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          * A not yet fixed binutils section handling bug prevents
 346          * alternatives-replacement from working reliably, so turn
 347          * it off:
 348          */
 349         printk("lockdep: not fixing up alternatives.\n");
 350         return;
 351 #endif
 352
 353         if (noreplace_smp || smp_alt_once)
 354                 return;
 355         BUG_ON(!smp && (num_online_cpus() > 1));
 356
 357         spin_lock_irqsave(&smp_alt, flags);
 358
 359         /*
 360          * Avoid unnecessary switches because it forces JIT based VMs to
 361          * throw away all cached translations, which can be quite costly.
 362          */
 363         if (smp == smp_mode) {
 364                 /* nothing */
 365         } else if (smp) {
 366                 printk(KERN_INFO "SMP alternatives: switching to SMP code\n");
 367                 clear_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
 368                 clear_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
 369                 list_for_each_entry(mod, &smp_alt_modules, next)
 370                         alternatives_smp_lock(mod->locks, mod->locks_end,
 371                                               mod->text, mod->text_end);
 372         } else {
 373                 printk(KERN_INFO "SMP alternatives: switching to UP code\n");
 374                 set_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
 375                 set_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
 376                 list_for_each_entry(mod, &smp_alt_modules, next)
 377                         alternatives_smp_unlock(mod->locks, mod->locks_end,
 378                                                 mod->text, mod->text_end);
 379         }
 380         smp_mode = smp;
 381         spin_unlock_irqrestore(&smp_alt, flags);
 382 }
 383
 384 #endif
 385
 386 #ifdef CONFIG_PARAVIRT
 387 void apply_paravirt(struct paravirt_patch_site *start,
 388                     struct paravirt_patch_site *end)
 389 {
 390         struct paravirt_patch_site *p;
 391         char insnbuf[MAX_PATCH_LEN];
 392
 393         if (noreplace_paravirt)
 394                 return;
 395
 396         for (p = start; p < end; p++) {
 397                 unsigned int used;
 398
 399                 BUG_ON(p->len > MAX_PATCH_LEN);
 400                 /* prep the buffer with the original instructions */
 401                 memcpy(insnbuf, p->instr, p->len);
 402                 used = pv_init_ops.patch(p->instrtype, p->clobbers, insnbuf,
 403                                          (unsigned long)p->instr, p->len);
 404
 405                 BUG_ON(used > p->len);
 406
 407                 /* Pad the rest with nops */
 408                 add_nops(insnbuf + used, p->len - used);
 409                 text_poke(p->instr, insnbuf, p->len);
 410         }
 411 }
 412 extern struct paravirt_patch_site __start_parainstructions[],
 413         __stop_parainstructions[];
 414 #endif  /* CONFIG_PARAVIRT */
 415
 416 void __init alternative_instructions(void)
 417 {
 418         unsigned long flags;
 419
 420         /* The patching is not fully atomic, so try to avoid local interruptions
 421            that might execute the to be patched code.
 422            Other CPUs are not running. */
 423         stop_nmi();
 424 #ifdef CONFIG_X86_MCE
 425         stop_mce();
 426 #endif
 427
 428         local_irq_save(flags);
 429         apply_alternatives(__alt_instructions, __alt_instructions_end);
 430
 431         /* switch to patch-once-at-boottime-only mode and free the
 432          * tables in case we know the number of CPUs will never ever
 433          * change */
 434 #ifdef CONFIG_HOTPLUG_CPU
 435         if (num_possible_cpus() < 2)
 436                 smp_alt_once = 1;
 437 #endif
 438
 439 #ifdef CONFIG_SMP
 440         if (smp_alt_once) {
 441                 if (1 == num_possible_cpus()) {
 442                         printk(KERN_INFO "SMP alternatives: switching to UP code\n");
 443                         set_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
 444                         set_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
 445
 446                         alternatives_smp_unlock(__smp_locks, __smp_locks_end,
 447                                                 _text, _etext);
 448                 }
 449         } else {
 450                 alternatives_smp_module_add(NULL, "core kernel",
 451                                             __smp_locks, __smp_locks_end,
 452                                             _text, _etext);
 453
 454                 /* Only switch to UP mode if we don't immediately boot others */
 455                 if (num_possible_cpus() == 1 || setup_max_cpus <= 1)
 456                         alternatives_smp_switch(0);
 457         }
 458 #endif
 459         apply_paravirt(__parainstructions, __parainstructions_end);
 460         local_irq_restore(flags);
 461
 462         if (smp_alt_once)
 463                 free_init_pages("SMP alternatives",
 464                                 (unsigned long)__smp_locks,
 465                                 (unsigned long)__smp_locks_end);
 466
 467         restart_nmi();
 468 #ifdef CONFIG_X86_MCE
 469         restart_mce();
 470 #endif
 471 }
 472
 473 /*
 474  * Warning:
 475  * When you use this code to patch more than one byte of an instruction
 476  * you need to make sure that other CPUs cannot execute this code in parallel.
 477  * Also no thread must be currently preempted in the middle of these instructions.
 478  * And on the local CPU you need to be protected again NMI or MCE handlers
 479  * seeing an inconsistent instruction while you patch.
 480  */
 481 void __kprobes text_poke(void *addr, unsigned char *opcode, int len)
 482 {
 483         memcpy(addr, opcode, len);
 484         sync_core();
 485         /* Could also do a CLFLUSH here to speed up CPU recovery; but
 486            that causes hangs on some VIA CPUs. */
 487 }