Tinkering with UUIDs is a perilious task, and the KVM UUID gets
broken at times. In order to spot this early enough, add a selftest
that will shout if the expected value isn't found.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Sebastian Ott <sebott@redhat.com>
Link: https://lore.kernel.org/r/20250721130558.50823-1-jackabt.amazon@gmail.com
---
 tools/testing/selftests/kvm/Makefile.kvm     |  1 +
 tools/testing/selftests/kvm/arm64/kvm-uuid.c | 70 ++++++++++++++++++++
 2 files changed, 71 insertions(+)
 create mode 100644 tools/testing/selftests/kvm/arm64/kvm-uuid.c

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index ce817a975e50a..e1eb1ba238a2a 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -167,6 +167,7 @@ TEST_GEN_PROGS_arm64 += arm64/vgic_irq
 TEST_GEN_PROGS_arm64 += arm64/vgic_lpi_stress
 TEST_GEN_PROGS_arm64 += arm64/vpmu_counter_access
 TEST_GEN_PROGS_arm64 += arm64/no-vgic-v3
+TEST_GEN_PROGS_arm64 += arm64/kvm-uuid
 TEST_GEN_PROGS_arm64 += access_tracking_perf_test
 TEST_GEN_PROGS_arm64 += arch_timer
 TEST_GEN_PROGS_arm64 += coalesced_io_test
diff --git a/tools/testing/selftests/kvm/arm64/kvm-uuid.c b/tools/testing/selftests/kvm/arm64/kvm-uuid.c
new file mode 100644
index 0000000000000..af9581b860f14
--- /dev/null
+++ b/tools/testing/selftests/kvm/arm64/kvm-uuid.c
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Check that nobody has tampered with KVM's UID
+
+#include <errno.h>
+#include <linux/arm-smccc.h>
+#include <asm/kvm.h>
+#include <kvm_util.h>
+
+#include "processor.h"
+
+/*
+ * Do NOT redefine these constants, or try to replace them with some
+ * "common" version. They are hardcoded here to detect any potential
+ * breakage happening in the rest of the kernel.
+ *
+ * KVM UID value: 28b46fb6-2ec5-11e9-a9ca-4b564d003a74
+ */
+#define ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_0	0xb66fb428U
+#define ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_1	0xe911c52eU
+#define ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_2	0x564bcaa9U
+#define ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_3	0x743a004dU
+
+static void guest_code(void)
+{
+	struct arm_smccc_res res = {};
+
+	smccc_hvc(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, 0, 0, 0, 0, 0, 0, 0, &res);
+
+	__GUEST_ASSERT(res.a0 == ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_0 &&
+		       res.a1 == ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_1 &&
+		       res.a2 == ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_2 &&
+		       res.a3 == ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_3,
+		       "Unexpected KVM-specific UID %lx %lx %lx %lx\n", res.a0, res.a1, res.a2, res.a3);
+	GUEST_DONE();
+}
+
+int main (int argc, char *argv[])
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	struct ucall uc;
+	bool guest_done = false;
+
+	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
+
+	while (!guest_done) {
+		vcpu_run(vcpu);
+
+		switch (get_ucall(vcpu, &uc)) {
+		case UCALL_SYNC:
+			break;
+		case UCALL_DONE:
+			guest_done = true;
+			break;
+		case UCALL_ABORT:
+			REPORT_GUEST_ASSERT(uc);
+			break;
+		case UCALL_PRINTF:
+			printf("%s", uc.buffer);
+			break;
+		default:
+			TEST_FAIL("Unexpected guest exit");
+		}
+	}
+
+	kvm_vm_free(vm);
+
+	return 0;
+}
-- 
2.39.2