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@intel.com Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Acked-by: Wander Lairson Costa wander@redhat.com Reviewed-by: Bagas Sanjaya bagasdotme@gmail.com Reviewed-by: Tony Luck tony.luck@intel.com Reviewed-by: Mika Westerberg mika.westerberg@linux.intel.com Signed-off-by: Kuppuswamy Sathyanarayanan sathyanarayanan.kuppuswamy@linux.intel.com ---

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@linux.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 | 121 ++++++++++++++++++++++++ include/uapi/linux/tdx-guest.h | 55 +++++++++++ 9 files changed, 277 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..4fe72829bdd0 --- /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 -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-t... + +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..12d05617e4f3 --- /dev/null +++ b/drivers/virt/coco/tdx-guest/tdx-guest.c @@ -0,0 +1,121 @@ +// 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(void __user *argp) +{ + u8 *reportdata, *tdreport; + struct tdx_report_req req; + long ret; + + if (copy_from_user(&req, argp, sizeof(req))) + return -EFAULT; + + /* + * Check for valid input values. Per TDX Module 1.0 + * specification, section titled "TDG.MR.REPORT", + * REPORTDATA length is fixed as TDX_REPORTDATA_LEN, + * TDREPORT length is fixed as TDX_REPORT_LEN, and + * TDREPORT subtype is fixed as 0. + */ + if (req.subtype || req.rpd_len != TDX_REPORTDATA_LEN || + req.tdr_len != TDX_REPORT_LEN) + return -EINVAL; + + if (memchr_inv(req.reserved, 0, sizeof(req.reserved))) + return -EINVAL; + + reportdata = kmalloc(req.rpd_len, GFP_KERNEL); + if (!reportdata) + return -ENOMEM; + + tdreport = kzalloc(req.tdr_len, GFP_KERNEL); + if (!tdreport) { + ret = -ENOMEM; + goto out; + } + + if (copy_from_user(reportdata, u64_to_user_ptr(req.reportdata), + req.rpd_len)) { + ret = -EFAULT; + goto out; + } + + /* Generate TDREPORT using "TDG.MR.REPORT" TDCALL */ + ret = tdx_mcall_get_report(reportdata, tdreport, req.subtype); + if (ret) + goto out; + + if (copy_to_user(u64_to_user_ptr(req.tdreport), tdreport, req.tdr_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((void __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@linux.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..29453e6a7ced --- /dev/null +++ b/include/uapi/linux/tdx-guest.h @@ -0,0 +1,55 @@ +/* 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-defined 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: TDREPORT output from TDCALL[TDG.MR.REPORT]. + * @rpd_len: Length of the REPORTDATA (fixed as 64 bytes by the TDX Module + * specification, but a parameter is added to handle future + * extension). + * @tdr_len: Length of the TDREPORT (fixed as 1024 bytes by the TDX Module + * specification, but a parameter is added to accommodate future + * extension). + * @subtype: Subtype of TDREPORT (fixed as 0 by the TDX Module specification, + * but added a parameter to handle future extension). + * @reserved: Reserved entries to handle future requirements. Must be filled + * with zeroes. + */ +struct tdx_report_req { + __u64 reportdata; + __u64 tdreport; + __u32 rpd_len; + __u32 tdr_len; + __u8 subtype; + __u8 reserved[7]; +}; + +/* + * 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_ */

On Thu, Oct 27, 2022 at 05:28:19PM -0700, Kuppuswamy Sathyanarayanan wrote:

• /*

• * Check for valid input values. Per TDX Module 1.0
  

• * specification, section titled "TDG.MR.REPORT",
  

• * REPORTDATA length is fixed as TDX_REPORTDATA_LEN,
  

If this length is fixed, then you can never change it, so why have it at all?

• * TDREPORT length is fixed as TDX_REPORT_LEN, and
  

• * TDREPORT subtype is fixed as 0.
  

