[PATCH] KVM: arm64: implement the TRNG hypervisor call

[Ard Biesheuvel <ardb@kernel.org>]

Provide a hypervisor implementation of the ARM architected TRNG firmware
interface described in ARM spec DEN0098. All function IDs are implemented,
including both 32-bit and 64-bit versions of the TRNG_RND service, which
is the centerpiece of the API.

The API is backed by arch_get_random_seed_long(), which is implemented
in terms of RNDR currently, and will be alternatively backed by a SMC
call to the secure firmware using same interface after a future patch.
If neither are available, the kernel's entropy pool is used instead.

Cc: Marc Zyngier <maz@kernel.org>
Cc: James Morse <james.morse@arm.com>
Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Sami Mujawar <sami.mujawar@arm.com>
Cc: Andre Przywara <andre.przywara@arm.com>
Cc: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm64/include/asm/kvm_host.h |  2 +
 arch/arm64/kvm/Makefile           |  2 +-
 arch/arm64/kvm/hypercalls.c       |  6 ++
 arch/arm64/kvm/trng.c             | 91 ++++++++++++++++++++
 include/linux/arm-smccc.h         | 31 +++++++
 5 files changed, 131 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 65568b23868a..f76164d390ea 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -688,4 +688,6 @@ bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu);
 #define kvm_arm_vcpu_sve_finalized(vcpu) \
 	((vcpu)->arch.flags & KVM_ARM64_VCPU_SVE_FINALIZED)
 
+int kvm_trng_call(struct kvm_vcpu *vcpu);
+
 #endif /* __ARM64_KVM_HOST_H__ */
diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
index 99977c1972cc..e117d7086500 100644
--- a/arch/arm64/kvm/Makefile
+++ b/arch/arm64/kvm/Makefile
@@ -16,7 +16,7 @@ kvm-y := $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o $(KVM)/eventfd.o \
 	 inject_fault.o regmap.o va_layout.o hyp.o handle_exit.o \
 	 guest.o debug.o reset.o sys_regs.o \
 	 vgic-sys-reg-v3.o fpsimd.o pmu.o \
-	 aarch32.o arch_timer.o \
+	 aarch32.o arch_timer.o trng.o \
 	 vgic/vgic.o vgic/vgic-init.o \
 	 vgic/vgic-irqfd.o vgic/vgic-v2.o \
 	 vgic/vgic-v3.o vgic/vgic-v4.o \
diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
index 550dfa3e53cd..70c5e815907d 100644
--- a/arch/arm64/kvm/hypercalls.c
+++ b/arch/arm64/kvm/hypercalls.c
@@ -62,6 +62,12 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
 		if (gpa != GPA_INVALID)
 			val = gpa;
 		break;
+	case ARM_SMCCC_TRNG_VERSION:
+	case ARM_SMCCC_TRNG_FEATURES:
+	case ARM_SMCCC_TRNG_GET_UUID:
+	case ARM_SMCCC_TRNG_RND:
+	case ARM_SMCCC_TRNG_RND64:
+		return kvm_trng_call(vcpu);
 	default:
 		return kvm_psci_call(vcpu);
 	}
diff --git a/arch/arm64/kvm/trng.c b/arch/arm64/kvm/trng.c
new file mode 100644
index 000000000000..71f704075e4a
--- /dev/null
+++ b/arch/arm64/kvm/trng.c
@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2020 Arm Ltd.
+
+#include <linux/arm-smccc.h>
+#include <linux/kvm_host.h>
+
+#include <asm/kvm_emulate.h>
+
+#include <kvm/arm_hypercalls.h>
+
+#define ARM_SMCCC_TRNG_VERSION_1_0	0x10000UL
+
+#define TRNG_SUCCESS			0UL
+#define TRNG_NOT_SUPPORTED		((unsigned long)-1)
+#define TRNG_INVALID_PARAMETER		((unsigned long)-2)
+#define TRNG_NO_ENTROPY			((unsigned long)-3)
+
+#define MAX_BITS32			96
+#define MAX_BITS64			192
+
+static const uuid_t arm_smc_trng_uuid __aligned(4) = UUID_INIT(
+	0x023534a2, 0xe0bc, 0x45ec, 0x95, 0xdd, 0x33, 0x34, 0xc1, 0xcc, 0x31, 0x89);
+
+static int kvm_trng_do_rnd(struct kvm_vcpu *vcpu, int size)
+{
+	u32 num_bits = smccc_get_arg1(vcpu);
+	u64 bits[3];
+	int i;
+
+	if (num_bits > 3 * size) {
+		smccc_set_retval(vcpu, TRNG_NOT_SUPPORTED, 0, 0, 0);
+		return 1;
+	}
+
+	/* get as many bits as we need to fulfil the request */
+	for (i = 0; i < DIV_ROUND_UP(num_bits, 64); i++)
+		/* use the arm64 specific backend directly if one exists */
+		if (!arch_get_random_seed_long((unsigned long *)&bits[i]))
+			bits[i] = get_random_long();
+
+	if (num_bits % 64)
+		bits[i - 1] &= U64_MAX >> (64 - (num_bits % 64));
+
+	while (i < ARRAY_SIZE(bits))
+		bits[i++] = 0;
+
+	if (size == 32)
+		smccc_set_retval(vcpu, TRNG_SUCCESS, lower_32_bits(bits[1]),
+				 upper_32_bits(bits[0]), lower_32_bits(bits[0]));
+	else
+		smccc_set_retval(vcpu, TRNG_SUCCESS, bits[2], bits[1], bits[0]);
+
+	memzero_explicit(bits, sizeof(bits));
+	return 1;
+}
+
+int kvm_trng_call(struct kvm_vcpu *vcpu)
+{
+	const __be32 *u = (__be32 *)arm_smc_trng_uuid.b;
+	u32 func_id = smccc_get_function(vcpu);
+	unsigned long val = TRNG_NOT_SUPPORTED;
+	int size = 64;
+
+	switch (func_id) {
+	case ARM_SMCCC_TRNG_VERSION:
+		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_RND:
+		case ARM_SMCCC_TRNG_RND64:
+			val = TRNG_SUCCESS;
+		}
+		break;
+	case ARM_SMCCC_TRNG_GET_UUID:
+		smccc_set_retval(vcpu, be32_to_cpu(u[3]), be32_to_cpu(u[2]),
+				 be32_to_cpu(u[1]), be32_to_cpu(u[0]));
+		return 1;
+	case ARM_SMCCC_TRNG_RND:
+		size = 32;
+		fallthrough;
+	case ARM_SMCCC_TRNG_RND64:
+		return kvm_trng_do_rnd(vcpu, size);
+	}
+
+	smccc_set_retval(vcpu, val, 0, 0, 0);
+	return 1;
+}
diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
index 15c706fb0a37..9c9decd329b7 100644
--- a/include/linux/arm-smccc.h
+++ b/include/linux/arm-smccc.h
@@ -99,6 +99,37 @@
 			   ARM_SMCCC_OWNER_STANDARD_HYP,	\
 			   0x21)
 
+/* TRNG entropy source calls (defined by ARM DEN0098) */
+#define ARM_SMCCC_TRNG_VERSION					\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,			\
+			   ARM_SMCCC_SMC_32,			\
+			   ARM_SMCCC_OWNER_STANDARD,		\
+			   0x50)
+
+#define ARM_SMCCC_TRNG_FEATURES					\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,			\
+			   ARM_SMCCC_SMC_32,			\
+			   ARM_SMCCC_OWNER_STANDARD,		\
+			   0x51)
+
+#define ARM_SMCCC_TRNG_GET_UUID					\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,			\
+			   ARM_SMCCC_SMC_32,			\
+			   ARM_SMCCC_OWNER_STANDARD,		\
+			   0x52)
+
+#define ARM_SMCCC_TRNG_RND					\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,			\
+			   ARM_SMCCC_SMC_32,			\
+			   ARM_SMCCC_OWNER_STANDARD,		\
+			   0x53)
+
+#define ARM_SMCCC_TRNG_RND64					\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,			\
+			   ARM_SMCCC_SMC_64,			\
+			   ARM_SMCCC_OWNER_STANDARD,		\
+			   0x53)
+
 /*
  * Return codes defined in ARM DEN 0070A
  * ARM DEN 0070A is now merged/consolidated into ARM DEN 0028 C
-- 
2.17.1

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