[PATCH] KVM: arm64: implement the TRNG hypervisor call
Ard Biesheuvel
ardb at kernel.org
Sat Oct 3 08:28:46 EDT 2020
On Sat, 3 Oct 2020 at 12:30, Andrew Jones <drjones at redhat.com> wrote:
>
> Hi Ard,
>
Hi Drew,
Thanks for taking a look.
> On Sat, Oct 03, 2020 at 10:56:04AM +0200, Ard Biesheuvel wrote:
> > 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 at kernel.org>
> > Cc: James Morse <james.morse at arm.com>
> > Cc: Julien Thierry <julien.thierry.kdev at gmail.com>
> > Cc: Suzuki K Poulose <suzuki.poulose at arm.com>
> > Cc: Catalin Marinas <catalin.marinas at arm.com>
> > Cc: Will Deacon <will at kernel.org>
> > Cc: Mark Rutland <mark.rutland at arm.com>
> > Cc: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
> > Cc: Sudeep Holla <sudeep.holla at arm.com>
> > Cc: Sami Mujawar <sami.mujawar at arm.com>
> > Cc: Andre Przywara <andre.przywara at arm.com>
> > Cc: Alexandru Elisei <alexandru.elisei at arm.com>
> > Cc: Laszlo Ersek <lersek at redhat.com>
> > Cc: Leif Lindholm <leif at nuviainc.com>
> > Signed-off-by: Ard Biesheuvel <ardb at 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);
>
> Where does this UUID come from?
>
uuidgen
The only requirement for the UUID is that we can distinguish
implementations, in order to be able to disregard them if they are
known to have flaws.
You could make a case for passing the firmware's UUID if the calls are
relayed directly, but that would remove the caller's ability to avoid
the KVM on specifically.
> > +
> > +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);
>
> The spec says we should return "INVALID_PARAMETERS" when N > MAX_BITS.
> Of course "INVALID_PARAMETERS", with the 'S', doesn't exist in "Return
> codes", but I guess they meant "INVALID_PARAMETER", not NOT_SUPPORTED.
>
Will fix that.
> > + 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]));
>
> What if our host CPU is BE? We need to return these words in LE according
> to 5.3 of DEN0028C.
>
I hadn't looked at DEN0028C 5.3 at all, to be honest.
So we should interpret the whole uuid_t as __le32[4] not __be32[4],
switch to the appropriate accessors, and reverse the order of the
registers. That way, the first byte of the uuid_t will end up in the
least significant byte of W0, etc etc.
> > + 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
> >
> > _______________________________________________
> > kvmarm mailing list
> > kvmarm at lists.cs.columbia.edu
> > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
> >
>
> Thanks,
> drew
>
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