arch/x86/kernel/alternative.c

   1 #include <linux/module.h>
   2 #include <linux/sched.h>
   3 #include <linux/spinlock.h>
   4 #include <linux/list.h>
   5 #include <linux/kprobes.h>
   6 #include <linux/mm.h>
   7 #include <linux/vmalloc.h>
   8 #include <asm/alternative.h>
   9 #include <asm/sections.h>
  10 #include <asm/pgtable.h>
  11 #include <asm/mce.h>
  12 #include <asm/nmi.h>
  13 #include <asm/vsyscall.h>
  14
  15 #define MAX_PATCH_LEN (255-1)
  16
  17 #ifdef CONFIG_HOTPLUG_CPU
  18 static int smp_alt_once;
  19
  20 static int __init bootonly(char *str)
  21 {
  22         smp_alt_once = 1;
  23         return 1;
  24 }
  25 __setup("smp-alt-boot", bootonly);
  26 #else
  27 #define smp_alt_once 1
  28 #endif
  29
  30 static int debug_alternative;
  31
  32 static int __init debug_alt(char *str)
  33 {
  34         debug_alternative = 1;
  35         return 1;
  36 }
  37 __setup("debug-alternative", debug_alt);
  38
  39 static int noreplace_smp;
  40
  41 static int __init setup_noreplace_smp(char *str)
  42 {
  43         noreplace_smp = 1;
  44         return 1;
  45 }
  46 __setup("noreplace-smp", setup_noreplace_smp);
  47
  48 #ifdef CONFIG_PARAVIRT
  49 static int noreplace_paravirt = 0;
  50
  51 static int __init setup_noreplace_paravirt(char *str)
  52 {
  53         noreplace_paravirt = 1;
  54         return 1;
  55 }
  56 __setup("noreplace-paravirt", setup_noreplace_paravirt);
  57 #endif
  58
  59 #define DPRINTK(fmt, args...) if (debug_alternative) \
  60         printk(KERN_DEBUG fmt, args)
  61
  62 #ifdef GENERIC_NOP1
  63 /* Use inline assembly to define this because the nops are defined
  64    as inline assembly strings in the include files and we cannot
  65    get them easily into strings. */
  66 asm("\t.section .rodata, \"a\"\nintelnops: "
  67         GENERIC_NOP1 GENERIC_NOP2 GENERIC_NOP3 GENERIC_NOP4 GENERIC_NOP5 GENERIC_NOP6
  68         GENERIC_NOP7 GENERIC_NOP8);
  69 extern const unsigned char intelnops[];
  70 static const unsigned char *const intel_nops[ASM_NOP_MAX+1] = {
  71         NULL,
  72         intelnops,
  73         intelnops + 1,
  74         intelnops + 1 + 2,
  75         intelnops + 1 + 2 + 3,
  76         intelnops + 1 + 2 + 3 + 4,
  77         intelnops + 1 + 2 + 3 + 4 + 5,
  78         intelnops + 1 + 2 + 3 + 4 + 5 + 6,
  79         intelnops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
  80 };
  81 #endif
  82
  83 #ifdef K8_NOP1
  84 asm("\t.section .rodata, \"a\"\nk8nops: "
  85         K8_NOP1 K8_NOP2 K8_NOP3 K8_NOP4 K8_NOP5 K8_NOP6
  86         K8_NOP7 K8_NOP8);
  87 extern const unsigned char k8nops[];
  88 static const unsigned char *const k8_nops[ASM_NOP_MAX+1] = {
  89         NULL,
  90         k8nops,
  91         k8nops + 1,
  92         k8nops + 1 + 2,
  93         k8nops + 1 + 2 + 3,
  94         k8nops + 1 + 2 + 3 + 4,
  95         k8nops + 1 + 2 + 3 + 4 + 5,
  96         k8nops + 1 + 2 + 3 + 4 + 5 + 6,
  97         k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
  98 };
  99 #endif
 100
 101 #ifdef K7_NOP1
 102 asm("\t.section .rodata, \"a\"\nk7nops: "
 103         K7_NOP1 K7_NOP2 K7_NOP3 K7_NOP4 K7_NOP5 K7_NOP6
 104         K7_NOP7 K7_NOP8);
 105 extern const unsigned char k7nops[];
 106 static const unsigned char *const k7_nops[ASM_NOP_MAX+1] = {
 107         NULL,
 108         k7nops,
 109         k7nops + 1,
 110         k7nops + 1 + 2,
 111         k7nops + 1 + 2 + 3,
 112         k7nops + 1 + 2 + 3 + 4,
 113         k7nops + 1 + 2 + 3 + 4 + 5,
 114         k7nops + 1 + 2 + 3 + 4 + 5 + 6,
 115         k7nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
 116 };
 117 #endif
 118
 119 #ifdef P6_NOP1
 120 asm("\t.section .rodata, \"a\"\np6nops: "
 121         P6_NOP1 P6_NOP2 P6_NOP3 P6_NOP4 P6_NOP5 P6_NOP6
 122         P6_NOP7 P6_NOP8);
 123 extern const unsigned char p6nops[];
 124 static const unsigned char *const p6_nops[ASM_NOP_MAX+1] = {
 125         NULL,
 126         p6nops,
 127         p6nops + 1,
 128         p6nops + 1 + 2,
 129         p6nops + 1 + 2 + 3,
 130         p6nops + 1 + 2 + 3 + 4,
 131         p6nops + 1 + 2 + 3 + 4 + 5,
 132         p6nops + 1 + 2 + 3 + 4 + 5 + 6,
