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

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Date: Thu, 22 Feb 2024 15:08:52 -0800
From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
To: "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>, x86@...nel.org
Cc: Dave Hansen <dave.hansen@...ux.intel.com>,
 Dan Williams <dan.j.williams@...el.com>, Xiaoyao Li <xiaoyao.li@...el.com>,
 linux-kernel@...r.kernel.org, linux-coco@...ts.linux.dev
Subject: Re: [PATCH v2] virt: tdx-guest: Handle GetQuote request error code

Hi x86 Maintainers,

On 1/10/24 7:32 PM, 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@...el.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@...ux.intel.com>
> ---

Can you consider merging this fix? It already got acks from Kirill, Kai and Li. Do
you want me rebase it and resend it with updated tags?

>
> 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;

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer