From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Hansen Subject: Re: [PATCH] Allow RDTSC and RDTSCP from userspace Date: Mon, 27 Apr 2020 11:47:07 -0700 Message-ID: <45000aa0-a6d1-03c3-069b-0e9a07c0284d@intel.com> References: <20200319091407.1481-56-joro@8bytes.org> <20200424210316.848878-1-mstunes@vmware.com> <2c49061d-eb84-032e-8dcb-dd36a891ce90@intel.com> <4d2ac222-a896-a60e-9b3c-b35aa7e81a97@intel.com> <20200425124909.GO30814@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20200425124909.GO30814@suse.de> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Joerg Roedel Cc: Tom Lendacky , Mike Stunes , joro@8bytes.org, dan.j.williams@intel.com, dave.hansen@linux.intel.com, hpa@zytor.com, jgross@suse.com, jslaby@suse.cz, keescook@chromium.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, luto@kernel.org, peterz@infradead.org, thellstrom@vmware.com, virtualization@lists.linux-foundation.org, x86@kernel.org, Sean Christopherson List-Id: virtualization@lists.linuxfoundation.org On 4/25/20 5:49 AM, Joerg Roedel wrote: >> That's a fun point because it means that the (untrusted) hypervisor can >> cause endless faults. I *guess* we have mitigation for this with our >> stack guard pages, but it's still a bit nasty that the hypervisor can >> arbitrarily land a guest in the double-fault handler. >> >> It just all seems a bit weak for the hypervisor to be considered >> untrusted. But, it's _certainly_ a steep in the right direction from SEV. > Yeah, a malicious hypervisor can do bad things to an SEV-ES VM, but it > can't easily steal its secrets from memory or registers. The #VC handler > does its best to just crash the VM if unexpected hypervisor behavior is > detected. This is the kind of design information that would be very useful to reviewers. Will some of this information make it into the cover letter eventually? Or, Documentation/? Also, for the security purists, an SEV-ES host is still trusted (in the same TCB as the guest). Truly guest-untrusted VMMs won't be available until SEV-SNP, right?