 133         p6nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
 134 };
 135 #endif
 136
 137 #ifdef CONFIG_X86_64
 138
 139 extern char __vsyscall_0;
 140 static inline const unsigned char*const * find_nop_table(void)
 141 {
 142         return boot_cpu_data.x86_vendor != X86_VENDOR_INTEL ||
 143                boot_cpu_data.x86 < 6 ? k8_nops : p6_nops;
 144 }
 145
 146 #else /* CONFIG_X86_64 */
 147
 148 static const struct nop {
 149         int cpuid;
 150         const unsigned char *const *noptable;
 151 } noptypes[] = {
 152         { X86_FEATURE_K8, k8_nops },
 153         { X86_FEATURE_K7, k7_nops },
 154         { X86_FEATURE_P4, p6_nops },
 155         { X86_FEATURE_P3, p6_nops },
 156         { -1, NULL }
 157 };
 158
 159 static const unsigned char*const * find_nop_table(void)
 160 {
 161         const unsigned char *const *noptable = intel_nops;
 162         int i;
 163
 164         for (i = 0; noptypes[i].cpuid >= 0; i++) {
 165                 if (boot_cpu_has(noptypes[i].cpuid)) {
 166                         noptable = noptypes[i].noptable;
 167                         break;
 168                 }
 169         }
 170         return noptable;
 171 }
 172
 173 #endif /* CONFIG_X86_64 */
 174
 175 /* Use this to add nops to a buffer, then text_poke the whole buffer. */
 176 static void add_nops(void *insns, unsigned int len)
 177 {
 178         const unsigned char *const *noptable = find_nop_table();
 179
 180         while (len > 0) {
 181                 unsigned int noplen = len;
 182                 if (noplen > ASM_NOP_MAX)
 183                         noplen = ASM_NOP_MAX;
 184                 memcpy(insns, noptable[noplen], noplen);
 185                 insns += noplen;
 186                 len -= noplen;
 187         }
 188 }
 189
 190 extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
 191 extern u8 *__smp_locks[], *__smp_locks_end[];
 192
 193 /* Replace instructions with better alternatives for this CPU type.
 194    This runs before SMP is initialized to avoid SMP problems with
 195    self modifying code. This implies that assymetric systems where
 196    APs have less capabilities than the boot processor are not handled.
 197    Tough. Make sure you disable such features by hand. */
 198
 199 void apply_alternatives(struct alt_instr *start, struct alt_instr *end)
 200 {
 201         struct alt_instr *a;
 202         char insnbuf[MAX_PATCH_LEN];
 203
 204         DPRINTK("%s: alt table %p -> %p\n", __FUNCTION__, start, end);
 205         for (a = start; a < end; a++) {
 206                 u8 *instr = a->instr;
 207                 BUG_ON(a->replacementlen > a->instrlen);
 208                 BUG_ON(a->instrlen > sizeof(insnbuf));
 209                 if (!boot_cpu_has(a->cpuid))
 210                         continue;
 211 #ifdef CONFIG_X86_64
 212                 /* vsyscall code is not mapped yet. resolve it manually. */
 213                 if (instr >= (u8 *)VSYSCALL_START && instr < (u8*)VSYSCALL_END) {
 214                         instr = __va(instr - (u8*)VSYSCALL_START + (u8*)__pa_symbol(&__vsyscall_0));
 215                         DPRINTK("%s: vsyscall fixup: %p => %p\n",
 216                                 __FUNCTION__, a->instr, instr);
 217                 }
 218 #endif
 219                 memcpy(insnbuf, a->replacement, a->replacementlen);
 220                 add_nops(insnbuf + a->replacementlen,
 221                          a->instrlen - a->replacementlen);
 222                 text_poke(instr, insnbuf, a->instrlen);
 223         }
 224 }
 225
 226 #ifdef CONFIG_SMP
 227
 228 static void alternatives_smp_lock(u8 **start, u8 **end, u8 *text, u8 *text_end)
 229 {
 230         u8 **ptr;
 231
 232         for (ptr = start; ptr < end; ptr++) {
 233                 if (*ptr < text)
 234                         continue;
 235                 if (*ptr > text_end)
 236                         continue;
 237                 text_poke(*ptr, ((unsigned char []){0xf0}), 1); /* add lock prefix */
 238         };
 239 }
 240
 241 static void alternatives_smp_unlock(u8 **start, u8 **end, u8 *text, u8 *text_end)
 242 {
 243         u8 **ptr;
 244         char insn[1];
 245
 246         if (noreplace_smp)
