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32 * Mach Operating System
33 * Copyright (c) 1991 Carnegie Mellon University
34 * All Rights Reserved.
36 * Permission to use, copy, modify and distribute this software and its
37 * documentation is hereby granted, provided that both the copyright
38 * notice and this permission notice appear in all copies of the
39 * software, derivative works or modified versions, and any portions
40 * thereof, and that both notices appear in supporting documentation.
42 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
43 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
44 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
46 * Carnegie Mellon requests users of this software to return to
48 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
49 * School of Computer Science
50 * Carnegie Mellon University
51 * Pittsburgh PA 15213-3890
53 * any improvements or extensions that they make and grant Carnegie Mellon
54 * the rights to redistribute these changes.
61 * User LDT management.
62 * Each task may have its own LDT.
65 #include <kern/kalloc.h>
66 #include <kern/thread.h>
67 #include <kern/misc_protos.h>
69 #include <vm/vm_kern.h>
71 #include <i386/machdep_call.h>
72 #include <i386/user_ldt.h>
74 #include <i386/machine_routines.h>
75 #include <i386/proc_reg.h>
76 #include <i386/mp_desc.h>
78 #include <i386/thread.h>
80 #include <sys/errno.h>
82 static void user_ldt_set_action(void *);
85 * Add the descriptors to the LDT, starting with
86 * the descriptor for 'first_selector'.
93 uint32_t descs
, /* out */
96 user_ldt_t new_ldt
, old_ldt
;
97 struct real_descriptor
*dp
;
99 unsigned int min_selector
= LDTSZ_MIN
; /* do not allow the system selectors to be changed */
100 task_t task
= current_task();
101 unsigned int ldt_count
;
104 if (start_sel
!= LDT_AUTO_ALLOC
105 && (start_sel
!= 0 || num_sels
!= 0)
106 && (start_sel
< min_selector
|| start_sel
>= LDTSZ
))
108 if (start_sel
!= LDT_AUTO_ALLOC
109 && (uint64_t)start_sel
+ (uint64_t)num_sels
> LDTSZ
) /* cast to uint64_t to detect wrap-around */
114 old_ldt
= task
->i386_ldt
;
116 if (start_sel
== LDT_AUTO_ALLOC
) {
118 unsigned int null_count
;
119 struct real_descriptor null_ldt
;
121 bzero(&null_ldt
, sizeof(null_ldt
));
124 * Look for null selectors among the already-allocated
129 while (i
< old_ldt
->count
)
131 if (!memcmp(&old_ldt
->ldt
[i
++], &null_ldt
, sizeof(null_ldt
))) {
133 if (null_count
== num_sels
)
134 break; /* break out of while loop */
141 * If we broke out of the while loop, i points to the selector
142 * after num_sels null selectors. Otherwise it points to the end
143 * of the old LDTs, and null_count is the number of null selectors
146 * Either way, there are null_count null selectors just prior to
147 * the i-indexed selector, and either null_count >= num_sels,
148 * or we're at the end, so we can extend.
150 start_sel
= old_ldt
->start
+ i
- null_count
;
152 start_sel
= LDTSZ_MIN
;
155 if ((uint64_t)start_sel
+ (uint64_t)num_sels
> LDTSZ
) {
161 if (start_sel
== 0 && num_sels
== 0) {
168 unsigned int begin_sel
= start_sel
;
169 unsigned int end_sel
= begin_sel
+ num_sels
;
171 if (old_ldt
!= NULL
) {
172 if (old_ldt
->start
< begin_sel
)
173 begin_sel
= old_ldt
->start
;
174 if (old_ldt
->start
+ old_ldt
->count
> end_sel
)
175 end_sel
= old_ldt
->start
+ old_ldt
->count
;
178 ldt_count
= end_sel
- begin_sel
;
179 /* XXX allocation under task lock */
180 new_ldt
= (user_ldt_t
)kalloc(sizeof(struct user_ldt
) + (ldt_count
* sizeof(struct real_descriptor
)));
181 if (new_ldt
== NULL
) {
186 new_ldt
->start
= begin_sel
;
187 new_ldt
->count
= ldt_count
;
190 * Have new LDT. If there was a an old ldt, copy descriptors
194 bcopy(&old_ldt
->ldt
[0],
195 &new_ldt
->ldt
[old_ldt
->start
- begin_sel
],
196 old_ldt
->count
* sizeof(struct real_descriptor
));
199 * If the old and new LDTs are non-overlapping, fill the
200 * center in with null selectors.
203 if (old_ldt
->start
+ old_ldt
->count
< start_sel
)
204 bzero(&new_ldt
->ldt
[old_ldt
->count
],
205 (start_sel
- (old_ldt
->start
+ old_ldt
->count
)) * sizeof(struct real_descriptor
));
206 else if (old_ldt
->start
> start_sel
+ num_sels
)
207 bzero(&new_ldt
->ldt
[num_sels
],
208 (old_ldt
->start
- (start_sel
+ num_sels
)) * sizeof(struct real_descriptor
));
212 * Install new descriptors.
215 /* XXX copyin under task lock */
216 err
= copyin(descs
, (char *)&new_ldt
->ldt
[start_sel
- begin_sel
],
217 num_sels
* sizeof(struct real_descriptor
));
221 user_ldt_free(new_ldt
);
225 bzero(&new_ldt
->ldt
[start_sel
- begin_sel
], num_sels
* sizeof(struct real_descriptor
));
228 * Validate descriptors.
229 * Only allow descriptors with user privileges.
231 for (i
= 0, dp
= (struct real_descriptor
*) &new_ldt
->ldt
[start_sel
- begin_sel
];
235 switch (dp
->access
& ~ACC_A
) {
238 /* valid empty descriptor, clear Present preemptively */
239 dp
->access
&= (~ACC_P
& 0xff);
241 case ACC_P
| ACC_PL_U
| ACC_DATA
:
242 case ACC_P
| ACC_PL_U
| ACC_DATA_W
:
243 case ACC_P
| ACC_PL_U
| ACC_DATA_E
:
244 case ACC_P
| ACC_PL_U
| ACC_DATA_EW
:
245 case ACC_P
| ACC_PL_U
| ACC_CODE
:
246 case ACC_P
| ACC_PL_U
| ACC_CODE_R
:
247 case ACC_P
| ACC_PL_U
| ACC_CODE_C
:
248 case ACC_P
| ACC_PL_U
| ACC_CODE_CR
:
252 user_ldt_free(new_ldt
);
255 /* Reject attempts to create segments with 64-bit granules */
256 if (dp
->granularity
& SZ_64
) {
258 user_ldt_free(new_ldt
);
264 task
->i386_ldt
= new_ldt
; /* new LDT for task */
267 * Switch to new LDT. We need to do this on all CPUs, since
268 * another thread in this same task may be currently running,
269 * and we need to make sure the new LDT is in place
270 * throughout the task before returning to the user.
272 mp_broadcast(user_ldt_set_action
, task
);
276 /* free old LDT. We can't do this until after we've
277 * rendezvoused with all CPUs, in case another thread
278 * in this task was in the process of context switching.
281 user_ldt_free(old_ldt
);
292 uint32_t descs
, /* out */
296 task_t task
= current_task();
297 unsigned int ldt_count
;
300 if (start_sel
>= LDTSZ
)
302 if ((uint64_t)start_sel
+ (uint64_t)num_sels
> LDTSZ
)
309 user_ldt
= task
->i386_ldt
;
313 * copy out the descriptors
317 ldt_count
= user_ldt
->start
+ user_ldt
->count
;
319 ldt_count
= LDTSZ_MIN
;
322 if (start_sel
< ldt_count
)
324 unsigned int copy_sels
= num_sels
;
326 if (start_sel
+ num_sels
> ldt_count
)
327 copy_sels
= ldt_count
- start_sel
;
329 err
= copyout((char *)(current_ldt() + start_sel
),
330 descs
, copy_sels
* sizeof(struct real_descriptor
));
344 kfree(user_ldt
, sizeof(struct user_ldt
) + (user_ldt
->count
* sizeof(struct real_descriptor
)));
351 if (user_ldt
!= NULL
) {
352 size_t size
= sizeof(struct user_ldt
) + (user_ldt
->count
* sizeof(struct real_descriptor
));
353 user_ldt_t new_ldt
= (user_ldt_t
)kalloc(size
);
355 bcopy(user_ldt
, new_ldt
, size
);
366 task_t arg_task
= (task_t
)arg
;
368 if (arg_task
== current_task()) {
369 user_ldt_set(current_thread());
374 * Set the LDT for the given thread on the current CPU. Should be invoked
375 * with interrupts disabled.
381 task_t task
= thread
->task
;
384 user_ldt
= task
->i386_ldt
;
387 struct real_descriptor
*ldtp
= (struct real_descriptor
*)current_ldt();
389 if (user_ldt
->start
> LDTSZ_MIN
) {
390 bzero(&ldtp
[LDTSZ_MIN
],
391 sizeof(struct real_descriptor
) * (user_ldt
->start
- LDTSZ_MIN
));
394 bcopy(user_ldt
->ldt
, &ldtp
[user_ldt
->start
],
395 sizeof(struct real_descriptor
) * (user_ldt
->count
));
397 gdt_desc_p(USER_LDT
)->limit_low
= (uint16_t)((sizeof(struct real_descriptor
) * (user_ldt
->start
+ user_ldt
->count
)) - 1);
399 ml_cpu_set_ldt(USER_LDT
);
401 ml_cpu_set_ldt(KERNEL_LDT
);