On Mon, Jan 07, 2019 at 12:05:36PM +0000, Andre Przywara wrote:
> KVM implements the firmware interface for mitigating cache speculation
> vulnerabilities. Guests may use this interface to ensure mitigation is
> active.
> If we want to migrate such a guest to a host with a different support
> level for those workarounds, migration might need to fail, to ensure that
> critical guests don't loose their protection.
>
> Introduce a way for userland to save and restore the workarounds state.
> On restoring we do checks that make sure we don't downgrade our
> mitigation level.
>
> Signed-off-by: Andre Przywara <andre.przyw...@arm.com>
> ---
> arch/arm/include/asm/kvm_emulate.h | 10 ++
> arch/arm/include/uapi/asm/kvm.h | 9 ++
> arch/arm64/include/asm/kvm_emulate.h | 14 +++
> arch/arm64/include/uapi/asm/kvm.h | 9 ++
> virt/kvm/arm/psci.c | 138 ++++++++++++++++++++++++++-
> 5 files changed, 178 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/include/asm/kvm_emulate.h
> b/arch/arm/include/asm/kvm_emulate.h
> index 77121b713bef..2255c50debab 100644
> --- a/arch/arm/include/asm/kvm_emulate.h
> +++ b/arch/arm/include/asm/kvm_emulate.h
> @@ -275,6 +275,16 @@ static inline unsigned long
> kvm_vcpu_get_mpidr_aff(struct kvm_vcpu *vcpu)
> return vcpu_cp15(vcpu, c0_MPIDR) & MPIDR_HWID_BITMASK;
> }
>
> +static inline bool kvm_arm_get_vcpu_workaround_2_flag(struct kvm_vcpu *vcpu)
> +{
> + return false;
> +}
> +
> +static inline void kvm_arm_set_vcpu_workaround_2_flag(struct kvm_vcpu *vcpu,
> + bool flag)
> +{
> +}
> +
> static inline void kvm_vcpu_set_be(struct kvm_vcpu *vcpu)
> {
> *vcpu_cpsr(vcpu) |= PSR_E_BIT;
> diff --git a/arch/arm/include/uapi/asm/kvm.h b/arch/arm/include/uapi/asm/kvm.h
> index 4602464ebdfb..02c93b1d8f6d 100644
> --- a/arch/arm/include/uapi/asm/kvm.h
> +++ b/arch/arm/include/uapi/asm/kvm.h
> @@ -214,6 +214,15 @@ struct kvm_vcpu_events {
> #define KVM_REG_ARM_FW_REG(r) (KVM_REG_ARM | KVM_REG_SIZE_U64
> | \
> KVM_REG_ARM_FW | ((r) & 0xffff))
> #define KVM_REG_ARM_PSCI_VERSION KVM_REG_ARM_FW_REG(0)
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1 KVM_REG_ARM_FW_REG(1)
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL 0
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_AVAIL 1
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2 KVM_REG_ARM_FW_REG(2)
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_MASK 0x3
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL 0
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL 1
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNAFFECTED 2
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED 4
>
> /* Device Control API: ARM VGIC */
> #define KVM_DEV_ARM_VGIC_GRP_ADDR 0
> diff --git a/arch/arm64/include/asm/kvm_emulate.h
> b/arch/arm64/include/asm/kvm_emulate.h
> index 506386a3edde..a44f07f68da4 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -336,6 +336,20 @@ static inline unsigned long
> kvm_vcpu_get_mpidr_aff(struct kvm_vcpu *vcpu)
> return vcpu_read_sys_reg(vcpu, MPIDR_EL1) & MPIDR_HWID_BITMASK;
> }
>
> +static inline bool kvm_arm_get_vcpu_workaround_2_flag(struct kvm_vcpu *vcpu)
> +{
> + return vcpu->arch.workaround_flags & VCPU_WORKAROUND_2_FLAG;
> +}
> +
> +static inline void kvm_arm_set_vcpu_workaround_2_flag(struct kvm_vcpu *vcpu,
> + bool flag)
> +{
> + if (flag)
> + vcpu->arch.workaround_flags |= VCPU_WORKAROUND_2_FLAG;
> + else
> + vcpu->arch.workaround_flags &= ~VCPU_WORKAROUND_2_FLAG;
> +}
> +
> static inline void kvm_vcpu_set_be(struct kvm_vcpu *vcpu)
> {
> if (vcpu_mode_is_32bit(vcpu)) {
> diff --git a/arch/arm64/include/uapi/asm/kvm.h
> b/arch/arm64/include/uapi/asm/kvm.h
> index 97c3478ee6e7..4a19ef199a99 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -225,6 +225,15 @@ struct kvm_vcpu_events {
> #define KVM_REG_ARM_FW_REG(r) (KVM_REG_ARM64 |
> KVM_REG_SIZE_U64 | \
> KVM_REG_ARM_FW | ((r) & 0xffff))
> #define KVM_REG_ARM_PSCI_VERSION KVM_REG_ARM_FW_REG(0)
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1 KVM_REG_ARM_FW_REG(1)
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL 0
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_AVAIL 1
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2 KVM_REG_ARM_FW_REG(2)
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_MASK 0x3
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL 0
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL 1
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNAFFECTED 2
> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED 4
If this is the first exposure of this information to userspace, I wonder
if we can come up with some common semantics that avoid having to add
new ad-hoc code (and bugs) every time a new vulnerability/workaround is
defined.
We seem to have at least the two following independent properties
for a vulnerability, with the listed values for each:
* vulnerability (Vulnerable, Unknown, Not Vulnerable)
* mitigation support (Not Requestable, Requestable)
Migrations must not move to the left in _either_ list for any
vulnerability.
If we want to hedge out bets we could follow the style of the ID
registers and allocate to each theoretical vulnerability a pair of
signed 2- or (for more expansion room if we think we might need it)
4-bit fields.
We could perhaps allocate as follows:
* -1=Vulnerable, 0=Unknown, 1=Not Vulnerable
* 0=Mitigation not requestable, 1=Mitigation requestable
Checking code wouldn't need to know which fields describe mitigation
mechanisms and which describe vulnerabilities: we'd just do a strict >=
comparison on each.
Further, if a register is never written before the vcpu is first run,
we should imply a write of 0 to it as part of KVM_RUN (so that if the
destination node has a negative value anywhere, KVM_RUN barfs cleanly.
(Those semantics should apply equally to the CPU ID registers, though
we don't currently do that.)
Thoughts?
[...]
Cheers
---Dave
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