• */
  

• if (req.subtype || req.rpd_len != TDX_REPORTDATA_LEN ||

•    req.tdr_len != TDX_REPORT_LEN)
  

• return -EINVAL;
  

• if (memchr_inv(req.reserved, 0, sizeof(req.reserved)))

• return -EINVAL;
  

• reportdata = kmalloc(req.rpd_len, GFP_KERNEL);
• if (!reportdata)

• return -ENOMEM;
  

• tdreport = kzalloc(req.tdr_len, GFP_KERNEL);
• if (!tdreport) {

• ret = -ENOMEM;
  

• goto out;
  

• }
• if (copy_from_user(reportdata, u64_to_user_ptr(req.reportdata),

• 	   req.rpd_len)) {
  

• ret = -EFAULT;
  

• goto out;
  

• }
• /* Generate TDREPORT using "TDG.MR.REPORT" TDCALL */
• ret = tdx_mcall_get_report(reportdata, tdreport, req.subtype);
• if (ret)

• goto out;
  

• if (copy_to_user(u64_to_user_ptr(req.tdreport), tdreport, req.tdr_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((void __user *)arg);
  

You know the type of this pointer here, why not cast it instead of having to cast it from void * again?

• 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@linux.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..29453e6a7ced --- /dev/null +++ b/include/uapi/linux/tdx-guest.h @@ -0,0 +1,55 @@ +/* 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

As these are fixed values, why do you have to say them again in the structure?

If you ever change them, wonderful, make a new ioctl. You can't change this one as userspace would have to also change, there is no way you could mix/match kernel versions and userspace and not have problems.

So just fix these values, like you have, and remove them from the structure definition as there's no way you can change them anyway.

+/**

• • struct tdx_report_req - Request struct for TDX_CMD_GET_REPORT IOCTL.
• • @reportdata: User-defined 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: TDREPORT output from TDCALL[TDG.MR.REPORT].

These are userspace pointers, document them as such please.

• • @rpd_len: Length of the REPORTDATA (fixed as 64 bytes by the TDX Module

• •       specification, but a parameter is added to handle future
    

• •       extension).
    

As I say above, this can't be changed, right?

• • @tdr_len: Length of the TDREPORT (fixed as 1024 bytes by the TDX Module

• •       specification, but a parameter is added to accommodate future
    

• •       extension).
    

Again, can't be changed.

• • @subtype: Subtype of TDREPORT (fixed as 0 by the TDX Module specification,

• •       but added a parameter to handle future extension).
    

If this too is fixed, you can't change it.

thanks,

greg k-h

On Sat, Oct 29, 2022 at 04:17:39PM -0700, Sathyanarayanan Kuppuswamy wrote:

Hi Greg

On 10/27/22 11:25 PM, Greg Kroah-Hartman wrote:

...

On Thu, Oct 27, 2022 at 05:28:19PM -0700, Kuppuswamy Sathyanarayanan wrote:

...

...

+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((void __user *)arg);
  

You know the type of this pointer here, why not cast it instead of having to cast it from void * again?

The only place we use arg pointer is in copy_from_user() function, which expects void __user * pointer. So why cast it as struct tdx_report_req * here?

Because then your function will show the true type and you don't have to cast it again.

...

...

+MODULE_AUTHOR("Kuppuswamy Sathyanarayanan sathyanarayanan.kuppuswamy@linux.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..29453e6a7ced --- /dev/null +++ b/include/uapi/linux/tdx-guest.h @@ -0,0 +1,55 @@ +/* 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

As these are fixed values, why do you have to say them again in the structure?

These length recommendations are provided by the TDX Module, and there is a slight possibility that the TDX Module will increase the maximum size of the REPORTDATA and TDREPORT in the future.

We do not write kernel code for "slight possibilities sometime in the future".

To handle such length changes, rather than inventing a new IOCTL for it in the future, making the current one flexible to handle such changes seems better.

Please work through the code and see how that would really look, and what would break if you were to change that in the future (remember kernel code and userspace code is not upgraded at the same time.)

One less ABI to maintain is always better, right? My initial design did use fixed size buffers like you have recommended, but later changed it as per review suggestion to make the ABI flexible.

Again, work through and try to determine if the added complexity will really work here.

What is wrong with just adding a new ioctl if in the future, you really do need to change something? That way you are sure that nothing will break and userspace will be finen with it. It is not like you are forbidden to add new ioctls later, you would have to change the kernel code no matter what anyway.

Keep it simple please.

greg k-h

On Thu, Oct 27, 2022 at 05:28:20PM -0700, Kuppuswamy Sathyanarayanan wrote:

Attestation is used to verify the trustworthiness of a TDX guest. During the guest bring-up, the Intel TDX module measures and records the initial contents and configuration of the guest, and at runtime, guest software uses runtime measurement registers (RMTRs) to measure and record details related to kernel image, command line params, ACPI tables, initrd, etc. At guest runtime, the attestation process is used to attest to these measurements.

The first step in the TDX attestation process is to get the TDREPORT data. It is a fixed size data structure generated by the TDX module which includes the above mentioned measurements data, a MAC ID to protect the integrity of the TDREPORT, and a 64-Byte of user specified data passed during TDREPORT request which can uniquely identify the TDREPORT.

Intel's TDX guest driver exposes TDX_CMD_GET_REPORT IOCTL interface to enable guest userspace to get the TDREPORT.

Add a kernel self test module to test this ABI and verify the validity of the generated TDREPORT.

Reviewed-by: Tony Luck tony.luck@intel.com Reviewed-by: Mika Westerberg mika.westerberg@linux.intel.com Acked-by: Kai Huang kai.huang@intel.com Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Signed-off-by: Kuppuswamy Sathyanarayanan sathyanarayanan.kuppuswamy@linux.intel.com

---

Changes since v15:

• None

Changes since v14:

• Fixed format issue in struct comments.
• Rebased on top of v6.1-rc1

Changes since v13:

• Removed __packed from TDREPORT structs.
• Since the guest driver is moved to drivers/virt/coco, removed tools/arch/x86/include header folder usage.
• Fixed struct comments to match kernel-doc format.
• Fixed commit log as per review comments.
• Fixed some format issues in the code.

Changes since v12:

• Changed #ifdef DEBUG usage with if (DEBUG).
• Initialized reserved entries values to zero.

Changes since v11:

• Renamed devname with TDX_GUEST_DEVNAME.

Changes since v10:

• Replaced TD/TD Guest usage with guest or TDX guest.
• Reworded the subject line.

Changes since v9:

• Copied arch/x86/include/uapi/asm/tdx.h to tools/arch/x86/include to decouple header dependency between kernel source and tools dir.
• Fixed Makefile to adapt to above change.
• Fixed commit log and comments.
• Added __packed to hardware structs.

Changes since v8:

• Please refer to https://lore.kernel.org/all/ \ 20220728034420.648314-1-sathyanarayanan.kuppuswamy@linux.intel.com/

tools/testing/selftests/Makefile | 1 + tools/testing/selftests/tdx/Makefile | 7 + tools/testing/selftests/tdx/config | 1 + tools/testing/selftests/tdx/tdx_guest_test.c | 175 +++++++++++++++++++ 4 files changed, 184 insertions(+) create mode 100644 tools/testing/selftests/tdx/Makefile create mode 100644 tools/testing/selftests/tdx/config create mode 100644 tools/testing/selftests/tdx/tdx_guest_test.c

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile index 0464b2c6c1e4..f60e14d16bfd 100644 --- a/tools/testing/selftests/Makefile +++ b/tools/testing/selftests/Makefile @@ -73,6 +73,7 @@ TARGETS += sync TARGETS += syscall_user_dispatch TARGETS += sysctl TARGETS += tc-testing +TARGETS += tdx TARGETS += timens ifneq (1, $(quicktest)) TARGETS += timers diff --git a/tools/testing/selftests/tdx/Makefile b/tools/testing/selftests/tdx/Makefile new file mode 100644 index 000000000000..8dd43517cd55 --- /dev/null +++ b/tools/testing/selftests/tdx/Makefile @@ -0,0 +1,7 @@ +# SPDX-License-Identifier: GPL-2.0

+CFLAGS += -O3 -Wl,-no-as-needed -Wall -static

+TEST_GEN_PROGS := tdx_guest_test

+include ../lib.mk diff --git a/tools/testing/selftests/tdx/config b/tools/testing/selftests/tdx/config new file mode 100644 index 000000000000..aa1edc829ab6 --- /dev/null +++ b/tools/testing/selftests/tdx/config @@ -0,0 +1 @@ +CONFIG_TDX_GUEST_DRIVER=y diff --git a/tools/testing/selftests/tdx/tdx_guest_test.c b/tools/testing/selftests/tdx/tdx_guest_test.c new file mode 100644 index 000000000000..a5c243f73adc --- /dev/null +++ b/tools/testing/selftests/tdx/tdx_guest_test.c @@ -0,0 +1,175 @@ +// SPDX-License-Identifier: GPL-2.0 +/*

