249 lines
6.9 KiB
C
249 lines
6.9 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Flexible mmap layout support
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*
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* Based on code by Ingo Molnar and Andi Kleen, copyrighted
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* as follows:
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*
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* Copyright 2003-2009 Red Hat Inc.
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* All Rights Reserved.
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* Copyright 2005 Andi Kleen, SUSE Labs.
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* Copyright 2007 Jiri Kosina, SUSE Labs.
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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/limits.h>
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#include <linux/sched/signal.h>
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#include <linux/sched/mm.h>
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#include <linux/compat.h>
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#include <asm/elf.h>
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#include "physaddr.h"
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struct va_alignment __read_mostly va_align = {
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.flags = -1,
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};
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unsigned long task_size_32bit(void)
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{
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return IA32_PAGE_OFFSET;
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}
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unsigned long task_size_64bit(int full_addr_space)
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{
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return full_addr_space ? TASK_SIZE_MAX : DEFAULT_MAP_WINDOW;
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}
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static unsigned long stack_maxrandom_size(unsigned long task_size)
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{
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unsigned long max = 0;
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if (current->flags & PF_RANDOMIZE) {
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max = (-1UL) & __STACK_RND_MASK(task_size == task_size_32bit());
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max <<= PAGE_SHIFT;
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}
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return max;
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}
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#ifdef CONFIG_COMPAT
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# define mmap32_rnd_bits mmap_rnd_compat_bits
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# define mmap64_rnd_bits mmap_rnd_bits
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#else
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# define mmap32_rnd_bits mmap_rnd_bits
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# define mmap64_rnd_bits mmap_rnd_bits
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#endif
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#define SIZE_128M (128 * 1024 * 1024UL)
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static 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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return sysctl_legacy_va_layout;
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}
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static unsigned long arch_rnd(unsigned int rndbits)
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{
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if (!(current->flags & PF_RANDOMIZE))
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return 0;
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return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT;
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}
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unsigned long arch_mmap_rnd(void)
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{
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return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
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}
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static unsigned long mmap_base(unsigned long rnd, unsigned long task_size,
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struct rlimit *rlim_stack)
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{
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unsigned long gap = rlim_stack->rlim_cur;
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unsigned long pad = stack_maxrandom_size(task_size) + stack_guard_gap;
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unsigned long gap_min, gap_max;
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/* Values close to RLIM_INFINITY can overflow. */
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if (gap + pad > gap)
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gap += pad;
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/*
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* Top of mmap area (just below the process stack).
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* Leave an at least ~128 MB hole with possible stack randomization.
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*/
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gap_min = SIZE_128M;
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gap_max = (task_size / 6) * 5;
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if (gap < gap_min)
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gap = gap_min;
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else if (gap > gap_max)
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gap = gap_max;
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return PAGE_ALIGN(task_size - gap - rnd);
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}
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static unsigned long mmap_legacy_base(unsigned long rnd,
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unsigned long task_size)
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{
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return __TASK_UNMAPPED_BASE(task_size) + 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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static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base,
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unsigned long random_factor, unsigned long task_size,
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struct rlimit *rlim_stack)
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{
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*legacy_base = mmap_legacy_base(random_factor, task_size);
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if (mmap_is_legacy())
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*base = *legacy_base;
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else
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*base = mmap_base(random_factor, task_size, rlim_stack);
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}
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void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
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{
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if (mmap_is_legacy())
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mm->get_unmapped_area = arch_get_unmapped_area;
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else
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mm->get_unmapped_area = arch_get_unmapped_area_topdown;
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arch_pick_mmap_base(&mm->mmap_base, &mm->mmap_legacy_base,
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arch_rnd(mmap64_rnd_bits), task_size_64bit(0),
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rlim_stack);
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#ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
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/*
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* The mmap syscall mapping base decision depends solely on the
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* syscall type (64-bit or compat). This applies for 64bit
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* applications and 32bit applications. The 64bit syscall uses
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* mmap_base, the compat syscall uses mmap_compat_base.
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*/
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arch_pick_mmap_base(&mm->mmap_compat_base, &mm->mmap_compat_legacy_base,
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arch_rnd(mmap32_rnd_bits), task_size_32bit(),
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rlim_stack);
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#endif
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}
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unsigned long get_mmap_base(int is_legacy)
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{
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struct mm_struct *mm = current->mm;
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#ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
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if (in_32bit_syscall()) {
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return is_legacy ? mm->mmap_compat_legacy_base
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: mm->mmap_compat_base;
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}
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#endif
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return is_legacy ? mm->mmap_legacy_base : mm->mmap_base;
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}
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const char *arch_vma_name(struct vm_area_struct *vma)
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{
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return NULL;
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}
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/**
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* mmap_address_hint_valid - Validate the address hint of mmap
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* @addr: Address hint
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* @len: Mapping length
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*
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* Check whether @addr and @addr + @len result in a valid mapping.
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*
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* On 32bit this only checks whether @addr + @len is <= TASK_SIZE.
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*
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* On 64bit with 5-level page tables another sanity check is required
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* because mappings requested by mmap(@addr, 0) which cross the 47-bit
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* virtual address boundary can cause the following theoretical issue:
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*
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* An application calls mmap(addr, 0), i.e. without MAP_FIXED, where @addr
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* is below the border of the 47-bit address space and @addr + @len is
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* above the border.
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*
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* With 4-level paging this request succeeds, but the resulting mapping
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* address will always be within the 47-bit virtual address space, because
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* the hint address does not result in a valid mapping and is
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* ignored. Hence applications which are not prepared to handle virtual
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* addresses above 47-bit work correctly.
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*
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* With 5-level paging this request would be granted and result in a
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* mapping which crosses the border of the 47-bit virtual address
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* space. If the application cannot handle addresses above 47-bit this
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* will lead to misbehaviour and hard to diagnose failures.
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*
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* Therefore ignore address hints which would result in a mapping crossing
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* the 47-bit virtual address boundary.
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*
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* Note, that in the same scenario with MAP_FIXED the behaviour is
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* different. The request with @addr < 47-bit and @addr + @len > 47-bit
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* fails on a 4-level paging machine but succeeds on a 5-level paging
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* machine. It is reasonable to expect that an application does not rely on
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* the failure of such a fixed mapping request, so the restriction is not
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* applied.
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*/
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bool mmap_address_hint_valid(unsigned long addr, unsigned long len)
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{
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if (TASK_SIZE - len < addr)
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return false;
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return (addr > DEFAULT_MAP_WINDOW) == (addr + len > DEFAULT_MAP_WINDOW);
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}
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/* Can we access it for direct reading/writing? Must be RAM: */
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int valid_phys_addr_range(phys_addr_t addr, size_t count)
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{
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return addr + count - 1 <= __pa(high_memory - 1);
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}
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/* Can we access it through mmap? Must be a valid physical address: */
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int valid_mmap_phys_addr_range(unsigned long pfn, size_t count)
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{
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phys_addr_t addr = (phys_addr_t)pfn << PAGE_SHIFT;
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return phys_addr_valid(addr + count - 1);
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}
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/*
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* Only allow root to set high MMIO mappings to PROT_NONE.
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* This prevents an unpriv. user to set them to PROT_NONE and invert
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* them, then pointing to valid memory for L1TF speculation.
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*
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* Note: for locked down kernels may want to disable the root override.
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*/
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bool pfn_modify_allowed(unsigned long pfn, pgprot_t prot)
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{
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if (!boot_cpu_has_bug(X86_BUG_L1TF))
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return true;
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if (!__pte_needs_invert(pgprot_val(prot)))
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return true;
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/* If it's real memory always allow */
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if (pfn_valid(pfn))
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return true;
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if (pfn >= l1tf_pfn_limit() && !capable(CAP_SYS_ADMIN))
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return false;
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return true;
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}
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