linux/arch/x86/mm/fault.c
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   1/*
   2 *  Copyright (C) 1995  Linus Torvalds
   3 *  Copyright (C) 2001, 2002 Andi Kleen, SuSE Labs.
   4 *  Copyright (C) 2008-2009, Red Hat Inc., Ingo Molnar
   5 */
   6#include <linux/magic.h>                /* STACK_END_MAGIC              */
   7#include <linux/sched.h>                /* test_thread_flag(), ...      */
   8#include <linux/kdebug.h>               /* oops_begin/end, ...          */
   9#include <linux/module.h>               /* search_exception_table       */
  10#include <linux/bootmem.h>              /* max_low_pfn                  */
  11#include <linux/kprobes.h>              /* __kprobes, ...               */
  12#include <linux/mmiotrace.h>            /* kmmio_handler, ...           */
  13#include <linux/perf_event.h>           /* perf_sw_event                */
  14#include <linux/hugetlb.h>              /* hstate_index_to_shift        */
  15#include <linux/prefetch.h>             /* prefetchw                    */
  16#include <linux/context_tracking.h>     /* exception_enter(), ...       */
  17
  18#include <asm/traps.h>                  /* dotraplinkage, ...           */
  19#include <asm/pgalloc.h>                /* pgd_*(), ...                 */
  20#include <asm/kmemcheck.h>              /* kmemcheck_*(), ...           */
  21#include <asm/fixmap.h>                 /* VSYSCALL_START               */
  22
  23#define CREATE_TRACE_POINTS
  24#include <asm/trace/exceptions.h>
  25
  26/*
  27 * Page fault error code bits:
  28 *
  29 *   bit 0 ==    0: no page found       1: protection fault
  30 *   bit 1 ==    0: read access         1: write access
  31 *   bit 2 ==    0: kernel-mode access  1: user-mode access
  32 *   bit 3 ==                           1: use of reserved bit detected
  33 *   bit 4 ==                           1: fault was an instruction fetch
  34 */
  35enum x86_pf_error_code {
  36
  37        PF_PROT         =               1 << 0,
  38        PF_WRITE        =               1 << 1,
  39        PF_USER         =               1 << 2,
  40        PF_RSVD         =               1 << 3,
  41        PF_INSTR        =               1 << 4,
  42};
  43
  44/*
  45 * Returns 0 if mmiotrace is disabled, or if the fault is not
  46 * handled by mmiotrace:
  47 */
  48static inline int __kprobes
  49kmmio_fault(struct pt_regs *regs, unsigned long addr)
  50{
  51        if (unlikely(is_kmmio_active()))
  52                if (kmmio_handler(regs, addr) == 1)
  53                        return -1;
  54        return 0;
  55}
  56
  57static inline int __kprobes kprobes_fault(struct pt_regs *regs)
  58{
  59        int ret = 0;
  60
  61        /* kprobe_running() needs smp_processor_id() */
  62        if (kprobes_built_in() && !user_mode_vm(regs)) {
  63                preempt_disable();
  64                if (kprobe_running() && kprobe_fault_handler(regs, 14))
  65                        ret = 1;
  66                preempt_enable();
  67        }
  68
  69        return ret;
  70}
  71
  72/*
  73 * Prefetch quirks:
  74 *
  75 * 32-bit mode:
  76 *
  77 *   Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
  78 *   Check that here and ignore it.
  79 *
  80 * 64-bit mode:
  81 *
  82 *   Sometimes the CPU reports invalid exceptions on prefetch.
  83 *   Check that here and ignore it.
  84 *
  85 * Opcode checker based on code by Richard Brunner.
  86 */
  87static inline int
  88check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr,
  89                      unsigned char opcode, int *prefetch)
  90{
  91        unsigned char instr_hi = opcode & 0xf0;
  92        unsigned char instr_lo = opcode & 0x0f;
  93
  94        switch (instr_hi) {
  95        case 0x20:
  96        case 0x30:
  97                /*
  98                 * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes.
  99                 * In X86_64 long mode, the CPU will signal invalid
 100                 * opcode if some of these prefixes are present so
 101                 * X86_64 will never get here anyway
 102                 */
 103                return ((instr_lo & 7) == 0x6);
 104#ifdef CONFIG_X86_64
 105        case 0x40:
 106                /*
 107                 * In AMD64 long mode 0x40..0x4F are valid REX prefixes
 108                 * Need to figure out under what instruction mode the
 109                 * instruction was issued. Could check the LDT for lm,
 110                 * but for now it's good enough to assume that long
 111                 * mode only uses well known segments or kernel.
