/* * Flexible mmap layout support * * Based on code by Ingo Molnar and Andi Kleen, copyrighted * as follows: * * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina. * 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> /* * Top of mmap area (just below the process stack). * * Leave an at least ~128 MB hole. */ #define MIN_GAP (128*1024*1024) #define MAX_GAP (TASK_SIZE/6*5) /* * True on X86_32 or when emulating IA32 on X86_64 */ static int mmap_is_ia32(void) { #ifdef CONFIG_X86_32 return 1; #endif #ifdef CONFIG_IA32_EMULATION if (test_thread_flag(TIF_IA32)) return 1; #endif return 0; } static int mmap_is_legacy(void) { if (current->personality & ADDR_COMPAT_LAYOUT) return 1; if (current->signal->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY) return 1; return sysctl_legacy_va_layout; } static unsigned long mmap_rnd(void) { unsigned long rnd = 0; /* * 8 bits of randomness in 32bit mmaps, 20 address space bits * 28 bits of randomness in 64bit mmaps, 40 address space bits */ if (current->flags & PF_RANDOMIZE) { if (mmap_is_ia32()) rnd = (long)get_random_int() % (1<<8); else rnd = (long)(get_random_int() % (1<<28)); } return rnd << PAGE_SHIFT; } static unsigned long mmap_base(void) { unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur; 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) { if (mmap_is_legacy()) { mm->mmap_base = mmap_legacy_base(); mm->get_unmapped_area = arch_get_unmapped_area; mm->unmap_area = arch_unmap_area; } else { mm->mmap_base = mmap_base(); mm->get_unmapped_area = arch_get_unmapped_area_topdown; mm->unmap_area = arch_unmap_area_topdown; } }