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,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 15184C47083 for ; Wed, 2 Jun 2021 13:12:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F145A613AA for ; Wed, 2 Jun 2021 13:12:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229640AbhFBNOa (ORCPT ); Wed, 2 Jun 2021 09:14:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49842 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229579AbhFBNO3 (ORCPT ); Wed, 2 Jun 2021 09:14:29 -0400 Received: from mail.skyhub.de (mail.skyhub.de [IPv6:2a01:4f8:190:11c2::b:1457]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3E419C061574; Wed, 2 Jun 2021 06:12:46 -0700 (PDT) Received: from zn.tnic (p200300ec2f0f0e00eeb0fb45e4479fa5.dip0.t-ipconnect.de [IPv6:2003:ec:2f0f:e00:eeb0:fb45:e447:9fa5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 8F2241EC03D2; Wed, 2 Jun 2021 15:12:44 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1622639564; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=IinqjbSWeoabF0QmaUNNBv38d7v6vXyIK8neZqnz8q4=; b=rycYARL02BpEmdJ1FQ3jhabykdaVumGareEHhsrECJc4ozzj9ncaby8N+ZOgPpufVUv391 vwuLqtQOTiy0BH07bATdt+7hpnl1fF4FKcwfoHJGtkK1wxUrE+hb0ZRscEpWsXcI+AkVKm Hm3Ezk4P3U9y/ixWfx4dhROc4lGCclE= Date: Wed, 2 Jun 2021 15:12:39 +0200 From: Borislav Petkov To: Thomas Gleixner Cc: LKML , x86@kernel.org, Andy Lutomirski , Dave Hansen , Fenghua Yu , Tony Luck , Yu-cheng Yu , syzbot+2067e764dbcd10721e2e@syzkaller.appspotmail.com, stable@vger.kernel.org Subject: Re: [patch 2/8] x86/fpu: Prevent state corruption in __fpu__restore_sig() Message-ID: References: <20210602095543.149814064@linutronix.de> <20210602101618.462908825@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20210602101618.462908825@linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 02, 2021 at 11:55:45AM +0200, Thomas Gleixner wrote: > From: Thomas Gleixner > > The non-compacted slowpath uses __copy_from_user() and copies the entire > user buffer into the kernel buffer, verbatim. This means that the kernel > buffer may now contain entirely invalid state on which XRSTOR will #GP. > validate_user_xstate_header() can detect some of that corruption, but that > leaves the onus on callers to clear the buffer. > > Prior to XSAVES support it was possible just to reinitialize the buffer, > completely, but with supervisor states that is not longer possible as the > buffer clearing code split got it backwards. Fixing that is possible, but > not corrupting the state in the first place is more robust. > > Avoid corruption of the kernel XSAVE buffer by using copy_user_to_xstate() > which validates the XSAVE header contents before copying the actual states > to the kernel. copy_user_to_xstate() was previously only called for > compacted-format kernel buffers, but it works for both compacted and > non-compacted forms. > > Using it for the non-compacted form is slower because of multiple > __copy_from_user() operations, but that cost is less important than robust > code in an already slow path. > > [ Changelog polished by Dave Hansen ] Nice polishing! > Fixes: b860eb8dce59 ("x86/fpu/xstate: Define new functions for clearing fpregs and xstates") > Reported-by: syzbot+2067e764dbcd10721e2e@syzkaller.appspotmail.com > Signed-off-by: Thomas Gleixner > Cc: stable@vger.kernel.org > --- > arch/x86/include/asm/fpu/xstate.h | 4 ---- > arch/x86/kernel/fpu/signal.c | 9 +-------- > arch/x86/kernel/fpu/xstate.c | 2 +- > 3 files changed, 2 insertions(+), 13 deletions(-) > > --- a/arch/x86/include/asm/fpu/xstate.h > +++ b/arch/x86/include/asm/fpu/xstate.h > @@ -112,8 +112,4 @@ void copy_supervisor_to_kernel(struct xr > void copy_dynamic_supervisor_to_kernel(struct xregs_state *xstate, u64 mask); > void copy_kernel_to_dynamic_supervisor(struct xregs_state *xstate, u64 mask); > > - > -/* Validate an xstate header supplied by userspace (ptrace or sigreturn) */ > -int validate_user_xstate_header(const struct xstate_header *hdr); > - > #endif > --- a/arch/x86/kernel/fpu/signal.c > +++ b/arch/x86/kernel/fpu/signal.c > @@ -405,14 +405,7 @@ static int __fpu__restore_sig(void __use > if (use_xsave() && !fx_only) { > u64 init_bv = xfeatures_mask_user() & ~user_xfeatures; > > - if (using_compacted_format()) { > - ret = copy_user_to_xstate(&fpu->state.xsave, buf_fx); > - } else { > - ret = __copy_from_user(&fpu->state.xsave, buf_fx, state_size); > - > - if (!ret && state_size > offsetof(struct xregs_state, header)) > - ret = validate_user_xstate_header(&fpu->state.xsave.header); > - } > + ret = copy_user_to_xstate(&fpu->state.xsave, buf_fx); > if (ret) > goto err_out; > > --- a/arch/x86/kernel/fpu/xstate.c > +++ b/arch/x86/kernel/fpu/xstate.c > @@ -515,7 +515,7 @@ int using_compacted_format(void) > } > > /* Validate an xstate header supplied by userspace (ptrace or sigreturn) */ > -int validate_user_xstate_header(const struct xstate_header *hdr) > +static int validate_user_xstate_header(const struct xstate_header *hdr) Can't do that yet - that one is still called from regset.c: arch/x86/kernel/fpu/regset.c: In function ‘xstateregs_set’: arch/x86/kernel/fpu/regset.c:135:10: error: implicit declaration of function ‘validate_user_xstate_header’ [-Werror=implicit-function-declaration] 135 | ret = validate_user_xstate_header(&xsave->header); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~ cc1: some warnings being treated as errors Maybe after the 5th patch which kills that usage too. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette