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>
8 #include <asm/uaccess.h>
11 #include <asm/processor.h>
12 #include <asm/proto.h>
17 * sys_alloc_thread_area: get a yet unused TLS descriptor index.
19 static int get_free_idx(void)
21 struct thread_struct *t = ¤t->thread;
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;
30 static bool tls_desc_okay(const struct user_desc *info)
36 * espfix is required for 16-bit data segments, but espfix
37 * only works for LDT segments.
42 /* Only allow data segments in the TLS array. */
43 if (info->contents > 1)
47 * Non-present segments with DPL 3 present an interesting attack
48 * surface. The kernel should handle such segments correctly,
49 * but TLS is very difficult to protect in a sandbox, so prevent
50 * such segments from being created.
52 * If userspace needs to remove a TLS entry, it can still delete
55 if (info->seg_not_present)
61 static void set_tls_desc(struct task_struct *p, int idx,
62 const struct user_desc *info, int n)
64 struct thread_struct *t = &p->thread;
65 struct desc_struct *desc = &t->tls_array[idx - GDT_ENTRY_TLS_MIN];
69 * We must not get preempted while modifying the TLS.
75 desc->a = desc->b = 0;
82 if (t == ¤t->thread)
89 * Set a given TLS descriptor:
91 int do_set_thread_area(struct task_struct *p, int idx,
92 struct user_desc __user *u_info,
95 struct user_desc info;
97 if (copy_from_user(&info, u_info, sizeof(info)))
100 if (!tls_desc_okay(&info))
104 idx = info.entry_number;
107 * index -1 means the kernel should try to find and
108 * allocate an empty descriptor:
110 if (idx == -1 && can_allocate) {
111 idx = get_free_idx();
114 if (put_user(idx, &u_info->entry_number))
118 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
121 set_tls_desc(p, idx, &info, 1);
126 SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, u_info)
128 return do_set_thread_area(current, -1, u_info, 1);
133 * Get the current Thread-Local Storage area:
136 static void fill_user_desc(struct user_desc *info, int idx,
137 const struct desc_struct *desc)
140 memset(info, 0, sizeof(*info));
141 info->entry_number = idx;
142 info->base_addr = get_desc_base(desc);
143 info->limit = get_desc_limit(desc);
144 info->seg_32bit = desc->d;
145 info->contents = desc->type >> 2;
146 info->read_exec_only = !(desc->type & 2);
147 info->limit_in_pages = desc->g;
148 info->seg_not_present = !desc->p;
149 info->useable = desc->avl;
155 int do_get_thread_area(struct task_struct *p, int idx,
156 struct user_desc __user *u_info)
158 struct user_desc info;
160 if (idx == -1 && get_user(idx, &u_info->entry_number))
163 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
166 fill_user_desc(&info, idx,
167 &p->thread.tls_array[idx - GDT_ENTRY_TLS_MIN]);
169 if (copy_to_user(u_info, &info, sizeof(info)))
174 SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, u_info)
176 return do_get_thread_area(current, -1, u_info);
179 int regset_tls_active(struct task_struct *target,
180 const struct user_regset *regset)
182 struct thread_struct *t = &target->thread;
183 int n = GDT_ENTRY_TLS_ENTRIES;
184 while (n > 0 && desc_empty(&t->tls_array[n - 1]))
189 int regset_tls_get(struct task_struct *target, const struct user_regset *regset,
190 unsigned int pos, unsigned int count,
191 void *kbuf, void __user *ubuf)
193 const struct desc_struct *tls;
195 if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
196 (pos % sizeof(struct user_desc)) != 0 ||
197 (count % sizeof(struct user_desc)) != 0)
200 pos /= sizeof(struct user_desc);
201 count /= sizeof(struct user_desc);
203 tls = &target->thread.tls_array[pos];
206 struct user_desc *info = kbuf;
208 fill_user_desc(info++, GDT_ENTRY_TLS_MIN + pos++,
211 struct user_desc __user *u_info = ubuf;
212 while (count-- > 0) {
213 struct user_desc info;
214 fill_user_desc(&info, GDT_ENTRY_TLS_MIN + pos++, tls++);
215 if (__copy_to_user(u_info++, &info, sizeof(info)))
223 int regset_tls_set(struct task_struct *target, const struct user_regset *regset,
224 unsigned int pos, unsigned int count,
225 const void *kbuf, const void __user *ubuf)
227 struct user_desc infobuf[GDT_ENTRY_TLS_ENTRIES];
228 const struct user_desc *info;
231 if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
232 (pos % sizeof(struct user_desc)) != 0 ||
233 (count % sizeof(struct user_desc)) != 0)
238 else if (__copy_from_user(infobuf, ubuf, count))
243 for (i = 0; i < count / sizeof(struct user_desc); i++)
244 if (!tls_desc_okay(info + i))
248 GDT_ENTRY_TLS_MIN + (pos / sizeof(struct user_desc)),
249 info, count / sizeof(struct user_desc));