mmap.c

/*
 *  flexible mmap layout support
 *
 * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
 * All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 *
 * Started by Ingo Molnar <mingo@elte.hu>
 */

#include <linux/personality.h>
#include <linux/mm.h>
#include <linux/random.h>
#include <linux/sched/signal.h>
#include <linux/sched/mm.h>
#include <linux/elf-randomize.h>
#include <linux/security.h>
#include <linux/mman.h>

/*
 * Top of mmap area (just below the process stack).
 *
 * Leave at least a ~128 MB hole on 32bit applications.
 *
 * On 64bit applications we randomise the stack by 1GB so we need to
 * space our mmap start address by a further 1GB, otherwise there is a
 * chance the mmap area will end up closer to the stack than our ulimit
 * requires.
 */
#define MIN_GAP32 (128*1024*1024)
#define MIN_GAP64 ((128 + 1024)*1024*1024UL)
#define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64)
#define MAX_GAP (TASK_SIZE/6*5)

static inline 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;
}

unsigned long arch_mmap_rnd(void)
{
	unsigned long shift, rnd;

	shift = mmap_rnd_bits;
#ifdef CONFIG_COMPAT
	if (is_32bit_task())
		shift = mmap_rnd_compat_bits;
#endif
	rnd = get_random_long() % (1ul << shift);

	return rnd << PAGE_SHIFT;
}

static inline 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(DEFAULT_MAP_WINDOW - gap - rnd);
}

#ifdef CONFIG_PPC_RADIX_MMU
/*
 * Same function as generic code used only for radix, because we don't need to overload
 * the generic one. But we will have to duplicate, because hash select
 * HAVE_ARCH_UNMAPPED_AREA
 */
static unsigned long
radix__arch_get_unmapped_area(struct file *filp, unsigned long addr,
			     unsigned long len, unsigned long pgoff,
			     unsigned long flags)
{
	struct mm_struct *mm = current->mm;
	struct vm_area_struct *vma;
	struct vm_unmapped_area_info info;

	if (unlikely(addr > mm->context.addr_limit &&
		     mm->context.addr_limit != TASK_SIZE))
		mm->context.addr_limit = TASK_SIZE;

	if (len > mm->task_size - mmap_min_addr)
		return -ENOMEM;

	if (flags & MAP_FIXED)
		return addr;

	if (addr) {
		addr = PAGE_ALIGN(addr);
		vma = find_vma(mm, addr);
		if (mm->task_size - len >= addr && addr >= mmap_min_addr &&
		    (!vma || addr + len <= vm_start_gap(vma)))
			return addr;
	}

	info.flags = 0;
	info.length = len;
	info.low_limit = mm->mmap_base;
	info.align_mask = 0;

	if (unlikely(addr > DEFAULT_MAP_WINDOW))
		info.high_limit = mm->context.addr_limit;
	else
		info.high_limit = DEFAULT_MAP_WINDOW;

	return vm_unmapped_area(&info);
}

static unsigned long
radix__arch_get_unmapped_area_topdown(struct file *filp,
				     const unsigned long addr0,
				     const unsigned long len,
				     const unsigned long pgoff,
				     const unsigned long flags)
{
	struct vm_area_struct *vma;
	struct mm_struct *mm = current->mm;
	unsigned long addr = addr0;
	struct vm_unmapped_area_info info;

	if (unlikely(addr > mm->context.addr_limit &&
		     mm->context.addr_limit != TASK_SIZE))
		mm->context.addr_limit = TASK_SIZE;

	/* requested length too big for entire address space */
	if (len > mm->task_size - mmap_min_addr)
		return -ENOMEM;

	if (flags & MAP_FIXED)
		return addr;

	/* requesting a specific address */
	if (addr) {
		addr = PAGE_ALIGN(addr);
		vma = find_vma(mm, addr);
		if (mm->task_size - len >= addr && addr >= mmap_min_addr &&
				(!vma || addr + len <= vm_start_gap(vma)))
			return addr;
	}

	info.flags = VM_UNMAPPED_AREA_TOPDOWN;
	info.length = len;
	info.low_limit = max(PAGE_SIZE, mmap_min_addr);
	info.high_limit = mm->mmap_base;
	info.align_mask = 0;

	if (addr > DEFAULT_MAP_WINDOW)
		info.high_limit += mm->context.addr_limit - DEFAULT_MAP_WINDOW;

	addr = vm_unmapped_area(&info);
	if (!(addr & ~PAGE_MASK))
		return addr;
	VM_BUG_ON(addr != -ENOMEM);

	/*
	 * 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.
	 */
	return radix__arch_get_unmapped_area(filp, addr0, len, pgoff, flags);
}

static void radix__arch_pick_mmap_layout(struct mm_struct *mm,
					unsigned long random_factor)
{
	if (mmap_is_legacy()) {
		mm->mmap_base = TASK_UNMAPPED_BASE;
		mm->get_unmapped_area = radix__arch_get_unmapped_area;
	} else {
		mm->mmap_base = mmap_base(random_factor);
		mm->get_unmapped_area = radix__arch_get_unmapped_area_topdown;
	}
}
#else
/* dummy */
extern void radix__arch_pick_mmap_layout(struct mm_struct *mm,
					unsigned long random_factor);
#endif
/*
 * This function, called very early during the creation of a new
 * process VM image, sets up which VM layout function to use:
 */
void arch_pick_mmap_layout(struct mm_struct *mm)
{
	unsigned long random_factor = 0UL;

	if (current->flags & PF_RANDOMIZE)
		random_factor = arch_mmap_rnd();

	if (radix_enabled())
		return radix__arch_pick_mmap_layout(mm, random_factor);
	/*
	 * Fall back to the standard layout if the personality
	 * bit is set, or if the expected stack growth is unlimited:
	 */
	if (mmap_is_legacy()) {
		mm->mmap_base = TASK_UNMAPPED_BASE;
		mm->get_unmapped_area = arch_get_unmapped_area;
	} else {
		mm->mmap_base = mmap_base(random_factor);
		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
	}
}