// SPDX-License-Identifier: GPL-2.0-only
/*
 * common.c - C code for kernel entry and exit
 * Copyright (c) 2015 Andrew Lutomirski
 *
 * 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/sched/task_stack.h>
#include <linux/entry-common.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/errno.h>
#include <linux/ptrace.h>
#include <linux/export.h>
#include <linux/nospec.h>
#include <linux/syscalls.h>
#include <linux/uaccess.h>

#ifdef CONFIG_XEN_PV
#include <xen/xen-ops.h>
#include <xen/events.h>
#endif

#include <asm/desc.h>
#include <asm/traps.h>
#include <asm/vdso.h>
#include <asm/cpufeature.h>
#include <asm/fpu/api.h>
#include <asm/nospec-branch.h>
#include <asm/io_bitmap.h>
#include <asm/syscall.h>
#include <asm/irq_stack.h>

#ifdef CONFIG_X86_64

static __always_inline bool do_syscall_x64(struct pt_regs *regs, int nr)
{
        /*
         * Convert negative numbers to very high and thus out of range
         * numbers for comparisons.
         */
        unsigned int unr = nr;

        if (likely(unr < NR_syscalls)) {
                unr = array_index_nospec(unr, NR_syscalls);
                regs->ax = sys_call_table[unr](regs);
                return true;
        }
        return false;
}

static __always_inline bool do_syscall_x32(struct pt_regs *regs, int nr)
{
        /*
         * Adjust the starting offset of the table, and convert numbers
         * < __X32_SYSCALL_BIT to very high and thus out of range
         * numbers for comparisons.
         */
        unsigned int xnr = nr - __X32_SYSCALL_BIT;

        if (IS_ENABLED(CONFIG_X86_X32_ABI) && likely(xnr < X32_NR_syscalls)) {
                xnr = array_index_nospec(xnr, X32_NR_syscalls);
                regs->ax = x32_sys_call_table[xnr](regs);
                return true;
        }
        return false;
}

__visible noinstr void do_syscall_64(struct pt_regs *regs, int nr)
{
        add_random_kstack_offset();
        nr = syscall_enter_from_user_mode(regs, nr);

        instrumentation_begin();

        if (!do_syscall_x64(regs, nr) && !do_syscall_x32(regs, nr) && nr != -1) {
                /* Invalid system call, but still a system call. */
                regs->ax = __x64_sys_ni_syscall(regs);
        }

        instrumentation_end();
        syscall_exit_to_user_mode(regs);
}
#endif

#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
static __always_inline int syscall_32_enter(struct pt_regs *regs)
{
        if (IS_ENABLED(CONFIG_IA32_EMULATION))
                current_thread_info()->status |= TS_COMPAT;

        return (int)regs->orig_ax;
}

/*
 * Invoke a 32-bit syscall.  Called with IRQs on in CONTEXT_KERNEL.
 */
static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs, int nr)
{
        /*
         * Convert negative numbers to very high and thus out of range
         * numbers for comparisons.
         */
        unsigned int unr = nr;

        if (likely(unr < IA32_NR_syscalls)) {
                unr = array_index_nospec(unr, IA32_NR_syscalls);
                regs->ax = ia32_sys_call_table[unr](regs);
        } else if (nr != -1) {
                regs->ax = __ia32_sys_ni_syscall(regs);
        }
}

/* Handles int $0x80 */
__visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
{
        int nr = syscall_32_enter(regs);

        add_random_kstack_offset();
        /*
         * Subtlety here: if ptrace pokes something larger than 2^31-1 into
         * orig_ax, the int return value truncates it. This matches
         * the semantics of syscall_get_nr().
         */
        nr = syscall_enter_from_user_mode(regs, nr);
        instrumentation_begin();

        do_syscall_32_irqs_on(regs, nr);

        instrumentation_end();
        syscall_exit_to_user_mode(regs);
}

static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
{
        int nr = syscall_32_enter(regs);
        int res;

