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2024-09-20 a36159eec6ca17402b0e146b86efaf76568dc353 
 kernel/arch/x86/kernel/ioport.c
....@@ -3,35 +3,75 @@
33  * This contains the io-permission bitmap code - written by obz, with changes
44  * by Linus. 32/64 bits code unification by Miguel Botón.
55  */
6
-
7
-#include <linux/sched.h>
8
-#include <linux/sched/task_stack.h>
9
-#include <linux/kernel.h>
106 #include <linux/capability.h>
11
-#include <linux/errno.h>
12
-#include <linux/types.h>
13
-#include <linux/ioport.h>
14
-#include <linux/smp.h>
15
-#include <linux/stddef.h>
16
-#include <linux/slab.h>
17
-#include <linux/thread_info.h>
7
+#include <linux/security.h>
188 #include <linux/syscalls.h>
199 #include <linux/bitmap.h>
20
-#include <asm/syscalls.h>
10
+#include <linux/ioport.h>
11
+#include <linux/sched.h>
12
+#include <linux/slab.h>
13
+
14
+#include <asm/io_bitmap.h>
2115 #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(&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
+
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
+
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
+}
2261 
2362 /*
24
- * this changes the io permissions bitmap in the current task.
63
+ * This changes the io permissions bitmap in the current task.
2564  */
2665 long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
2766 {
2867 	struct thread_struct *t = &current->thread;
29
-	struct tss_struct *tss;
30
-	unsigned int i, max_long, bytes, bytes_updated;
68
+	unsigned int i, max_long;
69
+	struct io_bitmap *iobm;
3170 
3271 	if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
3372 		return -EINVAL;
34
-	if (turn_on && !capable(CAP_SYS_RAWIO))
73
+	if (turn_on && (!capable(CAP_SYS_RAWIO) ||
74
+			security_locked_down(LOCKDOWN_IOPORT)))
3575 		return -EPERM;
3676 
3777 	/*
....@@ -39,59 +79,72 @@
3979 	 * IO bitmap up. ioperm() is much less timing critical than clone(),
4080 	 * this is why we delay this operation until now:
4181 	 */
42
-	if (!t->io_bitmap_ptr) {
43
-		unsigned long *bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
44
-
45
-		if (!bitmap)
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)
4689 			return -ENOMEM;
4790 
48
-		memset(bitmap, 0xff, IO_BITMAP_BYTES);
49
-		t->io_bitmap_ptr = bitmap;
50
-		set_thread_flag(TIF_IO_BITMAP);
51
-
52
-		/*
53
-		 * Now that we have an IO bitmap, we need our TSS limit to be
54
-		 * correct.  It's fine if we are preempted after doing this:
55
-		 * with TIF_IO_BITMAP set, context switches will keep our TSS
56
-		 * limit correct.
57
-		 */
58
-		preempt_disable();
59
-		refresh_tss_limit();
60
-		preempt_enable();
91
+		memset(iobm->bitmap, 0xff, sizeof(iobm->bitmap));
92
+		refcount_set(&iobm->refcnt, 1);
6193 	}
6294 
6395 	/*
64
-	 * do it in the per-thread copy and in the TSS ...
65
-	 *
66
-	 * Disable preemption via get_cpu() - we must not switch away
67
-	 * because the ->io_bitmap_max value must match the bitmap
68
-	 * contents:
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.
6999 	 */
70
-	tss = &per_cpu(cpu_tss_rw, get_cpu());
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
+	}
71107 
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
+	 */
72121 	if (turn_on)
73
-		bitmap_clear(t->io_bitmap_ptr, from, num);
122
+		bitmap_clear(iobm->bitmap, from, num);
74123 	else
75
-		bitmap_set(t->io_bitmap_ptr, from, num);
124
+		bitmap_set(iobm->bitmap, from, num);
76125 
77126 	/*
78127 	 * Search for a (possibly new) maximum. This is simple and stupid,
79128 	 * to keep it obviously correct:
80129 	 */
81
-	max_long = 0;
82
-	for (i = 0; i < IO_BITMAP_LONGS; i++)
83
-		if (t->io_bitmap_ptr[i] != ~0UL)
130
+	max_long = UINT_MAX;
131
+	for (i = 0; i < IO_BITMAP_LONGS; i++) {
132
+		if (iobm->bitmap[i] != ~0UL)
84133 			max_long = i;
134
+	}
135
+	/* All permissions dropped? */
136
+	if (max_long == UINT_MAX) {
137
+		io_bitmap_exit(current);
138
+		return 0;
139
+	}
85140 
86
-	bytes = (max_long + 1) * sizeof(unsigned long);
87
-	bytes_updated = max(bytes, t->io_bitmap_max);
141
+	iobm->max = (max_long + 1) * sizeof(unsigned long);
88142 
89
-	t->io_bitmap_max = bytes;
90
-
91
-	/* Update the TSS: */
92
-	memcpy(tss->io_bitmap, t->io_bitmap_ptr, bytes_updated);
93
-
94
-	put_cpu();
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);
95148 
96149 	return 0;
97150 }
....@@ -102,37 +155,61 @@
102155 }
103156 
104157 /*
105
- * sys_iopl has to be used when you want to access the IO ports
106
- * beyond the 0x3ff range: to get the full 65536 ports bitmapped
107
- * you'd need 8kB of bitmaps/process, which is a bit excessive.
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.
108160  *
109
- * Here we just change the flags value on the stack: we allow
110
- * only the super-user to do it. This depends on the stack-layout
111
- * on system-call entry - see also fork() and the signal handling
112
- * code.
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.
113172  */
114173 SYSCALL_DEFINE1(iopl, unsigned int, level)
115174 {
116
-	struct pt_regs *regs = current_pt_regs();
117175 	struct thread_struct *t = &current->thread;
118
-
119
-	/*
120
-	 * Careful: the IOPL bits in regs->flags are undefined under Xen PV
121
-	 * and changing them has no effect.
122
-	 */
123
-	unsigned int old = t->iopl >> X86_EFLAGS_IOPL_BIT;
176
+	unsigned int old;
124177 
125178 	if (level > 3)
126179 		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
+
127187 	/* Trying to gain more privileges? */
128188 	if (level > old) {
129
-		if (!capable(CAP_SYS_RAWIO))
189
+		if (!capable(CAP_SYS_RAWIO) ||
190
+		    security_locked_down(LOCKDOWN_IOPORT))
130191 			return -EPERM;
131192 	}
132
-	regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) |
133
-		(level << X86_EFLAGS_IOPL_BIT);
134
-	t->iopl = level << X86_EFLAGS_IOPL_BIT;
135
-	set_iopl_mask(t->iopl);
193
+
194
+	t->iopl_emul = level;
195
+	task_update_io_bitmap(current);
136196 
137197 	return 0;
138198 }
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