[kvm-unit-tests PATCH v3 09/17] x86: cet: Validate CET states during VMX transitions

Sean Christopherson
2025-11-14T00:13:16Z

From: Chao Gao <chao.gao@intel.com>

Add tests to verify that CET states are correctly handled during VMX
transitions.

The following behaviors are verified:

1. Host states are loaded from VMCS iff "Load CET" VM-exit control is set
2. Guest states are loaded from VMCS iff "Load CET" VM-entry control is set
3. Guest states are saved to VMCS during VM exits unconditionally
4. Invalid guest or host CET states leads to VM entry failures.

Signed-off-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
lib/x86/msr.h | 1 +
x86/unittests.cfg | 7 ++++
x86/vmx.h | 8 +++--
x86/vmx_tests.c | 81 +++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 95 insertions(+), 2 deletions(-)

diff --git a/lib/x86/msr.h b/lib/x86/msr.h
index cc4cb855..df6d3049 100644
--- a/lib/x86/msr.h
+++ b/lib/x86/msr.h
@@ -296,6 +296,7 @@
#define MSR_IA32_FEATURE_CONTROL 0x0000003a
#define MSR_IA32_TSC_ADJUST 0x0000003b
#define MSR_IA32_U_CET 0x000006a0
+#define MSR_IA32_S_CET 0x000006a2
#define MSR_IA32_PL3_SSP 0x000006a7
#define MSR_IA32_PKRS 0x000006e1

diff --git a/x86/unittests.cfg b/x86/unittests.cfg
index acb8a8ba..ec07d26b 100644
--- a/x86/unittests.cfg
+++ b/x86/unittests.cfg
@@ -453,6 +453,13 @@ arch = x86_64
groups = vmx nested_exception
check = /sys/module/kvm_intel/parameters/allow_smaller_maxphyaddr=Y

+[vmx_cet_test]
+file = vmx.flat
+extra_params = -cpu max,+vmx -append "vmx_cet_test"
+arch = x86_64
+groups = vmx
+timeout = 240
+
[debug]
file = debug.flat
arch = x86_64
diff --git a/x86/vmx.h b/x86/vmx.h
index 9cd90488..33373bd1 100644
--- a/x86/vmx.h
+++ b/x86/vmx.h
@@ -356,6 +356,7 @@ enum Encoding {
GUEST_PENDING_DEBUG = 0x6822ul,
GUEST_SYSENTER_ESP = 0x6824ul,
GUEST_SYSENTER_EIP = 0x6826ul,
+ GUEST_S_CET = 0x6828ul,

/* Natural-Width Host State Fields */
HOST_CR0 = 0x6c00ul,
@@ -369,7 +370,8 @@ enum Encoding {
HOST_SYSENTER_ESP = 0x6c10ul,
HOST_SYSENTER_EIP = 0x6c12ul,
HOST_RSP = 0x6c14ul,
- HOST_RIP = 0x6c16ul
+ HOST_RIP = 0x6c16ul,
+ HOST_S_CET = 0x6c18ul,
};

#define VMX_ENTRY_FAILURE (1ul << 31)
@@ -449,6 +451,7 @@ enum Ctrl_exi {
EXI_SAVE_EFER = 1UL << 20,
EXI_LOAD_EFER = 1UL << 21,
EXI_SAVE_PREEMPT = 1UL << 22,
+ EXI_LOAD_CET = 1UL << 28,
};

enum Ctrl_ent {
@@ -457,7 +460,8 @@ enum Ctrl_ent {
ENT_LOAD_PERF = 1UL << 13,
ENT_LOAD_PAT = 1UL << 14,
ENT_LOAD_EFER = 1UL << 15,
- ENT_LOAD_BNDCFGS = 1UL << 16
+ ENT_LOAD_BNDCFGS = 1UL << 16,
+ ENT_LOAD_CET = 1UL << 20,
};

enum Ctrl_pin {
diff --git a/x86/vmx_tests.c b/x86/vmx_tests.c
index 0b3cfe50..6383bc83 100644
--- a/x86/vmx_tests.c
+++ b/x86/vmx_tests.c
@@ -11377,6 +11377,85 @@ static void vmx_posted_interrupts_test(void)
enter_guest();
}

+static u64 guest_s_cet = -1;
+
+static void vmx_cet_test_guest(void)
+{
+ guest_s_cet = rdmsr(MSR_IA32_S_CET);
+ vmcall();
+}
+
+static void vmx_cet_test(void)
+{
+ struct vmcs *curr;
+ u64 val;
+
+ if (!(ctrl_exit_rev.clr & EXI_LOAD_CET)) {
+ report_skip("Load CET state exit control is not available");
+ return;
+ }
+
+ if (!(ctrl_enter_rev.clr & ENT_LOAD_CET)) {
+ report_skip("Load CET state entry control is not available");
+ return;
+ }
+
+ /* Allow the guest to read GUEST_S_CET directly */
+ msr_bmp_init();
+
+ /*
+ * Check whether VMCS transitions load host and guest values
+ * according to the settings of the relevant VM-entry and exit
+ * controls.
+ */
+ vmcs_write(HOST_S_CET, 2);
+ vmcs_write(GUEST_S_CET, 2);
+ test_set_guest(vmx_cet_test_guest);
+
+ enter_guest();
+ val = rdmsr(MSR_IA32_S_CET);
+
+ /* Validate both guest/host S_CET MSR have the default values */
+ report(val == 0 && guest_s_cet == 0, "Load CET state disabled");
+
+ /*
+ * CPU supports the 1-setting of the 'load CET' VM-entry control,
+ * the contents of the IA32_S_CET and IA32_INTERRUPT_SSP_TABLE_ADDR
+ * MSRs are saved into the corresponding fields
+ */
+ report(vmcs_read(GUEST_S_CET) == 0, "S_CET is unconditionally saved");
+
+ /* Enable load CET state entry/exit controls and retest */
+ vmcs_set_bits(EXI_CONTROLS, EXI_LOAD_CET);
+ vmcs_set_bits(ENT_CONTROLS, ENT_LOAD_CET);
+ vmcs_write(GUEST_S_CET, 2);
+ test_override_guest(vmx_cet_test_guest);
+
+ enter_guest();
+ val = rdmsr(MSR_IA32_S_CET);
+
+ /* Validate both guest/host S_CET MSR are loaded from VMCS */
+ report(val == 2 && guest_s_cet == 2, "Load CET state enabled");
+
+ /*
+ * Validate that bit 10 (SUPPRESS) and Bit 11 (TRACKER) cannot be
+ * both set
+ */
+ val = BIT(10) | BIT(11);
+ vmcs_write(GUEST_S_CET, val);
+ test_guest_state("Load invalid guest CET state", true, val, "GUEST_S_CET");
+
+ /* Following test_vmx_vmlaunch() needs a "not launched" VMCS */
+ vmcs_save(&curr);
+ vmcs_clear(curr);
+ make_vmcs_current(curr);
+
+ vmcs_write(HOST_S_CET, val);
+ test_vmx_vmlaunch(VMXERR_ENTRY_INVALID_HOST_STATE_FIELD);
+
+ test_set_guest_finished();
+}
+
#define TEST(name) { #name, .v2 = name }

/* name/init/guest_main/exit_handler/syscall_handler/guest_regs */
@@ -11490,5 +11569,7 @@ struct vmx_test vmx_tests[] = {
TEST(vmx_pf_vpid_test),
TEST(vmx_exception_test),
TEST(vmx_canonical_test),
+ /* "Load CET" VM-entry/exit controls tests. */
+ TEST(vmx_cet_test),
{ NULL, NULL, NULL, NULL, NULL, {0} },
};
--
2.52.0.rc1.455.g30608eb744-goog