From nobody Wed Apr 8 08:38:06 2026 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 A5F34C6FA83 for ; Sun, 11 Sep 2022 10:00:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230095AbiIKKAC (ORCPT ); Sun, 11 Sep 2022 06:00:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57540 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229997AbiIKJ7j (ORCPT ); Sun, 11 Sep 2022 05:59:39 -0400 Received: from mail-qt1-x82b.google.com (mail-qt1-x82b.google.com [IPv6:2607:f8b0:4864:20::82b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6B8E51150 for ; Sun, 11 Sep 2022 02:59:30 -0700 (PDT) Received: by mail-qt1-x82b.google.com with SMTP id cb8so4364451qtb.0 for ; Sun, 11 Sep 2022 02:59:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=soleen.com; s=google; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:to:from:from:to:cc:subject:date; bh=OPh2SoeDJ39bM1Jn5fFI8VsUd8dRA2153uVq4iTm5YA=; b=Cm/iwBj9qSxR6hNh4WkGnlY2rIhzISZ52M2GqSDfU7xNlfLTD1kDBK3GW4JyIWLpbF vFCNPAJLgXJtsglJR9PAeKY44F6cjvaw6tuS4MXxA20nHmxmD/wqzebHgdbHMGmAD61N ZV4Tr5DVsNuioBerAQQDoJ4+a5mniKGiZRxoUQiZlNMllJ4sclh03nAFz08cVB8ODhMT Skx+FX/f8czauTMll515ktdu7gVSZJA1f7251v/yIj0BzYslEFQQtKX5F2MkHK/8CwmU Hx7spxOmVfuUwec09wkdbVsfFyOD1wVjfc69FUWeWsnCvU5bgK+iVzVBPk9GSB7Lao7h VxvQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:to:from:x-gm-message-state:from:to:cc :subject:date; bh=OPh2SoeDJ39bM1Jn5fFI8VsUd8dRA2153uVq4iTm5YA=; b=kC7ZbpmxzSc7NBivbB4Pp3TUXZ0x12aLS2aiDKrdyhgSiTnXCpDGOGTLSUrwB45POq zG6c7LtN3X9itGrgloqs7VcUDml25/HhmlewPnOratRK5SivcFieOrIqSZ5YgKJJlTy5 GDC1LwlDReZx3ESrBjKMkeFsUyVnAO+eDOTWQv3CbBrPloDDUAY6xy6dNYa4rpceEGK1 AxZkx0SsrEzKrHrnL0RGlxoUlPaLMVcwZtV1cUz+JRAKK1KX0HlNVIh6oBtFloNz1yFP 30TzUAtWxE1O0p/YrMNI5hIiKTStsAoZyv1QIX1QaBaJsJ32VtmpzuCNn3KAwvJ8hPAF EU4A== X-Gm-Message-State: ACgBeo1zkHN1GR84iF2ClWsHScOPB4TQ1w5XVLMnlUIiqlqDNT/PDZiP dXEHIkxf8E6UIYqAxkm5dVtm1w== X-Google-Smtp-Source: AA6agR5J3Cn9HvOjdYaL72tcgWTBN3wcKIFFTOLz4o2e2o7b+hMrlixH3K7CPiJSXhwkuBn1HYdkSA== X-Received: by 2002:a05:622a:609:b0:35b:acd0:21ff with SMTP id z9-20020a05622a060900b0035bacd021ffmr3764909qta.321.1662890369441; Sun, 11 Sep 2022 02:59:29 -0700 (PDT) Received: from soleen.c.googlers.com.com (240.157.150.34.bc.googleusercontent.com. [34.150.157.240]) by smtp.gmail.com with ESMTPSA id y29-20020a37f61d000000b006cbd60c14c9sm4625233qkj.35.2022.09.11.02.59.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 11 Sep 2022 02:59:28 -0700 (PDT) From: Pasha Tatashin To: pasha.tatashin@soleen.com, akpm@linux-foundation.org, corbet@lwn.net, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, rick.p.edgecombe@intel.com Subject: [PATCH 1/3] mm/page_table_check: Check writable zero page in page table check Date: Sun, 11 Sep 2022 09:59:21 +0000 Message-Id: <20220911095923.3614387-2-pasha.tatashin@soleen.com> X-Mailer: git-send-email 2.37.2.789.g6183377224-goog In-Reply-To: <20220911095923.3614387-1-pasha.tatashin@soleen.com> References: <20220911095923.3614387-1-pasha.tatashin@soleen.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Rick Edgecombe The zero page should remain all zero, so that it can be mapped as read-only for read faults of memory that should be zeroed. If it is ever mapped writable to userspace, it could become non-zero and so other apps would unexpectedly get non-zero data. So the zero page should never be mapped writable to userspace. Check for this condition in page_table_check_set(). Signed-off-by: Rick Edgecombe Signed-off-by: Pasha Tatashin --- mm/page_table_check.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/page_table_check.c b/mm/page_table_check.c index e2062748791a..665ece0d55d4 100644 --- a/mm/page_table_check.c +++ b/mm/page_table_check.c @@ -102,6 +102,8 @@ static void page_table_check_set(struct mm_struct *mm, = unsigned long addr, if (!pfn_valid(pfn)) return; =20 + BUG_ON(is_zero_pfn(pfn) && rw); + page =3D pfn_to_page(pfn); page_ext =3D lookup_page_ext(page); anon =3D PageAnon(page); --=20 2.37.2.789.g6183377224-goog