arch/x86_64/kernel/ioport.c

/*
 *	linux/arch/x86_64/kernel/ioport.c
 *
 * This contains the io-permission bitmap code - written by obz, with changes
 * by Linus.
 */

#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/ioport.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>
#include <linux/stddef.h>

/* Set EXTENT bits starting at BASE in BITMAP to value TURN_ON. */
static void set_bitmap(unsigned long *bitmap, short base, short extent, int new_value)
{
	int i;
		if (new_value)
		for (i = base; i < base + extent; i++) 
			__set_bit(i, bitmap); 
		else
		for (i = base; i < base + extent; i++) 
			clear_bit(i, bitmap); 
}

/*
 * this changes the io permissions bitmap in the current task.
 */
asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
{
	struct thread_struct * t = &current->thread;
	struct tss_struct * tss = init_tss + smp_processor_id();

	if ((from + num <= from) || (from + num > IO_BITMAP_SIZE*32))
		return -EINVAL;
	if (turn_on && !capable(CAP_SYS_RAWIO))
		return -EPERM;
	/*
	 * If it's the first ioperm() call in this thread's lifetime, set the
	 * IO bitmap up. ioperm() is much less timing critical than clone(),
	 * this is why we delay this operation until now:
	 */
 	if (!t->io_bitmap_ptr) {
		t->io_bitmap_ptr = kmalloc((IO_BITMAP_SIZE+1)*4, GFP_KERNEL);
		if (!t->io_bitmap_ptr) 
			return -ENOMEM; 

		memset(t->io_bitmap_ptr,0xff,(IO_BITMAP_SIZE+1)*4);
		/*
		 * this activates it in the TSS
		 */
	}

	/*
	 * do it in the per-thread copy and in the TSS ...
	 */
	set_bitmap((unsigned long *) t->io_bitmap_ptr, from, num, !turn_on);
	if (tss->io_map_base != IO_BITMAP_OFFSET) { 
		memcpy(tss->io_bitmap, t->io_bitmap_ptr, sizeof(tss->io_bitmap));
		tss->io_map_base = IO_BITMAP_OFFSET;
	} else { 
	set_bitmap((unsigned long *) tss->io_bitmap, from, num, !turn_on);
	}

	return 0;
}

/*
 * sys_iopl has to be used when you want to access the IO ports
 * beyond the 0x3ff range: to get the full 65536 ports bitmapped
 * you'd need 8kB of bitmaps/process, which is a bit excessive.
 *
 * Here we just change the eflags value on the stack: we allow
 * only the super-user to do it. This depends on the stack-layout
 * on system-call entry - see also fork() and the signal handling
 * code.
 */

asmlinkage long sys_iopl(unsigned int level, struct pt_regs *regs)
{
	unsigned int old = (regs->eflags >> 12) & 3;

	if (level > 3)
		return -EINVAL;
	/* Trying to gain more privileges? */
	if (level > old) {
		if (!capable(CAP_SYS_RAWIO))
			return -EPERM;
	}
	regs->eflags = (regs->eflags &~ 0x3000UL) | (level << 12);
	return 0;
}