linux-kernel - Re: [PATCH v5 22/34] x86/fred: FRED initialization code

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Message-ID: <445ca5e5-e793-3b0a-b9b0-0dcefc6725c2@intel.com>
Date:   Wed, 22 Mar 2023 09:29:28 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        "Li, Xin3" <xin3.li@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Lai Jiangshan <jiangshanlai@...il.com>
Cc:     "H. Peter Anvin" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>
Subject: Re: [PATCH v5 22/34] x86/fred: FRED initialization code

On 3/20/23 18:02, andrew.cooper3@...rix.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