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     "\t.previous");
  70 extern const unsigned char intelnops[];
  71 static const unsigned char *const intel_nops[ASM_NOP_MAX+1] = {
  72         NULL,
  73         intelnops,
  74         intelnops + 1,
  75         intelnops + 1 + 2,
  76         intelnops + 1 + 2 + 3,
  77         intelnops + 1 + 2 + 3 + 4,
  78         intelnops + 1 + 2 + 3 + 4 + 5,
  79         intelnops + 1 + 2 + 3 + 4 + 5 + 6,
  80         intelnops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
  81 };
  82 #endif
  83
  84 #ifdef K8_NOP1
  85 asm("\t.section .rodata, \"a\"\nk8nops: "
  86         K8_NOP1 K8_NOP2 K8_NOP3 K8_NOP4 K8_NOP5 K8_NOP6
  87         K8_NOP7 K8_NOP8
  88     "\t.previous");
  89 extern const unsigned char k8nops[];
  90 static const unsigned char *const k8_nops[ASM_NOP_MAX+1] = {
  91         NULL,
  92         k8nops,
  93         k8nops + 1,
  94         k8nops + 1 + 2,
  95         k8nops + 1 + 2 + 3,
  96         k8nops + 1 + 2 + 3 + 4,
  97         k8nops + 1 + 2 + 3 + 4 + 5,
  98         k8nops + 1 + 2 + 3 + 4 + 5 + 6,
  99         k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
 100 };
 101 #endif
 102
 103 #ifdef K7_NOP1
 104 asm("\t.section .rodata, \"a\"\nk7nops: "
 105         K7_NOP1 K7_NOP2 K7_NOP3 K7_NOP4 K7_NOP5 K7_NOP6
 106         K7_NOP7 K7_NOP8
 107     "\t.previous");
 108 extern const unsigned char k7nops[];
 109 static const unsigned char *const k7_nops[ASM_NOP_MAX+1] = {
 110         NULL,
 111         k7nops,
 112         k7nops + 1,
 113         k7nops + 1 + 2,
 114         k7nops + 1 + 2 + 3,
 115         k7nops + 1 + 2 + 3 + 4,
 116         k7nops + 1 + 2 + 3 + 4 + 5,
 117         k7nops + 1 + 2 + 3 + 4 + 5 + 6,
 118         k7nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
 119 };
 120 #endif
 121
 122 #ifdef P6_NOP1
 123 asm("\t.section .rodata, \"a\"\np6nops: "
 124         P6_NOP1 P6_NOP2 P6_NOP3 P6_NOP4 P6_NOP5 P6_NOP6
 125         P6_NOP7 P6_NOP8
 126     "\t.previous");
 127 extern const unsigned char p6nops[];
 128 static const unsigned char *const p6_nops[ASM_NOP_MAX+1] = {
 129         NULL,
 130         p6nops,
 131         p6nops + 1,
 132         p6nops + 1 + 2,
 133         p6nops + 1 + 2 + 3,
 134         p6nops + 1 + 2 + 3 + 4,
 135         p6nops + 1 + 2 + 3 + 4 + 5,
 136         p6nops + 1 + 2 + 3 + 4 + 5 + 6,
 137         p6nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
 138 };
 139 #endif
 140
 141 #ifdef CONFIG_X86_64
 142
 143 extern char __vsyscall_0;
 144 static inline const unsigned char*const * find_nop_table(void)
 145 {
 146         return boot_cpu_data.x86_vendor != X86_VENDOR_INTEL ||
 147                boot_cpu_data.x86 < 6 ? k8_nops : p6_nops;
 148 }
 149
 150 #else /* CONFIG_X86_64 */
 151
 152 static const struct nop {
 153         int cpuid;
 154         const unsigned char *const *noptable;
 155 } noptypes[] = {
 156         { X86_FEATURE_K8, k8_nops },
 157         { X86_FEATURE_K7, k7_nops },
 158         { X86_FEATURE_P4, p6_nops },
 159         { X86_FEATURE_P3, p6_nops },
 160         { -1, NULL }
 161 };
 162
 163 static const unsigned char*const * find_nop_table(void)
 164 {
 165         const unsigned char *const *noptable = intel_nops;
 166         int i;
 167
 168         for (i = 0; noptypes[i].cpuid >= 0; i++) {
 169                 if (boot_cpu_has(noptypes[i].cpuid)) {
 170                         noptable = noptypes[i].noptable;
 171                         break;
 172                 }
 173         }
 174         return noptable;
 175 }
 176
 177 #endif /* CONFIG_X86_64 */
 178
 179 /* Use this to add nops to a buffer, then text_poke the whole buffer. */
 180 static void add_nops(void *insns, unsigned int len)
 181 {
 182         const unsigned char *const *noptable = find_nop_table();
 183
 184         while (len > 0) {
 185                 unsigned int noplen = len;
 186                 if (noplen > ASM_NOP_MAX)
 187                         noplen = ASM_NOP_MAX;
 188                 memcpy(insns, noptable[noplen], noplen);
 189                 insns += noplen;
 190                 len -= noplen;
 191         }
 192 }
 193
 194 extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
 195 extern u8 *__smp_locks[], *__smp_locks_end[];
 196
 197 /* Replace instructions with better alternatives for this CPU type.
 198    This runs before SMP is initialized to avoid SMP problems with
 199    self modifying code. This implies that assymetric systems where
 200    APs have less capabilities than the boot processor are not handled.
 201    Tough. Make sure you disable such features by hand. */
 202
 203 void apply_alternatives(struct alt_instr *start, struct alt_instr *end)
 204 {
 205         struct alt_instr *a;
 206         char insnbuf[MAX_PATCH_LEN];
 207
 208         DPRINTK("%s: alt table %p -> %p\n", __FUNCTION__, start, end);
 209         for (a = start; a < end; a++) {
 210                 u8 *instr = a->instr;
 211                 BUG_ON(a->replacementlen > a->instrlen);
 212                 BUG_ON(a->instrlen > sizeof(insnbuf));
 213                 if (!boot_cpu_has(a->cpuid))
 214                         continue;
 215 #ifdef CONFIG_X86_64
 216                 /* vsyscall code is not mapped yet. resolve it manually. */
 217                 if (instr >= (u8 *)VSYSCALL_START && instr < (u8*)VSYSCALL_END) {
 218                         instr = __va(instr - (u8*)VSYSCALL_START + (u8*)__pa_symbol(&__vsyscall_0));
 219                         DPRINTK("%s: vsyscall fixup: %p => %p\n",
 220                                 __FUNCTION__, a->instr, instr);
 221                 }
 222 #endif
 223                 memcpy(insnbuf, a->replacement, a->replacementlen);
 224                 add_nops(insnbuf + a->replacementlen,
 225                          a->instrlen - a->replacementlen);
 226                 text_poke(instr, insnbuf, a->instrlen);
 227         }
 228 }
 229
 230 #ifdef CONFIG_SMP
 231
 232 static void alternatives_smp_lock(u8 **start, u8 **end, u8 *text, u8 *text_end)
 233 {
 234         u8 **ptr;
 235
 236         for (ptr = start; ptr < end; ptr++) {
 237                 if (*ptr < text)
 238                         continue;
 239                 if (*ptr > text_end)
 240                         continue;
 241                 text_poke(*ptr, ((unsigned char []){0xf0}), 1); /* add lock prefix */
 242         };
 243 }
 244
 245 static void alternatives_smp_unlock(u8 **start, u8 **end, u8 *text, u8 *text_end)
 246 {
 247         u8 **ptr;
 248         char insn[1];
 249
 250         if (noreplace_smp)
 251                 return;
 252
 253         add_nops(insn, 1);
 254         for (ptr = start; ptr < end; ptr++) {
 255                 if (*ptr < text)
 256                         continue;
 257                 if (*ptr > text_end)
 258                         continue;
 259                 text_poke(*ptr, insn, 1);
 260         };
 261 }
 262
 263 struct smp_alt_module {
 264         /* what is this ??? */
 265         struct module   *mod;
 266         char            *name;
 267
 268         /* ptrs to lock prefixes */
 269         u8              **locks;
 270         u8              **locks_end;
 271
 272         /* .text segment, needed to avoid patching init code ;) */
 273         u8              *text;
 274         u8              *text_end;
 275
 276         struct list_head next;
 277 };
 278 static LIST_HEAD(smp_alt_modules);
 279 static DEFINE_SPINLOCK(smp_alt);
 280 static int smp_mode = 1;        /* protected by smp_alt */
 281
 282 void alternatives_smp_module_add(struct module *mod, char *name,
 283                                  void *locks, void *locks_end,
 284                                  void *text,  void *text_end)
 285 {
 286         struct smp_alt_module *smp;
 287         unsigned long flags;
 288
 289         if (noreplace_smp)
 290                 return;
 291
 292         if (smp_alt_once) {
 293                 if (boot_cpu_has(X86_FEATURE_UP))
 294                         alternatives_smp_unlock(locks, locks_end,
 295                                                 text, text_end);
 296                 return;
 297         }
 298
 299         smp = kzalloc(sizeof(*smp), GFP_KERNEL);
 300         if (NULL == smp)
 301                 return; /* we'll run the (safe but slow) SMP code then ... */
 302
 303         smp->mod        = mod;
 304         smp->name       = name;
 305         smp->locks      = locks;
 306         smp->locks_end  = locks_end;
 307         smp->text       = text;
 308         smp->text_end   = text_end;
 309         DPRINTK("%s: locks %p -> %p, text %p -> %p, name %s\n",
 310                 __FUNCTION__, smp->locks, smp->locks_end,
 311                 smp->text, smp->text_end, smp->name);
 312
 313         spin_lock_irqsave(&smp_alt, flags);
 314         list_add_tail(&smp->next, &smp_alt_modules);
 315         if (boot_cpu_has(X86_FEATURE_UP))
 316                 alternatives_smp_unlock(smp->locks, smp->locks_end,
 317                                         smp->text, smp->text_end);
 318         spin_unlock_irqrestore(&smp_alt, flags);
 319 }
 320
 321 void alternatives_smp_module_del(struct module *mod)
 322 {
 323         struct smp_alt_module *item;
 324         unsigned long flags;
 325
 326         if (smp_alt_once || noreplace_smp)
 327                 return;
 328
 329         spin_lock_irqsave(&smp_alt, flags);
 330         list_for_each_entry(item, &smp_alt_modules, next) {
 331                 if (mod != item->mod)
 332                         continue;
 333                 list_del(&item->next);
 334                 spin_unlock_irqrestore(&smp_alt, flags);
 335                 DPRINTK("%s: %s\n", __FUNCTION__, item->name);
 336                 kfree(item);
 337                 return;
 338         }
 339         spin_unlock_irqrestore(&smp_alt, flags);
 340 }
 341
 342 void alternatives_smp_switch(int smp)
 343 {
 344         struct smp_alt_module *mod;
 345         unsigned long flags;
 346
 347 #ifdef CONFIG_LOCKDEP
 348         /*
 349          * Older binutils section handling bug prevented
 350          * alternatives-replacement from working reliably.
 351          *
 352          * If this still occurs then you should see a hang
 353          * or crash shortly after this line:
 354          */
 355         printk("lockdep: fixing up alternatives.\n");
 356 #endif
 357
 358         if (noreplace_smp || smp_alt_once)
 359                 return;
 360         BUG_ON(!smp && (num_online_cpus() > 1));
 361
 362         spin_lock_irqsave(&smp_alt, flags);
 363
 364         /*
 365          * Avoid unnecessary switches because it forces JIT based VMs to
 366          * throw away all cached translations, which can be quite costly.
 367          */
 368         if (smp == smp_mode) {
 369                 /* nothing */
 370         } else if (smp) {
 371                 printk(KERN_INFO "SMP alternatives: switching to SMP code\n");
 372                 clear_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
 373                 clear_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
 374                 list_for_each_entry(mod, &smp_alt_modules, next)
 375                         alternatives_smp_lock(mod->locks, mod->locks_end,
 376                                               mod->text, mod->text_end);
 377         } else {
 378                 printk(KERN_INFO "SMP alternatives: switching to UP code\n");
 379                 set_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
 380                 set_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
 381                 list_for_each_entry(mod, &smp_alt_modules, next)
 382                         alternatives_smp_unlock(mod->locks, mod->locks_end,
 383                                                 mod->text, mod->text_end);
 384         }
 385         smp_mode = smp;
 386         spin_unlock_irqrestore(&smp_alt, flags);
 387 }
 388
 389 #endif
 390
 391 #ifdef CONFIG_PARAVIRT
 392 void apply_paravirt(struct paravirt_patch_site *start,
 393                     struct paravirt_patch_site *end)
 394 {
 395         struct paravirt_patch_site *p;
 396         char insnbuf[MAX_PATCH_LEN];
 397
 398         if (noreplace_paravirt)
 399                 return;
 400
 401         for (p = start; p < end; p++) {
 402                 unsigned int used;
 403
 404                 BUG_ON(p->len > MAX_PATCH_LEN);
 405                 /* prep the buffer with the original instructions */
 406                 memcpy(insnbuf, p->instr, p->len);
 407                 used = pv_init_ops.patch(p->instrtype, p->clobbers, insnbuf,
 408                                          (unsigned long)p->instr, p->len);
 409
 410                 BUG_ON(used > p->len);
 411
 412                 /* Pad the rest with nops */
 413                 add_nops(insnbuf + used, p->len - used);
 414                 text_poke(p->instr, insnbuf, p->len);
 415         }
 416 }
 417 extern struct paravirt_patch_site __start_parainstructions[],
 418         __stop_parainstructions[];
 419 #endif  /* CONFIG_PARAVIRT */
 420
 421 void __init alternative_instructions(void)
 422 {
 423         unsigned long flags;
 424
 425         /* The patching is not fully atomic, so try to avoid local interruptions
 426            that might execute the to be patched code.
 427            Other CPUs are not running. */
 428         stop_nmi();
 429 #ifdef CONFIG_X86_MCE
 430         stop_mce();
 431 #endif
 432
 433         local_irq_save(flags);
 434         apply_alternatives(__alt_instructions, __alt_instructions_end);
 435
 436         /* switch to patch-once-at-boottime-only mode and free the
 437          * tables in case we know the number of CPUs will never ever
 438          * change */
 439 #ifdef CONFIG_HOTPLUG_CPU
 440         if (num_possible_cpus() < 2)
 441                 smp_alt_once = 1;
 442 #endif
 443
 444 #ifdef CONFIG_SMP
 445         if (smp_alt_once) {
 446                 if (1 == num_possible_cpus()) {
 447                         printk(KERN_INFO "SMP alternatives: switching to UP code\n");
 448                         set_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
 449                         set_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
 450
 451                         alternatives_smp_unlock(__smp_locks, __smp_locks_end,
 452                                                 _text, _etext);
 453                 }
 454         } else {
 455                 alternatives_smp_module_add(NULL, "core kernel",
 456                                             __smp_locks, __smp_locks_end,
 457                                             _text, _etext);
 458
 459                 /* Only switch to UP mode if we don't immediately boot others */
 460                 if (num_possible_cpus() == 1 || setup_max_cpus <= 1)
 461                         alternatives_smp_switch(0);
 462         }
 463 #endif
 464         apply_paravirt(__parainstructions, __parainstructions_end);
 465         local_irq_restore(flags);
 466
 467         if (smp_alt_once)
 468                 free_init_pages("SMP alternatives",
 469                                 (unsigned long)__smp_locks,
 470                                 (unsigned long)__smp_locks_end);
 471
 472         restart_nmi();
 473 #ifdef CONFIG_X86_MCE
 474         restart_mce();
 475 #endif
 476 }
 477
 478 /*
 479  * Warning:
 480  * When you use this code to patch more than one byte of an instruction
 481  * you need to make sure that other CPUs cannot execute this code in parallel.
 482  * Also no thread must be currently preempted in the middle of these instructions.
 483  * And on the local CPU you need to be protected again NMI or MCE handlers
 484  * seeing an inconsistent instruction while you patch.
 485  */
 486 void __kprobes text_poke(void *addr, unsigned char *opcode, int len)
 487 {
 488         memcpy(addr, opcode, len);
 489         sync_core();
 490         /* Could also do a CLFLUSH here to speed up CPU recovery; but
 491            that causes hangs on some VIA CPUs. */
 492 }