ioport.c

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/*
 * 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 <linux/bitmap.h>
#include <asm/syscalls.h>

/*
 * 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());

    if (turn_on)
        bitmap_clear(t->io_bitmap_ptr, from, num);
    else
        bitmap_set(t->io_bitmap_ptr, from, num);

    /*
     * 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;

    /* Update the TSS: */
    memcpy(tss->io_bitmap, t->io_bitmap_ptr, bytes_updated);

    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.
 */
long sys_iopl(unsigned int level, struct pt_regs *regs)
{
    unsigned int old = (regs->flags >> 12) & 3;
    struct thread_struct *t = &current->thread;

    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);
    t->iopl = level << 12;
    set_iopl_mask(t->iopl);

    return 0;
}