• • Test TDX guest features
• • Copyright (C) 2022 Intel Corporation.
• • Author: Kuppuswamy Sathyanarayanan sathyanarayanan.kuppuswamy@linux.intel.com
• */

+#include <sys/ioctl.h>

+#include <errno.h> +#include <fcntl.h>

+#include "../kselftest_harness.h" +#include "../../../../include/uapi/linux/tdx-guest.h"

+#define TDX_GUEST_DEVNAME "/dev/tdx_guest" +#define HEX_DUMP_SIZE 8 +#define DEBUG 0

+/**

• • struct tdreport_type - Type header of TDREPORT_STRUCT.
• • @type: Type of the TDREPORT (0 - SGX, 81 - TDX, rest are reserved)
• • @sub_type: Subtype of the TDREPORT (Default value is 0).
• • @version: TDREPORT version (Default value is 0).
• • @reserved: Added for future extension.
• • More details can be found in TDX v1.0 module specification, sec
• • titled "REPORTTYPE".
• */

+struct tdreport_type {

• __u8 type;
• __u8 sub_type;
• __u8 version;
• __u8 reserved;

+};

+/**

• • struct reportmac - TDX guest report data, MAC and TEE hashes.
• • @type: TDREPORT type header.
• • @reserved1: Reserved for future extension.
• • @cpu_svn: CPU security version.
• • @tee_tcb_info_hash: SHA384 hash of TEE TCB INFO.
• • @tee_td_info_hash: SHA384 hash of TDINFO_STRUCT.
• • @reportdata: User defined unique data passed in TDG.MR.REPORT request.
• • @reserved2: Reserved for future extension.
• • @mac: CPU MAC ID.
• • It is MAC-protected and contains hashes of the remainder of the
• • report structure along with user provided report data. More details can
• • be found in TDX v1.0 Module specification, sec titled "REPORTMACSTRUCT"
• */

+struct reportmac {

• struct tdreport_type type;
• __u8 reserved1[12];
• __u8 cpu_svn[16];
• __u8 tee_tcb_info_hash[48];
• __u8 tee_td_info_hash[48];
• __u8 reportdata[64];
• __u8 reserved2[32];
• __u8 mac[32];

+};

+/**

• • struct td_info - TDX guest measurements and configuration.
• • @attr: TDX Guest attributes (like debug, spet_disable, etc).
• • @xfam: Extended features allowed mask.
• • @mrtd: Build time measurement register.
• • @mrconfigid: Software-defined ID for non-owner-defined configuration

• •          of the guest - e.g., run-time or OS configuration.
    

• • @mrowner: Software-defined ID for the guest owner.
• • @mrownerconfig: Software-defined ID for owner-defined configuration of

• •             the guest - e.g., specific to the workload.
    

• • @rtmr: Run time measurement registers.
• • @reserved: Added for future extension.
• • It contains the measurements and initial configuration of the TDX guest
• • that was locked at initialization and a set of measurement registers
• • that are run-time extendable. More details can be found in TDX v1.0
• • Module specification, sec titled "TDINFO_STRUCT".
• */

+struct td_info {

• __u8 attr[8];
• __u64 xfam;
• __u64 mrtd[6];
• __u64 mrconfigid[6];
• __u64 mrowner[6];
• __u64 mrownerconfig[6];
• __u64 rtmr[24];
• __u64 reserved[14];

+};

+/*

• • struct tdreport - Output of TDCALL[TDG.MR.REPORT].
• • @reportmac: Mac protected header of size 256 bytes.
• • @tee_tcb_info: Additional attestable elements in the TCB are not

• •            reflected in the reportmac.
    

• • @reserved: Added for future extension.
• • @tdinfo: Measurements and configuration data of size 512 bytes.
• • More details can be found in TDX v1.0 Module specification, sec
• • titled "TDREPORT_STRUCT".
• */

+struct tdreport {

• struct reportmac reportmac;
• __u8 tee_tcb_info[239];
• __u8 reserved[17];
• struct td_info tdinfo;

+};

+static void print_array_hex(const char *title, const char *prefix_str,

• 	    const void *buf, int len)
  

+{

• int i, j, line_len, rowsize = HEX_DUMP_SIZE;
• const __u8 *ptr = buf;
• if (!len || !buf)

If len is not zero and buf is null, this would be bug. It is better to let the code crash or assert buf isn't null after testing len.

On Tue, Nov 01, 2022 at 06:43:31AM -0700, Sathyanarayanan Kuppuswamy wrote:

On 11/1/22 6:35 AM, Wander Lairson Costa wrote:

...

On Thu, Oct 27, 2022 at 05:28:20PM -0700, Kuppuswamy Sathyanarayanan wrote:

...

Attestation is used to verify the trustworthiness of a TDX guest. During the guest bring-up, the Intel TDX module measures and records the initial contents and configuration of the guest, and at runtime, guest software uses runtime measurement registers (RMTRs) to measure and record details related to kernel image, command line params, ACPI tables, initrd, etc. At guest runtime, the attestation process is used to attest to these measurements.

The first step in the TDX attestation process is to get the TDREPORT data. It is a fixed size data structure generated by the TDX module which includes the above mentioned measurements data, a MAC ID to protect the integrity of the TDREPORT, and a 64-Byte of user specified data passed during TDREPORT request which can uniquely identify the TDREPORT.

Intel's TDX guest driver exposes TDX_CMD_GET_REPORT IOCTL interface to enable guest userspace to get the TDREPORT.

Add a kernel self test module to test this ABI and verify the validity of the generated TDREPORT.

Reviewed-by: Tony Luck tony.luck@intel.com Reviewed-by: Mika Westerberg mika.westerberg@linux.intel.com Acked-by: Kai Huang kai.huang@intel.com Acked-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Signed-off-by: Kuppuswamy Sathyanarayanan sathyanarayanan.kuppuswamy@linux.intel.com

---

Changes since v15:

• None

Changes since v14:

• Fixed format issue in struct comments.
• Rebased on top of v6.1-rc1

Changes since v13:

• Removed __packed from TDREPORT structs.
• Since the guest driver is moved to drivers/virt/coco, removed tools/arch/x86/include header folder usage.
• Fixed struct comments to match kernel-doc format.
• Fixed commit log as per review comments.
• Fixed some format issues in the code.

Changes since v12:

• Changed #ifdef DEBUG usage with if (DEBUG).
• Initialized reserved entries values to zero.

Changes since v11:

• Renamed devname with TDX_GUEST_DEVNAME.

Changes since v10:

• Replaced TD/TD Guest usage with guest or TDX guest.
• Reworded the subject line.

Changes since v9:

• Copied arch/x86/include/uapi/asm/tdx.h to tools/arch/x86/include to decouple header dependency between kernel source and tools dir.
• Fixed Makefile to adapt to above change.
• Fixed commit log and comments.
• Added __packed to hardware structs.

Changes since v8:

• Please refer to https://lore.kernel.org/all/ \ 20220728034420.648314-1-sathyanarayanan.kuppuswamy@linux.intel.com/

tools/testing/selftests/Makefile | 1 + tools/testing/selftests/tdx/Makefile | 7 + tools/testing/selftests/tdx/config | 1 + tools/testing/selftests/tdx/tdx_guest_test.c | 175 +++++++++++++++++++ 4 files changed, 184 insertions(+) create mode 100644 tools/testing/selftests/tdx/Makefile create mode 100644 tools/testing/selftests/tdx/config create mode 100644 tools/testing/selftests/tdx/tdx_guest_test.c

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile index 0464b2c6c1e4..f60e14d16bfd 100644 --- a/tools/testing/selftests/Makefile +++ b/tools/testing/selftests/Makefile @@ -73,6 +73,7 @@ TARGETS += sync TARGETS += syscall_user_dispatch TARGETS += sysctl TARGETS += tc-testing +TARGETS += tdx TARGETS += timens ifneq (1, $(quicktest)) TARGETS += timers diff --git a/tools/testing/selftests/tdx/Makefile b/tools/testing/selftests/tdx/Makefile new file mode 100644 index 000000000000..8dd43517cd55 --- /dev/null +++ b/tools/testing/selftests/tdx/Makefile @@ -0,0 +1,7 @@ +# SPDX-License-Identifier: GPL-2.0

+CFLAGS += -O3 -Wl,-no-as-needed -Wall -static

+TEST_GEN_PROGS := tdx_guest_test

+include ../lib.mk diff --git a/tools/testing/selftests/tdx/config b/tools/testing/selftests/tdx/config new file mode 100644 index 000000000000..aa1edc829ab6 --- /dev/null +++ b/tools/testing/selftests/tdx/config @@ -0,0 +1 @@ +CONFIG_TDX_GUEST_DRIVER=y diff --git a/tools/testing/selftests/tdx/tdx_guest_test.c b/tools/testing/selftests/tdx/tdx_guest_test.c new file mode 100644 index 000000000000..a5c243f73adc --- /dev/null +++ b/tools/testing/selftests/tdx/tdx_guest_test.c @@ -0,0 +1,175 @@ +// SPDX-License-Identifier: GPL-2.0 +/*

• • Test TDX guest features
• • Copyright (C) 2022 Intel Corporation.
• • Author: Kuppuswamy Sathyanarayanan sathyanarayanan.kuppuswamy@linux.intel.com
• */

+#include <sys/ioctl.h>

+#include <errno.h> +#include <fcntl.h>

+#include "../kselftest_harness.h" +#include "../../../../include/uapi/linux/tdx-guest.h"

+#define TDX_GUEST_DEVNAME "/dev/tdx_guest" +#define HEX_DUMP_SIZE 8 +#define DEBUG 0

+/**

• • struct tdreport_type - Type header of TDREPORT_STRUCT.
• • @type: Type of the TDREPORT (0 - SGX, 81 - TDX, rest are reserved)
• • @sub_type: Subtype of the TDREPORT (Default value is 0).
• • @version: TDREPORT version (Default value is 0).
• • @reserved: Added for future extension.
• • More details can be found in TDX v1.0 module specification, sec
• • titled "REPORTTYPE".
• */

+struct tdreport_type {

• __u8 type;
• __u8 sub_type;
• __u8 version;
• __u8 reserved;

+};

+/**

• • struct reportmac - TDX guest report data, MAC and TEE hashes.
• • @type: TDREPORT type header.
• • @reserved1: Reserved for future extension.
• • @cpu_svn: CPU security version.
• • @tee_tcb_info_hash: SHA384 hash of TEE TCB INFO.
• • @tee_td_info_hash: SHA384 hash of TDINFO_STRUCT.
• • @reportdata: User defined unique data passed in TDG.MR.REPORT request.
• • @reserved2: Reserved for future extension.
• • @mac: CPU MAC ID.
• • It is MAC-protected and contains hashes of the remainder of the
• • report structure along with user provided report data. More details can
• • be found in TDX v1.0 Module specification, sec titled "REPORTMACSTRUCT"
• */

+struct reportmac {

• struct tdreport_type type;
• __u8 reserved1[12];
• __u8 cpu_svn[16];
• __u8 tee_tcb_info_hash[48];
• __u8 tee_td_info_hash[48];
• __u8 reportdata[64];
• __u8 reserved2[32];
• __u8 mac[32];

+};

+/**

• • struct td_info - TDX guest measurements and configuration.
• • @attr: TDX Guest attributes (like debug, spet_disable, etc).
• • @xfam: Extended features allowed mask.
• • @mrtd: Build time measurement register.
• • @mrconfigid: Software-defined ID for non-owner-defined configuration

• •          of the guest - e.g., run-time or OS configuration.
    

• • @mrowner: Software-defined ID for the guest owner.
• • @mrownerconfig: Software-defined ID for owner-defined configuration of

• •             the guest - e.g., specific to the workload.
    

• • @rtmr: Run time measurement registers.
• • @reserved: Added for future extension.
• • It contains the measurements and initial configuration of the TDX guest
• • that was locked at initialization and a set of measurement registers
• • that are run-time extendable. More details can be found in TDX v1.0
• • Module specification, sec titled "TDINFO_STRUCT".
• */

+struct td_info {

• __u8 attr[8];
• __u64 xfam;
• __u64 mrtd[6];
• __u64 mrconfigid[6];
• __u64 mrowner[6];
• __u64 mrownerconfig[6];
• __u64 rtmr[24];
• __u64 reserved[14];

+};

+/*

• • struct tdreport - Output of TDCALL[TDG.MR.REPORT].
• • @reportmac: Mac protected header of size 256 bytes.
• • @tee_tcb_info: Additional attestable elements in the TCB are not

• •            reflected in the reportmac.
    

• • @reserved: Added for future extension.
• • @tdinfo: Measurements and configuration data of size 512 bytes.
• • More details can be found in TDX v1.0 Module specification, sec
• • titled "TDREPORT_STRUCT".
• */

+struct tdreport {

• struct reportmac reportmac;
• __u8 tee_tcb_info[239];
• __u8 reserved[17];
• struct td_info tdinfo;

+};

+static void print_array_hex(const char *title, const char *prefix_str,

• 	    const void *buf, int len)
  

+{

• int i, j, line_len, rowsize = HEX_DUMP_SIZE;
• const __u8 *ptr = buf;
• if (!len || !buf)

If len is not zero and buf is null, this would be bug. It is better to let the code crash or assert buf isn't null after testing len.

It is just a debug dump routine. So I don't think you need to add assert or crash here. If you really want some indication, maybe we can add an error message for invalid params.

Honestly, by design the code never enters in the `if` condition. So I am in favor of removing it.

...

-- Sathyanarayanan Kuppuswamy Linux Kernel Developer

On Tue, Nov 01, 2022 at 11:18:29PM -0700, Sathyanarayanan Kuppuswamy wrote:

Hi Greg,

On 10/29/22 11:53 PM, Greg Kroah-Hartman wrote:

...

On Sat, Oct 29, 2022 at 04:17:39PM -0700, Sathyanarayanan Kuppuswamy wrote:

...

Hi Greg

On 10/27/22 11:25 PM, Greg Kroah-Hartman wrote:

...

On Thu, Oct 27, 2022 at 05:28:19PM -0700, Kuppuswamy Sathyanarayanan wrote:

...

...

+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((void __user *)arg);
  

You know the type of this pointer here, why not cast it instead of having to cast it from void * again?

The only place we use arg pointer is in copy_from_user() function, which expects void __user * pointer. So why cast it as struct tdx_report_req * here?

Because then your function will show the true type and you don't have to cast it again.

...

...

...

+MODULE_AUTHOR("Kuppuswamy Sathyanarayanan sathyanarayanan.kuppuswamy@linux.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..29453e6a7ced --- /dev/null +++ b/include/uapi/linux/tdx-guest.h @@ -0,0 +1,55 @@ +/* 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

As these are fixed values, why do you have to say them again in the structure?

These length recommendations are provided by the TDX Module, and there is a slight possibility that the TDX Module will increase the maximum size of the REPORTDATA and TDREPORT in the future.

We do not write kernel code for "slight possibilities sometime in the future".

...

To handle such length changes, rather than inventing a new IOCTL for it in the future, making the current one flexible to handle such changes seems better.

Please work through the code and see how that would really look, and what would break if you were to change that in the future (remember kernel code and userspace code is not upgraded at the same time.)

...

One less ABI to maintain is always better, right? My initial design did use fixed size buffers like you have recommended, but later changed it as per review suggestion to make the ABI flexible.

Again, work through and try to determine if the added complexity will really work here.

What is wrong with just adding a new ioctl if in the future, you really do need to change something? That way you are sure that nothing will break and userspace will be finen with it. It is not like you are forbidden to add new ioctls later, you would have to change the kernel code no matter what anyway.

Keep it simple please.

The following are potential solutions to the possible kernel/userspace mix/match issue that may arise in the future if the acceptable reportdata length, tdreport length, or subtype values change.

I've attempted to do a sample implementation as you have suggested to check the pros and cons for both solutions. Please let me know what you think. Personally I prefer solution 2, as it handles the issue you have raised and also keeps the ABI flexible.

Solution 1:

This is based on your suggestion. I have dropped the IOCTL req members for reportdata length (rpd_len), tdreport length (tdr_len) and subtype. I have also used fixed size buffers to handle the current requirements.

Pros: Implementation is simple and clean.

Cons: May need to add new IOCTL for any future requirement updates.

Following are the ABI and IOCTL handler implementation details (Note: it is not the complete code, only included required details to show how the implementation looks):

Naturally, I like this one :)

And you can even make it go faster, with only one allocation, no need for 2 as your implementation did.

I don't know if speed matters on this, as I don't know how fast the actual hardware call takes, but making only 1 allocation and removing all need/worries about length checking and getting that correct is always a good thing.

Simple is good, especially if it works today.

If you have a new message size/type in the future, great, write a new ioctl and all is good!

Test your implementations out and see what you feel good about, but seriously consider keeping this simple if at all possible.

thanks,

greg k-h