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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id q20sm3987518pfn.111.2020.07.09.16.37.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Jul 2020 16:37:38 -0700 (PDT) Date: Thu, 9 Jul 2020 16:37:37 -0700 From: Kees Cook To: Dave Hansen Cc: Andy Lutomirski , "Andersen, John" , Paolo Bonzini , Sean Christopherson , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , X86 ML , "H. Peter Anvin" , Shuah Khan , Liran Alon , Andrew Jones , Rick Edgecombe , Kristen Carlson Accardi , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Mauro Carvalho Chehab , Greg KH , "Paul E. McKenney" , Pawan Gupta , Juergen Gross , Mike Kravetz , Oliver Neukum , Peter Zijlstra , Fenghua Yu , reinette.chatre@intel.com, vineela.tummalapalli@intel.com, Dave Hansen , Arjan van de Ven , caoj.fnst@cn.fujitsu.com, Baoquan He , Arvind Sankar , Dan Williams , eric.auger@redhat.com, aaronlewis@google.com, Peter Xu , makarandsonare@google.com, "open list:DOCUMENTATION" , LKML , kvm list , "open list:KERNEL SELFTEST FRAMEWORK" , Kernel Hardening Subject: Re: [PATCH 2/4] KVM: x86: Introduce paravirt feature CR0/CR4 pinning Message-ID: <202007091634.528B6641@keescook> References: <0fa9682e-59d4-75f7-366f-103d6b8e71b8@intel.com> <20200618144314.GB23@258ff54ff3c0> <124a59a3-a603-701b-e3bb-61e83d70b20d@intel.com> <20200707211244.GN20096@linux.intel.com> <19b97891-bbb0-1061-5971-549a386f7cfb@intel.com> <31eb5b00-9e2a-aa10-0f20-4abc3cd35112@redhat.com> <20200709154412.GA25@64c96d3be97b> <6040c3b3-cac9-cc0e-f0de-baaa274920a2@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6040c3b3-cac9-cc0e-f0de-baaa274920a2@intel.com> Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, Jul 09, 2020 at 09:22:09AM -0700, Dave Hansen wrote: > On 7/9/20 9:07 AM, Andy Lutomirski wrote: > > On Thu, Jul 9, 2020 at 8:56 AM Dave Hansen wrote: > >> On 7/9/20 8:44 AM, Andersen, John wrote: > >>> Bits which are allowed to be pinned default to WP for CR0 and SMEP, > >>> SMAP, and UMIP for CR4. > >> I think it also makes sense to have FSGSBASE in this set. > >> > >> I know it hasn't been tested, but I think we should do the legwork to > >> test it. If not in this set, can we agree that it's a logical next step? > > I have no objection to pinning FSGSBASE, but is there a clear > > description of the threat model that this whole series is meant to > > address? The idea is to provide a degree of protection against an > > attacker who is able to convince a guest kernel to write something > > inappropriate to CR4, right? How realistic is this? > > If a quick search can find this: > > > https://googleprojectzero.blogspot.com/2017/05/exploiting-linux-kernel-via-packet.html > > I'd pretty confident that the guys doing actual bad things have it in > their toolbox too. Right, it's common (see my commit log in 873d50d58f67), and having this enforced by the hypervisor is WAY better since it'll block gadgets or ROP. -- Kees Cook