Re: [PATCH v1 0/6] LASS KVM virtualization support

[Binbin Wu]

On 6/1/2023 10:23 PM, Zeng Guang wrote:
> Subject:
> [PATCH v1 0/6] LASS KVM virtualization support
> From:
> Zeng Guang <guang.zeng@xxxxxxxxx>
> Date:
> 6/1/2023, 10:23 PM
>
> To:
> Paolo Bonzini <pbonzini@xxxxxxxxxx>, Sean Christopherson 
> <seanjc@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar 
> <mingo@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Dave Hansen 
> <dave.hansen@xxxxxxxxxxxxxxx>, H Peter Anvin <hpa@xxxxxxxxx>, 
> kvm@xxxxxxxxxxxxxxx
> CC:
> x86@xxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Zeng Guang 
> <guang.zeng@xxxxxxxxx>
>
>
> Linear Address Space Separation (LASS)[1] is an independent mechanism
> that enforces the mode-based protections on any access to a linear
> address.
>
> Based on a linear-address organization, the 64-bit canonical linear
> address space is partitioned into two halves: all linear addresses
> whose most significant bit is 0 are user space addresses, while linear
> addresses whose most significant bit is 1 are supervisor space address.
>
> LASS aims to prevent any attempt to probe supervisor space addresses by
> user mode, and likewise stop any attempt to access (if SMAP enabled) or
> execute user space addresses from supervisor mode.
>
> When platform has LASS capability, KVM requires to expose this feature
> to guest VM enumerated by CPUID.(EAX=07H.ECX=1):EAX.LASS[bit 6], and
> allow guest to enable it via CR4.LASS[bit 27] on demand. For instruction
> executed in the guest directly, hardware will perform the check. But KVM
> also needs to behave same as hardware to apply LASS to kinds of guest
> memory accesses when emulating privileged instructions by software.
Not just privileged instructions, e.g. MMIO access instructions.

> KVM will take following LASS voilations check on emulation path.
/s/voilations/violations

> User-mode access to supervisor space address:
>          LA[bit 63] && (CPL == 3)
> Supervisor-mode access to user space address:
>          Instruction fetch: !LA[bit 63] && (CPL < 3)
>          Data access: !LA[bit 63] && (CR4.SMAP==1) && ((RFLAGS.AC == 0 &&
>                       CPL < 3) || Implicit supervisor access)
>
> This patch series provide a LASS KVM solution.
>
> We tested the basic function of LASS virtualization including LASS
> enumeration and enabling in non-root and nested environment. As KVM
> unittest framework is not compatible to LASS rule, we use kernel module
> and application test to emulate LASS violation instead. With KVM forced
> emulation mechanism, we also verified the LASS functionality on some
> emulation path with instruction fetch and data access to have same
> behavior as hardware.
>
> [1] Intel ISEhttps://cdrdv2.intel.com/v1/dl/getContent/671368
> Chapter Linear Address Space Separation (LASS)
>
> ------------------------------------------------------
>
> v0->v1
> 1. Adapt to new __linearize() API
> 2. Function refactor of vmx_check_lass()
> 3. Refine commit message to be more precise
> 4. Drop LASS kvm cap detection depending
>     on hardware capability
>
>
> Binbin Wu (1):
>    KVM: x86: Consolidate flags for __linearize()
>
> Zeng Guang (5):
>    KVM: x86: Virtualize CR4.LASS
>    KVM: VMX: Add new ops in kvm_x86_ops for LASS violation check
>    KVM: x86: Add emulator helper for LASS violation check
>    KVM: x86: LASS protection on KVM emulation
>    KVM: x86: Advertise LASS CPUID to user space
>
>   arch/x86/include/asm/kvm-x86-ops.h |  3 +-
>   arch/x86/include/asm/kvm_host.h    |  4 ++-
>   arch/x86/kvm/cpuid.c               |  5 ++-
>   arch/x86/kvm/emulate.c             | 47 +++++++++++++++++++++++-----
>   arch/x86/kvm/kvm_emulate.h         |  6 ++++
>   arch/x86/kvm/vmx/nested.c          |  3 ++
>   arch/x86/kvm/vmx/sgx.c             |  4 +++
>   arch/x86/kvm/vmx/vmx.c             | 50 ++++++++++++++++++++++++++++++
>   arch/x86/kvm/vmx/vmx.h             |  2 ++
>   arch/x86/kvm/x86.c                 | 12 +++++++
>   arch/x86/kvm/x86.h                 |  2 ++
>   11 files changed, 126 insertions(+), 12 deletions(-)
>
> -- 2.27.0