Re: [PATCH v5 17/26] KVM: arm64: Reject ioctl access to FPSIMD V-regs on SVE vcpus

[Julien Thierry <julien.thierry@arm.com>]

On 18/02/2019 19:52, Dave Martin wrote:
> 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>

> ---
>  arch/arm64/kvm/guest.c | 38 +++++++++++++++++++++++++++-----------
>  1 file changed, 27 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index f83fe22..f491456 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -95,7 +95,14 @@ static int core_reg_size_from_offset(u64 off)
>  	return -EINVAL;
>  }
>  
> -static int validate_core_offset(const struct kvm_one_reg *reg)
> +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 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 = core_reg_size_from_offset(off);
> @@ -103,10 +110,18 @@ static int validate_core_offset(const struct kvm_one_reg *reg)
>  	if (size < 0)
>  		return -EINVAL;
>  
> -	if (KVM_REG_SIZE(reg->id) == size)
> -		return 0;
> +	if (KVM_REG_SIZE(reg->id) != size)
> +		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)
> @@ -128,7 +143,7 @@ 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)))
> @@ -153,7 +168,7 @@ 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))
> @@ -206,7 +221,8 @@ int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
>  	return -EINVAL;
>  }
>  
> -static int copy_core_reg_indices(u64 __user **uind)
> +static int copy_core_reg_indices(const struct kvm_vcpu *vcpu,
> +				 u64 __user **uind)
>  {
>  	unsigned int i;
>  	int n = 0;
> @@ -248,9 +264,9 @@ static int copy_core_reg_indices(u64 __user **uind)
>  	return n;
>  }
>  
> -static unsigned long num_core_regs(void)
> +static unsigned long num_core_regs(const struct kvm_vcpu *vcpu)
>  {
> -	return copy_core_reg_indices(NULL);
> +	return copy_core_reg_indices(vcpu, NULL);
>  }
>  
>  /**
> @@ -315,7 +331,7 @@ 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;
> @@ -332,7 +348,7 @@ int kvm_arm_copy_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices)
>  {
>  	int ret;
>  
> -	ret = copy_core_reg_indices(&uindices);
> +	ret = copy_core_reg_indices(vcpu, &uindices);
>  	if (ret < 0)
>  		return ret;
>  
> 

-- 
Julien Thierry