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// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  flexible mmap layout support
 *
 * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
 * All Rights Reserved.
 *
 * Started by Ingo Molnar <mingo@elte.hu>
 */

#include <linux/personality.h>
#include <linux/mm.h>
#include <linux/random.h>
#include <linux/sched/signal.h>
#include <linux/sched/mm.h>
#include <linux/elf-randomize.h>
#include <linux/security.h>
#include <linux/mman.h>

/*
 * Top of mmap area (just below the process stack).
 *
 * Leave at least a ~128 MB hole.
 */
#define MIN_GAP (128*1024*1024)
#define MAX_GAP (TASK_SIZE/6*5)

static inline int mmap_is_legacy(struct rlimit *rlim_stack)
{
	if (current->personality & ADDR_COMPAT_LAYOUT)
		return 1;

	if (rlim_stack->rlim_cur == RLIM_INFINITY)
		return 1;

	return sysctl_legacy_va_layout;
}

unsigned long arch_mmap_rnd(void)
{
	unsigned long shift, rnd;

	shift = mmap_rnd_bits;
#ifdef CONFIG_COMPAT
	if (is_32bit_task())
		shift = mmap_rnd_compat_bits;
#endif
	rnd = get_random_long() % (1ul << shift);

	return rnd << PAGE_SHIFT;
}

static inline unsigned long stack_maxrandom_size(void)
{
	if (!(current->flags & PF_RANDOMIZE))
		return 0;

	/* 8MB for 32bit, 1GB for 64bit */
	if (is_32bit_task())
		return (1<<23);
	else
		return (1<<30);
}

static inline unsigned long mmap_base(unsigned long rnd,
				      struct rlimit *rlim_stack)
{
	unsigned long gap = rlim_stack->rlim_cur;
	unsigned long pad = stack_maxrandom_size() + stack_guard_gap;

	/* Values close to RLIM_INFINITY can overflow. */
	if (gap + pad > gap)
		gap += pad;

	if (gap < MIN_GAP)
		gap = MIN_GAP;
	else if (gap > MAX_GAP)
		gap = MAX_GAP;

	return PAGE_ALIGN(DEFAULT_MAP_WINDOW - gap - 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, struct rlimit *rlim_stack)
{
	unsigned long random_factor = 0UL;

	if (current->flags & PF_RANDOMIZE)
		random_factor = arch_mmap_rnd();

	/*
	 * Fall back to the standard layout if the personality
	 * bit is set, or if the expected stack growth is unlimited:
	 */
	if (mmap_is_legacy(rlim_stack)) {
		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
		mm->get_unmapped_area = arch_get_unmapped_area;
	} else {
		mm->mmap_base = mmap_base(random_factor, rlim_stack);
		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
	}
}