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