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References: <20220423000328.2103733-1-rananta@google.com> <20220423000328.2103733-3-rananta@google.com>
 <bbaf7dcf-e776-49df-7a12-04b45e4af881@redhat.com>
In-Reply-To: <bbaf7dcf-e776-49df-7a12-04b45e4af881@redhat.com>
From:   Raghavendra Rao Ananta <rananta@google.com>
Date:   Tue, 26 Apr 2022 09:44:41 -0700
Message-ID: <CAJHc60w6YngA7iz=mUfjAEjQdwjG_pj2T9Cpd21xzU1Y_APCwQ@mail.gmail.com>
Subject: Re: [PATCH v6 2/9] KVM: arm64: Setup a framework for hypercall bitmap
 firmware registers
To:     Gavin Shan <gshan@redhat.com>
Cc:     Marc Zyngier <maz@kernel.org>, Andrew Jones <drjones@redhat.com>,
        James Morse <james.morse@arm.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        kvm@vger.kernel.org, Catalin Marinas <catalin.marinas@arm.com>,
        Peter Shier <pshier@google.com>, linux-kernel@vger.kernel.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Will Deacon <will@kernel.org>, kvmarm@lists.cs.columbia.edu,
        linux-arm-kernel@lists.infradead.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hi Gavin,

On Mon, Apr 25, 2022 at 11:34 PM Gavin Shan <gshan@redhat.com> wrote:
>
> Hi Raghavendra,
>
> On 4/23/22 8:03 AM, Raghavendra Rao Ananta wrote:
> > KVM regularly introduces new hypercall services to the guests without
> > any consent from the userspace. This means, the guests can observe
> > hypercall services in and out as they migrate across various host
> > kernel versions. This could be a major problem if the guest
> > discovered a hypercall, started using it, and after getting migrated
> > to an older kernel realizes that it's no longer available. Depending
> > on how the guest handles the change, there's a potential chance that
> > the guest would just panic.
> >
> > As a result, there's a need for the userspace to elect the services
> > that it wishes the guest to discover. It can elect these services
> > based on the kernels spread across its (migration) fleet. To remedy
> > this, extend the existing firmware pseudo-registers, such as
> > KVM_REG_ARM_PSCI_VERSION, but by creating a new COPROC register space
> > for all the hypercall services available.
> >
> > These firmware registers are categorized based on the service call
> > owners, but unlike the existing firmware pseudo-registers, they hold
> > the features supported in the form of a bitmap.
> >
> > During the VM initialization, the registers are set to upper-limit of
> > the features supported by the corresponding registers. It's expected
> > that the VMMs discover the features provided by each register via
> > GET_ONE_REG, and write back the desired values using SET_ONE_REG.
> > KVM allows this modification only until the VM has started.
> >
> > Some of the standard features are not mapped to any bits of the
> > registers. But since they can recreate the original problem of
> > making it available without userspace's consent, they need to
> > be explicitly added to the case-list in
> > kvm_hvc_call_default_allowed(). Any function-id that's not enabled
> > via the bitmap, or not listed in kvm_hvc_call_default_allowed, will
> > be returned as SMCCC_RET_NOT_SUPPORTED to the guest.
> >
> > Older userspace code can simply ignore the feature and the
> > hypercall services will be exposed unconditionally to the guests,
> > thus ensuring backward compatibility.
> >
> > In this patch, the framework adds the register only for ARM's standard
> > secure services (owner value 4). 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. Other services are
> > momentarily added in the upcoming patches.
> >
> > Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
> > ---
> >   arch/arm64/include/asm/kvm_host.h | 12 ++++
> >   arch/arm64/include/uapi/asm/kvm.h |  9 +++
> >   arch/arm64/kvm/arm.c              |  1 +
> >   arch/arm64/kvm/guest.c            |  8 ++-
> >   arch/arm64/kvm/hypercalls.c       | 94 +++++++++++++++++++++++++++++++
> >   arch/arm64/kvm/psci.c             | 13 +++++
> >   include/kvm/arm_hypercalls.h      |  6 ++
> >   include/kvm/arm_psci.h            |  2 +-
> >   8 files changed, 142 insertions(+), 3 deletions(-)
> >
>
> Some nits as below, please consider to improve if you need another
> respin.
>
> Reviewed-by: Gavin Shan <gshan@redhat.com>
>
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index 94a27a7520f4..df07f4c10197 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -101,6 +101,15 @@ struct kvm_s2_mmu {
> >   struct kvm_arch_memory_slot {
> >   };
> >
> > +/**
> > + * struct kvm_smccc_features: Descriptor the hypercall services exposed to the guests
> > + *
> > + * @std_bmap: Bitmap of standard secure service calls
> > + */
> > +struct kvm_smccc_features {
> > +     unsigned long std_bmap;
> > +};
> > +
>
> s/Descriptor/Descriptor of
>
Nice catch!

> >   struct kvm_arch {
> >       struct kvm_s2_mmu mmu;
> >
> > @@ -150,6 +159,9 @@ struct kvm_arch {
> >
> >       u8 pfr0_csv2;
> >       u8 pfr0_csv3;
> > +
> > +     /* Hypercall features firmware registers' descriptor */
> > +     struct kvm_smccc_features smccc_feat;
> >   };
> >
> >   struct kvm_vcpu_fault_info {
> > diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> > index c1b6ddc02d2f..0b79d2dc6ffd 100644
> > --- a/arch/arm64/include/uapi/asm/kvm.h
> > +++ b/arch/arm64/include/uapi/asm/kvm.h
> > @@ -332,6 +332,15 @@ struct kvm_arm_copy_mte_tags {
> >   #define KVM_ARM64_SVE_VLS_WORDS     \
> >       ((KVM_ARM64_SVE_VQ_MAX - KVM_ARM64_SVE_VQ_MIN) / 64 + 1)
> >
> > +/* Bitmap feature firmware registers */
> > +#define KVM_REG_ARM_FW_FEAT_BMAP             (0x0016 << KVM_REG_ARM_COPROC_SHIFT)
> > +#define KVM_REG_ARM_FW_FEAT_BMAP_REG(r)              (KVM_REG_ARM64 | KVM_REG_SIZE_U64 | \
> > +                                             KVM_REG_ARM_FW_FEAT_BMAP |      \
> > +                                             ((r) & 0xffff))
> > +
> > +#define KVM_REG_ARM_STD_BMAP                 KVM_REG_ARM_FW_FEAT_BMAP_REG(0)
> > +#define KVM_REG_ARM_STD_BIT_TRNG_V1_0                0
> > +
> >   /* Device Control API: ARM VGIC */
> >   #define KVM_DEV_ARM_VGIC_GRP_ADDR   0
> >   #define KVM_DEV_ARM_VGIC_GRP_DIST_REGS      1
> > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > index 523bc934fe2f..a37fadbd617e 100644
> > --- a/arch/arm64/kvm/arm.c
> > +++ b/arch/arm64/kvm/arm.c
> > @@ -156,6 +156,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> >       kvm->arch.max_vcpus = kvm_arm_default_max_vcpus();
> >
> >       set_default_spectre(kvm);
> > +     kvm_arm_init_hypercalls(kvm);
> >
> >       return ret;
> >   out_free_stage2_pgd:
> > diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> > index 0d5cca56cbda..8c607199cad1 100644
> > --- a/arch/arm64/kvm/guest.c
> > +++ b/arch/arm64/kvm/guest.c
> > @@ -756,7 +756,9 @@ int kvm_arm_get_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> >
> >       switch (reg->id & KVM_REG_ARM_COPROC_MASK) {
> >       case KVM_REG_ARM_CORE:  return get_core_reg(vcpu, reg);
> > -     case KVM_REG_ARM_FW:    return kvm_arm_get_fw_reg(vcpu, reg);
> > +     case KVM_REG_ARM_FW:
> > +     case KVM_REG_ARM_FW_FEAT_BMAP:
> > +             return kvm_arm_get_fw_reg(vcpu, reg);
> >       case KVM_REG_ARM64_SVE: return get_sve_reg(vcpu, reg);
> >       }
> >
> > @@ -774,7 +776,9 @@ int kvm_arm_set_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> >
> >       switch (reg->id & KVM_REG_ARM_COPROC_MASK) {
> >       case KVM_REG_ARM_CORE:  return set_core_reg(vcpu, reg);
> > -     case KVM_REG_ARM_FW:    return kvm_arm_set_fw_reg(vcpu, reg);
> > +     case KVM_REG_ARM_FW:
> > +     case KVM_REG_ARM_FW_FEAT_BMAP:
> > +             return kvm_arm_set_fw_reg(vcpu, reg);
> >       case KVM_REG_ARM64_SVE: return set_sve_reg(vcpu, reg);
> >       }
> >
> > diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
> > index fa6d9378d8e7..df55a04d2fe8 100644
> > --- a/arch/arm64/kvm/hypercalls.c
> > +++ b/arch/arm64/kvm/hypercalls.c
> > @@ -58,6 +58,48 @@ static void kvm_ptp_get_time(struct kvm_vcpu *vcpu, u64 *val)
> >       val[3] = lower_32_bits(cycles);
> >   }
> >
> > +static bool kvm_arm_fw_reg_feat_enabled(unsigned long *reg_bmap, unsigned long feat_bit)
> > +{
> > +     return test_bit(feat_bit, reg_bmap);
> > +}
> > +
>
> Might be worhty to be 'inline'. This function would be called
> frequently.
