Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus

[mirror_ubuntu-bionic-kernel.git] / arch / x86 / kernel / traps.c

/*
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *  Copyright (C) 2000, 2001, 2002 Andi Kleen, SuSE Labs
 *
 *  Pentium III FXSR, SSE support
 *      Gareth Hughes <gareth@valinux.com>, May 2000
 */

/*
 * Handle hardware traps and faults.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/context_tracking.h>
#include <linux/interrupt.h>
#include <linux/kallsyms.h>
#include <linux/spinlock.h>
#include <linux/kprobes.h>
#include <linux/uaccess.h>
#include <linux/kdebug.h>
#include <linux/kgdb.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/ptrace.h>
#include <linux/uprobes.h>
#include <linux/string.h>
#include <linux/delay.h>
#include <linux/errno.h>
#include <linux/kexec.h>
#include <linux/sched.h>
#include <linux/timer.h>
#include <linux/init.h>
#include <linux/bug.h>
#include <linux/nmi.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/io.h>

#ifdef CONFIG_EISA
#include <linux/ioport.h>
#include <linux/eisa.h>
#endif

#if defined(CONFIG_EDAC)
#include <linux/edac.h>
#endif

#include <asm/kmemcheck.h>
#include <asm/stacktrace.h>
#include <asm/processor.h>
#include <asm/debugreg.h>
#include <linux/atomic.h>
#include <asm/ftrace.h>
#include <asm/traps.h>
#include <asm/desc.h>
#include <asm/i387.h>
#include <asm/fpu-internal.h>
#include <asm/mce.h>
#include <asm/fixmap.h>
#include <asm/mach_traps.h>
#include <asm/alternative.h>
#include <asm/mpx.h>

#ifdef CONFIG_X86_64
#include <asm/x86_init.h>
#include <asm/pgalloc.h>
#include <asm/proto.h>

/* No need to be aligned, but done to keep all IDTs defined the same way. */
gate_desc debug_idt_table[NR_VECTORS] __page_aligned_bss;
#else
#include <asm/processor-flags.h>
#include <asm/setup.h>

asmlinkage int system_call(void);
#endif

/* Must be page-aligned because the real IDT is used in a fixmap. */
gate_desc idt_table[NR_VECTORS] __page_aligned_bss;

DECLARE_BITMAP(used_vectors, NR_VECTORS);
EXPORT_SYMBOL_GPL(used_vectors);

static inline void conditional_sti(struct pt_regs *regs)
{
        if (regs->flags & X86_EFLAGS_IF)
                local_irq_enable();
}

static inline void preempt_conditional_sti(struct pt_regs *regs)
{
        preempt_count_inc();
        if (regs->flags & X86_EFLAGS_IF)
                local_irq_enable();
}

static inline void conditional_cli(struct pt_regs *regs)
{
        if (regs->flags & X86_EFLAGS_IF)
                local_irq_disable();
}

static inline void preempt_conditional_cli(struct pt_regs *regs)
{
        if (regs->flags & X86_EFLAGS_IF)
                local_irq_disable();
        preempt_count_dec();
}

enum ctx_state ist_enter(struct pt_regs *regs)
{
        enum ctx_state prev_state;

        if (user_mode_vm(regs)) {
                /* Other than that, we're just an exception. */
                prev_state = exception_enter();
        } else {
                /*
                 * We might have interrupted pretty much anything.  In
                 * fact, if we're a machine check, we can even interrupt
                 * NMI processing.  We don't want in_nmi() to return true,
                 * but we need to notify RCU.
                 */
                rcu_nmi_enter();
                prev_state = IN_KERNEL;  /* the value is irrelevant. */
        }

        /*
         * We are atomic because we're on the IST stack (or we're on x86_32,
         * in which case we still shouldn't schedule).
         *
         * This must be after exception_enter(), because exception_enter()
         * won't do anything if in_interrupt() returns true.
         */
        preempt_count_add(HARDIRQ_OFFSET);

        /* This code is a bit fragile.  Test it. */
        rcu_lockdep_assert(rcu_is_watching(), "ist_enter didn't work");

        return prev_state;
}

void ist_exit(struct pt_regs *regs, enum ctx_state prev_state)
{
        /* Must be before exception_exit. */
        preempt_count_sub(HARDIRQ_OFFSET);

        if (user_mode_vm(regs))
                return exception_exit(prev_state);
        else
                rcu_nmi_exit();
}

/**
 * ist_begin_non_atomic() - begin a non-atomic section in an IST exception
 * @regs:       regs passed to the IST exception handler
 *
 * IST exception handlers normally cannot schedule.  As a special
 * exception, if the exception interrupted userspace code (i.e.
 * user_mode_vm(regs) would return true) and the exception was not
 * a double fault, it can be safe to schedule.  ist_begin_non_atomic()
 * begins a non-atomic section within an ist_enter()/ist_exit() region.
 * Callers are responsible for enabling interrupts themselves inside
 * the non-atomic section, and callers must call is_end_non_atomic()
 * before ist_exit().
 */
void ist_begin_non_atomic(struct pt_regs *regs)
{
        BUG_ON(!user_mode_vm(regs));

        /*
         * Sanity check: we need to be on the normal thread stack.  This
         * will catch asm bugs and any attempt to use ist_preempt_enable
         * from double_fault.
         */
        BUG_ON(((current_stack_pointer() ^ this_cpu_read_stable(kernel_stack))
                & ~(THREAD_SIZE - 1)) != 0);

        preempt_count_sub(HARDIRQ_OFFSET);
}

/**
 * ist_end_non_atomic() - begin a non-atomic section in an IST exception
 *
 * Ends a non-atomic section started with ist_begin_non_atomic().
 */
void ist_end_non_atomic(void)
{
        preempt_count_add(HARDIRQ_OFFSET);
}

static nokprobe_inline int
do_trap_no_signal(struct task_struct *tsk, int trapnr, char *str,
                  struct pt_regs *regs, long error_code)
{
#ifdef CONFIG_X86_32
        if (regs->flags & X86_VM_MASK) {
                /*
                 * Traps 0, 1, 3, 4, and 5 should be forwarded to vm86.
                 * On nmi (interrupt 2), do_trap should not be called.
                 */
                if (trapnr < X86_TRAP_UD) {
                        if (!handle_vm86_trap((struct kernel_vm86_regs *) regs,
                                                error_code, trapnr))
                                return 0;
                }
                return -1;
        }
#endif
        if (!user_mode(regs)) {
                if (!fixup_exception(regs)) {
                        tsk->thread.error_code = error_code;
                        tsk->thread.trap_nr = trapnr;
                        die(str, regs, error_code);
                }
                return 0;
        }

        return -1;
}

static siginfo_t *fill_trap_info(struct pt_regs *regs, int signr, int trapnr,
                                siginfo_t *info)
{
        unsigned long siaddr;
        int sicode;

        switch (trapnr) {
        default:
                return SEND_SIG_PRIV;

        case X86_TRAP_DE:
                sicode = FPE_INTDIV;
                siaddr = uprobe_get_trap_addr(regs);
                break;
        case X86_TRAP_UD:
                sicode = ILL_ILLOPN;
                siaddr = uprobe_get_trap_addr(regs);
                break;
        case X86_TRAP_AC:
                sicode = BUS_ADRALN;
                siaddr = 0;
                break;
        }

        info->si_signo = signr;
        info->si_errno = 0;
        info->si_code = sicode;
        info->si_addr = (void __user *)siaddr;
        return info;
}

static void
do_trap(int trapnr, int signr, char *str, struct pt_regs *regs,
        long error_code, siginfo_t *info)
{
        struct task_struct *tsk = current;


        if (!do_trap_no_signal(tsk, trapnr, str, regs, error_code))
                return;
        /*
         * We want error_code and trap_nr set for userspace faults and
         * kernelspace faults which result in die(), but not
         * kernelspace faults which are fixed up.  die() gives the
         * process no chance to handle the signal and notice the
         * kernel fault information, so that won't result in polluting
         * the information about previously queued, but not yet
         * delivered, faults.  See also do_general_protection below.
         */
        tsk->thread.error_code = error_code;
        tsk->thread.trap_nr = trapnr;

