linux-kernel - Re: [PATCH v2 1/4] KVM: x86: invert KVM

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: <CALMp9eTTC0kFbRt8TBC3x8N4mDism-xg3xEFSCPGiGc20pZ3ZQ@mail.gmail.com>
Date:   Fri, 23 Apr 2021 09:31:07 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Ashish Kalra <Ashish.Kalra@....com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, Joerg Roedel <joro@...tes.org>,
        Borislav Petkov <bp@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Steve Rutherford <srutherford@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        venu.busireddy@...cle.com, Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v2 1/4] KVM: x86: invert KVM_HYPERCALL to default to VMMCALL

On Fri, Apr 23, 2021 at 9:00 AM Ashish Kalra <Ashish.Kalra@....com> wrote:
>
> From: Ashish Kalra <ashish.kalra@....com>
>
> KVM hypercall framework relies on alternative framework to patch the
> VMCALL -> VMMCALL on AMD platform. If a hypercall is made before
> apply_alternative() is called then it defaults to VMCALL. The approach
> works fine on non SEV guest. A VMCALL would causes #UD, and hypervisor
> will be able to decode the instruction and do the right things. But
> when SEV is active, guest memory is encrypted with guest key and
> hypervisor will not be able to decode the instruction bytes.
>
> So invert KVM_HYPERCALL and X86_FEATURE_VMMCALL to default to VMMCALL
> and opt into VMCALL.
>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Joerg Roedel <joro@...tes.org>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: x86@...nel.org
> Cc: kvm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
> ---
>  arch/x86/include/asm/kvm_para.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> index 338119852512..fda2fe0d1b10 100644
> --- a/arch/x86/include/asm/kvm_para.h
> +++ b/arch/x86/include/asm/kvm_para.h
> @@ -19,7 +19,7 @@ static inline bool kvm_check_and_clear_guest_paused(void)
>  #endif /* CONFIG_KVM_GUEST */
>
>  #define KVM_HYPERCALL \
> -        ALTERNATIVE("vmcall", "vmmcall", X86_FEATURE_VMMCALL)
> +       ALTERNATIVE("vmmcall", "vmcall", X86_FEATURE_VMCALL)
>
>  /* For KVM hypercalls, a three-byte sequence of either the vmcall or the vmmcall
>   * instruction.  The hypervisor may replace it with something else but only the
> --
> 2.17.1
>

Won't this result in the same problem when Intel implements full VM encryption?