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(¤t->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 = ¤t->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 = ¤t->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 = ¤t->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