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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 33BFFC433F5 for ; Thu, 26 May 2022 13:34:36 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9F2988D0003; Thu, 26 May 2022 09:34:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 97D898D0001; Thu, 26 May 2022 09:34:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8195F8D0003; Thu, 26 May 2022 09:34:35 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 72B8D8D0001 for ; Thu, 26 May 2022 09:34:35 -0400 (EDT) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 4200634CB6 for ; Thu, 26 May 2022 13:34:35 +0000 (UTC) X-FDA: 79507988910.12.0BE9ADA Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf28.hostedemail.com (Postfix) with ESMTP id 84C21C0049 for ; Thu, 26 May 2022 13:34:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=SlbzwgeVcIbkiDLid8eYrVjR73Fsp4oET2KHh+9DwAY=; b=HC5DPeqs8vrqrrDyfcDTUyvArs MLHy0inxmzbEGqRQQpStnYry1aptGoD6Hm3nq9gM8X5GxKptCCA8dhZ/4jzrYDBO21d5HB4xQLsVV qlKKntVjewPTgGS8TwQLS7eqJS5mNhMyllcsnKuPUAGqXZQBowB1Es3yBi4ninf2bo3JtjQIrLs4U 2O3evDVyqbJIbenC2u1ExWO29id/sftoUY6ZiC8oRdPt83irlDxlFVQO/4Oc9a1aZPzc8gVNIv1Nb I83hEqExyoiwTzAPI+EeEKEt+im338CLoQpC9RnsGe4+iygXY/r5iL719YLV1cU35RjtMgCkvkZfn vlZjPGew==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1nuDdB-001HHa-6e; Thu, 26 May 2022 13:34:25 +0000 Date: Thu, 26 May 2022 14:34:25 +0100 From: Matthew Wilcox To: Miaohe Lin Cc: akpm@linux-foundation.org, pasha.tatashin@soleen.com, rientjes@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/page_table_check: fix accessing unmapped ptep Message-ID: References: <20220526113350.30806-1-linmiaohe@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220526113350.30806-1-linmiaohe@huawei.com> X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 84C21C0049 X-Stat-Signature: wtqr5fosdyrh5kztmcsahjrf95ktkzwk Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=HC5DPeqs; spf=none (imf28.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none X-Rspam-User: X-HE-Tag: 1653572040-631295 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, May 26, 2022 at 07:33:50PM +0800, Miaohe Lin wrote: > ptep is unmapped too early, so ptep will be accessed while it's unmapped. > Fix it by deferring pte_unmap() until page table checking is done. > > Fixes: 80110bbfbba6 ("mm/page_table_check: check entries at pmd levels") > Signed-off-by: Miaohe Lin > --- > mm/page_table_check.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/page_table_check.c b/mm/page_table_check.c > index 3692bea2ea2c..971c3129b0e3 100644 > --- a/mm/page_table_check.c > +++ b/mm/page_table_check.c > @@ -234,11 +234,11 @@ void __page_table_check_pte_clear_range(struct mm_struct *mm, > pte_t *ptep = pte_offset_map(&pmd, addr); > unsigned long i; > > - pte_unmap(ptep); > for (i = 0; i < PTRS_PER_PTE; i++) { > __page_table_check_pte_clear(mm, addr, *ptep); > addr += PAGE_SIZE; > ptep++; > } > + pte_unmap(ptep); But ptep was mutated in the loop. So surely this needs to be: pte_unmap(ptep - PTRS_PER_PTE); or you'll be unmapping the wrong page.