2 * Copyright (C) 2005 Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
3 * Licensed under the GPL
6 #include <linux/percpu.h>
7 #include <linux/sched.h>
8 #include <linux/syscalls.h>
9 #include <asm/uaccess.h>
12 #include <sysdep/tls.h>
15 * If needed we can detect when it's uninitialized.
17 * These are initialized in an initcall and unchanged thereafter.
19 static int host_supports_tls = -1;
20 int host_gdt_entry_tls_min;
22 int do_set_thread_area(struct user_desc *info)
28 ret = os_set_thread_area(info, userspace_pid[cpu]);
32 printk(KERN_ERR "PTRACE_SET_THREAD_AREA failed, err = %d, "
33 "index = %d\n", ret, info->entry_number);
38 int do_get_thread_area(struct user_desc *info)
44 ret = os_get_thread_area(info, userspace_pid[cpu]);
48 printk(KERN_ERR "PTRACE_GET_THREAD_AREA failed, err = %d, "
49 "index = %d\n", ret, info->entry_number);
55 * sys_get_thread_area: get a yet unused TLS descriptor index.
56 * XXX: Consider leaving one free slot for glibc usage at first place. This must
57 * be done here (and by changing GDT_ENTRY_TLS_* macros) and nowhere else.
59 * Also, this must be tested when compiling in SKAS mode with dynamic linking
60 * and running against NPTL.
62 static int get_free_idx(struct task_struct* task)
64 struct thread_struct *t = &task->thread;
67 if (!t->arch.tls_array)
68 return GDT_ENTRY_TLS_MIN;
70 for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
71 if (!t->arch.tls_array[idx].present)
72 return idx + GDT_ENTRY_TLS_MIN;
76 static inline void clear_user_desc(struct user_desc* info)
78 /* Postcondition: LDT_empty(info) returns true. */
79 memset(info, 0, sizeof(*info));
82 * Check the LDT_empty or the i386 sys_get_thread_area code - we obtain
83 * indeed an empty user_desc.
85 info->read_exec_only = 1;
86 info->seg_not_present = 1;
91 static int load_TLS(int flags, struct task_struct *to)
96 for (idx = GDT_ENTRY_TLS_MIN; idx < GDT_ENTRY_TLS_MAX; idx++) {
97 struct uml_tls_struct* curr =
98 &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];
101 * Actually, now if it wasn't flushed it gets cleared and
102 * flushed to the host, which will clear it.
104 if (!curr->present) {
105 if (!curr->flushed) {
106 clear_user_desc(&curr->tls);
107 curr->tls.entry_number = idx;
109 WARN_ON(!LDT_empty(&curr->tls));
114 if (!(flags & O_FORCE) && curr->flushed)
117 ret = do_set_thread_area(&curr->tls);
128 * Verify if we need to do a flush for the new process, i.e. if there are any
129 * present desc's, only if they haven't been flushed.
131 static inline int needs_TLS_update(struct task_struct *task)
136 for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
137 struct uml_tls_struct* curr =
138 &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
141 * Can't test curr->present, we may need to clear a descriptor
153 * On a newly forked process, the TLS descriptors haven't yet been flushed. So
154 * we mark them as such and the first switch_to will do the job.
156 void clear_flushed_tls(struct task_struct *task)
160 for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
161 struct uml_tls_struct* curr =
162 &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
165 * Still correct to do this, if it wasn't present on the host it
166 * will remain as flushed as it was.
176 * In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
177 * common host process. So this is needed in SKAS0 too.
179 * However, if each thread had a different host process (and this was discussed
180 * for SMP support) this won't be needed.
182 * And this will not need be used when (and if) we'll add support to the host
186 int arch_switch_tls(struct task_struct *to)
188 if (!host_supports_tls)
192 * We have no need whatsoever to switch TLS for kernel threads; beyond
193 * that, that would also result in us calling os_set_thread_area with
194 * userspace_pid[cpu] == 0, which gives an error.
