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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 CC1EFC433B4 for ; Thu, 22 Apr 2021 11:34:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9448560FF1 for ; Thu, 22 Apr 2021 11:34:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236032AbhDVLfb (ORCPT ); Thu, 22 Apr 2021 07:35:31 -0400 Received: from foss.arm.com ([217.140.110.172]:50284 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230510AbhDVLfa (ORCPT ); Thu, 22 Apr 2021 07:35:30 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B25D113A1; Thu, 22 Apr 2021 04:34:55 -0700 (PDT) Received: from e120937-lin (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B75AC3F774; Thu, 22 Apr 2021 04:34:54 -0700 (PDT) Date: Thu, 22 Apr 2021 12:34:52 +0100 From: Cristian Marussi To: Sudeep Holla Cc: Dan Carpenter , "Jon Medhurst (Tixy)" , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org Subject: Re: [PATCH] firmware: arm_scpi: prevent ternary sign expansion bug Message-ID: <20210422113451.GG43717@e120937-lin> References: <20210422101709.GF43717@e120937-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210422101709.GF43717@e120937-lin> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: kernel-janitors@vger.kernel.org On Thu, Apr 22, 2021 at 11:17:09AM +0100, Cristian Marussi wrote: > Hi, > > On Thu, Apr 22, 2021 at 12:02:29PM +0300, Dan Carpenter wrote: > > How type promotion works in ternary expressions is a bit tricky. > > The problem is that scpi_clk_get_val() returns longs, "ret" is a int > > which holds a negative error code, and le32_to_cpu() is an unsigned int. > > We want the negative error code to be cast to a negative long. But > > because le32_to_cpu() is an u32 then "ret" is type promoted to u32 and > > becomes a high positive and then it is promoted to long and it is still > > a high positive value. > > > > Fix this by getting rid of the ternary. > > I wonder how/if the callers up in the stack check/expect ever effectively for a > 2-complement negative value inside the returned unsigned long...given that this > plugs finally into CLK framework struct clk_ops.recalc_rate via clk-scpi.c which > also expects unsigned long....but that's another story. > > FWIW regarding this patch: > > Reviewed-by: Cristian Marussi > > Thanks > > Cristian @Sudeep, as a second though, looking at .recalc_rate() definition inside include/linux/clk-provider.h:struct clk_ops which is the direct caller of this SCPI clk function, I wonder if, instead, on error we should not return here just ZERO as the returned clock rate value as in: if (ret) return 0; given that the error code returned inside the unsigned long won't be ever considerd as such apparently, so not sure if it'd be worst to return a very big fake value or zero... Thanks Cristian > > > > Fixes: 8cb7cf56c9fe ("firmware: add support for ARM System Control and Power Interface(SCPI) protocol") > > Signed-off-by: Dan Carpenter > > --- > > drivers/firmware/arm_scpi.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/firmware/arm_scpi.c b/drivers/firmware/arm_scpi.c > > index d0dee37ad522..3bf61854121d 100644 > > --- a/drivers/firmware/arm_scpi.c > > +++ b/drivers/firmware/arm_scpi.c > > @@ -552,8 +552,10 @@ static unsigned long scpi_clk_get_val(u16 clk_id) > > > > ret = scpi_send_message(CMD_GET_CLOCK_VALUE, &le_clk_id, > > sizeof(le_clk_id), &rate, sizeof(rate)); > > + if (ret) > > + return ret; > > > > - return ret ? ret : le32_to_cpu(rate); > > + return le32_to_cpu(rate); > > } > > > > static int scpi_clk_set_val(u16 clk_id, unsigned long rate) > > -- > > 2.30.2 > >