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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D345DC433F5 for ; Thu, 26 May 2022 13:38:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241285AbiEZNi0 (ORCPT ); Thu, 26 May 2022 09:38:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39016 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231466AbiEZNiW (ORCPT ); Thu, 26 May 2022 09:38:22 -0400 Received: from mail-ej1-x62c.google.com (mail-ej1-x62c.google.com [IPv6:2a00:1450:4864:20::62c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A068658E52 for ; Thu, 26 May 2022 06:38:21 -0700 (PDT) Received: by mail-ej1-x62c.google.com with SMTP id i27so3003227ejd.9 for ; Thu, 26 May 2022 06:38:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=soleen.com; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=zZ9DAhCNK6+O0V4masvprPNhs/nf8Fvi/U/e6pxEsj0=; b=T4I1s68XXJRufZfuiZ1VZqCrjcDXks8TmQ8oOs2CAd82x1Ea5MYgXQ/hfb66CkrVKh 5xOeCj8uHt2B+CgY6Q9qIMpIvsttNrIw4aGRB/7PctSnXHNgMY251O68aaf6GrtMnSxw Doy1oSWuSM7cQ7+q6k1B60IEafItMK0tUJHf/44SIx2D66qkNgFXDF6L2grXHIvKPwCO vHXqTLPG6SIeYKbhzT09p+jRk/c2LO6ko+9+u/LDyxvtUREQCd98SebqpPmUHdMuXze2 qXgOaZV4I7bUXjTMWtzpwUa3WnqrYGrGciOuF8smnswGCoeRXOcELI9l1MOExdSN7yj7 tMzw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=zZ9DAhCNK6+O0V4masvprPNhs/nf8Fvi/U/e6pxEsj0=; b=v44zFuIluDT7iPOD4EvxJyoxDtRa/UGuibtUR6+zoKE42+K0lXfLnR1gTH+QTOeRNP roh54mVlbjZjVLjh2Zb6M79aeY19NZrZmrWxDXibse34UuEe4JQaY8ToQyFNS5EP0eM1 MXIhJSCAWlgaKA5ulBaBOKUfdW+GQknlAsJopoS8KNJxpDshTolbOGhR/7Z7SZhAmELW 1yQwoDkeFuwxLB4nqwCMHJlgvS0IMYg64jYASw2+0+kfrNnmQRFY8/Qu50oH+Y9ieet0 Tp/JO9m9o5yTQuIEp77kIyIlcrTqCVqptT/h219kM/HXlHHxRkBy5O7H+ZlGDRbDo/Ym he0Q== X-Gm-Message-State: AOAM531QVRTpGXlaC7fcl5EStT96DOk3v8xhyK/dLbqLQTKZxtG+QBYT oozoeOXMMaq3Oqh7WXGol+euX5+3alwl7WLCGZGh+ejBvhheGg== X-Google-Smtp-Source: ABdhPJxwsu+q88tcq7anl1xlkA6jRqbX/Y2WxaXnApABL4iLZzEE9mWLZ5XTPYNtc14+W7qgANcEq8W+9zqihQphORo= X-Received: by 2002:a17:906:9b86:b0:6fe:d37f:b29d with SMTP id dd6-20020a1709069b8600b006fed37fb29dmr19980411ejc.327.1653572300197; Thu, 26 May 2022 06:38:20 -0700 (PDT) MIME-Version: 1.0 References: <20220526113350.30806-1-linmiaohe@huawei.com> In-Reply-To: From: Pasha Tatashin Date: Thu, 26 May 2022 09:37:43 -0400 Message-ID: Subject: Re: [PATCH] mm/page_table_check: fix accessing unmapped ptep To: Matthew Wilcox Cc: Miaohe Lin , Andrew Morton , David Rientjes , linux-mm , LKML Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 26, 2022 at 9:34 AM Matthew Wilcox wrote: > > 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. Right, thank you Matthew. Miaohe, please store the ptep, or maybe drop this patch entirely. Thanks, Pasha