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 
io_bitmap_share(struct task_struct * tsk)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(&current->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 
task_update_io_bitmap(struct task_struct * tsk)36 static void task_update_io_bitmap(struct task_struct *tsk)
37 {
38 	struct thread_struct *t = &tsk->thread;
39 
40 	if (t->iopl_emul == 3 || t->io_bitmap) {
41 		/* TSS update is handled on exit to user space */
42 		set_tsk_thread_flag(tsk, TIF_IO_BITMAP);
43 	} else {
44 		clear_tsk_thread_flag(tsk, TIF_IO_BITMAP);
45 		/* Invalidate TSS */
46 		preempt_disable();
47 		tss_update_io_bitmap();
48 		preempt_enable();
49 	}
50 }
51 
io_bitmap_exit(struct task_struct * tsk)52 void io_bitmap_exit(struct task_struct *tsk)
53 {
54 	struct io_bitmap *iobm = tsk->thread.io_bitmap;
55 
56 	tsk->thread.io_bitmap = NULL;
57 	task_update_io_bitmap(tsk);
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  */
ksys_ioperm(unsigned long from,unsigned long num,int turn_on)65 long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
66 {
67 	struct thread_struct *t = &current->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(current);
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(current);
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 
SYSCALL_DEFINE3(ioperm,unsigned long,from,unsigned long,num,int,turn_on)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  */
SYSCALL_DEFINE1(iopl,unsigned int,level)173 SYSCALL_DEFINE1(iopl, unsigned int, level)
174 {
175 	struct thread_struct *t = &current->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(current);
196 
197 	return 0;
198 }
199 
200 #else /* CONFIG_X86_IOPL_IOPERM */
201 
ksys_ioperm(unsigned long from,unsigned long num,int turn_on)202 long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
203 {
204 	return -ENOSYS;
205 }
SYSCALL_DEFINE3(ioperm,unsigned long,from,unsigned long,num,int,turn_on)206 SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on)
207 {
208 	return -ENOSYS;
209 }
210 
SYSCALL_DEFINE1(iopl,unsigned int,level)211 SYSCALL_DEFINE1(iopl, unsigned int, level)
212 {
213 	return -ENOSYS;
214 }
215 #endif
216