/*
 * Copyright (C) 2005 Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
 * Licensed under the GPL
 */

#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/syscalls.h>
#include <linux/uaccess.h>
#include <asm/ptrace-abi.h>
#include <os.h>
#include <skas.h>
#include <sysdep/tls.h>
#include <asm/desc.h>
#include <stub-data.h>

/*
 * If needed we can detect when it's uninitialized.
 *
 * These are initialized in an initcall and unchanged thereafter.
 */
static int host_supports_tls = -1;
int host_gdt_entry_tls_min;

static int do_set_thread_area(struct task_struct* task, struct user_desc *info)
{
        int ret;

        if (info->entry_number < host_gdt_entry_tls_min ||
            info->entry_number >= host_gdt_entry_tls_min + GDT_ENTRY_TLS_ENTRIES)
                return -EINVAL;

        if (using_seccomp) {
                int idx = info->entry_number - host_gdt_entry_tls_min;
                struct stub_data *data = (void *)task->mm->context.id.stack;

                data->arch_data.tls[idx] = *info;
                data->arch_data.sync |= BIT(idx);

                return 0;
        }

        ret = os_set_thread_area(info, task->mm->context.id.pid);

        if (ret)
                printk(KERN_ERR "PTRACE_SET_THREAD_AREA failed, err = %d, "
                       "index = %d\n", ret, info->entry_number);

        return ret;
}

/*
 * sys_get_thread_area: get a yet unused TLS descriptor index.
 * XXX: Consider leaving one free slot for glibc usage at first place. This must
 * be done here (and by changing GDT_ENTRY_TLS_* macros) and nowhere else.
 *
 * Also, this must be tested when compiling in SKAS mode with dynamic linking
 * and running against NPTL.
 */
static int get_free_idx(struct task_struct* task)
{
        struct thread_struct *t = &task->thread;
        int idx;

        for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
                if (!t->arch.tls_array[idx].present)
                        return idx + GDT_ENTRY_TLS_MIN;
        return -ESRCH;
}

static inline void clear_user_desc(struct user_desc* info)
{
        /* Postcondition: LDT_empty(info) returns true. */
        memset(info, 0, sizeof(*info));

        /*
         * Check the LDT_empty or the i386 sys_get_thread_area code - we obtain
         * indeed an empty user_desc.
         */
        info->read_exec_only = 1;
        info->seg_not_present = 1;
}

#define O_FORCE 1

static int load_TLS(int flags, struct task_struct *to)
{
        int ret = 0;
        int idx;

        for (idx = GDT_ENTRY_TLS_MIN; idx < GDT_ENTRY_TLS_MAX; idx++) {
                struct uml_tls_struct* curr =
                        &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];

                /*
                 * Actually, now if it wasn't flushed it gets cleared and
                 * flushed to the host, which will clear it.
                 */
                if (!curr->present) {
                        if (!curr->flushed) {
                                clear_user_desc(&curr->tls);
                                curr->tls.entry_number = idx;
                        } else {
                                WARN_ON(!LDT_empty(&curr->tls));
                                continue;
                        }
                }

                if (!(flags & O_FORCE) && curr->flushed)
                        continue;

                ret = do_set_thread_area(current, &curr->tls);
                if (ret)
                        goto out;

                curr->flushed = 1;
        }
out:
        return ret;
}

/*
 * Verify if we need to do a flush for the new process, i.e. if there are any
 * present desc's, only if they haven't been flushed.
 */
static inline int needs_TLS_update(struct task_struct *task)
{
        int i;
        int ret = 0;

        for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
                struct uml_tls_struct* curr =
                        &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];

                /*
                 * Can't test curr->present, we may need to clear a descriptor
                 * which had a value.
                 */
                if (curr->flushed)
                        continue;
                ret = 1;
                break;
        }
        return ret;
}

/*
 * On a newly forked process, the TLS descriptors haven't yet been flushed. So
 * we mark them as such and the first switch_to will do the job.
 */
void clear_flushed_tls(struct task_struct *task)
{
        int i;

        for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
                struct uml_tls_struct* curr =
                        &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];

                /*
                 * Still correct to do this, if it wasn't present on the host it
                 * will remain as flushed as it was.
                 */
                if (!curr->present)
                        continue;

                curr->flushed = 0;
        }
}

/*
 * In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
 * common host process. So this is needed in SKAS0 too.
 *
 * However, if each thread had a different host process (and this was discussed
 * for SMP support) this won't be needed.
 *
 * And this will not need be used when (and if) we'll add support to the host
 * SKAS patch.
 */

int arch_switch_tls(struct task_struct *to)
{
        if (!host_supports_tls)
                return 0;

        /*
         * We have no need whatsoever to switch TLS for kernel threads; beyond
         * that, that would also result in us calling os_set_thread_area with
         * task->mm == NULL, which would cause a crash.
         */
        if (likely(to->mm))
                return load_TLS(O_FORCE, to);

        return 0;
}

static int set_tls_entry(struct task_struct* task, struct user_desc *info,
                         int idx, int flushed)
{
        struct thread_struct *t = &task->thread;

        if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
                return -EINVAL;

        t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info;
        t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1;
        t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed;

        return 0;
}

int arch_set_tls(struct task_struct *new, unsigned long tls)
{
        struct user_desc info;
        int idx, ret = -EFAULT;

        if (copy_from_user(&info, (void __user *) tls, sizeof(info)))
                goto out;

        ret = -EINVAL;
        if (LDT_empty(&info))
                goto out;

        idx = info.entry_number;

        ret = set_tls_entry(new, &info, idx, 0);
out:
        return ret;
}

static int get_tls_entry(struct task_struct *task, struct user_desc *info,
                         int idx)
{
        struct thread_struct *t = &task->thread;

        if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
                return -EINVAL;

        if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present)
                goto clear;

        *info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls;

out:
        /*
         * Temporary debugging check, to make sure that things have been
         * flushed. This could be triggered if load_TLS() failed.
         */
        if (unlikely(task == current &&
                     !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) {
                printk(KERN_ERR "get_tls_entry: task with pid %d got here "
                                "without flushed TLS.", current->pid);
        }

        return 0;
clear:
        /*
         * When the TLS entry has not been set, the values read to user in the
         * tls_array are 0 (because it's cleared at boot, see
         * arch/i386/kernel/head.S:cpu_gdt_table). Emulate that.
         */
        clear_user_desc(info);
        info->entry_number = idx;
        goto out;
}

SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, user_desc)
{
        struct user_desc info;
        int idx, ret;

        if (!host_supports_tls)
                return -ENOSYS;

        if (copy_from_user(&info, user_desc, sizeof(info)))
                return -EFAULT;

        idx = info.entry_number;

        if (idx == -1) {
                idx = get_free_idx(current);
                if (idx < 0)
                        return idx;
                info.entry_number = idx;
                /* Tell the user which slot we chose for him.*/
                if (put_user(idx, &user_desc->entry_number))
                        return -EFAULT;
        }

        ret = do_set_thread_area(current, &info);
        if (ret)
                return ret;
        return set_tls_entry(current, &info, idx, 1);
}

/*
 * Perform set_thread_area on behalf of the traced child.
 * Note: error handling is not done on the deferred load, and this differ from
 * i386. However the only possible error are caused by bugs.
 */
int ptrace_set_thread_area(struct task_struct *child, int idx,
                           struct user_desc __user *user_desc)
{
        struct user_desc info;

        if (!host_supports_tls)
                return -EIO;

        if (copy_from_user(&info, user_desc, sizeof(info)))
                return -EFAULT;

        return set_tls_entry(child, &info, idx, 0);
}

SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, user_desc)
{
        struct user_desc info;
        int idx, ret;

        if (!host_supports_tls)
                return -ENOSYS;

        if (get_user(idx, &user_desc->entry_number))
                return -EFAULT;

        ret = get_tls_entry(current, &info, idx);
        if (ret < 0)
                goto out;

        if (copy_to_user(user_desc, &info, sizeof(info)))
                ret = -EFAULT;

out:
        return ret;
}

/*
 * Perform get_thread_area on behalf of the traced child.
 */
int ptrace_get_thread_area(struct task_struct *child, int idx,
                struct user_desc __user *user_desc)
{
        struct user_desc info;
        int ret;

        if (!host_supports_tls)
                return -EIO;

        ret = get_tls_entry(child, &info, idx);
        if (ret < 0)
                goto out;

        if (copy_to_user(user_desc, &info, sizeof(info)))
                ret = -EFAULT;
out:
        return ret;
}

/*
 * This code is really i386-only, but it detects and logs x86_64 GDT indexes
 * if a 32-bit UML is running on a 64-bit host.
 */
static int __init __setup_host_supports_tls(void)
{
        check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
        if (host_supports_tls) {
                printk(KERN_INFO "Host TLS support detected\n");
                printk(KERN_INFO "Detected host type: ");
                switch (host_gdt_entry_tls_min) {
                case GDT_ENTRY_TLS_MIN_I386:
                        printk(KERN_CONT "i386");
                        break;
                case GDT_ENTRY_TLS_MIN_X86_64:
                        printk(KERN_CONT "x86_64");
                        break;
                }
                printk(KERN_CONT " (GDT indexes %d to %d)\n",
                       host_gdt_entry_tls_min,
                       host_gdt_entry_tls_min + GDT_ENTRY_TLS_ENTRIES);
        } else
                printk(KERN_ERR "  Host TLS support NOT detected! "
                                "TLS support inside UML will not work\n");
        return 0;
}

__initcall(__setup_host_supports_tls);