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Linux/arch/x86/kernel/ioport.c

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  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
215 

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