 112                 */
 113                return (!user_mode(regs) || user_64bit_mode(regs));
 114#endif
 115        case 0x60:
 116                /* 0x64 thru 0x67 are valid prefixes in all modes. */
 117                return (instr_lo & 0xC) == 0x4;
 118        case 0xF0:
 119                /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */
 120                return !instr_lo || (instr_lo>>1) == 1;
 121        case 0x00:
 122                /* Prefetch instruction is 0x0F0D or 0x0F18 */
 123                if (probe_kernel_address(instr, opcode))
 124                        return 0;
 125
 126                *prefetch = (instr_lo == 0xF) &&
 127                        (opcode == 0x0D || opcode == 0x18);
 128                return 0;
 129        default:
 130                return 0;
 131        }
 132}
 133
 134static int
 135is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)
 136{
 137        unsigned char *max_instr;
 138        unsigned char *instr;
 139        int prefetch = 0;
 140
 141        /*
 142         * If it was a exec (instruction fetch) fault on NX page, then
 143         * do not ignore the fault:
 144         */
 145        if (error_code & PF_INSTR)
 146                return 0;
 147
 148        instr = (void *)convert_ip_to_linear(current, regs);
 149        max_instr = instr + 15;
 150
 151        if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE)
 152                return 0;
 153
 154        while (instr < max_instr) {
 155                unsigned char opcode;
 156
 157                if (probe_kernel_address(instr, opcode))
 158                        break;
 159
 160                instr++;
 161
 162                if (!check_prefetch_opcode(regs, instr, opcode, &prefetch))
 163                        break;
 164        }
 165        return prefetch;
 166}
 167
 168static void
 169force_sig_info_fault(int si_signo, int si_code, unsigned long address,
 170                     struct task_struct *tsk, int fault)
 171{
 172        unsigned lsb = 0;
 173        siginfo_t info;
 174
 175        info.si_signo   = si_signo;
 176        info.si_errno   = 0;
 177        info.si_code    = si_code;
 178        info.si_addr    = (void __user *)address;
 179        if (fault & VM_FAULT_HWPOISON_LARGE)
 180                lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault)); 
 181        if (fault & VM_FAULT_HWPOISON)
 182                lsb = PAGE_SHIFT;
 183        info.si_addr_lsb = lsb;
 184
 185        force_sig_info(si_signo, &info, tsk);
 186}
 187
 188DEFINE_SPINLOCK(pgd_lock);
 189LIST_HEAD(pgd_list);
 190
 191#ifdef CONFIG_X86_32
 192static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
 193{
 194        unsigned index = pgd_index(address);
 195        pgd_t *pgd_k;
 196        pud_t *pud, *pud_k;
 197        pmd_t *pmd, *pmd_k;
 198
 199        pgd += index;
 200        pgd_k = init_mm.pgd + index;
 201
 202        if (!pgd_present(*pgd_k))
 203                return NULL;
 204
 205        /*
 206         * set_pgd(pgd, *pgd_k); here would be useless on PAE
 207         * and redundant with the set_pmd() on non-PAE. As would
 208         * set_pud.
 209         */
 210        pud = pud_offset(pgd, address);
 211        pud_k = pud_offset(pgd_k, address);
 212        if (!pud_present(*pud_k))
 213                return NULL;
 214
 215        pmd = pmd_offset(pud, address);
 216        pmd_k = pmd_offset(pud_k, address);
 217        if (!pmd_present(*pmd_k))
 218                return NULL;
 219
 220        if (!pmd_present(*pmd))
 221                set_pmd(pmd, *pmd_k);
 222        else
 223                BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));
 224
 225        return pmd_k;
 226}
 227
 228void vmalloc_sync_all(void)
 229{
 230        unsigned long address;
 231
 232        if (SHARED_KERNEL_PMD)
 233                return;
 234
 235        for (address = VMALLOC_START & PMD_MASK;
 236             address >= TASK_SIZE && address < FIXADDR_TOP;
 237             address += PMD_SIZE) {
 238                struct page *page;
 239
 240                spin_lock(&pgd_lock);
 241                list_for_each_entry(page, &pgd_list, lru) {
 242                        spinlock_t *pgt_lock;
 243                        pmd_t *ret;
 244
 245                        /* the pgt_lock only for Xen */
 246                        pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
 247
 248                        spin_lock(pgt_lock);
 249                        ret = vmalloc_sync_one(page_address(page), address);
 250                        spin_unlock(pgt_lock);
 251
 252                        if (!ret)
 253                                break;
 254                }
 255                spin_unlock(&pgd_lock);
 256        }
 257}
 258
 259/*
 260 * 32-bit:
 261 *
 262 *   Handle a fault on the vmalloc or module mapping area
 263 */
 264static noinline __kprobes int vmalloc_fault(unsigned long address)
 265{
 266        unsigned long pgd_paddr;
 267        pmd_t *pmd_k;
 268        pte_t *pte_k;
 269
 270        /* Make sure we are in vmalloc area: */
 271        if (!(address >= VMALLOC_START && address < VMALLOC_END))
 272                return -1;
 273
 274        WARN_ON_ONCE(in_nmi());
 275
 276        /*
 277         * Synchronize this task's top level page-table
 278         * with the 'reference' page table.
 279         *
 280         * Do _not_ use "current" here. We might be inside
 281         * an interrupt in the middle of a task switch..
 282         */
 283        pgd_paddr = read_cr3();
 284        pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
 285        if (!pmd_k)
 286                return -1;
 287
 288        pte_k = pte_offset_kernel(pmd_k, address);
 289        if (!pte_present(*pte_k))
 290                return -1;
 291
 292        return 0;
 293}
 294
 295/*
 296 * Did it hit the DOS screen memory VA from vm86 mode?
 297 */
 298static inline void
 299check_v8086_mode(struct pt_regs *regs, unsigned long address,
 300                 struct task_struct *tsk)
 301{
 302        unsigned long bit;
 303
 304        if (!v8086_mode(regs))
 305                return;
 306
 307        bit = (address - 0xA0000) >> PAGE_SHIFT;
 308        if (bit < 32)
 309                tsk->thread.screen_bitmap |= 1 << bit;
 310}
 311
 312static bool low_pfn(unsigned long pfn)
 313{
 314        return pfn < max_low_pfn;
 315}
 316
 317static void dump_pagetable(unsigned long address)
 318{
 319        pgd_t *base = __va(read_cr3());
 320        pgd_t *pgd = &base[pgd_index(address)];
 321        pmd_t *pmd;
 322        pte_t *pte;
 323
 324#ifdef CONFIG_X86_PAE
 325        printk("*pdpt = %016Lx ", pgd_val(*pgd));
 326        if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd))
 327                goto out;
 328#endif
 329        pmd = pmd_offset(pud_offset(pgd, address), address);
 330        printk(KERN_CONT "*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd));
 331
 332        /*
 333         * We must not directly access the pte in the highpte
 334         * case if the page table is located in highmem.
 335         * And let's rather not kmap-atomic the pte, just in case
 336         * it's allocated already:
 337         */
 338        if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_large(*pmd))
 339                goto out;
 340
 341        pte = pte_offset_kernel(pmd, address);
 342        printk("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte));
 343out:
 344        printk("\n");
 345}
 346
 347#else /* CONFIG_X86_64: */
 348
 349void vmalloc_sync_all(void)
 350{
 351        sync_global_pgds(VMALLOC_START & PGDIR_MASK, VMALLOC_END);
 352}
 353
 354/*
 355 * 64-bit:
 356 *
 357 *   Handle a fault on the vmalloc area
 358 *
 359 * This assumes no large pages in there.
 360 */
 361static noinline __kprobes int vmalloc_fault(unsigned long address)
 362{
 363        pgd_t *pgd, *pgd_ref;
 364        pud_t *pud, *pud_ref;
 365        pmd_t *pmd, *pmd_ref;
 366        pte_t *pte, *pte_ref;
 367
 368        /* Make sure we are in vmalloc area: */
 369        if (!(address >= VMALLOC_START && address < VMALLOC_END))
 370                return -1;
 371
 372        WARN_ON_ONCE(in_nmi());
 373
 374        /*
 375         * Copy kernel mappings over when needed. This can also
 376         * happen within a race in page table update. In the later
 377         * case just flush:
 378         */
 379        pgd = pgd_offset(current->active_mm, address);
 380        pgd_ref = pgd_offset_k(address);
 381        if (pgd_none(*pgd_ref))
 382                return -1;
 383
 384        if (pgd_none(*pgd)) {
 385                set_pgd(pgd, *pgd_ref);
 386                arch_flush_lazy_mmu_mode();
 387        } else {
 388                BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref));
 389        }
 390
 391        /*
 392         * Below here mismatches are bugs because these lower tables
 393         * are shared:
 394         */
 395
 396        pud = pud_offset(pgd, address);
 397        pud_ref = pud_offset(pgd_ref, address);
 398        if (pud_none(*pud_ref))
 399                return -1;
 400
 401        if (pud_none(*pud) || pud_page_vaddr(*pud) != pud_page_vaddr(*pud_ref))
 402                BUG();
 403
 404        pmd = pmd_offset(pud, address);
 405        pmd_ref = pmd_offset(pud_ref, address);
 406        if (pmd_none(*pmd_ref))
 407                return -1;
 408
 409        if (pmd_none(*pmd) || pmd_page(*pmd) != pmd_page(*pmd_ref))
 410                BUG();
 411
 412        pte_ref = pte_offset_kernel(pmd_ref, address);
 413        if (!pte_present(*pte_ref))
 414                return -1;
 415
 416        pte = pte_offset_kernel(pmd, address);
 417
 418        /*
 419         * Don't use pte_page here, because the mappings can point
 420         * outside mem_map, and the NUMA hash lookup cannot handle
 421         * that:
 422         */
 423        if (!pte_present(*pte) || pte_pfn(*pte) != pte_pfn(*pte_ref))
 424                BUG();
 425
 426        return 0;
 427}
 428
 429#ifdef CONFIG_CPU_SUP_AMD
 430static const char errata93_warning[] =
 431KERN_ERR 
 432"******* Your BIOS seems to not contain a fix for K8 errata #93\n"
 433"******* Working around it, but it may cause SEGVs or burn power.\n"
 434"******* Please consider a BIOS update.\n"
 435"******* Disabling USB legacy in the BIOS may also help.\n";
 436#endif
 437
 438/*
 439 * No vm86 mode in 64-bit mode:
 440 */
 441static inline void
 442check_v8086_mode(struct pt_regs *regs, unsigned long address,
 443                 struct task_struct *tsk)
 444{
 445}
 446
 447static int bad_address(void *p)
 448{
 449        unsigned long dummy;
 450
 451        return probe_kernel_address((unsigned long *)p, dummy);
 452}
 453
 454static void dump_pagetable(unsigned long address)
 455{
 456        pgd_t *base = __va(read_cr3() & PHYSICAL_PAGE_MASK);
 457        pgd_t *pgd = base + pgd_index(address);
 458        pud_t *pud;
 459        pmd_t *pmd;
 460        pte_t *pte;
 461
 462        if (bad_address(pgd))
 463                goto bad;
 464
 465        printk("PGD %lx ", pgd_val(*pgd));
 466
 467        if (!pgd_present(*pgd))
 468                goto out;
 469
 470        pud = pud_offset(pgd, address);
 471        if (bad_address(pud))
 472                goto bad;
 473
 474        printk("PUD %lx ", pud_val(*pud));
 475        if (!pud_present(*pud) || pud_large(*pud))
 476                goto out;
 477
 478        pmd = pmd_offset(pud, address);
 479        if (bad_address(pmd))
 480                goto bad;
 481
 482        printk("PMD %lx ", pmd_val(*pmd));
 483        if (!pmd_present(*pmd) || pmd_large(*pmd))
 484                goto out;
 485
 486        pte = pte_offset_kernel(pmd, address);
 487        if (bad_address(pte))
 488                goto bad;
 489
 490        printk("PTE %lx", pte_val(*pte));
 491out:
 492        printk("\n");
 493        return;
 494bad:
 495        printk("BAD\n");
 496}
 497
 498#endif /* CONFIG_X86_64 */
 499
 500/*
 501 * Workaround for K8 erratum #93 & buggy BIOS.
 502 *
 503 * BIOS SMM functions are required to use a specific workaround
 504 * to avoid corruption of the 64bit RIP register on C stepping K8.
 505 *
 506 * A lot of BIOS that didn't get tested properly miss this.
 507 *
 508 * The OS sees this as a page fault with the upper 32bits of RIP cleared.
 509 * Try to work around it here.
 510 *
 511 * Note we only handle faults in kernel here.
 512 * Does nothing on 32-bit.
 513 */
 514static int is_errata93(struct pt_regs *regs, unsigned long address)
 515{
 516#if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD)
 517        if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD
 518            || boot_cpu_data.x86 != 0xf)
 519                return 0;
 520
 521        if (address != regs->ip)
 522                return 0;
 523
 524        if ((address >> 32) != 0)
 525                return 0;
 526
 527        address |= 0xffffffffUL << 32;
 528        if ((address >= (u64)_stext && address <= (u64)_etext) ||
 529            (address >= MODULES_VADDR && address <= MODULES_END)) {
 530                printk_once(errata93_warning);
 531                regs->ip = address;
 532                return 1;
 533        }
 534#endif
 535        return 0;
 536}
 537
 538/*
 539 * Work around K8 erratum #100 K8 in compat mode occasionally jumps
 540 * to illegal addresses >4GB.
 541 *
 542 * We catch this in the page fault handler because these addresses
 543 * are not reachable. Just detect this case and return.  Any code
 544 * segment in LDT is compatibility mode.
 545 */
 546static int is_errata100(struct pt_regs *regs, unsigned long address)
 547{
 548#ifdef CONFIG_X86_64
 549        if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32))
 550                return 1;
 551#endif
 552        return 0;
 553}
 554
 555static int is_f00f_bug(struct pt_regs *regs, unsigned long address)
 556{
 557#ifdef CONFIG_X86_F00F_BUG
 558        unsigned long nr;
 559
 560        /*
 561         * Pentium F0 0F C7 C8 bug workaround:
 562         */
 563        if (boot_cpu_has_bug(X86_BUG_F00F)) {
 564                nr = (address - idt_descr.address) >> 3;
 565
 566                if (nr == 6) {
 567                        do_invalid_op(regs, 0);
 568                        return 1;
 569                }
 570        }
 571#endif
 572        return 0;
 573}
 574
 575static const char nx_warning[] = KERN_CRIT
 576"kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n";
 577
 578static void
 579show_fault_oops(struct pt_regs *regs, unsigned long error_code,
 580                unsigned long address)
 581{
 582        if (!oops_may_print())
 583                return;
 584
 585        if (error_code & PF_INSTR) {
 586                unsigned int level;
 587
 588                pte_t *pte = lookup_address(address, &level);
 589
 590                if (pte && pte_present(*pte) && !pte_exec(*pte))
 591                        printk(nx_warning, from_kuid(&init_user_ns, current_uid()));
 592        }
 593
 594        printk(KERN_ALERT "BUG: unable to handle kernel ");
 595        if (address < PAGE_SIZE)
 596                printk(KERN_CONT "NULL pointer dereference");
 597        else
 598                printk(KERN_CONT "paging request");
 599
 600        printk(KERN_CONT " at %p\n", (void *) address);
 601        printk(KERN_ALERT "IP:");
 602        printk_address(regs->ip);
 603
 604        dump_pagetable(address);
 605}
 606
 607static noinline void
 608pgtable_bad(struct pt_regs *regs, unsigned long error_code,
 609            unsigned long address)
 610{
 611        struct task_struct *tsk;
 612        unsigned long flags;
 613        int sig;
 614
 615        flags = oops_begin();
 616        tsk = current;
 617        sig = SIGKILL;
 618
 619        printk(KERN_ALERT "%s: Corrupted page table at address %lx\n",
 620               tsk->comm, address);
 621        dump_pagetable(address);
 622
 623        tsk->thread.cr2         = address;
 624        tsk->thread.trap_nr     = X86_TRAP_PF;
 625        tsk->thread.error_code  = error_code;
 626
 627        if (__die("Bad pagetable", regs, error_code))
 628                sig = 0;
 629
 630        oops_end(flags, regs, sig);
 631}
 632
 633static noinline void
 634no_context(struct pt_regs *regs, unsigned long error_code,
 635           unsigned long address, int signal, int si_code)
 636{
 637        struct task_struct *tsk = current;
 638        unsigned long *stackend;
 639        unsigned long flags;
 640        int sig;
 641
 642        /* Are we prepared to handle this kernel fault? */
 643        if (fixup_exception(regs)) {
 644                /*
 645                 * Any interrupt that takes a fault gets the fixup. This makes
 646                 * the below recursive fault logic only apply to a faults from
 647                 * task context.
 648                 */
 649                if (in_interrupt())
 650                        return;
 651
 652                /*
 653                 * Per the above we're !in_interrupt(), aka. task context.
 654                 *
 655                 * In this case we need to make sure we're not recursively
 656                 * faulting through the emulate_vsyscall() logic.
 657                 */
 658                if (current_thread_info()->sig_on_uaccess_error && signal) {
 659                        tsk->thread.trap_nr = X86_TRAP_PF;
 660                        tsk->thread.error_code = error_code | PF_USER;
 661                        tsk->thread.cr2 = address;
 662
 663                        /* XXX: hwpoison faults will set the wrong code. */
 664                        force_sig_info_fault(signal, si_code, address, tsk, 0);
 665                }
 666
 667                /*
 668                 * Barring that, we can do the fixup and be happy.
 669                 */
 670                return;
 671        }
 672
 673        /*
 674         * 32-bit:
 675         *
 676         *   Valid to do another page fault here, because if this fault
 677         *   had been triggered by is_prefetch fixup_exception would have
 678         *   handled it.
 679         *
 680         * 64-bit:
 681         *
 682         *   Hall of shame of CPU/BIOS bugs.
 683         */
 684        if (is_prefetch(regs, error_code, address))
 685                return;
 686
 687        if (is_errata93(regs, address))
 688                return;
 689
 690        /*
 691         * Oops. The kernel tried to access some bad page. We'll have to
 692         * terminate things with extreme prejudice:
 693         */
 694        flags = oops_begin();
 695
 696        show_fault_oops(regs, error_code, address);
 697
 698        stackend = end_of_stack(tsk);
 699        if (tsk != &init_task && *stackend != STACK_END_MAGIC)
 700                printk(KERN_EMERG "Thread overran stack, or stack corrupted\n");
 701
 702        tsk->thread.cr2         = address;
 703        tsk->thread.trap_nr     = X86_TRAP_PF;
 704        tsk->thread.error_code  = error_code;
 705
 706        sig = SIGKILL;
 707        if (__die("Oops", regs, error_code))
 708                sig = 0;
 709
 710        /* Executive summary in case the body of the oops scrolled away */
 711        printk(KERN_DEFAULT "CR2: %016lx\n", address);
 712
 713        oops_end(flags, regs, sig);
 714}
 715
 716/*
 717 * Print out info about fatal segfaults, if the show_unhandled_signals
 718 * sysctl is set:
 719 */
 720static inline void
 721show_signal_msg(struct pt_regs *regs, unsigned long error_code,
 722                unsigned long address, struct task_struct *tsk)
 723{
 724        if (!unhandled_signal(tsk, SIGSEGV))
 725                return;
 726
 727        if (!printk_ratelimit())
 728                return;
 729
 730        printk("%s%s[%d]: segfault at %lx ip %p sp %p error %lx",
 731                task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
 732                tsk->comm, task_pid_nr(tsk), address,
 733                (void *)regs->ip, (void *)regs->sp, error_code);
 734
 735        print_vma_addr(KERN_CONT " in ", regs->ip);
 736
 737        printk(KERN_CONT "\n");
 738}
 739
 740static void
 741__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
 742                       unsigned long address, int si_code)
 743{
 744        struct task_struct *tsk = current;
 745
 746        /* User mode accesses just cause a SIGSEGV */
 747        if (error_code & PF_USER) {
 748                /*
 749                 * It's possible to have interrupts off here:
 750                 */
 751                local_irq_enable();
 752
 753                /*
 754                 * Valid to do another page fault here because this one came
 755                 * from user space:
 756                 */
 757                if (is_prefetch(regs, error_code, address))
 758                        return;
 759
 760                if (is_errata100(regs, address))
 761                        return;
 762
 763#ifdef CONFIG_X86_64
 764                /*
 765                 * Instruction fetch faults in the vsyscall page might need
 766                 * emulation.
 767                 */
 768                if (unlikely((error_code & PF_INSTR) &&
 769                             ((address & ~0xfff) == VSYSCALL_START))) {
 770                        if (emulate_vsyscall(regs, address))
 771                                return;
 772                }
 773#endif
 774                /* Kernel addresses are always protection faults: */
 775                if (address >= TASK_SIZE)
 776                        error_code |= PF_PROT;
 777
 778                if (likely(show_unhandled_signals))
 779                        show_signal_msg(regs, error_code, address, tsk);
 780
 781                tsk->thread.cr2         = address;
 782                tsk->thread.error_code  = error_code;
 783                tsk->thread.trap_nr     = X86_TRAP_PF;
 784
 785                force_sig_info_fault(SIGSEGV, si_code, address, tsk, 0);
 786
 787                return;
 788        }
 789
 790        if (is_f00f_bug(regs, address))
 791                return;
 792
 793        no_context(regs, error_code, address, SIGSEGV, si_code);
 794}
 795
 796static noinline void
 797bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
 798                     unsigned long address)
 799{
 800        __bad_area_nosemaphore(regs, error_code, address, SEGV_MAPERR);
 801}
 802
 803static void
 804__bad_area(struct pt_regs *regs, unsigned long error_code,
 805           unsigned long address, int si_code)
 806{
 807        struct mm_struct *mm = current->mm;
 808
 809        /*
 810         * Something tried to access memory that isn't in our memory map..
 811         * Fix it, but check if it's kernel or user first..
