KVM: arm64: Implement the TRNG hypervisor call

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>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210106103453.152275-6-andre.przywara@arm.com

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 8fcfab0c25672db32d47f7eb78fdda1671595ddc..084d11a2768ca66bc1dce3ec277079e07a92b2ed 100644 (file)
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -771,4 +771,6 @@ 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 13b017284bf96c761b040e7db41631afda275daf..589921392cb12b5bca9631f85984c0f135879f84 100644 (file)
--- 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 25ea4ecb6449fb3c6475af75723092a815d1059d..ead21b98b6209818f25e88b9dc6636c94454ea59 100644 (file)
--- 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 (file)
index 0000000..99bdd71
--- /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;
+}