root/arch/x86/kernel/ioport.c

DEFINITIONS

1. set_bitmap
2. sys_ioperm
3. do_iopl
4. sys_iopl
5. sys_iopl

/*
 * This contains the io-permission bitmap code - written by obz, with changes
 * by Linus. 32/64 bits code unification by Miguel Botón.
 */

#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/capability.h>
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/ioport.h>
#include <linux/smp.h>
#include <linux/stddef.h>
#include <linux/slab.h>
#include <linux/thread_info.h>
#include <linux/syscalls.h>
#include <asm/syscalls.h>

/* Set EXTENT bits starting at BASE in BITMAP to value TURN_ON. */
static void set_bitmap(unsigned long *bitmap, unsigned int base,
                       unsigned int extent, int new_value)
{
        unsigned int i;

        for (i = base; i < base + extent; i++) {
                if (new_value)
                        __set_bit(i, bitmap);
                else
                        __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;
        unsigned int i, max_long, bytes, bytes_updated;

        if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
                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) {
                unsigned long *bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);

                if (!bitmap)
                        return -ENOMEM;

                memset(bitmap, 0xff, IO_BITMAP_BYTES);
                t->io_bitmap_ptr = bitmap;
                set_thread_flag(TIF_IO_BITMAP);
        }

        /*
         * do it in the per-thread copy and in the TSS ...
         *
         * Disable preemption via get_cpu() - we must not switch away
         * because the ->io_bitmap_max value must match the bitmap
         * contents:
         */
        tss = &per_cpu(init_tss, get_cpu());

        set_bitmap(t->io_bitmap_ptr, from, num, !turn_on);

        /*
         * Search for a (possibly new) maximum. This is simple and stupid,
         * to keep it obviously correct:
         */
        max_long = 0;
        for (i = 0; i < IO_BITMAP_LONGS; i++)
                if (t->io_bitmap_ptr[i] != ~0UL)
                        max_long = i;

        bytes = (max_long + 1) * sizeof(unsigned long);
        bytes_updated = max(bytes, t->io_bitmap_max);

        t->io_bitmap_max = bytes;

#ifdef CONFIG_X86_32
        /*
         * Sets the lazy trigger so that the next I/O operation will
         * reload the correct bitmap.
         * Reset the owner so that a process switch will not set
         * tss->io_bitmap_base to IO_BITMAP_OFFSET.
         */
        tss->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET_LAZY;
        tss->io_bitmap_owner = NULL;
#else
        /* Update the TSS: */
        memcpy(tss->io_bitmap, t->io_bitmap_ptr, bytes_updated);
#endif

        put_cpu();

        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 flags 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.
 */
static int do_iopl(unsigned int level, struct pt_regs *regs)
{
        unsigned int old = (regs->flags >> 12) & 3;

        if (level > 3)
                return -EINVAL;
        /* Trying to gain more privileges? */
        if (level > old) {
                if (!capable(CAP_SYS_RAWIO))
                        return -EPERM;
        }
        regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) | (level << 12);

        return 0;
}

#ifdef CONFIG_X86_32
asmlinkage long sys_iopl(unsigned long regsp)
{
        struct pt_regs *regs = (struct pt_regs *)&regsp;
        unsigned int level = regs->bx;
        struct thread_struct *t = &current->thread;
        int rc;

        rc = do_iopl(level, regs);
        if (rc < 0)
                goto out;

        t->iopl = level << 12;
        set_iopl_mask(t->iopl);
out:
        return rc;
}
#else
asmlinkage long sys_iopl(unsigned int level, struct pt_regs *regs)
{
        return do_iopl(level, regs);
}
#endif