Re: [PATCH v4 1/3] x86/tdx: Add TDX Guest attestation interface driver

Isaku Yamahata
2022-04-27T05:45:34Z

On Fri, Apr 22, 2022 at 04:34:16PM -0700,
Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> wrote:

> In TDX guest, attestation is used to verify the trustworthiness of a TD
> to other entities before making any secure communication.
>
> One usage example is, when a TD guest uses encrypted drive and the
> decryption keys required to access the drive are stored in a secure
> 3rd party keyserver, TD guest can use the quote generated via the
> attestation process to prove its trustworthiness with keyserver and
> get access to the storage keys.
>
> General steps involved in attestation process are,
>
>   1. TD guest generates the TDREPORT that contains version information
>      about the Intel TDX module, measurement of the TD, along with a
>      TD-specified nonce.
>   2. TD guest shares the TDREPORT with TD host via GetQuote hypercall
>      which is used by the host to generate a quote via quoting
>      enclave (QE).
>   3. Quote generation completion notification is sent to TD OS via
>      callback interrupt vector configured by TD using
>      SetupEventNotifyInterrupt hypercall.
>   4. After receiving the generated TDQUOTE, a remote verifier can be
>      used to verify the quote and confirm the trustworthiness of the
>      TD.
>
> More details on above mentioned steps can be found in TDX Guest-Host
> Communication Interface (GHCI) for Intel TDX 1.0, section titled
> "TD attestation".
>
> To allow the attestation agent (user application) to implement this
> feature, add an IOCTL interface to get TDREPORT and TDQUOTE from the
> user space. Since attestation agent can also use methods like vosck or
> TCP/IP to get the TDQUOTE, adding an IOCTL interface for it is an
> optional feature. So to simplify the driver, first add support for
> TDX_CMD_GET_TDREPORT IOCTL. Support for TDQUOTE IOCTL will be added by
> follow-on patches.
>
> TDREPORT can be generated by sending a TDCALL with leaf ID as 0x04.
> More details about the TDREPORT TDCALL can be found in Intel Trust
> Domain Extensions (Intel TDX) Module specification, section titled
> "TDG.MR.REPORT Leaf". Add a wrapper function (tdx_mcall_tdreport())
> to get the TDREPORT from the TDX Module. This API will be used by the
> interface driver to request for TDREPORT.
>
> Also note that explicit access permissions are not enforced in this
> driver because the quote and measurements are not a secret. However
> the access permissions of the device node can be used to set any
> desired access policy. The udev default is usually root access
> only.
>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> Reviewed-by: Andi Kleen <ak@linux.intel.com>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> ---
> arch/x86/coco/tdx/Makefile | 2 +-
> arch/x86/coco/tdx/attest.c | 191 ++++++++++++++++++++++++++++++++
> arch/x86/coco/tdx/tdx.c | 45 ++++++++
> arch/x86/include/asm/tdx.h | 2 +
> arch/x86/include/uapi/asm/tdx.h | 23 ++++
> 5 files changed, 262 insertions(+), 1 deletion(-)
> create mode 100644 arch/x86/coco/tdx/attest.c
> create mode 100644 arch/x86/include/uapi/asm/tdx.h
>
> diff --git a/arch/x86/coco/tdx/Makefile b/arch/x86/coco/tdx/Makefile
> index 46c55998557d..d2db3e6770e5 100644
> --- a/arch/x86/coco/tdx/Makefile
> +++ b/arch/x86/coco/tdx/Makefile
> @@ -1,3 +1,3 @@
> # SPDX-License-Identifier: GPL-2.0
>
> -obj-y += tdx.o tdcall.o
> +obj-y += tdx.o tdcall.o attest.o
> diff --git a/arch/x86/coco/tdx/attest.c b/arch/x86/coco/tdx/attest.c
> new file mode 100644
> index 000000000000..b776e81f6c20
> --- /dev/null
> +++ b/arch/x86/coco/tdx/attest.c
> @@ -0,0 +1,191 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * attest.c - TDX guest attestation interface driver.
> + *
> + * Implements user interface to trigger attestation process and
> + * read the TD Quote result.
> + *
> + * Copyright (C) 2022 Intel Corporation
> + *
> + */
> +
> +#define pr_fmt(fmt) "x86/tdx: attest: " fmt
> +
> +#include <linux/module.h>
> +#include <linux/miscdevice.h>
> +#include <linux/uaccess.h>
> +#include <linux/fs.h>
> +#include <linux/mm.h>
> +#include <linux/slab.h>
> +#include <linux/set_memory.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/platform_device.h>
> +#include <linux/jiffies.h>
> +#include <linux/io.h>
> +#include <asm/apic.h>
> +#include <asm/tdx.h>
> +#include <asm/irq_vectors.h>
> +#include <uapi/asm/tdx.h>
> +
> +#define DRIVER_NAME "tdx-attest"
> +
> +static struct platform_device *pdev;
> +static struct miscdevice miscdev;
> +
> +static long tdx_get_tdreport(void __user *argp)
> +{
> + void *report_buf = NULL, *tdreport_buf = NULL;
> + long ret = 0, err;
> +
> + /* Allocate space for report data */
> + report_buf = kmalloc(TDX_REPORT_DATA_LEN, GFP_KERNEL);
> + if (!report_buf)
> + return -ENOMEM;
> +
> + /*
> + * Allocate space for TDREPORT buffer (1024-byte aligned).
> + * Full page alignment is more than enough.
> + */
> + tdreport_buf = (void *)get_zeroed_page(GFP_KERNEL);
> + if (!tdreport_buf) {
> + ret = -ENOMEM;
> + goto tdreport_failed;
> + }
> +
> + /* Copy report data to kernel buffer */
> + if (copy_from_user(report_buf, argp, TDX_REPORT_DATA_LEN)) {
> + ret = -EFAULT;
> + goto tdreport_failed;
> + }
> +
> + /* Generate TDREPORT using report data in report_buf */
> + err = tdx_mcall_tdreport(tdreport_buf, report_buf);
> + if (err) {
> + /* If failed, pass TDCALL error code back to user */
> + ret = put_user(err, (long __user *)argp);

