124 lines
3.0 KiB
C
124 lines
3.0 KiB
C
/*
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* Flexible mmap layout support
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*
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* Based on code by Ingo Molnar and Andi Kleen, copyrighted
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* as follows:
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*
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* Copyright 2003-2009 Red Hat Inc.
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* All Rights Reserved.
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* Copyright 2005 Andi Kleen, SUSE Labs.
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* Copyright 2007 Jiri Kosina, SUSE Labs.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#include <linux/personality.h>
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#include <linux/mm.h>
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#include <linux/random.h>
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#include <linux/limits.h>
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#include <linux/sched.h>
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/*
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* Top of mmap area (just below the process stack).
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*
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* Leave an at least ~128 MB hole.
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*/
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#define MIN_GAP (128*1024*1024)
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#define MAX_GAP (TASK_SIZE/6*5)
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/*
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* True on X86_32 or when emulating IA32 on X86_64
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*/
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static int mmap_is_ia32(void)
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{
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#ifdef CONFIG_X86_32
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return 1;
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#endif
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#ifdef CONFIG_IA32_EMULATION
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if (test_thread_flag(TIF_IA32))
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return 1;
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#endif
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return 0;
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}
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static int mmap_is_legacy(void)
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{
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if (current->personality & ADDR_COMPAT_LAYOUT)
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return 1;
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if (current->signal->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY)
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return 1;
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return sysctl_legacy_va_layout;
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}
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static unsigned long mmap_rnd(void)
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{
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unsigned long rnd = 0;
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/*
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* 8 bits of randomness in 32bit mmaps, 20 address space bits
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* 28 bits of randomness in 64bit mmaps, 40 address space bits
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*/
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if (current->flags & PF_RANDOMIZE) {
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if (mmap_is_ia32())
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rnd = (long)get_random_int() % (1<<8);
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else
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rnd = (long)(get_random_int() % (1<<28));
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}
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return rnd << PAGE_SHIFT;
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}
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static unsigned long mmap_base(void)
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{
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unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur;
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if (gap < MIN_GAP)
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gap = MIN_GAP;
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else if (gap > MAX_GAP)
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gap = MAX_GAP;
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return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd());
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}
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/*
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* Bottom-up (legacy) layout on X86_32 did not support randomization, X86_64
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* does, but not when emulating X86_32
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*/
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static unsigned long mmap_legacy_base(void)
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{
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if (mmap_is_ia32())
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return TASK_UNMAPPED_BASE;
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else
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return TASK_UNMAPPED_BASE + mmap_rnd();
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}
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/*
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* This function, called very early during the creation of a new
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* process VM image, sets up which VM layout function to use:
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*/
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void arch_pick_mmap_layout(struct mm_struct *mm)
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{
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if (mmap_is_legacy()) {
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mm->mmap_base = mmap_legacy_base();
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mm->get_unmapped_area = arch_get_unmapped_area;
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mm->unmap_area = arch_unmap_area;
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} else {
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mm->mmap_base = mmap_base();
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mm->get_unmapped_area = arch_get_unmapped_area_topdown;
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mm->unmap_area = arch_unmap_area_topdown;
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}
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}
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