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

Validate that writing invalid values to SSP MSRs triggers a #GP exception.
This verifies that necessary validity checks are performed by the hardware
or the underlying VMM.

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>
---
 x86/cet.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/x86/cet.c b/x86/cet.c
index 8c2cf8c6..80864fb1 100644
--- a/x86/cet.c
+++ b/x86/cet.c
@@ -56,6 +56,7 @@ int main(int ac, char **av)
 	char *shstk_virt;
 	unsigned long shstk_phys;
 	pteval_t pte = 0;
+	u8 vector;
 	bool rvc;
 
 	if (!this_cpu_has(X86_FEATURE_SHSTK)) {
@@ -105,5 +106,9 @@ int main(int ac, char **av)
 	write_cr4(read_cr4() & ~X86_CR4_CET);
 	wrmsr(MSR_IA32_U_CET, 0);
 
+	/* SSP should be 4-Byte aligned */
+	vector = wrmsr_safe(MSR_IA32_PL3_SSP, 0x1);
+	report(vector == GP_VECTOR, "MSR_IA32_PL3_SSP alignment test.");
+
 	return report_summary();
 }
-- 
2.52.0.rc1.455.g30608eb744-goog