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 lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C074FCD6E4A for ; Thu, 4 Jun 2026 16:11:19 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wVAeh-0003hN-5X; Thu, 04 Jun 2026 12:10:51 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wVAed-0003gU-7R for qemu-devel@nongnu.org; Thu, 04 Jun 2026 12:10:47 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wVAeb-00034o-9D for qemu-devel@nongnu.org; Thu, 04 Jun 2026 12:10:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1780589443; h=from:from:reply-to: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=GfY89U9FlEEQmVa9fIkSfj/aZdfhMPIj/WgntSo8CLM=; b=GJFc1HZoZwDbSoiZ1y9jYstt+kKiHRZOfRCmHQot4xM7HQCSoVG2SbFzl8todF+Xbg7SRj 3JIbxInHflXTsCaSAp9AeYuJyVTJpiocji3qPB7HKN/igTlfrgjb7xAR5NaeMcGsRDBaS5 BPXFNuUFzOmiriyfEnOiN0DmMY8rL/4= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-519-U74vHk0FMGWv-BJm2Qn-5A-1; Thu, 04 Jun 2026 12:10:42 -0400 X-MC-Unique: U74vHk0FMGWv-BJm2Qn-5A-1 X-Mimecast-MFC-AGG-ID: U74vHk0FMGWv-BJm2Qn-5A_1780589441 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 2ECEC180061E for ; Thu, 4 Jun 2026 16:10:41 +0000 (UTC) Received: from redhat.com (unknown [10.44.50.34]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A5C91180049F; Thu, 4 Jun 2026 16:10:39 +0000 (UTC) Date: Thu, 4 Jun 2026 17:10:36 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau Cc: qemu-devel@nongnu.org, armbru@redhat.com Subject: Re: [PATCH v3 23/24] hw/i2c/pmbus: fix undefined behavior in pmbus_direct_mode2data Message-ID: References: <20260516-qom-tests-v3-0-3f20c3a029a7@redhat.com> <20260516-qom-tests-v3-23-3f20c3a029a7@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260516-qom-tests-v3-23-3f20c3a029a7@redhat.com> User-Agent: Mutt/2.3.1 (2026-03-20) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Sat, May 16, 2026 at 11:59:22AM +0400, Marc-André Lureau wrote: > The intermediate result of (Y * 10^-R - b) / m can be negative when > the bias (b) is large and the raw register value is small (e.g. zero > on an uninitialized device). Assigning that negative double to uint32_t > is undefined behavior, caught by UBSan/clang. > > Use a double intermediate and clamp negative results to zero. > > Fixes: 3746d5c15e70 ("hw/i2c: add support for PMBus") > Signed-off-by: Marc-André Lureau > --- > hw/i2c/pmbus_device.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/hw/i2c/pmbus_device.c b/hw/i2c/pmbus_device.c > index 853dc4b4342..861f5b4fb63 100644 > --- a/hw/i2c/pmbus_device.c > +++ b/hw/i2c/pmbus_device.c > @@ -23,8 +23,8 @@ uint16_t pmbus_data2direct_mode(PMBusCoefficients c, uint32_t value) > uint32_t pmbus_direct_mode2data(PMBusCoefficients c, uint16_t value) > { > /* X = (Y * 10^-R - b) / m */ > - uint32_t x = (value / pow(10, c.R) - c.b) / c.m; > - return x; > + double x = (value / pow(10, c.R) - c.b) / c.m; > + return (x > 0) ? (uint32_t)x : 0; Couldn't 'x' exceed G_MAXUINT32 and thus truncate here which while not undefined would still seem undesirable ? If so, then perhaps return (x > 0 ? (x < G_MAXUINT32 ? (uint32_t)x : G_MAXUINT32) : 0); ? > } > > uint16_t pmbus_data2linear_mode(uint16_t value, int exp) > > -- > 2.54.0 > > With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|