ldt.c

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/*
 * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 * Licensed under the GPL
 */

#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <asm/unistd.h>
#include <os.h>
#include <proc_mm.h>
#include <skas.h>
#include <skas_ptrace.h>
#include <sysdep/tls.h>

extern int modify_ldt(int func, void *ptr, unsigned long bytecount);

static long write_ldt_entry(struct mm_id *mm_idp, int func,
             struct user_desc *desc, void **addr, int done)
{
    long res;

    if (proc_mm) {
        /*
         * This is a special handling for the case, that the mm to
         * modify isn't current->active_mm.
         * If this is called directly by modify_ldt,
         *     (current->active_mm->context.skas.u == mm_idp)
         * will be true. So no call to __switch_mm(mm_idp) is done.
         * If this is called in case of init_new_ldt or PTRACE_LDT,
         * mm_idp won't belong to current->active_mm, but child->mm.
         * So we need to switch child's mm into our userspace, then
         * later switch back.
         *
         * Note: I'm unsure: should interrupts be disabled here?
         */
        if (!current->active_mm || current->active_mm == &init_mm ||
            mm_idp != &current->active_mm->context.id)
            __switch_mm(mm_idp);
    }

    if (ptrace_ldt) {
        struct ptrace_ldt ldt_op = (struct ptrace_ldt) {
            .func = func,
            .ptr = desc,
            .bytecount = sizeof(*desc)};
        u32 cpu;
        int pid;

        if (!proc_mm)
            pid = mm_idp->u.pid;
        else {
            cpu = get_cpu();
            pid = userspace_pid[cpu];
        }

        res = os_ptrace_ldt(pid, 0, (unsigned long) &ldt_op);

        if (proc_mm)
            put_cpu();
    }
    else {
        void *stub_addr;
        res = syscall_stub_data(mm_idp, (unsigned long *)desc,
                    (sizeof(*desc) + sizeof(long) - 1) &
                        ~(sizeof(long) - 1),
                    addr, &stub_addr);
        if (!res) {
            unsigned long args[] = { func,
                         (unsigned long)stub_addr,
                         sizeof(*desc),
                         0, 0, 0 };
            res = run_syscall_stub(mm_idp, __NR_modify_ldt, args,
                           0, addr, done);
        }
    }

    if (proc_mm) {
        /*
         * This is the second part of special handling, that makes
         * PTRACE_LDT possible to implement.
         */
        if (current->active_mm && current->active_mm != &init_mm &&
            mm_idp != &current->active_mm->context.id)
            __switch_mm(&current->active_mm->context.id);
    }

    return res;
}

static long read_ldt_from_host(void __user * ptr, unsigned long bytecount)
{
    int res, n;
    struct ptrace_ldt ptrace_ldt = (struct ptrace_ldt) {
            .func = 0,
            .bytecount = bytecount,
            .ptr = kmalloc(bytecount, GFP_KERNEL)};
    u32 cpu;

    if (ptrace_ldt.ptr == NULL)
        return -ENOMEM;

    /*
     * This is called from sys_modify_ldt only, so userspace_pid gives
     * us the right number
     */

    cpu = get_cpu();
    res = os_ptrace_ldt(userspace_pid[cpu], 0, (unsigned long) &ptrace_ldt);
    put_cpu();
    if (res < 0)
        goto out;

    n = copy_to_user(ptr, ptrace_ldt.ptr, res);
    if (n != 0)
        res = -EFAULT;

  out:
    kfree(ptrace_ldt.ptr);

    return res;
}

/*
 * In skas mode, we hold our own ldt data in UML.
 * Thus, the code implementing sys_modify_ldt_skas
 * is very similar to (and mostly stolen from) sys_modify_ldt
 * for arch/i386/kernel/ldt.c
 * The routines copied and modified in part are:
 * - read_ldt
 * - read_default_ldt
 * - write_ldt
 * - sys_modify_ldt_skas
 */

static int read_ldt(void __user * ptr, unsigned long bytecount)
{
    int i, err = 0;
    unsigned long size;
    uml_ldt_t *ldt = &current->mm->context.arch.ldt;

    if (!ldt->entry_count)
        goto out;
    if (bytecount > LDT_ENTRY_SIZE*LDT_ENTRIES)
        bytecount = LDT_ENTRY_SIZE*LDT_ENTRIES;
    err = bytecount;

    if (ptrace_ldt)
        return read_ldt_from_host(ptr, bytecount);

    mutex_lock(&ldt->lock);
    if (ldt->entry_count <= LDT_DIRECT_ENTRIES) {
        size = LDT_ENTRY_SIZE*LDT_DIRECT_ENTRIES;
        if (size > bytecount)
            size = bytecount;
        if (copy_to_user(ptr, ldt->u.entries, size))
            err = -EFAULT;
        bytecount -= size;
        ptr += size;
    }
    else {
        for (i=0; i<ldt->entry_count/LDT_ENTRIES_PER_PAGE && bytecount;
             i++) {
            size = PAGE_SIZE;
            if (size > bytecount)
                size = bytecount;
            if (copy_to_user(ptr, ldt->u.pages[i], size)) {
                err = -EFAULT;
                break;
            }
            bytecount -= size;
            ptr += size;
        }
    }
    mutex_unlock(&ldt->lock);

    if (bytecount == 0 || err == -EFAULT)
        goto out;

    if (clear_user(ptr, bytecount))
        err = -EFAULT;

out:
    return err;
}

static int read_default_ldt(void __user * ptr, unsigned long bytecount)
{
    int err;

    if (bytecount > 5*LDT_ENTRY_SIZE)
        bytecount = 5*LDT_ENTRY_SIZE;

    err = bytecount;
    /*
     * UML doesn't support lcall7 and lcall27.
     * So, we don't really have a default ldt, but emulate
     * an empty ldt of common host default ldt size.
     */
    if (clear_user(ptr, bytecount))
        err = -EFAULT;

    return err;
}

static int write_ldt(void __user * ptr, unsigned long bytecount, int func)
{
    uml_ldt_t *ldt = &current->mm->context.arch.ldt;
    struct mm_id * mm_idp = &current->mm->context.id;
    int i, err;
    struct user_desc ldt_info;
    struct ldt_entry entry0, *ldt_p;
    void *addr = NULL;

    err = -EINVAL;
    if (bytecount != sizeof(ldt_info))
        goto out;
    err = -EFAULT;
    if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
        goto out;

    err = -EINVAL;
    if (ldt_info.entry_number >= LDT_ENTRIES)
        goto out;
    if (ldt_info.contents == 3) {
        if (func == 1)
            goto out;
        if (ldt_info.seg_not_present == 0)
            goto out;
    }

    if (!ptrace_ldt)
        mutex_lock(&ldt->lock);

    err = write_ldt_entry(mm_idp, func, &ldt_info, &addr, 1);
    if (err)
        goto out_unlock;
    else if (ptrace_ldt) {
        /* With PTRACE_LDT available, this is used as a flag only */
        ldt->entry_count = 1;
        goto out;
    }

    if (ldt_info.entry_number >= ldt->entry_count &&
        ldt_info.entry_number >= LDT_DIRECT_ENTRIES) {
        for (i=ldt->entry_count/LDT_ENTRIES_PER_PAGE;
             i*LDT_ENTRIES_PER_PAGE <= ldt_info.entry_number;
             i++) {
            if (i == 0)
                memcpy(&entry0, ldt->u.entries,
                       sizeof(entry0));
            ldt->u.pages[i] = (struct ldt_entry *)
                __get_free_page(GFP_KERNEL|__GFP_ZERO);
            if (!ldt->u.pages[i]) {
                err = -ENOMEM;
                /* Undo the change in host */
                memset(&ldt_info, 0, sizeof(ldt_info));
                write_ldt_entry(mm_idp, 1, &ldt_info, &addr, 1);
                goto out_unlock;
            }
            if (i == 0) {
                memcpy(ldt->u.pages[0], &entry0,
                       sizeof(entry0));
                memcpy(ldt->u.pages[0]+1, ldt->u.entries+1,
                       sizeof(entry0)*(LDT_DIRECT_ENTRIES-1));
            }
            ldt->entry_count = (i + 1) * LDT_ENTRIES_PER_PAGE;
        }
    }
    if (ldt->entry_count <= ldt_info.entry_number)
        ldt->entry_count = ldt_info.entry_number + 1;

    if (ldt->entry_count <= LDT_DIRECT_ENTRIES)
        ldt_p = ldt->u.entries + ldt_info.entry_number;
    else
        ldt_p = ldt->u.pages[ldt_info.entry_number/LDT_ENTRIES_PER_PAGE] +
            ldt_info.entry_number%LDT_ENTRIES_PER_PAGE;

    if (ldt_info.base_addr == 0 && ldt_info.limit == 0 &&
       (func == 1 || LDT_empty(&ldt_info))) {
        ldt_p->a = 0;
        ldt_p->b = 0;
    }
    else{
        if (func == 1)
            ldt_info.useable = 0;
        ldt_p->a = LDT_entry_a(&ldt_info);
        ldt_p->b = LDT_entry_b(&ldt_info);
    }
    err = 0;

out_unlock:
    mutex_unlock(&ldt->lock);
out:
    return err;
}

static long do_modify_ldt_skas(int func, void __user *ptr,
                   unsigned long bytecount)
{
    int ret = -ENOSYS;

    switch (func) {
        case 0:
            ret = read_ldt(ptr, bytecount);
            break;
        case 1:
        case 0x11:
            ret = write_ldt(ptr, bytecount, func);
            break;
        case 2:
            ret = read_default_ldt(ptr, bytecount);
            break;
    }
    return ret;
}

static DEFINE_SPINLOCK(host_ldt_lock);
static short dummy_list[9] = {0, -1};
static short * host_ldt_entries = NULL;

static void ldt_get_host_info(void)
{
    long ret;
    struct ldt_entry * ldt;
    short *tmp;
    int i, size, k, order;

    spin_lock(&host_ldt_lock);

    if (host_ldt_entries != NULL) {
        spin_unlock(&host_ldt_lock);
        return;
    }
    host_ldt_entries = dummy_list+1;

    spin_unlock(&host_ldt_lock);

    for (i = LDT_PAGES_MAX-1, order=0; i; i>>=1, order++)
        ;

    ldt = (struct ldt_entry *)
          __get_free_pages(GFP_KERNEL|__GFP_ZERO, order);
    if (ldt == NULL) {
        printk(KERN_ERR "ldt_get_host_info: couldn't allocate buffer "
               "for host ldt\n");
        return;
    }

    ret = modify_ldt(0, ldt, (1<<order)*PAGE_SIZE);
    if (ret < 0) {
        printk(KERN_ERR "ldt_get_host_info: couldn't read host ldt\n");
        goto out_free;
    }
    if (ret == 0) {
        /* default_ldt is active, simply write an empty entry 0 */
        host_ldt_entries = dummy_list;
        goto out_free;
    }

    for (i=0, size=0; i<ret/LDT_ENTRY_SIZE; i++) {
        if (ldt[i].a != 0 || ldt[i].b != 0)
            size++;
    }

    if (size < ARRAY_SIZE(dummy_list))
        host_ldt_entries = dummy_list;
    else {
        size = (size + 1) * sizeof(dummy_list[0]);
        tmp = kmalloc(size, GFP_KERNEL);
        if (tmp == NULL) {
            printk(KERN_ERR "ldt_get_host_info: couldn't allocate "
                   "host ldt list\n");
            goto out_free;
        }
        host_ldt_entries = tmp;
    }

    for (i=0, k=0; i<ret/LDT_ENTRY_SIZE; i++) {
        if (ldt[i].a != 0 || ldt[i].b != 0)
            host_ldt_entries[k++] = i;
    }
    host_ldt_entries[k] = -1;

