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 #include <linux/capability.h>
   7 #include <linux/security.h>
   8 #include <linux/syscalls.h>
   9 #include <linux/bitmap.h>
  10 #include <linux/ioport.h>
  11 #include <linux/sched.h>
  12 #include <linux/slab.h>
  13
  14 #include <asm/io_bitmap.h>
  15 #include <asm/desc.h>
  16 #include <asm/syscalls.h>
  17
  18 #ifdef CONFIG_X86_IOPL_IOPERM
  19
  20 static atomic64_t io_bitmap_sequence;
  21
  22 void io_bitmap_share(struct task_struct *tsk)
  23 {
  24         /* Can be NULL when current->thread.iopl_emul == 3 */
  25         if (current->thread.io_bitmap) {
  26                 /*
  27                  * Take a refcount on current's bitmap. It can be used by
  28                  * both tasks as long as none of them changes the bitmap.
  29                  */
  30                 refcount_inc(&current->thread.io_bitmap->refcnt);
  31                 tsk->thread.io_bitmap = current->thread.io_bitmap;
  32         }
  33         set_tsk_thread_flag(tsk, TIF_IO_BITMAP);
  34 }
  35
  36 static void task_update_io_bitmap(struct task_struct *tsk)
  37 {
  38         struct thread_struct *t = &tsk->thread;
  39
  40         if (t->iopl_emul == 3 || t->io_bitmap) {
  41                 /* TSS update is handled on exit to user space */
  42                 set_tsk_thread_flag(tsk, TIF_IO_BITMAP);
  43         } else {
  44                 clear_tsk_thread_flag(tsk, TIF_IO_BITMAP);
  45                 /* Invalidate TSS */
  46                 preempt_disable();
  47                 tss_update_io_bitmap();
  48                 preempt_enable();
  49         }
  50 }
  51
  52 void io_bitmap_exit(struct task_struct *tsk)
  53 {
  54         struct io_bitmap *iobm = tsk->thread.io_bitmap;
  55
  56         tsk->thread.io_bitmap = NULL;
  57         task_update_io_bitmap(tsk);
  58         if (iobm && refcount_dec_and_test(&iobm->refcnt))
  59                 kfree(iobm);
  60 }
  61
  62 /*
  63  * This changes the io permissions bitmap in the current task.
  64  */
  65 long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
  66 {
  67         struct thread_struct *t = &current->thread;
  68         unsigned int i, max_long;
  69         struct io_bitmap *iobm;
  70
  71         if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
  72                 return -EINVAL;
  73         if (turn_on && (!capable(CAP_SYS_RAWIO) ||
  74                         security_locked_down(LOCKDOWN_IOPORT)))
  75                 return -EPERM;
  76
  77         /*
  78          * If it's the first ioperm() call in this thread's lifetime, set the
  79          * IO bitmap up. ioperm() is much less timing critical than clone(),
  80          * this is why we delay this operation until now:
  81          */
  82         iobm = t->io_bitmap;
  83         if (!iobm) {
  84                 /* No point to allocate a bitmap just to clear permissions */
  85                 if (!turn_on)
  86                         return 0;
  87                 iobm = kmalloc(sizeof(*iobm), GFP_KERNEL);
  88                 if (!iobm)
  89                         return -ENOMEM;
  90
  91                 memset(iobm->bitmap, 0xff, sizeof(iobm->bitmap));
  92                 refcount_set(&iobm->refcnt, 1);
  93         }
  94
  95         /*
  96          * If the bitmap is not shared, then nothing can take a refcount as
  97          * current can obviously not fork at the same time. If it's shared
  98          * duplicate it and drop the refcount on the original one.
  99          */
 100         if (refcount_read(&iobm->refcnt) > 1) {
 101                 iobm = kmemdup(iobm, sizeof(*iobm), GFP_KERNEL);
 102                 if (!iobm)
 103                         return -ENOMEM;
 104                 refcount_set(&iobm->refcnt, 1);
 105                 io_bitmap_exit(current);
 106         }
 107
 108         /*
 109          * Store the bitmap pointer (might be the same if the task already
 110          * head one). Must be done here so freeing the bitmap when all
 111          * permissions are dropped has the pointer set up.
 112          */
 113         t->io_bitmap = iobm;
 114         /* Mark it active for context switching and exit to user mode */
 115         set_thread_flag(TIF_IO_BITMAP);
 116
 117         /*
 118          * Update the tasks bitmap. The update of the TSS bitmap happens on
 119          * exit to user mode. So this needs no protection.
 120          */
 121         if (turn_on)
 122                 bitmap_clear(iobm->bitmap, from, num);
 123         else
 124                 bitmap_set(iobm->bitmap, from, num);
 125
 126         /*
 127          * Search for a (possibly new) maximum. This is simple and stupid,
 128          * to keep it obviously correct:
 129          */
 130         max_long = UINT_MAX;
 131         for (i = 0; i < IO_BITMAP_LONGS; i++) {
 132                 if (iobm->bitmap[i] != ~0UL)
 133                         max_long = i;
 134         }
 135         /* All permissions dropped? */
 136         if (max_long == UINT_MAX) {
 137                 io_bitmap_exit(current);
 138                 return 0;
 139         }
 140
 141         iobm->max = (max_long + 1) * sizeof(unsigned long);
 142
 143         /*
 144          * Update the sequence number to force a TSS update on return to
 145          * user mode.
 146          */
 147         iobm->sequence = atomic64_add_return(1, &io_bitmap_sequence);
 148
 149         return 0;
 150 }
 151
 152 SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on)
 153 {
 154         return ksys_ioperm(from, num, turn_on);
 155 }
 156
 157 /*
 158  * The sys_iopl functionality depends on the level argument, which if
 159  * granted for the task is used to enable access to all 65536 I/O ports.
 160  *
 161  * This does not use the IOPL mechanism provided by the CPU as that would
 162  * also allow the user space task to use the CLI/STI instructions.
 163  *
 164  * Disabling interrupts in a user space task is dangerous as it might lock
 165  * up the machine and the semantics vs. syscalls and exceptions is
 166  * undefined.
 167  *
 168  * Setting IOPL to level 0-2 is disabling I/O permissions. Level 3
 169  * 3 enables them.
 170  *
 171  * IOPL is strictly per thread and inherited on fork.
 172  */
 173 SYSCALL_DEFINE1(iopl, unsigned int, level)
 174 {
 175         struct thread_struct *t = &current->thread;
 176         unsigned int old;
 177
 178         if (level > 3)
 179                 return -EINVAL;
 180
 181         old = t->iopl_emul;
 182
 183         /* No point in going further if nothing changes */
 184         if (level == old)
 185                 return 0;
 186
 187         /* Trying to gain more privileges? */
 188         if (level > old) {
 189                 if (!capable(CAP_SYS_RAWIO) ||
 190                     security_locked_down(LOCKDOWN_IOPORT))
 191                         return -EPERM;
 192         }
 193
 194         t->iopl_emul = level;
 195         task_update_io_bitmap(current);
 196
 197         return 0;
 198 }
 199
 200 #else /* CONFIG_X86_IOPL_IOPERM */
 201
 202 long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
 203 {
 204         return -ENOSYS;
 205 }
 206 SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on)
 207 {
 208         return -ENOSYS;
 209 }
 210
 211 SYSCALL_DEFINE1(iopl, unsigned int, level)
 212 {
 213         return -ENOSYS;
 214 }
 215 #endif