#ifdef CONFIG_X86_64
        if (show_unhandled_signals && unhandled_signal(tsk, signr) &&
            printk_ratelimit()) {
                pr_info("%s[%d] trap %s ip:%lx sp:%lx error:%lx",
                        tsk->comm, tsk->pid, str,
                        regs->ip, regs->sp, error_code);
                print_vma_addr(" in ", regs->ip);
                pr_cont("\n");
        }
#endif

        force_sig_info(signr, info ?: SEND_SIG_PRIV, tsk);
}
NOKPROBE_SYMBOL(do_trap);

static void do_error_trap(struct pt_regs *regs, long error_code, char *str,
                          unsigned long trapnr, int signr)
{
        enum ctx_state prev_state = exception_enter();
        siginfo_t info;

        if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) !=
                        NOTIFY_STOP) {
                conditional_sti(regs);
                do_trap(trapnr, signr, str, regs, error_code,
                        fill_trap_info(regs, signr, trapnr, &info));
        }

        exception_exit(prev_state);
}

#define DO_ERROR(trapnr, signr, str, name)                              \
dotraplinkage void do_##name(struct pt_regs *regs, long error_code)     \
{                                                                       \
        do_error_trap(regs, error_code, str, trapnr, signr);            \
}

DO_ERROR(X86_TRAP_DE,     SIGFPE,  "divide error",              divide_error)
DO_ERROR(X86_TRAP_OF,     SIGSEGV, "overflow",                  overflow)
DO_ERROR(X86_TRAP_UD,     SIGILL,  "invalid opcode",            invalid_op)
DO_ERROR(X86_TRAP_OLD_MF, SIGFPE,  "coprocessor segment overrun",coprocessor_segment_overrun)
DO_ERROR(X86_TRAP_TS,     SIGSEGV, "invalid TSS",               invalid_TSS)
DO_ERROR(X86_TRAP_NP,     SIGBUS,  "segment not present",       segment_not_present)
DO_ERROR(X86_TRAP_SS,     SIGBUS,  "stack segment",             stack_segment)
DO_ERROR(X86_TRAP_AC,     SIGBUS,  "alignment check",           alignment_check)

#ifdef CONFIG_X86_64
/* Runs on IST stack */
dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
{
        static const char str[] = "double fault";
        struct task_struct *tsk = current;

#ifdef CONFIG_X86_ESPFIX64
        extern unsigned char native_irq_return_iret[];

        /*
         * If IRET takes a non-IST fault on the espfix64 stack, then we
         * end up promoting it to a doublefault.  In that case, modify
         * the stack to make it look like we just entered the #GP
         * handler from user space, similar to bad_iret.
         *
         * No need for ist_enter here because we don't use RCU.
         */
        if (((long)regs->sp >> PGDIR_SHIFT) == ESPFIX_PGD_ENTRY &&
                regs->cs == __KERNEL_CS &&
                regs->ip == (unsigned long)native_irq_return_iret)
        {
                struct pt_regs *normal_regs = task_pt_regs(current);

                /* Fake a #GP(0) from userspace. */
                memmove(&normal_regs->ip, (void *)regs->sp, 5*8);
                normal_regs->orig_ax = 0;  /* Missing (lost) #GP error code */
                regs->ip = (unsigned long)general_protection;
                regs->sp = (unsigned long)&normal_regs->orig_ax;

                return;
        }
#endif

        ist_enter(regs);  /* Discard prev_state because we won't return. */
        notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV);

        tsk->thread.error_code = error_code;
        tsk->thread.trap_nr = X86_TRAP_DF;

#ifdef CONFIG_DOUBLEFAULT
        df_debug(regs, error_code);
#endif
        /*
         * This is always a kernel trap and never fixable (and thus must
         * never return).
         */
        for (;;)
                die(str, regs, error_code);
}
#endif

dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
{
        struct task_struct *tsk = current;
        struct xsave_struct *xsave_buf;
        enum ctx_state prev_state;
        struct bndcsr *bndcsr;
        siginfo_t *info;

        prev_state = exception_enter();
        if (notify_die(DIE_TRAP, "bounds", regs, error_code,
                        X86_TRAP_BR, SIGSEGV) == NOTIFY_STOP)
                goto exit;
        conditional_sti(regs);

        if (!user_mode(regs))
                die("bounds", regs, error_code);

        if (!cpu_feature_enabled(X86_FEATURE_MPX)) {
                /* The exception is not from Intel MPX */
                goto exit_trap;
        }

