIG_CMDLINE_BOOL)
 225         const char *builtin_cmdline = CONFIG_CMDLINE;
 226
 227         str = strstr(builtin_cmdline, "nokaslr");
 228         if (str == builtin_cmdline ||
 229             (str > builtin_cmdline && *(str - 1) == ' '))
 230                 return true;
 231 #endif
 232         str = strstr(arcs_cmdline, "nokaslr");
 233         if (str == arcs_cmdline || (str > arcs_cmdline && *(str - 1) == ' '))
 234                 return true;
 235
 236         return false;
 237 }
 238
 239 static inline void __init *determine_relocation_address(void)
 240 {
 241         /* Choose a new address for the kernel */
 242         unsigned long kernel_length;
 243         void *dest = &_text;
 244         unsigned long offset;
 245
 246         if (kaslr_disabled())
 247                 return dest;
 248
 249         kernel_length = (long)_end - (long)(&_text);
 250
 251         offset = get_random_boot() << 16;
 252         offset &= (CONFIG_RANDOMIZE_BASE_MAX_OFFSET - 1);
 253         if (offset < kernel_length)
 254                 offset += ALIGN(kernel_length, 0xffff);
 255
 256         return RELOCATED(dest);
 257 }
 258
 259 #else
 260
 261 static inline void __init *determine_relocation_address(void)
 262 {
 263         /*
 264          * Choose a new address for the kernel
 265          * For now we'll hard code the destination
 266          */
 267         return (void *)0xffffffff81000000;
 268 }
 269
 270 #endif
 271
 272 static inline int __init relocation_addr_valid(void *loc_new)
 273 {
 274         if ((unsigned long)loc_new & 0x0000ffff) {
 275                 /* Inappropriately aligned new location */
 276                 return 0;
 277         }
 278         if ((unsigned long)loc_new < (unsigned long)&_end) {
 279                 /* New location overlaps original kernel */
 280                 return 0;
 281         }
 282         return 1;
 283 }
 284
 285 void *__init relocate_kernel(void)
 286 {
 287         void *loc_new;
 288         unsigned long kernel_length;
 289         unsigned long bss_length;
 290         long offset = 0;
 291         int res = 1;
 292         /* Default to original kernel entry point */
 293         void *kernel_entry = start_kernel;
 294
 295         /* Get the command line */
 296         fw_init_cmdline();
 297 #if defined(CONFIG_USE_OF)
 298         /* Deal with the device tree */
 299         early_init_dt_scan(plat_get_fdt());
 300         if (boot_command_line[0]) {
 301                 /* Boot command line was passed in device tree */
 302                 strlcpy(arcs_cmdline, boot_command_line, COMMAND_LINE_SIZE);
 303         }
 304 #endif /* CONFIG_USE_OF */
 305
 306         kernel_length = (long)(&_relocation_start) - (long)(&_text);
 307         bss_length = (long)&__bss_stop - (long)&__bss_start;
 308
 309         loc_new = determine_relocation_address();
 310
 311         /* Sanity check relocation address */
 312         if (relocation_addr_valid(loc_new))
 313                 offset = (unsigned long)loc_new - (unsigned long)(&_text);
 314
 315         /* Reset the command line now so we don't end up with a duplicate */
 316         arcs_cmdline[0] = '\0';
 317
 318         if (offset) {
 319                 /* Copy the kernel to it's new location */
 320                 memcpy(loc_new, &_text, kernel_length);
 321
 322                 /* Perform relocations on the new kernel */
 323                 res = do_relocations(&_text, loc_new, offset);
 324                 if (res < 0)
 325                         goto out;
 326
 327                 /* Sync the caches ready for execution of new kernel */
 328                 sync_icache(loc_new, kernel_length);
 329
 330                 res = relocate_exception_table(offset);
 331                 if (res < 0)
 332                         goto out;
 333
 334                 /*
 335                  * The original .bss has already been cleared, and
 336                  * some variables such as command line parameters
 337                  * stored to it so make a copy in the new location.
 338                  */
 339                 memcpy(RELOCATED(&__bss_start), &__bss_start, bss_length);
 340
 341                 /* The current thread is now within the relocated image */
 342                 __current_thread_info = RELOCATED(&init_thread_union);
 343
 344                 /* Return the new kernel's entry point */
 345                 kernel_entry = RELOCATED(start_kernel);
 346         }
 347 out:
 348         return kernel_entry;
 349 }
 350
 351 /*
 352  * Show relocation information on panic.
 353  */
 354 void show_kernel_relocation(const char *level)
 355 {
 356         unsigned long offset;
 357
 358         offset = __pa_symbol(_text) - __pa_symbol(VMLINUX_LOAD_ADDRESS);
 359
 360         if (IS_ENABLED(CONFIG_RELOCATABLE) && offset > 0) {
 361                 printk(level);
 362                 pr_cont("Kernel relocated by 0x%pK\n", (void *)offset);
 363                 pr_cont(" .text @ 0x%pK\n", _text);
 364                 pr_cont(" .data @ 0x%pK\n", _sdata);
 365                 pr_cont(" .bss  @ 0x%pK\n", __bss_start);
 366         }
 367 }
 368
 369 static int kernel_location_notifier_fn(struct notifier_block *self,
 370                                        unsigned long v, void *p)
 371 {
 372         show_kernel_relocation(KERN_EMERG);
 373         return NOTIFY_DONE;
 374 }
 375
 376 static struct notifier_block kernel_location_notifier = {
 377         .notifier_call = kernel_location_notifier_fn
 378 };
 379
 380 static int __init register_kernel_offset_dumper(void)
 381 {
 382         atomic_notifier_chain_register(&panic_notifier_list,
 383                                        &kernel_location_notifier);
 384         return 0;
 385 }
 386 __initcall(register_kernel_offset_dumper);