linux/arch/x86/mm/mmap.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Flexible mmap layout support
 *
 * Based on code by Ingo Molnar and Andi Kleen, copyrighted
 * as follows:
 *
 * Copyright 2003-2009 Red Hat Inc.
 * All Rights Reserved.
 * Copyright 2005 Andi Kleen, SUSE Labs.
 * Copyright 2007 Jiri Kosina, SUSE Labs.
 */

#include <linux/personality.h>
#include <linux/mm.h>
#include <linux/random.h>
#include <linux/limits.h>
#include <linux/sched/signal.h>
#include <linux/sched/mm.h>
#include <linux/compat.h>
#include <linux/elf-randomize.h>
#include <asm/elf.h>
#include <asm/io.h>

#include "physaddr.h"

struct va_alignment __read_mostly va_align = …;

unsigned long task_size_32bit(void)
{ … }

unsigned long task_size_64bit(int full_addr_space)
{ … }

static unsigned long stack_maxrandom_size(unsigned long task_size)
{ … }

#ifdef CONFIG_COMPAT
#define mmap32_rnd_bits …
#define mmap64_rnd_bits …
#else
#define mmap32_rnd_bits …
#define mmap64_rnd_bits …
#endif

#define SIZE_128M …

static int mmap_is_legacy(void)
{ … }

static unsigned long arch_rnd(unsigned int rndbits)
{ … }

unsigned long arch_mmap_rnd(void)
{ … }

static unsigned long mmap_base(unsigned long rnd, unsigned long task_size,
			       struct rlimit *rlim_stack)
{ … }

static unsigned long mmap_legacy_base(unsigned long rnd,
				      unsigned long task_size)
{ … }

/*
 * This function, called very early during the creation of a new
 * process VM image, sets up which VM layout function to use:
 */
static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base,
		unsigned long random_factor, unsigned long task_size,
		struct rlimit *rlim_stack)
{ … }

void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
{ … }

unsigned long get_mmap_base(int is_legacy)
{ … }

const char *arch_vma_name(struct vm_area_struct *vma)
{ … }

/**
 * mmap_address_hint_valid - Validate the address hint of mmap
 * @addr:	Address hint
 * @len:	Mapping length
 *
 * Check whether @addr and @addr + @len result in a valid mapping.
 *
 * On 32bit this only checks whether @addr + @len is <= TASK_SIZE.
 *
 * On 64bit with 5-level page tables another sanity check is required
 * because mappings requested by mmap(@addr, 0) which cross the 47-bit
 * virtual address boundary can cause the following theoretical issue:
 *
 *  An application calls mmap(addr, 0), i.e. without MAP_FIXED, where @addr
 *  is below the border of the 47-bit address space and @addr + @len is
 *  above the border.
 *
 *  With 4-level paging this request succeeds, but the resulting mapping
 *  address will always be within the 47-bit virtual address space, because
 *  the hint address does not result in a valid mapping and is
 *  ignored. Hence applications which are not prepared to handle virtual
 *  addresses above 47-bit work correctly.
 *
 *  With 5-level paging this request would be granted and result in a
 *  mapping which crosses the border of the 47-bit virtual address
 *  space. If the application cannot handle addresses above 47-bit this
 *  will lead to misbehaviour and hard to diagnose failures.
 *
 * Therefore ignore address hints which would result in a mapping crossing
 * the 47-bit virtual address boundary.
 *
 * Note, that in the same scenario with MAP_FIXED the behaviour is
 * different. The request with @addr < 47-bit and @addr + @len > 47-bit
 * fails on a 4-level paging machine but succeeds on a 5-level paging
 * machine. It is reasonable to expect that an application does not rely on
 * the failure of such a fixed mapping request, so the restriction is not
 * applied.
 */
bool mmap_address_hint_valid(unsigned long addr, unsigned long len)
{ … }

/* Can we access it for direct reading/writing? Must be RAM: */
int valid_phys_addr_range(phys_addr_t addr, size_t count)
{ … }

/* Can we access it through mmap? Must be a valid physical address: */
int valid_mmap_phys_addr_range(unsigned long pfn, size_t count)
{ … }

/*
 * Only allow root to set high MMIO mappings to PROT_NONE.
 * This prevents an unpriv. user to set them to PROT_NONE and invert
 * them, then pointing to valid memory for L1TF speculation.
 *
 * Note: for locked down kernels may want to disable the root override.
 */
bool pfn_modify_allowed(unsigned long pfn, pgprot_t prot)
{ … }