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=-6.6 required=3.0 tests=DATE_IN_PAST_24_48, DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 E7F72C65BAE for ; Thu, 13 Dec 2018 16:31:30 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 B19EA2080F for ; Thu, 13 Dec 2018 16:31:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="MQsotdN5" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B19EA2080F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-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=bombadil.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=BZVSu/P3yu6fwMcQv/Iqliw3BQRsWEZxpYF9uCFQ7Zc=; b=MQsotdN5r3Wmne5Gdbzj6UW9+ iNE8D+bEXzpnXysB4+RxoIOUxvsExJB78um2ZZWrtc051WbW1pYHL+jl86oQ9/Vf5d653FUfQyYzY DpNqitFTvLTXlK+/c/10kjuZhJnUYTvg2zTkntNiLircMi/WQ/XVF40KK4Yz6XuV410eYQ2sk9ebj VM8Jkw7fWfobJAKp0Q8/GTga5TXqHBzCsDdBugP6muGgDpC90Y2ddzLiYorgH7Oq8bnWMyeDSQnTT 8q0JDLNRlnQOZtcJNiTAUUa0FtyyjqU8kJKgnIEluWG7MHdTu3pbumaw9HYT6l2iJaqkTvJS+THcD C9920261Q==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gXTtY-0004BK-RI; Thu, 13 Dec 2018 16:31:28 +0000 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70] helo=foss.arm.com) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gXTtQ-00048O-M9 for linux-arm-kernel@lists.infradead.org; Thu, 13 Dec 2018 16:31:26 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CAF3480D; Thu, 13 Dec 2018 08:31:09 -0800 (PST) Received: from [192.168.100.242] (usa-sjc-mx-foss1.foss.arm.com [217.140.101.70]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 23C733F614; Thu, 13 Dec 2018 08:31:09 -0800 (PST) Subject: Re: [PATCH 2/6] arm64: add sysfs vulnerability show for meltdown To: Julien Thierry , linux-arm-kernel@lists.infradead.org References: <20181206234408.1287689-1-jeremy.linton@arm.com> <20181206234408.1287689-3-jeremy.linton@arm.com> From: Jeremy Linton Message-ID: <3dfed0e1-9819-ccfd-1024-b6f64f5fbffe@arm.com> Date: Wed, 12 Dec 2018 08:49:48 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20181213_083121_376122_785430DD X-CRM114-Status: GOOD ( 22.07 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, suzuki.poulose@arm.com, marc.zyngier@arm.com, catalin.marinas@arm.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, ykaukab@suse.de, dave.martin@arm.com, shankerd@codeaurora.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Julien, Thanks for taking a look at this! On 12/13/2018 04:46 AM, Julien Thierry wrote: > > > On 13/12/2018 09:23, Julien Thierry wrote: >> Hi Jeremy, >> >> On 06/12/2018 23:44, Jeremy Linton wrote: >>> Add a simple state machine which will track whether >>> all the online cores in a machine are vulnerable. >>> >>> Once that is done we have a fairly authoritative view >>> of the machine vulnerability, which allows us to make a >>> judgment about machine safety if it hasn't been mitigated. >>> >>> Signed-off-by: Jeremy Linton >>> --- >>> arch/arm64/kernel/cpufeature.c | 31 ++++++++++++++++++++++++++----- >>> 1 file changed, 26 insertions(+), 5 deletions(-) >>> >>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c >>> index 242898395f68..bea9adfef7fa 100644 >>> --- a/arch/arm64/kernel/cpufeature.c >>> +++ b/arch/arm64/kernel/cpufeature.c >>> @@ -905,6 +905,8 @@ has_useable_cnp(const struct arm64_cpu_capabilities *entry, int scope) >>> return has_cpuid_feature(entry, scope); >>> } >>> >>> +static enum { A64_MELT_UNSET, A64_MELT_SAFE, A64_MELT_UNKN } __meltdown_safe = A64_MELT_UNSET; >>> + >> >> I'm wondering, do we really need that tri state? >> >> Can't we consider that we are safe an move to unsafe/unkown if any cpu >> during bring up is not in the safe list? >> >> The only user of this is cpu_show_meltdown, but I don't imagine it'll >> get called before unmap_kernel_at_el0() is called for the boot CPU which >> should initialise that state. >> >> Or is there another reason for having that UNSET state? >> > > Ok, I think I get the point of the UNSET as #ifndef > CONFIG_UNMAP_KERNEL_AT_EL0 we don't set the state. But does that mean we > always fall in the "Unknown" case when we don't build kpti in? Is that > desirable? > > If so, I'd suggest replacing the tri-state with the following change: > > >>> + >>> +#ifdef CONFIG_GENERIC_CPU_VULNERABILITIES >>> +ssize_t cpu_show_meltdown(struct device *dev, struct device_attribute *attr, >>> + char *buf) >>> +{ >>> + if (arm64_kernel_unmapped_at_el0()) >>> + return sprintf(buf, "Mitigation: KPTI\n"); >>> + > > if (!IS_ENABLED(UNMAP_KERNEL_AT_EL0) || !meltdown_safe) > sprintf(buf, "Unknown\n"); > else > sprintf(buf, "Not affected\n"); If I'm understanding what your suggesting: Isn't this only checking the current core, rather than the whole machine? IIRC that was the fundamental complaint with the original set. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel