x86/entry/32: Change INT80 to be an interrupt gate

[linux-2.6/btrfs-unstable.git] / arch / x86 / entry / common.c

/*
 * common.c - C code for kernel entry and exit
 * Copyright (c) 2015 Andrew Lutomirski
 * GPL v2
 *
 * Based on asm and ptrace code by many authors.  The code here originated
 * in ptrace.c and signal.c.
 */

#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/errno.h>
#include <linux/ptrace.h>
#include <linux/tracehook.h>
#include <linux/audit.h>
#include <linux/seccomp.h>
#include <linux/signal.h>
#include <linux/export.h>
#include <linux/context_tracking.h>
#include <linux/user-return-notifier.h>
#include <linux/uprobes.h>

#include <asm/desc.h>
#include <asm/traps.h>
#include <asm/vdso.h>
#include <asm/uaccess.h>
#include <asm/cpufeature.h>

#define CREATE_TRACE_POINTS
#include <trace/events/syscalls.h>

static struct thread_info *pt_regs_to_thread_info(struct pt_regs *regs)
{
        unsigned long top_of_stack =
                (unsigned long)(regs + 1) + TOP_OF_KERNEL_STACK_PADDING;
        return (struct thread_info *)(top_of_stack - THREAD_SIZE);
}

#ifdef CONFIG_CONTEXT_TRACKING
/* Called on entry from user mode with IRQs off. */
__visible void enter_from_user_mode(void)
{
        CT_WARN_ON(ct_state() != CONTEXT_USER);
        user_exit();
}
#endif

static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
{
#ifdef CONFIG_X86_64
        if (arch == AUDIT_ARCH_X86_64) {
                audit_syscall_entry(regs->orig_ax, regs->di,
                                    regs->si, regs->dx, regs->r10);
        } else
#endif
        {
                audit_syscall_entry(regs->orig_ax, regs->bx,
                                    regs->cx, regs->dx, regs->si);
        }
}

/*
 * We can return 0 to resume the syscall or anything else to go to phase
 * 2.  If we resume the syscall, we need to put something appropriate in
 * regs->orig_ax.
 *
 * NB: We don't have full pt_regs here, but regs->orig_ax and regs->ax
 * are fully functional.
 *
 * For phase 2's benefit, our return value is:
 * 0:                   resume the syscall
 * 1:                   go to phase 2; no seccomp phase 2 needed
 * anything else:       go to phase 2; pass return value to seccomp
 */
unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch)
{
        struct thread_info *ti = pt_regs_to_thread_info(regs);
        unsigned long ret = 0;
        u32 work;

        if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
                BUG_ON(regs != task_pt_regs(current));

        work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;

#ifdef CONFIG_CONTEXT_TRACKING
        /*
         * If TIF_NOHZ is set, we are required to call user_exit() before
         * doing anything that could touch RCU.
         */
        if (work & _TIF_NOHZ) {
                enter_from_user_mode();
                work &= ~_TIF_NOHZ;
        }
#endif

#ifdef CONFIG_SECCOMP
        /*
         * Do seccomp first -- it should minimize exposure of other
         * code, and keeping seccomp fast is probably more valuable
         * than the rest of this.
         */
        if (work & _TIF_SECCOMP) {
                struct seccomp_data sd;

                sd.arch = arch;
                sd.nr = regs->orig_ax;
                sd.instruction_pointer = regs->ip;
#ifdef CONFIG_X86_64
                if (arch == AUDIT_ARCH_X86_64) {
                        sd.args[0] = regs->di;
                        sd.args[1] = regs->si;
                        sd.args[2] = regs->dx;
                        sd.args[3] = regs->r10;
                        sd.args[4] = regs->r8;
                        sd.args[5] = regs->r9;
                } else
#endif
                {
                        sd.args[0] = regs->bx;
                        sd.args[1] = regs->cx;
                        sd.args[2] = regs->dx;
                        sd.args[3] = regs->si;
                        sd.args[4] = regs->di;
                        sd.args[5] = regs->bp;
                }

                BUILD_BUG_ON(SECCOMP_PHASE1_OK != 0);
                BUILD_BUG_ON(SECCOMP_PHASE1_SKIP != 1);

                ret = seccomp_phase1(&sd);
                if (ret == SECCOMP_PHASE1_SKIP) {
                        regs->orig_ax = -1;
                        ret = 0;
                } else if (ret != SECCOMP_PHASE1_OK) {
                        return ret;  /* Go directly to phase 2 */
                }

                work &= ~_TIF_SECCOMP;
        }
#endif

        /* Do our best to finish without phase 2. */
        if (work == 0)
                return ret;  /* seccomp and/or nohz only (ret == 0 here) */

#ifdef CONFIG_AUDITSYSCALL
        if (work == _TIF_SYSCALL_AUDIT) {
                /*
                 * If there is no more work to be done except auditing,
                 * then audit in phase 1.  Phase 2 always audits, so, if
                 * we audit here, then we can't go on to phase 2.
                 */
                do_audit_syscall_entry(regs, arch);
                return 0;
        }
#endif

        return 1;  /* Something is enabled that we can't handle in phase 1 */
}

/* Returns the syscall nr to run (which should match regs->orig_ax). */
long syscall_trace_enter_phase2(struct pt_regs *regs, u32 arch,
                                unsigned long phase1_result)
{
        struct thread_info *ti = pt_regs_to_thread_info(regs);
        long ret = 0;
        u32 work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;

        if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
                BUG_ON(regs != task_pt_regs(current));

#ifdef CONFIG_SECCOMP
        /*
         * Call seccomp_phase2 before running the other hooks so that
         * they can see any changes made by a seccomp tracer.
         */
        if (phase1_result > 1 && seccomp_phase2(phase1_result)) {
                /* seccomp failures shouldn't expose any additional code. */
                return -1;
        }
#endif

        if (unlikely(work & _TIF_SYSCALL_EMU))
                ret = -1L;

        if ((ret || test_thread_flag(TIF_SYSCALL_TRACE)) &&
            tracehook_report_syscall_entry(regs))
                ret = -1L;

        if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
                trace_sys_enter(regs, regs->orig_ax);

        do_audit_syscall_entry(regs, arch);

        return ret ?: regs->orig_ax;
}

long syscall_trace_enter(struct pt_regs *regs)
{
        u32 arch = is_ia32_task() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
        unsigned long phase1_result = syscall_trace_enter_phase1(regs, arch);

        if (phase1_result == 0)
                return regs->orig_ax;
        else
                return syscall_trace_enter_phase2(regs, arch, phase1_result);
}

#define EXIT_TO_USERMODE_LOOP_FLAGS                             \
        (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |   \
         _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY)

static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
{
        /*
         * In order to return to user mode, we need to have IRQs off with
         * none of _TIF_SIGPENDING, _TIF_NOTIFY_RESUME, _TIF_USER_RETURN_NOTIFY,
         * _TIF_UPROBE, or _TIF_NEED_RESCHED set.  Several of these flags
         * can be set at any time on preemptable kernels if we have IRQs on,
         * so we need to loop.  Disabling preemption wouldn't help: doing the
         * work to clear some of the flags can sleep.
         */
        while (true) {
                /* We have work to do. */
                local_irq_enable();

                if (cached_flags & _TIF_NEED_RESCHED)
                        schedule();

                if (cached_flags & _TIF_UPROBE)
                        uprobe_notify_resume(regs);

                /* deal with pending signal delivery */
                if (cached_flags & _TIF_SIGPENDING)
                        do_signal(regs);

                if (cached_flags & _TIF_NOTIFY_RESUME) {
                        clear_thread_flag(TIF_NOTIFY_RESUME);
                        tracehook_notify_resume(regs);
                }

                if (cached_flags & _TIF_USER_RETURN_NOTIFY)
                        fire_user_return_notifiers();

                /* Disable IRQs and retry */
                local_irq_disable();

                cached_flags = READ_ONCE(pt_regs_to_thread_info(regs)->flags);

                if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
                        break;

        }
}

/* Called with IRQs disabled. */
__visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
{
        struct thread_info *ti = pt_regs_to_thread_info(regs);
        u32 cached_flags;

        if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))
                local_irq_disable();

        lockdep_sys_exit();

        cached_flags = READ_ONCE(ti->flags);

        if (unlikely(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
                exit_to_usermode_loop(regs, cached_flags);

#ifdef CONFIG_COMPAT
        /*
         * Compat syscalls set TS_COMPAT.  Make sure we clear it before
         * returning to user mode.  We need to clear it *after* signal
         * handling, because syscall restart has a fixup for compat
         * syscalls.  The fixup is exercised by the ptrace_syscall_32
         * selftest.
         */
        ti->status &= ~TS_COMPAT;
#endif

        user_enter();
}

#define SYSCALL_EXIT_WORK_FLAGS                         \
        (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT |      \
         _TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)

static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
{
        bool step;

        audit_syscall_exit(regs);

        if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
                trace_sys_exit(regs, regs->ax);

        /*
         * If TIF_SYSCALL_EMU is set, we only get here because of
         * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
         * We already reported this syscall instruction in
         * syscall_trace_enter().
         */
        step = unlikely(
                (cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
                == _TIF_SINGLESTEP);
        if (step || cached_flags & _TIF_SYSCALL_TRACE)
                tracehook_report_syscall_exit(regs, step);
}

/*
 * Called with IRQs on and fully valid regs.  Returns with IRQs off in a
 * state such that we can immediately switch to user mode.
 */
__visible inline void syscall_return_slowpath(struct pt_regs *regs)
{
        struct thread_info *ti = pt_regs_to_thread_info(regs);
        u32 cached_flags = READ_ONCE(ti->flags);

        CT_WARN_ON(ct_state() != CONTEXT_KERNEL);

        if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
            WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
                local_irq_enable();

        /*
         * First do one-time work.  If these work items are enabled, we
         * want to run them exactly once per syscall exit with IRQs on.
         */
        if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
                syscall_slow_exit_work(regs, cached_flags);

        local_irq_disable();
        prepare_exit_to_usermode(regs);
}

#ifdef CONFIG_X86_64
__visible void do_syscall_64(struct pt_regs *regs)
{
        struct thread_info *ti = pt_regs_to_thread_info(regs);
        unsigned long nr = regs->orig_ax;

        local_irq_enable();

        if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
                nr = syscall_trace_enter(regs);

        /*
         * NB: Native and x32 syscalls are dispatched from the same
         * table.  The only functional difference is the x32 bit in
         * regs->orig_ax, which changes the behavior of some syscalls.
         */
        if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) {
                regs->ax = sys_call_table[nr & __SYSCALL_MASK](
                        regs->di, regs->si, regs->dx,
                        regs->r10, regs->r8, regs->r9);
        }

        syscall_return_slowpath(regs);
}
#endif

#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
/*
 * Does a 32-bit syscall.  Called with IRQs on and does all entry and
 * exit work and returns with IRQs off.  This function is extremely hot
 * in workloads that use it, and it's usually called from
 * do_fast_syscall_32, so forcibly inline it to improve performance.
 */
static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
{
        struct thread_info *ti = pt_regs_to_thread_info(regs);
        unsigned int nr = (unsigned int)regs->orig_ax;

#ifdef CONFIG_IA32_EMULATION
        ti->status |= TS_COMPAT;
#endif

        if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
                /*
                 * Subtlety here: if ptrace pokes something larger than
                 * 2^32-1 into orig_ax, this truncates it.  This may or
                 * may not be necessary, but it matches the old asm
                 * behavior.
                 */
                nr = syscall_trace_enter(regs);
        }

        if (likely(nr < IA32_NR_syscalls)) {
                /*
                 * It's possible that a 32-bit syscall implementation
                 * takes a 64-bit parameter but nonetheless assumes that
                 * the high bits are zero.  Make sure we zero-extend all
                 * of the args.
                 */
                regs->ax = ia32_sys_call_table[nr](
                        (unsigned int)regs->bx, (unsigned int)regs->cx,
                        (unsigned int)regs->dx, (unsigned int)regs->si,
                        (unsigned int)regs->di, (unsigned int)regs->bp);
        }

        syscall_return_slowpath(regs);
}

/* Handles int $0x80 */
__visible void do_int80_syscall_32(struct pt_regs *regs)
{
        local_irq_enable();
        do_syscall_32_irqs_on(regs);
}

/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
__visible long do_fast_syscall_32(struct pt_regs *regs)
{
        /*
         * Called using the internal vDSO SYSENTER/SYSCALL32 calling
         * convention.  Adjust regs so it looks like we entered using int80.
         */

        unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
                vdso_image_32.sym_int80_landing_pad;

        /*
         * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
         * so that 'regs->ip -= 2' lands back on an int $0x80 instruction.
         * Fix it up.
         */
        regs->ip = landing_pad;

        /*
         * Fetch EBP from where the vDSO stashed it.
         *
         * WARNING: We are in CONTEXT_USER and RCU isn't paying attention!
         */
        local_irq_enable();
        if (
#ifdef CONFIG_X86_64
                /*
                 * Micro-optimization: the pointer we're following is explicitly
                 * 32 bits, so it can't be out of range.
                 */
                __get_user(*(u32 *)&regs->bp,
                            (u32 __user __force *)(unsigned long)(u32)regs->sp)
#else
                get_user(*(u32 *)&regs->bp,
                         (u32 __user __force *)(unsigned long)(u32)regs->sp)
#endif
                ) {

                /* User code screwed up. */
                local_irq_disable();
                regs->ax = -EFAULT;
#ifdef CONFIG_CONTEXT_TRACKING
                enter_from_user_mode();
#endif
                prepare_exit_to_usermode(regs);
                return 0;       /* Keep it simple: use IRET. */
        }

        /* Now this is just like a normal syscall. */
        do_syscall_32_irqs_on(regs);

#ifdef CONFIG_X86_64
        /*
         * Opportunistic SYSRETL: if possible, try to return using SYSRETL.
         * SYSRETL is available on all 64-bit CPUs, so we don't need to
         * bother with SYSEXIT.
         *
         * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
         * because the ECX fixup above will ensure that this is essentially
         * never the case.
         */
        return regs->cs == __USER32_CS && regs->ss == __USER_DS &&
                regs->ip == landing_pad &&
                (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0;
#else
        /*
         * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT.
         *
         * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP,
         * because the ECX fixup above will ensure that this is essentially
         * never the case.
         *
         * We don't allow syscalls at all from VM86 mode, but we still
         * need to check VM, because we might be returning from sys_vm86.
         */
        return static_cpu_has(X86_FEATURE_SEP) &&
                regs->cs == __USER_CS && regs->ss == __USER_DS &&
                regs->ip == landing_pad &&
                (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0;
#endif
}
#endif