tls_32.c

Go to the documentation of this file.

/*
 * Copyright (C) 2005 Paolo 'Blaisorblade' Giarrusso <[email protected]>
 * Licensed under the GPL
 */

#include <linux/percpu.h>
#include <linux/sched.h>
#include <asm/uaccess.h>
#include <os.h>
#include <skas.h>
#include <sysdep/tls.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;

int do_set_thread_area(struct user_desc *info)
{
    int ret;
    u32 cpu;

    cpu = get_cpu();
    ret = os_set_thread_area(info, userspace_pid[cpu]);
    put_cpu();

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

    return ret;
}

int do_get_thread_area(struct user_desc *info)
{
    int ret;
    u32 cpu;

    cpu = get_cpu();
    ret = os_get_thread_area(info, userspace_pid[cpu]);
    put_cpu();

    if (ret)
        printk(KERN_ERR "PTRACE_GET_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;

    if (!t->arch.tls_array)
        return GDT_ENTRY_TLS_MIN;

    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(&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
     * userspace_pid[cpu] == 0, which gives an error.
     */
    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_copy_tls(struct task_struct *new)
{
    struct user_desc info;
    int idx, ret = -EFAULT;

    if (copy_from_user(&info,
               (void __user *) UPT_SI(&new->thread.regs.regs),
               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;
}

/* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */
static int get_tls_entry(struct task_struct *task, struct user_desc *info,
             int idx)
{
    struct thread_struct *t = &task->thread;

    if (!t->arch.tls_array)
        goto clear;

    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;
}

int sys_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(&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);
}

int sys_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);