Re: [RFC PATCH 0/4] KVM: Emulate UMIP (or almost do so)

[Yang Zhang]

On 2016/7/13 3:20, Paolo Bonzini wrote:
> UMIP (User-Mode Instruction Prevention) is a feature of future
> Intel processors (Cannonlake?) that blocks SLDT, SGDT, STR, SIDT

I remember there is no Cannonlake any more. It should be Icelake. :)

> and SMSW from user-mode processes.

Do you know the background of this feature? For security or other purpose?

> The idea here is to use virtualization intercepts to emulate UMIP; it
> slows down the instructions when they're executed in ring 0, but they
> are really never executed in practice.  On AMD systems it's possible
> to emulate it entirely; instead on Intel systems it's *almost* possible
> to emulate it, because SMSW doesn't cause a vmexit, and hence SMSW will
> not fault.
>
> This patch series provides the infrastructure and implements it on
> Intel.  I tested it through kvm-unit-tests.
>
> Still I think the idea is interesting, even if it's buggy for current
> Intel processors.  Any opinions?
>
> Paolo
>
> Paolo Bonzini (4):
>   x86: add UMIP feature and CR4 bit
>   KVM: x86: emulate sldt and str
>   KVM: x86: add support for emulating UMIP
>   KVM: vmx: add support for emulating UMIP
>
>  arch/x86/include/asm/cpufeatures.h          |  1 +
>  arch/x86/include/asm/kvm_host.h             |  3 ++-
>  arch/x86/include/asm/vmx.h                  |  1 +
>  arch/x86/include/uapi/asm/processor-flags.h |  2 ++
>  arch/x86/include/uapi/asm/vmx.h             |  4 +++
>  arch/x86/kvm/cpuid.c                        |  5 +++-
>  arch/x86/kvm/cpuid.h                        |  8 ++++++
>  arch/x86/kvm/emulate.c                      | 40 ++++++++++++++++++++++++-----
>  arch/x86/kvm/svm.c                          |  6 +++++
>  arch/x86/kvm/vmx.c                          | 40 ++++++++++++++++++++++++++++-
>  arch/x86/kvm/x86.c                          |  3 +++
>  11 files changed, 104 insertions(+), 9 deletions(-)


--
Yang
Alibaba Cloud Computing