ClabureDB: Classified Bug-Reports Database

  /*
   *        mm/mremap.c
   *
   *        (C) Copyright 1996 Linus Torvalds
   *
   *        Address space accounting code        <alan@redhat.com>
   *        (C) Copyright 2002 Red Hat Inc, All Rights Reserved
   */
  
 #include <linux/mm.h>
 #include <linux/hugetlb.h>
 #include <linux/slab.h>
 #include <linux/shm.h>
 #include <linux/mman.h>
 #include <linux/swap.h>
 #include <linux/capability.h>
 #include <linux/fs.h>
 #include <linux/highmem.h>
 #include <linux/security.h>
 #include <linux/syscalls.h>
 #include <linux/mmu_notifier.h>
 
 #include <asm/uaccess.h>
 #include <asm/cacheflush.h>
 #include <asm/tlbflush.h>
 
 #include "internal.h"
 
 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
 {
         pgd_t *pgd;
         pud_t *pud;
         pmd_t *pmd;
 
         pgd = pgd_offset(mm, addr);
         if (pgd_none_or_clear_bad(pgd))
                 return NULL;
 
         pud = pud_offset(pgd, addr);
         if (pud_none_or_clear_bad(pud))
                 return NULL;
 
         pmd = pmd_offset(pud, addr);
         if (pmd_none_or_clear_bad(pmd))
                 return NULL;
 
         return pmd;
 }
 
 static pmd_t *alloc_new_pmd(struct mm_struct *mm, unsigned long addr)
 {
         pgd_t *pgd;
         pud_t *pud;
         pmd_t *pmd;
 
         pgd = pgd_offset(mm, addr);
         pud = pud_alloc(mm, pgd, addr);
         if (!pud)
                 return NULL;
 
         pmd = pmd_alloc(mm, pud, addr);
         if (!pmd)
                 return NULL;
 
         if (!pmd_present(*pmd) && __pte_alloc(mm, pmd, addr))
                 return NULL;
 
         return pmd;
 }
 
 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
                 unsigned long old_addr, unsigned long old_end,
                 struct vm_area_struct *new_vma, pmd_t *new_pmd,
                 unsigned long new_addr)
 {
         struct address_space *mapping = NULL;
         struct mm_struct *mm = vma->vm_mm;
         pte_t *old_pte, *new_pte, pte;
         spinlock_t *old_ptl, *new_ptl;
         unsigned long old_start;
 
         old_start = old_addr;
         mmu_notifier_invalidate_range_start(vma->vm_mm,
                                             old_start, old_end);
         if (vma->vm_file) {
                 /*
                  * Subtle point from Rajesh Venkatasubramanian: before
                  * moving file-based ptes, we must lock vmtruncate out,
                  * since it might clean the dst vma before the src vma,
                  * and we propagate stale pages into the dst afterward.
                  */
                 mapping = vma->vm_file->f_mapping;
                 spin_lock(&mapping->i_mmap_lock);
                 if (new_vma->vm_truncate_count &&
                     new_vma->vm_truncate_count != vma->vm_truncate_count)
                         new_vma->vm_truncate_count = 0;
         }
 
         /*
         * We don't have to worry about the ordering of src and dst
         * pte locks because exclusive mmap_sem prevents deadlock.
         */
        old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
         new_pte = pte_offset_map_nested(new_pmd, new_addr);
        new_ptl = pte_lockptr(mm, new_pmd);
        if (new_ptl != old_ptl)
                spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
        arch_enter_lazy_mmu_mode();

        for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
                                   new_pte++, new_addr += PAGE_SIZE) {
                if (pte_none(*old_pte))
                        continue;
                pte = ptep_clear_flush(vma, old_addr, old_pte);
                pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
                set_pte_at(mm, new_addr, new_pte, pte);
        }

        arch_leave_lazy_mmu_mode();
        if (new_ptl != old_ptl)
                spin_unlock(new_ptl);
        pte_unmap_nested(new_pte - 1);
        pte_unmap_unlock(old_pte - 1, old_ptl);
        if (mapping)
                spin_unlock(&mapping->i_mmap_lock);
        mmu_notifier_invalidate_range_end(vma->vm_mm, old_start, old_end);
}

