On 2020-11-05 12:56, Andre Przywara wrote:
From: Ard Biesheuvel <ardb@xxxxxxxxxx>
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_unsigned_seed_long(), which is
implemented
in terms of RNDRRS 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.
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
---
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 +++++++++++++++++++++++++++++++
4 files changed, 100 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 781d029b8aa8..615932bacf76 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -652,4 +652,6 @@ 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 1504c81fbf5d..a510037e3270 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 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 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..5a27b2d99977
--- /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
SMCCC_RET_SUCCESS
+#define TRNG_NOT_SUPPORTED ((unsigned long)-1)
SMCCC_RET_NOT_SUPPORTED
+#define TRNG_INVALID_PARAMETER ((unsigned long)-2)
*crap*. Why isn't that the same value as SMCCC_RET_INVALID_PARAMETER?
Is it too late to fix the spec?
+#define TRNG_NO_ENTROPY ((unsigned long)-3)
+
+#define MAX_BITS32 96
+#define MAX_BITS64 192
Nothing seems to be using these definitions.
+
+static const uuid_t arm_smc_trng_uuid __aligned(4) = UUID_INIT(
+ 0x023534a2, 0xe0bc, 0x45ec, 0x95, 0xdd, 0x33, 0x34, 0xc1, 0xcc, 0x31,
0x89);
I object to the lack of Easter egg in this UUID. Or at least one I can
understand. ;-)
+
+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_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, 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;
I just wasted 3 minutes trying to understand what this was doing, only
to
realise this is clearing the [MAX_BITS:num_bits] range.
How about using a bitmap instead? It would result in the exact same data
structure, only much more readable (and no u64->unsigned long casts).
+
+ 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;
+}
Thanks,
M.
--
Who you jivin' with that Cosmik Debris?
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