LXR linux/arch/x86/kernel/ioport.c

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * This contains the io-permission bitmap code - written by obz, with changes
   4 * by Linus. 32/64 bits code unification by Miguel Botón.
   5 */
   6
   7#include <linux/sched.h>
   8#include <linux/sched/task_stack.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#include <linux/bitmap.h>
  20#include <asm/syscalls.h>
  21#include <asm/desc.h>
  22
  23/*
  24 * this changes the io permissions bitmap in the current task.
  25 */
  26long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
  27{
  28        struct thread_struct *t = &current->thread;
  29        struct tss_struct *tss;
  30        unsigned int i, max_long, bytes, bytes_updated;
  31
  32        if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
  33                return -EINVAL;
  34        if (turn_on && (!capable(CAP_SYS_RAWIO) ||
  35                        kernel_is_locked_down("ioperm")))
  36                return -EPERM;
  37
  38        /*
  39         * If it's the first ioperm() call in this thread's lifetime, set the
  40         * IO bitmap up. ioperm() is much less timing critical than clone(),
  41         * this is why we delay this operation until now:
  42         */
  43        if (!t->io_bitmap_ptr) {
  44                unsigned long *bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
  45
  46                if (!bitmap)
  47                        return -ENOMEM;
  48
  49                memset(bitmap, 0xff, IO_BITMAP_BYTES);
  50                t->io_bitmap_ptr = bitmap;
  51                set_thread_flag(TIF_IO_BITMAP);
  52
  53                /*
  54                 * Now that we have an IO bitmap, we need our TSS limit to be
  55                 * correct.  It's fine if we are preempted after doing this:
  56                 * with TIF_IO_BITMAP set, context switches will keep our TSS
  57                 * limit correct.
  58                 */
  59                preempt_disable();
  60                refresh_tss_limit();
  61                preempt_enable();
  62        }
  63
  64        /*
  65         * do it in the per-thread copy and in the TSS ...
  66         *
  67         * Disable preemption via get_cpu() - we must not switch away
  68         * because the ->io_bitmap_max value must match the bitmap
  69         * contents:
  70         */
  71        tss = &per_cpu(cpu_tss_rw, get_cpu());
  72
  73        if (turn_on)
  74                bitmap_clear(t->io_bitmap_ptr, from, num);
  75        else
  76                bitmap_set(t->io_bitmap_ptr, from, num);
  77
  78        /*
  79         * Search for a (possibly new) maximum. This is simple and stupid,
  80         * to keep it obviously correct:
  81         */
  82        max_long = 0;
  83        for (i = 0; i < IO_BITMAP_LONGS; i++)
  84                if (t->io_bitmap_ptr[i] != ~0UL)
  85                        max_long = i;
  86
  87        bytes = (max_long + 1) * sizeof(unsigned long);
  88        bytes_updated = max(bytes, t->io_bitmap_max);
  89
  90        t->io_bitmap_max = bytes;
  91
  92        /* Update the TSS: */
  93        memcpy(tss->io_bitmap, t->io_bitmap_ptr, bytes_updated);
  94
  95        put_cpu();
  96
  97        return 0;
  98}
  99
 100SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on)
 101{
 102        return ksys_ioperm(from, num, turn_on);
 103}
 104
 105/*
 106 * sys_iopl has to be used when you want to access the IO ports
 107 * beyond the 0x3ff range: to get the full 65536 ports bitmapped
 108 * you'd need 8kB of bitmaps/process, which is a bit excessive.
 109 *
 110 * Here we just change the flags value on the stack: we allow
 111 * only the super-user to do it. This depends on the stack-layout
 112 * on system-call entry - see also fork() and the signal handling
 113 * code.
 114 */
 115SYSCALL_DEFINE1(iopl, unsigned int, level)
 116{
 117        struct pt_regs *regs = current_pt_regs();
 118        struct thread_struct *t = &current->thread;
 119
 120        /*
 121         * Careful: the IOPL bits in regs->flags are undefined under Xen PV
 122         * and changing them has no effect.
 123         */
 124        unsigned int old = t->iopl >> X86_EFLAGS_IOPL_BIT;
 125
 126        if (level > 3)
 127                return -EINVAL;
 128        /* Trying to gain more privileges? */
 129        if (level > old) {
 130                if (!capable(CAP_SYS_RAWIO) ||
 131                    kernel_is_locked_down("iopl"))
 132                        return -EPERM;
 133        }
 134        regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) |
 135                (level << X86_EFLAGS_IOPL_BIT);
 136        t->iopl = level << X86_EFLAGS_IOPL_BIT;
 137        set_iopl_mask(t->iopl);
 138
 139        return 0;
 140}
 141