fault.c

Go to the documentation of this file.

/*
 *  Copyright (C) 1995  Linus Torvalds
 *  Copyright (C) 2001, 2002 Andi Kleen, SuSE Labs.
 *  Copyright (C) 2008-2009, Red Hat Inc., Ingo Molnar
 */
#include <linux/magic.h>        /* STACK_END_MAGIC      */
#include <linux/sched.h>        /* test_thread_flag(), ...  */
#include <linux/kdebug.h>       /* oops_begin/end, ...      */
#include <linux/module.h>       /* search_exception_table   */
#include <linux/bootmem.h>      /* max_low_pfn          */
#include <linux/kprobes.h>      /* __kprobes, ...       */
#include <linux/mmiotrace.h>        /* kmmio_handler, ...       */
#include <linux/perf_event.h>       /* perf_sw_event        */
#include <linux/hugetlb.h>      /* hstate_index_to_shift    */
#include <linux/prefetch.h>     /* prefetchw            */

#include <asm/traps.h>          /* dotraplinkage, ...       */
#include <asm/pgalloc.h>        /* pgd_*(), ...         */
#include <asm/kmemcheck.h>      /* kmemcheck_*(), ...       */
#include <asm/fixmap.h>         /* VSYSCALL_START       */
#include <asm/rcu.h>            /* exception_enter(), ...   */

/*
 * Page fault error code bits:
 *
 *   bit 0 ==    0: no page found   1: protection fault
 *   bit 1 ==    0: read access     1: write access
 *   bit 2 ==    0: kernel-mode access  1: user-mode access
 *   bit 3 ==               1: use of reserved bit detected
 *   bit 4 ==               1: fault was an instruction fetch
 */
enum x86_pf_error_code {

    PF_PROT     =       1 << 0,
    PF_WRITE    =       1 << 1,
    PF_USER     =       1 << 2,
    PF_RSVD     =       1 << 3,
    PF_INSTR    =       1 << 4,
};

/*
 * Returns 0 if mmiotrace is disabled, or if the fault is not
 * handled by mmiotrace:
 */
static inline int __kprobes
kmmio_fault(struct pt_regs *regs, unsigned long addr)
{
    if (unlikely(is_kmmio_active()))
        if (kmmio_handler(regs, addr) == 1)
            return -1;
    return 0;
}

static inline int __kprobes notify_page_fault(struct pt_regs *regs)
{
    int ret = 0;

    /* kprobe_running() needs smp_processor_id() */
    if (kprobes_built_in() && !user_mode_vm(regs)) {
        preempt_disable();
        if (kprobe_running() && kprobe_fault_handler(regs, 14))
            ret = 1;
        preempt_enable();
    }

    return ret;
}

/*
 * Prefetch quirks:
 *
 * 32-bit mode:
 *
 *   Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
 *   Check that here and ignore it.
 *
 * 64-bit mode:
 *
 *   Sometimes the CPU reports invalid exceptions on prefetch.
 *   Check that here and ignore it.
 *
 * Opcode checker based on code by Richard Brunner.
 */
static inline int
check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr,
              unsigned char opcode, int *prefetch)
{
    unsigned char instr_hi = opcode & 0xf0;
    unsigned char instr_lo = opcode & 0x0f;

    switch (instr_hi) {
    case 0x20:
    case 0x30:
        /*
         * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes.
         * In X86_64 long mode, the CPU will signal invalid
         * opcode if some of these prefixes are present so
         * X86_64 will never get here anyway
         */
        return ((instr_lo & 7) == 0x6);
#ifdef CONFIG_X86_64
    case 0x40:
        /*
         * In AMD64 long mode 0x40..0x4F are valid REX prefixes
         * Need to figure out under what instruction mode the
         * instruction was issued. Could check the LDT for lm,
         * but for now it's good enough to assume that long
         * mode only uses well known segments or kernel.
         */
        return (!user_mode(regs) || user_64bit_mode(regs));
#endif
    case 0x60:
        /* 0x64 thru 0x67 are valid prefixes in all modes. */
        return (instr_lo & 0xC) == 0x4;
    case 0xF0:
        /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */
        return !instr_lo || (instr_lo>>1) == 1;
    case 0x00:
        /* Prefetch instruction is 0x0F0D or 0x0F18 */
        if (probe_kernel_address(instr, opcode))
            return 0;

        *prefetch = (instr_lo == 0xF) &&
            (opcode == 0x0D || opcode == 0x18);
        return 0;
    default:
        return 0;
    }
}

static int
is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)
{
    unsigned char *max_instr;
    unsigned char *instr;
    int prefetch = 0;

    /*
     * If it was a exec (instruction fetch) fault on NX page, then
     * do not ignore the fault:
     */
    if (error_code & PF_INSTR)
        return 0;

    instr = (void *)convert_ip_to_linear(current, regs);
    max_instr = instr + 15;

    if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE)
        return 0;

    while (instr < max_instr) {
        unsigned char opcode;

        if (probe_kernel_address(instr, opcode))
            break;

        instr++;

        if (!check_prefetch_opcode(regs, instr, opcode, &prefetch))
            break;
    }
    return prefetch;
}

static void
force_sig_info_fault(int si_signo, int si_code, unsigned long address,
             struct task_struct *tsk, int fault)
{
    unsigned lsb = 0;
    siginfo_t info;

    info.si_signo   = si_signo;
    info.si_errno   = 0;
    info.si_code    = si_code;
    info.si_addr    = (void __user *)address;
    if (fault & VM_FAULT_HWPOISON_LARGE)
        lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault)); 
    if (fault & VM_FAULT_HWPOISON)
        lsb = PAGE_SHIFT;
    info.si_addr_lsb = lsb;

    force_sig_info(si_signo, &info, tsk);
}

DEFINE_SPINLOCK(pgd_lock);
LIST_HEAD(pgd_list);

#ifdef CONFIG_X86_32
static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
{
    unsigned index = pgd_index(address);
    pgd_t *pgd_k;
    pud_t *pud, *pud_k;
    pmd_t *pmd, *pmd_k;

    pgd += index;
    pgd_k = init_mm.pgd + index;

    if (!pgd_present(*pgd_k))
        return NULL;

    /*
     * set_pgd(pgd, *pgd_k); here would be useless on PAE
     * and redundant with the set_pmd() on non-PAE. As would
     * set_pud.
     */
    pud = pud_offset(pgd, address);
    pud_k = pud_offset(pgd_k, address);
    if (!pud_present(*pud_k))
        return NULL;

    pmd = pmd_offset(pud, address);
    pmd_k = pmd_offset(pud_k, address);
    if (!pmd_present(*pmd_k))
        return NULL;

    if (!pmd_present(*pmd))
        set_pmd(pmd, *pmd_k);
    else
        BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));

    return pmd_k;
}

void vmalloc_sync_all(void)
{
    unsigned long address;

    if (SHARED_KERNEL_PMD)
        return;

    for (address = VMALLOC_START & PMD_MASK;
         address >= TASK_SIZE && address < FIXADDR_TOP;
         address += PMD_SIZE) {
        struct page *page;

        spin_lock(&pgd_lock);
        list_for_each_entry(page, &pgd_list, lru) {
            spinlock_t *pgt_lock;
            pmd_t *ret;

            /* the pgt_lock only for Xen */
            pgt_lock = &pgd_page_get_mm(page)->page_table_lock;

            spin_lock(pgt_lock);
            ret = vmalloc_sync_one(page_address(page), address);
            spin_unlock(pgt_lock);

            if (!ret)
                break;
        }
        spin_unlock(&pgd_lock);
    }
}

/*
 * 32-bit:
 *
 *   Handle a fault on the vmalloc or module mapping area
 */
static noinline __kprobes int vmalloc_fault(unsigned long address)
{
    unsigned long pgd_paddr;
    pmd_t *pmd_k;
    pte_t *pte_k;

    /* Make sure we are in vmalloc area: */
    if (!(address >= VMALLOC_START && address < VMALLOC_END))
        return -1;

    WARN_ON_ONCE(in_nmi());

    /*
     * Synchronize this task's top level page-table
     * with the 'reference' page table.
     *
     * Do _not_ use "current" here. We might be inside
     * an interrupt in the middle of a task switch..
     */
    pgd_paddr = read_cr3();
    pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
    if (!pmd_k)
        return -1;

    pte_k = pte_offset_kernel(pmd_k, address);
    if (!pte_present(*pte_k))
        return -1;

    return 0;
}

/*
 * Did it hit the DOS screen memory VA from vm86 mode?
 */
static inline void
check_v8086_mode(struct pt_regs *regs, unsigned long address,
         struct task_struct *tsk)
{
    unsigned long bit;

    if (!v8086_mode(regs))
        return;

    bit = (address - 0xA0000) >> PAGE_SHIFT;
    if (bit < 32)
        tsk->thread.screen_bitmap |= 1 << bit;
}

static bool low_pfn(unsigned long pfn)
{
    return pfn < max_low_pfn;
}

static void dump_pagetable(unsigned long address)
{
    pgd_t *base = __va(read_cr3());
    pgd_t *pgd = &base[pgd_index(address)];
    pmd_t *pmd;
    pte_t *pte;

#ifdef CONFIG_X86_PAE
    printk("*pdpt = %016Lx ", pgd_val(*pgd));
    if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd))
        goto out;
#endif
    pmd = pmd_offset(pud_offset(pgd, address), address);
    printk(KERN_CONT "*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd));

    /*
     * We must not directly access the pte in the highpte
     * case if the page table is located in highmem.
     * And let's rather not kmap-atomic the pte, just in case
     * it's allocated already:
     */
    if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_large(*pmd))
        goto out;

    pte = pte_offset_kernel(pmd, address);
    printk("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte));
out:
    printk("\n");
}

#else /* CONFIG_X86_64: */

void vmalloc_sync_all(void)
{
    sync_global_pgds(VMALLOC_START & PGDIR_MASK, VMALLOC_END);
}

/*
 * 64-bit:
 *
 *   Handle a fault on the vmalloc area
 *
 * This assumes no large pages in there.
 */
static noinline __kprobes int vmalloc_fault(unsigned long address)
{
    pgd_t *pgd, *pgd_ref;
    pud_t *pud, *pud_ref;
    pmd_t *pmd, *pmd_ref;
    pte_t *pte, *pte_ref;

    /* Make sure we are in vmalloc area: */
    if (!(address >= VMALLOC_START && address < VMALLOC_END))
        return -1;

    WARN_ON_ONCE(in_nmi());

    /*
     * Copy kernel mappings over when needed. This can also
     * happen within a race in page table update. In the later
     * case just flush:
     */
    pgd = pgd_offset(current->active_mm, address);
    pgd_ref = pgd_offset_k(address);
    if (pgd_none(*pgd_ref))
        return -1;

    if (pgd_none(*pgd))
        set_pgd(pgd, *pgd_ref);
    else
        BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref));

    /*
     * Below here mismatches are bugs because these lower tables
     * are shared:
     */

    pud = pud_offset(pgd, address);
    pud_ref = pud_offset(pgd_ref, address);
    if (pud_none(*pud_ref))
        return -1;

    if (pud_none(*pud) || pud_page_vaddr(*pud) != pud_page_vaddr(*pud_ref))
        BUG();

    pmd = pmd_offset(pud, address);
    pmd_ref = pmd_offset(pud_ref, address);
    if (pmd_none(*pmd_ref))
        return -1;

    if (pmd_none(*pmd) || pmd_page(*pmd) != pmd_page(*pmd_ref))
        BUG();

    pte_ref = pte_offset_kernel(pmd_ref, address);
    if (!pte_present(*pte_ref))
        return -1;

    pte = pte_offset_kernel(pmd, address);

    /*
     * Don't use pte_page here, because the mappings can point
     * outside mem_map, and the NUMA hash lookup cannot handle
     * that:
     */
    if (!pte_present(*pte) || pte_pfn(*pte) != pte_pfn(*pte_ref))
        BUG();

    return 0;
}

#ifdef CONFIG_CPU_SUP_AMD
static const char errata93_warning[] =
KERN_ERR 
"******* Your BIOS seems to not contain a fix for K8 errata #93\n"
"******* Working around it, but it may cause SEGVs or burn power.\n"
"******* Please consider a BIOS update.\n"
"******* Disabling USB legacy in the BIOS may also help.\n";
#endif

/*
 * No vm86 mode in 64-bit mode:
 */
static inline void
check_v8086_mode(struct pt_regs *regs, unsigned long address,
         struct task_struct *tsk)
{
}

static int bad_address(void *p)
{
    unsigned long dummy;

    return probe_kernel_address((unsigned long *)p, dummy);
}

static void dump_pagetable(unsigned long address)
{
    pgd_t *base = __va(read_cr3() & PHYSICAL_PAGE_MASK);
    pgd_t *pgd = base + pgd_index(address);
    pud_t *pud;
    pmd_t *pmd;
    pte_t *pte;

    if (bad_address(pgd))
        goto bad;

    printk("PGD %lx ", pgd_val(*pgd));

    if (!pgd_present(*pgd))
        goto out;

    pud = pud_offset(pgd, address);
    if (bad_address(pud))
        goto bad;

    printk("PUD %lx ", pud_val(*pud));
    if (!pud_present(*pud) || pud_large(*pud))
        goto out;

    pmd = pmd_offset(pud, address);
    if (bad_address(pmd))
        goto bad;

    printk("PMD %lx ", pmd_val(*pmd));
    if (!pmd_present(*pmd) || pmd_large(*pmd))
        goto out;

    pte = pte_offset_kernel(pmd, address);
    if (bad_address(pte))
        goto bad;

    printk("PTE %lx", pte_val(*pte));
out:
    printk("\n");
    return;
bad:
    printk("BAD\n");
}

#endif /* CONFIG_X86_64 */

/*
 * Workaround for K8 erratum #93 & buggy BIOS.
 *
 * BIOS SMM functions are required to use a specific workaround
 * to avoid corruption of the 64bit RIP register on C stepping K8.
 *
 * A lot of BIOS that didn't get tested properly miss this.
 *
 * The OS sees this as a page fault with the upper 32bits of RIP cleared.
 * Try to work around it here.
 *
 * Note we only handle faults in kernel here.
 * Does nothing on 32-bit.
 */
static int is_errata93(struct pt_regs *regs, unsigned long address)
{
#if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD)
    if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD
        || boot_cpu_data.x86 != 0xf)
        return 0;

    if (address != regs->ip)
        return 0;

    if ((address >> 32) != 0)
        return 0;

    address |= 0xffffffffUL << 32;
    if ((address >= (u64)_stext && address <= (u64)_etext) ||
        (address >= MODULES_VADDR && address <= MODULES_END)) {
        printk_once(errata93_warning);
        regs->ip = address;
        return 1;
    }
#endif
    return 0;
}

/*
 * Work around K8 erratum #100 K8 in compat mode occasionally jumps
 * to illegal addresses >4GB.
 *
 * We catch this in the page fault handler because these addresses
 * are not reachable. Just detect this case and return.  Any code
 * segment in LDT is compatibility mode.
 */
static int is_errata100(struct pt_regs *regs, unsigned long address)
{
#ifdef CONFIG_X86_64
    if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32))
        return 1;
#endif
    return 0;
}

static int is_f00f_bug(struct pt_regs *regs, unsigned long address)
{
#ifdef CONFIG_X86_F00F_BUG
    unsigned long nr;

    /*
     * Pentium F0 0F C7 C8 bug workaround:
     */
    if (boot_cpu_data.f00f_bug) {
        nr = (address - idt_descr.address) >> 3;

        if (nr == 6) {
            do_invalid_op(regs, 0);
            return 1;
        }
    }
#endif
    return 0;
}

static const char nx_warning[] = KERN_CRIT
"kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n";

static void
show_fault_oops(struct pt_regs *regs, unsigned long error_code,
        unsigned long address)
{
    if (!oops_may_print())
        return;

    if (error_code & PF_INSTR) {
        unsigned int level;

        pte_t *pte = lookup_address(address, &level);

        if (pte && pte_present(*pte) && !pte_exec(*pte))
            printk(nx_warning, from_kuid(&init_user_ns, current_uid()));
    }

    printk(KERN_ALERT "BUG: unable to handle kernel ");
    if (address < PAGE_SIZE)
        printk(KERN_CONT "NULL pointer dereference");
    else
        printk(KERN_CONT "paging request");

    printk(KERN_CONT " at %p\n", (void *) address);
    printk(KERN_ALERT "IP:");
    printk_address(regs->ip, 1);

    dump_pagetable(address);
}

static noinline void
pgtable_bad(struct pt_regs *regs, unsigned long error_code,
        unsigned long address)
{
    struct task_struct *tsk;
    unsigned long flags;
    int sig;

    flags = oops_begin();
    tsk = current;
    sig = SIGKILL;

    printk(KERN_ALERT "%s: Corrupted page table at address %lx\n",
           tsk->comm, address);
    dump_pagetable(address);

    tsk->thread.cr2     = address;
    tsk->thread.trap_nr = X86_TRAP_PF;
    tsk->thread.error_code  = error_code;

    if (__die("Bad pagetable", regs, error_code))
        sig = 0;

    oops_end(flags, regs, sig);
}

static noinline void
no_context(struct pt_regs *regs, unsigned long error_code,
       unsigned long address, int signal, int si_code)
{
    struct task_struct *tsk = current;
    unsigned long *stackend;
    unsigned long flags;
    int sig;

    /* Are we prepared to handle this kernel fault? */
    if (fixup_exception(regs)) {
        if (current_thread_info()->sig_on_uaccess_error && signal) {
            tsk->thread.trap_nr = X86_TRAP_PF;
            tsk->thread.error_code = error_code | PF_USER;
            tsk->thread.cr2 = address;

            /* XXX: hwpoison faults will set the wrong code. */
            force_sig_info_fault(signal, si_code, address, tsk, 0);
        }
        return;
    }

    /*
     * 32-bit:
     *
     *   Valid to do another page fault here, because if this fault
     *   had been triggered by is_prefetch fixup_exception would have
     *   handled it.
     *
     * 64-bit:
     *
     *   Hall of shame of CPU/BIOS bugs.
     */
    if (is_prefetch(regs, error_code, address))
        return;

    if (is_errata93(regs, address))
        return;

    /*
     * Oops. The kernel tried to access some bad page. We'll have to
     * terminate things with extreme prejudice:
     */
    flags = oops_begin();

    show_fault_oops(regs, error_code, address);

    stackend = end_of_stack(tsk);
    if (tsk != &init_task && *stackend != STACK_END_MAGIC)
        printk(KERN_EMERG "Thread overran stack, or stack corrupted\n");

    tsk->thread.cr2     = address;
    tsk->thread.trap_nr = X86_TRAP_PF;
    tsk->thread.error_code  = error_code;

    sig = SIGKILL;
    if (__die("Oops", regs, error_code))
        sig = 0;

    /* Executive summary in case the body of the oops scrolled away */
    printk(KERN_DEFAULT "CR2: %016lx\n", address);

    oops_end(flags, regs, sig);
}

/*
 * Print out info about fatal segfaults, if the show_unhandled_signals
 * sysctl is set:
 */
static inline void
show_signal_msg(struct pt_regs *regs, unsigned long error_code,
        unsigned long address, struct task_struct *tsk)
{
    if (!unhandled_signal(tsk, SIGSEGV))
        return;

    if (!printk_ratelimit())
        return;

    printk("%s%s[%d]: segfault at %lx ip %p sp %p error %lx",
        task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
        tsk->comm, task_pid_nr(tsk), address,
        (void *)regs->ip, (void *)regs->sp, error_code);

    print_vma_addr(KERN_CONT " in ", regs->ip);

    printk(KERN_CONT "\n");
}

static void
__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
               unsigned long address, int si_code)
{
    struct task_struct *tsk = current;

    /* User mode accesses just cause a SIGSEGV */
    if (error_code & PF_USER) {
        /*
         * It's possible to have interrupts off here:
         */
        local_irq_enable();

        /*
         * Valid to do another page fault here because this one came
         * from user space:
         */
        if (is_prefetch(regs, error_code, address))
            return;

        if (is_errata100(regs, address))
            return;

#ifdef CONFIG_X86_64
        /*
         * Instruction fetch faults in the vsyscall page might need
         * emulation.
         */
        if (unlikely((error_code & PF_INSTR) &&
                 ((address & ~0xfff) == VSYSCALL_START))) {
            if (emulate_vsyscall(regs, address))
                return;
        }
#endif

        if (unlikely(show_unhandled_signals))
            show_signal_msg(regs, error_code, address, tsk);

        /* Kernel addresses are always protection faults: */
        tsk->thread.cr2     = address;
        tsk->thread.error_code  = error_code | (address >= TASK_SIZE);
        tsk->thread.trap_nr = X86_TRAP_PF;

        force_sig_info_fault(SIGSEGV, si_code, address, tsk, 0);

        return;
    }

    if (is_f00f_bug(regs, address))
        return;

    no_context(regs, error_code, address, SIGSEGV, si_code);
}

static noinline void
bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
             unsigned long address)
{
    __bad_area_nosemaphore(regs, error_code, address, SEGV_MAPERR);
}

static void
__bad_area(struct pt_regs *regs, unsigned long error_code,
       unsigned long address, int si_code)
{
    struct mm_struct *mm = current->mm;

