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)
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.
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.
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.
50 * Note that there's a similar kludge in modify_ldt -- look at
51 * the distinction between modes 1 and 0x11.
53 if (LDT_empty(info) || LDT_zero(info))
57 * espfix is required for 16-bit data segments, but espfix
58 * only works for LDT segments.
63 /* Only allow data segments in the TLS array. */
64 if (info->contents > 1)
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.
73 * If userspace needs to remove a TLS entry, it can still delete
76 if (info->seg_not_present)
82 static void set_tls_desc(struct task_struct *p, int idx,
83 const struct user_desc *info, int n)
85 struct thread_struct *t = &p->thread;
86 struct desc_struct *desc = &t->tls_array[idx - GDT_ENTRY_TLS_MIN];
90 * We must not get preempted while modifying the TLS.
95 if (LDT_empty(info) || LDT_zero(info))
96 desc->a = desc->b = 0;
103 if (t == ¤t->thread)
110 * Set a given TLS descriptor:
112 int do_set_thread_area(struct task_struct *p, int idx,
113 struct user_desc __user *u_info,
116 struct user_desc info;
117 unsigned short __maybe_unused sel, modified_sel;
119 if (copy_from_user(&info, u_info, sizeof(info)))
122 if (!tls_desc_okay(&info))
126 idx = info.entry_number;
129 * index -1 means the kernel should try to find and
130 * allocate an empty descriptor:
132 if (idx == -1 && can_allocate) {
133 idx = get_free_idx();
136 if (put_user(idx, &u_info->entry_number))
140 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
143 set_tls_desc(p, idx, &info, 1);
146 * If DS, ES, FS, or GS points to the modified segment, forcibly
147 * refresh it. Only needed on x86_64 because x86_32 reloads them
148 * on return to user mode.
150 modified_sel = (idx << 3) | 3;
154 savesegment(ds, sel);
155 if (sel == modified_sel)
156 loadsegment(ds, sel);
158 savesegment(es, sel);
159 if (sel == modified_sel)
160 loadsegment(es, sel);
162 savesegment(fs, sel);
163 if (sel == modified_sel)
164 loadsegment(fs, sel);
166 savesegment(gs, sel);
167 if (sel == modified_sel)
171 #ifdef CONFIG_X86_32_LAZY_GS
172 savesegment(gs, sel);
173 if (sel == modified_sel)
174 loadsegment(gs, sel);
178 if (p->thread.fsindex == modified_sel)
179 p->thread.fsbase = info.base_addr;
181 if (p->thread.gsindex == modified_sel)
182 p->thread.gsbase = info.base_addr;
189 SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, u_info)
191 return do_set_thread_area(current, -1, u_info, 1);
196 * Get the current Thread-Local Storage area:
199 static void fill_user_desc(struct user_desc *info, int idx,
200 const struct desc_struct *desc)
203 memset(info, 0, sizeof(*info));
204 info->entry_number = idx;
205 info->base_addr = get_desc_base(desc);
206 info->limit = get_desc_limit(desc);
207 info->seg_32bit = desc->d;
208 info->contents = desc->type >> 2;
209 info->read_exec_only = !(desc->type & 2);
210 info->limit_in_pages = desc->g;
211 info->seg_not_present = !desc->p;
212 info->useable = desc->avl;
218 int do_get_thread_area(struct task_struct *p, int idx,
219 struct user_desc __user *u_info)
221 struct user_desc info;
223 if (idx == -1 && get_user(idx, &u_info->entry_number))
226 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
229 fill_user_desc(&info, idx,
230 &p->thread.tls_array[idx - GDT_ENTRY_TLS_MIN]);
232 if (copy_to_user(u_info, &info, sizeof(info)))
237 SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, u_info)
239 return do_get_thread_area(current, -1, u_info);
242 int regset_tls_active(struct task_struct *target,
243 const struct user_regset *regset)
245 struct thread_struct *t = &target->thread;
246 int n = GDT_ENTRY_TLS_ENTRIES;
247 while (n > 0 && desc_empty(&t->tls_array[n - 1]))
252 int regset_tls_get(struct task_struct *target, const struct user_regset *regset,
253 unsigned int pos, unsigned int count,
254 void *kbuf, void __user *ubuf)
256 const struct desc_struct *tls;
258 if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
259 (pos % sizeof(struct user_desc)) != 0 ||
260 (count % sizeof(struct user_desc)) != 0)
263 pos /= sizeof(struct user_desc);
264 count /= sizeof(struct user_desc);
266 tls = &target->thread.tls_array[pos];
269 struct user_desc *info = kbuf;
271 fill_user_desc(info++, GDT_ENTRY_TLS_MIN + pos++,
274 struct user_desc __user *u_info = ubuf;
275 while (count-- > 0) {
276 struct user_desc info;
277 fill_user_desc(&info, GDT_ENTRY_TLS_MIN + pos++, tls++);
278 if (__copy_to_user(u_info++, &info, sizeof(info)))
286 int regset_tls_set(struct task_struct *target, const struct user_regset *regset,
287 unsigned int pos, unsigned int count,
288 const void *kbuf, const void __user *ubuf)
290 struct user_desc infobuf[GDT_ENTRY_TLS_ENTRIES];
291 const struct user_desc *info;
294 if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
295 (pos % sizeof(struct user_desc)) != 0 ||
296 (count % sizeof(struct user_desc)) != 0)
301 else if (__copy_from_user(infobuf, ubuf, count))
306 for (i = 0; i < count / sizeof(struct user_desc); i++)
307 if (!tls_desc_okay(info + i))
311 GDT_ENTRY_TLS_MIN + (pos / sizeof(struct user_desc)),
312 info, count / sizeof(struct user_desc));