mmap.c

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/*
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (C) 2011 Wind River Systems,
 *   written by Ralf Baechle <[email protected]>
 */
#include <linux/compiler.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/module.h>
#include <linux/personality.h>
#include <linux/random.h>
#include <linux/sched.h>

unsigned long shm_align_mask = PAGE_SIZE - 1;   /* Sane caches */
EXPORT_SYMBOL(shm_align_mask);

/* gap between mmap and stack */
#define MIN_GAP (128*1024*1024UL)
#define MAX_GAP ((TASK_SIZE)/6*5)

static int mmap_is_legacy(void)
{
    if (current->personality & ADDR_COMPAT_LAYOUT)
        return 1;

    if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
        return 1;

    return sysctl_legacy_va_layout;
}

static unsigned long mmap_base(unsigned long rnd)
{
    unsigned long gap = rlimit(RLIMIT_STACK);

    if (gap < MIN_GAP)
        gap = MIN_GAP;
    else if (gap > MAX_GAP)
        gap = MAX_GAP;

    return PAGE_ALIGN(TASK_SIZE - gap - rnd);
}

static inline unsigned long COLOUR_ALIGN_DOWN(unsigned long addr,
                          unsigned long pgoff)
{
    unsigned long base = addr & ~shm_align_mask;
    unsigned long off = (pgoff << PAGE_SHIFT) & shm_align_mask;

    if (base + off <= addr)
        return base + off;

    return base - off;
}

#define COLOUR_ALIGN(addr, pgoff)               \
    ((((addr) + shm_align_mask) & ~shm_align_mask) +    \
     (((pgoff) << PAGE_SHIFT) & shm_align_mask))

enum mmap_allocation_direction {UP, DOWN};

static unsigned long arch_get_unmapped_area_common(struct file *filp,
    unsigned long addr0, unsigned long len, unsigned long pgoff,
    unsigned long flags, enum mmap_allocation_direction dir)
{
    struct mm_struct *mm = current->mm;
    struct vm_area_struct *vma;
    unsigned long addr = addr0;
    int do_color_align;

    if (unlikely(len > TASK_SIZE))
        return -ENOMEM;

    if (flags & MAP_FIXED) {
        /* Even MAP_FIXED mappings must reside within TASK_SIZE */
        if (TASK_SIZE - len < addr)
            return -EINVAL;

        /*
         * We do not accept a shared mapping if it would violate
         * cache aliasing constraints.
         */
        if ((flags & MAP_SHARED) &&
            ((addr - (pgoff << PAGE_SHIFT)) & shm_align_mask))
            return -EINVAL;
        return addr;
    }

    do_color_align = 0;
    if (filp || (flags & MAP_SHARED))
        do_color_align = 1;

    /* requesting a specific address */
    if (addr) {
        if (do_color_align)
            addr = COLOUR_ALIGN(addr, pgoff);
        else
            addr = PAGE_ALIGN(addr);

        vma = find_vma(mm, addr);
        if (TASK_SIZE - len >= addr &&
            (!vma || addr + len <= vma->vm_start))
            return addr;
    }

    if (dir == UP) {
        addr = mm->mmap_base;
        if (do_color_align)
            addr = COLOUR_ALIGN(addr, pgoff);
        else
            addr = PAGE_ALIGN(addr);

        for (vma = find_vma(current->mm, addr); ; vma = vma->vm_next) {
            /* At this point:  (!vma || addr < vma->vm_end). */
            if (TASK_SIZE - len < addr)
                return -ENOMEM;
            if (!vma || addr + len <= vma->vm_start)
                return addr;
            addr = vma->vm_end;
            if (do_color_align)
                addr = COLOUR_ALIGN(addr, pgoff);
         }
     } else {
        /* check if free_area_cache is useful for us */
        if (len <= mm->cached_hole_size) {
            mm->cached_hole_size = 0;
            mm->free_area_cache = mm->mmap_base;
        }

        /*
         * either no address requested, or the mapping can't fit into
         * the requested address hole
         */
        addr = mm->free_area_cache;
        if (do_color_align) {
            unsigned long base =
                COLOUR_ALIGN_DOWN(addr - len, pgoff);
            addr = base + len;
        }

        /* make sure it can fit in the remaining address space */
        if (likely(addr > len)) {
            vma = find_vma(mm, addr - len);
            if (!vma || addr <= vma->vm_start) {
                /* cache the address as a hint for next time */
                return mm->free_area_cache = addr - len;
            }
        }

        if (unlikely(mm->mmap_base < len))
            goto bottomup;

        addr = mm->mmap_base - len;
        if (do_color_align)
            addr = COLOUR_ALIGN_DOWN(addr, pgoff);

        do {
            /*
             * Lookup failure means no vma is above this address,
             * else if new region fits below vma->vm_start,
             * return with success:
             */
            vma = find_vma(mm, addr);
            if (likely(!vma || addr + len <= vma->vm_start)) {
                /* cache the address as a hint for next time */
                return mm->free_area_cache = addr;
            }

            /* remember the largest hole we saw so far */
            if (addr + mm->cached_hole_size < vma->vm_start)
                mm->cached_hole_size = vma->vm_start - addr;

            /* try just below the current vma->vm_start */
            addr = vma->vm_start - len;
            if (do_color_align)
                addr = COLOUR_ALIGN_DOWN(addr, pgoff);
        } while (likely(len < vma->vm_start));

bottomup:
        /*
         * A failed mmap() very likely causes application failure,
         * so fall back to the bottom-up function here. This scenario
         * can happen with large stack limits and large mmap()
         * allocations.
         */
        mm->cached_hole_size = ~0UL;
        mm->free_area_cache = TASK_UNMAPPED_BASE;
        addr = arch_get_unmapped_area(filp, addr0, len, pgoff, flags);
        /*
         * Restore the topdown base:
         */
        mm->free_area_cache = mm->mmap_base;
        mm->cached_hole_size = ~0UL;

        return addr;
    }
}

unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr0,
    unsigned long len, unsigned long pgoff, unsigned long flags)
{
    return arch_get_unmapped_area_common(filp,
            addr0, len, pgoff, flags, UP);
}

/*
 * There is no need to export this but sched.h declares the function as
 * extern so making it static here results in an error.
 */
unsigned long arch_get_unmapped_area_topdown(struct file *filp,
    unsigned long addr0, unsigned long len, unsigned long pgoff,
    unsigned long flags)
{
    return arch_get_unmapped_area_common(filp,
            addr0, len, pgoff, flags, DOWN);
}

void arch_pick_mmap_layout(struct mm_struct *mm)
{
    unsigned long random_factor = 0UL;

    if (current->flags & PF_RANDOMIZE) {
        random_factor = get_random_int();
        random_factor = random_factor << PAGE_SHIFT;
        if (TASK_IS_32BIT_ADDR)
            random_factor &= 0xfffffful;
        else
            random_factor &= 0xffffffful;
    }

    if (mmap_is_legacy()) {
        mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
        mm->get_unmapped_area = arch_get_unmapped_area;
        mm->unmap_area = arch_unmap_area;
    } else {
        mm->mmap_base = mmap_base(random_factor);
        mm->get_unmapped_area = arch_get_unmapped_area_topdown;
        mm->unmap_area = arch_unmap_area_topdown;
    }
}

static inline unsigned long brk_rnd(void)
{
    unsigned long rnd = get_random_int();

    rnd = rnd << PAGE_SHIFT;
    /* 8MB for 32bit, 256MB for 64bit */
    if (TASK_IS_32BIT_ADDR)
        rnd = rnd & 0x7ffffful;
    else
        rnd = rnd & 0xffffffful;

    return rnd;
}

unsigned long arch_randomize_brk(struct mm_struct *mm)
{
    unsigned long base = mm->brk;
    unsigned long ret;

    ret = PAGE_ALIGN(base + brk_rnd());

    if (ret < mm->brk)
        return mm->brk;

    return ret;
}