linux-kernel - [PATCH 3/6] KVM: selftests: nVMX: Add enlightened MSR-Bitmap selftest

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Date:   Thu,  3 Feb 2022 11:46:17 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>, linux-kernel@...r.kernel.org
Subject: [PATCH 3/6] KVM: selftests: nVMX: Add enlightened MSR-Bitmap selftest

Introduce a test for enlightened MSR-Bitmap feature (Hyper-V on KVM):
- Intercept access to MSR_FS_BASE in L1 and check that this works
 with enlightened MSR-Bitmap disabled.
- Enabled enlightened MSR-Bitmap and check that the intercept still works
as expected.
- Intercept access to MSR_GS_BASE but don't clear the corresponding bit
from 'hv_clean_fields', KVM is supposed to skip updating MSR-Bitmap02 and
thus the consequent access to the MSR from L2 will not get intercepted.
- Finally, clear the corresponding bit from 'hv_clean_fields' and check
that access to MSR_GS_BASE is now intercepted.

The test works with the assumption, that access to MSR_FS_BASE/MSR_GS_BASE
is not intercepted for L1. If this ever becomes not true the test will
fail as nested_vmx_exit_handled_msr() always checks L1's MSR-Bitmap for
L2 irrespective of 'hv_clean_fields'. The behavior is correct as
enlightened MSR-Bitmap feature is just an optimization, KVM is not obliged
to ignore updates when the corresponding bit in 'hv_clean_fields' stays
clear.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 .../testing/selftests/kvm/x86_64/evmcs_test.c | 59 +++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/tools/testing/selftests/kvm/x86_64/evmcs_test.c b/tools/testing/selftests/kvm/x86_64/evmcs_test.c
index 655104051819..d12e043aa2ee 100644
--- a/tools/testing/selftests/kvm/x86_64/evmcs_test.c
+++ b/tools/testing/selftests/kvm/x86_64/evmcs_test.c
@@ -10,6 +10,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/ioctl.h>
+#include <linux/bitmap.h>
 
 #include "test_util.h"
 
@@ -32,6 +33,22 @@ static void guest_nmi_handler(struct ex_regs *regs)
 {
 }
 
+/* Exits to L1 destroy GRPs! */
+static inline void rdmsr_fs_base(void)
+{
+	__asm__ __volatile__ ("mov $0xc0000100, %%rcx; rdmsr" : : :
+			      "rax", "rbx", "rcx", "rdx",
+			      "rsi", "rdi", "r8", "r9", "r10", "r11", "r12",
+			      "r13", "r14", "r15");
+}
+static inline void rdmsr_gs_base(void)
+{
+	__asm__ __volatile__ ("mov $0xc0000101, %%rcx; rdmsr" : : :
+			      "rax", "rbx", "rcx", "rdx",
+			      "rsi", "rdi", "r8", "r9", "r10", "r11", "r12",
+			      "r13", "r14", "r15");
+}
+
 void l2_guest_code(void)
 {
 	GUEST_SYNC(7);
@@ -41,6 +58,15 @@ void l2_guest_code(void)
 	/* Forced exit to L1 upon restore */
 	GUEST_SYNC(9);
 
+	vmcall();
+
+	/* MSR-Bitmap tests */
+	rdmsr_fs_base(); /* intercepted */
+	rdmsr_fs_base(); /* intercepted */
+	rdmsr_gs_base(); /* not intercepted */
+	vmcall();
+	rdmsr_gs_base(); /* intercepted */
+
 	/* Done, exit to L1 and never come back.  */
 	vmcall();
 }
@@ -91,6 +117,39 @@ void guest_code(struct vmx_pages *vmx_pages)
 
 	GUEST_SYNC(10);
 
+	GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_VMCALL);
+	current_evmcs->guest_rip += 3; /* vmcall */
+
+	/* Intercept RDMSR 0xc0000100 */
+	vmwrite(CPU_BASED_VM_EXEC_CONTROL, vmreadz(CPU_BASED_VM_EXEC_CONTROL) |
+		CPU_BASED_USE_MSR_BITMAPS);
+	set_bit(MSR_FS_BASE & 0x1fff, vmx_pages->msr + 0x400);
+	GUEST_ASSERT(!vmresume());
+	GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_MSR_READ);
+	current_evmcs->guest_rip += 2; /* rdmsr */
+
+	/* Enable enlightened MSR bitmap */
+	current_evmcs->hv_enlightenments_control.msr_bitmap = 1;
+	GUEST_ASSERT(!vmresume());
+	GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_MSR_READ);
+	current_evmcs->guest_rip += 2; /* rdmsr */
+
+	/* Intercept RDMSR 0xc0000101 without telling KVM about it */
+	set_bit(MSR_GS_BASE & 0x1fff, vmx_pages->msr + 0x400);
+	/* Make sure HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP is set */
+	current_evmcs->hv_clean_fields |= HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP;
+	GUEST_ASSERT(!vmresume());
+	/* Make sure we don't see EXIT_REASON_MSR_READ here so eMSR bitmap works */
+	GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_VMCALL);
+	current_evmcs->guest_rip += 3; /* vmcall */
+
+	/* Now tell KVM we've changed MSR-Bitmap */
+	current_evmcs->hv_clean_fields &= ~HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP;
+	GUEST_ASSERT(!vmresume());
+	GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_MSR_READ);
+	current_evmcs->guest_rip += 2; /* rdmsr */
+
+	GUEST_ASSERT(!vmresume());
 	GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_VMCALL);
 	GUEST_SYNC(11);
 
-- 
2.34.1