4bf936b9e4
Make sure compiler won't do weird things with limits. E.g. fetching
them twice may return 2 different values after writable limits are
implemented.
I.e. either use rlimit helpers added in
3e10e716ab
or ACCESS_ONCE if not applicable.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@ozlabs.org
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
109 lines
3.1 KiB
C
109 lines
3.1 KiB
C
/*
|
|
* flexible mmap layout support
|
|
*
|
|
* Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
|
|
* All Rights Reserved.
|
|
*
|
|
* 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
|
|
*
|
|
*
|
|
* Started by Ingo Molnar <mingo@elte.hu>
|
|
*/
|
|
|
|
#include <linux/personality.h>
|
|
#include <linux/mm.h>
|
|
#include <linux/random.h>
|
|
#include <linux/sched.h>
|
|
|
|
/*
|
|
* Top of mmap area (just below the process stack).
|
|
*
|
|
* Leave at least a ~128 MB hole on 32bit applications.
|
|
*
|
|
* On 64bit applications we randomise the stack by 1GB so we need to
|
|
* space our mmap start address by a further 1GB, otherwise there is a
|
|
* chance the mmap area will end up closer to the stack than our ulimit
|
|
* requires.
|
|
*/
|
|
#define MIN_GAP32 (128*1024*1024)
|
|
#define MIN_GAP64 ((128 + 1024)*1024*1024UL)
|
|
#define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64)
|
|
#define MAX_GAP (TASK_SIZE/6*5)
|
|
|
|
static inline 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;
|
|
}
|
|
|
|
/*
|
|
* Since get_random_int() returns the same value within a 1 jiffy window,
|
|
* we will almost always get the same randomisation for the stack and mmap
|
|
* region. This will mean the relative distance between stack and mmap will
|
|
* be the same.
|
|
*
|
|
* To avoid this we can shift the randomness by 1 bit.
|
|
*/
|
|
static unsigned long mmap_rnd(void)
|
|
{
|
|
unsigned long rnd = 0;
|
|
|
|
if (current->flags & PF_RANDOMIZE) {
|
|
/* 8MB for 32bit, 1GB for 64bit */
|
|
if (is_32bit_task())
|
|
rnd = (long)(get_random_int() % (1<<(22-PAGE_SHIFT)));
|
|
else
|
|
rnd = (long)(get_random_int() % (1<<(29-PAGE_SHIFT)));
|
|
}
|
|
return (rnd << PAGE_SHIFT) * 2;
|
|
}
|
|
|
|
static inline 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());
|
|
}
|
|
|
|
/*
|
|
* 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)
|
|
{
|
|
/*
|
|
* Fall back to the standard layout if the personality
|
|
* bit is set, or if the expected stack growth is unlimited:
|
|
*/
|
|
if (mmap_is_legacy()) {
|
|
mm->mmap_base = TASK_UNMAPPED_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;
|
|
}
|
|
}
|