Re: [RFC PATCH 3/8] KVM: arm64: Add standard secure service calls firmware register

From: Raghavendra Rao Ananta
Date: Thu Nov 04 2021 - 14:01:08 EST

On Wed, Nov 3, 2021 at 5:15 PM Oliver Upton <oupton@xxxxxxxxxx> wrote:
>
> On Tue, Nov 02, 2021 at 12:21:58AM +0000, Raghavendra Rao Ananta wrote:
> > Introduce a firmware register that encapsulates standard secure
> > service calls (owner value 4) as a bitmap. Depending on how the
> > user-space configures the register, the features will be enabled
> > or disabled for the guest. Currently, this includes support only
> > for ARM True Random Number Generator (TRNG) service, with bit-0
> > of the register representing mandatory features of v1.0.
> >
> > Signed-off-by: Raghavendra Rao Ananta <rananta@xxxxxxxxxx>
> > ---
> > Documentation/virt/kvm/arm/hypercalls.rst | 17 +++++
> > arch/arm64/include/asm/kvm_host.h | 2 +
> > arch/arm64/include/uapi/asm/kvm.h | 6 ++
> > arch/arm64/kvm/arm.c | 8 +++
> > arch/arm64/kvm/hypercalls.c | 75 ++++++++++++++++++++++-
> > arch/arm64/kvm/trng.c | 9 +--
> > include/kvm/arm_hypercalls.h | 5 ++
> > 7 files changed, 113 insertions(+), 9 deletions(-)
> >
> > diff --git a/Documentation/virt/kvm/arm/hypercalls.rst b/Documentation/virt/kvm/arm/hypercalls.rst
> > index 85dfd682d811..1601919f256d 100644
> > --- a/Documentation/virt/kvm/arm/hypercalls.rst
> > +++ b/Documentation/virt/kvm/arm/hypercalls.rst
> > @@ -20,6 +20,14 @@ pseudo-registers" that can be manipulated using the GET/SET_ONE_REG
> > interface. These registers can be saved/restored by userspace, and set
> > to a convenient value if required.
> >
> > +The firmware register KVM_REG_ARM_STD exposes the hypercall services
>
> nit: try to cram BITMAP in the name. IMO, this will help disambiguate
> with version-based FW regs, like KVM_REG_ARM_PSCI_VERSION.
>
> > +in the form of a feature bitmap. Upon VM creation, by default, KVM exposes
> > +all the features to the guest, which can be learnt using GET_ONE_REG
> > +interface. Conversely, the features can be enabled or disabled via the
> > +SET_ONE_REG interface. These registers allow the user-space modification
> > +only until the VM has started running, after which they turn to read-only
> > +registers. SET_ONE_REG in this scenario will return -EBUSY.
> > +
> > The following register is defined:
> >
> > * KVM_REG_ARM_PSCI_VERSION:
> > @@ -74,4 +82,13 @@ The following register is defined:
> > KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED:
> > The workaround is always active on this vCPU or it is not needed.
> >
> > +* KVM_REG_ARM_STD:
> > + Controls the bitmap of the ARM Standard Secure Service Calls.
> > +
> > + The following bits are accepted:
> > +
> > + KVM_REG_ARM_STD_TRNG_V1_0:
>
> state the bit position as well
>
I was afraid of the name getting too long. But let me see.
> > + The bit represents the services offered under v1.0 of ARM True Random Number Generator
> > + (TRNG) specification (ARM DEN 0098).
> > +
> > .. [1] https://developer.arm.com/-/media/developer/pdf/ARM_DEN_0070A_Firmware_interfaces_for_mitigating_CVE-2017-5715.pdf
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index 0b2502494a17..176d6be7b4da 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -105,6 +105,8 @@ struct kvm_arch_memory_slot {
> > struct hvc_reg_desc {
> > bool write_disabled;
> > bool write_attempted;
> > +
> > + u64 kvm_std_bmap;
> > };
> >
> > struct kvm_arch {
> > diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> > index b3edde68bc3e..6387dea5396d 100644
> > --- a/arch/arm64/include/uapi/asm/kvm.h
> > +++ b/arch/arm64/include/uapi/asm/kvm.h
> > @@ -281,6 +281,12 @@ struct kvm_arm_copy_mte_tags {
> > #define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED 3
> > #define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED (1U << 4)
> >
> > +#define KVM_REG_ARM_STD KVM_REG_ARM_FW_REG(3)
> > +enum kvm_reg_arm_std_bmap {
> > + KVM_REG_ARM_STD_TRNG_V1_0,
> > + KVM_REG_ARM_STD_BMAP_MAX,
> > +};
> > +
>
> I would recommend just defining the bit values explicitly rather than
> using an enumeration:
>
> #define KVM_REG_ARM_STD_TRNG_V1_0 (1ULL << 0)
>
> You do lose the convenience of having KVM_REG_ARM_STD_BMAP_MAX.
