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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 E71CCC4361B for ; Fri, 4 Dec 2020 06:31:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9CF8422582 for ; Fri, 4 Dec 2020 06:31:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727995AbgLDGbh (ORCPT ); Fri, 4 Dec 2020 01:31:37 -0500 Received: from pegase1.c-s.fr ([93.17.236.30]:29290 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725372AbgLDGbh (ORCPT ); Fri, 4 Dec 2020 01:31:37 -0500 Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4CnNBP22Bcz9tyVM; Fri, 4 Dec 2020 07:30:53 +0100 (CET) X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id 7EEkoEIMxYcR; Fri, 4 Dec 2020 07:30:53 +0100 (CET) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 4CnNBP0qKPz9tyVJ; Fri, 4 Dec 2020 07:30:53 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id D73088B7F5; Fri, 4 Dec 2020 07:30:53 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id LesFRRD4IsuQ; Fri, 4 Dec 2020 07:30:53 +0100 (CET) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 21C0F8B75E; Fri, 4 Dec 2020 07:30:53 +0100 (CET) Subject: Re: [PATCH] powerpc/mm: Don't see NULL pointer dereference as a KUAP fault To: Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org References: <8b865b93d25c15c8e6d41e71c368bfc28da4489d.1606816701.git.christophe.leroy@csgroup.eu> <87mtyvumrn.fsf@mpe.ellerman.id.au> From: Christophe Leroy Message-ID: <16dd1637-cfaf-bfb3-07c6-7e71d33640b8@csgroup.eu> Date: Fri, 4 Dec 2020 07:30:52 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: <87mtyvumrn.fsf@mpe.ellerman.id.au> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 03/12/2020 à 12:55, Michael Ellerman a écrit : > Christophe Leroy writes: >> Sometimes, NULL pointer dereferences are expected. Even when they >> are accidental they are unlikely an exploit attempt because the >> first page is never mapped. > > The first page can be mapped if mmap_min_addr is 0. > > Blocking all faults to the first page would potentially break any > program that does that. > > Also if there is something mapped at 0 it's a good chance it is an > exploit attempt :) Ok, I see. In fact, we hit this warning because we don't provide copy_from_kernel_nofault_allowed() I'll cook a patch for that. Christophe