        add_random_kstack_offset();
        /*
         * This cannot use syscall_enter_from_user_mode() as it has to
         * fetch EBP before invoking any of the syscall entry work
         * functions.
         */
        syscall_enter_from_user_mode_prepare(regs);

        instrumentation_begin();
        /* Fetch EBP from where the vDSO stashed it. */
        if (IS_ENABLED(CONFIG_X86_64)) {
                /*
                 * Micro-optimization: the pointer we're following is
                 * explicitly 32 bits, so it can't be out of range.
                 */
                res = __get_user(*(u32 *)&regs->bp,
                         (u32 __user __force *)(unsigned long)(u32)regs->sp);
        } else {
                res = get_user(*(u32 *)&regs->bp,
                       (u32 __user __force *)(unsigned long)(u32)regs->sp);
        }

        if (res) {
                /* User code screwed up. */
                regs->ax = -EFAULT;

                local_irq_disable();
                instrumentation_end();
                irqentry_exit_to_user_mode(regs);
                return false;
        }

        nr = syscall_enter_from_user_mode_work(regs, nr);

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

        instrumentation_end();
        syscall_exit_to_user_mode(regs);
        return true;
}

/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
__visible noinstr 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;

        /* Invoke the syscall. If it failed, keep it simple: use IRET. */
        if (!__do_fast_syscall_32(regs))
                return 0;

#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
}

/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
__visible noinstr long do_SYSENTER_32(struct pt_regs *regs)
{
        /* SYSENTER loses RSP, but the vDSO saved it in RBP. */
        regs->sp = regs->bp;

        /* SYSENTER clobbers EFLAGS.IF.  Assume it was set in usermode. */
        regs->flags |= X86_EFLAGS_IF;

        return do_fast_syscall_32(regs);
}
#endif

SYSCALL_DEFINE0(ni_syscall)
{
        return -ENOSYS;
}

#ifdef CONFIG_XEN_PV
#ifndef CONFIG_PREEMPTION
/*
 * Some hypercalls issued by the toolstack can take many 10s of
 * seconds. Allow tasks running hypercalls via the privcmd driver to
 * be voluntarily preempted even if full kernel preemption is
 * disabled.
 *
 * Such preemptible hypercalls are bracketed by
 * xen_preemptible_hcall_begin() and xen_preemptible_hcall_end()
 * calls.
 */
DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);

/*
 * In case of scheduling the flag must be cleared and restored after
 * returning from schedule as the task might move to a different CPU.
 */
static __always_inline bool get_and_clear_inhcall(void)
{
        bool inhcall = __this_cpu_read(xen_in_preemptible_hcall);

        __this_cpu_write(xen_in_preemptible_hcall, false);
        return inhcall;
}

static __always_inline void restore_inhcall(bool inhcall)
{
        __this_cpu_write(xen_in_preemptible_hcall, inhcall);
}
#else
static __always_inline bool get_and_clear_inhcall(void) { return false; }
static __always_inline void restore_inhcall(bool inhcall) { }
#endif

static void __xen_pv_evtchn_do_upcall(struct pt_regs *regs)
{
        struct pt_regs *old_regs = set_irq_regs(regs);

        inc_irq_stat(irq_hv_callback_count);

        xen_hvm_evtchn_do_upcall();

        set_irq_regs(old_regs);
}

__visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs)
{
        irqentry_state_t state = irqentry_enter(regs);
        bool inhcall;

        instrumentation_begin();
        run_sysvec_on_irqstack_cond(__xen_pv_evtchn_do_upcall, regs);

        inhcall = get_and_clear_inhcall();
        if (inhcall && !WARN_ON_ONCE(state.exit_rcu)) {
                irqentry_exit_cond_resched();
                instrumentation_end();
                restore_inhcall(inhcall);
        } else {
                instrumentation_end();
                irqentry_exit(regs, state);
        }
}
#endif /* CONFIG_XEN_PV */