Re: [PATCH v2 03/10] selftests: kvm: s390: Add s390x ucontrol test suite with hpage test

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On 7/23/24 11:31, Christoph Schlameuss wrote:
Add test suite to validate the s390x architecture specific ucontrol KVM
interface.

Make use of the selftest test harness.

* uc_cap_hpage testcase verifies that a ucontrol VM cannot be run with
   hugepages.

To allow testing of the ucontrol interface the kernel needs a
non-default config containing CONFIG_KVM_S390_UCONTROL.
This config needs to be set to built-in (y) as this cannot be built as
module.

Signed-off-by: Christoph Schlameuss <schlameuss@xxxxxxxxxxxxx>
Reviewed-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
---

[...]

+#include "kselftest_harness.h"
+#include "kvm_util.h"
+
+#include <linux/capability.h>
+#include <linux/sizes.h>
+
+#define SYS_ADMIN_CAP 0x200000

This looked suspicious to me.
Surely this would be available in some form in capability.h since CAP_SYS_ADMIN is something that's regularly checked.

[...]

+
+/* so directly declare capget to check caps without libcap */
+int capget(cap_user_header_t header, cap_user_data_t data);
+
+/**
+ * In order to create user controlled virtual machines on S390,
+ * check KVM_CAP_S390_UCONTROL and use the flag KVM_VM_S390_UCONTROL
+ * as privileged user (SYS_ADMIN).
+ */
+void require_ucontrol_admin(void)
+{
+	struct __user_cap_data_struct data[_LINUX_CAPABILITY_U32S_3];
+	struct __user_cap_header_struct hdr = {
+		.version = _LINUX_CAPABILITY_VERSION_3,
+	};
+	int rc;
+
+	rc = capget(&hdr, data);
+	TEST_ASSERT_EQ(0, rc);
+	TEST_REQUIRE((data->effective & SYS_ADMIN_CAP) > 0);

And in fact capability.h does have defines which hide the magic constant:
data->effective & CAP_TO_MASK(CAP_SYS_ADMIN)


+
+	TEST_REQUIRE(kvm_has_cap(KVM_CAP_S390_UCONTROL));
+}
+





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