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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 861F8C00143 for ; Mon, 23 Aug 2021 04:56:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 70C9961186 for ; Mon, 23 Aug 2021 04:56:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233269AbhHWE4z (ORCPT ); Mon, 23 Aug 2021 00:56:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39114 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229462AbhHWE4u (ORCPT ); Mon, 23 Aug 2021 00:56:50 -0400 Received: from ozlabs.org (bilbo.ozlabs.org [IPv6:2401:3900:2:1::2]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BB190C061575; Sun, 22 Aug 2021 21:56:08 -0700 (PDT) Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 4GtKh13JJDz9sWS; Mon, 23 Aug 2021 14:56:01 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ellerman.id.au; s=201909; t=1629694564; bh=R8PBxC/HynH4xEcQANJCH6rE1jH+u8gsKBuxIbMNLTs=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=a1iW2Pt1kHHliRzWnsgUWnUPXzAPa6K0czSeVW/lgopJWaUMSBdXd9RvxA2oo+2Bi pmRIJH5PBg6bByQY/cxKNxkoprS4/Y5ACVbXiYIchmTaPZGQCOlmNym0Z7HGM2wM4c 4Fp2ulP/ZaQxpRgJz4EDHxe4xx6yYeKW+hpsTCDkiHP5QbMve8C48MLs61Q+vEPfdI VTqXFsDNZDd3tnl+2/9gl12uMzzs6VCYFegjMVs0YdD8TM9avqLkWjZK74C6aBMExz Etv9zteIN82cJPx68a7lGtZT15hKDTFtgcJJIQISdDBokbfeJWLCrCJY//wTldYX9G LRVCHoyBJgAkQ== From: Michael Ellerman To: Kees Cook 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 In-Reply-To: <202108200851.8AF09CDB71@keescook> References: <20210818060533.3569517-1-keescook@chromium.org> <20210818060533.3569517-58-keescook@chromium.org> <877dggeesw.fsf@mpe.ellerman.id.au> <202108200851.8AF09CDB71@keescook> Date: Mon, 23 Aug 2021 14:55:58 +1000 Message-ID: <87k0kcdajl.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Kees Cook writes: > 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. cheers