out_free:
    free_pages((unsigned long)ldt, order);
}

long init_new_ldt(struct mm_context *new_mm, struct mm_context *from_mm)
{
    struct user_desc desc;
    short * num_p;
    int i;
    long page, err=0;
    void *addr = NULL;
    struct proc_mm_op copy;


    if (!ptrace_ldt)
        mutex_init(&new_mm->arch.ldt.lock);

    if (!from_mm) {
        memset(&desc, 0, sizeof(desc));
        /*
         * We have to initialize a clean ldt.
         */
        if (proc_mm) {
            /*
             * If the new mm was created using proc_mm, host's
             * default-ldt currently is assigned, which normally
             * contains the call-gates for lcall7 and lcall27.
             * To remove these gates, we simply write an empty
             * entry as number 0 to the host.
             */
            err = write_ldt_entry(&new_mm->id, 1, &desc, &addr, 1);
        }
        else{
            /*
             * Now we try to retrieve info about the ldt, we
             * inherited from the host. All ldt-entries found
             * will be reset in the following loop
             */
            ldt_get_host_info();
            for (num_p=host_ldt_entries; *num_p != -1; num_p++) {
                desc.entry_number = *num_p;
                err = write_ldt_entry(&new_mm->id, 1, &desc,
                              &addr, *(num_p + 1) == -1);
                if (err)
                    break;
            }
        }
        new_mm->arch.ldt.entry_count = 0;

        goto out;
    }

    if (proc_mm) {
        /*
         * We have a valid from_mm, so we now have to copy the LDT of
         * from_mm to new_mm, because using proc_mm an new mm with
         * an empty/default LDT was created in new_mm()
         */
        copy = ((struct proc_mm_op) { .op   = MM_COPY_SEGMENTS,
                          .u    =
                          { .copy_segments =
                            from_mm->id.u.mm_fd } } );
        i = os_write_file(new_mm->id.u.mm_fd, &copy, sizeof(copy));
        if (i != sizeof(copy))
            printk(KERN_ERR "new_mm : /proc/mm copy_segments "
                   "failed, err = %d\n", -i);
    }

    if (!ptrace_ldt) {
        /*
         * Our local LDT is used to supply the data for
         * modify_ldt(READLDT), if PTRACE_LDT isn't available,
         * i.e., we have to use the stub for modify_ldt, which
         * can't handle the big read buffer of up to 64kB.
         */
        mutex_lock(&from_mm->arch.ldt.lock);
        if (from_mm->arch.ldt.entry_count <= LDT_DIRECT_ENTRIES)
            memcpy(new_mm->arch.ldt.u.entries, from_mm->arch.ldt.u.entries,
                   sizeof(new_mm->arch.ldt.u.entries));
        else {
            i = from_mm->arch.ldt.entry_count / LDT_ENTRIES_PER_PAGE;
            while (i-->0) {
                page = __get_free_page(GFP_KERNEL|__GFP_ZERO);
                if (!page) {
                    err = -ENOMEM;
                    break;
                }
                new_mm->arch.ldt.u.pages[i] =
                    (struct ldt_entry *) page;
                memcpy(new_mm->arch.ldt.u.pages[i],
                       from_mm->arch.ldt.u.pages[i], PAGE_SIZE);
            }
        }
        new_mm->arch.ldt.entry_count = from_mm->arch.ldt.entry_count;
        mutex_unlock(&from_mm->arch.ldt.lock);
    }

    out:
    return err;
}


void free_ldt(struct mm_context *mm)
{
    int i;

    if (!ptrace_ldt && mm->arch.ldt.entry_count > LDT_DIRECT_ENTRIES) {
        i = mm->arch.ldt.entry_count / LDT_ENTRIES_PER_PAGE;
        while (i-- > 0)
            free_page((long) mm->arch.ldt.u.pages[i]);
    }
    mm->arch.ldt.entry_count = 0;
}

int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount)
{
    return do_modify_ldt_skas(func, ptr, bytecount);
}