Commit message: mm/madvise.c: fix madvise() infinite loop under special circumstances

MADVISE_WILLNEED has always been a noop for DAX (formerly XIP) mappings.
Unfortunately madvise_willneed() doesn't communicate this information
properly to the generic madvise syscall implementation.  The calling
convention is quite subtle there.  madvise_vma() is supposed to either
return an error or update &prev otherwise the main loop will never
advance to the next vma and it will keep looping for ever without a way
to get out of the kernel.

It seems this has been broken since introduction.  Nobody has noticed
because nobody seems to be using MADVISE_WILLNEED on these DAX mappings.

[mhocko@suse.com: rewrite changelog]
Link: http://lkml.kernel.org/r/20171127115318.911-1-guoxuenan@huawei.com
Fixes: fe77ba6f4f97 ("[PATCH] xip: madvice/fadvice: execute in place")
Signed-off-by: chenjie <chenjie6@huawei.com>
Signed-off-by: guoxuenan <guoxuenan@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: zhangyi (F) <yi.zhang@huawei.com>
Cc: Miao Xie <miaoxie@huawei.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Carsten Otte <cotte@de.ibm.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
CVE: CVE-2017-18208
CWE: CWE-835
Vulnerability description: The madvise_willneed function in mm/madvise.c in the Linux kernel before 4.14.4 allows local users to cause a denial of service (infinite loop) by triggering use of MADVISE_WILLNEED for a DAX mapping.

Project: linux
File: madvise.c

SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
{
	unsigned long end, tmp;
	struct vm_area_struct *vma, *prev;
	int unmapped_error = 0;
	int error = -EINVAL;
	int write;
	size_t len;
	struct blk_plug plug;

	if (!madvise_behavior_valid(behavior))
		return error;

	if (start & ~PAGE_MASK)
		return error;
	len = (len_in + ~PAGE_MASK) & PAGE_MASK;

	/* Check to see whether len was rounded up from small -ve to zero */
	if (len_in && !len)
		return error;

	end = start + len;
	if (end < start)
		return error;

	error = 0;
	if (end == start)
		return error;

#ifdef CONFIG_MEMORY_FAILURE
	if (behavior == MADV_HWPOISON || behavior == MADV_SOFT_OFFLINE)
		return madvise_inject_error(behavior, start, start + len_in);
#endif

	write = madvise_need_mmap_write(behavior);
	if (write) {
		if (down_write_killable(&current->mm->mmap_sem))
			return -EINTR;
	} else {
		down_read(&current->mm->mmap_sem);
	}

	/*
	 * If the interval [start,end) covers some unmapped address
	 * ranges, just ignore them, but return -ENOMEM at the end.
	 * - different from the way of handling in mlock etc.
	 */
	vma = find_vma_prev(current->mm, start, &prev);
	if (vma && start > vma->vm_start)
		prev = vma;

	blk_start_plug(&plug);
	for (;;) {
		/* Still start < end. */
		error = -ENOMEM;
		if (!vma)
			goto out;

		/* Here start < (end|vma->vm_end). */
		if (start < vma->vm_start) {
			unmapped_error = -ENOMEM;
			start = vma->vm_start;
			if (start >= end)
				goto out;
		}

		/* Here vma->vm_start <= start < (end|vma->vm_end) */
		tmp = vma->vm_end;
		if (end < tmp)
			tmp = end;

		/* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
		error = madvise_vma(vma, &prev, start, tmp, behavior);
		if (error)
			goto out;
		start = tmp;
		if (prev && start < prev->vm_end)
			start = prev->vm_end;
		error = unmapped_error;
		if (start >= end)
			goto out;
		if (prev)
			vma = prev->vm_next;
		else	/* madvise_remove dropped mmap_sem */
			vma = find_vma(current->mm, start);
	}
out:
	blk_finish_plug(&plug);
	if (write)
		up_write(&current->mm->mmap_sem);
	else
		up_read(&current->mm->mmap_sem);

	return error;
}

Project: linux
File: madvise.c

static void force_shm_swapin_readahead(struct vm_area_struct *vma,
		unsigned long start, unsigned long end,
		struct address_space *mapping)
{
	pgoff_t index;
	struct page *page;
	swp_entry_t swap;

	for (; start < end; start += PAGE_SIZE) {
		index = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;

		page = find_get_entry(mapping, index);
		if (!radix_tree_exceptional_entry(page)) {
			if (page)
				put_page(page);
			continue;
		}
		swap = radix_to_swp_entry(page);
		page = read_swap_cache_async(swap, GFP_HIGHUSER_MOVABLE,
							NULL, 0, false);
		if (page)
			put_page(page);
	}

	lru_add_drain();	/* Push any new pages onto the LRU now */
}

Project: linux
File: madvise.c

static void force_swapin_readahead(struct vm_area_struct *vma,
		unsigned long start, unsigned long end)
{
	struct mm_walk walk = {
		.mm = vma->vm_mm,
		.pmd_entry = swapin_walk_pmd_entry,
		.private = vma,
	};

	walk_page_range(start, end, &walk);

	lru_add_drain();	/* Push any new pages onto the LRU now */
}

Project: linux
File: madvise.c

static long madvise_behavior(struct vm_area_struct *vma,
		     struct vm_area_struct **prev,
		     unsigned long start, unsigned long end, int behavior)
{
	struct mm_struct *mm = vma->vm_mm;
	int error = 0;
	pgoff_t pgoff;
	unsigned long new_flags = vma->vm_flags;

	switch (behavior) {
	case MADV_NORMAL:
		new_flags = new_flags & ~VM_RAND_READ & ~VM_SEQ_READ;
		break;
	case MADV_SEQUENTIAL:
		new_flags = (new_flags & ~VM_RAND_READ) | VM_SEQ_READ;
		break;
	case MADV_RANDOM:
		new_flags = (new_flags & ~VM_SEQ_READ) | VM_RAND_READ;
		break;
	case MADV_DONTFORK:
		new_flags |= VM_DONTCOPY;
		break;
	case MADV_DOFORK:
		if (vma->vm_flags & VM_IO) {
			error = -EINVAL;
			goto out;
		}
		new_flags &= ~VM_DONTCOPY;
		break;
	case MADV_WIPEONFORK:
		/* MADV_WIPEONFORK is only supported on anonymous memory. */
		if (vma->vm_file || vma->vm_flags & VM_SHARED) {
			error = -EINVAL;
			goto out;
		}
		new_flags |= VM_WIPEONFORK;
		break;
	case MADV_KEEPONFORK:
		new_flags &= ~VM_WIPEONFORK;
		break;
	case MADV_DONTDUMP:
		new_flags |= VM_DONTDUMP;
		break;
	case MADV_DODUMP:
		if (new_flags & VM_SPECIAL) {
			error = -EINVAL;
			goto out;
		}
		new_flags &= ~VM_DONTDUMP;
		break;
	case MADV_MERGEABLE:
	case MADV_UNMERGEABLE:
		error = ksm_madvise(vma, start, end, behavior, &new_flags);
		if (error) {
			/*
			 * madvise() returns EAGAIN if kernel resources, such as
			 * slab, are temporarily unavailable.
			 */
			if (error == -ENOMEM)
				error = -EAGAIN;
			goto out;
		}
		break;
	case MADV_HUGEPAGE:
	case MADV_NOHUGEPAGE:
		error = hugepage_madvise(vma, &new_flags, behavior);
		if (error) {
			/*
			 * madvise() returns EAGAIN if kernel resources, such as
			 * slab, are temporarily unavailable.
			 */
			if (error == -ENOMEM)
				error = -EAGAIN;
			goto out;
		}
		break;
	}

	if (new_flags == vma->vm_flags) {
		*prev = vma;
		goto out;
	}

	pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
	*prev = vma_merge(mm, *prev, start, end, new_flags, vma->anon_vma,
			  vma->vm_file, pgoff, vma_policy(vma),
			  vma->vm_userfaultfd_ctx);
	if (*prev) {
		vma = *prev;
		goto success;
	}

