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