KVM: arm64: Add kvm-arm.mode early kernel parameter

Add an early parameter that allows users to select the mode of operation
for KVM/arm64.

For now, the only supported value is "protected". By passing this flag
users opt into the hypervisor placing additional restrictions on the
host kernel. These allow the hypervisor to spawn guests whose state is
kept private from the host. Restrictions will include stage-2 address
translation to prevent host from accessing guest memory, filtering its
SMC calls, etc.

Without this parameter, the default behaviour remains selecting VHE/nVHE
based on hardware support and CONFIG_ARM64_VHE.

Signed-off-by: David Brazdil <dbrazdil@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201202184122.26046-2-dbrazdil@google.com

3 files changed, 35 insertions, 0 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 526d65d8573a..ee9f13776388 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2259,6 +2259,16 @@
 			for all guests.
 			Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
 
+	kvm-arm.mode=
+			[KVM,ARM] Select one of KVM/arm64's modes of operation.
+
+			protected: nVHE-based mode with support for guests whose
+				   state is kept private from the host.
+				   Not valid if the kernel is running in EL2.
+
+			Defaults to VHE/nVHE based on hardware support and
+			the value of CONFIG_ARM64_VHE.
+
 	kvm-arm.vgic_v3_group0_trap=
 			[KVM,ARM] Trap guest accesses to GICv3 group-0
 			system registers
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 781d029b8aa8..820954ad2477 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -50,6 +50,15 @@
 #define KVM_DIRTY_LOG_MANUAL_CAPS   (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE | \
 				     KVM_DIRTY_LOG_INITIALLY_SET)
 
+/*
+ * Mode of operation configurable with kvm-arm.mode early param.
+ * See Documentation/admin-guide/kernel-parameters.txt for more information.
+ */
+enum kvm_mode {
+	KVM_MODE_DEFAULT,
+	KVM_MODE_PROTECTED,
+};
+
 DECLARE_STATIC_KEY_FALSE(userspace_irqchip_in_use);
 
 extern unsigned int kvm_sve_max_vl;
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 5750ec34960e..5db90680742c 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -46,6 +46,8 @@
 __asm__(".arch_extension	virt");
 #endif
 
+static enum kvm_mode kvm_mode = KVM_MODE_DEFAULT;
+
 DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
 
 static DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
@@ -1790,6 +1792,20 @@ void kvm_arch_exit(void)
 	kvm_perf_teardown();
 }
 
+static int __init early_kvm_mode_cfg(char *arg)
+{
+	if (!arg)
+		return -EINVAL;
+
+	if (strcmp(arg, "protected") == 0) {
+		kvm_mode = KVM_MODE_PROTECTED;
+		return 0;
+	}
+
+	return -EINVAL;
+}
+early_param("kvm-arm.mode", early_kvm_mode_cfg);
+
 static int arm_init(void)
 {
 	int rc = kvm_init(NULL, sizeof(struct kvm_vcpu), 0, THIS_MODULE);