KVM: selftests: Add support for MSR_IA32_{S,U}_CET to MSRs test

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).

Reviewed-by: Chao Gao <chao.gao@intel.com>
Link: https://lore.kernel.org/r/20250919223258.1604852-47-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/tools/testing/selftests/kvm/x86/msrs_test.c b/tools/testing/selftests/kvm/x86/msrs_test.c
index 345a39030a0a63c8e62fabfd79dd6572e579c9c7..1efaebb986c4e8dd7da554b0f942844b94cf4747 100644 (file)
--- a/tools/testing/selftests/kvm/x86/msrs_test.c
+++ b/tools/testing/selftests/kvm/x86/msrs_test.c
@@ -132,13 +132,26 @@ 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));
@@ -276,6 +289,10 @@ 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),