mmap.c

/*
 * 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/errno.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/module.h>
#include <linux/random.h>
#include <linux/sched.h>

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

EXPORT_SYMBOL(shm_align_mask);

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

unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
	unsigned long len, unsigned long pgoff, unsigned long flags)
{
	struct vm_area_struct * vmm;
	int do_color_align;

	if (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;
	if (addr) {
		if (do_color_align)
			addr = COLOUR_ALIGN(addr, pgoff);
		else
			addr = PAGE_ALIGN(addr);
		vmm = find_vma(current->mm, addr);
		if (TASK_SIZE - len >= addr &&
		    (!vmm || addr + len <= vmm->vm_start))
			return addr;
	}
	addr = current->mm->mmap_base;
	if (do_color_align)
		addr = COLOUR_ALIGN(addr, pgoff);
	else
		addr = PAGE_ALIGN(addr);

	for (vmm = find_vma(current->mm, addr); ; vmm = vmm->vm_next) {
		/* At this point:  (!vmm || addr < vmm->vm_end). */
		if (TASK_SIZE - len < addr)
			return -ENOMEM;
		if (!vmm || addr + len <= vmm->vm_start)
			return addr;
		addr = vmm->vm_end;
		if (do_color_align)
			addr = COLOUR_ALIGN(addr, pgoff);
	}
}

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;
	}

	mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
	mm->get_unmapped_area = arch_get_unmapped_area;
	mm->unmap_area = arch_unmap_area;
}

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;
}