// 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);
}

#ifdef CONFIG_PPC_RADIX_MMU
/*
 * Same function as generic code used only for radix, because we don't need to overload
 * the generic one. But we will have to duplicate, because hash select
 * HAVE_ARCH_UNMAPPED_AREA
 */
static unsigned long
radix__arch_get_unmapped_area(struct file *filp, unsigned long addr,
                             unsigned long len, unsigned long pgoff,
                             unsigned long flags)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        int fixed = (flags & MAP_FIXED);
        unsigned long high_limit;
        struct vm_unmapped_area_info info;

        high_limit = DEFAULT_MAP_WINDOW;
        if (addr >= high_limit || (fixed && (addr + len > high_limit)))
                high_limit = TASK_SIZE;

        if (len > high_limit)
                return -ENOMEM;

        if (fixed) {
                if (addr > high_limit - len)
                        return -ENOMEM;
                return addr;
        }

        if (addr) {
                addr = PAGE_ALIGN(addr);
                vma = find_vma(mm, addr);
                if (high_limit - len >= addr && addr >= mmap_min_addr &&
                    (!vma || addr + len <= vm_start_gap(vma)))
                        return addr;
        }

        info.flags = 0;
        info.length = len;
        info.low_limit = mm->mmap_base;
        info.high_limit = high_limit;
        info.align_mask = 0;

        return vm_unmapped_area(&info);
}

static unsigned long
radix__arch_get_unmapped_area_topdown(struct file *filp,
                                     const unsigned long addr0,
                                     const unsigned long len,
                                     const unsigned long pgoff,
                                     const unsigned long flags)
{
        struct vm_area_struct *vma;
        struct mm_struct *mm = current->mm;
        unsigned long addr = addr0;
        int fixed = (flags & MAP_FIXED);
        unsigned long high_limit;
        struct vm_unmapped_area_info info;

        high_limit = DEFAULT_MAP_WINDOW;
        if (addr >= high_limit || (fixed && (addr + len > high_limit)))
                high_limit = TASK_SIZE;

        if (len > high_limit)
                return -ENOMEM;

        if (fixed) {
                if (addr > high_limit - len)
                        return -ENOMEM;
                return addr;
        }

        if (addr) {
                addr = PAGE_ALIGN(addr);
                vma = find_vma(mm, addr);
                if (high_limit - len >= addr && addr >= mmap_min_addr &&
                    (!vma || addr + len <= vm_start_gap(vma)))
                        return addr;
        }

        info.flags = VM_UNMAPPED_AREA_TOPDOWN;
        info.length = len;
        info.low_limit = max(PAGE_SIZE, mmap_min_addr);
        info.high_limit = mm->mmap_base + (high_limit - DEFAULT_MAP_WINDOW);
        info.align_mask = 0;

        addr = vm_unmapped_area(&info);
        if (!(addr & ~PAGE_MASK))
                return addr;
        VM_BUG_ON(addr != -ENOMEM);

        /*
         * A failed mmap() very likely causes application failure,
         * so fall back to the bottom-up function here. This scenario
         * can happen with large stack limits and large mmap()
         * allocations.
         */
        return radix__arch_get_unmapped_area(filp, addr0, len, pgoff, flags);
}

static void radix__arch_pick_mmap_layout(struct mm_struct *mm,
                                        unsigned long random_factor,
                                        struct rlimit *rlim_stack)
{
        if (mmap_is_legacy(rlim_stack)) {
                mm->mmap_base = TASK_UNMAPPED_BASE;
                mm->get_unmapped_area = radix__arch_get_unmapped_area;
        } else {
                mm->mmap_base = mmap_base(random_factor, rlim_stack);
                mm->get_unmapped_area = radix__arch_get_unmapped_area_topdown;
        }
}
#else
/* dummy */
extern void radix__arch_pick_mmap_layout(struct mm_struct *mm,
                                        unsigned long random_factor,
                                        struct rlimit *rlim_stack);
#endif
/*
 * 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();

        if (radix_enabled())
                return radix__arch_pick_mmap_layout(mm, random_factor,
                                                    rlim_stack);
        /*
         * 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;
                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;
        }
}