xref: /openbmc/linux/arch/x86/kernel/ioport.c (revision b6dcefde)
1 /*
2  * This contains the io-permission bitmap code - written by obz, with changes
3  * by Linus. 32/64 bits code unification by Miguel Botón.
4  */
5 
6 #include <linux/sched.h>
7 #include <linux/kernel.h>
8 #include <linux/capability.h>
9 #include <linux/errno.h>
10 #include <linux/types.h>
11 #include <linux/ioport.h>
12 #include <linux/smp.h>
13 #include <linux/stddef.h>
14 #include <linux/slab.h>
15 #include <linux/thread_info.h>
16 #include <linux/syscalls.h>
17 #include <asm/syscalls.h>
18 
19 /* Set EXTENT bits starting at BASE in BITMAP to value TURN_ON. */
20 static void set_bitmap(unsigned long *bitmap, unsigned int base,
21 		       unsigned int extent, int new_value)
22 {
23 	unsigned int i;
24 
25 	for (i = base; i < base + extent; i++) {
26 		if (new_value)
27 			__set_bit(i, bitmap);
28 		else
29 			__clear_bit(i, bitmap);
30 	}
31 }
32 
33 /*
34  * this changes the io permissions bitmap in the current task.
35  */
36 asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
37 {
38 	struct thread_struct *t = &current->thread;
39 	struct tss_struct *tss;
40 	unsigned int i, max_long, bytes, bytes_updated;
41 
42 	if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
43 		return -EINVAL;
44 	if (turn_on && !capable(CAP_SYS_RAWIO))
45 		return -EPERM;
46 
47 	/*
48 	 * If it's the first ioperm() call in this thread's lifetime, set the
49 	 * IO bitmap up. ioperm() is much less timing critical than clone(),
50 	 * this is why we delay this operation until now:
51 	 */
52 	if (!t->io_bitmap_ptr) {
53 		unsigned long *bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
54 
55 		if (!bitmap)
56 			return -ENOMEM;
57 
58 		memset(bitmap, 0xff, IO_BITMAP_BYTES);
59 		t->io_bitmap_ptr = bitmap;
60 		set_thread_flag(TIF_IO_BITMAP);
61 	}
62 
63 	/*
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:
69 	 */
70 	tss = &per_cpu(init_tss, get_cpu());
71 
72 	set_bitmap(t->io_bitmap_ptr, from, num, !turn_on);
73 
74 	/*
75 	 * Search for a (possibly new) maximum. This is simple and stupid,
76 	 * to keep it obviously correct:
77 	 */
78 	max_long = 0;
79 	for (i = 0; i < IO_BITMAP_LONGS; i++)
80 		if (t->io_bitmap_ptr[i] != ~0UL)
81 			max_long = i;
82 
83 	bytes = (max_long + 1) * sizeof(unsigned long);
84 	bytes_updated = max(bytes, t->io_bitmap_max);
85 
86 	t->io_bitmap_max = bytes;
87 
88 	/* Update the TSS: */
89 	memcpy(tss->io_bitmap, t->io_bitmap_ptr, bytes_updated);
90 
91 	put_cpu();
92 
93 	return 0;
94 }
95 
96 /*
97  * sys_iopl has to be used when you want to access the IO ports
98  * beyond the 0x3ff range: to get the full 65536 ports bitmapped
99  * you'd need 8kB of bitmaps/process, which is a bit excessive.
100  *
101  * Here we just change the flags value on the stack: we allow
102  * only the super-user to do it. This depends on the stack-layout
103  * on system-call entry - see also fork() and the signal handling
104  * code.
105  */
106 long sys_iopl(unsigned int level, struct pt_regs *regs)
107 {
108 	unsigned int old = (regs->flags >> 12) & 3;
109 	struct thread_struct *t = &current->thread;
110 
111 	if (level > 3)
112 		return -EINVAL;
113 	/* Trying to gain more privileges? */
114 	if (level > old) {
115 		if (!capable(CAP_SYS_RAWIO))
116 			return -EPERM;
117 	}
118 	regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) | (level << 12);
119 	t->iopl = level << 12;
120 	set_iopl_mask(t->iopl);
121 
122 	return 0;
123 }
124