    /*
     * Something tried to access memory that isn't in our memory map..
     * Fix it, but check if it's kernel or user first..
     */
    up_read(&mm->mmap_sem);

    __bad_area_nosemaphore(regs, error_code, address, si_code);
}

static noinline void
bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address)
{
    __bad_area(regs, error_code, address, SEGV_MAPERR);
}

static noinline void
bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
              unsigned long address)
{
    __bad_area(regs, error_code, address, SEGV_ACCERR);
}

/* TODO: fixup for "mm-invoke-oom-killer-from-page-fault.patch" */
static void
out_of_memory(struct pt_regs *regs, unsigned long error_code,
          unsigned long address)
{
    /*
     * We ran out of memory, call the OOM killer, and return the userspace
     * (which will retry the fault, or kill us if we got oom-killed):
     */
    up_read(&current->mm->mmap_sem);

    pagefault_out_of_memory();
}

static void
do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
      unsigned int fault)
{
    struct task_struct *tsk = current;
    struct mm_struct *mm = tsk->mm;
    int code = BUS_ADRERR;

    up_read(&mm->mmap_sem);

    /* Kernel mode? Handle exceptions or die: */
    if (!(error_code & PF_USER)) {
        no_context(regs, error_code, address, SIGBUS, BUS_ADRERR);
        return;
    }

    /* User-space => ok to do another page fault: */
    if (is_prefetch(regs, error_code, address))
        return;

    tsk->thread.cr2     = address;
    tsk->thread.error_code  = error_code;
    tsk->thread.trap_nr = X86_TRAP_PF;

#ifdef CONFIG_MEMORY_FAILURE
    if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
        printk(KERN_ERR
    "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
            tsk->comm, tsk->pid, address);
        code = BUS_MCEERR_AR;
    }
#endif
    force_sig_info_fault(SIGBUS, code, address, tsk, fault);
}

static noinline int
mm_fault_error(struct pt_regs *regs, unsigned long error_code,
           unsigned long address, unsigned int fault)
{
    /*
     * Pagefault was interrupted by SIGKILL. We have no reason to
     * continue pagefault.
     */
    if (fatal_signal_pending(current)) {
        if (!(fault & VM_FAULT_RETRY))
            up_read(&current->mm->mmap_sem);
        if (!(error_code & PF_USER))
            no_context(regs, error_code, address, 0, 0);
        return 1;
    }
    if (!(fault & VM_FAULT_ERROR))
        return 0;

    if (fault & VM_FAULT_OOM) {
        /* Kernel mode? Handle exceptions or die: */
        if (!(error_code & PF_USER)) {
            up_read(&current->mm->mmap_sem);
            no_context(regs, error_code, address,
                   SIGSEGV, SEGV_MAPERR);
            return 1;
        }

        out_of_memory(regs, error_code, address);
    } else {
        if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
                 VM_FAULT_HWPOISON_LARGE))
            do_sigbus(regs, error_code, address, fault);
        else
            BUG();
    }
    return 1;
}

static int spurious_fault_check(unsigned long error_code, pte_t *pte)
{
    if ((error_code & PF_WRITE) && !pte_write(*pte))
        return 0;

    if ((error_code & PF_INSTR) && !pte_exec(*pte))
        return 0;

    return 1;
}

/*
 * Handle a spurious fault caused by a stale TLB entry.
 *
 * This allows us to lazily refresh the TLB when increasing the
 * permissions of a kernel page (RO -> RW or NX -> X).  Doing it
 * eagerly is very expensive since that implies doing a full
 * cross-processor TLB flush, even if no stale TLB entries exist
 * on other processors.
 *
 * There are no security implications to leaving a stale TLB when
 * increasing the permissions on a page.
 */
static noinline __kprobes int
spurious_fault(unsigned long error_code, unsigned long address)
{
    pgd_t *pgd;
    pud_t *pud;
    pmd_t *pmd;
    pte_t *pte;
    int ret;

    /* Reserved-bit violation or user access to kernel space? */
    if (error_code & (PF_USER | PF_RSVD))
        return 0;

    pgd = init_mm.pgd + pgd_index(address);
    if (!pgd_present(*pgd))
        return 0;

    pud = pud_offset(pgd, address);
    if (!pud_present(*pud))
        return 0;

    if (pud_large(*pud))
        return spurious_fault_check(error_code, (pte_t *) pud);

    pmd = pmd_offset(pud, address);
    if (!pmd_present(*pmd))
        return 0;

    if (pmd_large(*pmd))
        return spurious_fault_check(error_code, (pte_t *) pmd);

    /*
     * Note: don't use pte_present() here, since it returns true
     * if the _PAGE_PROTNONE bit is set.  However, this aliases the
     * _PAGE_GLOBAL bit, which for kernel pages give false positives
     * when CONFIG_DEBUG_PAGEALLOC is used.
     */
    pte = pte_offset_kernel(pmd, address);
    if (!(pte_flags(*pte) & _PAGE_PRESENT))
        return 0;

    ret = spurious_fault_check(error_code, pte);
    if (!ret)
        return 0;

    /*
     * Make sure we have permissions in PMD.
     * If not, then there's a bug in the page tables:
     */
    ret = spurious_fault_check(error_code, (pte_t *) pmd);
    WARN_ONCE(!ret, "PMD has incorrect permission bits\n");

    return ret;
}

int show_unhandled_signals = 1;

static inline int
access_error(unsigned long error_code, struct vm_area_struct *vma)
{
    if (error_code & PF_WRITE) {
        /* write, present and write, not present: */
        if (unlikely(!(vma->vm_flags & VM_WRITE)))
            return 1;
        return 0;
    }

    /* read, present: */
    if (unlikely(error_code & PF_PROT))
        return 1;

    /* read, not present: */
    if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))))
        return 1;

    return 0;
}

static int fault_in_kernel_space(unsigned long address)
{
    return address >= TASK_SIZE_MAX;
}

static inline bool smap_violation(int error_code, struct pt_regs *regs)
{
    if (error_code & PF_USER)
        return false;

    if (!user_mode_vm(regs) && (regs->flags & X86_EFLAGS_AC))
        return false;

    return true;
}

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 */
static void __kprobes
__do_page_fault(struct pt_regs *regs, unsigned long error_code)
{
    struct vm_area_struct *vma;
    struct task_struct *tsk;
    unsigned long address;
    struct mm_struct *mm;
    int fault;
    int write = error_code & PF_WRITE;
    unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE |
                    (write ? FAULT_FLAG_WRITE : 0);

    tsk = current;
    mm = tsk->mm;

    /* Get the faulting address: */
    address = read_cr2();

    /*
     * Detect and handle instructions that would cause a page fault for
     * both a tracked kernel page and a userspace page.
     */
    if (kmemcheck_active(regs))
        kmemcheck_hide(regs);
    prefetchw(&mm->mmap_sem);

    if (unlikely(kmmio_fault(regs, address)))
        return;

    /*
     * We fault-in kernel-space virtual memory on-demand. The
     * 'reference' page table is init_mm.pgd.
     *
     * NOTE! We MUST NOT take any locks for this case. We may
     * be in an interrupt or a critical region, and should
     * only copy the information from the master page table,
     * nothing more.
     *
     * This verifies that the fault happens in kernel space
     * (error_code & 4) == 0, and that the fault was not a
     * protection error (error_code & 9) == 0.
     */
    if (unlikely(fault_in_kernel_space(address))) {
        if (!(error_code & (PF_RSVD | PF_USER | PF_PROT))) {
            if (vmalloc_fault(address) >= 0)
                return;

            if (kmemcheck_fault(regs, address, error_code))
                return;
        }

        /* Can handle a stale RO->RW TLB: */
        if (spurious_fault(error_code, address))
            return;

        /* kprobes don't want to hook the spurious faults: */
        if (notify_page_fault(regs))
            return;
        /*
         * Don't take the mm semaphore here. If we fixup a prefetch
         * fault we could otherwise deadlock:
         */
        bad_area_nosemaphore(regs, error_code, address);

        return;
    }

    /* kprobes don't want to hook the spurious faults: */
    if (unlikely(notify_page_fault(regs)))
        return;
    /*
     * It's safe to allow irq's after cr2 has been saved and the
     * vmalloc fault has been handled.
     *
     * User-mode registers count as a user access even for any
     * potential system fault or CPU buglet:
     */
    if (user_mode_vm(regs)) {
        local_irq_enable();
        error_code |= PF_USER;
    } else {
        if (regs->flags & X86_EFLAGS_IF)
            local_irq_enable();
    }

    if (unlikely(error_code & PF_RSVD))
        pgtable_bad(regs, error_code, address);

    if (static_cpu_has(X86_FEATURE_SMAP)) {
        if (unlikely(smap_violation(error_code, regs))) {
            bad_area_nosemaphore(regs, error_code, address);
            return;
        }
    }

    perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);

    /*
     * If we're in an interrupt, have no user context or are running
     * in an atomic region then we must not take the fault:
     */
    if (unlikely(in_atomic() || !mm)) {
        bad_area_nosemaphore(regs, error_code, address);
        return;
    }

    /*
     * When running in the kernel we expect faults to occur only to
     * addresses in user space.  All other faults represent errors in
     * the kernel and should generate an OOPS.  Unfortunately, in the
     * case of an erroneous fault occurring in a code path which already
     * holds mmap_sem we will deadlock attempting to validate the fault
     * against the address space.  Luckily the kernel only validly
     * references user space from well defined areas of code, which are
     * listed in the exceptions table.
     *
     * As the vast majority of faults will be valid we will only perform
     * the source reference check when there is a possibility of a
     * deadlock. Attempt to lock the address space, if we cannot we then
     * validate the source. If this is invalid we can skip the address
     * space check, thus avoiding the deadlock:
     */
    if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
        if ((error_code & PF_USER) == 0 &&
            !search_exception_tables(regs->ip)) {
            bad_area_nosemaphore(regs, error_code, address);
            return;
        }
retry:
        down_read(&mm->mmap_sem);
    } else {
        /*
         * The above down_read_trylock() might have succeeded in
         * which case we'll have missed the might_sleep() from
         * down_read():
         */
        might_sleep();
    }

    vma = find_vma(mm, address);
    if (unlikely(!vma)) {
        bad_area(regs, error_code, address);
        return;
    }
    if (likely(vma->vm_start <= address))
        goto good_area;
    if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
        bad_area(regs, error_code, address);
        return;
    }
    if (error_code & PF_USER) {
        /*
         * Accessing the stack below %sp is always a bug.
         * The large cushion allows instructions like enter
         * and pusha to work. ("enter $65535, $31" pushes
         * 32 pointers and then decrements %sp by 65535.)
         */
        if (unlikely(address + 65536 + 32 * sizeof(unsigned long) < regs->sp)) {
            bad_area(regs, error_code, address);
            return;
        }
    }
    if (unlikely(expand_stack(vma, address))) {
        bad_area(regs, error_code, address);
        return;
    }

    /*
     * Ok, we have a good vm_area for this memory access, so
     * we can handle it..
     */
good_area:
    if (unlikely(access_error(error_code, vma))) {
        bad_area_access_error(regs, error_code, address);
        return;
    }

    /*
     * If for any reason at all we couldn't handle the fault,
     * make sure we exit gracefully rather than endlessly redo
     * the fault:
     */
    fault = handle_mm_fault(mm, vma, address, flags);

    if (unlikely(fault & (VM_FAULT_RETRY|VM_FAULT_ERROR))) {
        if (mm_fault_error(regs, error_code, address, fault))
            return;
    }

    /*
     * Major/minor page fault accounting is only done on the
     * initial attempt. If we go through a retry, it is extremely
     * likely that the page will be found in page cache at that point.
     */
    if (flags & FAULT_FLAG_ALLOW_RETRY) {
        if (fault & VM_FAULT_MAJOR) {
            tsk->maj_flt++;
            perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
                      regs, address);
        } else {
            tsk->min_flt++;
            perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
                      regs, address);
        }
        if (fault & VM_FAULT_RETRY) {
            /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
             * of starvation. */
            flags &= ~FAULT_FLAG_ALLOW_RETRY;
            flags |= FAULT_FLAG_TRIED;
            goto retry;
        }
    }

    check_v8086_mode(regs, address, tsk);

    up_read(&mm->mmap_sem);
}

dotraplinkage void __kprobes
do_page_fault(struct pt_regs *regs, unsigned long error_code)
{
    exception_enter(regs);
    __do_page_fault(regs, error_code);
    exception_exit(regs);
}