Message-ID: <20221109142431.ffkhouuxewjajp6g@fedora>
Date:   Wed, 9 Nov 2022 11:24:31 -0300
From:   Wander Lairson Costa <wander@...hat.com>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        "H . Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Kai Huang <kai.huang@...el.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v17 2/3] virt: Add TDX guest driver

On Thu, Nov 03, 2022 at 08:23:54PM -0700, Kuppuswamy Sathyanarayanan wrote:
> TDX guest driver exposes IOCTL interfaces to service TDX guest
> user-specific requests. Currently, it is only used to allow the user to
> get the TDREPORT to support TDX attestation.
> 
> Details about the TDX attestation process are documented in
> Documentation/x86/tdx.rst, and the IOCTL details are documented in
> Documentation/virt/coco/tdx-guest.rst.
> 
> Operations like getting TDREPORT involves sending a blob of data as
> input and getting another blob of data as output. It was considered
> to use a sysfs interface for this, but it doesn't fit well into the
> standard sysfs model for configuring values. It would be possible to
> do read/write on files, but it would need multiple file descriptors,
> which would be somewhat messy. IOCTLs seems to be the best fitting
> and simplest model for this use case. The AMD sev-guest driver also
> uses IOCTL interface to support attestation.
> 
> [Bagas Sanjaya: Ack is for documentation portion]
> Acked-by: Kai Huang <kai.huang@...el.com>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Acked-by: Wander Lairson Costa <wander@...hat.com>
> Reviewed-by: Bagas Sanjaya <bagasdotme@...il.com>
> Reviewed-by: Tony Luck <tony.luck@...el.com>
> Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> ---
> 
> Changes since v16:
>  * Removed rpd_len, tdr_len and subtype members from
>    struct tdx_report_req.
>  * Used fixed size buffers for TDREPORT and REPORTDATA in
>    struct tdx_report_req.
> 
> Changes since v15:
>  * Removed error messages in tdx_get_report() as per Greg's suggestion.
>  * Removed #ifdef MODULE usage for MODULE_DEVICE_TABLE.
>  * Added copyright info for the header file.
> 
> Changes since v14:
>  * Used tdx_mcall_get_report() wrapper instead of __tdx_module_call()
>    call.
>  * Added pr_err() messages for some failure cases in tdx_get_report().
>  * Used KBUILD_MODNAME instead of device name.
>  * Rebased on top of v6.1-rc1
> 
> Changes since v13:
>  * Converted the driver from built-in to a driver module
>    as per Greg's suggestion.
>  * Moved the driver to drivers/virt/coco to match AMD SEV.
>  * Added support to autoload the driver based on
>    X86_FEATURE_TDX_GUEST CPU feature.
>  * Squashed patch titled "Documentation/x86: Document TDX
>    attestation process" with this patch.
>  * Since the attestation process is already documented in
>    Documentation/x86/tdx.rst, remove it from the commit log.
>  * Modified the commit log to match the new format.
>  * Explicitly included the required header files.
>  * Fixed magic number usage in reserved member check.
> 
> Changes since v13:
>  * Fixed the commit log as per review suggestion.
>  * Explicitly included the required header files.
>  * Fixed magic number usage in reserved member check.
> 
> Changes since v12:
>  * Added check to ensure reserved entries are set as 0.
> 
> Changes since v11:
>  * Renamed DRIVER_NAME to TDX_GUEST_DEVICE and moved it to
>    arch/x86/include/uapi/asm/tdx.h.
>  * Fixed default error number in tdx_guest_ioctl().
>  * Moved tdx_misc_dev definition out of tdx_guest_init() as
>    per Greg's suggestion.
>  * Reordered struct tdx_report_req to avoid holes and added
>    required padding.
> 
> Changes since v10:
>  * Replaced TD/TD Guest usage with TDX Guest or Guest.
>  * Removed unnecessary comments.
>  * Added more validation to user input in tdx_get_report().
>  * Used u64_to_user_ptr when reading user u64 pointers.
>  * Fixed commit log as per review comments.
> 
> Changes since v9:
>  * Dropped the cover letter. Since this patch set only adds
>    TDREPORT support, the commit log itself has all the required details.
>  * Dropped the Quote support and event IRQ support as per Dave's
>    review suggestion.
>  * Dropped attest.c and moved its contents to tdx.c
>  * Updated commit log and comments to reflect latest changes.
> 
> Changes since v8:
>  * Please refer to https://lore.kernel.org/all/ \
>    20220728034420.648314-1-sathyanarayanan.kuppuswamy@...ux.intel.com/
> 
>  Documentation/virt/coco/tdx-guest.rst   |  42 ++++++++++
>  Documentation/virt/index.rst            |   1 +
>  Documentation/x86/tdx.rst               |  43 ++++++++++
>  drivers/virt/Kconfig                    |   2 +
>  drivers/virt/Makefile                   |   1 +
>  drivers/virt/coco/tdx-guest/Kconfig     |  10 +++
>  drivers/virt/coco/tdx-guest/Makefile    |   2 +
>  drivers/virt/coco/tdx-guest/tdx-guest.c | 102 ++++++++++++++++++++++++
>  include/uapi/linux/tdx-guest.h          |  41 ++++++++++
>  9 files changed, 244 insertions(+)
>  create mode 100644 Documentation/virt/coco/tdx-guest.rst
>  create mode 100644 drivers/virt/coco/tdx-guest/Kconfig
>  create mode 100644 drivers/virt/coco/tdx-guest/Makefile
>  create mode 100644 drivers/virt/coco/tdx-guest/tdx-guest.c
>  create mode 100644 include/uapi/linux/tdx-guest.h
> 
> diff --git a/Documentation/virt/coco/tdx-guest.rst b/Documentation/virt/coco/tdx-guest.rst
> new file mode 100644
> index 000000000000..388d0ffb686b
> --- /dev/null
> +++ b/Documentation/virt/coco/tdx-guest.rst
> @@ -0,0 +1,42 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +===================================================================
> +TDX Guest API Documentation
> +===================================================================
> +
> +1. General description
> +======================
> +
> +The TDX guest driver exposes IOCTL interfaces via /dev/tdx-guest misc
> +device to allow userspace to get certain TDX guest specific details.
> +
> +2. API description
> +==================
> +
> +In this section, for each supported IOCTL, following information is
> +provided along with a generic description.
> +
> +:Input parameters: Parameters passed to the IOCTL and related details.
> +:Output: Details about output data and return value (with details about the non
> +         common error values).
> +
> +2.1 TDX_CMD_GET_REPORT
> +----------------------
> +
> +:Input parameters: struct tdx_report_req
> +:Output: Upon successful execution, TDREPORT data is copied to
> +         tdx_report_req.tdreport and return 0. Return -EINVAL for
> +         invalid operands, -EIO on TDCALL failure or standard error
> +         number on other common failures.
> +
> +The TDX_CMD_GET_REPORT IOCTL can be used by the attestation software to
> +get the TDREPORT from the TDX module using TDCALL[TDG.MR.REPORT].
> +
> +Reference
> +---------
> +
> +TDX reference material is collected here:
> +
> +https://www.intel.com/content/www/us/en/developer/articles/technical/intel-trust-domain-extensions.html
> +
> +The driver is based on TDX module specification v1.0 and TDX GHCI specification v1.0.
> diff --git a/Documentation/virt/index.rst b/Documentation/virt/index.rst
> index 2f1cffa87b1b..56e003ff28ff 100644
> --- a/Documentation/virt/index.rst
> +++ b/Documentation/virt/index.rst
> @@ -14,6 +14,7 @@ Linux Virtualization Support
>     ne_overview
>     acrn/index
>     coco/sev-guest
> +   coco/tdx-guest
>     hyperv/index
>  
>  .. only:: html and subproject
> diff --git a/Documentation/x86/tdx.rst b/Documentation/x86/tdx.rst
> index b8fa4329e1a5..014b769923a4 100644
> --- a/Documentation/x86/tdx.rst
> +++ b/Documentation/x86/tdx.rst
> @@ -210,6 +210,49 @@ converted to shared on boot.
>  For coherent DMA allocation, the DMA buffer gets converted on the
>  allocation. Check force_dma_unencrypted() for details.
>  
> +Attestation
> +===========
> +
> +Attestation is used to verify the TDX guest trustworthiness to other
> +entities before provisioning secrets to the guest. For example, a key
> +server may want to use attestation to verify that the guest is the
> +desired one before releasing the encryption keys to mount the encrypted
> +rootfs or secondary drive.
> +
> +The TDX module records the state of the TDX guest in various stages of
> +the guest boot process using build time measurement register (MRTD) and
> +runtime measurement registers (RTMR). Measurements related to guest
> +initial configuration and firmware image are recorded in the MRTD
> +register. Measurements related to initial state, kernel image, firmware
> +image, command line options, initrd, ACPI tables, etc are recorded in
> +RTMR registers. For more details as an example, please refer to TDX
> +Virtual Firmware design specification, sec titled "TD Measurement". At
> +TDX guest runtime, the attestation process is used to attest to these
> +measurements.
> +
> +The attestation process consists of two steps: TDREPORT generation and
> +Quote generation.