        /*
         * We need to look at BNDSTATUS to resolve this exception.
         * It is not directly accessible, though, so we need to
         * do an xsave and then pull it out of the xsave buffer.
         */
        fpu_save_init(&tsk->thread.fpu);
        xsave_buf = &(tsk->thread.fpu.state->xsave);
        bndcsr = get_xsave_addr(xsave_buf, XSTATE_BNDCSR);
        if (!bndcsr)
                goto exit_trap;

        /*
         * The error code field of the BNDSTATUS register communicates status
         * information of a bound range exception #BR or operation involving
         * bound directory.
         */
        switch (bndcsr->bndstatus & MPX_BNDSTA_ERROR_CODE) {
        case 2: /* Bound directory has invalid entry. */
                if (mpx_handle_bd_fault(xsave_buf))
                        goto exit_trap;
                break; /* Success, it was handled */
        case 1: /* Bound violation. */
                info = mpx_generate_siginfo(regs, xsave_buf);
                if (IS_ERR(info)) {
                        /*
                         * We failed to decode the MPX instruction.  Act as if
                         * the exception was not caused by MPX.
                         */
                        goto exit_trap;
                }
                /*
                 * Success, we decoded the instruction and retrieved
                 * an 'info' containing the address being accessed
                 * which caused the exception.  This information
                 * allows and application to possibly handle the
                 * #BR exception itself.
                 */
                do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, error_code, info);
                kfree(info);
                break;
        case 0: /* No exception caused by Intel MPX operations. */
                goto exit_trap;
        default:
                die("bounds", regs, error_code);
        }

exit:
        exception_exit(prev_state);
        return;
exit_trap:
        /*
         * This path out is for all the cases where we could not
         * handle the exception in some way (like allocating a
         * table or telling userspace about it.  We will also end
         * up here if the kernel has MPX turned off at compile
         * time..
         */
        do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, error_code, NULL);
        exception_exit(prev_state);
}

dotraplinkage void
do_general_protection(struct pt_regs *regs, long error_code)
{
        struct task_struct *tsk;
        enum ctx_state prev_state;

        prev_state = exception_enter();
        conditional_sti(regs);

#ifdef CONFIG_X86_32
        if (regs->flags & X86_VM_MASK) {
                local_irq_enable();
                handle_vm86_fault((struct kernel_vm86_regs *) regs, error_code);
                goto exit;
        }
#endif

        tsk = current;
        if (!user_mode(regs)) {
                if (fixup_exception(regs))
                        goto exit;

                tsk->thread.error_code = error_code;
                tsk->thread.trap_nr = X86_TRAP_GP;
                if (notify_die(DIE_GPF, "general protection fault", regs, error_code,
                               X86_TRAP_GP, SIGSEGV) != NOTIFY_STOP)
                        die("general protection fault", regs, error_code);
                goto exit;
        }

        tsk->thread.error_code = error_code;
        tsk->thread.trap_nr = X86_TRAP_GP;

        if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
                        printk_ratelimit()) {
                pr_info("%s[%d] general protection ip:%lx sp:%lx error:%lx",
                        tsk->comm, task_pid_nr(tsk),
                        regs->ip, regs->sp, error_code);
                print_vma_addr(" in ", regs->ip);
                pr_cont("\n");
        }

        force_sig_info(SIGSEGV, SEND_SIG_PRIV, tsk);
exit:
        exception_exit(prev_state);
}
NOKPROBE_SYMBOL(do_general_protection);

/* May run on IST stack. */
dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
{
        enum ctx_state prev_state;

#ifdef CONFIG_DYNAMIC_FTRACE
        /*
         * ftrace must be first, everything else may cause a recursive crash.
         * See note by declaration of modifying_ftrace_code in ftrace.c
         */
        if (unlikely(atomic_read(&modifying_ftrace_code)) &&
            ftrace_int3_handler(regs))
                return;
#endif
        if (poke_int3_handler(regs))
                return;

        prev_state = ist_enter(regs);
#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
        if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
                                SIGTRAP) == NOTIFY_STOP)
                goto exit;
#endif /* CONFIG_KGDB_LOW_LEVEL_TRAP */

