[PATCH v13 00/21] Enable CET Virtualization

[PATCH v13 00/21] Enable CET Virtualization

[Chao Gao]

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 v13
1. Add "arch" and "size" fields to the register ID used in
   KVM_GET/SET_ONE_REG ioctls
2. Add a kselftest for KVM_GET/SET_ONE_REG ioctls
3. Advertise KVM_CAP_ONE_REG
4. Document how the emulation of SSP MSRs is flawed for 32-bit guests
5. Don't pass-thru MSR_IA32_INT_SSP_TAB and report it as unsupported for
   32-bit guests
6. Refine changelog to clarify why CET MSRs are pass-thru'd.
7. Limit SHSTK to 64-bit kernels
8. Retain CET state if L1 doesn't set VM_EXIT_LOAD_CET_STATE
9. Rename a new functions for clarity

---
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 (4):
  KVM: nVMX: Add consistency checks for CR0.WP and CR4.CET
  KVM: nVMX: Add consistency checks for CET states
  KVM: nVMX: Advertise new VM-Entry/Exit control bits for CET state
  KVM: selftest: Add tests for KVM_{GET,SET}_ONE_REG

Sean Christopherson (2):
  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 (15):
  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: Prepare for enabling CET support for nested guest

 arch/x86/include/asm/kvm_host.h               |   5 +-
 arch/x86/include/asm/vmx.h                    |   9 +
 arch/x86/include/uapi/asm/kvm.h               |  24 ++
 arch/x86/kvm/cpuid.c                          |  17 +-
 arch/x86/kvm/emulate.c                        |  46 ++-
 arch/x86/kvm/smm.c                            |   8 +
 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                     | 163 ++++++++++-
 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                        |  84 +++++-
 arch/x86/kvm/vmx/vmx.h                        |   9 +-
 arch/x86/kvm/x86.c                            | 267 +++++++++++++++++-
 arch/x86/kvm/x86.h                            |  61 ++++
 tools/arch/x86/include/uapi/asm/kvm.h         |  24 ++
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../selftests/kvm/x86/get_set_one_reg.c       |  35 +++
 20 files changed, 752 insertions(+), 41 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/x86/get_set_one_reg.c

-- 
2.47.3

[PATCH v13 01/21] KVM: x86: Introduce KVM_{G,S}ET_ONE_REG uAPIs support

[Chao Gao]

From: Yang Weijiang <weijiang.yang@intel.com>

Enable KVM_{G,S}ET_ONE_REG uAPIs so that userspace can access HW MSR or
KVM synthetic MSR through it.

In CET KVM series [1], KVM "steals" an MSR from PV MSR space and access
it via KVM_{G,S}ET_MSRs uAPIs, but the approach pollutes PV MSR space
and hides the difference of synthetic MSRs and normal HW defined MSRs.

Now carve out a separate room in KVM-customized MSR address space for
synthetic MSRs. The synthetic MSRs are not exposed to userspace via
KVM_GET_MSR_INDEX_LIST, instead userspace complies with KVM's setup and
composes the uAPI params. KVM synthetic MSR indices start from 0 and
increase linearly. Userspace caller should tag MSR type correctly in
order to access intended HW or synthetic MSR.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Link: https://lore.kernel.org/all/20240219074733.122080-18-weijiang.yang@intel.com/ [1]
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>

---
v13:
 - Add vendor and size fields to the register ID to align with other
   architectures. (Sean)
 - Avoid exposing the struct overlay of the register ID to in uAPI
   headers (Sean)
 - Advertise KVM_CAP_ONE_REG
---
 arch/x86/include/uapi/asm/kvm.h | 21 +++++++++
 arch/x86/kvm/x86.c              | 82 +++++++++++++++++++++++++++++++++
 2 files changed, 103 insertions(+)

diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 0f15d683817d..969a63e73190 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -411,6 +411,27 @@ struct kvm_xcrs {
 	__u64 padding[16];
 };
 
+#define KVM_X86_REG_TYPE_MSR		2
+#define KVM_X86_REG_TYPE_SYNTHETIC_MSR	3
+
+#define KVM_X86_REG_TYPE_SIZE(type)						\
+({										\
+	__u64 type_size = (__u64)type << 32;					\
+										\
+	type_size |= type == KVM_X86_REG_TYPE_MSR ? KVM_REG_SIZE_U64 :		\
+		     type == KVM_X86_REG_TYPE_SYNTHETIC_MSR ? KVM_REG_SIZE_U64 :\
+		     0;								\
+	type_size;								\
+})
+
+#define KVM_X86_REG_ENCODE(type, index)				\
+	(KVM_REG_X86 | KVM_X86_REG_TYPE_SIZE(type) | index)
+
+#define KVM_X86_REG_MSR(index)					\
+	KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_MSR, index)
+#define KVM_X86_REG_SYNTHETIC_MSR(index)			\
+	KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_SYNTHETIC_MSR, index)
+
 #define KVM_SYNC_X86_REGS      (1UL << 0)
 #define KVM_SYNC_X86_SREGS     (1UL << 1)
 #define KVM_SYNC_X86_EVENTS    (1UL << 2)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7ba2cdfdac44..31a7e7ad310a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2254,6 +2254,31 @@ static int do_set_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
 	return kvm_set_msr_ignored_check(vcpu, index, *data, true);
 }
 
+static int kvm_get_one_msr(struct kvm_vcpu *vcpu, u32 msr, u64 __user *value)
+{
+	u64 val;
+	int r;
+
+	r = do_get_msr(vcpu, msr, &val);
+	if (r)
+		return r;
+
+	if (put_user(val, value))
+		return -EFAULT;
+
+	return 0;
+}
+
+static int kvm_set_one_msr(struct kvm_vcpu *vcpu, u32 msr, u64 __user *value)
+{
+	u64 val;
+
+	if (get_user(val, value))
+		return -EFAULT;
+
+	return do_set_msr(vcpu, msr, &val);
+}
+
 #ifdef CONFIG_X86_64
 struct pvclock_clock {
 	int vclock_mode;
@@ -4737,6 +4762,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_IRQFD_RESAMPLE:
 	case KVM_CAP_MEMORY_FAULT_INFO:
 	case KVM_CAP_X86_GUEST_MODE:
+	case KVM_CAP_ONE_REG:
 		r = 1;
 		break;
 	case KVM_CAP_PRE_FAULT_MEMORY:
@@ -5915,6 +5941,20 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
 	}
 }
 
+struct kvm_x86_reg_id {
+	__u32 index;
+	__u8  type;
+	__u8  rsvd;
+	__u8  rsvd4:4;
+	__u8  size:4;
+	__u8  x86;
+};
+
+static int kvm_translate_synthetic_msr(struct kvm_x86_reg_id *reg)
+{
+	return -EINVAL;
+}
+
 long kvm_arch_vcpu_ioctl(struct file *filp,
 			 unsigned int ioctl, unsigned long arg)
 {
@@ -6031,6 +6071,48 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 		srcu_read_unlock(&vcpu->kvm->srcu, idx);
 		break;
 	}
+	case KVM_GET_ONE_REG:
+	case KVM_SET_ONE_REG: {
+		struct kvm_x86_reg_id *id;
+		struct kvm_one_reg reg;
+		u64 __user *value;
+
+		r = -EFAULT;
+		if (copy_from_user(&reg, argp, sizeof(reg)))
+			break;
+
+		r = -EINVAL;
+		if ((reg.id & KVM_REG_ARCH_MASK) != KVM_REG_X86)
+			break;
+
+		id = (struct kvm_x86_reg_id *)&reg.id;
+		if (id->rsvd || id->rsvd4)
+			break;
+
+		if (id->type != KVM_X86_REG_TYPE_MSR &&
+		    id->type != KVM_X86_REG_TYPE_SYNTHETIC_MSR)
+			break;
+
+		if ((reg.id & KVM_REG_SIZE_MASK) != KVM_REG_SIZE_U64)
+			break;
+
+		if (id->type == KVM_X86_REG_TYPE_SYNTHETIC_MSR) {
+			r = kvm_translate_synthetic_msr(id);
+			if (r)
+				break;
+		}
+
+		r = -EINVAL;
+		if (id->type != KVM_X86_REG_TYPE_MSR)
+			break;
+
+		value = u64_to_user_ptr(reg.addr);
+		if (ioctl == KVM_GET_ONE_REG)
+			r = kvm_get_one_msr(vcpu, id->index, value);
+		else
+			r = kvm_set_one_msr(vcpu, id->index, value);
+		break;
+	}
 	case KVM_TPR_ACCESS_REPORTING: {
 		struct kvm_tpr_access_ctl tac;
 
-- 
2.47.3

Re: [PATCH v13 01/21] KVM: x86: Introduce KVM_{G,S}ET_ONE_REG uAPIs support

[Xiaoyao Li]

On 8/21/2025 9:30 PM, Chao Gao wrote:
> From: Yang Weijiang <weijiang.yang@intel.com>
> 
> Enable KVM_{G,S}ET_ONE_REG uAPIs so that userspace can access HW MSR or
> KVM synthetic MSR through it.
> 
> In CET KVM series [1], KVM "steals" an MSR from PV MSR space and access
> it via KVM_{G,S}ET_MSRs uAPIs, but the approach pollutes PV MSR space
> and hides the difference of synthetic MSRs and normal HW defined MSRs.
> 
> Now carve out a separate room in KVM-customized MSR address space for
> synthetic MSRs. The synthetic MSRs are not exposed to userspace via
> KVM_GET_MSR_INDEX_LIST, instead userspace complies with KVM's setup and
> composes the uAPI params. KVM synthetic MSR indices start from 0 and
> increase linearly. Userspace caller should tag MSR type correctly in
> order to access intended HW or synthetic MSR.

The old feedback[*] was to introduce support for SYNTHETIC registers 
instead of limiting it to MSR.

As in patch 09, it changes to name guest SSP as

   #define KVM_SYNTHETIC_GUEST_SSP 0

Nothing about MSR.

[*] https://lore.kernel.org/all/ZmelpPm5YfGifhIj@google.com/

> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> Link: https://lore.kernel.org/all/20240219074733.122080-18-weijiang.yang@intel.com/ [1]
> Tested-by: Mathias Krause <minipli@grsecurity.net>
> Tested-by: John Allen <john.allen@amd.com>
> Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Signed-off-by: Chao Gao <chao.gao@intel.com>
> 
> ---
> v13:
>   - Add vendor and size fields to the register ID to align with other
>     architectures. (Sean)
>   - Avoid exposing the struct overlay of the register ID to in uAPI
>     headers (Sean)
>   - Advertise KVM_CAP_ONE_REG
> ---
>   arch/x86/include/uapi/asm/kvm.h | 21 +++++++++
>   arch/x86/kvm/x86.c              | 82 +++++++++++++++++++++++++++++++++
>   2 files changed, 103 insertions(+)
> 
> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
> index 0f15d683817d..969a63e73190 100644
> --- a/arch/x86/include/uapi/asm/kvm.h
> +++ b/arch/x86/include/uapi/asm/kvm.h
> @@ -411,6 +411,27 @@ struct kvm_xcrs {
>   	__u64 padding[16];
>   };
>   
> +#define KVM_X86_REG_TYPE_MSR		2
> +#define KVM_X86_REG_TYPE_SYNTHETIC_MSR	3
> +
> +#define KVM_X86_REG_TYPE_SIZE(type)						\
> +({										\
> +	__u64 type_size = (__u64)type << 32;					\
> +										\
> +	type_size |= type == KVM_X86_REG_TYPE_MSR ? KVM_REG_SIZE_U64 :		\
> +		     type == KVM_X86_REG_TYPE_SYNTHETIC_MSR ? KVM_REG_SIZE_U64 :\
> +		     0;								\
> +	type_size;								\
> +})
> +
> +#define KVM_X86_REG_ENCODE(type, index)				\
> +	(KVM_REG_X86 | KVM_X86_REG_TYPE_SIZE(type) | index)
> +
> +#define KVM_X86_REG_MSR(index)					\
> +	KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_MSR, index)
> +#define KVM_X86_REG_SYNTHETIC_MSR(index)			\
> +	KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_SYNTHETIC_MSR, index)

BTW, do we need to add some doc of the IDs, e.g., to

4.68 KVM_SET_ONE_REG in Documentation/virt/kvm/api.rst ?

>   #define KVM_SYNC_X86_REGS      (1UL << 0)
>   #define KVM_SYNC_X86_SREGS     (1UL << 1)
>   #define KVM_SYNC_X86_EVENTS    (1UL << 2)
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 7ba2cdfdac44..31a7e7ad310a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2254,6 +2254,31 @@ static int do_set_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
>   	return kvm_set_msr_ignored_check(vcpu, index, *data, true);
>   }
>   
> +static int kvm_get_one_msr(struct kvm_vcpu *vcpu, u32 msr, u64 __user *value)
> +{
> +	u64 val;
> +	int r;
> +
> +	r = do_get_msr(vcpu, msr, &val);
> +	if (r)
> +		return r;
> +
> +	if (put_user(val, value))
> +		return -EFAULT;
> +
> +	return 0;
> +}
> +
> +static int kvm_set_one_msr(struct kvm_vcpu *vcpu, u32 msr, u64 __user *value)
> +{
> +	u64 val;
> +
> +	if (get_user(val, value))
> +		return -EFAULT;
> +
> +	return do_set_msr(vcpu, msr, &val);
> +}
> +
>   #ifdef CONFIG_X86_64
>   struct pvclock_clock {
>   	int vclock_mode;
> @@ -4737,6 +4762,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>   	case KVM_CAP_IRQFD_RESAMPLE:
>   	case KVM_CAP_MEMORY_FAULT_INFO:
>   	case KVM_CAP_X86_GUEST_MODE:
> +	case KVM_CAP_ONE_REG:
>   		r = 1;
>   		break;
>   	case KVM_CAP_PRE_FAULT_MEMORY:
> @@ -5915,6 +5941,20 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
>   	}
>   }
>   
> +struct kvm_x86_reg_id {
> +	__u32 index;
> +	__u8  type;
> +	__u8  rsvd;
> +	__u8  rsvd4:4;

why naming it rsvd4? because it's 4-bit bit-field ?

> +	__u8  size:4;
> +	__u8  x86;
> +};
> +
> +static int kvm_translate_synthetic_msr(struct kvm_x86_reg_id *reg)
> +{
> +	return -EINVAL;
> +}
> +
>   long kvm_arch_vcpu_ioctl(struct file *filp,
>   			 unsigned int ioctl, unsigned long arg)
>   {
> @@ -6031,6 +6071,48 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
>   		srcu_read_unlock(&vcpu->kvm->srcu, idx);
>   		break;
>   	}
> +	case KVM_GET_ONE_REG:
> +	case KVM_SET_ONE_REG: {
> +		struct kvm_x86_reg_id *id;
> +		struct kvm_one_reg reg;
> +		u64 __user *value;
> +
> +		r = -EFAULT;
> +		if (copy_from_user(&reg, argp, sizeof(reg)))
> +			break;
> +
> +		r = -EINVAL;
> +		if ((reg.id & KVM_REG_ARCH_MASK) != KVM_REG_X86)
> +			break;
> +
> +		id = (struct kvm_x86_reg_id *)&reg.id;
> +		if (id->rsvd || id->rsvd4)
> +			break;
> +
> +		if (id->type != KVM_X86_REG_TYPE_MSR &&
> +		    id->type != KVM_X86_REG_TYPE_SYNTHETIC_MSR)
> +			break;
> +
> +		if ((reg.id & KVM_REG_SIZE_MASK) != KVM_REG_SIZE_U64)
> +			break;
> +
> +		if (id->type == KVM_X86_REG_TYPE_SYNTHETIC_MSR) {
> +			r = kvm_translate_synthetic_msr(id);
> +			if (r)
> +				break;
> +		}
> +
> +		r = -EINVAL;
> +		if (id->type != KVM_X86_REG_TYPE_MSR)
> +			break;
> +
> +		value = u64_to_user_ptr(reg.addr);
> +		if (ioctl == KVM_GET_ONE_REG)
> +			r = kvm_get_one_msr(vcpu, id->index, value);
> +		else
> +			r = kvm_set_one_msr(vcpu, id->index, value);
> +		break;
> +	}
>   	case KVM_TPR_ACCESS_REPORTING: {
>   		struct kvm_tpr_access_ctl tac;
>   

Re: [PATCH v13 01/21] KVM: x86: Introduce KVM_{G,S}ET_ONE_REG uAPIs support

[Chao Gao]

On Thu, Aug 28, 2025 at 08:58:07PM +0800, Xiaoyao Li wrote:
>On 8/21/2025 9:30 PM, Chao Gao wrote:
>> From: Yang Weijiang <weijiang.yang@intel.com>
>> 
>> Enable KVM_{G,S}ET_ONE_REG uAPIs so that userspace can access HW MSR or
>> KVM synthetic MSR through it.
>> 
>> In CET KVM series [1], KVM "steals" an MSR from PV MSR space and access
>> it via KVM_{G,S}ET_MSRs uAPIs, but the approach pollutes PV MSR space
>> and hides the difference of synthetic MSRs and normal HW defined MSRs.
>> 
>> Now carve out a separate room in KVM-customized MSR address space for
>> synthetic MSRs. The synthetic MSRs are not exposed to userspace via
>> KVM_GET_MSR_INDEX_LIST, instead userspace complies with KVM's setup and
>> composes the uAPI params. KVM synthetic MSR indices start from 0 and
>> increase linearly. Userspace caller should tag MSR type correctly in
>> order to access intended HW or synthetic MSR.
>
>The old feedback[*] was to introduce support for SYNTHETIC registers instead
>of limiting it to MSR.

GUEST_SSP is a real register but not an MSR, so it's ok to treat it as a
synthetic MSR. But, it's probably inappropriate/inaccurate to call it a
synthetic register.

I think we need a clear definition for "synthetic register" to determine what
should be included in this category. "synthetic MSR" is clear - it refers to
something that isn't an MSR in hardware but is handled by KVM as an MSR.

That said, I'm still fine with renaming all "synthetic MSR" to "synthetic
register" in this series. :)

Sean, which do you prefer with fresh eyes?

If we make this change, I suppose KVM_x86_REG_TYPE_SIZE() should be dropped, as
we can't guarantee that the size will remain constant for the "synthetic
register" type, since it could be extended to include registers with different
sizes in the future.

>
>As in patch 09, it changes to name guest SSP as
>
>  #define KVM_SYNTHETIC_GUEST_SSP 0
>
>Nothing about MSR.
>
>[*] https://lore.kernel.org/all/ZmelpPm5YfGifhIj@google.com/
>

<snip>

>> +
>> +#define KVM_X86_REG_MSR(index)					\
>> +	KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_MSR, index)
>> +#define KVM_X86_REG_SYNTHETIC_MSR(index)			\
>> +	KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_SYNTHETIC_MSR, index)
>
>BTW, do we need to add some doc of the IDs, e.g., to
>
>4.68 KVM_SET_ONE_REG in Documentation/virt/kvm/api.rst ?

Yes. Will do.

<snip>
>> +struct kvm_x86_reg_id {
>> +	__u32 index;
>> +	__u8  type;
>> +	__u8  rsvd;
>> +	__u8  rsvd4:4;
>
>why naming it rsvd4? because it's 4-bit bit-field ?

I believe so. I copied this from here:

https://lore.kernel.org/kvm/aKS2WKBbZn6U1uqx@google.com/

I can rename rsvd and rsvd4 to rsvd1 and rsvd2 if that would be clearer.

>
>> +	__u8  size:4;
>> +	__u8  x86;
>> +};

Re: [PATCH v13 01/21] KVM: x86: Introduce KVM_{G,S}ET_ONE_REG uAPIs support

[Sean Christopherson]

On Fri, Aug 29, 2025, Chao Gao wrote:
> On Thu, Aug 28, 2025 at 08:58:07PM +0800, Xiaoyao Li wrote:
> >On 8/21/2025 9:30 PM, Chao Gao wrote:
> >> From: Yang Weijiang <weijiang.yang@intel.com>
> >> 
> >> Enable KVM_{G,S}ET_ONE_REG uAPIs so that userspace can access HW MSR or
> >> KVM synthetic MSR through it.
> >> 
> >> In CET KVM series [1], KVM "steals" an MSR from PV MSR space and access
> >> it via KVM_{G,S}ET_MSRs uAPIs, but the approach pollutes PV MSR space
> >> and hides the difference of synthetic MSRs and normal HW defined MSRs.
> >> 
> >> Now carve out a separate room in KVM-customized MSR address space for
> >> synthetic MSRs. The synthetic MSRs are not exposed to userspace via
> >> KVM_GET_MSR_INDEX_LIST, instead userspace complies with KVM's setup and
> >> composes the uAPI params. KVM synthetic MSR indices start from 0 and
> >> increase linearly. Userspace caller should tag MSR type correctly in
> >> order to access intended HW or synthetic MSR.
> >
> >The old feedback[*]

Good sleuthing!  I completely forgot about that...

> was to introduce support for SYNTHETIC registers instead of limiting it to MSR.
> 
> GUEST_SSP is a real register but not an MSR, 

Eh, yes and no.  The vCPU's current SSP is a real register, but there's no
interface to access it.  The "synthetic" part here the interface that KVM is
defining.  Though I can see where that gets confusing since "synthetic" in KVM
usually means a completely made up register/MSR.

> so it's ok to treat it as a synthetic MSR. But, it's probably
> inappropriate/inaccurate to call it a synthetic register.
> 
> I think we need a clear definition for "synthetic register" to determine what
> should be included in this category. "synthetic MSR" is clear - it refers to
> something that isn't an MSR in hardware but is handled by KVM as an MSR.

Ah, but I specifically want to avoid bleeding those details into userspace.
I.e. I don't want userspace to know that internally, KVM handles GUEST_SSP via
the MSR infrastructure, so that if for whatever reason we want to do something
different (very unlikely), then we don't create a contradiction.

> That said, I'm still fine with renaming all "synthetic MSR" to "synthetic
> register" in this series. :)
> 
> Sean, which do you prefer with fresh eyes?
> 
> If we make this change, I suppose KVM_x86_REG_TYPE_SIZE() should be dropped, as
> we can't guarantee that the size will remain constant for the "synthetic
> register" type, since it could be extended to include registers with different
> sizes in the future.

Ooh, good catch.  We can keep it, we just need to be more conservative and only
define a valid size for GUEST_SSP.

To avoid confusion with "synthetic", what if we go with a more literal type of
"KVM"?  That's vague enough that it gives KVM a lot of flexibility, but specific
enough that it'll be intuitive for readers, hopefully.

---
 arch/x86/include/uapi/asm/kvm.h | 21 +++++++++++++--------
 arch/x86/kvm/x86.c              | 18 +++++++-----------
 2 files changed, 20 insertions(+), 19 deletions(-)

diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 478d9b63a9db..eeefc03120fc 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -412,28 +412,33 @@ struct kvm_xcrs {
 };
 
 #define KVM_X86_REG_TYPE_MSR		2
-#define KVM_X86_REG_TYPE_SYNTHETIC_MSR	3
+#define KVM_X86_REG_TYPE_KVM		3
 
-#define KVM_X86_REG_TYPE_SIZE(type)						\
+#define KVM_X86_KVM_REG_SIZE(reg)						\
+({										\
+	reg == KVM_REG_GUEST_SSP ? KVM_REG_SIZE_U64 : 0;			\
+})
+
+#define KVM_X86_REG_TYPE_SIZE(type, reg)					\
 ({										\
 	__u64 type_size = (__u64)type << 32;					\
 										\
 	type_size |= type == KVM_X86_REG_TYPE_MSR ? KVM_REG_SIZE_U64 :		\
-		     type == KVM_X86_REG_TYPE_SYNTHETIC_MSR ? KVM_REG_SIZE_U64 :\
+		     type == KVM_X86_REG_TYPE_KVM ? KVM_X86_KVM_REG_SIZE(reg) :	\
 		     0;								\
 	type_size;								\
 })
 
 #define KVM_X86_REG_ENCODE(type, index)				\
-	(KVM_REG_X86 | KVM_X86_REG_TYPE_SIZE(type) | index)
+	(KVM_REG_X86 | KVM_X86_REG_TYPE_SIZE(type, index) | index)
 
 #define KVM_X86_REG_MSR(index)					\
 	KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_MSR, index)
-#define KVM_X86_REG_SYNTHETIC_MSR(index)			\
-	KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_SYNTHETIC_MSR, index)
+#define KVM_X86_REG_KVM(index)			\
+	KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_KVM, index)
 
-/* KVM synthetic MSR index staring from 0 */
-#define KVM_SYNTHETIC_GUEST_SSP 0
+/* KVM-defined registers staring from 0 */
+#define KVM_REG_GUEST_SSP 0
 
 #define KVM_SYNC_X86_REGS      (1UL << 0)
 #define KVM_SYNC_X86_SREGS     (1UL << 1)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9930678f5a3b..e0d7298aea94 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6057,10 +6057,10 @@ struct kvm_x86_reg_id {
 	__u8  x86;
 };
 
-static int kvm_translate_synthetic_msr(struct kvm_x86_reg_id *reg)
+static int kvm_translate_kvm_reg(struct kvm_x86_reg_id *reg)
 {
 	switch (reg->index) {
-	case KVM_SYNTHETIC_GUEST_SSP:
+	case KVM_REG_GUEST_SSP:
 		reg->type = KVM_X86_REG_TYPE_MSR;
 		reg->index = MSR_KVM_INTERNAL_GUEST_SSP;
 		break;
@@ -6204,15 +6204,8 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 		if (id->rsvd || id->rsvd4)
 			break;
 
-		if (id->type != KVM_X86_REG_TYPE_MSR &&
-		    id->type != KVM_X86_REG_TYPE_SYNTHETIC_MSR)
-			break;
-
-		if ((reg.id & KVM_REG_SIZE_MASK) != KVM_REG_SIZE_U64)
-			break;
-
-		if (id->type == KVM_X86_REG_TYPE_SYNTHETIC_MSR) {
-			r = kvm_translate_synthetic_msr(id);
+		if (id->type == KVM_X86_REG_TYPE_KVM) {
+			r = kvm_translate_kvm_reg(id);
 			if (r)
 				break;
 		}
@@ -6221,6 +6214,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 		if (id->type != KVM_X86_REG_TYPE_MSR)
 			break;
 
+		if ((reg.id & KVM_REG_SIZE_MASK) != KVM_REG_SIZE_U64)
+			break;
+
 		value = u64_to_user_ptr(reg.addr);
 		if (ioctl == KVM_GET_ONE_REG)
 			r = kvm_get_one_msr(vcpu, id->index, value);

base-commit: eb92644efe58ecb8d00a83ef1788871404116001
--

[PATCH v13 02/21] KVM: x86: Report XSS as to-be-saved if there are supported features

[Chao Gao]

From: Sean Christopherson <seanjc@google.com>

Add MSR_IA32_XSS to list of MSRs reported to userspace if supported_xss
is non-zero, i.e. KVM supports at least one XSS based feature.

Before enabling CET virtualization series, guest IA32_MSR_XSS is
guaranteed to be 0, i.e., XSAVES/XRSTORS is executed in non-root mode
with XSS == 0, which equals to the effect of XSAVE/XRSTOR.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
 arch/x86/kvm/x86.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 31a7e7ad310a..569583943779 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -335,7 +335,7 @@ static const u32 msrs_to_save_base[] = {
 	MSR_IA32_RTIT_ADDR3_A, MSR_IA32_RTIT_ADDR3_B,
 	MSR_IA32_UMWAIT_CONTROL,
 
-	MSR_IA32_XFD, MSR_IA32_XFD_ERR,
+	MSR_IA32_XFD, MSR_IA32_XFD_ERR, MSR_IA32_XSS,
 };
 
 static const u32 msrs_to_save_pmu[] = {
@@ -7474,6 +7474,10 @@ static void kvm_probe_msr_to_save(u32 msr_index)
 		if (!(kvm_get_arch_capabilities() & ARCH_CAP_TSX_CTRL_MSR))
 			return;
 		break;
+	case MSR_IA32_XSS:
+		if (!kvm_caps.supported_xss)
+			return;
+		break;
 	default:
 		break;
 	}
-- 
2.47.3

Re: [PATCH v13 02/21] KVM: x86: Report XSS as to-be-saved if there are supported features

[Xiaoyao Li]

On 8/21/2025 9:30 PM, Chao Gao wrote:
> From: Sean Christopherson <seanjc@google.com>
> 
> Add MSR_IA32_XSS to list of MSRs reported to userspace if supported_xss
> is non-zero, i.e. KVM supports at least one XSS based feature.
> 
> Before enabling CET virtualization series, guest IA32_MSR_XSS is
> guaranteed to be 0, i.e., XSAVES/XRSTORS is executed in non-root mode
> with XSS == 0, which equals to the effect of XSAVE/XRSTOR.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
> Reviewed-by: Chao Gao <chao.gao@intel.com>
> Tested-by: Mathias Krause <minipli@grsecurity.net>
> Tested-by: John Allen <john.allen@amd.com>
> Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Signed-off-by: Chao Gao <chao.gao@intel.com>

Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>

> ---
>   arch/x86/kvm/x86.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 31a7e7ad310a..569583943779 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -335,7 +335,7 @@ static const u32 msrs_to_save_base[] = {
>   	MSR_IA32_RTIT_ADDR3_A, MSR_IA32_RTIT_ADDR3_B,
>   	MSR_IA32_UMWAIT_CONTROL,
>   
> -	MSR_IA32_XFD, MSR_IA32_XFD_ERR,
> +	MSR_IA32_XFD, MSR_IA32_XFD_ERR, MSR_IA32_XSS,
>   };
>   
>   static const u32 msrs_to_save_pmu[] = {
> @@ -7474,6 +7474,10 @@ static void kvm_probe_msr_to_save(u32 msr_index)
>   		if (!(kvm_get_arch_capabilities() & ARCH_CAP_TSX_CTRL_MSR))
>   			return;
>   		break;
> +	case MSR_IA32_XSS:
> +		if (!kvm_caps.supported_xss)
> +			return;
> +		break;
>   	default:
>   		break;
>   	}

[PATCH v13 03/21] KVM: x86: Refresh CPUID on write to guest MSR_IA32_XSS

[Chao Gao]

From: Yang Weijiang <weijiang.yang@intel.com>

Update CPUID.(EAX=0DH,ECX=1).EBX to reflect current required xstate size
due to XSS MSR modification.
CPUID(EAX=0DH,ECX=1).EBX reports the required storage size of all enabled
xstate features in (XCR0 | IA32_XSS). The CPUID value can be used by guest
before allocate sufficient xsave buffer.

Note, KVM does not yet support any XSS based features, i.e. supported_xss
is guaranteed to be zero at this time.

Opportunistically return KVM_MSR_RET_UNSUPPORTED if guest CPUID doesn't
enumerate it. Since KVM_MSR_RET_UNSUPPORTED takes care of host_initiated
cases, drop the host_initiated check.

Suggested-by: Sean Christopherson <seanjc@google.com>
Co-developed-by: Zhang Yi Z <yi.z.zhang@linux.intel.com>
Signed-off-by: Zhang Yi Z <yi.z.zhang@linux.intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
 arch/x86/include/asm/kvm_host.h |  3 ++-
 arch/x86/kvm/cpuid.c            | 15 ++++++++++++++-
 arch/x86/kvm/x86.c              |  9 +++++----
 3 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 0d3cc0fc27af..b7f82a421718 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -815,7 +815,6 @@ struct kvm_vcpu_arch {
 	bool at_instruction_boundary;
 	bool tpr_access_reporting;
 	bool xfd_no_write_intercept;
-	u64 ia32_xss;
 	u64 microcode_version;
 	u64 arch_capabilities;
 	u64 perf_capabilities;
@@ -876,6 +875,8 @@ struct kvm_vcpu_arch {
 
 	u64 xcr0;
 	u64 guest_supported_xcr0;
+	u64 guest_supported_xss;
+	u64 ia32_xss;
 
 	struct kvm_pio_request pio;
 	void *pio_data;
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index ad6cadf09930..b5f87254ced7 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -263,6 +263,17 @@ static u64 cpuid_get_supported_xcr0(struct kvm_vcpu *vcpu)
 	return (best->eax | ((u64)best->edx << 32)) & kvm_caps.supported_xcr0;
 }
 
+static u64 cpuid_get_supported_xss(struct kvm_vcpu *vcpu)
+{
+	struct kvm_cpuid_entry2 *best;
+
+	best = kvm_find_cpuid_entry_index(vcpu, 0xd, 1);
+	if (!best)
+		return 0;
+
+	return (best->ecx | ((u64)best->edx << 32)) & kvm_caps.supported_xss;
+}
+
 static __always_inline void kvm_update_feature_runtime(struct kvm_vcpu *vcpu,
 						       struct kvm_cpuid_entry2 *entry,
 						       unsigned int x86_feature,
@@ -305,7 +316,8 @@ static void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
 	best = kvm_find_cpuid_entry_index(vcpu, 0xD, 1);
 	if (best && (cpuid_entry_has(best, X86_FEATURE_XSAVES) ||
 		     cpuid_entry_has(best, X86_FEATURE_XSAVEC)))
-		best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
+		best->ebx = xstate_required_size(vcpu->arch.xcr0 |
+						 vcpu->arch.ia32_xss, true);
 }
 
 static bool kvm_cpuid_has_hyperv(struct kvm_vcpu *vcpu)
@@ -424,6 +436,7 @@ void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 	}
 
 	vcpu->arch.guest_supported_xcr0 = cpuid_get_supported_xcr0(vcpu);
+	vcpu->arch.guest_supported_xss = cpuid_get_supported_xss(vcpu);
 
 	vcpu->arch.pv_cpuid.features = kvm_apply_cpuid_pv_features_quirk(vcpu);
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 569583943779..75b7a29721bb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4011,16 +4011,17 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		}
 		break;
 	case MSR_IA32_XSS:
-		if (!msr_info->host_initiated &&
-		    !guest_cpuid_has(vcpu, X86_FEATURE_XSAVES))
-			return 1;
+		if (!guest_cpuid_has(vcpu, X86_FEATURE_XSAVES))
+			return KVM_MSR_RET_UNSUPPORTED;
 		/*
 		 * KVM supports exposing PT to the guest, but does not support
 		 * IA32_XSS[bit 8]. Guests have to use RDMSR/WRMSR rather than
 		 * XSAVES/XRSTORS to save/restore PT MSRs.
 		 */
-		if (data & ~kvm_caps.supported_xss)
+		if (data & ~vcpu->arch.guest_supported_xss)
 			return 1;
+		if (vcpu->arch.ia32_xss == data)
+			break;
 		vcpu->arch.ia32_xss = data;
 		vcpu->arch.cpuid_dynamic_bits_dirty = true;
 		break;
-- 
2.47.3

Re: [PATCH v13 03/21] KVM: x86: Refresh CPUID on write to guest MSR_IA32_XSS

[Xiaoyao Li]

On 8/21/2025 9:30 PM, Chao Gao wrote:
> From: Yang Weijiang <weijiang.yang@intel.com>
> 
> Update CPUID.(EAX=0DH,ECX=1).EBX to reflect current required xstate size
> due to XSS MSR modification.
> CPUID(EAX=0DH,ECX=1).EBX reports the required storage size of all enabled
> xstate features in (XCR0 | IA32_XSS). The CPUID value can be used by guest
> before allocate sufficient xsave buffer.
> 
> Note, KVM does not yet support any XSS based features, i.e. supported_xss
> is guaranteed to be zero at this time.
> 
> Opportunistically return KVM_MSR_RET_UNSUPPORTED if guest CPUID doesn't
> enumerate it. Since KVM_MSR_RET_UNSUPPORTED takes care of host_initiated
> cases, drop the host_initiated check.

It looks most of this patch is introducing

   vcpu->arch.guest_supported_xss

and use it to guard the wrmsr of MSR_IA32_XSS instead of KVM global 
kvm_caps.supported_xss.

So it's better to split it into two patches?

> Suggested-by: Sean Christopherson <seanjc@google.com>
> Co-developed-by: Zhang Yi Z <yi.z.zhang@linux.intel.com>
> Signed-off-by: Zhang Yi Z <yi.z.zhang@linux.intel.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
> Reviewed-by: Chao Gao <chao.gao@intel.com>
> Tested-by: Mathias Krause <minipli@grsecurity.net>
> Tested-by: John Allen <john.allen@amd.com>
> Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Signed-off-by: Chao Gao <chao.gao@intel.com>
> ---
>   arch/x86/include/asm/kvm_host.h |  3 ++-
>   arch/x86/kvm/cpuid.c            | 15 ++++++++++++++-
>   arch/x86/kvm/x86.c              |  9 +++++----
>   3 files changed, 21 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 0d3cc0fc27af..b7f82a421718 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -815,7 +815,6 @@ struct kvm_vcpu_arch {
>   	bool at_instruction_boundary;
>   	bool tpr_access_reporting;
>   	bool xfd_no_write_intercept;
> -	u64 ia32_xss;
>   	u64 microcode_version;
>   	u64 arch_capabilities;
>   	u64 perf_capabilities;
> @@ -876,6 +875,8 @@ struct kvm_vcpu_arch {
>   
>   	u64 xcr0;
>   	u64 guest_supported_xcr0;
> +	u64 guest_supported_xss;
> +	u64 ia32_xss;
>   
>   	struct kvm_pio_request pio;
>   	void *pio_data;
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index ad6cadf09930..b5f87254ced7 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -263,6 +263,17 @@ static u64 cpuid_get_supported_xcr0(struct kvm_vcpu *vcpu)
>   	return (best->eax | ((u64)best->edx << 32)) & kvm_caps.supported_xcr0;
>   }
>   
> +static u64 cpuid_get_supported_xss(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_cpuid_entry2 *best;
> +
> +	best = kvm_find_cpuid_entry_index(vcpu, 0xd, 1);
> +	if (!best)
> +		return 0;
> +
> +	return (best->ecx | ((u64)best->edx << 32)) & kvm_caps.supported_xss;
> +}
> +
>   static __always_inline void kvm_update_feature_runtime(struct kvm_vcpu *vcpu,
>   						       struct kvm_cpuid_entry2 *entry,
>   						       unsigned int x86_feature,
> @@ -305,7 +316,8 @@ static void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
>   	best = kvm_find_cpuid_entry_index(vcpu, 0xD, 1);
>   	if (best && (cpuid_entry_has(best, X86_FEATURE_XSAVES) ||
>   		     cpuid_entry_has(best, X86_FEATURE_XSAVEC)))
> -		best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
> +		best->ebx = xstate_required_size(vcpu->arch.xcr0 |
> +						 vcpu->arch.ia32_xss, true);
>   }
>   
>   static bool kvm_cpuid_has_hyperv(struct kvm_vcpu *vcpu)
> @@ -424,6 +436,7 @@ void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
>   	}
>   
>   	vcpu->arch.guest_supported_xcr0 = cpuid_get_supported_xcr0(vcpu);
> +	vcpu->arch.guest_supported_xss = cpuid_get_supported_xss(vcpu);
>   
>   	vcpu->arch.pv_cpuid.features = kvm_apply_cpuid_pv_features_quirk(vcpu);
>   
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 569583943779..75b7a29721bb 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4011,16 +4011,17 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   		}
>   		break;
>   	case MSR_IA32_XSS:
> -		if (!msr_info->host_initiated &&
> -		    !guest_cpuid_has(vcpu, X86_FEATURE_XSAVES))
> -			return 1;
> +		if (!guest_cpuid_has(vcpu, X86_FEATURE_XSAVES))
> +			return KVM_MSR_RET_UNSUPPORTED;
>   		/*
>   		 * KVM supports exposing PT to the guest, but does not support
>   		 * IA32_XSS[bit 8]. Guests have to use RDMSR/WRMSR rather than
>   		 * XSAVES/XRSTORS to save/restore PT MSRs.
>   		 */
> -		if (data & ~kvm_caps.supported_xss)
> +		if (data & ~vcpu->arch.guest_supported_xss)
>   			return 1;
> +		if (vcpu->arch.ia32_xss == data)
> +			break;
>   		vcpu->arch.ia32_xss = data;
>   		vcpu->arch.cpuid_dynamic_bits_dirty = true;
>   		break;

Re: [PATCH v13 03/21] KVM: x86: Refresh CPUID on write to guest MSR_IA32_XSS

[Chao Gao]

On Fri, Aug 29, 2025 at 02:47:37PM +0800, Xiaoyao Li wrote:
>On 8/21/2025 9:30 PM, Chao Gao wrote:
>> From: Yang Weijiang <weijiang.yang@intel.com>
>> 
>> Update CPUID.(EAX=0DH,ECX=1).EBX to reflect current required xstate size
>> due to XSS MSR modification.
>> CPUID(EAX=0DH,ECX=1).EBX reports the required storage size of all enabled
>> xstate features in (XCR0 | IA32_XSS). The CPUID value can be used by guest
>> before allocate sufficient xsave buffer.
>> 
>> Note, KVM does not yet support any XSS based features, i.e. supported_xss
>> is guaranteed to be zero at this time.
>> 
>> Opportunistically return KVM_MSR_RET_UNSUPPORTED if guest CPUID doesn't
>> enumerate it. Since KVM_MSR_RET_UNSUPPORTED takes care of host_initiated
>> cases, drop the host_initiated check.
>
>It looks most of this patch is introducing
>
>  vcpu->arch.guest_supported_xss
>
>and use it to guard the wrmsr of MSR_IA32_XSS instead of KVM global
>kvm_caps.supported_xss.
>
>So it's better to split it into two patches?