>
Just curious, any particular reason for this? IMO, going an enum route
could avoid human errors. Anything I'm missing?
> > /* SVE registers */
> > #define KVM_REG_ARM64_SVE (0x15 << KVM_REG_ARM_COPROC_SHIFT)
> >
> > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > index f9a25e439e99..1cf58aa49222 100644
> > --- a/arch/arm64/kvm/arm.c
> > +++ b/arch/arm64/kvm/arm.c
> > @@ -130,6 +130,13 @@ static void set_default_spectre(struct kvm *kvm)
> > kvm->arch.pfr0_csv3 = 1;
> > }
> >
> > +static void set_default_hypercalls(struct kvm *kvm)
> > +{
> > + struct hvc_reg_desc *hvc_desc = &kvm->arch.hvc_desc;
> > +
> > + hvc_desc->kvm_std_bmap = ARM_SMCCC_STD_FEATURES;
> > +}
> > +
> > /**
> > * kvm_arch_init_vm - initializes a VM data structure
> > * @kvm: pointer to the KVM struct
> > @@ -156,6 +163,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> > kvm->arch.max_vcpus = kvm_arm_default_max_vcpus();
> >
> > set_default_spectre(kvm);
> > + set_default_hypercalls(kvm);
> >
> > return ret;
> > out_free_stage2_pgd:
> > diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
> > index 7e873206a05b..0b3006353bf6 100644
> > --- a/arch/arm64/kvm/hypercalls.c
> > +++ b/arch/arm64/kvm/hypercalls.c
> > @@ -60,8 +60,64 @@ static void kvm_ptp_get_time(struct kvm_vcpu *vcpu, u64 *val)
> >
> > static u64 *kvm_fw_reg_to_bmap(struct kvm *kvm, u64 fw_reg)
> > {
> > - /* No firmware registers supporting hvc bitmaps exits yet */
> > - return NULL;
> > + struct hvc_reg_desc *hvc_desc = &kvm->arch.hvc_desc;
> > +
> > + switch (fw_reg) {
> > + case KVM_REG_ARM_STD:
> > + return &hvc_desc->kvm_std_bmap;
> > + default:
> > + return NULL;
> > + }
> > +}
> > +
> > +struct kvm_hvc_func_map {
> > + u32 func_id;
> > + u64 bmap_bit;
> > +};
> > +
> > +#define HVC_FUNC_MAP_DESC(func, bit) \
> > + { \
> > + .func_id = func, \
> > + .bmap_bit = bit, \
> > + }
> > +
> > +static const struct kvm_hvc_func_map hvc_std_map[] = {
> > + HVC_FUNC_MAP_DESC(ARM_SMCCC_TRNG_GET_UUID, KVM_REG_ARM_STD_TRNG_V1_0),
> > + HVC_FUNC_MAP_DESC(ARM_SMCCC_TRNG_RND32, KVM_REG_ARM_STD_TRNG_V1_0),
> > + HVC_FUNC_MAP_DESC(ARM_SMCCC_TRNG_RND64, KVM_REG_ARM_STD_TRNG_V1_0),
> > +};
> > +
> > +bool kvm_hvc_call_supported(struct kvm_vcpu *vcpu, u32 func_id)
> > +{
> > + struct kvm *kvm = vcpu->kvm;
> > + u8 hvc_owner = ARM_SMCCC_OWNER_NUM(func_id);
> > + const struct kvm_hvc_func_map *hvc_func_map = NULL;
> > +
> > + u64 fw_reg, *hc_bmap;
> > + unsigned int map_sz, i;
> > +
> > + switch (hvc_owner) {
> > + case ARM_SMCCC_OWNER_STANDARD:
> > + fw_reg = KVM_REG_ARM_STD;
> > + hvc_func_map = hvc_std_map;
> > + map_sz = ARRAY_SIZE(hvc_std_map);
> > + break;
> > + default:
> > + /* Allow all the owners that aren't mapped */
> > + return true;
> > + }
> > +
> > + hc_bmap = kvm_fw_reg_to_bmap(kvm, fw_reg);
> > + if (!hc_bmap)
> > + return true;
> > +
> > + for (i = 0; i < map_sz; i++) {
> > + if (func_id == hvc_func_map[i].func_id)
> > + return *hc_bmap & BIT(hvc_func_map[i].bmap_bit);
> > + }
>
> Hrm...
>
> Could you instead define a helper function for each service and use a
> switch statement to ensure each function tests the correct bit? This
> would avoid the need to loop over a map.
>
I think so.. I guess I was trying to avoid making too many changes if
we want to support a new func_id.
> > +
> > + /* Allow all the functions of an owner that aren't mapped */
> > + return true;
> > }
> >
> > int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
> > @@ -71,6 +127,9 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
> > u32 feature;
> > gpa_t gpa;
> >
> > + if (!kvm_hvc_call_supported(vcpu, func_id))
> > + goto out;
> > +
> > switch (func_id) {
> > case ARM_SMCCC_VERSION_FUNC_ID:
> > val[0] = ARM_SMCCC_VERSION_1_1;
> > @@ -149,6 +208,7 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
> > return kvm_psci_call(vcpu);
> > }
> >
> > +out:
> > smccc_set_retval(vcpu, val[0], val[1], val[2], val[3]);
> > return 1;
> > }
> > @@ -157,6 +217,7 @@ static const u64 fw_reg_ids[] = {
> > KVM_REG_ARM_PSCI_VERSION,
> > KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1,
> > KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2,
> > + KVM_REG_ARM_STD,
>
> This (and all other FW regs you add) need to be added to the
> get-reg-list selftest. Marc/Andrew have reminded me enough times to do
> this myself, so I'll share suggestion :-P
>
Yes, of course. It's on my todo list. I'll try to include that in the
next patchset.
> > };
> >
> > int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu)
> > @@ -219,6 +280,7 @@ static int get_kernel_wa_level(u64 regid)
> >
> > int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> > {
> > + struct hvc_reg_desc *hvc_desc = &vcpu->kvm->arch.hvc_desc;
> > void __user *uaddr = (void __user *)(long)reg->addr;
> > u64 val;
> >
> > @@ -230,6 +292,9 @@ int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> > case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2:
> > val = get_kernel_wa_level(reg->id) & KVM_REG_FEATURE_LEVEL_MASK;
> > break;
> > + case KVM_REG_ARM_STD:
> > + val = hvc_desc->kvm_std_bmap;
> > + break;
> > default:
> > return -ENOENT;
> > }
> > @@ -352,6 +417,12 @@ int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> > if (get_kernel_wa_level(reg->id) < wa_level)
> > return -EINVAL;
> >
> > + return 0;
> > + case KVM_REG_ARM_STD:
> > + if (val & ~ARM_SMCCC_STD_FEATURES)
> > + return -EINVAL;
> > +
> > + hvc_desc->kvm_std_bmap = val;
> > return 0;
> > default:
> > return -ENOENT;
> > diff --git a/arch/arm64/kvm/trng.c b/arch/arm64/kvm/trng.c
> > index 99bdd7103c9c..6dff765f5b9b 100644
> > --- a/arch/arm64/kvm/trng.c
> > +++ b/arch/arm64/kvm/trng.c
> > @@ -60,14 +60,9 @@ int kvm_trng_call(struct kvm_vcpu *vcpu)
> > 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:
> > + if (kvm_hvc_call_supported(vcpu, smccc_get_arg1(vcpu)))
> > val = TRNG_SUCCESS;
> > - }
> > +
> > break;
> > case ARM_SMCCC_TRNG_GET_UUID:
> > smccc_set_retval(vcpu, le32_to_cpu(u[0]), le32_to_cpu(u[1]),
> > diff --git a/include/kvm/arm_hypercalls.h b/include/kvm/arm_hypercalls.h
> > index 5d38628a8d04..5f01bb139312 100644
> > --- a/include/kvm/arm_hypercalls.h
> > +++ b/include/kvm/arm_hypercalls.h
> > @@ -6,6 +6,9 @@
> >
> > #include <asm/kvm_emulate.h>
> >
> > +#define ARM_SMCCC_STD_FEATURES \
> > + GENMASK_ULL(KVM_REG_ARM_STD_BMAP_MAX - 1, 0)
> > +
> > int kvm_hvc_call_handler(struct kvm_vcpu *vcpu);
> >
> > static inline u32 smccc_get_function(struct kvm_vcpu *vcpu)
> > @@ -47,4 +50,6 @@ int kvm_arm_copy_fw_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices);
> > int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg);
> > int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg);
> >
> > +bool kvm_hvc_call_supported(struct kvm_vcpu *vcpu, u32 func_id);
> > +
> > #endif
> > --
> > 2.33.1.1089.g2158813163f-goog
> >