 812         */
 813        up_read(&mm->mmap_sem);
 814
 815        __bad_area_nosemaphore(regs, error_code, address, si_code);
 816}
 817
 818static noinline void
 819bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address)
 820{
 821        __bad_area(regs, error_code, address, SEGV_MAPERR);
 822}
 823
 824static noinline void
 825bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
 826                      unsigned long address)
 827{
 828        __bad_area(regs, error_code, address, SEGV_ACCERR);
 829}
 830
 831static void
 832do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
 833          unsigned int fault)
 834{
 835        struct task_struct *tsk = current;
 836        struct mm_struct *mm = tsk->mm;
 837        int code = BUS_ADRERR;
 838
 839        up_read(&mm->mmap_sem);
 840
 841        /* Kernel mode? Handle exceptions or die: */
 842        if (!(error_code & PF_USER)) {
 843                no_context(regs, error_code, address, SIGBUS, BUS_ADRERR);
 844                return;
 845        }
 846
 847        /* User-space => ok to do another page fault: */
 848        if (is_prefetch(regs, error_code, address))
 849                return;
 850
 851        tsk->thread.cr2         = address;
 852        tsk->thread.error_code  = error_code;
 853        tsk->thread.trap_nr     = X86_TRAP_PF;
 854
 855#ifdef CONFIG_MEMORY_FAILURE
 856        if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
 857                printk(KERN_ERR
 858        "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
 859                        tsk->comm, tsk->pid, address);
 860                code = BUS_MCEERR_AR;
 861        }
 862#endif
 863        force_sig_info_fault(SIGBUS, code, address, tsk, fault);
 864}
 865
 866static noinline void
 867mm_fault_error(struct pt_regs *regs, unsigned long error_code,
 868               unsigned long address, unsigned int fault)
 869{
 870        if (fatal_signal_pending(current) && !(error_code & PF_USER)) {
 871                up_read(&current->mm->mmap_sem);
 872                no_context(regs, error_code, address, 0, 0);
 873                return;
 874        }
 875
 876        if (fault & VM_FAULT_OOM) {
 877                /* Kernel mode? Handle exceptions or die: */
 878                if (!(error_code & PF_USER)) {
 879                        up_read(&current->mm->mmap_sem);
 880                        no_context(regs, error_code, address,
 881                                   SIGSEGV, SEGV_MAPERR);
 882                        return;
 883                }
 884
 885                up_read(&current->mm->mmap_sem);
 886
 887                /*
 888                 * We ran out of memory, call the OOM killer, and return the
 889                 * userspace (which will retry the fault, or kill us if we got
 890                 * oom-killed):
 891                 */
 892                pagefault_out_of_memory();
 893        } else {
 894                if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
 895                             VM_FAULT_HWPOISON_LARGE))
 896                        do_sigbus(regs, error_code, address, fault);
 897                else
 898                        BUG();
 899        }
 900}
 901
 902static int spurious_fault_check(unsigned long error_code, pte_t *pte)
 903{
 904        if ((error_code & PF_WRITE) && !pte_write(*pte))
 905                return 0;
 906
 907        if ((error_code & PF_INSTR) && !pte_exec(*pte))
 908                return 0;
 909
 910        return 1;
 911}
 912
 913/*
 914 * Handle a spurious fault caused by a stale TLB entry.
 915 *
 916 * This allows us to lazily refresh the TLB when increasing the
 917 * permissions of a kernel page (RO -> RW or NX -> X).  Doing it
 918 * eagerly is very expensive since that implies doing a full
 919 * cross-processor TLB flush, even if no stale TLB entries exist
 920 * on other processors.
 921 *
 922 * There are no security implications to leaving a stale TLB when
 923 * increasing the permissions on a page.
 924 */
 925static noinline __kprobes int
 926spurious_fault(unsigned long error_code, unsigned long address)
 927{
 928        pgd_t *pgd;
 929        pud_t *pud;
 930        pmd_t *pmd;
 931        pte_t *pte;
 932        int ret;
 933
 934        /* Reserved-bit violation or user access to kernel space? */
 935        if (error_code & (PF_USER | PF_RSVD))
 936                return 0;
 937
 938        pgd = init_mm.pgd + pgd_index(address);
 939        if (!pgd_present(*pgd))
 940                return 0;
 941
 942        pud = pud_offset(pgd, address);
 943        if (!pud_present(*pud))
 944                return 0;
 945
 946        if (pud_large(*pud))
 947                return spurious_fault_check(error_code, (pte_t *) pud);
 948
 949        pmd = pmd_offset(pud, address);
 950        if (!pmd_present(*pmd))
 951                return 0;
 952
 953        if (pmd_large(*pmd))
 954                return spurious_fault_check(error_code, (pte_t *) pmd);
 955
 956        pte = pte_offset_kernel(pmd, address);
 957        if (!pte_present(*pte))
 958                return 0;
 959
 960        ret = spurious_fault_check(error_code, pte);
 961        if (!ret)
 962                return 0;
 963
 964        /*
 965         * Make sure we have permissions in PMD.
 966         * If not, then there's a bug in the page tables:
 967         */
 968        ret = spurious_fault_check(error_code, (pte_t *) pmd);
 969        WARN_ONCE(!ret, "PMD has incorrect permission bits\n");
 970
 971        return ret;
 972}
 973
 974int show_unhandled_signals = 1;
 975
 976static inline int
 977access_error(unsigned long error_code, struct vm_area_struct *vma)
 978{
 979        if (error_code & PF_WRITE) {
 980                /* write, present and write, not present: */
 981                if (unlikely(!(vma->vm_flags & VM_WRITE)))
 982                        return 1;
 983                return 0;
 984        }
 985
 986        /* read, present: */
 987        if (unlikely(error_code & PF_PROT))
 988                return 1;
 989
 990        /* read, not present: */
 991        if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))))
 992                return 1;
 993
 994        return 0;
 995}
 996
 997static int fault_in_kernel_space(unsigned long address)
 998{
 999        return address >= TASK_SIZE_MAX;
1000}
1001
1002static inline bool smap_violation(int error_code, struct pt_regs *regs)
1003{
1004        if (!IS_ENABLED(CONFIG_X86_SMAP))
1005                return false;
1006
1007        if (!static_cpu_has(X86_FEATURE_SMAP))
1008                return false;
1009
1010        if (error_code & PF_USER)
1011                return false;
1012
1013        if (!user_mode_vm(regs) && (regs->flags & X86_EFLAGS_AC))
1014                return false;
1015
1016        return true;
1017}
1018
1019/*
1020 * This routine handles page faults.  It determines the address,
1021 * and the problem, and then passes it off to one of the appropriate
1022 * routines.
1023 *
1024 * This function must have noinline because both callers
1025 * {,trace_}do_page_fault() have notrace on. Having this an actual function
1026 * guarantees there's a function trace entry.
1027 */
1028static void __kprobes noinline
1029__do_page_fault(struct pt_regs *regs, unsigned long error_code,
1030                unsigned long address)
1031{
1032        struct vm_area_struct *vma;
1033        struct task_struct *tsk;
1034        struct mm_struct *mm;
1035        int fault;
1036        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
1037
1038        tsk = current;
1039        mm = tsk->mm;
1040
1041        /*
1042         * Detect and handle instructions that would cause a page fault for
1043         * both a tracked kernel page and a userspace page.
1044         */
1045        if (kmemcheck_active(regs))
1046                kmemcheck_hide(regs);
1047        prefetchw(&mm->mmap_sem);
1048
1049        if (unlikely(kmmio_fault(regs, address)))
1050                return;
1051
1052        /*
1053         * We fault-in kernel-space virtual memory on-demand. The
1054         * 'reference' page table is init_mm.pgd.
1055         *
1056         * NOTE! We MUST NOT take any locks for this case. We may
1057         * be in an interrupt or a critical region, and should
1058         * only copy the information from the master page table,
1059         * nothing more.
1060         *
1061         * This verifies that the fault happens in kernel space
1062         * (error_code & 4) == 0, and that the fault was not a
1063         * protection error (error_code & 9) == 0.
1064         */
1065        if (unlikely(fault_in_kernel_space(address))) {
1066                if (!(error_code & (PF_RSVD | PF_USER | PF_PROT))) {
1067                        if (vmalloc_fault(address) >= 0)
1068                                return;
1069
1070                        if (kmemcheck_fault(regs, address, error_code))
1071                                return;
1072                }
1073
1074                /* Can handle a stale RO->RW TLB: */
1075                if (spurious_fault(error_code, address))
1076                        return;
1077
1078                /* kprobes don't want to hook the spurious faults: */
1079                if (kprobes_fault(regs))
1080                        return;
1081                /*
1082                 * Don't take the mm semaphore here. If we fixup a prefetch
1083                 * fault we could otherwise deadlock:
1084                 */
1085                bad_area_nosemaphore(regs, error_code, address);
1086
1087                return;
1088        }
1089
1090        /* kprobes don't want to hook the spurious faults: */
1091        if (unlikely(kprobes_fault(regs)))
1092                return;
1093
1094        if (unlikely(error_code & PF_RSVD))
1095                pgtable_bad(regs, error_code, address);
1096
1097        if (unlikely(smap_violation(error_code, regs))) {
1098                bad_area_nosemaphore(regs, error_code, address);
1099                return;
1100        }
1101
1102        /*
1103         * If we're in an interrupt, have no user context or are running
1104         * in an atomic region then we must not take the fault:
1105         */
1106        if (unlikely(in_atomic() || !mm)) {
1107                bad_area_nosemaphore(regs, error_code, address);
1108                return;
1109        }
1110
1111        /*
1112         * It's safe to allow irq's after cr2 has been saved and the
1113         * vmalloc fault has been handled.
1114         *
1115         * User-mode registers count as a user access even for any
1116         * potential system fault or CPU buglet:
1117         */
1118        if (user_mode_vm(regs)) {
1119                local_irq_enable();
1120                error_code |= PF_USER;
1121                flags |= FAULT_FLAG_USER;
1122        } else {
1123                if (regs->flags & X86_EFLAGS_IF)
1124                        local_irq_enable();
1125        }
1126
1127        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
1128
1129        if (error_code & PF_WRITE)
1130                flags |= FAULT_FLAG_WRITE;
1131
1132        /*
1133         * When running in the kernel we expect faults to occur only to
1134         * addresses in user space.  All other faults represent errors in
1135         * the kernel and should generate an OOPS.  Unfortunately, in the
1136         * case of an erroneous fault occurring in a code path which already
1137         * holds mmap_sem we will deadlock attempting to validate the fault
1138         * against the address space.  Luckily the kernel only validly
1139         * references user space from well defined areas of code, which are
1140         * listed in the exceptions table.
1141         *
1142         * As the vast majority of faults will be valid we will only perform
1143         * the source reference check when there is a possibility of a
1144         * deadlock. Attempt to lock the address space, if we cannot we then
1145         * validate the source. If this is invalid we can skip the address
1146         * space check, thus avoiding the deadlock:
1147         */
1148        if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
1149                if ((error_code & PF_USER) == 0 &&
1150                    !search_exception_tables(regs->ip)) {
1151                        bad_area_nosemaphore(regs, error_code, address);
1152                        return;
1153                }
1154retry:
1155                down_read(&mm->mmap_sem);
1156        } else {
1157                /*
1158                 * The above down_read_trylock() might have succeeded in
1159                 * which case we'll have missed the might_sleep() from
1160                 * down_read():
1161                 */
1162                might_sleep();
1163        }
1164
1165        vma = find_vma(mm, address);
1166        if (unlikely(!vma)) {
1167                bad_area(regs, error_code, address);
1168                return;
1169        }
1170        if (likely(vma->vm_start <= address))
1171                goto good_area;
1172        if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
1173                bad_area(regs, error_code, address);
1174                return;
1175        }
1176        if (error_code & PF_USER) {
1177                /*
1178                 * Accessing the stack below %sp is always a bug.
1179                 * The large cushion allows instructions like enter
1180                 * and pusha to work. ("enter $65535, $31" pushes
1181                 * 32 pointers and then decrements %sp by 65535.)
1182                 */
1183                if (unlikely(address + 65536 + 32 * sizeof(unsigned long) < regs->sp)) {
1184                        bad_area(regs, error_code, address);
1185                        return;
1186                }
1187        }
1188        if (unlikely(expand_stack(vma, address))) {
1189                bad_area(regs, error_code, address);
1190                return;
1191        }
1192
1193        /*
1194         * Ok, we have a good vm_area for this memory access, so
1195         * we can handle it..
1196         */
1197good_area:
1198        if (unlikely(access_error(error_code, vma))) {
1199                bad_area_access_error(regs, error_code, address);
1200                return;
1201        }
1202
1203        /*
1204         * If for any reason at all we couldn't handle the fault,
1205         * make sure we exit gracefully rather than endlessly redo
1206         * the fault:
1207         */
1208        fault = handle_mm_fault(mm, vma, address, flags);
1209
1210        /*
1211         * If we need to retry but a fatal signal is pending, handle the
1212         * signal first. We do not need to release the mmap_sem because it
1213         * would already be released in __lock_page_or_retry in mm/filemap.c.
1214         */
1215        if (unlikely((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)))
1216                return;
1217
1218        if (unlikely(fault & VM_FAULT_ERROR)) {
1219                mm_fault_error(regs, error_code, address, fault);
1220                return;
1221        }
1222
1223        /*
1224         * Major/minor page fault accounting is only done on the
1225         * initial attempt. If we go through a retry, it is extremely
1226         * likely that the page will be found in page cache at that point.
1227         */
1228        if (flags & FAULT_FLAG_ALLOW_RETRY) {
1229                if (fault & VM_FAULT_MAJOR) {
1230                        tsk->maj_flt++;
1231                        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
1232                                      regs, address);
1233                } else {
1234                        tsk->min_flt++;
1235                        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
1236                                      regs, address);
1237                }
1238                if (fault & VM_FAULT_RETRY) {
1239                        /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
1240                         * of starvation. */
1241                        flags &= ~FAULT_FLAG_ALLOW_RETRY;
1242                        flags |= FAULT_FLAG_TRIED;
1243                        goto retry;
1244                }
1245        }
1246
1247        check_v8086_mode(regs, address, tsk);
1248
1249        up_read(&mm->mmap_sem);
1250}
1251
1252dotraplinkage void __kprobes notrace
1253do_page_fault(struct pt_regs *regs, unsigned long error_code)
1254{
1255        unsigned long address = read_cr2(); /* Get the faulting address */
1256        enum ctx_state prev_state;
1257
1258        /*
1259         * We must have this function tagged with __kprobes, notrace and call
1260         * read_cr2() before calling anything else. To avoid calling any kind
1261         * of tracing machinery before we've observed the CR2 value.
1262         *
1263         * exception_{enter,exit}() contain all sorts of tracepoints.
1264         */
1265
1266        prev_state = exception_enter();
1267        __do_page_fault(regs, error_code, address);
1268        exception_exit(prev_state);
1269}
1270
1271#ifdef CONFIG_TRACING
1272static void trace_page_fault_entries(unsigned long address, struct pt_regs *regs,
1273                                     unsigned long error_code)
1274{
1275        if (user_mode(regs))
1276                trace_page_fault_user(address, regs, error_code);
1277        else
1278                trace_page_fault_kernel(address, regs, error_code);
1279}
1280
1281dotraplinkage void __kprobes notrace
1282trace_do_page_fault(struct pt_regs *regs, unsigned long error_code)
1283{
1284        /*
1285         * The exception_enter and tracepoint processing could
1286         * trigger another page faults (user space callchain
1287         * reading) and destroy the original cr2 value, so read
1288         * the faulting address now.
1289         */
1290        unsigned long address = read_cr2();
1291        enum ctx_state prev_state;
1292
1293        prev_state = exception_enter();
1294        trace_page_fault_entries(address, regs, error_code);
1295        __do_page_fault(regs, error_code, address);
1296        exception_exit(prev_state);
1297}
1298#endif /* CONFIG_TRACING */
1299
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