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

["Alex Bennée" <alex.bennee@linaro.org>]

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

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel