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 5A1AFC433E1 for ; Fri, 24 Jul 2020 10:26:33 +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 266562065C for ; Fri, 24 Jul 2020 10:26:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Ow2Q9QZm"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=mediatek.com header.i=@mediatek.com header.b="T4Vc6ETY" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 266562065C 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=3NA/NMOvm1ctEXCgiYAyXyPl5rgQX+NvN/uO23+5g6U=; b=Ow2Q9QZmJa4KRsXz8JhAaC+iY CNyDE2+xpM9/rD71n1kVAu/JjiUUGYFQUlqUA6Vsbh3YdQ61Z7YSewLZvh9r+FeGapfY9yPz0/UoZ mNmnmw3IbtOEPYl4XXHVGRmWUAwaIurPds0Sz/LG5o3cc6Iiukk7yZ1mbpaHPVIt3bqFcU79nGrJp 1JWK/ccHV/JTWHpO+d/eFc1Be49pTzIOHIEJUSc7B10cde3bTa7pPBQEVNobWgQucxHrO8nQOlnyR 0777p7Kn1et+n+OhalJclXsHNyyfU/2rnwRASsc9rHv8EYPqrYtiRDaXeJV1Ooj/192uF0JRok1tF OaDcduo0A==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jyusx-0004Il-Ax; Fri, 24 Jul 2020 10:25:03 +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 1jyuss-0004Gn-HQ; Fri, 24 Jul 2020 10:24:59 +0000 X-UUID: 37f2fbbed1444ab58557fbc44221d74b-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=QxNgObDGJzQxDLrTGZIVOSiVP4T6qaCHpTNaWSH+6v0=; b=T4Vc6ETYgYl2HSKtiO14Zo86gMkawoJLP9w6Grp+FKu5Wyn3/T5N80+BOzjV7vw4E7mg3VuEKD4jXUCcaIe+5Tm2525Q0yh6NPNDBcNjXiuZQ7ALGY5TlQKC8Yx5mLi6B2MNTmz5UVGaBHM7J3p6VIRMpkRLzuHT/RNut3/sbsQ=; X-UUID: 37f2fbbed1444ab58557fbc44221d74b-20200724 Received: from mtkcas68.mediatek.inc [(172.29.94.19)] by mailgw01.mediatek.com (envelope-from ) (musrelay.mediatek.com ESMTP with TLS) with ESMTP id 1981341024; Fri, 24 Jul 2020 02:24:45 -0800 Received: from MTKMBS02N2.mediatek.inc (172.21.101.101) by MTKMBS62N2.mediatek.inc (172.29.193.42) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Fri, 24 Jul 2020 03:24:50 -0700 Received: from mtkcas07.mediatek.inc (172.21.101.84) by mtkmbs02n2.mediatek.inc (172.21.101.101) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Fri, 24 Jul 2020 18:24:47 +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 18:24:49 +0800 Message-ID: <1595586289.14121.5.camel@mtkswgap22> Subject: Re: [PATCH v2] cpuidle: change enter_s2idle() prototype From: Neal Liu To: "Rafael J. Wysocki" Date: Fri, 24 Jul 2020 18:24:49 +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> X-Mailer: Evolution 3.2.3-0ubuntu6 MIME-Version: 1.0 X-TM-SNTS-SMTP: 525C25BBD1A36A92A548897BC52B0D2A9C1552ADE0B6EEB53F27D34A63DF52742000:8 X-MTK: N X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200724_062458_742431_F3E7D55D X-CRM114-Status: GOOD ( 33.45 ) 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 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 * function to both enter and enter_s2idle despite mismatching function * types, which trips indirect call checking with Control-Flow Integrity * (CFI). */ int (*enter_s2idle)(struct cpuidle_device *dev, struct cpuidle_driver *drv, int index); _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel