| /* |
| * Flexible mmap layout support |
| * |
| * Based on code by Ingo Molnar and Andi Kleen, copyrighted |
| * as follows: |
| * |
| * Copyright 2003-2009 Red Hat Inc. |
| * All Rights Reserved. |
| * Copyright 2005 Andi Kleen, SUSE Labs. |
| * Copyright 2007 Jiri Kosina, SUSE Labs. |
| * |
| * 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 |
| */ |
| |
| #include <linux/personality.h> |
| #include <linux/mm.h> |
| #include <linux/random.h> |
| #include <linux/limits.h> |
| #include <linux/sched.h> |
| #include <asm/elf.h> |
| |
| struct __read_mostly va_alignment va_align = { |
| .flags = -1, |
| }; |
| |
| static unsigned int stack_maxrandom_size(void) |
| { |
| unsigned int max = 0; |
| if ((current->flags & PF_RANDOMIZE) && |
| !(current->personality & ADDR_NO_RANDOMIZE)) { |
| max = ((-1U) & STACK_RND_MASK) << PAGE_SHIFT; |
| } |
| |
| return max; |
| } |
| |
| /* |
| * Top of mmap area (just below the process stack). |
| * |
| * Leave an at least ~128 MB hole with possible stack randomization. |
| */ |
| #define MIN_GAP (128*1024*1024UL + stack_maxrandom_size()) |
| #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_rnd(void) |
| { |
| unsigned long rnd = 0; |
| |
| if (current->flags & PF_RANDOMIZE) { |
| if (mmap_is_ia32()) |
| #ifdef CONFIG_COMPAT |
| rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1); |
| #else |
| rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1); |
| #endif |
| else |
| rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1); |
| } |
| return rnd << PAGE_SHIFT; |
| } |
| |
| static unsigned long mmap_base(void) |
| { |
| 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 - mmap_rnd()); |
| } |
| |
| /* |
| * Bottom-up (legacy) layout on X86_32 did not support randomization, X86_64 |
| * does, but not when emulating X86_32 |
| */ |
| static unsigned long mmap_legacy_base(void) |
| { |
| if (mmap_is_ia32()) |
| return TASK_UNMAPPED_BASE; |
| else |
| return TASK_UNMAPPED_BASE + mmap_rnd(); |
| } |
| |
| /* |
| * 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) |
| { |
| mm->mmap_legacy_base = mmap_legacy_base(); |
| mm->mmap_base = mmap_base(); |
| |
| if (mmap_is_legacy()) { |
| mm->mmap_base = mm->mmap_legacy_base; |
| mm->get_unmapped_area = arch_get_unmapped_area; |
| } else { |
| mm->get_unmapped_area = arch_get_unmapped_area_topdown; |
| } |
| } |