ioport.c

  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
 20static atomic64_t io_bitmap_sequence;
 21
 22void 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
 36static 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
 53void 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 */
 71long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
 72{
 73	struct thread_struct *t = &current->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
158SYSCALL_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 */
179SYSCALL_DEFINE1(iopl, unsigned int, level)
180{
181	struct thread_struct *t = &current->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
207long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
208{
209	return -ENOSYS;
210}
211SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on)
212{
213	return -ENOSYS;
214}
215
216SYSCALL_DEFINE1(iopl, unsigned int, level)
217{
218	return -ENOSYS;
219}
220#endif