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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 11A7FC07E8E for ; Wed, 24 Apr 2024 10:25:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=sAd+nhaPAr40UpKx3K5+nylZYDNMIqPOyYNz4uD1uKg=; b=25cIbXiV4t7i3C IWc6Gn55ujTcMzqCDGv13shCd43yXp/zALo6XaLEHrSw9UzvVo68AVQOT6NR4k6eh5iWLNgHcD+Eg UB4mN0FDUEtg8XKmQcmINxs6rHbFTSd9bepNeAgXRXeHf8fdNDQ9Ptk13hm7N3RgbLdMgSjMypz5k f170UWjEBhfYId0zwdBr+blwlyOxKXhoER6rBsSA9uhDorqlag3fKV2OBbrY7esMxgop5D0ujp5K1 O9GF42pZnUlMtI5/rYMMfK5C8adKkmW3HdjuiRln610dd6lUkH/uYxUWsZ+bb+39VGJ+Zp0kiGqVL 8zUfXWg35L5zdDqLELqQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1rzZon-00000003gaK-2oVd; Wed, 24 Apr 2024 10:25:37 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1rzZok-00000003gYe-2bRt for linux-arm-kernel@lists.infradead.org; Wed, 24 Apr 2024 10:25:35 +0000 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 B6715339; Wed, 24 Apr 2024 03:25:59 -0700 (PDT) Received: from bogus (unknown [10.57.84.59]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 37D0E3F73F; Wed, 24 Apr 2024 03:25:30 -0700 (PDT) Date: Wed, 24 Apr 2024 11:25:27 +0100 From: Sudeep Holla To: Beata Michalska Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Sudeep Holla , ionela.voinescu@arm.com, vanshikonda@os.amperecomputing.com, will@kernel.org, catalin.marinas@arm.com, vincent.guittot@linaro.org, sumitg@nvidia.com, yang@os.amperecomputing.com, lihuisong@huawei.com, viresh.kumar@linaro.org Subject: Re: [PATCH v5 2/5] arm64: amu: Rule out potential use after free Message-ID: <20240424102527.3s4ebjnaai2md5pa@bogus> References: <20240417093848.1555462-1-beata.michalska@arm.com> <20240417093848.1555462-3-beata.michalska@arm.com> <20240418105052.zvkomz5yeayie4ph@bogus> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240424_032534_773907_5437F293 X-CRM114-Status: GOOD ( 33.60 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 Thu, Apr 18, 2024 at 05:55:43PM +0200, Beata Michalska wrote: > On Thu, Apr 18, 2024 at 11:50:52AM +0100, Sudeep Holla wrote: > > On Wed, Apr 17, 2024 at 10:38:45AM +0100, Beata Michalska wrote: > > > For the time being, the amu_fie_cpus cpumask is being exclusively used > > > by the AMU-related internals of FIE support and is guaranteed to be > > > valid on every access currently made. Still the mask is not being > > > invalidated on one of the error handling code paths, which leaves > > > a soft spot with potential risk of uaf for CPUMASK_OFFSTACK cases. > > > To make things sound, set the cpumaks pointer explicitly to NULL upon > > > failing to register the cpufreq notifier. > > > Note that, due to the quirks of CPUMASK_OFFSTACK, this change needs to > > > be wrapped with grim ifdefing (it would be better served by > > > incorporating this into free_cpumask_var ...) > > > > > > > Yes it doesn't look neat. > > > > > Signed-off-by: Beata Michalska > > > --- > > > arch/arm64/kernel/topology.c | 6 +++++- > > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c > > > index 1a2c72f3e7f8..3c814a278534 100644 > > > --- a/arch/arm64/kernel/topology.c > > > +++ b/arch/arm64/kernel/topology.c > > > @@ -244,8 +244,12 @@ static int __init init_amu_fie(void) > > > > > > ret = cpufreq_register_notifier(&init_amu_fie_notifier, > > > CPUFREQ_POLICY_NOTIFIER); > > > - if (ret) > > > + if (ret) { > > > free_cpumask_var(amu_fie_cpus); > > > +#ifdef CONFIG_CPUMASK_OFFSTACK > > > + amu_fie_cpus = NULL; > > > +#endif > > > + } > > > > Instead of this #ifdeffery, I was wondering if we can actually do the > > allocation in init_amu_fie_callback() the first time it gets called > > checking if amu_fie_cpus is NULL. init_amu_fie_callback() must get called > > only if the cpufreq_register_notifier() succeeds right ? > > > Delayed allocation ... I guess this will do the trick. I prefer that if we can't find any other alternative. Do you see any issues with that ? That said I am fine if Will/Catalin is happy with this. > > Also I don't see anyone calling amu_fie_setup(), so where do you think > > the possible use after free could occur for amu_fie_cpus. Just thinking > > out loud to check if I missed anything. > > > You haven't missed anything. Currently the uaf is purely theoretical as the code > that relies on that mask will only be executed if we have succeeded to register > the amu fie support: so far so good. Yes it is better to handle it even if it is theoretical. I assume you get some compiler error if you assign unconditionally and if(IS_ENABLED()) also doesn't work in this case as it would still give error ? -- Regards, Sudeep _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel