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=-16.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 D40E9C43214 for ; Fri, 20 Aug 2021 15:56:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B9BD260EFE for ; Fri, 20 Aug 2021 15:56:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241195AbhHTP4j (ORCPT ); Fri, 20 Aug 2021 11:56:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55522 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241289AbhHTP4g (ORCPT ); Fri, 20 Aug 2021 11:56:36 -0400 Received: from mail-pg1-x533.google.com (mail-pg1-x533.google.com [IPv6:2607:f8b0:4864:20::533]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2CEF2C061756 for ; Fri, 20 Aug 2021 08:55:58 -0700 (PDT) Received: by mail-pg1-x533.google.com with SMTP id r2so9586983pgl.10 for ; Fri, 20 Aug 2021 08:55:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=DfMkWVrhrXjOa4WT8fjUg2g99cfma/KNVtPegOy6YVA=; b=Tn/7uDGMiPjXxAM3ovBYEVyLtygFwlSJAWHrob1PWt4oz/x2Imgk0GhPN2Q3ecFemj 9aGJEzabYG/yp6A5N5Z9cTlvPVLlh/yP6oNypqN5vG8oOziU+OSzJRTu7fqXk/NgneL3 +EIYwoyeYH2hiFo8BxwiCpYmqjeLAOAaaL9bA= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=DfMkWVrhrXjOa4WT8fjUg2g99cfma/KNVtPegOy6YVA=; b=TTrbnRwkF75oo8YlMCs1zQfMye6dQ/JmIGlSrnfd1Jb8wogNt5QMbKzI70dBVasLhi dlkp6bnnnpx28TE3MrdnkFE+NKfhQv5G2uWzU9lW027RcLY00VTcL3gzqL34KJgf8KTY W+xuksy+pIOVY2G0dR1DnnT+SG+ojXj/JrcgcUOyXS6FCVOGHZUjdtvOvQi+5Y9I8wdk 4yj0WbZ1aX/jpACNVpTItkhWpPFDLxgletIbB/sAtCd1Tz0J78EK4CvYeNqbkL4ZbypP FWciX1zR2YnNAMvoZdtsZKt+So8oMC/zPtAdl8nuMlPdoAzilRq2YgAedRrC/p6Og9PL rZ3A== X-Gm-Message-State: AOAM530nEY4zDwWxn2E17ndyPiqHWDnI8ZrnGvMQIuwKOZmlc1N7bKj+ /TmbBxRQWEAovaDWOv87/F6oqg== X-Google-Smtp-Source: ABdhPJxNmkkLS0IYvcJdUty1efO3ATpriVc4oMEh5d9+VW4AFW/Rt8LdZFCR+Kj2vvrc2GQCiXZJ9w== X-Received: by 2002:a63:4d24:: with SMTP id a36mr6002323pgb.37.1629474957688; Fri, 20 Aug 2021 08:55:57 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id o10sm6412690pjg.34.2021.08.20.08.55.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Aug 2021 08:55:57 -0700 (PDT) Date: Fri, 20 Aug 2021 08:55:56 -0700 From: Kees Cook To: Michael Ellerman Cc: linux-kernel@vger.kernel.org, Benjamin Herrenschmidt , Paul Mackerras , Christophe Leroy , Sudeep Holla , linuxppc-dev@lists.ozlabs.org, kernel test robot , "Gustavo A. R. Silva" , Greg Kroah-Hartman , Andrew Morton , linux-wireless@vger.kernel.org, netdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-staging@lists.linux.dev, linux-block@vger.kernel.org, linux-kbuild@vger.kernel.org, clang-built-linux@googlegroups.com, Rasmus Villemoes , linux-hardening@vger.kernel.org Subject: Re: [PATCH v2 57/63] powerpc/signal32: Use struct_group() to zero spe regs Message-ID: <202108200851.8AF09CDB71@keescook> References: <20210818060533.3569517-1-keescook@chromium.org> <20210818060533.3569517-58-keescook@chromium.org> <877dggeesw.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <877dggeesw.fsf@mpe.ellerman.id.au> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 20, 2021 at 05:49:35PM +1000, Michael Ellerman wrote: > Kees Cook writes: > > In preparation for FORTIFY_SOURCE performing compile-time and run-time > > field bounds checking for memset(), avoid intentionally writing across > > neighboring fields. > > > > Add a struct_group() for the spe registers so that memset() can correctly reason > > about the size: > > > > In function 'fortify_memset_chk', > > inlined from 'restore_user_regs.part.0' at arch/powerpc/kernel/signal_32.c:539:3: > >>> include/linux/fortify-string.h:195:4: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning] > > 195 | __write_overflow_field(); > > | ^~~~~~~~~~~~~~~~~~~~~~~~ > > > > Cc: Michael Ellerman > > Cc: Benjamin Herrenschmidt > > Cc: Paul Mackerras > > Cc: Christophe Leroy > > Cc: Sudeep Holla > > Cc: linuxppc-dev@lists.ozlabs.org > > Reported-by: kernel test robot > > Signed-off-by: Kees Cook > > --- > > arch/powerpc/include/asm/processor.h | 6 ++++-- > > arch/powerpc/kernel/signal_32.c | 6 +++--- > > 2 files changed, 7 insertions(+), 5 deletions(-) > > > > diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h > > index f348e564f7dd..05dc567cb9a8 100644 > > --- a/arch/powerpc/include/asm/processor.h > > +++ b/arch/powerpc/include/asm/processor.h > > @@ -191,8 +191,10 @@ struct thread_struct { > > int used_vsr; /* set if process has used VSX */ > > #endif /* CONFIG_VSX */ > > #ifdef CONFIG_SPE > > - unsigned long evr[32]; /* upper 32-bits of SPE regs */ > > - u64 acc; /* Accumulator */ > > + struct_group(spe, > > + unsigned long evr[32]; /* upper 32-bits of SPE regs */ > > + u64 acc; /* Accumulator */ > > + ); > > unsigned long spefscr; /* SPE & eFP status */ > > unsigned long spefscr_last; /* SPEFSCR value on last prctl > > call or trap return */ > > diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c > > index 0608581967f0..77b86caf5c51 100644 > > --- a/arch/powerpc/kernel/signal_32.c > > +++ b/arch/powerpc/kernel/signal_32.c > > @@ -532,11 +532,11 @@ static long restore_user_regs(struct pt_regs *regs, > > regs_set_return_msr(regs, regs->msr & ~MSR_SPE); > > if (msr & MSR_SPE) { > > /* restore spe registers from the stack */ > > - unsafe_copy_from_user(current->thread.evr, &sr->mc_vregs, > > - ELF_NEVRREG * sizeof(u32), failed); > > + unsafe_copy_from_user(¤t->thread.spe, &sr->mc_vregs, > > + sizeof(current->thread.spe), failed); > > This makes me nervous, because the ABI is that we copy ELF_NEVRREG * > sizeof(u32) bytes, not whatever sizeof(current->thread.spe) happens to > be. > > ie. if we use sizeof an inadvertent change to the fields in > thread_struct could change how many bytes we copy out to userspace, > which would be an ABI break. > > And that's not that hard to do, because it's not at all obvious that the > size and layout of fields in thread_struct affects the user ABI. > > At the same time we don't want to copy the right number of bytes but > the wrong content, so from that point of view using sizeof is good :) > > The way we handle it in ptrace is to have BUILD_BUG_ON()s to verify that > things match up, so maybe we should do that here too. > > ie. add: > > BUILD_BUG_ON(sizeof(current->thread.spe) == ELF_NEVRREG * sizeof(u32)); > > Not sure if you are happy doing that as part of this patch. I can always > do it later if not. Sounds good to me; I did that in a few other cases in the series where the relationships between things seemed tenuous. :) I'll add this (as !=) in v3. Thanks! -- Kees Cook