> +
> +TDX guest uses TDCALL[TDG.MR.REPORT] to get the TDREPORT (TDREPORT_STRUCT)
> +from the TDX module. TDREPORT is a fixed-size data structure generated by
> +the TDX module which contains guest-specific information (such as build
> +and boot measurements), platform security version, and the MAC to protect
> +the integrity of the TDREPORT. A user-provided 64-Byte REPORTDATA is used
> +as input and included in the TDREPORT. Typically it can be some nonce
> +provided by attestation service so the TDREPORT can be verified uniquely.
> +More details about the TDREPORT can be found in Intel TDX Module
> +specification, section titled "TDG.MR.REPORT Leaf".
> +
> +After getting the TDREPORT, the second step of the attestation process
> +is to send it to the Quoting Enclave (QE) to generate the Quote. TDREPORT
> +by design can only be verified on the local platform as the MAC key is
> +bound to the platform. To support remote verification of the TDREPORT,
> +TDX leverages Intel SGX Quoting Enclave to verify the TDREPORT locally
> +and convert it to a remotely verifiable Quote. Method of sending TDREPORT
> +to QE is implementation specific. Attestation software can choose
> +whatever communication channel available (i.e. vsock or TCP/IP) to
> +send the TDREPORT to QE and receive the Quote.
> +
>  References
>  ==========
>  
> diff --git a/drivers/virt/Kconfig b/drivers/virt/Kconfig
> index 87ef258cec64..f79ab13a5c28 100644
> --- a/drivers/virt/Kconfig
> +++ b/drivers/virt/Kconfig
> @@ -52,4 +52,6 @@ source "drivers/virt/coco/efi_secret/Kconfig"
>  
>  source "drivers/virt/coco/sev-guest/Kconfig"
>  
> +source "drivers/virt/coco/tdx-guest/Kconfig"
> +
>  endif
> diff --git a/drivers/virt/Makefile b/drivers/virt/Makefile
> index 093674e05c40..e9aa6fc96fab 100644
> --- a/drivers/virt/Makefile
> +++ b/drivers/virt/Makefile
> @@ -11,3 +11,4 @@ obj-$(CONFIG_NITRO_ENCLAVES)	+= nitro_enclaves/
>  obj-$(CONFIG_ACRN_HSM)		+= acrn/
>  obj-$(CONFIG_EFI_SECRET)	+= coco/efi_secret/
>  obj-$(CONFIG_SEV_GUEST)		+= coco/sev-guest/
> +obj-$(CONFIG_INTEL_TDX_GUEST)	+= coco/tdx-guest/
> diff --git a/drivers/virt/coco/tdx-guest/Kconfig b/drivers/virt/coco/tdx-guest/Kconfig
> new file mode 100644
> index 000000000000..14246fc2fb02
> --- /dev/null
> +++ b/drivers/virt/coco/tdx-guest/Kconfig
> @@ -0,0 +1,10 @@
> +config TDX_GUEST_DRIVER
> +	tristate "TDX Guest driver"
> +	depends on INTEL_TDX_GUEST
> +	help
> +	  The driver provides userspace interface to communicate with
> +	  the TDX module to request the TDX guest details like attestation
> +	  report.
> +
> +	  To compile this driver as module, choose M here. The module will
> +	  be called tdx-guest.
> diff --git a/drivers/virt/coco/tdx-guest/Makefile b/drivers/virt/coco/tdx-guest/Makefile
> new file mode 100644
> index 000000000000..775cb463f9c8
> --- /dev/null
> +++ b/drivers/virt/coco/tdx-guest/Makefile
> @@ -0,0 +1,2 @@
> +# SPDX-License-Identifier: GPL-2.0
> +obj-$(CONFIG_TDX_GUEST_DRIVER) += tdx-guest.o
> diff --git a/drivers/virt/coco/tdx-guest/tdx-guest.c b/drivers/virt/coco/tdx-guest/tdx-guest.c
> new file mode 100644
> index 000000000000..40e7c1881fa9
> --- /dev/null
> +++ b/drivers/virt/coco/tdx-guest/tdx-guest.c
> @@ -0,0 +1,102 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * TDX guest user interface driver
> + *
> + * Copyright (C) 2022 Intel Corporation
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/miscdevice.h>
> +#include <linux/mm.h>
> +#include <linux/module.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/string.h>
> +#include <linux/uaccess.h>
> +
> +#include <uapi/linux/tdx-guest.h>
> +
> +#include <asm/cpu_device_id.h>
> +#include <asm/tdx.h>
> +
> +static long tdx_get_report(struct tdx_report_req __user *req)
> +{
> +	u8 *reportdata, *tdreport;
> +	long ret;
> +
> +	reportdata = kmalloc(TDX_REPORTDATA_LEN, GFP_KERNEL);
> +	if (!reportdata)
> +		return -ENOMEM;
> +
> +	tdreport = kzalloc(TDX_REPORT_LEN, GFP_KERNEL);
> +	if (!tdreport) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}

Isn't simpler just allocating a struct tdx_report_req? You would save
one allocation and a few lines of code.

