// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
 * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
 * Copyright (C) 2002 Andi Kleen
 *
 * This handles calls from both 32bit and 64bit mode.
 */

#include <linux/errno.h>
#include <linux/gfp.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/uaccess.h>

#include <asm/ldt.h>
#include <asm/desc.h>
#include <asm/mmu_context.h>
#include <asm/syscalls.h>

static void refresh_ldt_segments(void)
{
#ifdef CONFIG_X86_64
        unsigned short sel;

        /*
         * Make sure that the cached DS and ES descriptors match the updated
         * LDT.
         */
        savesegment(ds, sel);
        if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT)
                loadsegment(ds, sel);

        savesegment(es, sel);
        if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT)
                loadsegment(es, sel);
#endif
}

/* context.lock is held for us, so we don't need any locking. */
static void flush_ldt(void *__mm)
{
        struct mm_struct *mm = __mm;
        mm_context_t *pc;

        if (this_cpu_read(cpu_tlbstate.loaded_mm) != mm)
                return;

        pc = &mm->context;
        set_ldt(pc->ldt->entries, pc->ldt->nr_entries);

        refresh_ldt_segments();
}

/* The caller must call finalize_ldt_struct on the result. LDT starts zeroed. */
static struct ldt_struct *alloc_ldt_struct(unsigned int num_entries)
{
        struct ldt_struct *new_ldt;
        unsigned int alloc_size;

        if (num_entries > LDT_ENTRIES)
                return NULL;

        new_ldt = kmalloc(sizeof(struct ldt_struct), GFP_KERNEL);
        if (!new_ldt)
                return NULL;

        BUILD_BUG_ON(LDT_ENTRY_SIZE != sizeof(struct desc_struct));
        alloc_size = num_entries * LDT_ENTRY_SIZE;

        /*
         * Xen is very picky: it requires a page-aligned LDT that has no
         * trailing nonzero bytes in any page that contains LDT descriptors.
         * Keep it simple: zero the whole allocation and never allocate less
         * than PAGE_SIZE.
         */
        if (alloc_size > PAGE_SIZE)
                new_ldt->entries = vzalloc(alloc_size);
        else
                new_ldt->entries = (void *)get_zeroed_page(GFP_KERNEL);

        if (!new_ldt->entries) {
                kfree(new_ldt);
                return NULL;
        }

        new_ldt->nr_entries = num_entries;
        return new_ldt;
}

/* After calling this, the LDT is immutable. */
static void finalize_ldt_struct(struct ldt_struct *ldt)
{
        paravirt_alloc_ldt(ldt->entries, ldt->nr_entries);
}

/* context.lock is held */
static void install_ldt(struct mm_struct *current_mm,
                        struct ldt_struct *ldt)
{
        /* Synchronizes with lockless_dereference in load_mm_ldt. */
        smp_store_release(&current_mm->context.ldt, ldt);

        /* Activate the LDT for all CPUs using current_mm. */
        on_each_cpu_mask(mm_cpumask(current_mm), flush_ldt, current_mm, true);
}

static void free_ldt_struct(struct ldt_struct *ldt)
{
        if (likely(!ldt))
                return;

        paravirt_free_ldt(ldt->entries, ldt->nr_entries);
        if (ldt->nr_entries * LDT_ENTRY_SIZE > PAGE_SIZE)
                vfree_atomic(ldt->entries);
        else
                free_page((unsigned long)ldt->entries);
        kfree(ldt);
}

/*
 * we do not have to muck with descriptors here, that is
 * done in switch_mm() as needed.
 */
int init_new_context_ldt(struct task_struct *tsk, struct mm_struct *mm)
{
        struct ldt_struct *new_ldt;
        struct mm_struct *old_mm;
        int retval = 0;

        mutex_init(&mm->context.lock);
        old_mm = current->mm;
        if (!old_mm) {
                mm->context.ldt = NULL;
                return 0;
        }

        mutex_lock(&old_mm->context.lock);
        if (!old_mm->context.ldt) {
                mm->context.ldt = NULL;
                goto out_unlock;
        }

        new_ldt = alloc_ldt_struct(old_mm->context.ldt->nr_entries);
        if (!new_ldt) {
                retval = -ENOMEM;
                goto out_unlock;
        }

        memcpy(new_ldt->entries, old_mm->context.ldt->entries,
               new_ldt->nr_entries * LDT_ENTRY_SIZE);
        finalize_ldt_struct(new_ldt);

        mm->context.ldt = new_ldt;

out_unlock:
        mutex_unlock(&old_mm->context.lock);
        return retval;
}

/*
 * No need to lock the MM as we are the last user
 *
 * 64bit: Don't touch the LDT register - we're already in the next thread.
 */
void destroy_context_ldt(struct mm_struct *mm)
{
        free_ldt_struct(mm->context.ldt);
        mm->context.ldt = NULL;
}

static int read_ldt(void __user *ptr, unsigned long bytecount)
{
        struct mm_struct *mm = current->mm;
        unsigned long entries_size;
        int retval;

        mutex_lock(&mm->context.lock);

        if (!mm->context.ldt) {
                retval = 0;
                goto out_unlock;
        }

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

        entries_size = mm->context.ldt->nr_entries * LDT_ENTRY_SIZE;
        if (entries_size > bytecount)
                entries_size = bytecount;

        if (copy_to_user(ptr, mm->context.ldt->entries, entries_size)) {
                retval = -EFAULT;
                goto out_unlock;
        }

        if (entries_size != bytecount) {
                /* Zero-fill the rest and pretend we read bytecount bytes. */
                if (clear_user(ptr + entries_size, bytecount - entries_size)) {
                        retval = -EFAULT;
                        goto out_unlock;
                }
        }
        retval = bytecount;

out_unlock:
        mutex_unlock(&mm->context.lock);
        return retval;
}

static int read_default_ldt(void __user *ptr, unsigned long bytecount)
{
        /* CHECKME: Can we use _one_ random number ? */
#ifdef CONFIG_X86_32
        unsigned long size = 5 * sizeof(struct desc_struct);
#else
        unsigned long size = 128;
#endif
        if (bytecount > size)
                bytecount = size;
        if (clear_user(ptr, bytecount))
                return -EFAULT;
        return bytecount;
}

static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
{
        struct mm_struct *mm = current->mm;
        struct ldt_struct *new_ldt, *old_ldt;
        unsigned int old_nr_entries, new_nr_entries;
        struct user_desc ldt_info;
        struct desc_struct ldt;
        int error;

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

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

        if ((oldmode && !ldt_info.base_addr && !ldt_info.limit) ||
            LDT_empty(&ldt_info)) {
                /* The user wants to clear the entry. */
                memset(&ldt, 0, sizeof(ldt));
        } else {
                if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) {
                        error = -EINVAL;
                        goto out;
                }

                fill_ldt(&ldt, &ldt_info);
                if (oldmode)
                        ldt.avl = 0;
        }

        mutex_lock(&mm->context.lock);

        old_ldt       = mm->context.ldt;
        old_nr_entries = old_ldt ? old_ldt->nr_entries : 0;
        new_nr_entries = max(ldt_info.entry_number + 1, old_nr_entries);

        error = -ENOMEM;
        new_ldt = alloc_ldt_struct(new_nr_entries);
        if (!new_ldt)
                goto out_unlock;

        if (old_ldt)
                memcpy(new_ldt->entries, old_ldt->entries, old_nr_entries * LDT_ENTRY_SIZE);

        new_ldt->entries[ldt_info.entry_number] = ldt;
        finalize_ldt_struct(new_ldt);

        install_ldt(mm, new_ldt);
        free_ldt_struct(old_ldt);
        error = 0;

out_unlock:
        mutex_unlock(&mm->context.lock);
out:
        return error;
}

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

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