#ifdef CONFIG_KPROBES
        if (kprobe_int3_handler(regs))
                goto exit;
#endif

        if (notify_die(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
                        SIGTRAP) == NOTIFY_STOP)
                goto exit;

        /*
         * Let others (NMI) know that the debug stack is in use
         * as we may switch to the interrupt stack.
         */
        debug_stack_usage_inc();
        preempt_conditional_sti(regs);
        do_trap(X86_TRAP_BP, SIGTRAP, "int3", regs, error_code, NULL);
        preempt_conditional_cli(regs);
        debug_stack_usage_dec();
exit:
        ist_exit(regs, prev_state);
}
NOKPROBE_SYMBOL(do_int3);

#ifdef CONFIG_X86_64
/*
 * Help handler running on IST stack to switch off the IST stack if the
 * interrupted code was in user mode. The actual stack switch is done in
 * entry_64.S
 */
asmlinkage __visible notrace struct pt_regs *sync_regs(struct pt_regs *eregs)
{
        struct pt_regs *regs = task_pt_regs(current);
        *regs = *eregs;
        return regs;
}
NOKPROBE_SYMBOL(sync_regs);

struct bad_iret_stack {
        void *error_entry_ret;
        struct pt_regs regs;
};

asmlinkage __visible notrace
struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
{
        /*
         * This is called from entry_64.S early in handling a fault
         * caused by a bad iret to user mode.  To handle the fault
         * correctly, we want move our stack frame to task_pt_regs
         * and we want to pretend that the exception came from the
         * iret target.
         */
        struct bad_iret_stack *new_stack =
                container_of(task_pt_regs(current),
                             struct bad_iret_stack, regs);

        /* Copy the IRET target to the new stack. */
        memmove(&new_stack->regs.ip, (void *)s->regs.sp, 5*8);

        /* Copy the remainder of the stack from the current stack. */
        memmove(new_stack, s, offsetof(struct bad_iret_stack, regs.ip));

        BUG_ON(!user_mode_vm(&new_stack->regs));
        return new_stack;
}
NOKPROBE_SYMBOL(fixup_bad_iret);
#endif

/*
 * Our handling of the processor debug registers is non-trivial.
 * We do not clear them on entry and exit from the kernel. Therefore
 * it is possible to get a watchpoint trap here from inside the kernel.
 * However, the code in ./ptrace.c has ensured that the user can
 * only set watchpoints on userspace addresses. Therefore the in-kernel
 * watchpoint trap can only occur in code which is reading/writing
 * from user space. Such code must not hold kernel locks (since it
 * can equally take a page fault), therefore it is safe to call
 * force_sig_info even though that claims and releases locks.
 *
 * Code in ./signal.c ensures that the debug control register
 * is restored before we deliver any signal, and therefore that
 * user code runs with the correct debug control register even though
 * we clear it here.
 *
 * Being careful here means that we don't have to be as careful in a
 * lot of more complicated places (task switching can be a bit lazy
 * about restoring all the debug state, and ptrace doesn't have to
 * find every occurrence of the TF bit that could be saved away even
 * by user code)
 *
 * May run on IST stack.
 */
dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
{
        struct task_struct *tsk = current;
        enum ctx_state prev_state;
        int user_icebp = 0;
        unsigned long dr6;
        int si_code;

        prev_state = ist_enter(regs);

        get_debugreg(dr6, 6);

        /* Filter out all the reserved bits which are preset to 1 */
        dr6 &= ~DR6_RESERVED;

        /*
         * If dr6 has no reason to give us about the origin of this trap,
         * then it's very likely the result of an icebp/int01 trap.
         * User wants a sigtrap for that.
         */
        if (!dr6 && user_mode(regs))
                user_icebp = 1;

        /* Catch kmemcheck conditions first of all! */
        if ((dr6 & DR_STEP) && kmemcheck_trap(regs))
                goto exit;

        /* DR6 may or may not be cleared by the CPU */
        set_debugreg(0, 6);

