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 34CB8C433EF for ; Fri, 17 Dec 2021 11:29:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233548AbhLQL3r (ORCPT ); Fri, 17 Dec 2021 06:29:47 -0500 Received: from mail.skyhub.de ([5.9.137.197]:52822 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229817AbhLQL3r (ORCPT ); Fri, 17 Dec 2021 06:29:47 -0500 Received: from zn.tnic (dslb-088-067-202-008.088.067.pools.vodafone-ip.de [88.67.202.8]) (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 663061EC01A2; Fri, 17 Dec 2021 12:29:42 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1639740582; 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:in-reply-to:in-reply-to: references:references; bh=0dsuzqrpYsFL/K0AJrrGFcR61xzUAu7ie3t40tDlXQY=; b=auit6a3pktzqkzNQIzLGjJzaN/5YSK4WbaJxDFChnx2ufBfcei61QU7oJ7wVLMHnO8vpOY zyxkCkV1SDSKzKww0YZL6ZxgRXqzzrUDF6e7QSyS+NXHPThEO+1hZVMEuEPSflj8rieW1e 3nQzGdLcc7UGwREIv9nmsRXvpyJ6a68= Date: Fri, 17 Dec 2021 12:29:45 +0100 From: Borislav Petkov To: Dan Carpenter Cc: linux-edac@vger.kernel.org, Tony Luck 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=utf-8 Content-Disposition: inline In-Reply-To: <20211217102029.GA29708@kili> Precedence: bulk List-ID: X-Mailing-List: linux-edac@vger.kernel.org + 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; -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette