[PATCH v16 46/51] KVM: selftests: Add support for MSR_IA32_{S,U}_CET to MSRs test

Sean Christopherson
2025-09-19T22:34:27Z

Extend the MSRs test to support {S,U}_CET, which are a bit of a pain to
handled due to the MSRs existing if IBT *or* SHSTK is supported. To deal
with Intel's wonderful decision to bundle IBT and SHSTK under CET, track
the second feature, but skip only RDMSR #GP tests to avoid false failures
when running on a CPU with only one of IBT or SHSTK (the WRMSR #GP tests
are still valid since the enable bits are per-feature).

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
tools/testing/selftests/kvm/x86/msrs_test.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86/msrs_test.c b/tools/testing/selftests/kvm/x86/msrs_test.c
index 9285cf51ef75..952439e0c754 100644
--- a/tools/testing/selftests/kvm/x86/msrs_test.c
+++ b/tools/testing/selftests/kvm/x86/msrs_test.c
@@ -125,13 +125,26 @@ static void guest_test_unsupported_msr(const struct kvm_msr *msr)
if (ignore_unsupported_msrs)
goto skip_wrmsr_gp;

- if (this_cpu_has(msr->feature2))
- goto skip_wrmsr_gp;
+ /*
+ * {S,U}_CET exist if IBT or SHSTK is supported, but with bits that are
+ * writable only if their associated feature is supported. Skip the
+ * RDMSR #GP test if the secondary feature is supported, but perform
+ * the WRMSR #GP test as the to-be-written value is tied to the primary
+ * feature. For all other MSRs, simply do nothing.
+ */
+ if (this_cpu_has(msr->feature2)) {
+ if (msr->index != MSR_IA32_U_CET &&
+ msr->index != MSR_IA32_S_CET)
+ goto skip_wrmsr_gp;
+
+ goto skip_rdmsr_gp;
+ }

vec = rdmsr_safe(msr->index, &val);
__GUEST_ASSERT(vec == GP_VECTOR, "Wanted #GP on RDMSR(0x%x), got %s",
msr->index, ex_str(vec));

+skip_rdmsr_gp:
vec = wrmsr_safe(msr->index, msr->write_val);
__GUEST_ASSERT(vec == GP_VECTOR, "Wanted #GP on WRMSR(0x%x, 0x%lx), got %s",
msr->index, msr->write_val, ex_str(vec));
@@ -269,6 +282,10 @@ static void test_msrs(void)
MSR_TEST_CANONICAL(MSR_CSTAR, LM),
MSR_TEST(MSR_SYSCALL_MASK, 0xffffffff, 0, LM),

+ MSR_TEST2(MSR_IA32_S_CET, CET_SHSTK_EN, CET_RESERVED, SHSTK, IBT),
+ MSR_TEST2(MSR_IA32_S_CET, CET_ENDBR_EN, CET_RESERVED, IBT, SHSTK),
+ MSR_TEST2(MSR_IA32_U_CET, CET_SHSTK_EN, CET_RESERVED, SHSTK, IBT),
+ MSR_TEST2(MSR_IA32_U_CET, CET_ENDBR_EN, CET_RESERVED, IBT, SHSTK),
MSR_TEST_CANONICAL(MSR_IA32_PL0_SSP, SHSTK),
MSR_TEST(MSR_IA32_PL0_SSP, canonical_val, canonical_val | 1, SHSTK),
MSR_TEST_CANONICAL(MSR_IA32_PL1_SSP, SHSTK),
--
2.51.0.470.ga7dc726c21-goog