Messages in this thread | | | Date | Mon, 24 Apr 2023 09:20:22 +0800 | Subject | Re: [PATCH 0/6] LASS KVM virtualization support | From | Binbin Wu <> |
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On 4/20/2023 9:37 PM, Zeng Guang wrote: > Linear Address Space Separation (LASS)[1] is a new mechanism that > enforces the same mode-based protections as paging, i.e. SMAP/SMEP but > without traversing the paging structures. Because the protections > enforced by LASS are applied before paging, "probes" by malicious > software will provide no paging-based timing information. > > LASS works in long mode and partitions the 64-bit canonical linear > address space into two halves: > 1. Lower half (LA[63]=0) --> user space > 2. Upper half (LA[63]=1) --> kernel space > > When LASS is enabled, a general protection #GP fault or a stack fault > #SS will be generated if software accesses the address from the half > in which it resides to another half,
The accessor's mode is based on CPL, not the address range, so it feels a bit inaccurate of descripton "in which it resides".
> e.g., either from user space to > upper half, or from kernel space to lower half. This protection applies > to data access, code execution. > > This series add KVM LASS virtualization support. > > 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 LASS violation > check, while KVM also needs to apply LASS to instructions emulated by > software and injects #GP or #SS fault to the guest. > > Following LASS voilations check will be taken on KVM 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) > > We tested the basic function of LASS virtualization including LASS > enumeration and enabling in non-root and nested environment. As current > KVM unittest framework is not compatible to LASS rule that kernel should > run in the upper half, we use kernel module and application test to verify > LASS functionalities in guest instead. The data access related x86 emulator > code is verified with forced emulation prefix (FEP) mechanism. Other test > cases are working in progress. > > How to add tests for LASS in KUT or kselftest is still under investigation. > > [1] Intel Architecutre Instruction Set Extensions and Future Features
/s/Architecutre/Architecture
> Programming Reference: Chapter Linear Address Space Separation (LASS) > https://cdrdv2.intel.com/v1/dl/getContent/671368 > > Zeng Guang (6): > 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 when LASS enabled > KVM: x86: Advertise LASS CPUID to user space > KVM: x86: Set KVM LASS based on hardware capability > > arch/x86/include/asm/cpuid.h | 36 +++++++++++++++++++ > arch/x86/include/asm/kvm-x86-ops.h | 1 + > arch/x86/include/asm/kvm_host.h | 7 +++- > arch/x86/kvm/cpuid.c | 8 +++-- > arch/x86/kvm/emulate.c | 36 ++++++++++++++++--- > arch/x86/kvm/kvm_emulate.h | 1 + > arch/x86/kvm/vmx/nested.c | 3 ++ > arch/x86/kvm/vmx/sgx.c | 2 ++ > arch/x86/kvm/vmx/vmx.c | 58 ++++++++++++++++++++++++++++++ > arch/x86/kvm/vmx/vmx.h | 2 ++ > arch/x86/kvm/x86.c | 9 +++++ > arch/x86/kvm/x86.h | 2 ++ > 12 files changed, 157 insertions(+), 8 deletions(-) >
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