197 return load_TLS(O_FORCE, to);
202 static int set_tls_entry(struct task_struct* task, struct user_desc *info,
203 int idx, int flushed)
205 struct thread_struct *t = &task->thread;
207 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
210 t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info;
211 t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1;
212 t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed;
217 int arch_copy_tls(struct task_struct *new)
219 struct user_desc info;
220 int idx, ret = -EFAULT;
222 if (copy_from_user(&info,
223 (void __user *) UPT_SI(&new->thread.regs.regs),
228 if (LDT_empty(&info))
231 idx = info.entry_number;
233 ret = set_tls_entry(new, &info, idx, 0);
238 /* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */
239 static int get_tls_entry(struct task_struct *task, struct user_desc *info,
242 struct thread_struct *t = &task->thread;
244 if (!t->arch.tls_array)
247 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
250 if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present)
253 *info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls;
257 * Temporary debugging check, to make sure that things have been
258 * flushed. This could be triggered if load_TLS() failed.
260 if (unlikely(task == current &&
261 !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) {
262 printk(KERN_ERR "get_tls_entry: task with pid %d got here "
263 "without flushed TLS.", current->pid);
269 * When the TLS entry has not been set, the values read to user in the
270 * tls_array are 0 (because it's cleared at boot, see
271 * arch/i386/kernel/head.S:cpu_gdt_table). Emulate that.
273 clear_user_desc(info);
274 info->entry_number = idx;
278 SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, user_desc)
280 struct user_desc info;
283 if (!host_supports_tls)
286 if (copy_from_user(&info, user_desc, sizeof(info)))
289 idx = info.entry_number;
292 idx = get_free_idx(current);
295 info.entry_number = idx;
296 /* Tell the user which slot we chose for him.*/
297 if (put_user(idx, &user_desc->entry_number))
301 ret = do_set_thread_area(&info);
304 return set_tls_entry(current, &info, idx, 1);
308 * Perform set_thread_area on behalf of the traced child.
309 * Note: error handling is not done on the deferred load, and this differ from
310 * i386. However the only possible error are caused by bugs.
312 int ptrace_set_thread_area(struct task_struct *child, int idx,
313 struct user_desc __user *user_desc)
315 struct user_desc info;
317 if (!host_supports_tls)
320 if (copy_from_user(&info, user_desc, sizeof(info)))
323 return set_tls_entry(child, &info, idx, 0);
326 SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, user_desc)
328 struct user_desc info;
331 if (!host_supports_tls)
334 if (get_user(idx, &user_desc->entry_number))
337 ret = get_tls_entry(current, &info, idx);
341 if (copy_to_user(user_desc, &info, sizeof(info)))
349 * Perform get_thread_area on behalf of the traced child.
351 int ptrace_get_thread_area(struct task_struct *child, int idx,
352 struct user_desc __user *user_desc)
354 struct user_desc info;
357 if (!host_supports_tls)
360 ret = get_tls_entry(child, &info, idx);
364 if (copy_to_user(user_desc, &info, sizeof(info)))
371 * This code is really i386-only, but it detects and logs x86_64 GDT indexes
372 * if a 32-bit UML is running on a 64-bit host.
374 static int __init __setup_host_supports_tls(void)
376 check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
377 if (host_supports_tls) {
378 printk(KERN_INFO "Host TLS support detected\n");
379 printk(KERN_INFO "Detected host type: ");
380 switch (host_gdt_entry_tls_min) {
381 case GDT_ENTRY_TLS_MIN_I386:
382 printk(KERN_CONT "i386");
384 case GDT_ENTRY_TLS_MIN_X86_64:
385 printk(KERN_CONT "x86_64");
388 printk(KERN_CONT " (GDT indexes %d to %d)\n",
389 host_gdt_entry_tls_min,
390 host_gdt_entry_tls_min + GDT_ENTRY_TLS_ENTRIES);
392 printk(KERN_ERR " Host TLS support NOT detected! "
393 "TLS support inside UML will not work\n");
397 __initcall(__setup_host_supports_tls);