>
I was hoping the compiler would optimize it for us as needed.

> > +static bool kvm_hvc_call_default_allowed(struct kvm_vcpu *vcpu, u32 func_id)
> > +{
> > +     switch (func_id) {
> > +     /*
> > +      * List of function-ids that are not gated with the bitmapped feature
> > +      * firmware registers, and are to be allowed for servicing the call by default.
> > +      */
> > +     case ARM_SMCCC_VERSION_FUNC_ID:
> > +     case ARM_SMCCC_ARCH_FEATURES_FUNC_ID:
> > +     case ARM_SMCCC_HV_PV_TIME_FEATURES:
> > +     case ARM_SMCCC_HV_PV_TIME_ST:
> > +     case ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID:
> > +     case ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID:
> > +     case ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID:
> > +             return true;
> > +     default:
> > +             return kvm_psci_func_id_is_valid(vcpu, func_id);
> > +     }
> > +}
> > +
> > +static bool kvm_hvc_call_allowed(struct kvm_vcpu *vcpu, u32 func_id)
> > +{
> > +     struct kvm_smccc_features *smccc_feat = &vcpu->kvm->arch.smccc_feat;
> > +
> > +     switch (func_id) {
> > +     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_arm_fw_reg_feat_enabled(&smccc_feat->std_bmap,
> > +                                             KVM_REG_ARM_STD_BIT_TRNG_V1_0);
> > +     default:
> > +             return kvm_hvc_call_default_allowed(vcpu, func_id);
> > +     }
> > +}
> > +
> >   int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
> >   {
> >       u32 func_id = smccc_get_function(vcpu);
> > @@ -65,6 +107,9 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
> >       u32 feature;
> >       gpa_t gpa;
> >
> > +     if (!kvm_hvc_call_allowed(vcpu, func_id))
> > +             goto out;
> > +
> >       switch (func_id) {
> >       case ARM_SMCCC_VERSION_FUNC_ID:
> >               val[0] = ARM_SMCCC_VERSION_1_1;
> > @@ -155,6 +200,7 @@ 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;
> >   }
> > @@ -164,8 +210,16 @@ static const u64 kvm_arm_fw_reg_ids[] = {
> >       KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1,
> >       KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2,
> >       KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3,
> > +     KVM_REG_ARM_STD_BMAP,
> >   };
> >
> > +void kvm_arm_init_hypercalls(struct kvm *kvm)
> > +{
> > +     struct kvm_smccc_features *smccc_feat = &kvm->arch.smccc_feat;
> > +
> > +     smccc_feat->std_bmap = KVM_ARM_SMCCC_STD_FEATURES;
> > +}
> > +
> >   int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu)
> >   {
> >       return ARRAY_SIZE(kvm_arm_fw_reg_ids);
> > @@ -237,6 +291,7 @@ 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 kvm_smccc_features *smccc_feat = &vcpu->kvm->arch.smccc_feat;
> >       void __user *uaddr = (void __user *)(long)reg->addr;
> >       u64 val;
> >
> > @@ -249,6 +304,9 @@ int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> >       case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_3:
> >               val = get_kernel_wa_level(reg->id) & KVM_REG_FEATURE_LEVEL_MASK;
> >               break;
> > +     case KVM_REG_ARM_STD_BMAP:
> > +             val = READ_ONCE(smccc_feat->std_bmap);
> > +             break;
> >       default:
> >               return -ENOENT;
> >       }
> > @@ -259,6 +317,40 @@ int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> >       return 0;
> >   }
> >
> > +static int kvm_arm_set_fw_reg_bmap(struct kvm_vcpu *vcpu, u64 reg_id, u64 val)
> > +{
> > +     int ret = 0;
> > +     struct kvm *kvm = vcpu->kvm;
> > +     struct kvm_smccc_features *smccc_feat = &kvm->arch.smccc_feat;
> > +     unsigned long *fw_reg_bmap, fw_reg_features;
> > +
> > +     switch (reg_id) {
> > +     case KVM_REG_ARM_STD_BMAP:
> > +             fw_reg_bmap = &smccc_feat->std_bmap;
> > +             fw_reg_features = KVM_ARM_SMCCC_STD_FEATURES;
> > +             break;
> > +     default:
> > +             return -ENOENT;
> > +     }
> > +
> > +     /* Check for unsupported bit */
> > +     if (val & ~fw_reg_features)
> > +             return -EINVAL;
> > +
> > +     mutex_lock(&kvm->lock);
> > +
> > +     /* Return -EBUSY if the VM (any vCPU) has already started running. */
> > +     if (test_bit(KVM_ARCH_FLAG_HAS_RAN_ONCE, &kvm->arch.flags)) {
> > +             ret = -EBUSY;
> > +             goto out;
> > +     }
> > +
> > +     WRITE_ONCE(*fw_reg_bmap, val);
> > +out:
> > +     mutex_unlock(&kvm->lock);
> > +     return ret;
> > +}
> > +
> >   int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> >   {
> >       void __user *uaddr = (void __user *)(long)reg->addr;
> > @@ -337,6 +429,8 @@ int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> >                       return -EINVAL;
> >
> >               return 0;
> > +     case KVM_REG_ARM_STD_BMAP:
> > +             return kvm_arm_set_fw_reg_bmap(vcpu, reg->id, val);
> >       default:
> >               return -ENOENT;
> >       }
> > diff --git a/arch/arm64/kvm/psci.c b/arch/arm64/kvm/psci.c
> > index 346535169faa..67d1273e8086 100644
> > --- a/arch/arm64/kvm/psci.c
> > +++ b/arch/arm64/kvm/psci.c
> > @@ -436,3 +436,16 @@ int kvm_psci_call(struct kvm_vcpu *vcpu)
> >               return -EINVAL;
> >       }
> >   }
> > +
> > +bool kvm_psci_func_id_is_valid(struct kvm_vcpu *vcpu, u32 func_id)
> > +{
> > +     /* PSCI 0.1 doesn't comply with the standard SMCCC */
> > +     if (kvm_psci_version(vcpu) == KVM_ARM_PSCI_0_1)
> > +             return (func_id == KVM_PSCI_FN_CPU_OFF || func_id == KVM_PSCI_FN_CPU_ON);
> > +
> > +     if (ARM_SMCCC_OWNER_NUM(func_id) == ARM_SMCCC_OWNER_STANDARD &&
> > +             ARM_SMCCC_FUNC_NUM(func_id) >= 0 && ARM_SMCCC_FUNC_NUM(func_id) <= 0x1f)
> > +             return true;
> > +
> > +     return false;
> > +}
> > diff --git a/include/kvm/arm_hypercalls.h b/include/kvm/arm_hypercalls.h
> > index 5d38628a8d04..499b45b607b6 100644
> > --- a/include/kvm/arm_hypercalls.h
> > +++ b/include/kvm/arm_hypercalls.h
> > @@ -6,6 +6,11 @@
> >
> >   #include <asm/kvm_emulate.h>
> >
> > +/* Last valid bits of the bitmapped firmware registers */
> > +#define KVM_REG_ARM_STD_BMAP_BIT_MAX         0
> > +
> > +#define KVM_ARM_SMCCC_STD_FEATURES           GENMASK(KVM_REG_ARM_STD_BMAP_BIT_MAX, 0)
> > +
>
> s/bits of/bit of
>
Great catch again!

> >   int kvm_hvc_call_handler(struct kvm_vcpu *vcpu);
> >
> >   static inline u32 smccc_get_function(struct kvm_vcpu *vcpu)
> > @@ -42,6 +47,7 @@ static inline void smccc_set_retval(struct kvm_vcpu *vcpu,
> >
> >   struct kvm_one_reg;
> >
> > +void kvm_arm_init_hypercalls(struct kvm *kvm);
> >   int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu);
> >   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);
> > diff --git a/include/kvm/arm_psci.h b/include/kvm/arm_psci.h
> > index 6e55b9283789..c47be3e26965 100644
> > --- a/include/kvm/arm_psci.h
> > +++ b/include/kvm/arm_psci.h
> > @@ -36,7 +36,7 @@ static inline int kvm_psci_version(struct kvm_vcpu *vcpu)
> >       return KVM_ARM_PSCI_0_1;
> >   }
> >
> > -
> >   int kvm_psci_call(struct kvm_vcpu *vcpu);
> > +bool kvm_psci_func_id_is_valid(struct kvm_vcpu *vcpu, u32 func_id);
> >
> >   #endif /* __KVM_ARM_PSCI_H__ */
> >
>
> Thanks,
> Gavin
>

Thanks for the review, Gavin.

- Raghavendra