110 lines
3.1 KiB
C
110 lines
3.1 KiB
C
/*
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* flexible mmap layout support
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*
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* Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
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* All Rights Reserved.
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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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*
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* Started by Ingo Molnar <mingo@elte.hu>
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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/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 at least a ~128 MB hole on 32bit applications.
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*
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* On 64bit applications we randomise the stack by 1GB so we need to
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* space our mmap start address by a further 1GB, otherwise there is a
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* chance the mmap area will end up closer to the stack than our ulimit
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* requires.
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*/
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#define MIN_GAP32 (128*1024*1024)
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#define MIN_GAP64 ((128 + 1024)*1024*1024UL)
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#define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64)
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#define MAX_GAP (TASK_SIZE/6*5)
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static inline 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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/*
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* Since get_random_int() returns the same value within a 1 jiffy window,
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* we will almost always get the same randomisation for the stack and mmap
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* region. This will mean the relative distance between stack and mmap will
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* be the same.
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*
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* To avoid this we can shift the randomness by 1 bit.
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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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if (current->flags & PF_RANDOMIZE) {
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/* 8MB for 32bit, 1GB for 64bit */
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if (is_32bit_task())
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rnd = (long)(get_random_int() % (1<<(22-PAGE_SHIFT)));
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else
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rnd = (long)(get_random_int() % (1<<(29-PAGE_SHIFT)));
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}
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return (rnd << PAGE_SHIFT) * 2;
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}
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static inline 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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* 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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/*
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* Fall back to the standard layout if the personality
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* bit is set, or if the expected stack growth is unlimited:
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*/
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if (mmap_is_legacy()) {
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mm->mmap_base = TASK_UNMAPPED_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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