Re: [PATCH v7 17/27] KVM: arm64: Reject ioctl access to FPSIMD V-regs on SVE vcpus

Alex Bennée
2019-04-24T13:45:40Z

Dave Martin <Dave.Martin@arm.com> writes:

> In order to avoid the pointless complexity of maintaining two ioctl
> register access views of the same data, this patch blocks ioctl
> access to the FPSIMD V-registers on vcpus that support SVE.
>
> This will make it more straightforward to add SVE register access
> support.
>
> Since SVE is an opt-in feature for userspace, this will not affect
> existing users.
>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> Reviewed-by: Julien Thierry <julien.thierry@arm.com>
> Tested-by: zhang.lei <zhang.lei@jp.fujitsu.com>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

>
> ---
>
> Changes since v5:
>
> * Refactored to cope with the removal of core_reg_size_from_offset()
> (which was added by another series which will now be handled
> independently).
>
> This leaves some duplication in that we still filter the V-regs out
> in two places, but this no worse than other existing code in guest.c.
> I plan to tidy this up independently later on.
> ---
> arch/arm64/kvm/guest.c | 48 ++++++++++++++++++++++++++++++++++++------------
> 1 file changed, 36 insertions(+), 12 deletions(-)
>
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index a391a61..756d0d6 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -54,12 +54,19 @@ int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)
> return 0;
> }
>
> +static bool core_reg_offset_is_vreg(u64 off)
> +{
> + return off >= KVM_REG_ARM_CORE_REG(fp_regs.vregs) &&
> + off < KVM_REG_ARM_CORE_REG(fp_regs.fpsr);
> +}
> +
> static u64 core_reg_offset_from_id(u64 id)
> {
> return id & ~(KVM_REG_ARCH_MASK | KVM_REG_SIZE_MASK | KVM_REG_ARM_CORE);
> }
>
> -static int validate_core_offset(const struct kvm_one_reg *reg)
> +static int validate_core_offset(const struct kvm_vcpu *vcpu,
> + const struct kvm_one_reg *reg)
> {
> u64 off = core_reg_offset_from_id(reg->id);
> int size;
> @@ -91,11 +98,19 @@ static int validate_core_offset(const struct kvm_one_reg *reg)
> return -EINVAL;
> }
>
> - if (KVM_REG_SIZE(reg->id) == size &&
> - IS_ALIGNED(off, size / sizeof(__u32)))
> - return 0;
> + if (KVM_REG_SIZE(reg->id) != size ||
> + !IS_ALIGNED(off, size / sizeof(__u32)))
> + return -EINVAL;
>
> - return -EINVAL;
> + /*
> + * The KVM_REG_ARM64_SVE regs must be used instead of
> + * KVM_REG_ARM_CORE for accessing the FPSIMD V-registers on
> + * SVE-enabled vcpus:
> + */
> + if (vcpu_has_sve(vcpu) && core_reg_offset_is_vreg(off))
> + return -EINVAL;
> +
> + return 0;
> }
>
> static int get_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> @@ -117,7 +132,7 @@ static int get_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> (off + (KVM_REG_SIZE(reg->id) / sizeof(__u32))) >= nr_regs)
> return -ENOENT;
>
> - if (validate_core_offset(reg))
> + if (validate_core_offset(vcpu, reg))
> return -EINVAL;
>
> if (copy_to_user(uaddr, ((u32 *)regs) + off, KVM_REG_SIZE(reg->id)))
> @@ -142,7 +157,7 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> (off + (KVM_REG_SIZE(reg->id) / sizeof(__u32))) >= nr_regs)
> return -ENOENT;
>
> - if (validate_core_offset(reg))
> + if (validate_core_offset(vcpu, reg))
> return -EINVAL;
>
> if (KVM_REG_SIZE(reg->id) > sizeof(tmp))
> @@ -195,13 +210,22 @@ int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
> return -EINVAL;
> }
>
> -static int kvm_arm_copy_core_reg_indices(u64 __user *uindices)
> +static int copy_core_reg_indices(const struct kvm_vcpu *vcpu,
> + u64 __user *uindices)
> {
> unsigned int i;
> int n = 0;
> const u64 core_reg = KVM_REG_ARM64 | KVM_REG_SIZE_U64 | KVM_REG_ARM_CORE;
>
> for (i = 0; i < sizeof(struct kvm_regs) / sizeof(__u32); i++) {
> + /*
> + * The KVM_REG_ARM64_SVE regs must be used instead of
> + * KVM_REG_ARM_CORE for accessing the FPSIMD V-registers on
> + * SVE-enabled vcpus:
> + */
> + if (vcpu_has_sve(vcpu) && core_reg_offset_is_vreg(i))
> + continue;
> +
> if (uindices) {
> if (put_user(core_reg | i, uindices))
> return -EFAULT;
> @@ -214,9 +238,9 @@ static int kvm_arm_copy_core_reg_indices(u64 __user *uindices)
> return n;
> }
>
> -static unsigned long num_core_regs(void)
> +static unsigned long num_core_regs(const struct kvm_vcpu *vcpu)
> {
> - return kvm_arm_copy_core_reg_indices(NULL);
> + return copy_core_reg_indices(vcpu, NULL);
> }
>
> /**
> @@ -281,7 +305,7 @@ unsigned long kvm_arm_num_regs(struct kvm_vcpu *vcpu)
> {
> unsigned long res = 0;
>
> - res += num_core_regs();
> + res += num_core_regs(vcpu);
> res += kvm_arm_num_sys_reg_descs(vcpu);
> res += kvm_arm_get_fw_num_regs(vcpu);
> res += NUM_TIMER_REGS;
> @@ -298,7 +322,7 @@ int kvm_arm_copy_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices)
> {
> int ret;
>
> - ret = kvm_arm_copy_core_reg_indices(uindices);
> + ret = copy_core_reg_indices(vcpu, uindices);
> if (ret)
> return ret;
> uindices += ret;

--
Alex Bennée