Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <445ca5e5-e793-3b0a-b9b0-0dcefc6725c2@intel.com>
Date:   Wed, 22 Mar 2023 09:29:28 -0700
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.7.1
Subject: Re: [PATCH v5 22/34] x86/fred: FRED initialization code
Content-Language: en-US
To:     "andrew.cooper3@citrix.com" <andrew.cooper3@citrix.com>,
        "Li, Xin3" <xin3.li@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>
Cc:     "H. Peter Anvin" <hpa@zytor.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "Christopherson,, Sean" <seanjc@google.com>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "Shankar, Ravi V" <ravi.v.shankar@intel.com>
References: <20230307023946.14516-1-xin3.li@intel.com>
 <20230307023946.14516-23-xin3.li@intel.com>
 <CAJhGHyADXz-3PCFS3M_7TJ8qLGJ=4NcV9aBWrpjemuXB_SnMGg@mail.gmail.com>
 <5D679723-D84F-42F0-AD8A-8BD1A38FB6CD@zytor.com>
 <CAJhGHyC0_1xJD2R03-NoRVpMXFTHR4v8CdzyJOZe_k0rdv=NfQ@mail.gmail.com>
 <20230320164950.GR2194297@hirez.programming.kicks-ass.net>
 <SA1PR11MB67345D935A2368261E584085A8819@SA1PR11MB6734.namprd11.prod.outlook.com>
 <5f81c066-d82f-b66f-9c6d-a9e6a0d5aa4f@citrix.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <5f81c066-d82f-b66f-9c6d-a9e6a0d5aa4f@citrix.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 3/20/23 18:02, andrew.cooper3@citrix.com wrote:
> There are fewer cases where a non-IST #VE ends up in a re-entrant fault
> (IIRC, you can still manage it by unmapping the entry stack), but you're
> still trusting the outer hypervisor to not e.g. unmap the SYSCALL entry
> point.

This is a general weakness of #VE.  But, the current Linux TDX guest
implementation is not vulnerable to it.  If the host unmaps something
unexpectedly, the guest will just die because of ATTR_SEPT_VE_DISABLE.
No #VE:

> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/coco/tdx/tdx.c#n216