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