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Peter Anvin" , Ingo Molnar , Paolo Bonzini , Sean Christopherson , Thomas Gleixner , x86@kernel.org Subject: [PATCH v12 00/24] Enable CET Virtualization Date: Mon, 11 Aug 2025 19:55:08 -0700 Message-ID: <20250812025606.74625-1-chao.gao@intel.com> X-Mailer: git-send-email 2.47.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The FPU support for CET virtualization has already been merged into 6.17-rc1. Building on that, this series introduces Intel CET virtualization support for KVM. Changes in v12: 1. collect Tested-by tags from John and Mathias. 2. use less verbose names for KVM rdmsr/wrmsr emulation APIs in patch 1/2 (Sean/Xin) 3. refer to s_cet, ssp, and ssp_table in a consistent order in patch 22 (Xin) Please note that I didn't include Mathias' patch, which makes CR4.CET guest-owned. I expect that patch to be posted separately. --- Control-flow Enforcement Technology (CET) is a kind of CPU feature used to prevent Return/CALL/Jump-Oriented Programming (ROP/COP/JOP) attacks. It provides two sub-features(SHSTK,IBT) to defend against ROP/COP/JOP style control-flow subversion attacks. Shadow Stack (SHSTK): A shadow stack is a second stack used exclusively for control transfer operations. The shadow stack is separate from the data/normal stack and can be enabled individually in user and kernel mode. When shadow stack is enabled, CALL pushes the return address on both the data and shadow stack. RET pops the return address from both stacks and compares them. If the return addresses from the two stacks do not match, the processor generates a #CP. Indirect Branch Tracking (IBT): IBT introduces new instruction(ENDBRANCH)to mark valid target addresses of indirect branches (CALL, JMP etc...). If an indirect branch is executed and the next instruction is _not_ an ENDBRANCH, the processor generates a #CP. These instruction behaves as a NOP on platforms that doesn't support CET. CET states management ===================== KVM cooperates with host kernel FPU framework to manage guest CET registers. With CET supervisor mode state support in this series, KVM can save/restore full guest CET xsave-managed states. CET user mode and supervisor mode xstates, i.e., MSR_IA32_{U_CET,PL3_SSP} and MSR_IA32_PL{0,1,2}, depend on host FPU framework to swap guest and host xstates. On VM-Exit, guest CET xstates are saved to guest fpu area and host CET xstates are loaded from task/thread context before vCPU returns to userspace, vice-versa on VM-Entry. See details in kvm_{load,put}_guest_fpu(). CET supervisor mode states are grouped into two categories : XSAVE-managed and non-XSAVE-managed, the former includes MSR_IA32_PL{0,1,2}_SSP and are controlled by CET supervisor mode bit(S_CET bit) in XSS, the later consists of MSR_IA32_S_CET and MSR_IA32_INTR_SSP_TBL. VMX introduces new VMCS fields, {GUEST|HOST}_{S_CET,SSP,INTR_SSP_TABL}, to facilitate guest/host non-XSAVES-managed states. When VMX CET entry/exit load bits are set, guest/host MSR_IA32_{S_CET,INTR_SSP_TBL,SSP} are loaded from equivalent fields at VM-Exit/Entry. With these new fields, such supervisor states require no addtional KVM save/reload actions. Tests ====== This series has successfully passed the basic CET user shadow stack test and kernel IBT test in both L1 and L2 guests. The newly added KVM-unit-tests [2] also passed, and its v11 has been tested with the AMD CET series by John [3]. For your convenience, you can use my WIP QEMU [1] for testing. [1]: https://github.com/gaochaointel/qemu-dev qemu-cet [2]: https://lore.kernel.org/kvm/20250626073459.12990-1-minipli@grsecurity.net/ [3]: https://lore.kernel.org/kvm/aH6CH+x5mCDrvtoz@AUSJOHALLEN.amd.com/ Chao Gao (3): KVM: x86: Zero XSTATE components on INIT by iterating over supported features KVM: nVMX: Add consistency checks for CR0.WP and CR4.CET KVM: nVMX: Add consistency checks for CET states Sean Christopherson (4): KVM: x86: Use double-underscore read/write MSR helpers as appropriate KVM: x86: Manually clear MPX state only on INIT KVM: x86: Report XSS as to-be-saved if there are supported features KVM: x86: Load guest FPU state when access XSAVE-managed MSRs Yang Weijiang (17): KVM: x86: Rename kvm_{g,s}et_msr()* to show that they emulate guest accesses KVM: x86: Add kvm_msr_{read,write}() helpers KVM: x86: Introduce KVM_{G,S}ET_ONE_REG uAPIs support KVM: x86: Refresh CPUID on write to guest MSR_IA32_XSS KVM: x86: Initialize kvm_caps.supported_xss KVM: x86: Add fault checks for guest CR4.CET setting KVM: x86: Report KVM supported CET MSRs as to-be-saved KVM: VMX: Introduce CET VMCS fields and control bits KVM: x86: Enable guest SSP read/write interface with new uAPIs KVM: VMX: Emulate read and write to CET MSRs KVM: x86: Save and reload SSP to/from SMRAM KVM: VMX: Set up interception for CET MSRs KVM: VMX: Set host constant supervisor states to VMCS fields KVM: x86: Don't emulate instructions guarded by CET KVM: x86: Enable CET virtualization for VMX and advertise to userspace KVM: nVMX: Virtualize NO_HW_ERROR_CODE_CC for L1 event injection to L2 KVM: nVMX: Enable CET support for nested guest arch/x86/include/asm/kvm_host.h | 16 +- arch/x86/include/asm/vmx.h | 9 + arch/x86/include/uapi/asm/kvm.h | 13 ++ arch/x86/kvm/cpuid.c | 19 +- arch/x86/kvm/emulate.c | 46 +++-- arch/x86/kvm/smm.c | 12 +- arch/x86/kvm/smm.h | 2 +- arch/x86/kvm/svm/svm.c | 4 + arch/x86/kvm/vmx/capabilities.h | 9 + arch/x86/kvm/vmx/nested.c | 175 +++++++++++++++-- arch/x86/kvm/vmx/nested.h | 5 + arch/x86/kvm/vmx/vmcs12.c | 6 + arch/x86/kvm/vmx/vmcs12.h | 14 +- arch/x86/kvm/vmx/vmx.c | 85 +++++++- arch/x86/kvm/vmx/vmx.h | 9 +- arch/x86/kvm/x86.c | 339 +++++++++++++++++++++++++++----- arch/x86/kvm/x86.h | 61 ++++++ 17 files changed, 732 insertions(+), 92 deletions(-) base-commit: 8f5ae30d69d7543eee0d70083daf4de8fe15d585 -- 2.47.1