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=-5.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=no 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 33E24C433E5 for ; Fri, 24 Jul 2020 11:51:34 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id F393820737 for ; Fri, 24 Jul 2020 11:51:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="IBocAXdX"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=mediatek.com header.i=@mediatek.com header.b="TyLyg7rg" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F393820737 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=mediatek.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To:Date:To:From: Subject:Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=iXE2/J9Pvzqgg83F81s3D03Ni8WCcdOGU1TDUneSBE4=; b=IBocAXdXhrLNTDSJf4r3T6uR9 +OGK60jyOzoaiT5ZWRptmUScij5FJefsO1nGQXK+eLqv4+5tbTep+X8GZ/s2k+UatyzBlZxo2+bwE MiCGpWIga0f3Im1Jb/aVdgk1z7Bf3aL5aERe101jLXsO42T9/WMk10NzX1A63h8SFmCcRBlaXox90 fZR8WvZLt3jC/W853fEiuDES2ELmFmud6dvH59PfdDEn5LTKNEaNl4SdtqteYggco4x1ZDshrqlMM A3LJAR6xfI3w4XOqBjWbhRLhHofiyde3aygD9nwoAB0VEHiyzwpMlfeLnFIln06oH4p22zVFVcd3J h6Fi7fqVg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jywDJ-0005Xv-Jt; Fri, 24 Jul 2020 11:50:09 +0000 Received: from mailgw01.mediatek.com ([216.200.240.184]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jywDD-0005WL-GF; Fri, 24 Jul 2020 11:50:05 +0000 X-UUID: a4191b97fdfe4002a0f107ccb8ac027d-20200724 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=mediatek.com; s=dk; h=Content-Transfer-Encoding:MIME-Version:Content-Type:References:In-Reply-To:Date:CC:To:From:Subject:Message-ID; bh=/zejYp/GTVn0VhxNwV3OAw/hISSDpVJ/mNNf/5S0Uhs=; b=TyLyg7rgvvUqo/RpluGg2OI2+byHaZ1GrIE+r/XGB9fx7FFhVycXJ4P9Q2yNWwtTixPRFOBpGLScsJcmFZHUCINHrP8EomgdqzTlIcZkb+bt9vn62+LNRxUmwPb949yVCP8o9YlBsVdJFsRDKbErP0zNeRPk8EOvaNLDdfl03WM=; X-UUID: a4191b97fdfe4002a0f107ccb8ac027d-20200724 Received: from mtkcas67.mediatek.inc [(172.29.193.45)] by mailgw01.mediatek.com (envelope-from ) (musrelay.mediatek.com ESMTP with TLS) with ESMTP id 1542992297; Fri, 24 Jul 2020 03:49:42 -0800 Received: from MTKMBS01N1.mediatek.inc (172.21.101.68) by MTKMBS62N1.mediatek.inc (172.29.193.41) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Fri, 24 Jul 2020 04:49:55 -0700 Received: from mtkcas07.mediatek.inc (172.21.101.84) by mtkmbs01n1.mediatek.inc (172.21.101.68) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Fri, 24 Jul 2020 19:49:47 +0800 Received: from [172.21.77.33] (172.21.77.33) by mtkcas07.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Fri, 24 Jul 2020 19:49:48 +0800 Message-ID: <1595591389.14564.3.camel@mtkswgap22> Subject: Re: [PATCH v2] cpuidle: change enter_s2idle() prototype From: Neal Liu To: "Rafael J. Wysocki" Date: Fri, 24 Jul 2020 19:49:49 +0800 In-Reply-To: References: <1594005196-16327-1-git-send-email-neal.liu@mediatek.com> <1594005196-16327-2-git-send-email-neal.liu@mediatek.com> <1594350535.4670.13.camel@mtkswgap22> <1595233294.8055.0.camel@mtkswgap22> <20200723190724.GA1339461@google.com> <1595586289.14121.5.camel@mtkswgap22> X-Mailer: Evolution 3.2.3-0ubuntu6 MIME-Version: 1.0 X-MTK: N X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200724_075004_373410_E1DC58E8 X-CRM114-Status: GOOD ( 38.73 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jacob Pan , linux-tegra , wsd_upstream , Linux PM , Daniel Lezcano , "Rafael J. Wysocki" , lkml , Jonathan Hunter , ACPI Devel Maling List , Thierry Reding , Neal Liu , Sami Tolvanen , Matthias Brugger , "moderated list:ARM/Mediatek SoC..." , Linux ARM , Len Brown Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, 2020-07-24 at 13:20 +0200, Rafael J. Wysocki wrote: > On Fri, Jul 24, 2020 at 12:24 PM Neal Liu wrote: > > > > On Fri, 2020-07-24 at 11:57 +0200, Rafael J. Wysocki wrote: > > > On Thu, Jul 23, 2020 at 9:07 PM Sami Tolvanen wrote: > > > > > > > > On Mon, Jul 20, 2020 at 04:21:34PM +0800, Neal Liu wrote: > > > > > Gentle ping on this patch. > > > > > > > > > > > > > > > On Fri, 2020-07-10 at 11:08 +0800, Neal Liu wrote: > > > > > > On Thu, 2020-07-09 at 14:18 +0200, Rafael J. Wysocki wrote: > > > > > > > On Mon, Jul 6, 2020 at 5:13 AM Neal Liu wrote: > > > > > > > > > > > > > > > > Control Flow Integrity(CFI) is a security mechanism that disallows > > > > > > > > changes to the original control flow graph of a compiled binary, > > > > > > > > making