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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
7#include <asm/uaccess.h>
8#include <asm/desc.h>
9#include <asm/system.h>
10#include <asm/ldt.h>
11#include <asm/processor.h>
12#include <asm/proto.h>
13#include <asm/syscalls.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 void set_tls_desc(struct task_struct *p, int idx,
32 const struct user_desc *info, int n)
33{
34 struct thread_struct *t = &p->thread;
35 struct desc_struct *desc = &t->tls_array[idx - GDT_ENTRY_TLS_MIN];
36 int cpu;
37
38 /*
39 * We must not get preempted while modifying the TLS.
40 */
41 cpu = get_cpu();
42
43 while (n-- > 0) {
44 if (LDT_empty(info))
45 desc->a = desc->b = 0;
46 else
47 fill_ldt(desc, info);
48 ++info;
49 ++desc;
50 }
51
52 if (t == ¤t->thread)
53 load_TLS(t, cpu);
54
55 put_cpu();
56}
57
58/*
59 * Set a given TLS descriptor:
60 */
61int do_set_thread_area(struct task_struct *p, int idx,
62 struct user_desc __user *u_info,
63 int can_allocate)
64{
65 struct user_desc info;
66
67 if (copy_from_user(&info, u_info, sizeof(info)))
68 return -EFAULT;
69
70 if (idx == -1)
71 idx = info.entry_number;
72
73 /*
74 * index -1 means the kernel should try to find and
75 * allocate an empty descriptor:
76 */
77 if (idx == -1 && can_allocate) {
78 idx = get_free_idx();
79 if (idx < 0)
80 return idx;
81 if (put_user(idx, &u_info->entry_number))
82 return -EFAULT;
83 }
84
85 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
86 return -EINVAL;
87
88 set_tls_desc(p, idx, &info, 1);
89
90 return 0;
91}
92
93asmlinkage int sys_set_thread_area(struct user_desc __user *u_info)
94{
95 int ret = do_set_thread_area(current, -1, u_info, 1);
96 asmlinkage_protect(1, ret, u_info);
97 return ret;
98}
99
100
101/*
102 * Get the current Thread-Local Storage area:
103 */
104
105static void fill_user_desc(struct user_desc *info, int idx,
106 const struct desc_struct *desc)
107
108{
109 memset(info, 0, sizeof(*info));
110 info->entry_number = idx;
111 info->base_addr = get_desc_base(desc);
112 info->limit = get_desc_limit(desc);
113 info->seg_32bit = desc->d;
114 info->contents = desc->type >> 2;
115 info->read_exec_only = !(desc->type & 2);
116 info->limit_in_pages = desc->g;
117 info->seg_not_present = !desc->p;
118 info->useable = desc->avl;
119#ifdef CONFIG_X86_64
120 info->lm = desc->l;
121#endif
122}
123
124int do_get_thread_area(struct task_struct *p, int idx,
125 struct user_desc __user *u_info)
126{
127 struct user_desc info;
128
129 if (idx == -1 && get_user(idx, &u_info->entry_number))
130 return -EFAULT;
131
132 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
133 return -EINVAL;
134
135 fill_user_desc(&info, idx,
136 &p->thread.tls_array[idx - GDT_ENTRY_TLS_MIN]);
137
138 if (copy_to_user(u_info, &info, sizeof(info)))
139 return -EFAULT;
140 return 0;
141}
142
143asmlinkage int sys_get_thread_area(struct user_desc __user *u_info)
144{
145 int ret = do_get_thread_area(current, -1, u_info);
146 asmlinkage_protect(1, ret, u_info);
147 return ret;
148}
149
150int regset_tls_active(struct task_struct *target,
151 const struct user_regset *regset)
152{
153 struct thread_struct *t = &target->thread;
154 int n = GDT_ENTRY_TLS_ENTRIES;
155 while (n > 0 && desc_empty(&t->tls_array[n - 1]))
156 --n;
157 return n;
158}
159
160int regset_tls_get(struct task_struct *target, const struct user_regset *regset,
161 unsigned int pos, unsigned int count,
162 void *kbuf, void __user *ubuf)
163{
164 const struct desc_struct *tls;
165
166 if (pos > GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
167 (pos % sizeof(struct user_desc)) != 0 ||
168 (count % sizeof(struct user_desc)) != 0)
169 return -EINVAL;
170
171 pos /= sizeof(struct user_desc);
172 count /= sizeof(struct user_desc);
173
174 tls = &target->thread.tls_array[pos];
175
176 if (kbuf) {
177 struct user_desc *info = kbuf;
178 while (count-- > 0)
179 fill_user_desc(info++, GDT_ENTRY_TLS_MIN + pos++,
180 tls++);
181 } else {
182 struct user_desc __user *u_info = ubuf;
183 while (count-- > 0) {
184 struct user_desc info;
185 fill_user_desc(&info, GDT_ENTRY_TLS_MIN + pos++, tls++);
186 if (__copy_to_user(u_info++, &info, sizeof(info)))
187 return -EFAULT;
188 }
189 }
190
191 return 0;
192}
193
194int regset_tls_set(struct task_struct *target, const struct user_regset *regset,
195 unsigned int pos, unsigned int count,
196 const void *kbuf, const void __user *ubuf)
197{
198 struct user_desc infobuf[GDT_ENTRY_TLS_ENTRIES];
199 const struct user_desc *info;
200
201 if (pos > GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
202 (pos % sizeof(struct user_desc)) != 0 ||
203 (count % sizeof(struct user_desc)) != 0)
204 return -EINVAL;
205
206 if (kbuf)
207 info = kbuf;
208 else if (__copy_from_user(infobuf, ubuf, count))
209 return -EFAULT;
210 else
211 info = infobuf;
212
213 set_tls_desc(target,
214 GDT_ENTRY_TLS_MIN + (pos / sizeof(struct user_desc)),
215 info, count / sizeof(struct user_desc));
216
217 return 0;
218}
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}