#define LATENCY_LIMIT        (64 * PAGE_SIZE)

unsigned long move_page_tables(struct vm_area_struct *vma,
                unsigned long old_addr, struct vm_area_struct *new_vma,
                unsigned long new_addr, unsigned long len)
{
        unsigned long extent, next, old_end;
        pmd_t *old_pmd, *new_pmd;

        old_end = old_addr + len;
        flush_cache_range(vma, old_addr, old_end);

        for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
                cond_resched();
                next = (old_addr + PMD_SIZE) & PMD_MASK;
                if (next - 1 > old_end)
                        next = old_end;
                extent = next - old_addr;
                old_pmd = get_old_pmd(vma->vm_mm, old_addr);
                if (!old_pmd)
                        continue;
                new_pmd = alloc_new_pmd(vma->vm_mm, new_addr);
                if (!new_pmd)
                        break;
                next = (new_addr + PMD_SIZE) & PMD_MASK;
                if (extent > next - new_addr)
                        extent = next - new_addr;
                if (extent > LATENCY_LIMIT)
                        extent = LATENCY_LIMIT;
                move_ptes(vma, old_pmd, old_addr, old_addr + extent,
                                new_vma, new_pmd, new_addr);
        }

        return len + old_addr - old_end;        /* how much done */
}

static unsigned long move_vma(struct vm_area_struct *vma,
                unsigned long old_addr, unsigned long old_len,
                unsigned long new_len, unsigned long new_addr)
{
        struct mm_struct *mm = vma->vm_mm;
        struct vm_area_struct *new_vma;
        unsigned long vm_flags = vma->vm_flags;
        unsigned long new_pgoff;
        unsigned long moved_len;
        unsigned long excess = 0;
        unsigned long hiwater_vm;
        int split = 0;

        /*
         * We'd prefer to avoid failure later on in do_munmap:
         * which may split one vma into three before unmapping.
         */
        if (mm->map_count >= sysctl_max_map_count - 3)
                return -ENOMEM;

        new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
        new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff);
        if (!new_vma)
                return -ENOMEM;

        moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len);
        if (moved_len < old_len) {
                /*
                 * On error, move entries back from new area to old,
                 * which will succeed since page tables still there,
                 * and then proceed to unmap new area instead of old.
                 */
                move_page_tables(new_vma, new_addr, vma, old_addr, moved_len);
                vma = new_vma;
                old_len = new_len;
                old_addr = new_addr;
                new_addr = -ENOMEM;
        }

        /* Conceal VM_ACCOUNT so old reservation is not undone */
        if (vm_flags & VM_ACCOUNT) {
                vma->vm_flags &= ~VM_ACCOUNT;
                excess = vma->vm_end - vma->vm_start - old_len;
                if (old_addr > vma->vm_start &&
                    old_addr + old_len < vma->vm_end)
                        split = 1;
        }

        /*
         * If we failed to move page tables we still do total_vm increment
         * since do_munmap() will decrement it by old_len == new_len.
         *
         * Since total_vm is about to be raised artificially high for a
         * moment, we need to restore high watermark afterwards: if stats
         * are taken meanwhile, total_vm and hiwater_vm appear too high.
         * If this were a serious issue, we'd add a flag to do_munmap().
         */
        hiwater_vm = mm->hiwater_vm;
        mm->total_vm += new_len >> PAGE_SHIFT;
        vm_stat_account(mm, vma->vm_flags, vma->vm_file, new_len>>PAGE_SHIFT);

        if (do_munmap(mm, old_addr, old_len) < 0) {
                /* OOM: unable to split vma, just get accounts right */
                vm_unacct_memory(excess >> PAGE_SHIFT);
                excess = 0;
        }
        mm->hiwater_vm = hiwater_vm;

        /* Restore VM_ACCOUNT if one or two pieces of vma left */
        if (excess) {
                vma->vm_flags |= VM_ACCOUNT;
                if (split)
                        vma->vm_next->vm_flags |= VM_ACCOUNT;
        }

        if (vm_flags & VM_LOCKED) {
                mm->locked_vm += new_len >> PAGE_SHIFT;
                if (new_len > old_len)
                        mlock_vma_pages_range(new_vma, new_addr + old_len,
                                                       new_addr + new_len);
        }

        return new_addr;
}

/*
 * Expand (or shrink) an existing mapping, potentially moving it at the
 * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 *
 * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 * This option implies MREMAP_MAYMOVE.
 */
unsigned long do_mremap(unsigned long addr,
        unsigned long old_len, unsigned long new_len,
        unsigned long flags, unsigned long new_addr)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        unsigned long ret = -EINVAL;
        unsigned long charged = 0;

        if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
                goto out;

        if (addr & ~PAGE_MASK)
                goto out;

        old_len = PAGE_ALIGN(old_len);
        new_len = PAGE_ALIGN(new_len);

        /*
         * We allow a zero old-len as a special case
         * for DOS-emu "duplicate shm area" thing. But
         * a zero new-len is nonsensical.
         */
        if (!new_len)
                goto out;

        /* new_addr is only valid if MREMAP_FIXED is specified */
        if (flags & MREMAP_FIXED) {
                if (new_addr & ~PAGE_MASK)
                        goto out;
                if (!(flags & MREMAP_MAYMOVE))
                        goto out;

                if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
                        goto out;

                /* Check if the location we're moving into overlaps the
                 * old location at all, and fail if it does.
                 */
                if ((new_addr <= addr) && (new_addr+new_len) > addr)
                        goto out;

                if ((addr <= new_addr) && (addr+old_len) > new_addr)
                        goto out;

                ret = security_file_mmap(NULL, 0, 0, 0, new_addr, 1);
                if (ret)
                        goto out;

                ret = do_munmap(mm, new_addr, new_len);
                if (ret)
                        goto out;
        }

        /*
         * Always allow a shrinking remap: that just unmaps
         * the unnecessary pages..
         * do_munmap does all the needed commit accounting
         */
        if (old_len >= new_len) {
                ret = do_munmap(mm, addr+new_len, old_len - new_len);
                if (ret && old_len != new_len)
                        goto out;
                ret = addr;
                if (!(flags & MREMAP_FIXED) || (new_addr == addr))
                        goto out;
                old_len = new_len;
        }

        /*
         * Ok, we need to grow..  or relocate.
         */
        ret = -EFAULT;
        vma = find_vma(mm, addr);
        if (!vma || vma->vm_start > addr)
                goto out;
        if (is_vm_hugetlb_page(vma)) {
                ret = -EINVAL;
                goto out;
        }
        /* We can't remap across vm area boundaries */
        if (old_len > vma->vm_end - addr)
                goto out;
        if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)) {
                if (new_len > old_len)
                        goto out;
        }
        if (vma->vm_flags & VM_LOCKED) {
                unsigned long locked, lock_limit;
                locked = mm->locked_vm << PAGE_SHIFT;
                lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
                locked += new_len - old_len;
                ret = -EAGAIN;
                if (locked > lock_limit && !capable(CAP_IPC_LOCK))
                        goto out;
        }
        if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT)) {
                ret = -ENOMEM;
                goto out;
        }

        if (vma->vm_flags & VM_ACCOUNT) {
                charged = (new_len - old_len) >> PAGE_SHIFT;
                if (security_vm_enough_memory(charged))
                        goto out_nc;
        }

        /* old_len exactly to the end of the area..
         * And we're not relocating the area.
         */
        if (old_len == vma->vm_end - addr &&
            !((flags & MREMAP_FIXED) && (addr != new_addr)) &&
            (old_len != new_len || !(flags & MREMAP_MAYMOVE))) {
                unsigned long max_addr = TASK_SIZE;
                if (vma->vm_next)
                        max_addr = vma->vm_next->vm_start;
                /* can we just expand the current mapping? */
                if (max_addr - addr >= new_len) {
                        int pages = (new_len - old_len) >> PAGE_SHIFT;

                        vma_adjust(vma, vma->vm_start,
                                addr + new_len, vma->vm_pgoff, NULL);

                        mm->total_vm += pages;
                        vm_stat_account(mm, vma->vm_flags, vma->vm_file, pages);
                        if (vma->vm_flags & VM_LOCKED) {
                                mm->locked_vm += pages;
                                mlock_vma_pages_range(vma, addr + old_len,
                                                   addr + new_len);
                        }
                        ret = addr;
                        goto out;
                }
        }

        /*
         * We weren't able to just expand or shrink the area,
         * we need to create a new one and move it..
         */
        ret = -ENOMEM;
        if (flags & MREMAP_MAYMOVE) {
                if (!(flags & MREMAP_FIXED)) {
                        unsigned long map_flags = 0;
                        if (vma->vm_flags & VM_MAYSHARE)
                                map_flags |= MAP_SHARED;

                        new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
                                                vma->vm_pgoff, map_flags);
                        if (new_addr & ~PAGE_MASK) {
                                ret = new_addr;
                                goto out;
                        }

                        ret = security_file_mmap(NULL, 0, 0, 0, new_addr, 1);
                        if (ret)
                                goto out;
                }
                ret = move_vma(vma, addr, old_len, new_len, new_addr);
        }
out:
        if (ret & ~PAGE_MASK)
                vm_unacct_memory(charged);
out_nc:
        return ret;
}

asmlinkage unsigned long sys_mremap(unsigned long addr,
        unsigned long old_len, unsigned long new_len,
        unsigned long flags, unsigned long new_addr)
{
        unsigned long ret;

        down_write(&current->mm->mmap_sem);
        ret = do_mremap(addr, old_len, new_len, flags, new_addr);
        up_write(&current->mm->mmap_sem);
        return ret;
}