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=-11.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 AE683C433DF for ; Tue, 21 Jul 2020 04:58:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 901D72176B for ; Tue, 21 Jul 2020 04:58:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726990AbgGUE6j (ORCPT ); Tue, 21 Jul 2020 00:58:39 -0400 Received: from verein.lst.de ([213.95.11.211]:50449 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725294AbgGUE6j (ORCPT ); Tue, 21 Jul 2020 00:58:39 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id E950E68AFE; Tue, 21 Jul 2020 06:58:34 +0200 (CEST) Date: Tue, 21 Jul 2020 06:58:34 +0200 From: Christoph Hellwig To: Guenter Roeck Cc: Christoph Hellwig , Nick Hu , Greentime Hu , Vincent Chen , Paul Walmsley , Palmer Dabbelt , Andrew Morton , Linus Torvalds , linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/6] syscalls: use uaccess_kernel in addr_limit_user_check Message-ID: <20200721045834.GA9613@lst.de> References: <20200714105505.935079-1-hch@lst.de> <20200714105505.935079-2-hch@lst.de> <20200718013849.GA157764@roeck-us.net> <20200718094846.GA8593@lst.de> <20200720221046.GA86726@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200720221046.GA86726@roeck-us.net> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 20, 2020 at 03:10:46PM -0700, Guenter Roeck wrote: > I had another look into the code. Right after this patch, I see > > #define uaccess_kernel() segment_eq(get_fs(), KERNEL_DS) > > Yet, this patch is: > > - if (CHECK_DATA_CORRUPTION(!segment_eq(get_fs(), USER_DS), > + if (CHECK_DATA_CORRUPTION(uaccess_kernel(), > > So there is a negation in the condition. Indeed, the following change > on top of next-20200720 fixes the problem for mps2-an385. > > - if (CHECK_DATA_CORRUPTION(uaccess_kernel(), > + if (CHECK_DATA_CORRUPTION(!uaccess_kernel(), > > How does this work anywhere ? No, that is the wrong check - we want to make sure the address space override doesn't leak to userspace. The problem is that armnommu (and m68knommu, but that doesn't call the offending function) pretends to not have a kernel address space, which doesn't really work. Here is the fix I sent out yesterday, which I should have Cc'ed you on, sorry: --- >From 2bb889b2d99a2d978e90640ade8fe02359287092 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Mon, 20 Jul 2020 17:46:50 +0200 Subject: arm: don't call addr_limit_user_check for nommu On arm nommu kernel use the same constant for USER_DS and KERNEL_DS, and seqment_eq always returns false. With the current check in addr_limit_user_check that works by accident, but when replacing seqment_eq with uaccess_kerne it will fail. Just remove the not needed check entirely. Signed-off-by: Christoph Hellwig Reported-by: Guenter Roeck --- arch/arm/kernel/signal.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c index ab2568996ddb0c..c9dc912b83f012 100644 --- a/arch/arm/kernel/signal.c +++ b/arch/arm/kernel/signal.c @@ -713,7 +713,9 @@ struct page *get_signal_page(void) /* Defer to generic check */ asmlinkage void addr_limit_check_failed(void) { +#ifdef CONFIG_MMU addr_limit_user_check(); +#endif } #ifdef CONFIG_DEBUG_RSEQ -- 2.27.0