Yes. it makes sense. will do.

[PATCH v13 04/21] KVM: x86: Initialize kvm_caps.supported_xss

[Chao Gao]

From: Yang Weijiang <weijiang.yang@intel.com>

Set original kvm_caps.supported_xss to (host_xss & KVM_SUPPORTED_XSS) if
XSAVES is supported. host_xss contains the host supported xstate feature
bits for thread FPU context switch, KVM_SUPPORTED_XSS includes all KVM
enabled XSS feature bits, the resulting value represents the supervisor
xstates that are available to guest and are backed by host FPU framework
for swapping {guest,host} XSAVE-managed registers/MSRs.

Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
 arch/x86/kvm/x86.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 75b7a29721bb..6b01c6e9330e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -220,6 +220,8 @@ static struct kvm_user_return_msrs __percpu *user_return_msrs;
 				| XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
 				| XFEATURE_MASK_PKRU | XFEATURE_MASK_XTILE)
 
+#define KVM_SUPPORTED_XSS     0
+
 bool __read_mostly allow_smaller_maxphyaddr = 0;
 EXPORT_SYMBOL_GPL(allow_smaller_maxphyaddr);
 
@@ -9793,14 +9795,17 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
 		kvm_host.xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);
 		kvm_caps.supported_xcr0 = kvm_host.xcr0 & KVM_SUPPORTED_XCR0;
 	}
+
+	if (boot_cpu_has(X86_FEATURE_XSAVES)) {
+		rdmsrq(MSR_IA32_XSS, kvm_host.xss);
+		kvm_caps.supported_xss = kvm_host.xss & KVM_SUPPORTED_XSS;
+	}
+
 	kvm_caps.supported_quirks = KVM_X86_VALID_QUIRKS;
 	kvm_caps.inapplicable_quirks = KVM_X86_CONDITIONAL_QUIRKS;
 
 	rdmsrq_safe(MSR_EFER, &kvm_host.efer);
 
-	if (boot_cpu_has(X86_FEATURE_XSAVES))
-		rdmsrq(MSR_IA32_XSS, kvm_host.xss);
-
 	kvm_init_pmu_capability(ops->pmu_ops);
 
 	if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))
-- 
2.47.3

Re: [PATCH v13 04/21] KVM: x86: Initialize kvm_caps.supported_xss

[Xiaoyao Li]

On 8/21/2025 9:30 PM, Chao Gao wrote:
> From: Yang Weijiang <weijiang.yang@intel.com>
> 
> Set original kvm_caps.supported_xss to (host_xss & KVM_SUPPORTED_XSS) if
> XSAVES is supported. host_xss contains the host supported xstate feature
> bits for thread FPU context switch, KVM_SUPPORTED_XSS includes all KVM
> enabled XSS feature bits, the resulting value represents the supervisor
> xstates that are available to guest and are backed by host FPU framework
> for swapping {guest,host} XSAVE-managed registers/MSRs.
> 
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
> Reviewed-by: Chao Gao <chao.gao@intel.com>
> Tested-by: Mathias Krause <minipli@grsecurity.net>
> Tested-by: John Allen <john.allen@amd.com>
> Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Signed-off-by: Chao Gao <chao.gao@intel.com>
> ---
>   arch/x86/kvm/x86.c | 11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 75b7a29721bb..6b01c6e9330e 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -220,6 +220,8 @@ static struct kvm_user_return_msrs __percpu *user_return_msrs;
>   				| XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
>   				| XFEATURE_MASK_PKRU | XFEATURE_MASK_XTILE)
>   
> +#define KVM_SUPPORTED_XSS     0
> +
>   bool __read_mostly allow_smaller_maxphyaddr = 0;
>   EXPORT_SYMBOL_GPL(allow_smaller_maxphyaddr);
>   
> @@ -9793,14 +9795,17 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
>   		kvm_host.xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);
>   		kvm_caps.supported_xcr0 = kvm_host.xcr0 & KVM_SUPPORTED_XCR0;
>   	}
> +
> +	if (boot_cpu_has(X86_FEATURE_XSAVES)) {
> +		rdmsrq(MSR_IA32_XSS, kvm_host.xss);
> +		kvm_caps.supported_xss = kvm_host.xss & KVM_SUPPORTED_XSS;
> +	}

Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>

Btw, since we now have KVM_SUPPORTED_XSS to cap the supported bits, it 
seems we can remove the

	kvm_caps.supported_xss = 0;

in both vmx_set_cpu_caps() and svm_set_cpu_caps().

>   	kvm_caps.supported_quirks = KVM_X86_VALID_QUIRKS;
>   	kvm_caps.inapplicable_quirks = KVM_X86_CONDITIONAL_QUIRKS;
>   
>   	rdmsrq_safe(MSR_EFER, &kvm_host.efer);
>   
> -	if (boot_cpu_has(X86_FEATURE_XSAVES))
> -		rdmsrq(MSR_IA32_XSS, kvm_host.xss);
> -
>   	kvm_init_pmu_capability(ops->pmu_ops);
>   
>   	if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))

Re: [PATCH v13 04/21] KVM: x86: Initialize kvm_caps.supported_xss

[Chao Gao]

On Fri, Aug 29, 2025 at 03:05:01PM +0800, Xiaoyao Li wrote:
>On 8/21/2025 9:30 PM, Chao Gao wrote:
>> From: Yang Weijiang <weijiang.yang@intel.com>
>> 
>> Set original kvm_caps.supported_xss to (host_xss & KVM_SUPPORTED_XSS) if
>> XSAVES is supported. host_xss contains the host supported xstate feature
>> bits for thread FPU context switch, KVM_SUPPORTED_XSS includes all KVM
>> enabled XSS feature bits, the resulting value represents the supervisor
>> xstates that are available to guest and are backed by host FPU framework
>> for swapping {guest,host} XSAVE-managed registers/MSRs.
>> 
>> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
>> Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
>> Reviewed-by: Chao Gao <chao.gao@intel.com>
>> Tested-by: Mathias Krause <minipli@grsecurity.net>
>> Tested-by: John Allen <john.allen@amd.com>
>> Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
>> Signed-off-by: Chao Gao <chao.gao@intel.com>
>> ---
>>   arch/x86/kvm/x86.c | 11 ++++++++---
>>   1 file changed, 8 insertions(+), 3 deletions(-)
>> 
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 75b7a29721bb..6b01c6e9330e 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -220,6 +220,8 @@ static struct kvm_user_return_msrs __percpu *user_return_msrs;
>>   				| XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
>>   				| XFEATURE_MASK_PKRU | XFEATURE_MASK_XTILE)
>> +#define KVM_SUPPORTED_XSS     0
>> +
>>   bool __read_mostly allow_smaller_maxphyaddr = 0;
>>   EXPORT_SYMBOL_GPL(allow_smaller_maxphyaddr);
>> @@ -9793,14 +9795,17 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
>>   		kvm_host.xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);
>>   		kvm_caps.supported_xcr0 = kvm_host.xcr0 & KVM_SUPPORTED_XCR0;
>>   	}
>> +
>> +	if (boot_cpu_has(X86_FEATURE_XSAVES)) {
>> +		rdmsrq(MSR_IA32_XSS, kvm_host.xss);
>> +		kvm_caps.supported_xss = kvm_host.xss & KVM_SUPPORTED_XSS;
>> +	}
>
>Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
>
>Btw, since we now have KVM_SUPPORTED_XSS to cap the supported bits, it seems
>we can remove the
>
>	kvm_caps.supported_xss = 0;
>
>in both vmx_set_cpu_caps() and svm_set_cpu_caps().

This will enable SHSTK for SVM before SVM's CET series is merged.

>
>>   	kvm_caps.supported_quirks = KVM_X86_VALID_QUIRKS;
>>   	kvm_caps.inapplicable_quirks = KVM_X86_CONDITIONAL_QUIRKS;
>>   	rdmsrq_safe(MSR_EFER, &kvm_host.efer);
>> -	if (boot_cpu_has(X86_FEATURE_XSAVES))
>> -		rdmsrq(MSR_IA32_XSS, kvm_host.xss);
>> -
>>   	kvm_init_pmu_capability(ops->pmu_ops);
>>   	if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))
>

[PATCH v13 05/21] KVM: x86: Load guest FPU state when access XSAVE-managed MSRs

[Chao Gao]

From: Sean Christopherson <seanjc@google.com>

Load the guest's FPU state if userspace is accessing MSRs whose values
are managed by XSAVES. Introduce two helpers, kvm_{get,set}_xstate_msr(),
to facilitate access to such kind of MSRs.

If MSRs supported in kvm_caps.supported_xss are passed through to guest,
the guest MSRs are swapped with host's before vCPU exits to userspace and
after it reenters kernel before next VM-entry.

Because the modified code is also used for the KVM_GET_MSRS device ioctl(),
explicitly check @vcpu is non-null before attempting to load guest state.
The XSAVE-managed MSRs cannot be retrieved via the device ioctl() without
loading guest FPU state (which doesn't exist).

Note that guest_cpuid_has() is not queried as host userspace is allowed to
access MSRs that have not been exposed to the guest, e.g. it might do
KVM_SET_MSRS prior to KVM_SET_CPUID2.

The two helpers are put here in order to manifest accessing xsave-managed
MSRs requires special check and handling to guarantee the correctness of
read/write to the MSRs.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Co-developed-by: Yang Weijiang <weijiang.yang@intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
 arch/x86/kvm/x86.c | 35 ++++++++++++++++++++++++++++++++++-
 arch/x86/kvm/x86.h | 24 ++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6b01c6e9330e..799ac76679c9 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -136,6 +136,9 @@ static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2);
 static void __get_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2);
 
 static DEFINE_MUTEX(vendor_module_lock);
+static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu);
+static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu);
+
 struct kvm_x86_ops kvm_x86_ops __read_mostly;
 
 #define KVM_X86_OP(func)					     \
@@ -4566,6 +4569,21 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 }
 EXPORT_SYMBOL_GPL(kvm_get_msr_common);
 
+/*
+ *  Returns true if the MSR in question is managed via XSTATE, i.e. is context
+ *  switched with the rest of guest FPU state.
+ */
+static bool is_xstate_managed_msr(u32 index)
+{
+	switch (index) {
+	case MSR_IA32_U_CET:
+	case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
+		return true;
+	default:
+		return false;
+	}
+}
+
 /*
  * Read or write a bunch of msrs. All parameters are kernel addresses.
  *
@@ -4576,11 +4594,26 @@ static int __msr_io(struct kvm_vcpu *vcpu, struct kvm_msrs *msrs,
 		    int (*do_msr)(struct kvm_vcpu *vcpu,
 				  unsigned index, u64 *data))
 {
+	bool fpu_loaded = false;
 	int i;
 
-	for (i = 0; i < msrs->nmsrs; ++i)
+	for (i = 0; i < msrs->nmsrs; ++i) {
+		/*
+		 * If userspace is accessing one or more XSTATE-managed MSRs,
+		 * temporarily load the guest's FPU state so that the guest's
+		 * MSR value(s) is resident in hardware, i.e. so that KVM can
+		 * get/set the MSR via RDMSR/WRMSR.
+		 */
+		if (vcpu && !fpu_loaded && kvm_caps.supported_xss &&
+		    is_xstate_managed_msr(entries[i].index)) {
+			kvm_load_guest_fpu(vcpu);
+			fpu_loaded = true;
+		}
 		if (do_msr(vcpu, entries[i].index, &entries[i].data))
 			break;
+	}
+	if (fpu_loaded)
+		kvm_put_guest_fpu(vcpu);
 
 	return i;
 }
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index eb3088684e8a..d90f1009ac10 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -701,4 +701,28 @@ int ____kvm_emulate_hypercall(struct kvm_vcpu *vcpu, int cpl,
 
 int kvm_emulate_hypercall(struct kvm_vcpu *vcpu);
 
+/*
+ * Lock and/or reload guest FPU and access xstate MSRs. For accesses initiated
+ * by host, guest FPU is loaded in __msr_io(). For accesses initiated by guest,
+ * guest FPU should have been loaded already.
+ */
+
+static inline void kvm_get_xstate_msr(struct kvm_vcpu *vcpu,
+				      struct msr_data *msr_info)
+{
+	KVM_BUG_ON(!vcpu->arch.guest_fpu.fpstate->in_use, vcpu->kvm);
+	kvm_fpu_get();
+	rdmsrl(msr_info->index, msr_info->data);
+	kvm_fpu_put();
+}
+
+static inline void kvm_set_xstate_msr(struct kvm_vcpu *vcpu,
+				      struct msr_data *msr_info)
+{
+	KVM_BUG_ON(!vcpu->arch.guest_fpu.fpstate->in_use, vcpu->kvm);
+	kvm_fpu_get();
+	wrmsrl(msr_info->index, msr_info->data);
+	kvm_fpu_put();
+}
+
 #endif
-- 
2.47.3

Re: [PATCH v13 05/21] KVM: x86: Load guest FPU state when access XSAVE-managed MSRs

[Xin Li]

> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 6b01c6e9330e..799ac76679c9 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4566,6 +4569,21 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   }
>   EXPORT_SYMBOL_GPL(kvm_get_msr_common);
>   
> +/*
> + *  Returns true if the MSR in question is managed via XSTATE, i.e. is context
> + *  switched with the rest of guest FPU state.
> + */
> +static bool is_xstate_managed_msr(u32 index)
> +{
> +	switch (index) {
> +	case MSR_IA32_U_CET:


Why MSR_IA32_S_CET is not included here?


> +	case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
> +		return true;
> +	default:
> +		return false;
> +	}
> +}


Is it better to do?

static bool is_xstate_managed_msr(u32 index)
{
          if (!kvm_caps.supported_xss)
                  return false;

          switch (index) {
          case MSR_IA32_U_CET:
          case MSR_IA32_S_CET:
          case MSR_IA32_PL1_SSP ... MSR_IA32_PL3_SSP:
                  return kvm_caps.supported_xss & XFEATURE_MASK_CET_USER &&
                         kvm_caps.supported_xss & XFEATURE_MASK_CET_KERNEL;
          default:
                  return false;
          }
}

And it would be obvious how to add new MSRs related to other XFEATURE bits.

Thanks!
     Xin

Re: [PATCH v13 05/21] KVM: x86: Load guest FPU state when access XSAVE-managed MSRs

[Chao Gao]

On Sun, Aug 24, 2025 at 06:52:55PM -0700, Xin Li wrote:
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 6b01c6e9330e..799ac76679c9 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -4566,6 +4569,21 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>   }
>>   EXPORT_SYMBOL_GPL(kvm_get_msr_common);
>> +/*
>> + *  Returns true if the MSR in question is managed via XSTATE, i.e. is context
>> + *  switched with the rest of guest FPU state.
>> + */
>> +static bool is_xstate_managed_msr(u32 index)
>> +{
>> +	switch (index) {
>> +	case MSR_IA32_U_CET:
>
>
>Why MSR_IA32_S_CET is not included here?

Emm. I didn't think about this.

MSR_IA32_S_CET is read from or written to a dedicated VMCS/B field, so KVM
doesn't need to load the guest FPU to access MSR_IA32_S_CET. This pairs with
the kvm_{get,set}_xstate_msr() in kvm_{get,set}_msr_common().

That said, userspace writes can indeed cause an inconsistency between the guest
FPU and VMCS fields regarding MSR_IA32_S_CET. If migration occurs right after a
userspace write (without a VM-entry, which would bring them in sync) and
userspace just restores MSR_IA32_S_CET from the guest FPU, the write before
migration could be lost.

If that migration issue is a practical problem, I think MSR_IA32_S_CET should
be included here, and we need to perform a kvm_set_xstate_msr() after writing
to the VMCS/B.

>
>
>> +	case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
>> +		return true;
>> +	default:
>> +		return false;
>> +	}
>> +}
>
>
>Is it better to do?
>
>static bool is_xstate_managed_msr(u32 index)
>{
>         if (!kvm_caps.supported_xss)
>                 return false;
>
>         switch (index) {
>         case MSR_IA32_U_CET:
>         case MSR_IA32_S_CET:
>         case MSR_IA32_PL1_SSP ... MSR_IA32_PL3_SSP:
>                 return kvm_caps.supported_xss & XFEATURE_MASK_CET_USER &&
>                        kvm_caps.supported_xss & XFEATURE_MASK_CET_KERNEL;
>         default:
>                 return false;

This will duplicate checks in other functions. I slightly prefer to keep this
function super simple and do all capability checks in __kvm_{set,get}_msr()
or kvm_emulate_msr_{write,read}.

>         }
>}
>
>And it would be obvious how to add new MSRs related to other XFEATURE bits.

Just return true for all those MSRs, regardless of host capabilities. If
kvm_caps doesn't support them, those MSRs are not advertised to userspace
either (see kvm_probe_msr_to_save()). Loading or putting the guest FPU when
userspace attempts to read/write those unsupported MSRs shouldn't cause any
performance issues, as userspace is unlikely to access them in hot paths.

>
>Thanks!
>    Xin

Re: [PATCH v13 05/21] KVM: x86: Load guest FPU state when access XSAVE-managed MSRs

[Xin Li]

On 8/24/2025 7:55 PM, Chao Gao wrote:
>> static bool is_xstate_managed_msr(u32 index)
>> {
>>          if (!kvm_caps.supported_xss)
>>                  return false;
>>
>>          switch (index) {
>>          case MSR_IA32_U_CET:
>>          case MSR_IA32_S_CET:
>>          case MSR_IA32_PL1_SSP ... MSR_IA32_PL3_SSP:
>>                  return kvm_caps.supported_xss & XFEATURE_MASK_CET_USER &&
>>                         kvm_caps.supported_xss & XFEATURE_MASK_CET_KERNEL;
>>          default:
>>                  return false;
> This will duplicate checks in other functions. I slightly prefer to keep this
> function super simple and do all capability checks in __kvm_{set,get}_msr()
> or kvm_emulate_msr_{write,read}.
> 
>>          }
>> }
>>
>> And it would be obvious how to add new MSRs related to other XFEATURE bits.
> Just return true for all those MSRs, regardless of host capabilities. If
> kvm_caps doesn't support them, those MSRs are not advertised to userspace
> either (see kvm_probe_msr_to_save()). Loading or putting the guest FPU when
> userspace attempts to read/write those unsupported MSRs shouldn't cause any
> performance issues, as userspace is unlikely to access them in hot paths.

There is no problem as of now, because there are only two CET related bits
set in KVM_SUPPORTED_XSS.  So if !CET, the two bits are cleared thus
kvm_caps.supported_xss is 0, and kvm_load_guest_fpu() is never executed in
__msr_io().

However after any new bit is added to KVM_SUPPORTED_XSS in future, if !CET,
kvm_caps.supported_xss could be non-zero.  There should still be no problem
because we don't expect any access to CET MSRs.

The trouble comes with MSR_IA32_PL0_SSP when FRED and !CET, because it will
be accessed even !CET.  And we need to have to do the following:

static bool is_xstate_managed_msr(u32 index)
{
	switch (index) {
	case MSR_IA32_U_CET:
	case MSR_IA32_PL1_SSP ... MSR_IA32_PL3_SSP:
		return true;
	case MSR_IA32_PL0_SSP:
		return kvm_caps.supported_xss & XFEATURE_MASK_CET_USER &&
		       kvm_caps.supported_xss & XFEATURE_MASK_CET_KERNEL;
	default:
		return false;
	}
}

Then it makes more sense to handle all CET MSRs consistently.

