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1// SPDX-License-Identifier: GPL-2.0
2#include <linux/kernel.h>
3#include <linux/errno.h>
4#include <linux/sched.h>
5#include <linux/user.h>
6#include <linux/regset.h>
7#include <linux/syscalls.h>
8#include <linux/nospec.h>
9
10#include <linux/uaccess.h>
11#include <asm/desc.h>
12#include <asm/ldt.h>
13#include <asm/processor.h>
14#include <asm/proto.h>
15
16#include "tls.h"
17
18/*
19 * sys_alloc_thread_area: get a yet unused TLS descriptor index.
20 */
21static int get_free_idx(void)
22{
23 struct thread_struct *t = ¤t->thread;
24 int idx;
25
26 for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
27 if (desc_empty(&t->tls_array[idx]))
28 return idx + GDT_ENTRY_TLS_MIN;
29 return -ESRCH;
30}
31
32static bool tls_desc_okay(const struct user_desc *info)
33{
34 /*
35 * For historical reasons (i.e. no one ever documented how any
36 * of the segmentation APIs work), user programs can and do
37 * assume that a struct user_desc that's all zeros except for
38 * entry_number means "no segment at all". This never actually
39 * worked. In fact, up to Linux 3.19, a struct user_desc like
40 * this would create a 16-bit read-write segment with base and
41 * limit both equal to zero.
42 *
43 * That was close enough to "no segment at all" until we
44 * hardened this function to disallow 16-bit TLS segments. Fix
45 * it up by interpreting these zeroed segments the way that they
46 * were almost certainly intended to be interpreted.
47 *
48 * The correct way to ask for "no segment at all" is to specify
49 * a user_desc that satisfies LDT_empty. To keep everything
50 * working, we accept both.
51 *
52 * Note that there's a similar kludge in modify_ldt -- look at
53 * the distinction between modes 1 and 0x11.
54 */
55 if (LDT_empty(info) || LDT_zero(info))
56 return true;
57
58 /*
59 * espfix is required for 16-bit data segments, but espfix
60 * only works for LDT segments.
61 */
62 if (!info->seg_32bit)
63 return false;
64
65 /* Only allow data segments in the TLS array. */
66 if (info->contents > 1)
67 return false;
68
69 /*
70 * Non-present segments with DPL 3 present an interesting attack
71 * surface. The kernel should handle such segments correctly,
72 * but TLS is very difficult to protect in a sandbox, so prevent
73 * such segments from being created.
74 *
75 * If userspace needs to remove a TLS entry, it can still delete
76 * it outright.
77 */
78 if (info->seg_not_present)
79 return false;
80
81 return true;
82}
83
84static void set_tls_desc(struct task_struct *p, int idx,
85 const struct user_desc *info, int n)
86{
87 struct thread_struct *t = &p->thread;
88 struct desc_struct *desc = &t->tls_array[idx - GDT_ENTRY_TLS_MIN];
89 int cpu;
90
91 /*
92 * We must not get preempted while modifying the TLS.
93 */
94 cpu = get_cpu();
95
96 while (n-- > 0) {
97 if (LDT_empty(info) || LDT_zero(info))
98 memset(desc, 0, sizeof(*desc));
99 else
100 fill_ldt(desc, info);
101 ++info;
102 ++desc;
103 }
104
105 if (t == ¤t->thread)
106 load_TLS(t, cpu);
107
108 put_cpu();
109}
110
111/*
112 * Set a given TLS descriptor:
113 */
114int do_set_thread_area(struct task_struct *p, int idx,
115 struct user_desc __user *u_info,
116 int can_allocate)
117{
118 struct user_desc info;
119 unsigned short __maybe_unused sel, modified_sel;
120
121 if (copy_from_user(&info, u_info, sizeof(info)))
122 return -EFAULT;
123
124 if (!tls_desc_okay(&info))
125 return -EINVAL;
126
127 if (idx == -1)
128 idx = info.entry_number;
129
130 /*
131 * index -1 means the kernel should try to find and
132 * allocate an empty descriptor:
133 */
134 if (idx == -1 && can_allocate) {
135 idx = get_free_idx();
136 if (idx < 0)
137 return idx;
138 if (put_user(idx, &u_info->entry_number))
139 return -EFAULT;
140 }
141
142 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
143 return -EINVAL;
144
145 set_tls_desc(p, idx, &info, 1);
146
147 /*
148 * If DS, ES, FS, or GS points to the modified segment, forcibly
149 * refresh it. Only needed on x86_64 because x86_32 reloads them
150 * on return to user mode.
151 */
152 modified_sel = (idx << 3) | 3;
153
154 if (p == current) {
155#ifdef CONFIG_X86_64
156 savesegment(ds, sel);
157 if (sel == modified_sel)
158 loadsegment(ds, sel);
159
160 savesegment(es, sel);
161 if (sel == modified_sel)
162 loadsegment(es, sel);
163
164 savesegment(fs, sel);
165 if (sel == modified_sel)
166 loadsegment(fs, sel);
167
168 savesegment(gs, sel);
169 if (sel == modified_sel)
170 load_gs_index(sel);
171#endif
172
173#ifdef CONFIG_X86_32_LAZY_GS
174 savesegment(gs, sel);
175 if (sel == modified_sel)
176 loadsegment(gs, sel);
177#endif
178 } else {
179#ifdef CONFIG_X86_64
180 if (p->thread.fsindex == modified_sel)
181 p->thread.fsbase = info.base_addr;
182
183 if (p->thread.gsindex == modified_sel)
184 p->thread.gsbase = info.base_addr;
185#endif
186 }
187
188 return 0;
189}
190
191SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, u_info)
192{
193 return do_set_thread_area(current, -1, u_info, 1);
194}
195
196
197/*
198 * Get the current Thread-Local Storage area:
199 */
200
201static void fill_user_desc(struct user_desc *info, int idx,
202 const struct desc_struct *desc)
203
204{
205 memset(info, 0, sizeof(*info));
206 info->entry_number = idx;
207 info->base_addr = get_desc_base(desc);
208 info->limit = get_desc_limit(desc);
209 info->seg_32bit = desc->d;
210 info->contents = desc->type >> 2;
211 info->read_exec_only = !(desc->type & 2);
212 info->limit_in_pages = desc->g;
213 info->seg_not_present = !desc->p;
214 info->useable = desc->avl;
215#ifdef CONFIG_X86_64
216 info->lm = desc->l;
217#endif
218}
219
220int do_get_thread_area(struct task_struct *p, int idx,
221 struct user_desc __user *u_info)
222{
223 struct user_desc info;
224 int index;
225
226 if (idx == -1 && get_user(idx, &u_info->entry_number))
227 return -EFAULT;
228
229 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
230 return -EINVAL;
231
232 index = idx - GDT_ENTRY_TLS_MIN;
233 index = array_index_nospec(index,
234 GDT_ENTRY_TLS_MAX - GDT_ENTRY_TLS_MIN + 1);
235
236 fill_user_desc(&info, idx, &p->thread.tls_array[index]);
237
238 if (copy_to_user(u_info, &info, sizeof(info)))
239 return -EFAULT;
240 return 0;
241}
242
243SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, u_info)
244{
245 return do_get_thread_area(current, -1, u_info);
246}
247
248int regset_tls_active(struct task_struct *target,
249 const struct user_regset *regset)
250{
251 struct thread_struct *t = &target->thread;
252 int n = GDT_ENTRY_TLS_ENTRIES;
253 while (n > 0 && desc_empty(&t->tls_array[n - 1]))
254 --n;
255 return n;
256}
257
258int regset_tls_get(struct task_struct *target, const struct user_regset *regset,
259 unsigned int pos, unsigned int count,
260 void *kbuf, void __user *ubuf)
261{
262 const struct desc_struct *tls;
263
264 if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
265 (pos % sizeof(struct user_desc)) != 0 ||
266 (count % sizeof(struct user_desc)) != 0)
267 return -EINVAL;
268
269 pos /= sizeof(struct user_desc);
270 count /= sizeof(struct user_desc);
271
272 tls = &target->thread.tls_array[pos];
273
274 if (kbuf) {
275 struct user_desc *info = kbuf;
276 while (count-- > 0)
277 fill_user_desc(info++, GDT_ENTRY_TLS_MIN + pos++,
278 tls++);
279 } else {
280 struct user_desc __user *u_info = ubuf;
281 while (count-- > 0) {
282 struct user_desc info;
283 fill_user_desc(&info, GDT_ENTRY_TLS_MIN + pos++, tls++);
284 if (__copy_to_user(u_info++, &info, sizeof(info)))
285 return -EFAULT;
286 }
287 }
288
289 return 0;
290}
291
292int regset_tls_set(struct task_struct *target, const struct user_regset *regset,
293 unsigned int pos, unsigned int count,
294 const void *kbuf, const void __user *ubuf)
295{
296 struct user_desc infobuf[GDT_ENTRY_TLS_ENTRIES];
297 const struct user_desc *info;
298 int i;
299
300 if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
301 (pos % sizeof(struct user_desc)) != 0 ||
302 (count % sizeof(struct user_desc)) != 0)
303 return -EINVAL;
304
305 if (kbuf)
306 info = kbuf;
307 else if (__copy_from_user(infobuf, ubuf, count))
308 return -EFAULT;
309 else
310 info = infobuf;
311
312 for (i = 0; i < count / sizeof(struct user_desc); i++)
313 if (!tls_desc_okay(info + i))
314 return -EINVAL;
315
316 set_tls_desc(target,
317 GDT_ENTRY_TLS_MIN + (pos / sizeof(struct user_desc)),
318 info, count / sizeof(struct user_desc));
319
320 return 0;
321}
1// SPDX-License-Identifier: GPL-2.0
2#include <linux/kernel.h>
3#include <linux/errno.h>
4#include <linux/sched.h>
5#include <linux/user.h>
6#include <linux/regset.h>
7#include <linux/syscalls.h>
8
9#include <linux/uaccess.h>
10#include <asm/desc.h>
11#include <asm/ldt.h>
12#include <asm/processor.h>
13#include <asm/proto.h>
14
15#include "tls.h"
16
17/*
18 * sys_alloc_thread_area: get a yet unused TLS descriptor index.
19 */
20static int get_free_idx(void)
21{
22 struct thread_struct *t = ¤t->thread;
23 int idx;
24
25 for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
26 if (desc_empty(&t->tls_array[idx]))
27 return idx + GDT_ENTRY_TLS_MIN;
28 return -ESRCH;
29}
30
31static bool tls_desc_okay(const struct user_desc *info)
32{
33 /*
34 * For historical reasons (i.e. no one ever documented how any
35 * of the segmentation APIs work), user programs can and do
36 * assume that a struct user_desc that's all zeros except for
37 * entry_number means "no segment at all". This never actually
38 * worked. In fact, up to Linux 3.19, a struct user_desc like
39 * this would create a 16-bit read-write segment with base and
40 * limit both equal to zero.
41 *
42 * That was close enough to "no segment at all" until we
43 * hardened this function to disallow 16-bit TLS segments. Fix
44 * it up by interpreting these zeroed segments the way that they
45 * were almost certainly intended to be interpreted.
46 *
47 * The correct way to ask for "no segment at all" is to specify
48 * a user_desc that satisfies LDT_empty. To keep everything
49 * working, we accept both.
50 *
51 * Note that there's a similar kludge in modify_ldt -- look at
52 * the distinction between modes 1 and 0x11.
53 */
54 if (LDT_empty(info) || LDT_zero(info))
55 return true;
56
57 /*
58 * espfix is required for 16-bit data segments, but espfix
59 * only works for LDT segments.
60 */
61 if (!info->seg_32bit)
62 return false;
63
64 /* Only allow data segments in the TLS array. */
65 if (info->contents > 1)
66 return false;
67
68 /*
69 * Non-present segments with DPL 3 present an interesting attack
70 * surface. The kernel should handle such segments correctly,
71 * but TLS is very difficult to protect in a sandbox, so prevent
72 * such segments from being created.
73 *
74 * If userspace needs to remove a TLS entry, it can still delete
75 * it outright.
76 */
77 if (info->seg_not_present)
78 return false;
79
80 return true;
81}
82
83static void set_tls_desc(struct task_struct *p, int idx,
84 const struct user_desc *info, int n)
85{
86 struct thread_struct *t = &p->thread;
87 struct desc_struct *desc = &t->tls_array[idx - GDT_ENTRY_TLS_MIN];
88 int cpu;
89
90 /*
91 * We must not get preempted while modifying the TLS.
92 */
93 cpu = get_cpu();
94
95 while (n-- > 0) {
96 if (LDT_empty(info) || LDT_zero(info))
97 memset(desc, 0, sizeof(*desc));
98 else
99 fill_ldt(desc, info);
100 ++info;
101 ++desc;
102 }
103
104 if (t == ¤t->thread)
105 load_TLS(t, cpu);
106
107 put_cpu();
108}
109
110/*
111 * Set a given TLS descriptor:
112 */
113int do_set_thread_area(struct task_struct *p, int idx,
114 struct user_desc __user *u_info,
115 int can_allocate)
116{
117 struct user_desc info;
118 unsigned short __maybe_unused sel, modified_sel;
119
120 if (copy_from_user(&info, u_info, sizeof(info)))
121 return -EFAULT;
122
123 if (!tls_desc_okay(&info))
124 return -EINVAL;
125
126 if (idx == -1)
127 idx = info.entry_number;
128
129 /*
130 * index -1 means the kernel should try to find and
131 * allocate an empty descriptor:
132 */
133 if (idx == -1 && can_allocate) {
134 idx = get_free_idx();
135 if (idx < 0)
136 return idx;
137 if (put_user(idx, &u_info->entry_number))
138 return -EFAULT;
139 }
140
141 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
142 return -EINVAL;
143
144 set_tls_desc(p, idx, &info, 1);
145
146 /*
147 * If DS, ES, FS, or GS points to the modified segment, forcibly
148 * refresh it. Only needed on x86_64 because x86_32 reloads them
149 * on return to user mode.
150 */
151 modified_sel = (idx << 3) | 3;
152
153 if (p == current) {
154#ifdef CONFIG_X86_64
155 savesegment(ds, sel);
156 if (sel == modified_sel)
157 loadsegment(ds, sel);
158
159 savesegment(es, sel);
160 if (sel == modified_sel)
161 loadsegment(es, sel);
162
163 savesegment(fs, sel);
164 if (sel == modified_sel)
165 loadsegment(fs, sel);
166
167 savesegment(gs, sel);
168 if (sel == modified_sel)
169 load_gs_index(sel);
170#endif
171
172#ifdef CONFIG_X86_32_LAZY_GS
173 savesegment(gs, sel);
174 if (sel == modified_sel)
175 loadsegment(gs, sel);
176#endif
177 } else {
178#ifdef CONFIG_X86_64
179 if (p->thread.fsindex == modified_sel)
180 p->thread.fsbase = info.base_addr;
181
182 if (p->thread.gsindex == modified_sel)
183 p->thread.gsbase = info.base_addr;
184#endif
185 }
186
187 return 0;
188}
189
190SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, u_info)
191{
192 return do_set_thread_area(current, -1, u_info, 1);
193}
194
195
196/*
197 * Get the current Thread-Local Storage area:
198 */
199
200static void fill_user_desc(struct user_desc *info, int idx,
201 const struct desc_struct *desc)
202
203{
204 memset(info, 0, sizeof(*info));
205 info->entry_number = idx;
206 info->base_addr = get_desc_base(desc);
207 info->limit = get_desc_limit(desc);
208 info->seg_32bit = desc->d;
209 info->contents = desc->type >> 2;
210 info->read_exec_only = !(desc->type & 2);
211 info->limit_in_pages = desc->g;
212 info->seg_not_present = !desc->p;
213 info->useable = desc->avl;
214#ifdef CONFIG_X86_64
215 info->lm = desc->l;
216#endif
217}
218
219int do_get_thread_area(struct task_struct *p, int idx,
220 struct user_desc __user *u_info)
221{
222 struct user_desc info;
223
224 if (idx == -1 && get_user(idx, &u_info->entry_number))
225 return -EFAULT;
226
227 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
228 return -EINVAL;
229
230 fill_user_desc(&info, idx,
231 &p->thread.tls_array[idx - GDT_ENTRY_TLS_MIN]);
232
233 if (copy_to_user(u_info, &info, sizeof(info)))
234 return -EFAULT;
235 return 0;
236}
237
238SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, u_info)
239{
240 return do_get_thread_area(current, -1, u_info);
241}
242
243int regset_tls_active(struct task_struct *target,
244 const struct user_regset *regset)
245{
246 struct thread_struct *t = &target->thread;
247 int n = GDT_ENTRY_TLS_ENTRIES;
248 while (n > 0 && desc_empty(&t->tls_array[n - 1]))
249 --n;
250 return n;
251}
252
253int regset_tls_get(struct task_struct *target, const struct user_regset *regset,
254 unsigned int pos, unsigned int count,
255 void *kbuf, void __user *ubuf)
256{
257 const struct desc_struct *tls;
258
259 if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
260 (pos % sizeof(struct user_desc)) != 0 ||
261 (count % sizeof(struct user_desc)) != 0)
262 return -EINVAL;
263
264 pos /= sizeof(struct user_desc);
265 count /= sizeof(struct user_desc);
266
267 tls = &target->thread.tls_array[pos];
268
269 if (kbuf) {
270 struct user_desc *info = kbuf;
271 while (count-- > 0)
272 fill_user_desc(info++, GDT_ENTRY_TLS_MIN + pos++,
273 tls++);
274 } else {
275 struct user_desc __user *u_info = ubuf;
276 while (count-- > 0) {
277 struct user_desc info;
278 fill_user_desc(&info, GDT_ENTRY_TLS_MIN + pos++, tls++);
279 if (__copy_to_user(u_info++, &info, sizeof(info)))
280 return -EFAULT;
281 }
282 }
283
284 return 0;
285}
286
287int regset_tls_set(struct task_struct *target, const struct user_regset *regset,
288 unsigned int pos, unsigned int count,
289 const void *kbuf, const void __user *ubuf)
290{
291 struct user_desc infobuf[GDT_ENTRY_TLS_ENTRIES];
292 const struct user_desc *info;
293 int i;
294
295 if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
296 (pos % sizeof(struct user_desc)) != 0 ||
297 (count % sizeof(struct user_desc)) != 0)
298 return -EINVAL;
299
300 if (kbuf)
301 info = kbuf;
302 else if (__copy_from_user(infobuf, ubuf, count))
303 return -EFAULT;
304 else
305 info = infobuf;
306
307 for (i = 0; i < count / sizeof(struct user_desc); i++)
308 if (!tls_desc_okay(info + i))
309 return -EINVAL;
310
311 set_tls_desc(target,
312 GDT_ENTRY_TLS_MIN + (pos / sizeof(struct user_desc)),
313 info, count / sizeof(struct user_desc));
314
315 return 0;
316}