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(¤t->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(void) 37 { 38 struct task_struct *tsk = current; 39 struct thread_struct *t = &tsk->thread; 40 41 if (t->iopl_emul == 3 || t->io_bitmap) { 42 /* TSS update is handled on exit to user space */ 43 set_tsk_thread_flag(tsk, TIF_IO_BITMAP); 44 } else { 45 clear_tsk_thread_flag(tsk, TIF_IO_BITMAP); 46 /* Invalidate TSS */ 47 preempt_disable(); 48 tss_update_io_bitmap(); 49 preempt_enable(); 50 } 51 } 52 53 void io_bitmap_exit(struct task_struct *tsk) 54 { 55 struct io_bitmap *iobm = tsk->thread.io_bitmap; 56 57 tsk->thread.io_bitmap = NULL; 58 /* 59 * Don't touch the TSS when invoked on a failed fork(). TSS 60 * reflects the state of @current and not the state of @tsk. 61 */ 62 if (tsk == current) 63 task_update_io_bitmap(); 64 if (iobm && refcount_dec_and_test(&iobm->refcnt)) 65 kfree(iobm); 66 } 67 68 /* 69 * This changes the io permissions bitmap in the current task. 70 */ 71 long ksys_ioperm(unsigned long from, unsigned long num, int turn_on) 72 { 73 struct thread_struct *t = ¤t->thread; 74 unsigned int i, max_long; 75 struct io_bitmap *iobm; 76 77 if ((from + num <= from) || (from + num > IO_BITMAP_BITS)) 78 return -EINVAL; 79 if (turn_on && (!capable(CAP_SYS_RAWIO) || 80 security_locked_down(LOCKDOWN_IOPORT))) 81 return -EPERM; 82 83 /* 84 * If it's the first ioperm() call in this thread's lifetime, set the 85 * IO bitmap up. ioperm() is much less timing critical than clone(), 86 * this is why we delay this operation until now: 87 */ 88 iobm = t->io_bitmap; 89 if (!iobm) { 90 /* No point to allocate a bitmap just to clear permissions */ 91 if (!turn_on) 92 return 0; 93 iobm = kmalloc(sizeof(*iobm), GFP_KERNEL); 94 if (!iobm) 95 return -ENOMEM; 96 97 memset(iobm->bitmap, 0xff, sizeof(iobm->bitmap)); 98 refcount_set(&iobm->refcnt, 1); 99 } 100 101 /* 102 * If the bitmap is not shared, then nothing can take a refcount as 103 * current can obviously not fork at the same time. If it's shared 104 * duplicate it and drop the refcount on the original one. 105 */ 106 if (refcount_read(&iobm->refcnt) > 1) { 107 iobm = kmemdup(iobm, sizeof(*iobm), GFP_KERNEL); 108 if (!iobm) 109 return -ENOMEM; 110 refcount_set(&iobm->refcnt, 1); 111 io_bitmap_exit(current); 112 } 113 114 /* 115 * Store the bitmap pointer (might be the same if the task already 116 * head one). Must be done here so freeing the bitmap when all 117 * permissions are dropped has the pointer set up. 118 */ 119 t->io_bitmap = iobm; 120 /* Mark it active for context switching and exit to user mode */ 121 set_thread_flag(TIF_IO_BITMAP); 122 123 /* 124 * Update the tasks bitmap. The update of the TSS bitmap happens on 125 * exit to user mode. So this needs no protection. 126 */ 127 if (turn_on) 128 bitmap_clear(iobm->bitmap, from, num); 129 else 130 bitmap_set(iobm->bitmap, from, num); 131 132 /* 133 * Search for a (possibly new) maximum. This is simple and stupid, 134 * to keep it obviously correct: 135 */ 136 max_long = UINT_MAX; 137 for (i = 0; i < IO_BITMAP_LONGS; i++) { 138 if (iobm->bitmap[i] != ~0UL) 139 max_long = i; 140 } 141 /* All permissions dropped? */ 142 if (max_long == UINT_MAX) { 143 io_bitmap_exit(current); 144 return 0; 145 } 146 147 iobm->max = (max_long + 1) * sizeof(unsigned long); 148 149 /* 150 * Update the sequence number to force a TSS update on return to 151 * user mode. 152 */ 153 iobm->sequence = atomic64_inc_return(&io_bitmap_sequence); 154 155 return 0; 156 } 157 158 SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on) 159 { 160 return ksys_ioperm(from, num, turn_on); 161 } 162 163 /* 164 * The sys_iopl functionality depends on the level argument, which if 165 * granted for the task is used to enable access to all 65536 I/O ports. 166 * 167 * This does not use the IOPL mechanism provided by the CPU as that would 168 * also allow the user space task to use the CLI/STI instructions. 169 * 170 * Disabling interrupts in a user space task is dangerous as it might lock 171 * up the machine and the semantics vs. syscalls and exceptions is 172 * undefined. 173 * 174 * Setting IOPL to level 0-2 is disabling I/O permissions. Level 3 175 * 3 enables them. 176 * 177 * IOPL is strictly per thread and inherited on fork. 178 */ 179 SYSCALL_DEFINE1(iopl, unsigned int, level) 180 { 181 struct thread_struct *t = ¤t->thread; 182 unsigned int old; 183 184 if (level > 3) 185 return -EINVAL; 186 187 old = t->iopl_emul; 188 189 /* No point in going further if nothing changes */ 190 if (level == old) 191 return 0; 192 193 /* Trying to gain more privileges? */ 194 if (level > old) { 195 if (!capable(CAP_SYS_RAWIO) || 196 security_locked_down(LOCKDOWN_IOPORT)) 197 return -EPERM; 198 } 199 200 t->iopl_emul = level; 201 task_update_io_bitmap(); 202 return 0; 203 } 204 205 #else /* CONFIG_X86_IOPL_IOPERM */ 206 207 long ksys_ioperm(unsigned long from, unsigned long num, int turn_on) 208 { 209 return -ENOSYS; 210 } 211 SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on) 212 { 213 return -ENOSYS; 214 } 215 216 SYSCALL_DEFINE1(iopl, unsigned int, level) 217 { 218 return -ENOSYS; 219 } 220 #endif 221