> +
> +	if (copy_from_user(reportdata, req->reportdata, TDX_REPORTDATA_LEN)) {
> +		ret = -EFAULT;
> +		goto out;
> +	}
> +
> +	/* Generate TDREPORT using "TDG.MR.REPORT" TDCALL */
> +	ret = tdx_mcall_get_report(reportdata, tdreport);
> +	if (ret)
> +		goto out;
> +
> +	if (copy_to_user(req->tdreport, tdreport, TDX_REPORT_LEN))
> +		ret = -EFAULT;
> +
> +out:
> +	kfree(reportdata);
> +	kfree(tdreport);
> +
> +	return ret;
> +}
> +
> +static long tdx_guest_ioctl(struct file *file, unsigned int cmd,
> +			    unsigned long arg)
> +{
> +	switch (cmd) {
> +	case TDX_CMD_GET_REPORT:
> +		return tdx_get_report((struct tdx_report_req __user *)arg);
> +	default:
> +		return -ENOTTY;
> +	}
> +}
> +
> +static const struct file_operations tdx_guest_fops = {
> +	.owner = THIS_MODULE,
> +	.unlocked_ioctl = tdx_guest_ioctl,
> +	.llseek = no_llseek,
> +};
> +
> +static struct miscdevice tdx_misc_dev = {
> +	.name = KBUILD_MODNAME,
> +	.minor = MISC_DYNAMIC_MINOR,
> +	.fops = &tdx_guest_fops,
> +};
> +
> +static const struct x86_cpu_id tdx_guest_ids[] = {
> +	X86_MATCH_FEATURE(X86_FEATURE_TDX_GUEST, NULL),
> +	{}
> +};
> +MODULE_DEVICE_TABLE(x86cpu, tdx_guest_ids);
> +
> +static int __init tdx_guest_init(void)
> +{
> +	if (!x86_match_cpu(tdx_guest_ids))
> +		return -ENODEV;
> +
> +	return misc_register(&tdx_misc_dev);
> +}
> +module_init(tdx_guest_init);
> +
> +static void __exit tdx_guest_exit(void)
> +{
> +	misc_deregister(&tdx_misc_dev);
> +}
> +module_exit(tdx_guest_exit);
> +
> +MODULE_AUTHOR("Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>");
> +MODULE_DESCRIPTION("TDX Guest Driver");
> +MODULE_LICENSE("GPL");
> diff --git a/include/uapi/linux/tdx-guest.h b/include/uapi/linux/tdx-guest.h
> new file mode 100644
> index 000000000000..c1d52bc3a62e
> --- /dev/null
> +++ b/include/uapi/linux/tdx-guest.h
> @@ -0,0 +1,41 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +/*
> + * Userspace interface for TDX guest driver
> + *
> + * Copyright (C) 2022 Intel Corporation
> + */
> +
> +#ifndef _UAPI_LINUX_TDX_GUEST_H_
> +#define _UAPI_LINUX_TDX_GUEST_H_
> +
> +#include <linux/ioctl.h>
> +#include <linux/types.h>
> +
> +/* Length of the REPORTDATA used in TDG.MR.REPORT TDCALL */
> +#define TDX_REPORTDATA_LEN              64
> +
> +/* Length of TDREPORT used in TDG.MR.REPORT TDCALL */
> +#define TDX_REPORT_LEN                  1024
> +
> +/**
> + * struct tdx_report_req - Request struct for TDX_CMD_GET_REPORT IOCTL.
> + *
> + * @reportdata: User buffer with REPORTDATA to be included into TDREPORT.
> + *              Typically it can be some nonce provided by attestation
> + *              service, so the generated TDREPORT can be uniquely verified.
> + * @tdreport: User buffer to store TDREPORT output from TDCALL[TDG.MR.REPORT].
> + */
> +struct tdx_report_req {
> +	__u8 reportdata[TDX_REPORTDATA_LEN];
> +	__u8 tdreport[TDX_REPORT_LEN];
> +};
> +
> +/*
> + * TDX_CMD_GET_REPORT - Get TDREPORT using TDCALL[TDG.MR.REPORT]
> + *
> + * Return 0 on success, -EIO on TDCALL execution failure, and
> + * standard errno on other general error cases.
> + */
> +#define TDX_CMD_GET_REPORT              _IOWR('T', 1, struct tdx_report_req)
> +
> +#endif /* _UAPI_LINUX_TDX_GUEST_H_ */
> -- 
> 2.34.1
> 
> 

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