linux-kernel - Re: [FYI PATCH 1/3] KVM: nVMX: Don't emulate instructions in guest mode

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: <CALMp9eRETy1RLWHWKtFHqpcpFHbQKtPgJHDD_N+LPzaUPx-Jvg@mail.gmail.com>
Date:   Sat, 29 Feb 2020 11:00:44 -0800
From:   Jim Mattson <jmattson@...gle.com>
To:     Oliver Upton <oupton@...gle.com>
Cc:     Jan Kiszka <jan.kiszka@....de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>, stable@...r.kernel.org
Subject: Re: [FYI PATCH 1/3] KVM: nVMX: Don't emulate instructions in guest mode

On Sat, Feb 29, 2020 at 10:33 AM Oliver Upton <oupton@...gle.com> wrote:
>
> Hi Jan,
>
> On Sat, Feb 29, 2020 at 10:00 AM Jan Kiszka <jan.kiszka@....de> wrote:
> > Is this expected to cause regressions on less common workloads?
> > Jailhouse as L1 now fails when Linux as L2 tries to boot a CPU: L2-Linux
> > gets a triple fault on load_current_idt() in start_secondary(). Only
> > bisected so far, didn't debug further.
>
> I'm guessing that Jailhouse doesn't use 'descriptor table exiting', so
> when KVM gets the corresponding exit from L2 the emulation burden is
> on L0. We now refuse the emulation, which kicks a #UD back to L2. I
> can get a patch out quickly to address this case (like the PIO exiting
> one that came in this series) but the eventual solution is to map
> emulator intercept checks into VM-exits + call into the
> nested_vmx_exit_reflected() plumbing.

If Jailhouse doesn't use descriptor table exiting, why is L0
intercepting descriptor table instructions? Is this just so that L0
can partially emulate UMIP on hardware that doesn't support it?