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

From: Oliver Upton
Date: Wed Nov 03 2021 - 20:16:03 EST

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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

> + 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.

> /* 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.

> +
> + /* 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

> };
>
> 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
>

Next message: davidcomponentone: "[PATCH] locking/ww-mutex: use swap() to make code cleaner"
Previous message: Sergey Senozhatsky: "Re: [PATCH] zram: use ATTRIBUTE_GROUPS"
In reply to: Raghavendra Rao Ananta: "[RFC PATCH 3/8] KVM: arm64: Add standard secure service calls firmware register"
Next in thread: Raghavendra Rao Ananta: "Re: [RFC PATCH 3/8] KVM: arm64: Add standard secure service calls firmware register"
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