Add test for CVE 2021-3656

Signed-off-by: Martin Doucha <[email protected]>
Acked-by: Petr Vorel <[email protected]>
Acked-by: Cyril Hrubis <[email protected]>

Author: mdoucha

runtest/kvm

@@ -1,2 +1,3 @@
 kvm_pagefault01 kvm_pagefault01
 kvm_svm01 kvm_svm01
+kvm_svm02 kvm_svm02

testcases/kernel/kvm/.gitignore

@@ -1,2 +1,3 @@
 /kvm_pagefault01
 /kvm_svm01
+/kvm_svm02

testcases/kernel/kvm/kvm_svm02.c

@@ -0,0 +1,152 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2023 SUSE LLC
+ * Author: Nicolai Stange <[email protected]>
+ * LTP port: Martin Doucha <[email protected]>
+ */
+
+/*\
+ * CVE 2021-3656
+ *
+ * Check that KVM correctly intercepts VMSAVE and VMLOAD instructions
+ * in a nested virtual machine even when the parent guest disables
+ * intercepting either instruction. If KVM does not override the disabled
+ * intercepts, it'll give the nested VM read/write access to a few bytes
+ * of an arbitrary physical memory page. Unauthorized memory access fixed in:
+ *
+ *  commit c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc
+ *  Author: Maxim Levitsky <[email protected]>
+ *  Date:   Mon Jul 19 16:05:00 2021 +0300
+ *
+ *  KVM: nSVM: always intercept VMLOAD/VMSAVE when nested (CVE-2021-3656)
+ */
+
+#include "kvm_test.h"
+
+#ifdef COMPILE_PAYLOAD
+#if defined(__i386__) || defined(__x86_64__)
+
+#include "kvm_x86_svm.h"
+
+static void *vmsave_buf;
+
+/* Load FS, GS, TR and LDTR state from vmsave_buf */
+static int guest_vmload(void)
+{
+	asm (
+		"vmload %0\n"
+		:
+		: "a" (vmsave_buf)
+	);
+	return 0;
+}
+
+/* Save current FS, GS, TR and LDTR state to vmsave_buf */
+static int guest_vmsave(void)
+{
+	asm (
+		"vmsave %0\n"
+		:
+		: "a" (vmsave_buf)
+	);
+	return 0;
+}
+
+static int cmp_descriptor(const struct kvm_vmcb_descriptor *a,
+	const struct kvm_vmcb_descriptor *b)
+{
+	int ret;
+
+	ret = a->selector != b->selector;
+	ret = ret || a->attrib != b->attrib;
+	ret = ret || a->limit != b->limit;
+	ret = ret || a->base != b->base;
+	return ret;
+}
+
+/* Return non-zero if the VMCB fields touched by vmsave/vmload differ */
+static int cmp_vmcb(const struct kvm_vmcb *a, const struct kvm_vmcb *b)
+{
+	int ret;
+
+	ret = cmp_descriptor(&a->fs, &b->fs);
+	ret = ret || cmp_descriptor(&a->gs, &b->gs);
+	ret = ret || cmp_descriptor(&a->tr, &b->tr);
+	ret = ret || cmp_descriptor(&a->ldtr, &b->ldtr);
+	ret = ret || a->kernel_gs_base != b->kernel_gs_base;
+	ret = ret || a->star != b->star;
+	ret = ret || a->lstar != b->lstar;
+	ret = ret || a->cstar != b->cstar;
+	ret = ret || a->sfmask != b->sfmask;
+	ret = ret || a->sysenter_cs != b->sysenter_cs;
+	ret = ret || a->sysenter_esp != b->sysenter_esp;
+	ret = ret || a->sysenter_eip != b->sysenter_eip;
+	return ret;
+}
+
+void main(void)
+{
+	uint16_t ss;
+	uint64_t rsp;
+	struct kvm_svm_vcpu *vcpu;
+
+	kvm_init_svm();
+	vcpu = kvm_create_svm_vcpu(guest_vmload, 1);
+	kvm_vmcb_set_intercept(vcpu->vmcb, SVM_INTERCEPT_VMLOAD, 0);
+	vmsave_buf = kvm_alloc_vmcb();
+
+	/* Save allocated stack for later VM reinit */
+	ss = vcpu->vmcb->ss.selector;
+	rsp = vcpu->vmcb->rsp;
+
+	/* Load partial state from vmsave_buf and save it to vcpu->vmcb */
+	kvm_svm_vmrun(vcpu);
+
+	if (vcpu->vmcb->exitcode != SVM_EXIT_HLT)
+		tst_brk(TBROK, "Nested VM exited unexpectedly");
+
+	if (cmp_vmcb(vcpu->vmcb, vmsave_buf)) {
+		tst_res(TFAIL, "Nested VM can read host memory");
+		return;
+	}
+
+	/* Load state from vcpu->vmcb and save it to vmsave_buf */
+	memset(vmsave_buf, 0xaa, sizeof(struct kvm_vmcb));
+	kvm_init_guest_vmcb(vcpu->vmcb, 1, ss, (void *)rsp, guest_vmsave);
+	kvm_vmcb_set_intercept(vcpu->vmcb, SVM_INTERCEPT_VMSAVE, 0);
+	kvm_svm_vmrun(vcpu);
+
+	if (vcpu->vmcb->exitcode != SVM_EXIT_HLT)
+		tst_brk(TBROK, "Nested VM exited unexpectedly");
+
+	if (cmp_vmcb(vcpu->vmcb, vmsave_buf)) {
+		tst_res(TFAIL, "Nested VM can overwrite host memory");
+		return;
+	}
+
+	tst_res(TPASS, "VMLOAD and VMSAVE were intercepted by kernel");
+}
+
+#else /* defined(__i386__) || defined(__x86_64__) */
+TST_TEST_TCONF("Test supported only on x86");
+#endif /* defined(__i386__) || defined(__x86_64__) */
+
+#else /* COMPILE_PAYLOAD */
+
+static struct tst_test test = {
+	.test_all = tst_kvm_run,
+	.setup = tst_kvm_setup,
+	.cleanup = tst_kvm_cleanup,
+	.supported_archs = (const char *const []) {
+		"x86_64",
+		"x86",
+		NULL
+	},
+	.tags = (struct tst_tag[]){
+		{"linux-git", "c7dfa4009965"},
+		{"CVE", "2021-3656"},
+		{}
+	}
+};
+
+#endif /* COMPILE_PAYLOAD */