 247                 return;
 248
 249         add_nops(insn, 1);
 250         for (ptr = start; ptr < end; ptr++) {
 251                 if (*ptr < text)
 252                         continue;
 253                 if (*ptr > text_end)
 254                         continue;
 255                 text_poke(*ptr, insn, 1);
 256         };
 257 }
 258
 259 struct smp_alt_module {
 260         /* what is this ??? */
 261         struct module   *mod;
 262         char            *name;
 263
 264         /* ptrs to lock prefixes */
 265         u8              **locks;
 266         u8              **locks_end;
 267
 268         /* .text segment, needed to avoid patching init code ;) */
 269         u8              *text;
 270         u8              *text_end;
 271
 272         struct list_head next;
 273 };
 274 static LIST_HEAD(smp_alt_modules);
 275 static DEFINE_SPINLOCK(smp_alt);
 276 static int smp_mode = 1;        /* protected by smp_alt */
 277
 278 void alternatives_smp_module_add(struct module *mod, char *name,
 279                                  void *locks, void *locks_end,
 280                                  void *text,  void *text_end)
 281 {
 282         struct smp_alt_module *smp;
 283         unsigned long flags;
 284
 285         if (noreplace_smp)
 286                 return;
 287
 288         if (smp_alt_once) {
 289                 if (boot_cpu_has(X86_FEATURE_UP))
 290                         alternatives_smp_unlock(locks, locks_end,
 291                                                 text, text_end);
 292                 return;
 293         }
 294
 295         smp = kzalloc(sizeof(*smp), GFP_KERNEL);
 296         if (NULL == smp)
 297                 return; /* we'll run the (safe but slow) SMP code then ... */
 298
 299         smp->mod        = mod;
 300         smp->name       = name;
 301         smp->locks      = locks;
 302         smp->locks_end  = locks_end;
 303         smp->text       = text;
 304         smp->text_end   = text_end;
 305         DPRINTK("%s: locks %p -> %p, text %p -> %p, name %s\n",
 306                 __FUNCTION__, smp->locks, smp->locks_end,
 307                 smp->text, smp->text_end, smp->name);
 308
 309         spin_lock_irqsave(&smp_alt, flags);
 310         list_add_tail(&smp->next, &smp_alt_modules);
 311         if (boot_cpu_has(X86_FEATURE_UP))
 312                 alternatives_smp_unlock(smp->locks, smp->locks_end,
 313                                         smp->text, smp->text_end);
 314         spin_unlock_irqrestore(&smp_alt, flags);
 315 }
 316
 317 void alternatives_smp_module_del(struct module *mod)
 318 {
 319         struct smp_alt_module *item;
 320         unsigned long flags;
 321
 322         if (smp_alt_once || noreplace_smp)
 323                 return;
 324
 325         spin_lock_irqsave(&smp_alt, flags);
 326         list_for_each_entry(item, &smp_alt_modules, next) {
 327                 if (mod != item->mod)
 328                         continue;
 329                 list_del(&item->next);
 330                 spin_unlock_irqrestore(&smp_alt, flags);
 331                 DPRINTK("%s: %s\n", __FUNCTION__, item->name);
 332                 kfree(item);
 333                 return;
 334         }
 335         spin_unlock_irqrestore(&smp_alt, flags);
 336 }
 337
 338 void alternatives_smp_switch(int smp)
 339 {
 340         struct smp_alt_module *mod;
 341         unsigned long flags;
 342
 343 #ifdef CONFIG_LOCKDEP
 344         /*
 345          * Older binutils section handling bug prevented
 346          * alternatives-replacement from working reliably.
 347          *
 348          * If this still occurs then you should see a hang
 349          * or crash shortly after this line:
 350          */
 351         printk("lockdep: fixing up alternatives.\n");
 352 #endif
 353
 354         if (noreplace_smp || smp_alt_once)
 355                 return;
 356         BUG_ON(!smp && (num_online_cpus() > 1));
 357
 358         spin_lock_irqsave(&smp_alt, flags);
 359
 360         /*
 361          * Avoid unnecessary switches because it forces JIT based VMs to
 362          * throw away all cached translations, which can be quite costly.
 363          */
 364         if (smp == smp_mode) {
 365                 /* nothing */
 366         } else if (smp) {
 367                 printk(KERN_INFO "SMP alternatives: switching to SMP code\n");
 368                 clear_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
 369                 clear_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
 370                 list_for_each_entry(mod, &smp_alt_modules, next)
 371                         alternatives_smp_lock(mod->locks, mod->locks_end,
 372                                               mod->text, mod->text_end);
 373         } else {
 374                 printk(KERN_INFO "SMP alternatives: switching to UP code\n");
 375                 set_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
 376                 set_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
 377                 list_for_each_entry(mod, &smp_alt_modules, next)
 378                         alternatives_smp_unlock(mod->locks, mod->locks_end,
 379                                                 mod->text, mod->text_end);
 380         }
 381         smp_mode = smp;
 382         spin_unlock_irqrestore(&smp_alt, flags);
 383 }
 384
 385 #endif
 386
 387 #ifdef CONFIG_PARAVIRT
 388 void apply_paravirt(struct paravirt_patch_site *start,
 389                     struct paravirt_patch_site *end)
 390 {
 391         struct paravirt_patch_site *p;
 392         char insnbuf[MAX_PATCH_LEN];
 393
 394         if (noreplace_paravirt)
 395                 return;
 396
 397         for (p = start; p < end; p++) {
 398                 unsigned int used;
 399
 400                 BUG_ON(p->len > MAX_PATCH_LEN);
 401                 /* prep the buffer with the original instructions */
 402                 memcpy(insnbuf, p->instr, p->len);
 403                 used = pv_init_ops.patch(p->instrtype, p->clobbers, insnbuf,
 404                                          (unsigned long)p->instr, p->len);
 405
 406                 BUG_ON(used > p->len);
 407
 408                 /* Pad the rest with nops */
 409                 add_nops(insnbuf + used, p->len - used);
 410                 text_poke(p->instr, insnbuf, p->len);
 411         }
 412 }
 413 extern struct paravirt_patch_site __start_parainstructions[],
 414         __stop_parainstructions[];
 415 #endif  /* CONFIG_PARAVIRT */
 416
 417 void __init alternative_instructions(void)
 418 {
 419         unsigned long flags;
 420
 421         /* The patching is not fully atomic, so try to avoid local interruptions
 422            that might execute the to be patched code.
 423            Other CPUs are not running. */
 424         stop_nmi();
 425 #ifdef CONFIG_X86_MCE
 426         stop_mce();
 427 #endif
 428
 429         local_irq_save(flags);
 430         apply_alternatives(__alt_instructions, __alt_instructions_end);
 431
 432         /* switch to patch-once-at-boottime-only mode and free the
 433          * tables in case we know the number of CPUs will never ever
 434          * change */
 435 #ifdef CONFIG_HOTPLUG_CPU
 436         if (num_possible_cpus() < 2)
 437                 smp_alt_once = 1;
 438 #endif
 439
 440 #ifdef CONFIG_SMP
 441         if (smp_alt_once) {
 442                 if (1 == num_possible_cpus()) {
 443                         printk(KERN_INFO "SMP alternatives: switching to UP code\n");
 444                         set_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
 445                         set_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
 446
 447                         alternatives_smp_unlock(__smp_locks, __smp_locks_end,
 448                                                 _text, _etext);
 449                 }
 450         } else {
 451                 alternatives_smp_module_add(NULL, "core kernel",
 452                                             __smp_locks, __smp_locks_end,
 453                                             _text, _etext);
 454
 455                 /* Only switch to UP mode if we don't immediately boot others */
 456                 if (num_possible_cpus() == 1 || setup_max_cpus <= 1)
 457                         alternatives_smp_switch(0);
 458         }
 459 #endif
 460         apply_paravirt(__parainstructions, __parainstructions_end);
 461         local_irq_restore(flags);
 462
 463         if (smp_alt_once)
 464                 free_init_pages("SMP alternatives",
 465                                 (unsigned long)__smp_locks,
 466                                 (unsigned long)__smp_locks_end);
 467
 468         restart_nmi();
 469 #ifdef CONFIG_X86_MCE
 470         restart_mce();
 471 #endif
 472 }
 473
 474 /*
 475  * Warning:
 476  * When you use this code to patch more than one byte of an instruction
 477  * you need to make sure that other CPUs cannot execute this code in parallel.
 478  * Also no thread must be currently preempted in the middle of these instructions.
 479  * And on the local CPU you need to be protected again NMI or MCE handlers
 480  * seeing an inconsistent instruction while you patch.
 481  */
 482 void __kprobes text_poke(void *addr, unsigned char *opcode, int len)
 483 {
 484         memcpy(addr, opcode, len);
 485         sync_core();
 486         /* Could also do a CLFLUSH here to speed up CPU recovery; but
 487            that causes hangs on some VIA CPUs. */
 488 }