linux-kernel - Re: [PATCH] x86/tdx: Allow extended topology CPUID leafs to be emulated by hypercall

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Message-ID: <d08303a4-321b-419c-5b3b-11f05e4286ae@intel.com>
Date:   Fri, 8 Sep 2023 11:00:08 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Sagi Shahar <sagis@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Isaku Yamahata <isaku.yamahata@...el.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Vishal Annapurve <vannapurve@...gle.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Nikolay Borisov <nik.borisov@...e.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/tdx: Allow extended topology CPUID leafs to be
 emulated by hypercall

On 9/8/23 10:56, Sagi Shahar wrote:
> The current TDX module does not handle extended topology leaves
> explicitly and will generate a #VE but the current #VE handler
> implementation blindly returns 0 for those CPUID leaves.
> 
> This currently causes TDX guests to see 0 values when querying the numa
> topology leading to incorrect numa configurations.
> 
> This patch fixes this behavior by emulating the extended topology leaves
> using the CPUID hypercall.

... and thus acquires the data from the untrusted VMM.  Right?

What are the security implications of consuming this untrusted data?