Re: [PATCH v2] virt: tdx-guest: Handle GetQuote request error code

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 1/11/2024 11:32 AM, Kuppuswamy Sathyanarayanan wrote:
> During the TDX guest attestation process, TSM ConfigFS ABI is used by
> the user attestation agent to get the signed VM measurement data (a.k.a
> Quote), which can be used by a remote verifier to validate the
> trustworthiness of the guest. When a user requests for the Quote data
> via the ConfigFS ABI, the TDX Quote generation handler
> (tdx_report_new()) forwards the request to VMM (or QE) via a hypercall,
> and then shares the output with the user.
> 
> Currently, when handling the Quote generation request, tdx_report_new()
> handler only checks whether the VMM successfully processed the request
> and if it is true it returns success and shares the output to the user
> without actually validating the output data. Since the VMM can return
> error even after processing the Quote request, always returning success
> for the processed requests is incorrect and will create confusion to
> the user. Although for the failed request, output buffer length will
> be zero and can also be used by the user to identify the failure case,
> it will be more clear to return error for all failed cases.
> 
> Validate the Quote data output status and return error code for all
> failed cases.
> 
> Fixes: f4738f56d1dc ("virt: tdx-guest: Add Quote generation support using TSM_REPORTS")
> Reported-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Closes: https://lore.kernel.org/linux-coco/6bdf569c-684a-4459-af7c-4430691804eb@linux.intel.com/T/#u
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>

> ---
> 
> Changes since v1:
>   * Updated the commit log (Kirill)
> 
>   drivers/virt/coco/tdx-guest/tdx-guest.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/virt/coco/tdx-guest/tdx-guest.c b/drivers/virt/coco/tdx-guest/tdx-guest.c
> index 1253bf76b570..61368318fa39 100644
> --- a/drivers/virt/coco/tdx-guest/tdx-guest.c
> +++ b/drivers/virt/coco/tdx-guest/tdx-guest.c
> @@ -228,6 +228,12 @@ static int tdx_report_new(struct tsm_report *report, void *data)
>   		goto done;
>   	}
>   
> +	if (quote_buf->status != GET_QUOTE_SUCCESS) {
> +		pr_err("GetQuote request failed, ret %llx\n", quote_buf->status);
> +		ret = -EIO;
> +		goto done;
> +	}
> +
>   	buf = kvmemdup(quote_buf->data, quote_buf->out_len, GFP_KERNEL);
>   	if (!buf) {
>   		ret = -ENOMEM;