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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6D461C433F5 for ; Fri, 17 Dec 2021 17:13:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239698AbhLQRNl (ORCPT ); Fri, 17 Dec 2021 12:13:41 -0500 Received: from mga05.intel.com ([192.55.52.43]:14809 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239702AbhLQRNl (ORCPT ); Fri, 17 Dec 2021 12:13:41 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1639761221; x=1671297221; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=SX/r6niEbIpbvqmzbfR8jaqmQcZv+84O1KgVGiU0qww=; b=lU0G+nzYf2GDTudqJm4a0miIsKKjxOP9KWGx14tfqlX633xLq9QYfaB6 BDCe9n4MyLwEpw7klnNNNYRKlJHwZlrifMFWH9MIJ55c/3ZbffXobrvtJ V50qUp4QNGchVPSTxgBkQqkZNb5EbEaAdjMxgudkQEYhtAbZsNH2U0IxO 3iQg3k3hH77aQFj+UUccoZCwynWPmII1EoSxkSH++bvC6L8uMUh6pd6CM 938uT+R5B1i0pGZY6zHjG26A8n9g630qNSagbOHj4mX5QZoyBi5fvmeLH Bs9eU1/7Rb8l4RZ0wJ+TFD+E4kHi2/nmhK4Jn4OeJCVbkRWmci0cSEg1v A==; X-IronPort-AV: E=McAfee;i="6200,9189,10201"; a="326083627" X-IronPort-AV: E=Sophos;i="5.88,213,1635231600"; d="scan'208";a="326083627" Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Dec 2021 09:13:40 -0800 X-IronPort-AV: E=Sophos;i="5.88,213,1635231600"; d="scan'208";a="683451552" Received: from agluck-desk2.sc.intel.com (HELO agluck-desk2.amr.corp.intel.com) ([10.3.52.146]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Dec 2021 09:13:40 -0800 Date: Fri, 17 Dec 2021 09:13:39 -0800 From: "Luck, Tony" To: Borislav Petkov Cc: Dan Carpenter , linux-edac@vger.kernel.org Subject: Re: [bug report] x86/mce: Prevent severity computation from being instrumented Message-ID: References: <20211217102029.GA29708@kili> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-edac@vger.kernel.org On Fri, Dec 17, 2021 at 12:29:45PM +0100, Borislav Petkov wrote: > + Tony. > > On Fri, Dec 17, 2021 at 01:20:29PM +0300, Dan Carpenter wrote: > > Hello Borislav Petkov, > > > > This is a semi-automatic email about new static checker warnings. > > > > The patch 0a5b288e85bb: "x86/mce: Prevent severity computation from > > being instrumented" from Oct 13, 2021, leads to the following Smatch > > complaint: > > > > arch/x86/kernel/cpu/mce/severity.c:286 error_context() > > warn: variable dereferenced before check 'regs' (see line 280) > > > > arch/x86/kernel/cpu/mce/severity.c > > 279 fixup_type = ex_get_fixup_type(m->ip); > > 280 copy_user = is_copy_from_user(regs); > > ^^^^ > > New unchecked dereference > > > > 281 instrumentation_end(); > > 282 > > 283 switch (fixup_type) { > > 284 case EX_TYPE_UACCESS: > > 285 case EX_TYPE_COPY: > > 286 if (!regs || !copy_user) > > ^^^^ > > Old code checked for NULL > > > > 287 return IN_KERNEL; > > 288 m->kflags |= MCE_IN_KERNEL_COPYIN; > > Good catch, thanks! > > I guess we can do something like this: > > --- > diff --git a/arch/x86/kernel/cpu/mce/severity.c b/arch/x86/kernel/cpu/mce/severity.c > index a32646769705..7aa2bda93cbb 100644 > --- a/arch/x86/kernel/cpu/mce/severity.c > +++ b/arch/x86/kernel/cpu/mce/severity.c > @@ -222,6 +222,9 @@ static bool is_copy_from_user(struct pt_regs *regs) > struct insn insn; > int ret; > > + if (!regs) > + return false; > + > if (copy_from_kernel_nofault(insn_buf, (void *)regs->ip, MAX_INSN_SIZE)) > return false; > > @@ -283,7 +286,7 @@ static noinstr int error_context(struct mce *m, struct pt_regs *regs) > switch (fixup_type) { > case EX_TYPE_UACCESS: > case EX_TYPE_COPY: > - if (!regs || !copy_user) > + if (!copy_user) > return IN_KERNEL; > m->kflags |= MCE_IN_KERNEL_COPYIN; > fallthrough; > Looks good to me. Reviewed-by: Tony Luck -Tony