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=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 5D2B9C432C0 for ; Tue, 3 Dec 2019 12:23:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3BCCE20684 for ; Tue, 3 Dec 2019 12:23:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726115AbfLCMXD (ORCPT ); Tue, 3 Dec 2019 07:23:03 -0500 Received: from imap1.codethink.co.uk ([176.9.8.82]:39981 "EHLO imap1.codethink.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725907AbfLCMXD (ORCPT ); Tue, 3 Dec 2019 07:23:03 -0500 Received: from [167.98.27.226] (helo=xylophone) by imap1.codethink.co.uk with esmtpsa (Exim 4.84_2 #1 (Debian)) id 1ic7Cl-0000E5-7a; Tue, 03 Dec 2019 12:22:59 +0000 Message-ID: <645311d0c03b3ae4604ac297e15af6471a6b0fb4.camel@codethink.co.uk> Subject: Re: [PATCH STABLE 4.9 1/1] mm, gup: add missing refcount overflow checks on x86 and s390 From: Ben Hutchings To: Vlastimil Babka , stable@vger.kernel.org Cc: Matthew Wilcox , Ajay Kaher , linux-mm@kvack.org, linux-kernel@vger.kernel.org Date: Tue, 03 Dec 2019 12:22:58 +0000 In-Reply-To: <20191129090351.3507-2-vbabka@suse.cz> References: <20191129090351.3507-1-vbabka@suse.cz> <20191129090351.3507-2-vbabka@suse.cz> Organization: Codethink Ltd. Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.5-1.1 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Fri, 2019-11-29 at 10:03 +0100, Vlastimil Babka wrote: > The mainline commit 8fde12ca79af ("mm: prevent get_user_pages() from > overflowing page refcount") was backported to 4.9.y stable as commit > 2ed768cfd895. The backport however missed that in 4.9, there are several > arch-specific gup.c versions with fast gup implementations, so these do not > prevent refcount overflow. > > This is partially fixed for x86 in stable-only commit d73af79742e7 ("x86, mm, > gup: prevent get_page() race with munmap in paravirt guest"). This stable-only > commit adds missing parts to x86 version, as well as s390 version, both taken > from the SUSE SLES/openSUSE 4.12-based kernels. > > The remaining architectures with own gup.c are sparc, mips, sh. It's unlikely > the known overflow scenario based on FUSE, which needs 140GB of RAM, is a > problem for those architectures, and I don't feel confident enough to patch > them. > > Signed-off-by: Vlastimil Babka > --- > arch/s390/mm/gup.c | 9 ++++++--- > arch/x86/mm/gup.c | 10 ++++++++-- > 2 files changed, 14 insertions(+), 5 deletions(-) > > diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c > index 97fc449a7470..33a940389a6d 100644 > --- a/arch/s390/mm/gup.c > +++ b/arch/s390/mm/gup.c > @@ -38,7 +38,8 @@ static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr, > VM_BUG_ON(!pfn_valid(pte_pfn(pte))); > page = pte_page(pte); > head = compound_head(page); > - if (!page_cache_get_speculative(head)) > + if (unlikely(WARN_ON_ONCE(page_ref_count(head) < 0) No need for unlikely(); WARN_ON() includes that. > + || !page_cache_get_speculative(head))) > return 0; > if (unlikely(pte_val(pte) != pte_val(*ptep))) { > put_page(head); [...] > --- a/arch/x86/mm/gup.c > +++ b/arch/x86/mm/gup.c > @@ -202,10 +202,12 @@ static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr, > undo_dev_pagemap(nr, nr_start, pages); > return 0; > } > + if (unlikely(!try_get_page(page))) { > + put_dev_pagemap(pgmap); > + return 0; > + } > SetPageReferenced(page); > pages[*nr] = page; > - get_page(page); > - put_dev_pagemap(pgmap); This leaks a pgmap reference on success! > (*nr)++; > pfn++; > } while (addr += PAGE_SIZE, addr != end); > @@ -230,6 +232,8 @@ static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr, > > refs = 0; > head = pmd_page(pmd); > + if (WARN_ON_ONCE(page_ref_count(head) <= 0)) Why <= 0, given we use < 0 elsewhere? > + return 0; > page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT); > do { > VM_BUG_ON_PAGE(compound_head(page) != head, page); > @@ -289,6 +293,8 @@ static noinline int gup_huge_pud(pud_t pud, unsigned long addr, > > refs = 0; > head = pud_page(pud); > + if (WARN_ON_ONCE(page_ref_count(head) <= 0)) Same question here. Ben. > + return 0; > page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT); > do { > VM_BUG_ON_PAGE(compound_head(page) != head, page); -- Ben Hutchings, Software Developer Codethink Ltd https://www.codethink.co.uk/ Dale House, 35 Dale Street Manchester, M1 2HF, United Kingdom