Thanks!
      Xin

Re: [PATCH v13 05/21] KVM: x86: Load guest FPU state when access XSAVE-managed MSRs

[Xin Li]

On 8/21/2025 6:30 AM, Chao Gao wrote:
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index eb3088684e8a..d90f1009ac10 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -701,4 +701,28 @@ int ____kvm_emulate_hypercall(struct kvm_vcpu *vcpu, int cpl,
>   
>   int kvm_emulate_hypercall(struct kvm_vcpu *vcpu);
>   
> +/*
> + * Lock and/or reload guest FPU and access xstate MSRs. For accesses initiated
> + * by host, guest FPU is loaded in __msr_io(). For accesses initiated by guest,
> + * guest FPU should have been loaded already.
> + */
> +
> +static inline void kvm_get_xstate_msr(struct kvm_vcpu *vcpu,
> +				      struct msr_data *msr_info)
> +{
> +	KVM_BUG_ON(!vcpu->arch.guest_fpu.fpstate->in_use, vcpu->kvm);
> +	kvm_fpu_get();
> +	rdmsrl(msr_info->index, msr_info->data);

s/rdmsrl/rdmsrq/

> +	kvm_fpu_put();
> +}
> +
> +static inline void kvm_set_xstate_msr(struct kvm_vcpu *vcpu,
> +				      struct msr_data *msr_info)
> +{
> +	KVM_BUG_ON(!vcpu->arch.guest_fpu.fpstate->in_use, vcpu->kvm);
> +	kvm_fpu_get();
> +	wrmsrl(msr_info->index, msr_info->data);

s/wrmsrl/wrmsrq/


Perhaps it's time to remove rdmsrl() and wrmsrl(), as keeping them around
won't trigger any errors when the old APIs are still being used.

> +	kvm_fpu_put();
> +}
> +
>   #endif

Re: [PATCH v13 05/21] KVM: x86: Load guest FPU state when access XSAVE-managed MSRs

[Sean Christopherson]

On Tue, Aug 26, 2025, Xin Li wrote:
> On 8/21/2025 6:30 AM, Chao Gao wrote:
> > diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> > index eb3088684e8a..d90f1009ac10 100644
> > --- a/arch/x86/kvm/x86.h
> > +++ b/arch/x86/kvm/x86.h
> > @@ -701,4 +701,28 @@ int ____kvm_emulate_hypercall(struct kvm_vcpu *vcpu, int cpl,
> >   int kvm_emulate_hypercall(struct kvm_vcpu *vcpu);
> > +/*
> > + * Lock and/or reload guest FPU and access xstate MSRs. For accesses initiated
> > + * by host, guest FPU is loaded in __msr_io(). For accesses initiated by guest,
> > + * guest FPU should have been loaded already.
> > + */
> > +
> > +static inline void kvm_get_xstate_msr(struct kvm_vcpu *vcpu,
> > +				      struct msr_data *msr_info)
> > +{
> > +	KVM_BUG_ON(!vcpu->arch.guest_fpu.fpstate->in_use, vcpu->kvm);
> > +	kvm_fpu_get();
> > +	rdmsrl(msr_info->index, msr_info->data);
> 
> s/rdmsrl/rdmsrq/
> 
> > +	kvm_fpu_put();
> > +}
> > +
> > +static inline void kvm_set_xstate_msr(struct kvm_vcpu *vcpu,
> > +				      struct msr_data *msr_info)
> > +{
> > +	KVM_BUG_ON(!vcpu->arch.guest_fpu.fpstate->in_use, vcpu->kvm);
> > +	kvm_fpu_get();
> > +	wrmsrl(msr_info->index, msr_info->data);
> 
> s/wrmsrl/wrmsrq/
> 
> 
> Perhaps it's time to remove rdmsrl() and wrmsrl(), as keeping them around
> won't trigger any errors when the old APIs are still being used.

Yeah, we should bite the bullet and force in-flight code to adapt.  I was _this_
close to making the same goof in the mediated PMU series, and IIRC it was only
some random conflict that alerted me to using the old/wrong APIs.

[PATCH v13 06/21] KVM: x86: Add fault checks for guest CR4.CET setting

[Chao Gao]

From: Yang Weijiang <weijiang.yang@intel.com>

Check potential faults for CR4.CET setting per Intel SDM requirements.
CET can be enabled if and only if CR0.WP == 1, i.e. setting CR4.CET ==
1 faults if CR0.WP == 0 and setting CR0.WP == 0 fails if CR4.CET == 1.

Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
 arch/x86/kvm/x86.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 799ac76679c9..c363f7df279f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1173,6 +1173,9 @@ int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 	    (is_64_bit_mode(vcpu) || kvm_is_cr4_bit_set(vcpu, X86_CR4_PCIDE)))
 		return 1;
 
+	if (!(cr0 & X86_CR0_WP) && kvm_is_cr4_bit_set(vcpu, X86_CR4_CET))
+		return 1;
+
 	kvm_x86_call(set_cr0)(vcpu, cr0);
 
 	kvm_post_set_cr0(vcpu, old_cr0, cr0);
@@ -1372,6 +1375,9 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 			return 1;
 	}
 
+	if ((cr4 & X86_CR4_CET) && !kvm_is_cr0_bit_set(vcpu, X86_CR0_WP))
+		return 1;
+
 	kvm_x86_call(set_cr4)(vcpu, cr4);
 
 	kvm_post_set_cr4(vcpu, old_cr4, cr4);
-- 
2.47.3

[PATCH v13 07/21] KVM: x86: Report KVM supported CET MSRs as to-be-saved

[Chao Gao]

From: Yang Weijiang <weijiang.yang@intel.com>

Add CET MSRs to the list of MSRs reported to userspace if the feature,
i.e. IBT or SHSTK, associated with the MSRs is supported by KVM.

Suggested-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
 arch/x86/kvm/x86.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c363f7df279f..61e008be172d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -341,6 +341,10 @@ static const u32 msrs_to_save_base[] = {
 	MSR_IA32_UMWAIT_CONTROL,
 
 	MSR_IA32_XFD, MSR_IA32_XFD_ERR, MSR_IA32_XSS,
+
+	MSR_IA32_U_CET, MSR_IA32_S_CET,
+	MSR_IA32_PL0_SSP, MSR_IA32_PL1_SSP, MSR_IA32_PL2_SSP,
+	MSR_IA32_PL3_SSP, MSR_IA32_INT_SSP_TAB,
 };
 
 static const u32 msrs_to_save_pmu[] = {
@@ -7520,6 +7524,20 @@ static void kvm_probe_msr_to_save(u32 msr_index)
 		if (!kvm_caps.supported_xss)
 			return;
 		break;
+	case MSR_IA32_U_CET:
+	case MSR_IA32_S_CET:
+		if (!kvm_cpu_cap_has(X86_FEATURE_SHSTK) &&
+		    !kvm_cpu_cap_has(X86_FEATURE_IBT))
+			return;
+		break;
+	case MSR_IA32_INT_SSP_TAB:
+		if (!kvm_cpu_cap_has(X86_FEATURE_LM))
+			return;
+		fallthrough;
+	case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
+		if (!kvm_cpu_cap_has(X86_FEATURE_SHSTK))
+			return;
+		break;
 	default:
 		break;
 	}
-- 
2.47.3

[PATCH v13 08/21] KVM: VMX: Introduce CET VMCS fields and control bits

[Chao Gao]

From: Yang Weijiang <weijiang.yang@intel.com>

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 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 have no CET.

Several new CET MSRs are defined to support CET:
  MSR_IA32_{U,S}_CET: CET settings for {user,supervisor} CET respectively.

  MSR_IA32_PL{0,1,2,3}_SSP: SHSTK pointer linear address for CPL{0,1,2,3}.

  MSR_IA32_INT_SSP_TAB: Linear address of SHSTK pointer table, whose entry
			is indexed by IST of interrupt gate desc.

Two XSAVES state bits are introduced for CET:
  IA32_XSS:[bit 11]: Control saving/restoring user mode CET states
  IA32_XSS:[bit 12]: Control saving/restoring supervisor mode CET states.

Six VMCS fields are introduced for CET:
  {HOST,GUEST}_S_CET: Stores CET settings for kernel mode.
  {HOST,GUEST}_SSP: Stores current active SSP.
  {HOST,GUEST}_INTR_SSP_TABLE: Stores current active MSR_IA32_INT_SSP_TAB.

On Intel platforms, two additional bits are defined in VM_EXIT and VM_ENTRY
control fields:
If VM_EXIT_LOAD_CET_STATE = 1, host CET states are loaded from following
VMCS fields at VM-Exit:
  HOST_S_CET
  HOST_SSP
  HOST_INTR_SSP_TABLE

If VM_ENTRY_LOAD_CET_STATE = 1, guest CET states are loaded from following
VMCS fields at VM-Entry:
  GUEST_S_CET
  GUEST_SSP
  GUEST_INTR_SSP_TABLE

Co-developed-by: Zhang Yi Z <yi.z.zhang@linux.intel.com>
Signed-off-by: Zhang Yi Z <yi.z.zhang@linux.intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
 arch/x86/include/asm/vmx.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
index cca7d6641287..ce10a7e2d3d9 100644
--- a/arch/x86/include/asm/vmx.h
+++ b/arch/x86/include/asm/vmx.h
@@ -106,6 +106,7 @@
 #define VM_EXIT_CLEAR_BNDCFGS                   0x00800000
 #define VM_EXIT_PT_CONCEAL_PIP			0x01000000
 #define VM_EXIT_CLEAR_IA32_RTIT_CTL		0x02000000
+#define VM_EXIT_LOAD_CET_STATE                  0x10000000
 
 #define VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR	0x00036dff
 
@@ -119,6 +120,7 @@
 #define VM_ENTRY_LOAD_BNDCFGS                   0x00010000
 #define VM_ENTRY_PT_CONCEAL_PIP			0x00020000
 #define VM_ENTRY_LOAD_IA32_RTIT_CTL		0x00040000
+#define VM_ENTRY_LOAD_CET_STATE                 0x00100000
 
 #define VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR	0x000011ff
 
@@ -369,6 +371,9 @@ enum vmcs_field {
 	GUEST_PENDING_DBG_EXCEPTIONS    = 0x00006822,
 	GUEST_SYSENTER_ESP              = 0x00006824,
 	GUEST_SYSENTER_EIP              = 0x00006826,
+	GUEST_S_CET                     = 0x00006828,
+	GUEST_SSP                       = 0x0000682a,
+	GUEST_INTR_SSP_TABLE            = 0x0000682c,
 	HOST_CR0                        = 0x00006c00,
 	HOST_CR3                        = 0x00006c02,
 	HOST_CR4                        = 0x00006c04,
@@ -381,6 +386,9 @@ enum vmcs_field {
 	HOST_IA32_SYSENTER_EIP          = 0x00006c12,
 	HOST_RSP                        = 0x00006c14,
 	HOST_RIP                        = 0x00006c16,
+	HOST_S_CET                      = 0x00006c18,
+	HOST_SSP                        = 0x00006c1a,
+	HOST_INTR_SSP_TABLE             = 0x00006c1c
 };
 
 /*
-- 
2.47.3

[PATCH v13 09/21] KVM: x86: Enable guest SSP read/write interface with new uAPIs

[Chao Gao]

From: Yang Weijiang <weijiang.yang@intel.com>

Enable guest shadow stack pointer(SSP) access interface with new uAPIs.
CET guest SSP is HW register which has corresponding VMCS field to save
/restore guest values when VM-{Exit,Entry} happens. KVM handles SSP as
a synthetic MSR for userspace access.

Use a translation helper to set up mapping for SSP synthetic index and
KVM-internal MSR index so that userspace doesn't need to take care of
KVM's management for synthetic MSRs and avoid conflicts.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
 arch/x86/include/uapi/asm/kvm.h |  3 +++
 arch/x86/kvm/x86.c              | 10 +++++++++-
 arch/x86/kvm/x86.h              | 10 ++++++++++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 969a63e73190..478d9b63a9db 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -432,6 +432,9 @@ struct kvm_xcrs {
 #define KVM_X86_REG_SYNTHETIC_MSR(index)			\
 	KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_SYNTHETIC_MSR, index)
 
+/* KVM synthetic MSR index staring from 0 */
+#define KVM_SYNTHETIC_GUEST_SSP 0
+
 #define KVM_SYNC_X86_REGS      (1UL << 0)
 #define KVM_SYNC_X86_SREGS     (1UL << 1)
 #define KVM_SYNC_X86_EVENTS    (1UL << 2)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 61e008be172d..a48e53b98c95 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5998,7 +5998,15 @@ struct kvm_x86_reg_id {
 
 static int kvm_translate_synthetic_msr(struct kvm_x86_reg_id *reg)
 {
-	return -EINVAL;
+	switch (reg->index) {
+	case KVM_SYNTHETIC_GUEST_SSP:
+		reg->type = KVM_X86_REG_TYPE_MSR;
+		reg->index = MSR_KVM_INTERNAL_GUEST_SSP;
+		break;
+	default:
+		return -EINVAL;
+	}
+	return 0;
 }
 
 long kvm_arch_vcpu_ioctl(struct file *filp,
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index d90f1009ac10..0d11115dcd2a 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -101,6 +101,16 @@ do {											\
 #define KVM_SVM_DEFAULT_PLE_WINDOW_MAX	USHRT_MAX
 #define KVM_SVM_DEFAULT_PLE_WINDOW	3000
 
+/*
+ * KVM's internal, non-ABI indices for synthetic MSRs. The values themselves
+ * are arbitrary and have no meaning, the only requirement is that they don't
+ * conflict with "real" MSRs that KVM supports. Use values at the upper end
+ * of KVM's reserved paravirtual MSR range to minimize churn, i.e. these values
+ * will be usable until KVM exhausts its supply of paravirtual MSR indices.
+ */
+
+#define MSR_KVM_INTERNAL_GUEST_SSP	0x4b564dff
+
 static inline unsigned int __grow_ple_window(unsigned int val,
 		unsigned int base, unsigned int modifier, unsigned int max)
 {
-- 
2.47.3

[PATCH v13 10/21] KVM: VMX: Emulate read and write to CET MSRs

[Chao Gao]

From: Yang Weijiang <weijiang.yang@intel.com>

Add emulation interface for CET MSR access. The emulation code is split
into common part and vendor specific part. The former does common checks
for MSRs, e.g., accessibility, data validity etc., then passes operation
to either XSAVE-managed MSRs via the helpers or CET VMCS fields.

SSP can only be read via RDSSP. Writing even requires destructive and
potentially faulting operations such as SAVEPREVSSP/RSTORSSP or
SETSSBSY/CLRSSBSY. Let the host use a pseudo-MSR that is just a wrapper
for the GUEST_SSP field of the VMCS.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>

---
v13
- Add a comment to state how the SSP MSR emulation is flawed
- rename is_cet_msr_valid() to kvm_is_valid_u_s_cet()
- Report MSR_IA32_INT_SSP_TAB as unsupported for 32-bit guests
---
 arch/x86/kvm/vmx/vmx.c | 18 +++++++++++++
 arch/x86/kvm/x86.c     | 60 ++++++++++++++++++++++++++++++++++++++++++
 arch/x86/kvm/x86.h     | 23 ++++++++++++++++
 3 files changed, 101 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 227b45430ad8..4fc1dbba2eb0 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2106,6 +2106,15 @@ int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		else
 			msr_info->data = vmx->pt_desc.guest.addr_a[index / 2];
 		break;
+	case MSR_IA32_S_CET:
+		msr_info->data = vmcs_readl(GUEST_S_CET);
+		break;
+	case MSR_KVM_INTERNAL_GUEST_SSP:
+		msr_info->data = vmcs_readl(GUEST_SSP);
+		break;
+	case MSR_IA32_INT_SSP_TAB:
+		msr_info->data = vmcs_readl(GUEST_INTR_SSP_TABLE);
+		break;
 	case MSR_IA32_DEBUGCTLMSR:
 		msr_info->data = vmx_guest_debugctl_read();
 		break;
@@ -2424,6 +2433,15 @@ int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		else
 			vmx->pt_desc.guest.addr_a[index / 2] = data;
 		break;
+	case MSR_IA32_S_CET:
+		vmcs_writel(GUEST_S_CET, data);
+		break;
+	case MSR_KVM_INTERNAL_GUEST_SSP:
+		vmcs_writel(GUEST_SSP, data);
+		break;
+	case MSR_IA32_INT_SSP_TAB:
+		vmcs_writel(GUEST_INTR_SSP_TABLE, data);
+		break;
 	case MSR_IA32_PERF_CAPABILITIES:
 		if (data & PMU_CAP_LBR_FMT) {
 			if ((data & PMU_CAP_LBR_FMT) !=
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a48e53b98c95..dfd94146846e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1886,6 +1886,44 @@ static int __kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data,
 
 		data = (u32)data;
 		break;
+	case MSR_IA32_U_CET:
+	case MSR_IA32_S_CET:
+		if (!guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK) &&
+		    !guest_cpu_cap_has(vcpu, X86_FEATURE_IBT))
+			return KVM_MSR_RET_UNSUPPORTED;
+		if (!kvm_is_valid_u_s_cet(vcpu, data))
+			return 1;
+		break;
+	case MSR_KVM_INTERNAL_GUEST_SSP:
+		if (!host_initiated)
+			return 1;
+		fallthrough;
+		/*
+		 * Note that the MSR emulation here is flawed when a vCPU
+		 * doesn't support the Intel 64 architecture. The expected
+		 * architectural behavior in this case is that the upper 32
+		 * bits do not exist and should always read '0'. However,
+		 * because the actual hardware on which the virtual CPU is
+		 * running does support Intel 64, XRSTORS/XSAVES in the
+		 * guest could observe behavior that violates the
+		 * architecture. Intercepting XRSTORS/XSAVES for this
+		 * special case isn't deemed worthwhile.
+		 */
+	case MSR_IA32_PL0_SSP ... MSR_IA32_INT_SSP_TAB:
+		if (!guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK))
+			return KVM_MSR_RET_UNSUPPORTED;
+		/*
+		 * MSR_IA32_INT_SSP_TAB is not present on processors that do
+		 * not support Intel 64 architecture.
+		 */
+		if (index == MSR_IA32_INT_SSP_TAB && !guest_cpu_cap_has(vcpu, X86_FEATURE_LM))
+			return KVM_MSR_RET_UNSUPPORTED;
+		if (is_noncanonical_msr_address(data, vcpu))
+			return 1;
+		/* All SSP MSRs except MSR_IA32_INT_SSP_TAB must be 4-byte aligned */
+		if (index != MSR_IA32_INT_SSP_TAB && !IS_ALIGNED(data, 4))
+			return 1;
+		break;
 	}
 
 	msr.data = data;
@@ -1930,6 +1968,20 @@ static int __kvm_get_msr(struct kvm_vcpu *vcpu, u32 index, u64 *data,
 		    !guest_cpu_cap_has(vcpu, X86_FEATURE_RDPID))
 			return 1;
 		break;
+	case MSR_IA32_U_CET:
+	case MSR_IA32_S_CET:
+		if (!guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK) &&
+		    !guest_cpu_cap_has(vcpu, X86_FEATURE_IBT))
+			return KVM_MSR_RET_UNSUPPORTED;
+		break;
+	case MSR_KVM_INTERNAL_GUEST_SSP:
+		if (!host_initiated)
+			return 1;
+		fallthrough;
+	case MSR_IA32_PL0_SSP ... MSR_IA32_INT_SSP_TAB:
+		if (!guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK))
+			return KVM_MSR_RET_UNSUPPORTED;
+		break;
 	}
 
 	msr.index = index;
@@ -4220,6 +4272,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		vcpu->arch.guest_fpu.xfd_err = data;
 		break;
 #endif
+	case MSR_IA32_U_CET:
+	case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
+		kvm_set_xstate_msr(vcpu, msr_info);
+		break;
 	default:
 		if (kvm_pmu_is_valid_msr(vcpu, msr))
 			return kvm_pmu_set_msr(vcpu, msr_info);
@@ -4569,6 +4625,10 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		msr_info->data = vcpu->arch.guest_fpu.xfd_err;
 		break;
 #endif
+	case MSR_IA32_U_CET:
+	case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
+		kvm_get_xstate_msr(vcpu, msr_info);
+		break;
 	default:
 		if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
 			return kvm_pmu_get_msr(vcpu, msr_info);
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 0d11115dcd2a..256e59aa9359 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -735,4 +735,27 @@ static inline void kvm_set_xstate_msr(struct kvm_vcpu *vcpu,
 	kvm_fpu_put();
 }
 
