Re: [PATCH v2 03/10] KVM: arm/arm64: vgic-its: Improve error reporting on device table save

[Christoffer Dall]

On Wed, Sep 27, 2017 at 03:28:33PM +0200, Eric Auger wrote:
> At the moment the device table save() returns -EINVAL if
> vgic_its_check_id() fails to return the gpa of the entry
> associated to the device/collection id. Let vgic_its_check_id()
> return an int instead of a bool and return a more precised
> error value:
> - EINVAL in case the id is out of range
> - EFAULT if the gpa is not provisionned or is not valid
> 

This is just to ease debugging, yes?

Seems a bit invasive to me for that purpose.

> We also check first the GITS_BASER<n> Valid bit is set.
> 
> This allows the userspace to discriminate failure reasons.
> 
> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
> 
> ---
> 
> need to CC stable

Is this solving a real issue that someone has?  Otherwise I don't think
it should be cc'ed to stable, nor am I sure it warrants merging as a
fix.

Thanks,
-Christoffer

> ---
>  virt/kvm/arm/vgic/vgic-its.c | 53 ++++++++++++++++++++++++++++++--------------
>  1 file changed, 36 insertions(+), 17 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index 76bed2d..c1f7972 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -688,14 +688,24 @@ static int vgic_its_cmd_handle_movi(struct kvm *kvm, struct vgic_its *its,
>  }
>  
>  /*
> - * Check whether an ID can be stored into the corresponding guest table.
> + * vgic_its_check_id - Check whether an ID can be stored into
> + * the corresponding guest table.
> + *
>   * For a direct table this is pretty easy, but gets a bit nasty for
>   * indirect tables. We check whether the resulting guest physical address
>   * is actually valid (covered by a memslot and guest accessible).
>   * For this we have to read the respective first level entry.
> + *
> + * @its: its handle
> + * @baser: GITS_BASER<n> register
> + * @id: id of the device/collection
> + * @eaddr: output gpa of the corresponding table entry
> + *
> + * Return: 0 on success, -EINVAL if @id is out of range, -EFAULT if
> + * the address cannot be computed or is not valid
>   */
> -static bool vgic_its_check_id(struct vgic_its *its, u64 baser, u32 id,
> -			      gpa_t *eaddr)
> +static int vgic_its_check_id(struct vgic_its *its, u64 baser, u32 id,
> +			     gpa_t *eaddr)
>  {
>  	int l1_tbl_size = GITS_BASER_NR_PAGES(baser) * SZ_64K;
>  	u64 indirect_ptr, type = GITS_BASER_TYPE(baser);
> @@ -703,50 +713,56 @@ static bool vgic_its_check_id(struct vgic_its *its, u64 baser, u32 id,
>  	int index;
>  	gfn_t gfn;
>  
> +	if (!(baser & GITS_BASER_VALID))
> +		return -EFAULT;
> +
>  	switch (type) {
>  	case GITS_BASER_TYPE_DEVICE:
>  		if (id >= BIT_ULL(VITS_TYPER_DEVBITS))
> -			return false;
> +			return -EINVAL;
>  		break;
>  	case GITS_BASER_TYPE_COLLECTION:
>  		/* as GITS_TYPER.CIL == 0, ITS supports 16-bit collection ID */
>  		if (id >= BIT_ULL(16))
> -			return false;
> +			return -EINVAL;
>  		break;
>  	default:
> -		return false;
> +		return -EINVAL;
>  	}
>  
>  	if (!(baser & GITS_BASER_INDIRECT)) {
>  		phys_addr_t addr;
>  
>  		if (id >= (l1_tbl_size / esz))
> -			return false;
> +			return -EINVAL;
>  
>  		addr = BASER_ADDRESS(baser) + id * esz;
>  		gfn = addr >> PAGE_SHIFT;
>  
>  		if (eaddr)
>  			*eaddr = addr;
> -		return kvm_is_visible_gfn(its->dev->kvm, gfn);
> +		if (kvm_is_visible_gfn(its->dev->kvm, gfn))
> +			return 0;
> +		else
> +			return -EFAULT;
>  	}
>  
>  	/* calculate and check the index into the 1st level */
>  	index = id / (SZ_64K / esz);
>  	if (index >= (l1_tbl_size / sizeof(u64)))
> -		return false;
> +		return -EINVAL;
>  
>  	/* Each 1st level entry is represented by a 64-bit value. */
>  	if (kvm_read_guest(its->dev->kvm,
>  			   BASER_ADDRESS(baser) + index * sizeof(indirect_ptr),
>  			   &indirect_ptr, sizeof(indirect_ptr)))
> -		return false;
> +		return -EFAULT;
>  
>  	indirect_ptr = le64_to_cpu(indirect_ptr);
>  
>  	/* check the valid bit of the first level entry */
>  	if (!(indirect_ptr & BIT_ULL(63)))
> -		return false;
> +		return -EFAULT;
>  
>  	/*
>  	 * Mask the guest physical address and calculate the frame number.
> @@ -762,7 +778,10 @@ static bool vgic_its_check_id(struct vgic_its *its, u64 baser, u32 id,
>  
>  	if (eaddr)
>  		*eaddr = indirect_ptr;
> -	return kvm_is_visible_gfn(its->dev->kvm, gfn);
> +	if (kvm_is_visible_gfn(its->dev->kvm, gfn))
> +		return 0;
> +	else
> +		return -EFAULT;
>  }
>  
>  static int vgic_its_alloc_collection(struct vgic_its *its,
> @@ -771,7 +790,7 @@ static int vgic_its_alloc_collection(struct vgic_its *its,
>  {
>  	struct its_collection *collection;
>  
> -	if (!vgic_its_check_id(its, its->baser_coll_table, coll_id, NULL))
> +	if (vgic_its_check_id(its, its->baser_coll_table, coll_id, NULL))
>  		return E_ITS_MAPC_COLLECTION_OOR;
>  
>  	collection = kzalloc(sizeof(*collection), GFP_KERNEL);
> @@ -943,7 +962,7 @@ static int vgic_its_cmd_handle_mapd(struct kvm *kvm, struct vgic_its *its,
>  	gpa_t itt_addr = its_cmd_get_ittaddr(its_cmd);
>  	struct its_device *device;
>  
> -	if (!vgic_its_check_id(its, its->baser_device_table, device_id, NULL))
> +	if (vgic_its_check_id(its, its->baser_device_table, device_id, NULL))
>  		return E_ITS_MAPD_DEVICE_OOR;
>  
>  	if (valid && num_eventid_bits > VITS_TYPER_IDBITS)
> @@ -2060,9 +2079,9 @@ static int vgic_its_save_device_tables(struct vgic_its *its)
>  		int ret;
>  		gpa_t eaddr;
>  
> -		if (!vgic_its_check_id(its, baser,
> -				       dev->device_id, &eaddr))
> -			return -EINVAL;
> +		ret = vgic_its_check_id(its, baser, dev->device_id, &eaddr);
> +		if (ret)
> +			return ret;
>  
>  		ret = vgic_its_save_itt(its, dev);
>  		if (ret)
> -- 
> 2.5.5
>