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=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,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 B3E80C4320A for ; Fri, 20 Aug 2021 07:53:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8FAE66103C for ; Fri, 20 Aug 2021 07:53:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238848AbhHTHy0 (ORCPT ); Fri, 20 Aug 2021 03:54:26 -0400 Received: from pegase2.c-s.fr ([93.17.235.10]:41517 "EHLO pegase2.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236378AbhHTHy0 (ORCPT ); Fri, 20 Aug 2021 03:54:26 -0400 Received: from localhost (mailhub3.si.c-s.fr [172.26.127.67]) by localhost (Postfix) with ESMTP id 4GrYmV3rRlz9sTr; Fri, 20 Aug 2021 09:53:46 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from pegase2.c-s.fr ([172.26.127.65]) by localhost (pegase2.c-s.fr [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id E8Ffz9K-cCxD; Fri, 20 Aug 2021 09:53:46 +0200 (CEST) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase2.c-s.fr (Postfix) with ESMTP id 4GrYmV2jCFz9sTj; Fri, 20 Aug 2021 09:53:46 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 3A2918B868; Fri, 20 Aug 2021 09:53:46 +0200 (CEST) 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 GYJg-josgfgQ; Fri, 20 Aug 2021 09:53:46 +0200 (CEST) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 0AEB28B862; Fri, 20 Aug 2021 09:53:45 +0200 (CEST) Subject: Re: [PATCH v2 57/63] powerpc/signal32: Use struct_group() to zero spe regs To: Michael Ellerman , Kees Cook , linux-kernel@vger.kernel.org Cc: Benjamin Herrenschmidt , Paul Mackerras , 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 References: <20210818060533.3569517-1-keescook@chromium.org> <20210818060533.3569517-58-keescook@chromium.org> <877dggeesw.fsf@mpe.ellerman.id.au> From: Christophe Leroy Message-ID: <0f6e508e-62b6-3840-5ff4-eb5a77635bd1@csgroup.eu> Date: Fri, 20 Aug 2021 09:53:41 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <877dggeesw.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-block@vger.kernel.org Le 20/08/2021 à 09:49, Michael Ellerman a écrit : > 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)); You mean != I guess ? > > > Not sure if you are happy doing that as part of this patch. I can always > do it later if not. > > cheers >