002b0ec73d
On 64bit there is a possibility our stack and mmap randomisation will put the two close enough such that we can't expand our stack to match the ulimit specified. To avoid this, start the upper mmap address at 1GB + 128MB below the top of our address space, so in the worst case we end up with the same ~128MB hole as in 32bit. This works because we randomise the stack over a 1GB range. Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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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