RE: [PATCH v4 07/10] KVM: arm/arm64: vgic: Return error on incompatible uaccess GICD_IIDR writes

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Hi Christoffer,

> -----Original Message-----
> From: kvmarm-bounces@xxxxxxxxxxxxxxxxxxxxx [mailto:kvmarm-
> bounces@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of Christoffer Dall
> Sent: Monday, July 16, 2018 6:36 PM
> To: kvmarm@xxxxxxxxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: kvm@xxxxxxxxxxxxxxx; Marc Zyngier <marc.zyngier@xxxxxxx>; Andre
> Przywara <andre.przywara@xxxxxxx>
> Subject: [PATCH v4 07/10] KVM: arm/arm64: vgic: Return error on
> incompatible uaccess GICD_IIDR writes
> 
> If userspace attempts to write a GICD_IIDR that does not match the
> kernel version, return an error to userspace.  The intention is to allow
> implementation changes inside KVM while avoiding silently breaking
> migration resulting in guests not running without any clear indication
> of what went wrong.
> 
> Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxx>
> ---
>  virt/kvm/arm/vgic/vgic-mmio-v2.c | 21 ++++++++++++++++++---
>  virt/kvm/arm/vgic/vgic-mmio-v3.c | 21 ++++++++++++++++++---
>  2 files changed, 36 insertions(+), 6 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-mmio-v2.c b/virt/kvm/arm/vgic/vgic-
> mmio-v2.c
> index db646f1..4f0f2c4 100644
> --- a/virt/kvm/arm/vgic/vgic-mmio-v2.c
> +++ b/virt/kvm/arm/vgic/vgic-mmio-v2.c
> @@ -75,6 +75,20 @@ static void vgic_mmio_write_v2_misc(struct kvm_vcpu
> *vcpu,
>  	}
>  }
> 
> +static int vgic_mmio_uaccess_write_v2_misc(struct kvm_vcpu *vcpu,
> +					   gpa_t addr, unsigned int len,
> +					   unsigned long val)
> +{
> +	switch (addr & 0x0c) {

I am just understanding the code, not sure if it make sense to replace hardcoded "0x0c".

Thanks
-Bharat

> +	case GIC_DIST_IIDR:
> +		if (val != vgic_mmio_read_v2_misc(vcpu, addr, len))
> +			return -EINVAL;
> +	}
> +
> +	vgic_mmio_write_v2_misc(vcpu, addr, len, val);
> +	return 0;
> +}
> +
>  static void vgic_mmio_write_sgir(struct kvm_vcpu *source_vcpu,
>  				 gpa_t addr, unsigned int len,
>  				 unsigned long val)
> @@ -367,9 +381,10 @@ static void vgic_mmio_write_apr(struct kvm_vcpu
> *vcpu,
>  }
> 
>  static const struct vgic_register_region vgic_v2_dist_registers[] = {
> -	REGISTER_DESC_WITH_LENGTH(GIC_DIST_CTRL,
> -		vgic_mmio_read_v2_misc, vgic_mmio_write_v2_misc, 12,
> -		VGIC_ACCESS_32bit),
> +	REGISTER_DESC_WITH_LENGTH_UACCESS(GIC_DIST_CTRL,
> +		vgic_mmio_read_v2_misc, vgic_mmio_write_v2_misc,
> +		NULL, vgic_mmio_uaccess_write_v2_misc,
> +		12, VGIC_ACCESS_32bit),
>  	REGISTER_DESC_WITH_BITS_PER_IRQ(GIC_DIST_IGROUP,
>  		vgic_mmio_read_raz, vgic_mmio_write_wi, NULL, NULL, 1,
>  		VGIC_ACCESS_32bit),
> diff --git a/virt/kvm/arm/vgic/vgic-mmio-v3.c b/virt/kvm/arm/vgic/vgic-
> mmio-v3.c
> index ef57a1a..abdb0ec 100644
> --- a/virt/kvm/arm/vgic/vgic-mmio-v3.c
> +++ b/virt/kvm/arm/vgic/vgic-mmio-v3.c
> @@ -113,6 +113,20 @@ static void vgic_mmio_write_v3_misc(struct
> kvm_vcpu *vcpu,
>  	}
>  }
> 
> +static int vgic_mmio_uaccess_write_v3_misc(struct kvm_vcpu *vcpu,
> +					   gpa_t addr, unsigned int len,
> +					   unsigned long val)
> +{
> +	switch (addr & 0x0c) {
> +	case GICD_IIDR:
> +		if (val != vgic_mmio_read_v3_misc(vcpu, addr, len))
> +			return -EINVAL;
> +	}
> +
> +	vgic_mmio_write_v3_misc(vcpu, addr, len, val);
> +	return 0;
> +}
> +
>  static unsigned long vgic_mmio_read_irouter(struct kvm_vcpu *vcpu,
>  					    gpa_t addr, unsigned int len)
>  {
> @@ -449,9 +463,10 @@ static void vgic_mmio_write_pendbase(struct
> kvm_vcpu *vcpu,
>  	}
> 
>  static const struct vgic_register_region vgic_v3_dist_registers[] = {
> -	REGISTER_DESC_WITH_LENGTH(GICD_CTLR,
> -		vgic_mmio_read_v3_misc, vgic_mmio_write_v3_misc, 16,
> -		VGIC_ACCESS_32bit),
> +	REGISTER_DESC_WITH_LENGTH_UACCESS(GICD_CTLR,
> +		vgic_mmio_read_v3_misc, vgic_mmio_write_v3_misc,
> +		NULL, vgic_mmio_uaccess_write_v3_misc,
> +		16, VGIC_ACCESS_32bit),
>  	REGISTER_DESC_WITH_LENGTH(GICD_STATUSR,
>  		vgic_mmio_read_rao, vgic_mmio_write_wi, 4,
>  		VGIC_ACCESS_32bit),
> --
> 2.7.4
> 
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