Messages in this thread | | | Date | Tue, 25 Apr 2023 09:49:00 +0800 | Subject | Re: [PATCH 0/6] LASS KVM virtualization support | From | Zeng Guang <> |
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On 4/24/2023 9:20 AM, Binbin Wu wrote: > 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". > This is alternative description to implicitly signify the privilege level, i.e. code running in upper half means it is in supervisor mode, otherwise it's in user mode. :)
>> 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 > Sorry for typos above. Thanks. >> 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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