it significantly harder to perform such attacks. > > > > > > > > > > > > > > > > init_state_node() assign same function callback to different > > > > > > > > function pointer declarations. > > > > > > > > > > > > > > > > static int init_state_node(struct cpuidle_state *idle_state, > > > > > > > > const struct of_device_id *matches, > > > > > > > > struct device_node *state_node) { ... > > > > > > > > idle_state->enter = match_id->data; ... > > > > > > > > idle_state->enter_s2idle = match_id->data; } > > > > > > > > > > > > > > > > Function declarations: > > > > > > > > > > > > > > > > struct cpuidle_state { ... > > > > > > > > int (*enter) (struct cpuidle_device *dev, > > > > > > > > struct cpuidle_driver *drv, > > > > > > > > int index); > > > > > > > > > > > > > > > > void (*enter_s2idle) (struct cpuidle_device *dev, > > > > > > > > struct cpuidle_driver *drv, > > > > > > > > int index); }; > > > > > > > > > > > > > > > > In this case, either enter() or enter_s2idle() would cause CFI check > > > > > > > > failed since they use same callee. > > > > > > > > > > > > > > Can you please explain this in a bit more detail? > > > > > > > > > > > > > > As it stands, I don't understand the problem statement enough to apply > > > > > > > the patch. > > > > > > > > > > > > > > > > > > > Okay, Let's me try to explain more details. > > > > > > Control Flow Integrity(CFI) is a security mechanism that disallows > > > > > > changes to the original control flow graph of a compiled binary, making > > > > > > it significantly harder to perform such attacks. > > > > > > > > > > > > There are multiple control flow instructions that could be manipulated > > > > > > by the attacker and subvert control flow. The target instructions that > > > > > > use data to determine the actual destination. > > > > > > - indirect jump > > > > > > - indirect call > > > > > > - return > > > > > > > > > > > > In this case, function prototype between caller and callee are mismatch. > > > > > > Caller: (type A)funcA > > > > > > Callee: (type A)funcB > > > > > > Callee: (type C)funcC > > > > > > > > > > > > funcA calls funcB -> no problem > > > > > > funcA calls funcC -> CFI check failed > > > > > > > > > > > > That's why we try to align function prototype. > > > > > > Please feel free to feedback if you have any questions. > > > > > > > > I think you should include a better explanation in the commit message. > > > > Perhaps something like this? > > > > > > > > init_state_node assigns the same callback function to both enter and > > > > enter_s2idle despite mismatching function types, which trips indirect > > > > call checking with Control-Flow Integrity (CFI). > > > > > > > > > > > > Align function prototype of enter() since it needs return value for > > > > > > > > some use cases. The return value of enter_s2idle() is no > > > > > > > > need currently. > > > > > > > > > > > > > > So last time I requested you to document why ->enter_s2idle needs to > > > > > > > return an int in the code, which has not been done. Please do that. > > > > > > > > Rafael, are you happy with the commit message documenting the reason, > > > > or would you prefer to also add a comment before enter_s2idle? > > > > > > As I said before, it would be good to have a comment in the code as > > > well or people will be wondering why it is necessary to return > > > anything from that callback, because its return value is never used. > > > > > > Thanks! > > > > Is it okay to add these comments before enter_s2idle? > > > > /* > > * Align function type since init_state_node assigns the same callback > > init_state_node() > > > * function to both enter and enter_s2idle despite mismatching function > > ->enter_s2idle > > > * types, which trips indirect call checking with Control-Flow Integrity > > * (CFI). > > */ > > int (*enter_s2idle)(struct cpuidle_device *dev, > > struct cpuidle_driver *drv, > > int index); > > But IMO it would be sufficient to add something like this to the > existing comment regarding ->enter_s2idle: > > "This callback may point to the same function as ->enter if all of the > above requirements are met by it." > > That would explain why the signature is the same sufficiently in my view. > > Thanks! For clarification, do you mean add this comment on enter_s2idle function pointer declaration is enough? _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel