LXR linux/arch/i386/kernel/ioport.c

   1/*
   2 *      linux/arch/i386/kernel/ioport.c
   3 *
   4 * This contains the io-permission bitmap code - written by obz, with changes
   5 * by Linus.
   6 */
   7
   8#include <linux/sched.h>
   9#include <linux/kernel.h>
  10#include <linux/capability.h>
  11#include <linux/errno.h>
  12#include <linux/types.h>
  13#include <linux/ioport.h>
  14#include <linux/smp.h>
  15#include <linux/stddef.h>
  16#include <linux/slab.h>
  17#include <linux/thread_info.h>
  18#include <linux/syscalls.h>
  19
  20/* Set EXTENT bits starting at BASE in BITMAP to value TURN_ON. */
  21static void set_bitmap(unsigned long *bitmap, unsigned int base, unsigned int extent, int new_value)
  22{
  23        unsigned long mask;
  24        unsigned long *bitmap_base = bitmap + (base / BITS_PER_LONG);
  25        unsigned int low_index = base & (BITS_PER_LONG-1);
  26        int length = low_index + extent;
  27
  28        if (low_index != 0) {
  29                mask = (~0UL << low_index);
  30                if (length < BITS_PER_LONG)
  31                        mask &= ~(~0UL << length);
  32                if (new_value)
  33                        *bitmap_base++ |= mask;
  34                else
  35                        *bitmap_base++ &= ~mask;
  36                length -= BITS_PER_LONG;
  37        }
  38
  39        mask = (new_value ? ~0UL : 0UL);
  40        while (length >= BITS_PER_LONG) {
  41                *bitmap_base++ = mask;
  42                length -= BITS_PER_LONG;
  43        }
  44
  45        if (length > 0) {
  46                mask = ~(~0UL << length);
  47                if (new_value)
  48                        *bitmap_base++ |= mask;
  49                else
  50                        *bitmap_base++ &= ~mask;
  51        }
  52}
  53
  54
  55/*
  56 * this changes the io permissions bitmap in the current task.
  57 */
  58asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
  59{
  60        unsigned long i, max_long, bytes, bytes_updated;
  61        struct thread_struct * t = &current->thread;
  62        struct tss_struct * tss;
  63        unsigned long *bitmap;
  64
  65        if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
  66                return -EINVAL;
  67        if (turn_on && !capable(CAP_SYS_RAWIO))
  68                return -EPERM;
  69
  70        /*
  71         * If it's the first ioperm() call in this thread's lifetime, set the
  72         * IO bitmap up. ioperm() is much less timing critical than clone(),
  73         * this is why we delay this operation until now:
  74         */
  75        if (!t->io_bitmap_ptr) {
  76                bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
  77                if (!bitmap)
  78                        return -ENOMEM;
  79
  80                memset(bitmap, 0xff, IO_BITMAP_BYTES);
  81                t->io_bitmap_ptr = bitmap;
  82                set_thread_flag(TIF_IO_BITMAP);
  83        }
  84
  85        /*
  86         * do it in the per-thread copy and in the TSS ...
  87         *
  88         * Disable preemption via get_cpu() - we must not switch away
  89         * because the ->io_bitmap_max value must match the bitmap
  90         * contents:
  91         */
  92        tss = &per_cpu(init_tss, get_cpu());
  93
  94        set_bitmap(t->io_bitmap_ptr, from, num, !turn_on);
  95
  96        /*
  97         * Search for a (possibly new) maximum. This is simple and stupid,
  98         * to keep it obviously correct:
  99         */
 100        max_long = 0;
 101        for (i = 0; i < IO_BITMAP_LONGS; i++)
 102                if (t->io_bitmap_ptr[i] != ~0UL)
 103                        max_long = i;
 104
 105        bytes = (max_long + 1) * sizeof(long);
 106        bytes_updated = max(bytes, t->io_bitmap_max);
 107
 108        t->io_bitmap_max = bytes;
 109
 110        /*
 111         * Sets the lazy trigger so that the next I/O operation will
 112         * reload the correct bitmap.
 113         * Reset the owner so that a process switch will not set
 114         * tss->io_bitmap_base to IO_BITMAP_OFFSET.
 115         */
 116        tss->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET_LAZY;
 117        tss->io_bitmap_owner = NULL;
 118
 119        put_cpu();
 120
 121        return 0;
 122}
 123
 124/*
 125 * sys_iopl has to be used when you want to access the IO ports
 126 * beyond the 0x3ff range: to get the full 65536 ports bitmapped
 127 * you'd need 8kB of bitmaps/process, which is a bit excessive.
 128 *
 129 * Here we just change the eflags value on the stack: we allow
 130 * only the super-user to do it. This depends on the stack-layout
 131 * on system-call entry - see also fork() and the signal handling
 132 * code.
 133 */
 134
 135asmlinkage long sys_iopl(unsigned long unused)
 136{
 137        volatile struct pt_regs * regs = (struct pt_regs *) &unused;
 138        unsigned int level = regs->ebx;
 139        unsigned int old = (regs->eflags >> 12) & 3;
 140        struct thread_struct *t = &current->thread;
 141
 142        if (level > 3)
 143                return -EINVAL;
 144        /* Trying to gain more privileges? */
 145        if (level > old) {
 146                if (!capable(CAP_SYS_RAWIO))
 147                        return -EPERM;
 148        }
 149        t->iopl = level << 12;
 150        regs->eflags = (regs->eflags & ~X86_EFLAGS_IOPL) | t->iopl;
 151        set_iopl_mask(t->iopl);
 152        return 0;
 153}
 154