Re: [PATCH v2 3/5] virt: sevguest: Prep for kernel internal {get, get_ext}_report()

[Tom Lendacky <thomas.lendacky@amd.com>]

On 8/14/23 02:43, Dan Williams wrote:
> In preparation for using the TSM key facility to convey attestation blobs
> to userspace, add an argument to flag whether @arg is a user buffer or a
> kernel buffer.
> 
> While TSM keys is meant to replace existing confidenital computing

s/confidenital/confidential/

> ioctl() implementations for attestation report retrieval the old ioctl()
> path needs to stick around for a deprecation period.
> 
> No behavior change intended, just introduce the copy wrappers and @type
> argument.
> 
> Note that these wrappers are similar to copy_{to,from}_sockptr(). If
> this approach moves forward that concept is something that can be
> generalized into a helper with a generic name.
> 
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Dionna Glaze <dionnaglaze@google.com>
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>   drivers/virt/coco/sev-guest/sev-guest.c |   48 ++++++++++++++++++++++++-------
>   1 file changed, 37 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
> index 97dbe715e96a..f48c4764a7a2 100644
> --- a/drivers/virt/coco/sev-guest/sev-guest.c
> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
> @@ -470,7 +470,32 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
>   	return 0;
>   }
>   
> -static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
> +enum snp_arg_type {
> +	SNP_UARG,
> +	SNP_KARG,
> +};
> +
> +static unsigned long copy_from(void *to, unsigned long from, unsigned long n,
> +			       enum snp_arg_type type)
> +{
> +	if (type == SNP_UARG)
> +		return copy_from_user(to, (void __user *)from, n);

I'm a fan of blank lines to make reading functions easier. A blank line 
here and below after the memcpy() would be nice.

Ditto in the copy_to() function.

> +	memcpy(to, (void *)from, n);
> +	return 0;
> +}
> +
> +static unsigned long copy_to(unsigned long to, const void *from,
> +			     unsigned long n, enum snp_arg_type type)
> +{
> +	if (type == SNP_UARG)
> +		return copy_to_user((void __user *)to, from, n);
> +	memcpy((void *)to, from, n);
> +	return 0;
> +}
> +
> +static int get_report(struct snp_guest_dev *snp_dev,
> +		      struct snp_guest_request_ioctl *arg,
> +		      enum snp_arg_type type)

You can go out to 100 characters now, so you can put "struct .. *arg" on 
the top line and just put the enum on a new line.

>   {
>   	struct snp_guest_crypto *crypto = snp_dev->crypto;
>   	struct snp_report_resp *resp;
> @@ -482,7 +507,7 @@ static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_io
>   	if (!arg->req_data || !arg->resp_data)
>   		return -EINVAL;
>   
> -	if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req)))
> +	if (copy_from(&req, arg->req_data, sizeof(req), type))
>   		return -EFAULT;
>   
>   	/*
> @@ -501,7 +526,7 @@ static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_io
>   	if (rc)
>   		goto e_free;
>   
> -	if (copy_to_user((void __user *)arg->resp_data, resp, sizeof(*resp)))
> +	if (copy_to(arg->resp_data, resp, sizeof(*resp), type))
>   		rc = -EFAULT;
>   
>   e_free:
> @@ -550,7 +575,9 @@ static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_reque
>   	return rc;
>   }
>   
> -static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
> +static int get_ext_report(struct snp_guest_dev *snp_dev,
> +			  struct snp_guest_request_ioctl *arg,
> +			  enum snp_arg_type type)

Ditto here on the 100 characters.

>   {
>   	struct snp_guest_crypto *crypto = snp_dev->crypto;
>   	struct snp_ext_report_req req;
> @@ -562,7 +589,7 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques
>   	if (!arg->req_data || !arg->resp_data)
>   		return -EINVAL;
>   
> -	if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req)))
> +	if (copy_from(&req, arg->req_data, sizeof(req), type))
>   		return -EFAULT;
>   
>   	/* userspace does not want certificate data */
> @@ -611,14 +638,13 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques
>   	if (ret)
>   		goto e_free;
>   
> -	if (npages &&
> -	    copy_to_user((void __user *)req.certs_address, snp_dev->certs_data,
> -			 req.certs_len)) {
> +	if (npages && copy_to(req.certs_address, snp_dev->certs_data,
> +			      req.certs_len, type)) {

This can also be a single line now.

Thanks,
Tom

>   		ret = -EFAULT;
>   		goto e_free;
>   	}
>   
> -	if (copy_to_user((void __user *)arg->resp_data, resp, sizeof(*resp)))
> +	if (copy_to(arg->resp_data, resp, sizeof(*resp), type))
>   		ret = -EFAULT;
>   
>   e_free:
> @@ -653,13 +679,13 @@ static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long
>   
>   	switch (ioctl) {
>   	case SNP_GET_REPORT:
> -		ret = get_report(snp_dev, &input);
> +		ret = get_report(snp_dev, &input, SNP_UARG);
>   		break;
>   	case SNP_GET_DERIVED_KEY:
>   		ret = get_derived_key(snp_dev, &input);
>   		break;
>   	case SNP_GET_EXT_REPORT:
> -		ret = get_ext_report(snp_dev, &input);
> +		ret = get_ext_report(snp_dev, &input, SNP_UARG);
>   		break;
>   	default:
>   		break;
>