        /*
         * The processor cleared BTF, so don't mark that we need it set.
         */
        clear_tsk_thread_flag(tsk, TIF_BLOCKSTEP);

        /* Store the virtualized DR6 value */
        tsk->thread.debugreg6 = dr6;

#ifdef CONFIG_KPROBES
        if (kprobe_debug_handler(regs))
                goto exit;
#endif

        if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, error_code,
                                                        SIGTRAP) == NOTIFY_STOP)
                goto exit;

        /*
         * Let others (NMI) know that the debug stack is in use
         * as we may switch to the interrupt stack.
         */
        debug_stack_usage_inc();

        /* It's safe to allow irq's after DR6 has been saved */
        preempt_conditional_sti(regs);

        if (regs->flags & X86_VM_MASK) {
                handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code,
                                        X86_TRAP_DB);
                preempt_conditional_cli(regs);
                debug_stack_usage_dec();
                goto exit;
        }

        /*
         * Single-stepping through system calls: ignore any exceptions in
         * kernel space, but re-enable TF when returning to user mode.
         *
         * We already checked v86 mode above, so we can check for kernel mode
         * by just checking the CPL of CS.
         */
        if ((dr6 & DR_STEP) && !user_mode(regs)) {
                tsk->thread.debugreg6 &= ~DR_STEP;
                set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
                regs->flags &= ~X86_EFLAGS_TF;
        }
        si_code = get_si_code(tsk->thread.debugreg6);
        if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp)
                send_sigtrap(tsk, regs, error_code, si_code);
        preempt_conditional_cli(regs);
        debug_stack_usage_dec();

exit:
        ist_exit(regs, prev_state);
}
NOKPROBE_SYMBOL(do_debug);

/*
 * Note that we play around with the 'TS' bit in an attempt to get
 * the correct behaviour even in the presence of the asynchronous
 * IRQ13 behaviour
 */
static void math_error(struct pt_regs *regs, int error_code, int trapnr)
{
        struct task_struct *task = current;
        siginfo_t info;
        unsigned short err;
        char *str = (trapnr == X86_TRAP_MF) ? "fpu exception" :
                                                "simd exception";

        if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, SIGFPE) == NOTIFY_STOP)
                return;
        conditional_sti(regs);

        if (!user_mode_vm(regs))
        {
                if (!fixup_exception(regs)) {
                        task->thread.error_code = error_code;
                        task->thread.trap_nr = trapnr;
                        die(str, regs, error_code);
                }
                return;
        }

        /*
         * Save the info for the exception handler and clear the error.
         */
        save_init_fpu(task);
        task->thread.trap_nr = trapnr;
        task->thread.error_code = error_code;
        info.si_signo = SIGFPE;
        info.si_errno = 0;
        info.si_addr = (void __user *)uprobe_get_trap_addr(regs);
        if (trapnr == X86_TRAP_MF) {
                unsigned short cwd, swd;
                /*
                 * (~cwd & swd) will mask out exceptions that are not set to unmasked
                 * status.  0x3f is the exception bits in these regs, 0x200 is the
                 * C1 reg you need in case of a stack fault, 0x040 is the stack
                 * fault bit.  We should only be taking one exception at a time,
                 * so if this combination doesn't produce any single exception,
                 * then we have a bad program that isn't synchronizing its FPU usage
                 * and it will suffer the consequences since we won't be able to
                 * fully reproduce the context of the exception
                 */
                cwd = get_fpu_cwd(task);
                swd = get_fpu_swd(task);

                err = swd & ~cwd;
        } else {
                /*
                 * The SIMD FPU exceptions are handled a little differently, as there
                 * is only a single status/control register.  Thus, to determine which
                 * unmasked exception was caught we must mask the exception mask bits
                 * at 0x1f80, and then use these to mask the exception bits at 0x3f.
                 */
                unsigned short mxcsr = get_fpu_mxcsr(task);
                err = ~(mxcsr >> 7) & mxcsr;
        }