	*prev = vma;

	if (start != vma->vm_start) {
		if (unlikely(mm->map_count >= sysctl_max_map_count)) {
			error = -ENOMEM;
			goto out;
		}
		error = __split_vma(mm, vma, start, 1);
		if (error) {
			/*
			 * madvise() returns EAGAIN if kernel resources, such as
			 * slab, are temporarily unavailable.
			 */
			if (error == -ENOMEM)
				error = -EAGAIN;
			goto out;
		}
	}

	if (end != vma->vm_end) {
		if (unlikely(mm->map_count >= sysctl_max_map_count)) {
			error = -ENOMEM;
			goto out;
		}
		error = __split_vma(mm, vma, end, 0);
		if (error) {
			/*
			 * madvise() returns EAGAIN if kernel resources, such as
			 * slab, are temporarily unavailable.
			 */
			if (error == -ENOMEM)
				error = -EAGAIN;
			goto out;
		}
	}

success:
	/*
	 * vm_flags is protected by the mmap_sem held in write mode.
	 */
	vma->vm_flags = new_flags;
out:
	return error;
}

Project: linux
File: madvise.c

madvise_behavior_valid(int behavior)
{
	switch (behavior) {
	case MADV_DOFORK:
	case MADV_DONTFORK:
	case MADV_NORMAL:
	case MADV_SEQUENTIAL:
	case MADV_RANDOM:
	case MADV_REMOVE:
	case MADV_WILLNEED:
	case MADV_DONTNEED:
	case MADV_FREE:
#ifdef CONFIG_KSM
	case MADV_MERGEABLE:
	case MADV_UNMERGEABLE:
#endif
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
	case MADV_HUGEPAGE:
	case MADV_NOHUGEPAGE:
#endif
	case MADV_DONTDUMP:
	case MADV_DODUMP:
	case MADV_WIPEONFORK:
	case MADV_KEEPONFORK:
#ifdef CONFIG_MEMORY_FAILURE
	case MADV_SOFT_OFFLINE:
	case MADV_HWPOISON:
#endif
		return true;

	default:
		return false;
	}
}

Project: linux
File: madvise.c

static long madvise_dontneed_free(struct vm_area_struct *vma,
				  struct vm_area_struct **prev,
				  unsigned long start, unsigned long end,
				  int behavior)
{
	*prev = vma;
	if (!can_madv_dontneed_vma(vma))
		return -EINVAL;

	if (!userfaultfd_remove(vma, start, end)) {
		*prev = NULL; /* mmap_sem has been dropped, prev is stale */

		down_read(&current->mm->mmap_sem);
		vma = find_vma(current->mm, start);
		if (!vma)
			return -ENOMEM;
		if (start < vma->vm_start) {
			/*
			 * This "vma" under revalidation is the one
			 * with the lowest vma->vm_start where start
			 * is also < vma->vm_end. If start <
			 * vma->vm_start it means an hole materialized
			 * in the user address space within the
			 * virtual range passed to MADV_DONTNEED
			 * or MADV_FREE.
			 */
			return -ENOMEM;
		}
		if (!can_madv_dontneed_vma(vma))
			return -EINVAL;
		if (end > vma->vm_end) {
			/*
			 * Don't fail if end > vma->vm_end. If the old
			 * vma was splitted while the mmap_sem was
			 * released the effect of the concurrent
			 * operation may not cause madvise() to
			 * have an undefined result. There may be an
			 * adjacent next vma that we'll walk
			 * next. userfaultfd_remove() will generate an
			 * UFFD_EVENT_REMOVE repetition on the
			 * end-vma->vm_end range, but the manager can
			 * handle a repetition fine.
			 */
			end = vma->vm_end;
		}
		VM_WARN_ON(start >= end);
	}

	if (behavior == MADV_DONTNEED)
		return madvise_dontneed_single_vma(vma, start, end);
	else if (behavior == MADV_FREE)
		return madvise_free_single_vma(vma, start, end);
	else
		return -EINVAL;
}

Project: linux
File: madvise.c

static long madvise_dontneed_single_vma(struct vm_area_struct *vma,
					unsigned long start, unsigned long end)
{
	zap_page_range(vma, start, end - start);
	return 0;
}

Project: linux
File: madvise.c

static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
				unsigned long end, struct mm_walk *walk)

{
	struct mmu_gather *tlb = walk->private;
	struct mm_struct *mm = tlb->mm;
	struct vm_area_struct *vma = walk->vma;
	spinlock_t *ptl;
	pte_t *orig_pte, *pte, ptent;
	struct page *page;
	int nr_swap = 0;
	unsigned long next;

	next = pmd_addr_end(addr, end);
	if (pmd_trans_huge(*pmd))
		if (madvise_free_huge_pmd(tlb, vma, pmd, addr, next))
			goto next;

	if (pmd_trans_unstable(pmd))
		return 0;

	tlb_remove_check_page_size_change(tlb, PAGE_SIZE);
	orig_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
	flush_tlb_batched_pending(mm);
	arch_enter_lazy_mmu_mode();
	for (; addr != end; pte++, addr += PAGE_SIZE) {
		ptent = *pte;

		if (pte_none(ptent))
			continue;
		/*
		 * If the pte has swp_entry, just clear page table to
		 * prevent swap-in which is more expensive rather than
		 * (page allocation + zeroing).
		 */
		if (!pte_present(ptent)) {
			swp_entry_t entry;

			entry = pte_to_swp_entry(ptent);
			if (non_swap_entry(entry))
				continue;
			nr_swap--;
			free_swap_and_cache(entry);
			pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
			continue;
		}

		page = _vm_normal_page(vma, addr, ptent, true);
		if (!page)
			continue;

		/*
		 * If pmd isn't transhuge but the page is THP and
		 * is owned by only this process, split it and
		 * deactivate all pages.
		 */
		if (PageTransCompound(page)) {
			if (page_mapcount(page) != 1)
				goto out;
			get_page(page);
			if (!trylock_page(page)) {
				put_page(page);
				goto out;
			}
			pte_unmap_unlock(orig_pte, ptl);
			if (split_huge_page(page)) {
				unlock_page(page);
				put_page(page);
				pte_offset_map_lock(mm, pmd, addr, &ptl);
				goto out;
			}
			unlock_page(page);
			put_page(page);
			pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
			pte--;
			addr -= PAGE_SIZE;
			continue;
		}

		VM_BUG_ON_PAGE(PageTransCompound(page), page);

		if (PageSwapCache(page) || PageDirty(page)) {
			if (!trylock_page(page))
				continue;
			/*
			 * If page is shared with others, we couldn't clear
			 * PG_dirty of the page.
			 */
			if (page_mapcount(page) != 1) {
				unlock_page(page);
				continue;
			}

			if (PageSwapCache(page) && !try_to_free_swap(page)) {
				unlock_page(page);
				continue;
			}

			ClearPageDirty(page);
			unlock_page(page);
		}

		if (pte_young(ptent) || pte_dirty(ptent)) {
			/*
			 * Some of architecture(ex, PPC) don't update TLB
			 * with set_pte_at and tlb_remove_tlb_entry so for
			 * the portability, remap the pte with old|clean
			 * after pte clearing.
			 */
			ptent = ptep_get_and_clear_full(mm, addr, pte,
							tlb->fullmm);

			ptent = pte_mkold(ptent);
			ptent = pte_mkclean(ptent);
			set_pte_at(mm, addr, pte, ptent);
			tlb_remove_tlb_entry(tlb, pte, addr);
		}
		mark_page_lazyfree(page);
	}
out:
	if (nr_swap) {
		if (current->mm == mm)
			sync_mm_rss(mm);

		add_mm_counter(mm, MM_SWAPENTS, nr_swap);
	}
	arch_leave_lazy_mmu_mode();
	pte_unmap_unlock(orig_pte, ptl);
	cond_resched();
next:
	return 0;
}

Project: linux
File: madvise.c

static int madvise_free_single_vma(struct vm_area_struct *vma,
			unsigned long start_addr, unsigned long end_addr)
{
	unsigned long start, end;
	struct mm_struct *mm = vma->vm_mm;
	struct mmu_gather tlb;

	/* MADV_FREE works for only anon vma at the moment */
	if (!vma_is_anonymous(vma))
		return -EINVAL;

	start = max(vma->vm_start, start_addr);
	if (start >= vma->vm_end)
		return -EINVAL;
	end = min(vma->vm_end, end_addr);
	if (end <= vma->vm_start)
		return -EINVAL;

	lru_add_drain();
	tlb_gather_mmu(&tlb, mm, start, end);
	update_hiwater_rss(mm);

	mmu_notifier_invalidate_range_start(mm, start, end);
	madvise_free_page_range(&tlb, vma, start, end);
	mmu_notifier_invalidate_range_end(mm, start, end);
	tlb_finish_mmu(&tlb, start, end);

	return 0;
}

Project: linux
File: madvise.c

static int madvise_inject_error(int behavior,
		unsigned long start, unsigned long end)
{
	struct page *page;
	struct zone *zone;
	unsigned int order;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;


	for (; start < end; start += PAGE_SIZE << order) {
		int ret;

		ret = get_user_pages_fast(start, 1, 0, &page);
		if (ret != 1)
			return ret;

		/*
		 * When soft offlining hugepages, after migrating the page
		 * we dissolve it, therefore in the second loop "page" will
		 * no longer be a compound page, and order will be 0.
		 */
		order = compound_order(compound_head(page));

		if (PageHWPoison(page)) {
			put_page(page);
			continue;
		}

		if (behavior == MADV_SOFT_OFFLINE) {
			pr_info("Soft offlining pfn %#lx at process virtual address %#lx\n",
						page_to_pfn(page), start);

			ret = soft_offline_page(page, MF_COUNT_INCREASED);
			if (ret)
				return ret;
			continue;
		}
		pr_info("Injecting memory failure for pfn %#lx at process virtual address %#lx\n",
						page_to_pfn(page), start);

		ret = memory_failure(page_to_pfn(page), 0, MF_COUNT_INCREASED);
		if (ret)
			return ret;
	}

	/* Ensure that all poisoned pages are removed from per-cpu lists */
	for_each_populated_zone(zone)
		drain_all_pages(zone);

	return 0;
}

Project: linux
File: madvise.c

static int madvise_need_mmap_write(int behavior)
{
	switch (behavior) {
	case MADV_REMOVE:
	case MADV_WILLNEED:
	case MADV_DONTNEED:
	case MADV_FREE:
		return 0;
	default:
		/* be safe, default to 1. list exceptions explicitly */
		return 1;
	}
}

Project: linux
File: madvise.c

static long madvise_remove(struct vm_area_struct *vma,
				struct vm_area_struct **prev,
				unsigned long start, unsigned long end)
{
	loff_t offset;
	int error;
	struct file *f;

	*prev = NULL;	/* tell sys_madvise we drop mmap_sem */

	if (vma->vm_flags & VM_LOCKED)
		return -EINVAL;

	f = vma->vm_file;

	if (!f || !f->f_mapping || !f->f_mapping->host) {
			return -EINVAL;
	}

	if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) != (VM_SHARED|VM_WRITE))
		return -EACCES;

	offset = (loff_t)(start - vma->vm_start)
			+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);

	/*
	 * Filesystem's fallocate may need to take i_mutex.  We need to
	 * explicitly grab a reference because the vma (and hence the
	 * vma's reference to the file) can go away as soon as we drop
	 * mmap_sem.
	 */
	get_file(f);
	if (userfaultfd_remove(vma, start, end)) {
		/* mmap_sem was not released by userfaultfd_remove() */
		up_read(&current->mm->mmap_sem);
	}
	error = vfs_fallocate(f,
				FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
				offset, end - start);
	fput(f);
	down_read(&current->mm->mmap_sem);
	return error;
}

Project: linux
File: madvise.c

madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
		unsigned long start, unsigned long end, int behavior)
{
	switch (behavior) {
	case MADV_REMOVE:
		return madvise_remove(vma, prev, start, end);
	case MADV_WILLNEED:
		return madvise_willneed(vma, prev, start, end);
	case MADV_FREE:
	case MADV_DONTNEED:
		return madvise_dontneed_free(vma, prev, start, end, behavior);
	default:
		return madvise_behavior(vma, prev, start, end, behavior);
	}
}

Project: linux
File: madvise.c

static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
	unsigned long end, struct mm_walk *walk)
{
	pte_t *orig_pte;
	struct vm_area_struct *vma = walk->private;
	unsigned long index;

	if (pmd_none_or_trans_huge_or_clear_bad(pmd))
		return 0;

	for (index = start; index != end; index += PAGE_SIZE) {
		pte_t pte;
		swp_entry_t entry;
		struct page *page;
		spinlock_t *ptl;

		orig_pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
		pte = *(orig_pte + ((index - start) / PAGE_SIZE));
		pte_unmap_unlock(orig_pte, ptl);

		if (pte_present(pte) || pte_none(pte))
			continue;
		entry = pte_to_swp_entry(pte);
		if (unlikely(non_swap_entry(entry)))
			continue;

		page = read_swap_cache_async(entry, GFP_HIGHUSER_MOVABLE,
							vma, index, false);
		if (page)
			put_page(page);
	}

	return 0;
}