[RFC PATCH 3/8] KVM: arm64: Add standard secure service calls firmware register

[Raghavendra Rao Ananta <rananta@google.com>]

Introduce a firmware register that encapsulates standard secure
service calls (owner value 4) as a bitmap. Depending on how the
user-space configures the register, the features will be enabled
or disabled for the guest. Currently, this includes support only
for ARM True Random Number Generator (TRNG) service, with bit-0
of the register representing mandatory features of v1.0.

Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
---
 Documentation/virt/kvm/arm/hypercalls.rst | 17 +++++
 arch/arm64/include/asm/kvm_host.h         |  2 +
 arch/arm64/include/uapi/asm/kvm.h         |  6 ++
 arch/arm64/kvm/arm.c                      |  8 +++
 arch/arm64/kvm/hypercalls.c               | 75 ++++++++++++++++++++++-
 arch/arm64/kvm/trng.c                     |  9 +--
 include/kvm/arm_hypercalls.h              |  5 ++
 7 files changed, 113 insertions(+), 9 deletions(-)

diff --git a/Documentation/virt/kvm/arm/hypercalls.rst b/Documentation/virt/kvm/arm/hypercalls.rst
index 85dfd682d811..1601919f256d 100644
--- a/Documentation/virt/kvm/arm/hypercalls.rst
+++ b/Documentation/virt/kvm/arm/hypercalls.rst
@@ -20,6 +20,14 @@ pseudo-registers" that can be manipulated using the GET/SET_ONE_REG
 interface. These registers can be saved/restored by userspace, and set
 to a convenient value if required.
 
+The firmware register KVM_REG_ARM_STD exposes the hypercall services
+in the form of a feature bitmap. Upon VM creation, by default, KVM exposes
+all the features to the guest, which can be learnt using GET_ONE_REG
+interface. Conversely, the features can be enabled or disabled via the
+SET_ONE_REG interface. These registers allow the user-space modification
+only until the VM has started running, after which they turn to read-only
+registers. SET_ONE_REG in this scenario will return -EBUSY.
+
 The following register is defined:
 
 * KVM_REG_ARM_PSCI_VERSION:
@@ -74,4 +82,13 @@ The following register is defined:
     KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED:
       The workaround is always active on this vCPU or it is not needed.
 
+* KVM_REG_ARM_STD:
+    Controls the bitmap of the ARM Standard Secure Service Calls.
+
+    The following bits are accepted:
+
+      KVM_REG_ARM_STD_TRNG_V1_0:
+        The bit represents the services offered under v1.0 of ARM True Random Number Generator
+        (TRNG) specification (ARM DEN 0098).
+
 .. [1] https://developer.arm.com/-/media/developer/pdf/ARM_DEN_0070A_Firmware_interfaces_for_mitigating_CVE-2017-5715.pdf
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 0b2502494a17..176d6be7b4da 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -105,6 +105,8 @@ struct kvm_arch_memory_slot {
 struct hvc_reg_desc {
 	bool write_disabled;
 	bool write_attempted;
+
+	u64 kvm_std_bmap;
 };
 
 struct kvm_arch {
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index b3edde68bc3e..6387dea5396d 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -281,6 +281,12 @@ struct kvm_arm_copy_mte_tags {
 #define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED	3
 #define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED     	(1U << 4)
 
+#define KVM_REG_ARM_STD			KVM_REG_ARM_FW_REG(3)
+enum kvm_reg_arm_std_bmap {
+	KVM_REG_ARM_STD_TRNG_V1_0,
+	KVM_REG_ARM_STD_BMAP_MAX,
+};
+
 /* SVE registers */
 #define KVM_REG_ARM64_SVE		(0x15 << KVM_REG_ARM_COPROC_SHIFT)
 
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index f9a25e439e99..1cf58aa49222 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -130,6 +130,13 @@ static void set_default_spectre(struct kvm *kvm)
 		kvm->arch.pfr0_csv3 = 1;
 }
 
+static void set_default_hypercalls(struct kvm *kvm)
+{
+	struct hvc_reg_desc *hvc_desc = &kvm->arch.hvc_desc;
+
+	hvc_desc->kvm_std_bmap = ARM_SMCCC_STD_FEATURES;
+}
+
 /**
  * kvm_arch_init_vm - initializes a VM data structure
  * @kvm:	pointer to the KVM struct
@@ -156,6 +163,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	kvm->arch.max_vcpus = kvm_arm_default_max_vcpus();
 
 	set_default_spectre(kvm);
+	set_default_hypercalls(kvm);
 
 	return ret;
 out_free_stage2_pgd:
diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
index 7e873206a05b..0b3006353bf6 100644
--- a/arch/arm64/kvm/hypercalls.c
+++ b/arch/arm64/kvm/hypercalls.c
@@ -60,8 +60,64 @@ static void kvm_ptp_get_time(struct kvm_vcpu *vcpu, u64 *val)
 
 static u64 *kvm_fw_reg_to_bmap(struct kvm *kvm, u64 fw_reg)
 {
-	/* No firmware registers supporting hvc bitmaps exits yet */
-	return NULL;
+	struct hvc_reg_desc *hvc_desc = &kvm->arch.hvc_desc;
+
+	switch (fw_reg) {
+	case KVM_REG_ARM_STD:
+		return &hvc_desc->kvm_std_bmap;
+	default:
+		return NULL;
+	}
+}
+
+struct kvm_hvc_func_map {
+	u32 func_id;
+	u64 bmap_bit;
+};
+
+#define HVC_FUNC_MAP_DESC(func, bit)	\
+	{					\
+		.func_id = func,		\
+		.bmap_bit = bit,		\
+	}
+
+static const struct kvm_hvc_func_map hvc_std_map[] = {
+	HVC_FUNC_MAP_DESC(ARM_SMCCC_TRNG_GET_UUID, KVM_REG_ARM_STD_TRNG_V1_0),
+	HVC_FUNC_MAP_DESC(ARM_SMCCC_TRNG_RND32, KVM_REG_ARM_STD_TRNG_V1_0),
+	HVC_FUNC_MAP_DESC(ARM_SMCCC_TRNG_RND64, KVM_REG_ARM_STD_TRNG_V1_0),
+};
+
+bool kvm_hvc_call_supported(struct kvm_vcpu *vcpu, u32 func_id)
+{
+	struct kvm *kvm = vcpu->kvm;
+	u8 hvc_owner = ARM_SMCCC_OWNER_NUM(func_id);
+	const struct kvm_hvc_func_map *hvc_func_map = NULL;
+
+	u64 fw_reg, *hc_bmap;
+	unsigned int map_sz, i;
+
+	switch (hvc_owner) {
+	case ARM_SMCCC_OWNER_STANDARD:
+		fw_reg = KVM_REG_ARM_STD;
+		hvc_func_map = hvc_std_map;
+		map_sz = ARRAY_SIZE(hvc_std_map);
+		break;
+	default:
+		/* Allow all the owners that aren't mapped */
+		return true;
+	}
+
+	hc_bmap = kvm_fw_reg_to_bmap(kvm, fw_reg);
+	if (!hc_bmap)
+		return true;
+
+	for (i = 0; i < map_sz; i++) {
+		if (func_id == hvc_func_map[i].func_id)
+			return *hc_bmap & BIT(hvc_func_map[i].bmap_bit);
+	}
+
+	/* Allow all the functions of an owner that aren't mapped */
+	return true;
 }
 
 int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
@@ -71,6 +127,9 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
 	u32 feature;
 	gpa_t gpa;
 
+	if (!kvm_hvc_call_supported(vcpu, func_id))
+		goto out;
+
 	switch (func_id) {
 	case ARM_SMCCC_VERSION_FUNC_ID:
 		val[0] = ARM_SMCCC_VERSION_1_1;
@@ -149,6 +208,7 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
 		return kvm_psci_call(vcpu);
 	}
 
+out:
 	smccc_set_retval(vcpu, val[0], val[1], val[2], val[3]);
 	return 1;
 }
@@ -157,6 +217,7 @@ static const u64 fw_reg_ids[] = {
 	KVM_REG_ARM_PSCI_VERSION,
 	KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1,
 	KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2,
+	KVM_REG_ARM_STD,
 };
 
 int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu)
@@ -219,6 +280,7 @@ static int get_kernel_wa_level(u64 regid)
 
 int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 {
+	struct hvc_reg_desc *hvc_desc = &vcpu->kvm->arch.hvc_desc;
 	void __user *uaddr = (void __user *)(long)reg->addr;
 	u64 val;
 
@@ -230,6 +292,9 @@ int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2:
 		val = get_kernel_wa_level(reg->id) & KVM_REG_FEATURE_LEVEL_MASK;
 		break;
+	case KVM_REG_ARM_STD:
+		val = hvc_desc->kvm_std_bmap;
+		break;
 	default:
 		return -ENOENT;
 	}
@@ -352,6 +417,12 @@ int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 		if (get_kernel_wa_level(reg->id) < wa_level)
 			return -EINVAL;
 
+		return 0;
+	case KVM_REG_ARM_STD:
+		if (val & ~ARM_SMCCC_STD_FEATURES)
+			return -EINVAL;
+
+		hvc_desc->kvm_std_bmap = val;
 		return 0;
 	default:
 		return -ENOENT;
diff --git a/arch/arm64/kvm/trng.c b/arch/arm64/kvm/trng.c
index 99bdd7103c9c..6dff765f5b9b 100644
--- a/arch/arm64/kvm/trng.c
+++ b/arch/arm64/kvm/trng.c
@@ -60,14 +60,9 @@ int kvm_trng_call(struct kvm_vcpu *vcpu)
 		val = ARM_SMCCC_TRNG_VERSION_1_0;
 		break;
 	case ARM_SMCCC_TRNG_FEATURES:
-		switch (smccc_get_arg1(vcpu)) {
-		case ARM_SMCCC_TRNG_VERSION:
-		case ARM_SMCCC_TRNG_FEATURES:
-		case ARM_SMCCC_TRNG_GET_UUID:
-		case ARM_SMCCC_TRNG_RND32:
-		case ARM_SMCCC_TRNG_RND64:
+		if (kvm_hvc_call_supported(vcpu, smccc_get_arg1(vcpu)))
 			val = TRNG_SUCCESS;
-		}
+
 		break;
 	case ARM_SMCCC_TRNG_GET_UUID:
 		smccc_set_retval(vcpu, le32_to_cpu(u[0]), le32_to_cpu(u[1]),
diff --git a/include/kvm/arm_hypercalls.h b/include/kvm/arm_hypercalls.h
index 5d38628a8d04..5f01bb139312 100644
--- a/include/kvm/arm_hypercalls.h
+++ b/include/kvm/arm_hypercalls.h
@@ -6,6 +6,9 @@
 
 #include <asm/kvm_emulate.h>
 
+#define ARM_SMCCC_STD_FEATURES \
+	GENMASK_ULL(KVM_REG_ARM_STD_BMAP_MAX - 1, 0)
+
 int kvm_hvc_call_handler(struct kvm_vcpu *vcpu);
 
 static inline u32 smccc_get_function(struct kvm_vcpu *vcpu)
@@ -47,4 +50,6 @@ int kvm_arm_copy_fw_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices);
 int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg);
 int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg);
 
+bool kvm_hvc_call_supported(struct kvm_vcpu *vcpu, u32 func_id);
+
 #endif
-- 
2.33.1.1089.g2158813163f-goog

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