linux-kernel - Re: [RFC v2-fix-v2 2/2] x86/tdx: Ignore WBINVD instruction for TDX guest

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <b420a7af-5202-fee9-9e0b-39680d0cc9c8@linux.intel.com>
Date:   Mon, 24 May 2021 17:29:48 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v2-fix-v2 2/2] x86/tdx: Ignore WBINVD instruction for TDX
 guest



On 5/24/21 4:39 PM, Dan Williams wrote:
>> Functionally only DMA devices can notice a side effect from
>> WBINVD's cache flushing. But, TDX does not support DMA,
>> because DMA typically needs uncached access for MMIO, and
>> the current TDX module always sets the IgnorePAT bit, which
>> prevents that.

> I thought we discussed that there are other considerations for wbinvd
> besides DMA? In any event this paragraph is actively misleading
> because it disregards ACPI and Persistent Memory secure-erase whose
> usages of wbinvd have nothing to do with DMA. I would much prefer a
> patch to shutdown all the known wbinvd users as a precursor to this
> patch rather than assuming it's ok to simply ignore it. You have
> mentioned that TDX does not need to use those paths, but rather than
> assume they can't be used why not do the audit to explicitly disable
> them? Otherwise this statement seems to imply that the audit has not
> been done.

But KVM also emulates WBINVD only if DMA is supported. Otherwise it
will be treated as noop.

static bool need_emulate_wbinvd(struct kvm_vcpu *vcpu)
{
         return kvm_arch_has_noncoherent_dma(vcpu->kvm);
}



-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer