From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id D9FB83D0BD for ; Tue, 7 May 2024 07:24:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715066656; cv=none; b=nW+rkpJtjIZkrFrWgA8WBqfRKexj3wjU1/KgHrUl9bV2mAcYNv0GWiWCw0US2/QO8hFZiWQ2NE9u+UO1/TFJfE6VZzkmd/dcJYQf+Eua0HKbNMKUVlU1EXmEf8+qbp+DwzC5O4nAS56GJca4U2eOypLB+wgJUsu4FE6xhAI15O0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715066656; c=relaxed/simple; bh=vk0o87GrkY34i9rzC7biQa1F6bB1Y/3n0n+jCi1/UvE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=F5oJ60rDYv/BfWBgtdgIE3LlGI7S7a3s4UCoxklN2yR4HTGkgpheCO9Qan+Zi2s6UfxiV+E12Wa0urMXJfLvuEkYvQeVyw3g2kBXvHhUzBLIHDEXZ88LxlUo0B04d9LmINLdBbvPtYmHfapUnCQMFqNVm4bZStSgnTWzj5AESAw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 139DA106F; Tue, 7 May 2024 00:24:38 -0700 (PDT) Received: from localhost (ionvoi01-desktop.cambridge.arm.com [10.2.80.58]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9BA963F762; Tue, 7 May 2024 00:24:11 -0700 (PDT) Date: Tue, 7 May 2024 08:24:10 +0100 From: Ionela Voinescu To: Beata Michalska Cc: Sudeep Holla , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, 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: References: <20240417093848.1555462-1-beata.michalska@arm.com> <20240417093848.1555462-3-beata.michalska@arm.com> <20240418105052.zvkomz5yeayie4ph@bogus> <20240424102527.3s4ebjnaai2md5pa@bogus> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Hi Beata, On Thursday 25 Apr 2024 at 16:27:37 (+0200), Beata Michalska wrote: > On Wed, Apr 24, 2024 at 11:25:27AM +0100, Sudeep Holla wrote: > > 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. > > > We could actually move it up further to amu_fie_setup and potentially save on > memory if none of the present CPUs have valid AMU counters. This is unlikely but > still. So it could look like: > > --- a/arch/arm64/kernel/topology.c > +++ b/arch/arm64/kernel/topology.c > @@@ -297,7 -194,7 +297,8 @@@ static void amu_fie_setup(const struct > int cpu; > > /* We are already set since the last insmod of cpufreq driver */ > ++ if (cpumask_available(amu_fie_cpus) && > -- if (unlikely(cpumask_subset(cpus, amu_fie_cpus))) > ++ unlikely(cpumask_subset(cpus, amu_fie_cpus))) > return; > > for_each_cpu(cpu, cpus) { > @@@ -305,6 -202,6 +306,10 @@@ > return; > } > > ++ if (!cpumask_available(amu_fie_cpus) && > ++ !zalloc_cpumask_var(&amu_fie_cpus, GFP_KERNEL)) > ++ return; > ++ > > In both cases we risk not setting up AMUs for FIE for all or some CPUs > if we fail to allocate the memory but I guess we are already there. > @Ionela: What do you think? It looks good to me. Many thanks for the fix. Ionela. > > > > > 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 ? > Yes, the #if is needed to exclude it from compilation if !CPUMASK_OFFSTACK. > > --- > BR > Beata > > > > -- > > Regards, > > Sudeep