From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4CAB5C433DF for ; Tue, 13 Oct 2020 23:56:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 16CC42223F for ; Tue, 13 Oct 2020 23:56:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602633366; bh=VfQN9E6poNj/sdDbidNqV36Gaxlw/gWKlBTqZOr3+CY=; h=Date:From:To:Subject:In-Reply-To:Reply-To:List-ID:From; b=MWGBY48RVPn/NB9pz2GnyerTzqvua03OIw1Gz5U7+n3gFjDdUqh2foqU20Ticw3CE mZbo3CWUCoS56U2Xs0gP9FC5/7285YufKn7KmzvLUX3CF7Fa9e3Sf/6EEdc85EWLPN Nc48Z796oKQ38u6LVWsKnuqu3N9xaRApAkSbXqfs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388596AbgJMX4F (ORCPT ); Tue, 13 Oct 2020 19:56:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:41694 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387742AbgJMX4F (ORCPT ); Tue, 13 Oct 2020 19:56:05 -0400 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7A88A2222E; Tue, 13 Oct 2020 23:56:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602633364; bh=VfQN9E6poNj/sdDbidNqV36Gaxlw/gWKlBTqZOr3+CY=; h=Date:From:To:Subject:In-Reply-To:From; b=hAH2HHVdU0nCem90B+a5Mdt+mP8bt5eR8+ag5tYaDLKOqkmJ7iaAG4AnZOU+TWaAE Sspx/+FX2DW/yUj+D/rH8fLYw3sA36GIE3uiwX44ZKWwWGV4EMlj9XNyC9p13jTBv4 thqohzIDZiE2zNkVEy2VNUGiJ7woPgDBVVBnZoPY= Date: Tue, 13 Oct 2020 16:56:04 -0700 From: Andrew Morton To: akpm@linux-foundation.org, hughd@google.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, npiggin@gmail.com, peterz@infradead.org, rppt@linux.ibm.com, torvalds@linux-foundation.org, willy@infradead.org Subject: [patch 139/181] mm/page_alloc.c: fix freeing non-compound pages Message-ID: <20201013235604.YBEl7k9r2%akpm@linux-foundation.org> In-Reply-To: <20201013164658.3bfd96cc224d8923e66a9f4e@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: "Matthew Wilcox (Oracle)" Subject: mm/page_alloc.c: fix freeing non-compound pages Here is a very rare race which leaks memory: Page P0 is allocated to the page cache. Page P1 is free. Thread A Thread B Thread C find_get_entry(): xas_load() returns P0 Removes P0 from page cache P0 finds its buddy P1 alloc_pages(GFP_KERNEL, 1) returns P0 P0 has refcount 1 page_cache_get_speculative(P0) P0 has refcount 2 __free_pages(P0) P0 has refcount 1 put_page(P0) P1 is not freed Fix this by freeing all the pages in __free_pages() that won't be freed by the call to put_page(). It's usually not a good idea to split a page, but this is a very unlikely scenario. Link: https://lkml.kernel.org/r/20200926213919.26642-1-willy@infradead.org Fixes: e286781d5f2e ("mm: speculative page references") Signed-off-by: Matthew Wilcox (Oracle) Acked-by: Mike Rapoport Cc: Nick Piggin Cc: Hugh Dickins Cc: Peter Zijlstra Signed-off-by: Andrew Morton --- lib/Kconfig.debug | 9 ++++++++ lib/Makefile | 1 lib/test_free_pages.c | 42 ++++++++++++++++++++++++++++++++++++++++ mm/page_alloc.c | 3 ++ 4 files changed, 55 insertions(+) --- a/lib/Kconfig.debug~page_alloc-fix-freeing-non-compound-pages +++ a/lib/Kconfig.debug @@ -2367,6 +2367,15 @@ config TEST_HMM If unsure, say N. +config TEST_FREE_PAGES + tristate "Test freeing pages" + help + Test that a memory leak does not occur due to a race between + freeing a block of pages and a speculative page reference. + Loading this module is safe if your kernel has the bug fixed. + If the bug is not fixed, it will leak gigabytes of memory and + probably OOM your system. + config TEST_FPU tristate "Test floating point operations in kernel space" depends on X86 && !KCOV_INSTRUMENT_ALL --- a/lib/Makefile~page_alloc-fix-freeing-non-compound-pages +++ a/lib/Makefile @@ -101,6 +101,7 @@ obj-$(CONFIG_TEST_BLACKHOLE_DEV) += test obj-$(CONFIG_TEST_MEMINIT) += test_meminit.o obj-$(CONFIG_TEST_LOCKUP) += test_lockup.o obj-$(CONFIG_TEST_HMM) += test_hmm.o +obj-$(CONFIG_TEST_FREE_PAGES) += test_free_pages.o # # CFLAGS for compiling floating point code inside the kernel. x86/Makefile turns --- /dev/null +++ a/lib/test_free_pages.c @@ -0,0 +1,42 @@ +// SPDX-License-Identifier: GPL-2.0+ +/* + * test_free_pages.c: Check that free_pages() doesn't leak memory + * Copyright (c) 2020 Oracle + * Author: Matthew Wilcox + */ + +#include +#include +#include + +static void test_free_pages(gfp_t gfp) +{ + unsigned int i; + + for (i = 0; i < 1000 * 1000; i++) { + unsigned long addr = __get_free_pages(gfp, 3); + struct page *page = virt_to_page(addr); + + /* Simulate page cache getting a speculative reference */ + get_page(page); + free_pages(addr, 3); + put_page(page); + } +} + +static int m_in(void) +{ + test_free_pages(GFP_KERNEL); + test_free_pages(GFP_KERNEL | __GFP_COMP); + + return 0; +} + +static void m_ex(void) +{ +} + +module_init(m_in); +module_exit(m_ex); +MODULE_AUTHOR("Matthew Wilcox "); +MODULE_LICENSE("GPL"); --- a/mm/page_alloc.c~page_alloc-fix-freeing-non-compound-pages +++ a/mm/page_alloc.c @@ -4952,6 +4952,9 @@ void __free_pages(struct page *page, uns { if (put_page_testzero(page)) free_the_page(page, order); + else if (!PageHead(page)) + while (order-- > 0) + free_the_page(page + (1 << order), order); } EXPORT_SYMBOL(__free_pages); _