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 thread_struct *t = ¤t->thread; 39 40 if (t->iopl_emul == 3 || t->io_bitmap) { 41 /* TSS update is handled on exit to user space */ 42 set_thread_flag(TIF_IO_BITMAP); 43 } else { 44 clear_thread_flag(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(void) 53 { 54 struct io_bitmap *iobm = current->thread.io_bitmap; 55 56 current->thread.io_bitmap = NULL; 57 task_update_io_bitmap(); 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 = ¤t->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(); 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(); 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 = ¤t->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(); 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 216