+#define CET_US_RESERVED_BITS		GENMASK(9, 6)
+#define CET_US_SHSTK_MASK_BITS		GENMASK(1, 0)
+#define CET_US_IBT_MASK_BITS		(GENMASK_ULL(5, 2) | GENMASK_ULL(63, 10))
+#define CET_US_LEGACY_BITMAP_BASE(data)	((data) >> 12)
+
+static inline bool kvm_is_valid_u_s_cet(struct kvm_vcpu *vcpu, u64 data)
+{
+	if (data & CET_US_RESERVED_BITS)
+		return false;
+	if (!guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK) &&
+	    (data & CET_US_SHSTK_MASK_BITS))
+		return false;
+	if (!guest_cpu_cap_has(vcpu, X86_FEATURE_IBT) &&
+	    (data & CET_US_IBT_MASK_BITS))
+		return false;
+	if (!IS_ALIGNED(CET_US_LEGACY_BITMAP_BASE(data), 4))
+		return false;
+	/* IBT can be suppressed iff the TRACKER isn't WAIT_ENDBR. */
+	if ((data & CET_SUPPRESS) && (data & CET_WAIT_ENDBR))
+		return false;
+
+	return true;
+}
 #endif
-- 
2.47.3

[PATCH v13 11/21] KVM: x86: Save and reload SSP to/from SMRAM

[Chao Gao]

From: Yang Weijiang <weijiang.yang@intel.com>

Save CET SSP to SMRAM on SMI and reload it on RSM. KVM emulates HW arch
behavior when guest enters/leaves SMM mode,i.e., save registers to SMRAM
at the entry of SMM and reload them at the exit to SMM. Per SDM, SSP is
one of such registers on 64-bit Arch, and add the support for SSP.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
 arch/x86/kvm/smm.c | 8 ++++++++
 arch/x86/kvm/smm.h | 2 +-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/smm.c b/arch/x86/kvm/smm.c
index 5dd8a1646800..b0b14ba37f9a 100644
--- a/arch/x86/kvm/smm.c
+++ b/arch/x86/kvm/smm.c
@@ -269,6 +269,10 @@ static void enter_smm_save_state_64(struct kvm_vcpu *vcpu,
 	enter_smm_save_seg_64(vcpu, &smram->gs, VCPU_SREG_GS);
 
 	smram->int_shadow = kvm_x86_call(get_interrupt_shadow)(vcpu);
+
+	if (guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK) &&
+	    kvm_msr_read(vcpu, MSR_KVM_INTERNAL_GUEST_SSP, &smram->ssp))
+		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
 }
 #endif
 
@@ -558,6 +562,10 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt,
 	kvm_x86_call(set_interrupt_shadow)(vcpu, 0);
 	ctxt->interruptibility = (u8)smstate->int_shadow;
 
+	if (guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK) &&
+	    kvm_msr_write(vcpu, MSR_KVM_INTERNAL_GUEST_SSP, smstate->ssp))
+		return X86EMUL_UNHANDLEABLE;
+
 	return X86EMUL_CONTINUE;
 }
 #endif
diff --git a/arch/x86/kvm/smm.h b/arch/x86/kvm/smm.h
index 551703fbe200..db3c88f16138 100644
--- a/arch/x86/kvm/smm.h
+++ b/arch/x86/kvm/smm.h
@@ -116,8 +116,8 @@ struct kvm_smram_state_64 {
 	u32 smbase;
 	u32 reserved4[5];
 
-	/* ssp and svm_* fields below are not implemented by KVM */
 	u64 ssp;
+	/* svm_* fields below are not implemented by KVM */
 	u64 svm_guest_pat;
 	u64 svm_host_efer;
 	u64 svm_host_cr4;
-- 
2.47.3

[PATCH v13 12/21] KVM: VMX: Set up interception for CET MSRs

[Chao Gao]

From: Yang Weijiang <weijiang.yang@intel.com>

Enable/disable CET MSRs interception per associated feature configuration.

Pass through CET MSRs that are managed by XSAVE, as they cannot be
intercepted without also intercepting XSAVE. However, intercepting XSAVE
would likely cause unacceptable performance overhead.
MSR_IA32_INT_SSP_TAB is not managed by XSAVE, so it is intercepted.

Note, this MSR design introduced an architectural limitation of SHSTK and
IBT control for guest, i.e., when SHSTK is exposed, IBT is also available
to guest from architectural perspective since IBT relies on subset of SHSTK
relevant MSRs.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
v13
- document the real reason why MSRs are pass-thru'd
- Rename the local variable that indicates whether interception is
  needed.
---
 arch/x86/kvm/vmx/vmx.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 4fc1dbba2eb0..adf5af30e537 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4101,6 +4101,8 @@ void pt_update_intercept_for_msr(struct kvm_vcpu *vcpu)
 
 void vmx_recalc_msr_intercepts(struct kvm_vcpu *vcpu)
 {
+	bool intercept;
+
 	if (!cpu_has_vmx_msr_bitmap())
 		return;
 
@@ -4146,6 +4148,23 @@ void vmx_recalc_msr_intercepts(struct kvm_vcpu *vcpu)
 		vmx_set_intercept_for_msr(vcpu, MSR_IA32_FLUSH_CMD, MSR_TYPE_W,
 					  !guest_cpu_cap_has(vcpu, X86_FEATURE_FLUSH_L1D));
 
+	if (kvm_cpu_cap_has(X86_FEATURE_SHSTK)) {
+		intercept = !guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK);
+
+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL0_SSP, MSR_TYPE_RW, intercept);
+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL1_SSP, MSR_TYPE_RW, intercept);
+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL2_SSP, MSR_TYPE_RW, intercept);
+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL3_SSP, MSR_TYPE_RW, intercept);
+	}
+
+	if (kvm_cpu_cap_has(X86_FEATURE_SHSTK) || kvm_cpu_cap_has(X86_FEATURE_IBT)) {
+		intercept = !guest_cpu_cap_has(vcpu, X86_FEATURE_IBT) &&
+			    !guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK);
+
+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_U_CET, MSR_TYPE_RW, intercept);
+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_S_CET, MSR_TYPE_RW, intercept);
+	}
+
 	/*
 	 * x2APIC and LBR MSR intercepts are modified on-demand and cannot be
 	 * filtered by userspace.
-- 
2.47.3

[PATCH v13 13/21] KVM: VMX: Set host constant supervisor states to VMCS fields

[Chao Gao]

From: Yang Weijiang <weijiang.yang@intel.com>

Save constant values to HOST_{S_CET,SSP,INTR_SSP_TABLE} field explicitly.
Kernel IBT is supported and the setting in MSR_IA32_S_CET is static after
post-boot(The exception is BIOS call case but vCPU thread never across it)
and KVM doesn't need to refresh HOST_S_CET field before every VM-Enter/
VM-Exit sequence.

Host supervisor shadow stack is not enabled now and SSP is not accessible
to kernel mode, thus it's safe to set host IA32_INT_SSP_TAB/SSP VMCS field
to 0s. When shadow stack is enabled for CPL3, SSP is reloaded from PL3_SSP
before it exits to userspace. Check SDM Vol 2A/B Chapter 3/4 for SYSCALL/
SYSRET/SYSENTER SYSEXIT/RDSSP/CALL etc.

Prevent KVM module loading if host supervisor shadow stack SHSTK_EN is set
in MSR_IA32_S_CET as KVM cannot co-exit with it correctly.

Suggested-by: Sean Christopherson <seanjc@google.com>
Suggested-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
 arch/x86/kvm/vmx/capabilities.h |  4 ++++
 arch/x86/kvm/vmx/vmx.c          | 15 +++++++++++++++
 arch/x86/kvm/x86.c              | 12 ++++++++++++
 arch/x86/kvm/x86.h              |  1 +
 4 files changed, 32 insertions(+)

diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
index 5316c27f6099..7d290b2cb0f4 100644
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -103,6 +103,10 @@ static inline bool cpu_has_load_perf_global_ctrl(void)
 	return vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL;
 }
 
+static inline bool cpu_has_load_cet_ctrl(void)
+{
+	return (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_CET_STATE);
+}
 static inline bool cpu_has_vmx_mpx(void)
 {
 	return vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_BNDCFGS;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index adf5af30e537..e8155635cb42 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4320,6 +4320,21 @@ void vmx_set_constant_host_state(struct vcpu_vmx *vmx)
 
 	if (cpu_has_load_ia32_efer())
 		vmcs_write64(HOST_IA32_EFER, kvm_host.efer);
+
+	/*
+	 * Supervisor shadow stack is not enabled on host side, i.e.,
+	 * host IA32_S_CET.SHSTK_EN bit is guaranteed to 0 now, per SDM
+	 * description(RDSSP instruction), SSP is not readable in CPL0,
+	 * so resetting the two registers to 0s at VM-Exit does no harm
+	 * to kernel execution. When execution flow exits to userspace,
+	 * SSP is reloaded from IA32_PL3_SSP. Check SDM Vol.2A/B Chapter
+	 * 3 and 4 for details.
+	 */
+	if (cpu_has_load_cet_ctrl()) {
+		vmcs_writel(HOST_S_CET, kvm_host.s_cet);
+		vmcs_writel(HOST_SSP, 0);
+		vmcs_writel(HOST_INTR_SSP_TABLE, 0);
+	}
 }
 
 void set_cr4_guest_host_mask(struct vcpu_vmx *vmx)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index dfd94146846e..34e4b2c4b892 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9893,6 +9893,18 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
 		return -EIO;
 	}
 
+	if (boot_cpu_has(X86_FEATURE_SHSTK)) {
+		rdmsrq(MSR_IA32_S_CET, kvm_host.s_cet);
+		/*
+		 * Linux doesn't yet support supervisor shadow stacks (SSS), so
+		 * KVM doesn't save/restore the associated MSRs, i.e. KVM may
+		 * clobber the host values.  Yell and refuse to load if SSS is
+		 * unexpectedly enabled, e.g. to avoid crashing the host.
+		 */
+		if (WARN_ON_ONCE(kvm_host.s_cet & CET_SHSTK_EN))
+			return -EIO;
+	}
+
 	memset(&kvm_caps, 0, sizeof(kvm_caps));
 
 	x86_emulator_cache = kvm_alloc_emulator_cache();
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 256e59aa9359..27fec4ed4c4e 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -50,6 +50,7 @@ struct kvm_host_values {
 	u64 efer;
 	u64 xcr0;
 	u64 xss;
+	u64 s_cet;
 	u64 arch_capabilities;
 };
 
-- 
2.47.3

[PATCH v13 14/21] KVM: x86: Don't emulate instructions guarded by CET

[Chao Gao]

From: Yang Weijiang <weijiang.yang@intel.com>

Don't emulate the branch instructions, e.g., CALL/RET/JMP etc., when CET
is active in guest, return KVM_INTERNAL_ERROR_EMULATION to userspace to
handle it.

KVM doesn't emulate CPU behaviors to check CET protected stuffs while
emulating guest instructions, instead it stops emulation on detecting
the instructions in process are CET protected. By doing so, it can avoid
generating bogus #CP in guest and preventing CET protected execution flow
subversion from guest side.

Suggested-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
 arch/x86/kvm/emulate.c | 46 ++++++++++++++++++++++++++++++++----------
 1 file changed, 35 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 542d3664afa3..97a4d1e69583 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -178,6 +178,8 @@
 #define IncSP       ((u64)1 << 54)  /* SP is incremented before ModRM calc */
 #define TwoMemOp    ((u64)1 << 55)  /* Instruction has two memory operand */
 #define IsBranch    ((u64)1 << 56)  /* Instruction is considered a branch. */
+#define ShadowStack ((u64)1 << 57)  /* Instruction protected by Shadow Stack. */
+#define IndirBrnTrk ((u64)1 << 58)  /* Instruction protected by IBT. */
 
 #define DstXacc     (DstAccLo | SrcAccHi | SrcWrite)
 
@@ -4068,9 +4070,11 @@ static const struct opcode group4[] = {
 static const struct opcode group5[] = {
 	F(DstMem | SrcNone | Lock,		em_inc),
 	F(DstMem | SrcNone | Lock,		em_dec),
-	I(SrcMem | NearBranch | IsBranch,       em_call_near_abs),
-	I(SrcMemFAddr | ImplicitOps | IsBranch, em_call_far),
-	I(SrcMem | NearBranch | IsBranch,       em_jmp_abs),
+	I(SrcMem | NearBranch | IsBranch | ShadowStack | IndirBrnTrk,
+	em_call_near_abs),
+	I(SrcMemFAddr | ImplicitOps | IsBranch | ShadowStack | IndirBrnTrk,
+	em_call_far),
+	I(SrcMem | NearBranch | IsBranch | IndirBrnTrk, em_jmp_abs),
 	I(SrcMemFAddr | ImplicitOps | IsBranch, em_jmp_far),
 	I(SrcMem | Stack | TwoMemOp,		em_push), D(Undefined),
 };
@@ -4332,11 +4336,11 @@ static const struct opcode opcode_table[256] = {
 	/* 0xC8 - 0xCF */
 	I(Stack | SrcImmU16 | Src2ImmByte | IsBranch, em_enter),
 	I(Stack | IsBranch, em_leave),
-	I(ImplicitOps | SrcImmU16 | IsBranch, em_ret_far_imm),
-	I(ImplicitOps | IsBranch, em_ret_far),
-	D(ImplicitOps | IsBranch), DI(SrcImmByte | IsBranch, intn),
+	I(ImplicitOps | SrcImmU16 | IsBranch | ShadowStack, em_ret_far_imm),
+	I(ImplicitOps | IsBranch | ShadowStack, em_ret_far),
+	D(ImplicitOps | IsBranch), DI(SrcImmByte | IsBranch | ShadowStack, intn),
 	D(ImplicitOps | No64 | IsBranch),
-	II(ImplicitOps | IsBranch, em_iret, iret),
+	II(ImplicitOps | IsBranch | ShadowStack, em_iret, iret),
 	/* 0xD0 - 0xD7 */
 	G(Src2One | ByteOp, group2), G(Src2One, group2),
 	G(Src2CL | ByteOp, group2), G(Src2CL, group2),
@@ -4352,7 +4356,7 @@ static const struct opcode opcode_table[256] = {
 	I2bvIP(SrcImmUByte | DstAcc, em_in,  in,  check_perm_in),
 	I2bvIP(SrcAcc | DstImmUByte, em_out, out, check_perm_out),
 	/* 0xE8 - 0xEF */
-	I(SrcImm | NearBranch | IsBranch, em_call),
+	I(SrcImm | NearBranch | IsBranch | ShadowStack, em_call),
 	D(SrcImm | ImplicitOps | NearBranch | IsBranch),
 	I(SrcImmFAddr | No64 | IsBranch, em_jmp_far),
 	D(SrcImmByte | ImplicitOps | NearBranch | IsBranch),
@@ -4371,7 +4375,8 @@ static const struct opcode opcode_table[256] = {
 static const struct opcode twobyte_table[256] = {
 	/* 0x00 - 0x0F */
 	G(0, group6), GD(0, &group7), N, N,
-	N, I(ImplicitOps | EmulateOnUD | IsBranch, em_syscall),
+	N, I(ImplicitOps | EmulateOnUD | IsBranch | ShadowStack | IndirBrnTrk,
+	em_syscall),
 	II(ImplicitOps | Priv, em_clts, clts), N,
 	DI(ImplicitOps | Priv, invd), DI(ImplicitOps | Priv, wbinvd), N, N,
 	N, D(ImplicitOps | ModRM | SrcMem | NoAccess), N, N,
@@ -4402,8 +4407,9 @@ static const struct opcode twobyte_table[256] = {
 	IIP(ImplicitOps, em_rdtsc, rdtsc, check_rdtsc),
 	II(ImplicitOps | Priv, em_rdmsr, rdmsr),
 	IIP(ImplicitOps, em_rdpmc, rdpmc, check_rdpmc),
-	I(ImplicitOps | EmulateOnUD | IsBranch, em_sysenter),
-	I(ImplicitOps | Priv | EmulateOnUD | IsBranch, em_sysexit),
+	I(ImplicitOps | EmulateOnUD | IsBranch | ShadowStack | IndirBrnTrk,
+	em_sysenter),
+	I(ImplicitOps | Priv | EmulateOnUD | IsBranch | ShadowStack, em_sysexit),
 	N, N,
 	N, N, N, N, N, N, N, N,
 	/* 0x40 - 0x4F */
@@ -4941,6 +4947,24 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len, int
 	if (ctxt->d == 0)
 		return EMULATION_FAILED;
 
+	if (ctxt->ops->get_cr(ctxt, 4) & X86_CR4_CET) {
+		u64 u_cet, s_cet;
+		bool stop_em;
+
+		if (ctxt->ops->get_msr(ctxt, MSR_IA32_U_CET, &u_cet) ||
+		    ctxt->ops->get_msr(ctxt, MSR_IA32_S_CET, &s_cet))
+			return EMULATION_FAILED;
+
+		stop_em = ((u_cet & CET_SHSTK_EN) || (s_cet & CET_SHSTK_EN)) &&
+			  (opcode.flags & ShadowStack);
+
+		stop_em |= ((u_cet & CET_ENDBR_EN) || (s_cet & CET_ENDBR_EN)) &&
+			   (opcode.flags & IndirBrnTrk);
+
+		if (stop_em)
+			return EMULATION_FAILED;
+	}
+
 	ctxt->execute = opcode.u.execute;
 
 	if (unlikely(emulation_type & EMULTYPE_TRAP_UD) &&
-- 
2.47.3

[PATCH v13 15/21] KVM: x86: Enable CET virtualization for VMX and advertise to userspace

[Chao Gao]

From: Yang Weijiang <weijiang.yang@intel.com>

Expose CET features to guest if KVM/host can support them, clear CPUID
feature bits if KVM/host cannot support.

Set CPUID feature bits so that CET features are available in guest CPUID.
Add CR4.CET bit support in order to allow guest set CET master control
bit.

Disable KVM CET feature if unrestricted_guest is unsupported/disabled as
KVM does not support emulating CET.

The CET load-bits in VM_ENTRY/VM_EXIT control fields should be set to make
guest CET xstates isolated from host's.

On platforms with VMX_BASIC[bit56] == 0, inject #CP at VMX entry with error
code will fail, and if VMX_BASIC[bit56] == 1, #CP injection with or without
error code is allowed. Disable CET feature bits if the MSR bit is cleared
so that nested VMM can inject #CP if and only if VMX_BASIC[bit56] == 1.

Don't expose CET feature if either of {U,S}_CET xstate bits is cleared
in host XSS or if XSAVES isn't supported.

CET MSRs are reset to 0s after RESET, power-up and INIT, clear guest CET
xsave-area fields so that guest CET MSRs are reset to 0s after the events.

Meanwhile explicitly disable SHSTK and IBT for SVM because CET KVM enabling
for SVM is not ready.

Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
v13: Limit SHSTK to 64-bit kernels
---
 arch/x86/include/asm/kvm_host.h |  2 +-
 arch/x86/include/asm/vmx.h      |  1 +
 arch/x86/kvm/cpuid.c            |  2 ++
 arch/x86/kvm/svm/svm.c          |  4 ++++
 arch/x86/kvm/vmx/capabilities.h |  5 +++++
 arch/x86/kvm/vmx/vmx.c          | 30 +++++++++++++++++++++++++++++-
 arch/x86/kvm/vmx/vmx.h          |  6 ++++--
 arch/x86/kvm/x86.c              | 22 +++++++++++++++++++---
 arch/x86/kvm/x86.h              |  3 +++
 9 files changed, 68 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index b7f82a421718..061c0cd73d39 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -142,7 +142,7 @@
 			  | X86_CR4_OSXSAVE | X86_CR4_SMEP | X86_CR4_FSGSBASE \
 			  | X86_CR4_OSXMMEXCPT | X86_CR4_LA57 | X86_CR4_VMXE \
 			  | X86_CR4_SMAP | X86_CR4_PKE | X86_CR4_UMIP \
-			  | X86_CR4_LAM_SUP))
+			  | X86_CR4_LAM_SUP | X86_CR4_CET))
 
 #define CR8_RESERVED_BITS (~(unsigned long)X86_CR8_TPR)
 
diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
index ce10a7e2d3d9..c85c50019523 100644
--- a/arch/x86/include/asm/vmx.h
+++ b/arch/x86/include/asm/vmx.h
@@ -134,6 +134,7 @@
 #define VMX_BASIC_DUAL_MONITOR_TREATMENT	BIT_ULL(49)
 #define VMX_BASIC_INOUT				BIT_ULL(54)
 #define VMX_BASIC_TRUE_CTLS			BIT_ULL(55)
+#define VMX_BASIC_NO_HW_ERROR_CODE_CC		BIT_ULL(56)
 
 static inline u32 vmx_basic_vmcs_revision_id(u64 vmx_basic)
 {
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index b5f87254ced7..ee05b876c656 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -944,6 +944,7 @@ void kvm_set_cpu_caps(void)
 		VENDOR_F(WAITPKG),
 		F(SGX_LC),
 		F(BUS_LOCK_DETECT),
+		X86_64_F(SHSTK),
 	);
 
 	/*
@@ -970,6 +971,7 @@ void kvm_set_cpu_caps(void)
 		F(AMX_INT8),
 		F(AMX_BF16),
 		F(FLUSH_L1D),
+		F(IBT),
 	);
 
 	if (boot_cpu_has(X86_FEATURE_AMD_IBPB_RET) &&
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 7e7821ee8ee1..0e2c60466797 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -5241,6 +5241,10 @@ static __init void svm_set_cpu_caps(void)
 	kvm_caps.supported_perf_cap = 0;
 	kvm_caps.supported_xss = 0;
 
+	/* KVM doesn't yet support CET virtualization for SVM. */
+	kvm_cpu_cap_clear(X86_FEATURE_SHSTK);
+	kvm_cpu_cap_clear(X86_FEATURE_IBT);
+
 	/* CPUID 0x80000001 and 0x8000000A (SVM features) */
 	if (nested) {
 		kvm_cpu_cap_set(X86_FEATURE_SVM);
diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
index 7d290b2cb0f4..47b0dec8665a 100644
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -76,6 +76,11 @@ static inline bool cpu_has_vmx_basic_inout(void)
 	return	vmcs_config.basic & VMX_BASIC_INOUT;
 }
 
+static inline bool cpu_has_vmx_basic_no_hw_errcode(void)
+{
+	return	vmcs_config.basic & VMX_BASIC_NO_HW_ERROR_CODE_CC;
+}
+
 static inline bool cpu_has_virtual_nmis(void)
 {
 	return vmcs_config.pin_based_exec_ctrl & PIN_BASED_VIRTUAL_NMIS &&
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index e8155635cb42..8d2186d6549f 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2615,6 +2615,7 @@ static int setup_vmcs_config(struct vmcs_config *vmcs_conf,
 		{ VM_ENTRY_LOAD_IA32_EFER,		VM_EXIT_LOAD_IA32_EFER },
 		{ VM_ENTRY_LOAD_BNDCFGS,		VM_EXIT_CLEAR_BNDCFGS },
 		{ VM_ENTRY_LOAD_IA32_RTIT_CTL,		VM_EXIT_CLEAR_IA32_RTIT_CTL },
+		{ VM_ENTRY_LOAD_CET_STATE,		VM_EXIT_LOAD_CET_STATE },
 	};
 
 	memset(vmcs_conf, 0, sizeof(*vmcs_conf));
@@ -4882,6 +4883,14 @@ void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 
 	vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, 0);  /* 22.2.1 */
 
+	if (kvm_cpu_cap_has(X86_FEATURE_SHSTK)) {
+		vmcs_writel(GUEST_SSP, 0);
+		vmcs_writel(GUEST_INTR_SSP_TABLE, 0);
+	}
+	if (kvm_cpu_cap_has(X86_FEATURE_IBT) ||
+	    kvm_cpu_cap_has(X86_FEATURE_SHSTK))
+		vmcs_writel(GUEST_S_CET, 0);
+
 	kvm_make_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu);
 
 	vpid_sync_context(vmx->vpid);
@@ -6349,6 +6358,10 @@ void dump_vmcs(struct kvm_vcpu *vcpu)
 	if (vmcs_read32(VM_EXIT_MSR_STORE_COUNT) > 0)
 		vmx_dump_msrs("guest autostore", &vmx->msr_autostore.guest);
 
+	if (vmentry_ctl & VM_ENTRY_LOAD_CET_STATE)
+		pr_err("S_CET = 0x%016lx, SSP = 0x%016lx, SSP TABLE = 0x%016lx\n",
+		       vmcs_readl(GUEST_S_CET), vmcs_readl(GUEST_SSP),
+		       vmcs_readl(GUEST_INTR_SSP_TABLE));
 	pr_err("*** Host State ***\n");
 	pr_err("RIP = 0x%016lx  RSP = 0x%016lx\n",
 	       vmcs_readl(HOST_RIP), vmcs_readl(HOST_RSP));
@@ -6379,6 +6392,10 @@ void dump_vmcs(struct kvm_vcpu *vcpu)
 		       vmcs_read64(HOST_IA32_PERF_GLOBAL_CTRL));
 	if (vmcs_read32(VM_EXIT_MSR_LOAD_COUNT) > 0)
 		vmx_dump_msrs("host autoload", &vmx->msr_autoload.host);
+	if (vmexit_ctl & VM_EXIT_LOAD_CET_STATE)
+		pr_err("S_CET = 0x%016lx, SSP = 0x%016lx, SSP TABLE = 0x%016lx\n",
+		       vmcs_readl(HOST_S_CET), vmcs_readl(HOST_SSP),
+		       vmcs_readl(HOST_INTR_SSP_TABLE));
 
 	pr_err("*** Control State ***\n");
 	pr_err("CPUBased=0x%08x SecondaryExec=0x%08x TertiaryExec=0x%016llx\n",
@@ -7963,7 +7980,6 @@ static __init void vmx_set_cpu_caps(void)
 		kvm_cpu_cap_set(X86_FEATURE_UMIP);
 
 	/* CPUID 0xD.1 */
-	kvm_caps.supported_xss = 0;
 	if (!cpu_has_vmx_xsaves())
 		kvm_cpu_cap_clear(X86_FEATURE_XSAVES);
 
@@ -7975,6 +7991,18 @@ static __init void vmx_set_cpu_caps(void)
 
 	if (cpu_has_vmx_waitpkg())
 		kvm_cpu_cap_check_and_set(X86_FEATURE_WAITPKG);
+
+	/*
+	 * Disable CET if unrestricted_guest is unsupported as KVM doesn't
+	 * enforce CET HW behaviors in emulator. On platforms with
+	 * VMX_BASIC[bit56] == 0, inject #CP at VMX entry with error code
+	 * fails, so disable CET in this case too.
+	 */
+	if (!cpu_has_load_cet_ctrl() || !enable_unrestricted_guest ||
+	    !cpu_has_vmx_basic_no_hw_errcode()) {
+		kvm_cpu_cap_clear(X86_FEATURE_SHSTK);
+		kvm_cpu_cap_clear(X86_FEATURE_IBT);
+	}
 }
 
 static bool vmx_is_io_intercepted(struct kvm_vcpu *vcpu,
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 24d65dac5e89..08a9a0075404 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -484,7 +484,8 @@ static inline u8 vmx_get_rvi(void)
 	 VM_ENTRY_LOAD_IA32_EFER |					\
 	 VM_ENTRY_LOAD_BNDCFGS |					\
 	 VM_ENTRY_PT_CONCEAL_PIP |					\
-	 VM_ENTRY_LOAD_IA32_RTIT_CTL)
+	 VM_ENTRY_LOAD_IA32_RTIT_CTL |					\
+	 VM_ENTRY_LOAD_CET_STATE)
 
 #define __KVM_REQUIRED_VMX_VM_EXIT_CONTROLS				\
 	(VM_EXIT_SAVE_DEBUG_CONTROLS |					\
@@ -506,7 +507,8 @@ static inline u8 vmx_get_rvi(void)
 	       VM_EXIT_LOAD_IA32_EFER |					\
 	       VM_EXIT_CLEAR_BNDCFGS |					\
 	       VM_EXIT_PT_CONCEAL_PIP |					\
-	       VM_EXIT_CLEAR_IA32_RTIT_CTL)
+	       VM_EXIT_CLEAR_IA32_RTIT_CTL |				\
+	       VM_EXIT_LOAD_CET_STATE)
 
 #define KVM_REQUIRED_VMX_PIN_BASED_VM_EXEC_CONTROL			\
 	(PIN_BASED_EXT_INTR_MASK |					\
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 34e4b2c4b892..9930678f5a3b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -223,7 +223,8 @@ static struct kvm_user_return_msrs __percpu *user_return_msrs;
 				| XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
 				| XFEATURE_MASK_PKRU | XFEATURE_MASK_XTILE)
 
-#define KVM_SUPPORTED_XSS     0
+#define KVM_SUPPORTED_XSS	(XFEATURE_MASK_CET_USER | \
+				 XFEATURE_MASK_CET_KERNEL)
 
 bool __read_mostly allow_smaller_maxphyaddr = 0;
 EXPORT_SYMBOL_GPL(allow_smaller_maxphyaddr);
@@ -9991,6 +9992,20 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
 	if (!kvm_cpu_cap_has(X86_FEATURE_XSAVES))
 		kvm_caps.supported_xss = 0;
 
+	if (!kvm_cpu_cap_has(X86_FEATURE_SHSTK) &&
+	    !kvm_cpu_cap_has(X86_FEATURE_IBT))
+		kvm_caps.supported_xss &= ~(XFEATURE_MASK_CET_USER |
+					    XFEATURE_MASK_CET_KERNEL);
+
+	if ((kvm_caps.supported_xss & (XFEATURE_MASK_CET_USER |
+	     XFEATURE_MASK_CET_KERNEL)) !=
+	    (XFEATURE_MASK_CET_USER | XFEATURE_MASK_CET_KERNEL)) {
+		kvm_cpu_cap_clear(X86_FEATURE_SHSTK);
+		kvm_cpu_cap_clear(X86_FEATURE_IBT);
+		kvm_caps.supported_xss &= ~(XFEATURE_MASK_CET_USER |
+					    XFEATURE_MASK_CET_KERNEL);
+	}
+
 	if (kvm_caps.has_tsc_control) {
 		/*
 		 * Make sure the user can only configure tsc_khz values that
@@ -12646,10 +12661,11 @@ static void kvm_xstate_reset(struct kvm_vcpu *vcpu, bool init_event)
 	/*
 	 * On INIT, only select XSTATE components are zeroed, most components
 	 * are unchanged.  Currently, the only components that are zeroed and
-	 * supported by KVM are MPX related.
+	 * supported by KVM are MPX and CET related.
 	 */
 	xfeatures_mask = (kvm_caps.supported_xcr0 | kvm_caps.supported_xss) &
-			 (XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR);
+			 (XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR |
+			  XFEATURE_MASK_CET_USER | XFEATURE_MASK_CET_KERNEL);
 	if (!xfeatures_mask)
 		return;
 
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 27fec4ed4c4e..d6b21ba41416 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -681,6 +681,9 @@ static inline bool __kvm_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 		__reserved_bits |= X86_CR4_PCIDE;       \
 	if (!__cpu_has(__c, X86_FEATURE_LAM))           \
 		__reserved_bits |= X86_CR4_LAM_SUP;     \
+	if (!__cpu_has(__c, X86_FEATURE_SHSTK) &&       \
+	    !__cpu_has(__c, X86_FEATURE_IBT))           \
+		__reserved_bits |= X86_CR4_CET;         \
 	__reserved_bits;                                \
 })
 
-- 
2.47.3

[PATCH v13 16/21] KVM: nVMX: Virtualize NO_HW_ERROR_CODE_CC for L1 event injection to L2

[Chao Gao]

From: Yang Weijiang <weijiang.yang@intel.com>

Per SDM description(Vol.3D, Appendix A.1):
"If bit 56 is read as 1, software can use VM entry to deliver a hardware
exception with or without an error code, regardless of vector"

Modify has_error_code check before inject events to nested guest. Only
enforce the check when guest is in real mode, the exception is not hard
exception and the platform doesn't enumerate bit56 in VMX_BASIC, in all
other case ignore the check to make the logic consistent with SDM.

Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
 arch/x86/kvm/vmx/nested.c | 28 +++++++++++++++++++---------
 arch/x86/kvm/vmx/nested.h |  5 +++++
 2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 2156c9a854f4..14f9822b611d 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -1272,9 +1272,10 @@ static int vmx_restore_vmx_basic(struct vcpu_vmx *vmx, u64 data)
 {
 	const u64 feature_bits = VMX_BASIC_DUAL_MONITOR_TREATMENT |
 				 VMX_BASIC_INOUT |
-				 VMX_BASIC_TRUE_CTLS;
+				 VMX_BASIC_TRUE_CTLS |
+				 VMX_BASIC_NO_HW_ERROR_CODE_CC;
 
-	const u64 reserved_bits = GENMASK_ULL(63, 56) |
+	const u64 reserved_bits = GENMASK_ULL(63, 57) |
 				  GENMASK_ULL(47, 45) |
 				  BIT_ULL(31);
 
@@ -2949,7 +2950,6 @@ static int nested_check_vm_entry_controls(struct kvm_vcpu *vcpu,
 		u8 vector = intr_info & INTR_INFO_VECTOR_MASK;
 		u32 intr_type = intr_info & INTR_INFO_INTR_TYPE_MASK;
 		bool has_error_code = intr_info & INTR_INFO_DELIVER_CODE_MASK;
-		bool should_have_error_code;
 		bool urg = nested_cpu_has2(vmcs12,
 					   SECONDARY_EXEC_UNRESTRICTED_GUEST);
 		bool prot_mode = !urg || vmcs12->guest_cr0 & X86_CR0_PE;
@@ -2966,12 +2966,20 @@ static int nested_check_vm_entry_controls(struct kvm_vcpu *vcpu,
 		    CC(intr_type == INTR_TYPE_OTHER_EVENT && vector != 0))
 			return -EINVAL;
 
-		/* VM-entry interruption-info field: deliver error code */
-		should_have_error_code =
-			intr_type == INTR_TYPE_HARD_EXCEPTION && prot_mode &&
-			x86_exception_has_error_code(vector);
-		if (CC(has_error_code != should_have_error_code))
-			return -EINVAL;
+		/*
+		 * Cannot deliver error code in real mode or if the interrupt
+		 * type is not hardware exception. For other cases, do the
+		 * consistency check only if the vCPU doesn't enumerate
+		 * VMX_BASIC_NO_HW_ERROR_CODE_CC.
+		 */
+		if (!prot_mode || intr_type != INTR_TYPE_HARD_EXCEPTION) {
+			if (CC(has_error_code))
+				return -EINVAL;
+		} else if (!nested_cpu_has_no_hw_errcode_cc(vcpu)) {
+			if (CC(has_error_code !=
+			       x86_exception_has_error_code(vector)))
+				return -EINVAL;
+		}
 
 		/* VM-entry exception error code */
 		if (CC(has_error_code &&
@@ -7214,6 +7222,8 @@ static void nested_vmx_setup_basic(struct nested_vmx_msrs *msrs)
 	msrs->basic |= VMX_BASIC_TRUE_CTLS;
 	if (cpu_has_vmx_basic_inout())
 		msrs->basic |= VMX_BASIC_INOUT;
+	if (cpu_has_vmx_basic_no_hw_errcode())
+		msrs->basic |= VMX_BASIC_NO_HW_ERROR_CODE_CC;
 }
 
 static void nested_vmx_setup_cr_fixed(struct nested_vmx_msrs *msrs)
diff --git a/arch/x86/kvm/vmx/nested.h b/arch/x86/kvm/vmx/nested.h
index 6eedcfc91070..983484d42ebf 100644
--- a/arch/x86/kvm/vmx/nested.h
+++ b/arch/x86/kvm/vmx/nested.h
@@ -309,6 +309,11 @@ static inline bool nested_cr4_valid(struct kvm_vcpu *vcpu, unsigned long val)
 	       __kvm_is_valid_cr4(vcpu, val);
 }
 
+static inline bool nested_cpu_has_no_hw_errcode_cc(struct kvm_vcpu *vcpu)
+{
+	return to_vmx(vcpu)->nested.msrs.basic & VMX_BASIC_NO_HW_ERROR_CODE_CC;
+}
+
 /* No difference in the restrictions on guest and host CR4 in VMX operation. */
 #define nested_guest_cr4_valid	nested_cr4_valid
 #define nested_host_cr4_valid	nested_cr4_valid
-- 
2.47.3

[PATCH v13 17/21] KVM: nVMX: Prepare for enabling CET support for nested guest

[Chao Gao]

From: Yang Weijiang <weijiang.yang@intel.com>

Set up CET MSRs, related VM_ENTRY/EXIT control bits and fixed CR4 setting
to enable CET for nested VM.

vmcs12 and vmcs02 needs to be synced when L2 exits to L1 or when L1 wants
to resume L2, that way correct CET states can be observed by one another.

Please note that consistency checks regarding CET state during VM-Entry
will be added later to prevent this patch from becoming too large.
Advertising the new CET VM_ENTRY/EXIT control bits are also be deferred
until after the consistency checks are added.

Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
v13:
 - retain CET state if L1 doesn't set VM_EXIT_LOAD_CET_STATE (Xin)
 - don't pass-thru MSR_IA32_INT_SSP_TAB
 - drop inline from local functions
 - rename cet_vmcs_fields_{get,set}() to vmcs_{read,write}_cet_state()
 - split out advertising new CET VM_ENTRY/EXIT control bits.
---
 arch/x86/kvm/vmx/nested.c | 77 +++++++++++++++++++++++++++++++++++++++
 arch/x86/kvm/vmx/vmcs12.c |  6 +++
 arch/x86/kvm/vmx/vmcs12.h | 14 ++++++-
 arch/x86/kvm/vmx/vmx.c    |  2 +
 arch/x86/kvm/vmx/vmx.h    |  3 ++
 5 files changed, 101 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 14f9822b611d..51d69f368689 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -721,6 +721,24 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
 	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
 					 MSR_IA32_MPERF, MSR_TYPE_R);
 
+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
+					 MSR_IA32_U_CET, MSR_TYPE_RW);
+
+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
+					 MSR_IA32_S_CET, MSR_TYPE_RW);
+
+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
+					 MSR_IA32_PL0_SSP, MSR_TYPE_RW);
+
+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
+					 MSR_IA32_PL1_SSP, MSR_TYPE_RW);
+
+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
+					 MSR_IA32_PL2_SSP, MSR_TYPE_RW);
+
+	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
+					 MSR_IA32_PL3_SSP, MSR_TYPE_RW);
+
 	kvm_vcpu_unmap(vcpu, &map);
 
 	vmx->nested.force_msr_bitmap_recalc = false;
@@ -2521,6 +2539,32 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct loaded_vmcs *vmcs0
 	}
 }
 
+static void vmcs_read_cet_state(struct kvm_vcpu *vcpu, u64 *s_cet,
+				u64 *ssp, u64 *ssp_tbl)
+{
+	if (guest_cpu_cap_has(vcpu, X86_FEATURE_IBT) ||
+	    guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK))
+		*s_cet = vmcs_readl(GUEST_S_CET);
+
+	if (guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK)) {
+		*ssp = vmcs_readl(GUEST_SSP);
+		*ssp_tbl = vmcs_readl(GUEST_INTR_SSP_TABLE);
+	}
+}
+
+static void vmcs_write_cet_state(struct kvm_vcpu *vcpu, u64 s_cet,
+				 u64 ssp, u64 ssp_tbl)
+{
+	if (guest_cpu_cap_has(vcpu, X86_FEATURE_IBT) ||
+	    guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK))
+		vmcs_writel(GUEST_S_CET, s_cet);
+
+	if (guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK)) {
+		vmcs_writel(GUEST_SSP, ssp);
+		vmcs_writel(GUEST_INTR_SSP_TABLE, ssp_tbl);
+	}
+}
+
 static void prepare_vmcs02_rare(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
 {
 	struct hv_enlightened_vmcs *hv_evmcs = nested_vmx_evmcs(vmx);
@@ -2637,6 +2681,10 @@ static void prepare_vmcs02_rare(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
 	vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, vmx->msr_autoload.host.nr);
 	vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, vmx->msr_autoload.guest.nr);
 
+	if (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_CET_STATE)
+		vmcs_write_cet_state(&vmx->vcpu, vmcs12->guest_s_cet,
+				     vmcs12->guest_ssp, vmcs12->guest_ssp_tbl);
+
 	set_cr4_guest_host_mask(vmx);
 }
 
@@ -2676,6 +2724,13 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
 		kvm_set_dr(vcpu, 7, vcpu->arch.dr7);
 		vmx_guest_debugctl_write(vcpu, vmx->nested.pre_vmenter_debugctl);
 	}
+
+	if (!vmx->nested.nested_run_pending ||
+	    !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_CET_STATE))
+		vmcs_write_cet_state(vcpu, vmx->nested.pre_vmenter_s_cet,
+				     vmx->nested.pre_vmenter_ssp,
+				     vmx->nested.pre_vmenter_ssp_tbl);
+
 	if (kvm_mpx_supported() && (!vmx->nested.nested_run_pending ||
 	    !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_BNDCFGS)))
 		vmcs_write64(GUEST_BNDCFGS, vmx->nested.pre_vmenter_bndcfgs);
@@ -3552,6 +3607,12 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
 	     !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_BNDCFGS)))
 		vmx->nested.pre_vmenter_bndcfgs = vmcs_read64(GUEST_BNDCFGS);
 
+	if (!vmx->nested.nested_run_pending ||
+	    !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_CET_STATE))
+		vmcs_read_cet_state(vcpu, &vmx->nested.pre_vmenter_s_cet,
+				    &vmx->nested.pre_vmenter_ssp,
+				    &vmx->nested.pre_vmenter_ssp_tbl);
+
 	/*
 	 * Overwrite vmcs01.GUEST_CR3 with L1's CR3 if EPT is disabled *and*
 	 * nested early checks are disabled.  In the event of a "late" VM-Fail,
@@ -4635,6 +4696,10 @@ static void sync_vmcs02_to_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 
 	if (vmcs12->vm_exit_controls & VM_EXIT_SAVE_IA32_EFER)
 		vmcs12->guest_ia32_efer = vcpu->arch.efer;
+
+	vmcs_read_cet_state(&vmx->vcpu, &vmcs12->guest_s_cet,
+			    &vmcs12->guest_ssp,
+			    &vmcs12->guest_ssp_tbl);
 }
 
 /*
@@ -4760,6 +4825,18 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
 	if (vmcs12->vm_exit_controls & VM_EXIT_CLEAR_BNDCFGS)
 		vmcs_write64(GUEST_BNDCFGS, 0);
 
+	/*
+	 * Load CET state from host state if VM_EXIT_LOAD_CET_STATE is set.
+	 * otherwise CET state should be retained across VM-exit, i.e.,
+	 * guest values should be propagated from vmcs12 to vmcs01.
+	 */
+	if (vmcs12->vm_exit_controls & VM_EXIT_LOAD_CET_STATE)
+		vmcs_write_cet_state(vcpu, vmcs12->host_s_cet, vmcs12->host_ssp,
+				     vmcs12->host_ssp_tbl);
+	else
+		vmcs_write_cet_state(vcpu, vmcs12->guest_s_cet, vmcs12->guest_ssp,
+				     vmcs12->guest_ssp_tbl);
+
 	if (vmcs12->vm_exit_controls & VM_EXIT_LOAD_IA32_PAT) {
 		vmcs_write64(GUEST_IA32_PAT, vmcs12->host_ia32_pat);
 		vcpu->arch.pat = vmcs12->host_ia32_pat;
diff --git a/arch/x86/kvm/vmx/vmcs12.c b/arch/x86/kvm/vmx/vmcs12.c
index 106a72c923ca..4233b5ca9461 100644
--- a/arch/x86/kvm/vmx/vmcs12.c
+++ b/arch/x86/kvm/vmx/vmcs12.c
@@ -139,6 +139,9 @@ const unsigned short vmcs12_field_offsets[] = {
 	FIELD(GUEST_PENDING_DBG_EXCEPTIONS, guest_pending_dbg_exceptions),
 	FIELD(GUEST_SYSENTER_ESP, guest_sysenter_esp),
 	FIELD(GUEST_SYSENTER_EIP, guest_sysenter_eip),
+	FIELD(GUEST_S_CET, guest_s_cet),
+	FIELD(GUEST_SSP, guest_ssp),
+	FIELD(GUEST_INTR_SSP_TABLE, guest_ssp_tbl),
 	FIELD(HOST_CR0, host_cr0),
 	FIELD(HOST_CR3, host_cr3),
 	FIELD(HOST_CR4, host_cr4),
@@ -151,5 +154,8 @@ const unsigned short vmcs12_field_offsets[] = {
 	FIELD(HOST_IA32_SYSENTER_EIP, host_ia32_sysenter_eip),
 	FIELD(HOST_RSP, host_rsp),
 	FIELD(HOST_RIP, host_rip),
+	FIELD(HOST_S_CET, host_s_cet),
+	FIELD(HOST_SSP, host_ssp),
+	FIELD(HOST_INTR_SSP_TABLE, host_ssp_tbl),
 };
 const unsigned int nr_vmcs12_fields = ARRAY_SIZE(vmcs12_field_offsets);
diff --git a/arch/x86/kvm/vmx/vmcs12.h b/arch/x86/kvm/vmx/vmcs12.h
index 56fd150a6f24..4ad6b16525b9 100644
--- a/arch/x86/kvm/vmx/vmcs12.h
+++ b/arch/x86/kvm/vmx/vmcs12.h
@@ -117,7 +117,13 @@ struct __packed vmcs12 {
 	natural_width host_ia32_sysenter_eip;
 	natural_width host_rsp;
 	natural_width host_rip;
-	natural_width paddingl[8]; /* room for future expansion */
+	natural_width host_s_cet;
+	natural_width host_ssp;
+	natural_width host_ssp_tbl;
+	natural_width guest_s_cet;
+	natural_width guest_ssp;
+	natural_width guest_ssp_tbl;
+	natural_width paddingl[2]; /* room for future expansion */
 	u32 pin_based_vm_exec_control;
 	u32 cpu_based_vm_exec_control;
 	u32 exception_bitmap;
@@ -294,6 +300,12 @@ static inline void vmx_check_vmcs12_offsets(void)
 	CHECK_OFFSET(host_ia32_sysenter_eip, 656);
 	CHECK_OFFSET(host_rsp, 664);
 	CHECK_OFFSET(host_rip, 672);
+	CHECK_OFFSET(host_s_cet, 680);
+	CHECK_OFFSET(host_ssp, 688);
+	CHECK_OFFSET(host_ssp_tbl, 696);
+	CHECK_OFFSET(guest_s_cet, 704);
+	CHECK_OFFSET(guest_ssp, 712);
+	CHECK_OFFSET(guest_ssp_tbl, 720);
 	CHECK_OFFSET(pin_based_vm_exec_control, 744);
 	CHECK_OFFSET(cpu_based_vm_exec_control, 748);
 	CHECK_OFFSET(exception_bitmap, 752);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 8d2186d6549f..989008f5307e 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7749,6 +7749,8 @@ static void nested_vmx_cr_fixed1_bits_update(struct kvm_vcpu *vcpu)
 	cr4_fixed1_update(X86_CR4_PKE,        ecx, feature_bit(PKU));
 	cr4_fixed1_update(X86_CR4_UMIP,       ecx, feature_bit(UMIP));
 	cr4_fixed1_update(X86_CR4_LA57,       ecx, feature_bit(LA57));
+	cr4_fixed1_update(X86_CR4_CET,	      ecx, feature_bit(SHSTK));
+	cr4_fixed1_update(X86_CR4_CET,	      edx, feature_bit(IBT));
 
 	entry = kvm_find_cpuid_entry_index(vcpu, 0x7, 1);
 	cr4_fixed1_update(X86_CR4_LAM_SUP,    eax, feature_bit(LAM));
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 08a9a0075404..ecfdba666465 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -181,6 +181,9 @@ struct nested_vmx {
 	 */
 	u64 pre_vmenter_debugctl;
 	u64 pre_vmenter_bndcfgs;
+	u64 pre_vmenter_s_cet;
+	u64 pre_vmenter_ssp;
+	u64 pre_vmenter_ssp_tbl;
 
 	/* to migrate it to L1 if L2 writes to L1's CR8 directly */
 	int l1_tpr_threshold;
-- 
2.47.3

[PATCH v13 18/21] KVM: nVMX: Add consistency checks for CR0.WP and CR4.CET

[Chao Gao]

Add consistency checks for CR4.CET and CR0.WP in guest-state or host-state
area in the VMCS12. This ensures that configurations with CR4.CET set and
CR0.WP not set result in VM-entry failure, aligning with architectural
behavior.

Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
 arch/x86/kvm/vmx/nested.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 51d69f368689..a73f38d7eea1 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3111,6 +3111,9 @@ static int nested_vmx_check_host_state(struct kvm_vcpu *vcpu,
 	    CC(!kvm_vcpu_is_legal_cr3(vcpu, vmcs12->host_cr3)))
 		return -EINVAL;
 
+	if (CC(vmcs12->host_cr4 & X86_CR4_CET && !(vmcs12->host_cr0 & X86_CR0_WP)))
+		return -EINVAL;
+
 	if (CC(is_noncanonical_msr_address(vmcs12->host_ia32_sysenter_esp, vcpu)) ||
 	    CC(is_noncanonical_msr_address(vmcs12->host_ia32_sysenter_eip, vcpu)))
 		return -EINVAL;
@@ -3225,6 +3228,9 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
 	    CC(!nested_guest_cr4_valid(vcpu, vmcs12->guest_cr4)))
 		return -EINVAL;
 
+	if (CC(vmcs12->guest_cr4 & X86_CR4_CET && !(vmcs12->guest_cr0 & X86_CR0_WP)))
+		return -EINVAL;
+
 	if ((vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS) &&
 	    (CC(!kvm_dr7_valid(vmcs12->guest_dr7)) ||
 	     CC(!vmx_is_valid_debugctl(vcpu, vmcs12->guest_ia32_debugctl, false))))
-- 
2.47.3

[PATCH v13 19/21] KVM: nVMX: Add consistency checks for CET states

[Chao Gao]

Introduce consistency checks for CET states during nested VM-entry.

A VMCS contains both guest and host CET states, each comprising the
IA32_S_CET MSR, SSP, and IA32_INTERRUPT_SSP_TABLE_ADDR MSR. Various
checks are applied to CET states during VM-entry as documented in SDM
Vol3 Chapter "VM ENTRIES". Implement all these checks during nested
VM-entry to emulate the architectural behavior.

In summary, there are three kinds of checks on guest/host CET states
during VM-entry:

A. Checks applied to both guest states and host states:

 * The IA32_S_CET field must not set any reserved bits; bits 10 (SUPPRESS)
   and 11 (TRACKER) cannot both be set.
 * SSP should not have bits 1:0 set.
 * The IA32_INTERRUPT_SSP_TABLE_ADDR field must be canonical.

B. Checks applied to host states only

 * IA32_S_CET MSR and SSP must be canonical if the CPU enters 64-bit mode
   after VM-exit. Otherwise, IA32_S_CET and SSP must have their higher 32
   bits cleared.

C. Checks applied to guest states only:

 * IA32_S_CET MSR and SSP are not required to be canonical (i.e., 63:N-1
   are identical, where N is the CPU's maximum linear-address width). But,
   bits 63:N of SSP must be identical.

Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
 arch/x86/kvm/vmx/nested.c | 47 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index a73f38d7eea1..edb3b877a0f6 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3101,6 +3101,17 @@ static bool is_l1_noncanonical_address_on_vmexit(u64 la, struct vmcs12 *vmcs12)
 	return !__is_canonical_address(la, l1_address_bits_on_exit);
 }
 
+static bool is_valid_cet_state(struct kvm_vcpu *vcpu, u64 s_cet, u64 ssp, u64 ssp_tbl)
+{
+	if (!kvm_is_valid_u_s_cet(vcpu, s_cet) || !IS_ALIGNED(ssp, 4))
+		return false;
+
+	if (is_noncanonical_msr_address(ssp_tbl, vcpu))
+		return false;
+
+	return true;
+}
+
 static int nested_vmx_check_host_state(struct kvm_vcpu *vcpu,
 				       struct vmcs12 *vmcs12)
 {
@@ -3170,6 +3181,26 @@ static int nested_vmx_check_host_state(struct kvm_vcpu *vcpu,
 			return -EINVAL;
 	}
 
+	if (vmcs12->vm_exit_controls & VM_EXIT_LOAD_CET_STATE) {
+		if (CC(!is_valid_cet_state(vcpu, vmcs12->host_s_cet, vmcs12->host_ssp,
+					   vmcs12->host_ssp_tbl)))
+			return -EINVAL;
+
+		/*
+		 * IA32_S_CET and SSP must be canonical if the host will
+		 * enter 64-bit mode after VM-exit; otherwise, higher
+		 * 32-bits must be all 0s.
+		 */
+		if (ia32e) {
+			if (CC(is_noncanonical_msr_address(vmcs12->host_s_cet, vcpu)) ||
+			    CC(is_noncanonical_msr_address(vmcs12->host_ssp, vcpu)))
+				return -EINVAL;
+		} else {
+			if (CC(vmcs12->host_s_cet >> 32) || CC(vmcs12->host_ssp >> 32))
+				return -EINVAL;
+		}
+	}
+
 	return 0;
 }
 
@@ -3280,6 +3311,22 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
 	     CC((vmcs12->guest_bndcfgs & MSR_IA32_BNDCFGS_RSVD))))
 		return -EINVAL;
 
+	if (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_CET_STATE) {
+		if (CC(!is_valid_cet_state(vcpu, vmcs12->guest_s_cet, vmcs12->guest_ssp,
+					   vmcs12->guest_ssp_tbl)))
+			return -EINVAL;
+
+		/*
+		 * Guest SSP must have 63:N bits identical, rather than
+		 * be canonical (i.e., 63:N-1 bits identical), where N is
+		 * the CPU's maximum linear-address width. Similar to
+		 * is_noncanonical_msr_address(), use the host's
+		 * linear-address width.
+		 */
+		if (CC(!__is_canonical_address(vmcs12->guest_ssp, max_host_virt_addr_bits() + 1)))
+			return -EINVAL;
+	}
+
 	if (nested_check_guest_non_reg_state(vmcs12))
 		return -EINVAL;
 
-- 
2.47.3

[PATCH v13 20/21] KVM: nVMX: Advertise new VM-Entry/Exit control bits for CET state

[Chao Gao]

Advertise new VM-Entry/Exit control bits as all nested support for
CET virtualization, including consistency checks, is in place.

Signed-off-by: Chao Gao <chao.gao@intel.com>
---
v13: new
---
 arch/x86/kvm/vmx/nested.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index edb3b877a0f6..d7e2fb30fc1a 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -7176,7 +7176,7 @@ static void nested_vmx_setup_exit_ctls(struct vmcs_config *vmcs_conf,
 		VM_EXIT_HOST_ADDR_SPACE_SIZE |
 #endif
 		VM_EXIT_LOAD_IA32_PAT | VM_EXIT_SAVE_IA32_PAT |
-		VM_EXIT_CLEAR_BNDCFGS;
+		VM_EXIT_CLEAR_BNDCFGS | VM_EXIT_LOAD_CET_STATE;
 	msrs->exit_ctls_high |=
 		VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR |
 		VM_EXIT_LOAD_IA32_EFER | VM_EXIT_SAVE_IA32_EFER |
@@ -7198,7 +7198,8 @@ static void nested_vmx_setup_entry_ctls(struct vmcs_config *vmcs_conf,
 #ifdef CONFIG_X86_64
 		VM_ENTRY_IA32E_MODE |
 #endif
-		VM_ENTRY_LOAD_IA32_PAT | VM_ENTRY_LOAD_BNDCFGS;
+		VM_ENTRY_LOAD_IA32_PAT | VM_ENTRY_LOAD_BNDCFGS |
+		VM_ENTRY_LOAD_CET_STATE;
 	msrs->entry_ctls_high |=
 		(VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR | VM_ENTRY_LOAD_IA32_EFER |
 		 VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL);
-- 
2.47.3

[PATCH v13 21/21] KVM: selftest: Add tests for KVM_{GET,SET}_ONE_REG

[Chao Gao]

Add tests for newly added KVM_{GET,SET}_ONE_REG support for x86. Verify the
new ioctls can read and write real MSRs and synthetic MSRs.

Signed-off-by: Chao Gao <chao.gao@intel.com>
---
 tools/arch/x86/include/uapi/asm/kvm.h         | 24 +++++++++++++
 tools/testing/selftests/kvm/Makefile.kvm      |  1 +
 .../selftests/kvm/x86/get_set_one_reg.c       | 35 +++++++++++++++++++
 3 files changed, 60 insertions(+)
 create mode 100644 tools/testing/selftests/kvm/x86/get_set_one_reg.c

diff --git a/tools/arch/x86/include/uapi/asm/kvm.h b/tools/arch/x86/include/uapi/asm/kvm.h
index 6f3499507c5e..590762820a61 100644
--- a/tools/arch/x86/include/uapi/asm/kvm.h
+++ b/tools/arch/x86/include/uapi/asm/kvm.h
@@ -411,6 +411,30 @@ struct kvm_xcrs {
 	__u64 padding[16];
 };
 
+#define KVM_X86_REG_TYPE_MSR		2
+#define KVM_X86_REG_TYPE_SYNTHETIC_MSR	3
+
+#define KVM_X86_REG_TYPE_SIZE(type)						\
+({										\
+	__u64 type_size = (__u64)type << 32;					\
+										\
+	type_size |= type == KVM_X86_REG_TYPE_MSR ? KVM_REG_SIZE_U64 :		\
+		     type == KVM_X86_REG_TYPE_SYNTHETIC_MSR ? KVM_REG_SIZE_U64 :\
+		     0;								\
+	type_size;								\
+})
+
+#define KVM_X86_REG_ENCODE(type, index)				\
+	(KVM_REG_X86 | KVM_X86_REG_TYPE_SIZE(type) | index)
+
+#define KVM_X86_REG_MSR(index)					\
+	KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_MSR, index)
+#define KVM_X86_REG_SYNTHETIC_MSR(index)			\
+	KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_SYNTHETIC_MSR, index)
+
+/* KVM synthetic MSR index staring from 0 */
+#define KVM_SYNTHETIC_GUEST_SSP 0
+
 #define KVM_SYNC_X86_REGS      (1UL << 0)
 #define KVM_SYNC_X86_SREGS     (1UL << 1)
 #define KVM_SYNC_X86_EVENTS    (1UL << 2)
diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index f6fe7a07a0a2..9a375d5faf1c 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -136,6 +136,7 @@ TEST_GEN_PROGS_x86 += x86/max_vcpuid_cap_test
 TEST_GEN_PROGS_x86 += x86/triple_fault_event_test
 TEST_GEN_PROGS_x86 += x86/recalc_apic_map_test
 TEST_GEN_PROGS_x86 += x86/aperfmperf_test
+TEST_GEN_PROGS_x86 += x86/get_set_one_reg
 TEST_GEN_PROGS_x86 += access_tracking_perf_test
 TEST_GEN_PROGS_x86 += coalesced_io_test
 TEST_GEN_PROGS_x86 += dirty_log_perf_test
diff --git a/tools/testing/selftests/kvm/x86/get_set_one_reg.c b/tools/testing/selftests/kvm/x86/get_set_one_reg.c
new file mode 100644
index 000000000000..8b069155ddc7
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86/get_set_one_reg.c
@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <fcntl.h>
+#include <stdint.h>
+#include <sys/ioctl.h>
+
+#include "test_util.h"
+#include "kvm_util.h"
+#include "processor.h"
+
+int main(int argc, char *argv[])
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	u64 data;
+	int r;
+
+	TEST_REQUIRE(kvm_has_cap(KVM_CAP_ONE_REG));
+
+	vm = vm_create_with_one_vcpu(&vcpu, NULL);
+
+	TEST_ASSERT_EQ(__vcpu_get_reg(vcpu, KVM_X86_REG_MSR(MSR_EFER), &data), 0);
+	TEST_ASSERT_EQ(__vcpu_set_reg(vcpu, KVM_X86_REG_MSR(MSR_EFER), data), 0);
+
+	if (kvm_cpu_has(X86_FEATURE_SHSTK)) {
+		r = __vcpu_get_reg(vcpu, KVM_X86_REG_SYNTHETIC_MSR(KVM_SYNTHETIC_GUEST_SSP),
+				   &data);
+		TEST_ASSERT_EQ(r, 0);
+		r = __vcpu_set_reg(vcpu, KVM_X86_REG_SYNTHETIC_MSR(KVM_SYNTHETIC_GUEST_SSP),
+				   data);
+		TEST_ASSERT_EQ(r, 0);
+	}
+
+	kvm_vm_free(vm);
+	return 0;
+}
-- 
2.47.3

Re: [PATCH v13 00/21] Enable CET Virtualization

[Chao Gao]

On Thu, Aug 21, 2025 at 06:30:34AM -0700, Chao Gao wrote:
>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 v13
>1. Add "arch" and "size" fields to the register ID used in
>   KVM_GET/SET_ONE_REG ioctls
>2. Add a kselftest for KVM_GET/SET_ONE_REG ioctls
>3. Advertise KVM_CAP_ONE_REG
>4. Document how the emulation of SSP MSRs is flawed for 32-bit guests
>5. Don't pass-thru MSR_IA32_INT_SSP_TAB and report it as unsupported for
>   32-bit guests
>6. Refine changelog to clarify why CET MSRs are pass-thru'd.
>7. Limit SHSTK to 64-bit kernels
>8. Retain CET state if L1 doesn't set VM_EXIT_LOAD_CET_STATE
>9. Rename a new functions for clarity

below is the diff between v12 and v13:

diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index a4870d9c9279..478d9b63a9db 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -411,15 +411,26 @@ struct kvm_xcrs {
 	__u64 padding[16];
 };
 
-#define KVM_X86_REG_MSR			(1 << 2)
-#define KVM_X86_REG_SYNTHETIC		(1 << 3)
-
-struct kvm_x86_reg_id {
-	__u32 index;
-	__u8 type;
-	__u8 rsvd;
-	__u16 rsvd16;
-};
+#define KVM_X86_REG_TYPE_MSR		2
+#define KVM_X86_REG_TYPE_SYNTHETIC_MSR	3
+
+#define KVM_X86_REG_TYPE_SIZE(type)						\
+({										\
+	__u64 type_size = (__u64)type << 32;					\
+										\
+	type_size |= type == KVM_X86_REG_TYPE_MSR ? KVM_REG_SIZE_U64 :		\
+		     type == KVM_X86_REG_TYPE_SYNTHETIC_MSR ? KVM_REG_SIZE_U64 :\
+		     0;								\
+	type_size;								\
+})
+
+#define KVM_X86_REG_ENCODE(type, index)				\
+	(KVM_REG_X86 | KVM_X86_REG_TYPE_SIZE(type) | index)
+
+#define KVM_X86_REG_MSR(index)					\
+	KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_MSR, index)
+#define KVM_X86_REG_SYNTHETIC_MSR(index)			\
+	KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_SYNTHETIC_MSR, index)
 
 /* KVM synthetic MSR index staring from 0 */
 #define KVM_SYNTHETIC_GUEST_SSP 0
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index d0c08aab3e3a..ee05b876c656 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -944,7 +944,7 @@ void kvm_set_cpu_caps(void)
 		VENDOR_F(WAITPKG),
 		F(SGX_LC),
 		F(BUS_LOCK_DETECT),
-		F(SHSTK),
+		X86_64_F(SHSTK),
 	);
 
 	/*
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 092c91af8f0c..d7e2fb30fc1a 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -739,9 +739,6 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
 	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
 					 MSR_IA32_PL3_SSP, MSR_TYPE_RW);
 
-	nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
-					 MSR_IA32_INT_SSP_TAB, MSR_TYPE_RW);
-
 	kvm_vcpu_unmap(vcpu, &map);
 
 	vmx->nested.force_msr_bitmap_recalc = false;
@@ -2542,8 +2539,8 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct loaded_vmcs *vmcs0
 	}
 }
 
-static inline void cet_vmcs_fields_get(struct kvm_vcpu *vcpu, u64 *s_cet,
-				       u64 *ssp, u64 *ssp_tbl)
+static void vmcs_read_cet_state(struct kvm_vcpu *vcpu, u64 *s_cet,
+				u64 *ssp, u64 *ssp_tbl)
 {
 	if (guest_cpu_cap_has(vcpu, X86_FEATURE_IBT) ||
 	    guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK))
@@ -2555,8 +2552,8 @@ static inline void cet_vmcs_fields_get(struct kvm_vcpu *vcpu, u64 *s_cet,
 	}
 }
 
-static inline void cet_vmcs_fields_set(struct kvm_vcpu *vcpu, u64 s_cet,
-				       u64 ssp, u64 ssp_tbl)
+static void vmcs_write_cet_state(struct kvm_vcpu *vcpu, u64 s_cet,
+				 u64 ssp, u64 ssp_tbl)
 {
 	if (guest_cpu_cap_has(vcpu, X86_FEATURE_IBT) ||
 	    guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK))
@@ -2685,8 +2682,8 @@ static void prepare_vmcs02_rare(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
 	vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, vmx->msr_autoload.guest.nr);
 
 	if (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_CET_STATE)
-		cet_vmcs_fields_set(&vmx->vcpu, vmcs12->guest_s_cet,
-				    vmcs12->guest_ssp, vmcs12->guest_ssp_tbl);
+		vmcs_write_cet_state(&vmx->vcpu, vmcs12->guest_s_cet,
+				     vmcs12->guest_ssp, vmcs12->guest_ssp_tbl);
 
 	set_cr4_guest_host_mask(vmx);
 }
@@ -2730,9 +2727,9 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
 
 	if (!vmx->nested.nested_run_pending ||
 	    !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_CET_STATE))
-		cet_vmcs_fields_set(vcpu, vmx->nested.pre_vmenter_s_cet,
-				    vmx->nested.pre_vmenter_ssp,
-				    vmx->nested.pre_vmenter_ssp_tbl);
+		vmcs_write_cet_state(vcpu, vmx->nested.pre_vmenter_s_cet,
+				     vmx->nested.pre_vmenter_ssp,
+				     vmx->nested.pre_vmenter_ssp_tbl);
 
 	if (kvm_mpx_supported() && (!vmx->nested.nested_run_pending ||
 	    !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_BNDCFGS)))
@@ -3106,7 +3103,7 @@ static bool is_l1_noncanonical_address_on_vmexit(u64 la, struct vmcs12 *vmcs12)
 
 static bool is_valid_cet_state(struct kvm_vcpu *vcpu, u64 s_cet, u64 ssp, u64 ssp_tbl)
 {
-	if (!is_cet_msr_valid(vcpu, s_cet) || !IS_ALIGNED(ssp, 4))
+	if (!kvm_is_valid_u_s_cet(vcpu, s_cet) || !IS_ALIGNED(ssp, 4))
 		return false;
 
 	if (is_noncanonical_msr_address(ssp_tbl, vcpu))
@@ -3665,7 +3662,7 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
 
 	if (!vmx->nested.nested_run_pending ||
 	    !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_CET_STATE))
-		cet_vmcs_fields_get(vcpu, &vmx->nested.pre_vmenter_s_cet,
+		vmcs_read_cet_state(vcpu, &vmx->nested.pre_vmenter_s_cet,
 				    &vmx->nested.pre_vmenter_ssp,
 				    &vmx->nested.pre_vmenter_ssp_tbl);
 
@@ -4596,9 +4593,6 @@ static bool is_vmcs12_ext_field(unsigned long field)
 	case GUEST_IDTR_BASE:
 	case GUEST_PENDING_DBG_EXCEPTIONS:
 	case GUEST_BNDCFGS:
-	case GUEST_S_CET:
-	case GUEST_SSP:
-	case GUEST_INTR_SSP_TABLE:
 		return true;
 	default:
 		break;
@@ -4649,10 +4643,6 @@ static void sync_vmcs02_to_vmcs12_rare(struct kvm_vcpu *vcpu,
 	vmcs12->guest_pending_dbg_exceptions =
 		vmcs_readl(GUEST_PENDING_DBG_EXCEPTIONS);
 
-	cet_vmcs_fields_get(&vmx->vcpu, &vmcs12->guest_s_cet,
-			    &vmcs12->guest_ssp,
-			    &vmcs12->guest_ssp_tbl);
-
 	vmx->nested.need_sync_vmcs02_to_vmcs12_rare = false;
 }
 
@@ -4759,6 +4749,10 @@ static void sync_vmcs02_to_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 
 	if (vmcs12->vm_exit_controls & VM_EXIT_SAVE_IA32_EFER)
 		vmcs12->guest_ia32_efer = vcpu->arch.efer;
+
+	vmcs_read_cet_state(&vmx->vcpu, &vmcs12->guest_s_cet,
+			    &vmcs12->guest_ssp,
+			    &vmcs12->guest_ssp_tbl);
 }
 
 /*
@@ -4884,9 +4878,17 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
 	if (vmcs12->vm_exit_controls & VM_EXIT_CLEAR_BNDCFGS)
 		vmcs_write64(GUEST_BNDCFGS, 0);
 
+	/*
+	 * Load CET state from host state if VM_EXIT_LOAD_CET_STATE is set.
+	 * otherwise CET state should be retained across VM-exit, i.e.,
+	 * guest values should be propagated from vmcs12 to vmcs01.
+	 */
 	if (vmcs12->vm_exit_controls & VM_EXIT_LOAD_CET_STATE)
-		cet_vmcs_fields_set(vcpu, vmcs12->host_s_cet, vmcs12->host_ssp,
-				    vmcs12->host_ssp_tbl);
+		vmcs_write_cet_state(vcpu, vmcs12->host_s_cet, vmcs12->host_ssp,
+				     vmcs12->host_ssp_tbl);
+	else
+		vmcs_write_cet_state(vcpu, vmcs12->guest_s_cet, vmcs12->guest_ssp,
+				     vmcs12->guest_ssp_tbl);
 
 	if (vmcs12->vm_exit_controls & VM_EXIT_LOAD_IA32_PAT) {
 		vmcs_write64(GUEST_IA32_PAT, vmcs12->host_ia32_pat);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 294a294f0d0d..989008f5307e 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4102,7 +4102,7 @@ void pt_update_intercept_for_msr(struct kvm_vcpu *vcpu)
 
 void vmx_recalc_msr_intercepts(struct kvm_vcpu *vcpu)
 {
-	bool set;
+	bool intercept;
 
 	if (!cpu_has_vmx_msr_bitmap())
 		return;
@@ -4150,21 +4150,20 @@ void vmx_recalc_msr_intercepts(struct kvm_vcpu *vcpu)
 					  !guest_cpu_cap_has(vcpu, X86_FEATURE_FLUSH_L1D));
 
 	if (kvm_cpu_cap_has(X86_FEATURE_SHSTK)) {
-		set = !guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK);
+		intercept = !guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK);
 
-		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL0_SSP, MSR_TYPE_RW, set);
-		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL1_SSP, MSR_TYPE_RW, set);
-		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL2_SSP, MSR_TYPE_RW, set);
-		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL3_SSP, MSR_TYPE_RW, set);
-		vmx_set_intercept_for_msr(vcpu, MSR_IA32_INT_SSP_TAB, MSR_TYPE_RW, set);
+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL0_SSP, MSR_TYPE_RW, intercept);
+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL1_SSP, MSR_TYPE_RW, intercept);
+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL2_SSP, MSR_TYPE_RW, intercept);
+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL3_SSP, MSR_TYPE_RW, intercept);
 	}
 
 	if (kvm_cpu_cap_has(X86_FEATURE_SHSTK) || kvm_cpu_cap_has(X86_FEATURE_IBT)) {
-		set = !guest_cpu_cap_has(vcpu, X86_FEATURE_IBT) &&
-		      !guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK);
+		intercept = !guest_cpu_cap_has(vcpu, X86_FEATURE_IBT) &&
+			    !guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK);
 
-		vmx_set_intercept_for_msr(vcpu, MSR_IA32_U_CET, MSR_TYPE_RW, set);
-		vmx_set_intercept_for_msr(vcpu, MSR_IA32_S_CET, MSR_TYPE_RW, set);
+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_U_CET, MSR_TYPE_RW, intercept);
+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_S_CET, MSR_TYPE_RW, intercept);
 	}
 
 	/*
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f2b89190a200..9930678f5a3b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1892,16 +1892,33 @@ static int __kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data,
 		if (!guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK) &&
 		    !guest_cpu_cap_has(vcpu, X86_FEATURE_IBT))
 			return KVM_MSR_RET_UNSUPPORTED;
-		if (!is_cet_msr_valid(vcpu, data))
+		if (!kvm_is_valid_u_s_cet(vcpu, data))
 			return 1;
 		break;
 	case MSR_KVM_INTERNAL_GUEST_SSP:
 		if (!host_initiated)
 			return 1;
 		fallthrough;
+		/*
+		 * Note that the MSR emulation here is flawed when a vCPU
+		 * doesn't support the Intel 64 architecture. The expected
+		 * architectural behavior in this case is that the upper 32
+		 * bits do not exist and should always read '0'. However,
+		 * because the actual hardware on which the virtual CPU is
+		 * running does support Intel 64, XRSTORS/XSAVES in the
+		 * guest could observe behavior that violates the
+		 * architecture. Intercepting XRSTORS/XSAVES for this
+		 * special case isn't deemed worthwhile.
+		 */
 	case MSR_IA32_PL0_SSP ... MSR_IA32_INT_SSP_TAB:
 		if (!guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK))
 			return KVM_MSR_RET_UNSUPPORTED;
+		/*
+		 * MSR_IA32_INT_SSP_TAB is not present on processors that do
+		 * not support Intel 64 architecture.
+		 */
+		if (index == MSR_IA32_INT_SSP_TAB && !guest_cpu_cap_has(vcpu, X86_FEATURE_LM))
+			return KVM_MSR_RET_UNSUPPORTED;
 		if (is_noncanonical_msr_address(data, vcpu))
 			return 1;
 		/* All SSP MSRs except MSR_IA32_INT_SSP_TAB must be 4-byte aligned */
@@ -4852,6 +4869,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_IRQFD_RESAMPLE:
 	case KVM_CAP_MEMORY_FAULT_INFO:
 	case KVM_CAP_X86_GUEST_MODE:
+	case KVM_CAP_ONE_REG:
 		r = 1;
 		break;
 	case KVM_CAP_PRE_FAULT_MEMORY:
@@ -6030,11 +6048,20 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
 	}
 }
 
+struct kvm_x86_reg_id {
+	__u32 index;
+	__u8  type;
+	__u8  rsvd;
+	__u8  rsvd4:4;
+	__u8  size:4;
+	__u8  x86;
+};
+
 static int kvm_translate_synthetic_msr(struct kvm_x86_reg_id *reg)
 {
 	switch (reg->index) {
 	case KVM_SYNTHETIC_GUEST_SSP:
-		reg->type = KVM_X86_REG_MSR;
+		reg->type = KVM_X86_REG_TYPE_MSR;
 		reg->index = MSR_KVM_INTERNAL_GUEST_SSP;
 		break;
 	default:
@@ -6170,22 +6197,28 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 			break;
 
 		r = -EINVAL;
+		if ((reg.id & KVM_REG_ARCH_MASK) != KVM_REG_X86)
+			break;
+
 		id = (struct kvm_x86_reg_id *)&reg.id;
-		if (id->rsvd || id->rsvd16)
+		if (id->rsvd || id->rsvd4)
+			break;
+
+		if (id->type != KVM_X86_REG_TYPE_MSR &&
+		    id->type != KVM_X86_REG_TYPE_SYNTHETIC_MSR)
 			break;
 
-		if (id->type != KVM_X86_REG_MSR &&
-		    id->type != KVM_X86_REG_SYNTHETIC)
+		if ((reg.id & KVM_REG_SIZE_MASK) != KVM_REG_SIZE_U64)
 			break;
 
-		if (id->type == KVM_X86_REG_SYNTHETIC) {
+		if (id->type == KVM_X86_REG_TYPE_SYNTHETIC_MSR) {
 			r = kvm_translate_synthetic_msr(id);
 			if (r)
 				break;
 		}
 
 		r = -EINVAL;
-		if (id->type != KVM_X86_REG_MSR)
+		if (id->type != KVM_X86_REG_TYPE_MSR)
 			break;
 
 		value = u64_to_user_ptr(reg.addr);
@@ -9862,7 +9895,7 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
 	}
 
 	if (boot_cpu_has(X86_FEATURE_SHSTK)) {
-		rdmsrl(MSR_IA32_S_CET, kvm_host.s_cet);
+		rdmsrq(MSR_IA32_S_CET, kvm_host.s_cet);
 		/*
 		 * Linux doesn't yet support supervisor shadow stacks (SSS), so
 		 * KVM doesn't save/restore the associated MSRs, i.e. KVM may
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index d0b91e3ad9ec..d6b21ba41416 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -744,7 +744,7 @@ static inline void kvm_set_xstate_msr(struct kvm_vcpu *vcpu,
 #define CET_US_IBT_MASK_BITS		(GENMASK_ULL(5, 2) | GENMASK_ULL(63, 10))
 #define CET_US_LEGACY_BITMAP_BASE(data)	((data) >> 12)
 
-static inline bool is_cet_msr_valid(struct kvm_vcpu *vcpu, u64 data)
+static inline bool kvm_is_valid_u_s_cet(struct kvm_vcpu *vcpu, u64 data)
 {
 	if (data & CET_US_RESERVED_BITS)
 		return false;
diff --git a/tools/arch/x86/include/uapi/asm/kvm.h b/tools/arch/x86/include/uapi/asm/kvm.h
index 6f3499507c5e..590762820a61 100644
--- a/tools/arch/x86/include/uapi/asm/kvm.h
+++ b/tools/arch/x86/include/uapi/asm/kvm.h
@@ -411,6 +411,30 @@ struct kvm_xcrs {
 	__u64 padding[16];
 };
 
+#define KVM_X86_REG_TYPE_MSR		2
+#define KVM_X86_REG_TYPE_SYNTHETIC_MSR	3
+
+#define KVM_X86_REG_TYPE_SIZE(type)						\
+({										\
+	__u64 type_size = (__u64)type << 32;					\
+										\
+	type_size |= type == KVM_X86_REG_TYPE_MSR ? KVM_REG_SIZE_U64 :		\
+		     type == KVM_X86_REG_TYPE_SYNTHETIC_MSR ? KVM_REG_SIZE_U64 :\
+		     0;								\
+	type_size;								\
+})
+
+#define KVM_X86_REG_ENCODE(type, index)				\
+	(KVM_REG_X86 | KVM_X86_REG_TYPE_SIZE(type) | index)
+
+#define KVM_X86_REG_MSR(index)					\
+	KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_MSR, index)
+#define KVM_X86_REG_SYNTHETIC_MSR(index)			\
+	KVM_X86_REG_ENCODE(KVM_X86_REG_TYPE_SYNTHETIC_MSR, index)
+
+/* KVM synthetic MSR index staring from 0 */
+#define KVM_SYNTHETIC_GUEST_SSP 0
+
 #define KVM_SYNC_X86_REGS      (1UL << 0)
 #define KVM_SYNC_X86_SREGS     (1UL << 1)
 #define KVM_SYNC_X86_EVENTS    (1UL << 2)
diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index f6fe7a07a0a2..9a375d5faf1c 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -136,6 +136,7 @@ TEST_GEN_PROGS_x86 += x86/max_vcpuid_cap_test
 TEST_GEN_PROGS_x86 += x86/triple_fault_event_test
 TEST_GEN_PROGS_x86 += x86/recalc_apic_map_test
 TEST_GEN_PROGS_x86 += x86/aperfmperf_test
+TEST_GEN_PROGS_x86 += x86/get_set_one_reg
 TEST_GEN_PROGS_x86 += access_tracking_perf_test
 TEST_GEN_PROGS_x86 += coalesced_io_test
 TEST_GEN_PROGS_x86 += dirty_log_perf_test
diff --git a/tools/testing/selftests/kvm/x86/get_set_one_reg.c b/tools/testing/selftests/kvm/x86/get_set_one_reg.c
new file mode 100644
index 000000000000..8b069155ddc7
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86/get_set_one_reg.c
@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <fcntl.h>
+#include <stdint.h>
+#include <sys/ioctl.h>
+
+#include "test_util.h"
+#include "kvm_util.h"
+#include "processor.h"
+
+int main(int argc, char *argv[])
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	u64 data;
+	int r;
+
+	TEST_REQUIRE(kvm_has_cap(KVM_CAP_ONE_REG));
+
+	vm = vm_create_with_one_vcpu(&vcpu, NULL);
+
+	TEST_ASSERT_EQ(__vcpu_get_reg(vcpu, KVM_X86_REG_MSR(MSR_EFER), &data), 0);
+	TEST_ASSERT_EQ(__vcpu_set_reg(vcpu, KVM_X86_REG_MSR(MSR_EFER), data), 0);
+
+	if (kvm_cpu_has(X86_FEATURE_SHSTK)) {
+		r = __vcpu_get_reg(vcpu, KVM_X86_REG_SYNTHETIC_MSR(KVM_SYNTHETIC_GUEST_SSP),
+				   &data);
+		TEST_ASSERT_EQ(r, 0);
+		r = __vcpu_set_reg(vcpu, KVM_X86_REG_SYNTHETIC_MSR(KVM_SYNTHETIC_GUEST_SSP),
+				   data);
+		TEST_ASSERT_EQ(r, 0);
+	}
+
+	kvm_vm_free(vm);
+	return 0;
+}