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 <m...@kernel.org>
Cc: James Morse <james.mo...@arm.com>
Cc: Julien Thierry <julien.thierry.k...@gmail.com>
Cc: Suzuki K Poulose <suzuki.poul...@arm.com>
Cc: Catalin Marinas <catalin.mari...@arm.com>
Cc: Will Deacon <w...@kernel.org>
Cc: Mark Rutland <mark.rutl...@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieral...@arm.com>
Cc: Sudeep Holla <sudeep.ho...@arm.com>
Cc: Sami Mujawar <sami.muja...@arm.com>
Cc: Andre Przywara <andre.przyw...@arm.com>
Cc: Alexandru Elisei <alexandru.eli...@arm.com>
Cc: Laszlo Ersek <ler...@redhat.com>
Cc: Leif Lindholm <l...@nuviainc.com>
Signed-off-by: Ard Biesheuvel <a...@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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