        if (err & 0x001) {      /* Invalid op */
                /*
                 * swd & 0x240 == 0x040: Stack Underflow
                 * swd & 0x240 == 0x240: Stack Overflow
                 * User must clear the SF bit (0x40) if set
                 */
                info.si_code = FPE_FLTINV;
        } else if (err & 0x004) { /* Divide by Zero */
                info.si_code = FPE_FLTDIV;
        } else if (err & 0x008) { /* Overflow */
                info.si_code = FPE_FLTOVF;
        } else if (err & 0x012) { /* Denormal, Underflow */
                info.si_code = FPE_FLTUND;
        } else if (err & 0x020) { /* Precision */
                info.si_code = FPE_FLTRES;
        } else {
                /*
                 * If we're using IRQ 13, or supposedly even some trap
                 * X86_TRAP_MF implementations, it's possible
                 * we get a spurious trap, which is not an error.
                 */
                return;
        }
        force_sig_info(SIGFPE, &info, task);
}

dotraplinkage void do_coprocessor_error(struct pt_regs *regs, long error_code)
{
        enum ctx_state prev_state;

        prev_state = exception_enter();
        math_error(regs, error_code, X86_TRAP_MF);
        exception_exit(prev_state);
}

dotraplinkage void
do_simd_coprocessor_error(struct pt_regs *regs, long error_code)
{
        enum ctx_state prev_state;

        prev_state = exception_enter();
        math_error(regs, error_code, X86_TRAP_XF);
        exception_exit(prev_state);
}

dotraplinkage void
do_spurious_interrupt_bug(struct pt_regs *regs, long error_code)
{
        conditional_sti(regs);
#if 0
        /* No need to warn about this any longer. */
        pr_info("Ignoring P6 Local APIC Spurious Interrupt Bug...\n");
#endif
}

asmlinkage __visible void __attribute__((weak)) smp_thermal_interrupt(void)
{
}

asmlinkage __visible void __attribute__((weak)) smp_threshold_interrupt(void)
{
}

/*
 * 'math_state_restore()' saves the current math information in the
 * old math state array, and gets the new ones from the current task
 *
 * Careful.. There are problems with IBM-designed IRQ13 behaviour.
 * Don't touch unless you *really* know how it works.
 *
 * Must be called with kernel preemption disabled (eg with local
 * local interrupts as in the case of do_device_not_available).
 */
void math_state_restore(void)
{
        struct task_struct *tsk = current;

        if (!tsk_used_math(tsk)) {
                local_irq_enable();
                /*
                 * does a slab alloc which can sleep
                 */
                if (init_fpu(tsk)) {
                        /*
                         * ran out of memory!
                         */
                        do_group_exit(SIGKILL);
                        return;
                }
                local_irq_disable();
        }

        /* Avoid __kernel_fpu_begin() right after __thread_fpu_begin() */
        kernel_fpu_disable();
        __thread_fpu_begin(tsk);
        if (unlikely(restore_fpu_checking(tsk))) {
                drop_init_fpu(tsk);
                force_sig_info(SIGSEGV, SEND_SIG_PRIV, tsk);
        } else {
                tsk->thread.fpu_counter++;
        }
        kernel_fpu_enable();
}
EXPORT_SYMBOL_GPL(math_state_restore);

dotraplinkage void
do_device_not_available(struct pt_regs *regs, long error_code)
{
        enum ctx_state prev_state;

        prev_state = exception_enter();
        BUG_ON(use_eager_fpu());

#ifdef CONFIG_MATH_EMULATION
        if (read_cr0() & X86_CR0_EM) {
                struct math_emu_info info = { };

                conditional_sti(regs);

                info.regs = regs;
                math_emulate(&info);
                exception_exit(prev_state);
                return;
        }
#endif
        math_state_restore(); /* interrupts still off */
#ifdef CONFIG_X86_32
        conditional_sti(regs);
#endif
        exception_exit(prev_state);
}
NOKPROBE_SYMBOL(do_device_not_available);

#ifdef CONFIG_X86_32
dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code)
{
        siginfo_t info;
        enum ctx_state prev_state;

        prev_state = exception_enter();
        local_irq_enable();

        info.si_signo = SIGILL;
        info.si_errno = 0;
        info.si_code = ILL_BADSTK;
        info.si_addr = NULL;
        if (notify_die(DIE_TRAP, "iret exception", regs, error_code,
                        X86_TRAP_IRET, SIGILL) != NOTIFY_STOP) {
                do_trap(X86_TRAP_IRET, SIGILL, "iret exception", regs, error_code,
                        &info);
        }
        exception_exit(prev_state);
}
#endif

