linux/arch/x86/kernel/ioport.c

// SPDX-License-Identifier: GPL-2.0
/*
 * This contains the io-permission bitmap code - written by obz, with changes
 * by Linus. 32/64 bits code unification by Miguel Botón.
 */
#include <linux/capability.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/bitmap.h>
#include <linux/ioport.h>
#include <linux/sched.h>
#include <linux/slab.h>

#include <asm/io_bitmap.h>
#include <asm/desc.h>
#include <asm/syscalls.h>

#ifdef CONFIG_X86_IOPL_IOPERM

static atomic64_t io_bitmap_sequence;

void io_bitmap_share(struct task_struct *tsk)
{ … }

static void task_update_io_bitmap(struct task_struct *tsk)
{ … }

void io_bitmap_exit(struct task_struct *tsk)
{ … }

/*
 * This changes the io permissions bitmap in the current task.
 */
long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
{ … }

SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on)
{ … }

/*
 * The sys_iopl functionality depends on the level argument, which if
 * granted for the task is used to enable access to all 65536 I/O ports.
 *
 * This does not use the IOPL mechanism provided by the CPU as that would
 * also allow the user space task to use the CLI/STI instructions.
 *
 * Disabling interrupts in a user space task is dangerous as it might lock
 * up the machine and the semantics vs. syscalls and exceptions is
 * undefined.
 *
 * Setting IOPL to level 0-2 is disabling I/O permissions. Level 3
 * 3 enables them.
 *
 * IOPL is strictly per thread and inherited on fork.
 */
SYSCALL_DEFINE1(iopl, unsigned int, level)
{ … }

#else /* CONFIG_X86_IOPL_IOPERM */

long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
{
	return -ENOSYS;
}
SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on)
{
	return -ENOSYS;
}

SYSCALL_DEFINE1(iopl, unsigned int, level)
{
	return -ENOSYS;
}
#endif