linux-kernel - Re: [RFC PATCH v3 53/59] KVM: x86: Add a helper function to restore 4 host MSRs on exit to user space

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]

Date:   Tue, 30 Nov 2021 19:18:32 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     Chao Gao <chao.gao@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>, isaku.yamahata@...el.com,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
        isaku.yamahata@...il.com
Subject: Re: [RFC PATCH v3 53/59] KVM: x86: Add a helper function to restore 4
 host MSRs on exit to user space

On Tue, Nov 30, 2021 at 4:10 PM Chao Gao <chao.gao@...el.com> wrote:

>
> No, it is already documented in public spec.

In intel-tdx-module-1.5-base-spec-348549001.pdf, page 79
"recoverability hist",  I think it is a "hint".

>
> TDX module spec just says some MSRs are reset to INIT state by TDX module
> (un)conditionally during TD exit. When to restore these MSRs to host's
> values is decided by host.
>

Sigh, it is quite a common solution to reset a register to a default
value here, for example in VMX, the host GDT.limit and host TSS.limit
is reset after VMEXIT, so load_fixmap_gdt() and invalidate_tss_limit()
have to be called in host in vmx_vcpu_put().

Off-topic: Is it a good idea to also put load_fixmap_gdt() and
invalidate_tss_limit() in user-return-notfier?