[PATCH v6 5/5] KVM: arm64: implement the TRNG hypervisor call

Andre Przywara
2021-01-06T10:36:50Z

From: 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 the kernel's entropy pool only, to avoid guests
draining more precious direct entropy sources.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
[Andre: minor fixes, drop arch_get_random() usage]
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
arch/arm64/include/asm/kvm_host.h | 2 +
arch/arm64/kvm/Makefile | 2 +-
arch/arm64/kvm/hypercalls.c | 6 +++
arch/arm64/kvm/trng.c | 85 +++++++++++++++++++++++++++++++
4 files changed, 94 insertions(+), 1 deletion(-)
create mode 100644 arch/arm64/kvm/trng.c

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 11beda85ee7e..271c79914afd 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -748,4 +748,6 @@ bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu);
#define kvm_vcpu_has_pmu(vcpu) \
(test_bit(KVM_ARM_VCPU_PMU_V3, (vcpu)->arch.features))

+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 60fd181df624..8d2b9984ac36 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 va_layout.o handle_exit.o \
guest.o debug.o reset.o sys_regs.o \
vgic-sys-reg-v3.o fpsimd.o pmu.o \
- arch_timer.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 25ea4ecb6449..ead21b98b620 100644
--- a/arch/arm64/kvm/hypercalls.c
+++ b/arch/arm64/kvm/hypercalls.c
@@ -71,6 +71,12 @@ 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_RND32:
+ 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..99bdd7103c9c
--- /dev/null
+++ b/arch/arm64/kvm/trng.c
@@ -0,0 +1,85 @@
+// 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
+
+/* Those values are deliberately separate from the generic SMCCC definitions. */
+#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 TRNG_MAX_BITS64 192
+
+static const uuid_t arm_smc_trng_uuid __aligned(4) = UUID_INIT(
+ 0x0d21e000, 0x4384, 0x11eb, 0x80, 0x70, 0x52, 0x44, 0x55, 0x4e, 0x5a, 0x4c);
+
+static int kvm_trng_do_rnd(struct kvm_vcpu *vcpu, int size)
+{
+ DECLARE_BITMAP(bits, TRNG_MAX_BITS64);
+ u32 num_bits = smccc_get_arg1(vcpu);
+ int i;
+
+ if (num_bits > 3 * size) {
+ smccc_set_retval(vcpu, TRNG_INVALID_PARAMETER, 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, BITS_PER_LONG); i++)
+ bits[i] = get_random_long();
+
+ bitmap_clear(bits, num_bits, TRNG_MAX_BITS64 - num_bits);
+
+ 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 __le32 *u = (__le32 *)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_RND32:
+ case ARM_SMCCC_TRNG_RND64:
+ val = TRNG_SUCCESS;
+ }
+ break;
+ case ARM_SMCCC_TRNG_GET_UUID:
+ smccc_set_retval(vcpu, le32_to_cpu(u[0]), le32_to_cpu(u[1]),
+ le32_to_cpu(u[2]), le32_to_cpu(u[3]));
+ return 1;
+ case ARM_SMCCC_TRNG_RND32:
+ 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;
+}
--
2.17.1