/* Set of traps needed for early debugging. */
void __init early_trap_init(void)
{
        set_intr_gate_ist(X86_TRAP_DB, &debug, DEBUG_STACK);
        /* int3 can be called from all */
        set_system_intr_gate_ist(X86_TRAP_BP, &int3, DEBUG_STACK);
#ifdef CONFIG_X86_32
        set_intr_gate(X86_TRAP_PF, page_fault);
#endif
        load_idt(&idt_descr);
}

void __init early_trap_pf_init(void)
{
#ifdef CONFIG_X86_64
        set_intr_gate(X86_TRAP_PF, page_fault);
#endif
}

void __init trap_init(void)
{
        int i;

#ifdef CONFIG_EISA
        void __iomem *p = early_ioremap(0x0FFFD9, 4);

        if (readl(p) == 'E' + ('I'<<8) + ('S'<<16) + ('A'<<24))
                EISA_bus = 1;
        early_iounmap(p, 4);
#endif

        set_intr_gate(X86_TRAP_DE, divide_error);
        set_intr_gate_ist(X86_TRAP_NMI, &nmi, NMI_STACK);
        /* int4 can be called from all */
        set_system_intr_gate(X86_TRAP_OF, &overflow);
        set_intr_gate(X86_TRAP_BR, bounds);
        set_intr_gate(X86_TRAP_UD, invalid_op);
        set_intr_gate(X86_TRAP_NM, device_not_available);
#ifdef CONFIG_X86_32
        set_task_gate(X86_TRAP_DF, GDT_ENTRY_DOUBLEFAULT_TSS);
#else
        set_intr_gate_ist(X86_TRAP_DF, &double_fault, DOUBLEFAULT_STACK);
#endif
        set_intr_gate(X86_TRAP_OLD_MF, coprocessor_segment_overrun);
        set_intr_gate(X86_TRAP_TS, invalid_TSS);
        set_intr_gate(X86_TRAP_NP, segment_not_present);
        set_intr_gate(X86_TRAP_SS, stack_segment);
        set_intr_gate(X86_TRAP_GP, general_protection);
        set_intr_gate(X86_TRAP_SPURIOUS, spurious_interrupt_bug);
        set_intr_gate(X86_TRAP_MF, coprocessor_error);
        set_intr_gate(X86_TRAP_AC, alignment_check);
#ifdef CONFIG_X86_MCE
        set_intr_gate_ist(X86_TRAP_MC, &machine_check, MCE_STACK);
#endif
        set_intr_gate(X86_TRAP_XF, simd_coprocessor_error);

        /* Reserve all the builtin and the syscall vector: */
        for (i = 0; i < FIRST_EXTERNAL_VECTOR; i++)
                set_bit(i, used_vectors);

#ifdef CONFIG_IA32_EMULATION
        set_system_intr_gate(IA32_SYSCALL_VECTOR, ia32_syscall);
        set_bit(IA32_SYSCALL_VECTOR, used_vectors);
#endif

#ifdef CONFIG_X86_32
        set_system_trap_gate(SYSCALL_VECTOR, &system_call);
        set_bit(SYSCALL_VECTOR, used_vectors);
#endif

        /*
         * Set the IDT descriptor to a fixed read-only location, so that the
         * "sidt" instruction will not leak the location of the kernel, and
         * to defend the IDT against arbitrary memory write vulnerabilities.
         * It will be reloaded in cpu_init() */
        __set_fixmap(FIX_RO_IDT, __pa_symbol(idt_table), PAGE_KERNEL_RO);
        idt_descr.address = fix_to_virt(FIX_RO_IDT);

        /*
         * Should be a barrier for any external CPU state:
         */
        cpu_init();

        x86_init.irqs.trap_init();

#ifdef CONFIG_X86_64
        memcpy(&debug_idt_table, &idt_table, IDT_ENTRIES * 16);
        set_nmi_gate(X86_TRAP_DB, &debug);
        set_nmi_gate(X86_TRAP_BP, &int3);
#endif
}