ret is ignored. ret should be checked or ignore it explicitly by (void).

> + ret = -EIO;
> + goto tdreport_failed;
> + }
> +
> + /* Copy TDREPORT data back to user buffer */
> + if (copy_to_user(argp, tdreport_buf, TDX_TDREPORT_LEN))
> + ret = -EFAULT;
> +
> +tdreport_failed:
> + kfree(report_buf);
> + if (tdreport_buf)
> + free_pages((unsigned long)tdreport_buf, 0);
> +
> + return ret;
> +}
> +
> +static long tdx_attest_ioctl(struct file *file, unsigned int cmd,
> + unsigned long arg)
> +{
> + void __user *argp = (void __user *)arg;
> + long ret = 0;
> +
> + switch (cmd) {
> + case TDX_CMD_GET_TDREPORT:
> + ret = tdx_get_tdreport(argp);
> + break;
> + default:
> + pr_err("cmd %d not supported\n", cmd);

pr_debug()? At least error should be returned to user space.

> + break;
> + }
> +
> + return ret;
> +}
> +
> +static const struct file_operations tdx_attest_fops = {
> + .owner = THIS_MODULE,
> + .unlocked_ioctl = tdx_attest_ioctl,
> + .llseek = no_llseek,
> +};
> +
> +static int tdx_attest_probe(struct platform_device *attest_pdev)
> +{
> + struct device *dev = &attest_pdev->dev;
> + long ret = 0;
> +
> + /* Only single device is allowed */
> + if (pdev)
> + return -EBUSY;
> +
> + pdev = attest_pdev;
> +
> + miscdev.name = DRIVER_NAME;
> + miscdev.minor = MISC_DYNAMIC_MINOR;
> + miscdev.fops = &tdx_attest_fops;
> + miscdev.parent = dev;
> +
> + ret = misc_register(&miscdev);
> + if (ret) {
> + pr_err("misc device registration failed\n");
> + goto failed;
> + }
> +
> + pr_debug("module initialization success\n");
> +
> + return 0;
> +
> +failed:
> + misc_deregister(&miscdev);
> +
> + pr_debug("module initialization failed\n");
> +
> + return ret;
> +}
> +
> +static int tdx_attest_remove(struct platform_device *attest_pdev)
> +{
> + misc_deregister(&miscdev);
> + pr_debug("module is successfully removed\n");
> + return 0;
> +}
> +
> +static struct platform_driver tdx_attest_driver = {
> + .probe = tdx_attest_probe,
> + .remove = tdx_attest_remove,
> + .driver = {
> + .name = DRIVER_NAME,
> + },
> +};
> +
> +static int __init tdx_attest_init(void)
> +{
> + int ret;
> +
> + /* Make sure we are in a valid TDX platform */
> + if (!cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
> + return -EIO;
> +
> + ret = platform_driver_register(&tdx_attest_driver);
> + if (ret) {
> + pr_err("failed to register driver, err=%d\n", ret);
> + return ret;
> + }
> +
> + pdev = platform_device_register_simple(DRIVER_NAME, -1, NULL, 0);
> + if (IS_ERR(pdev)) {
> + ret = PTR_ERR(pdev);
> + pr_err("failed to allocate device, err=%d\n", ret);
> + platform_driver_unregister(&tdx_attest_driver);
> + return ret;
> + }
> +
> + return 0;
> +}
> +
> +static void __exit tdx_attest_exit(void)
> +{
> + platform_device_unregister(pdev);
> + platform_driver_unregister(&tdx_attest_driver);
> +}
> +
> +module_init(tdx_attest_init);
> +module_exit(tdx_attest_exit);
> +
> +MODULE_AUTHOR("Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>");
> +MODULE_DESCRIPTION("TDX attestation driver");
> +MODULE_LICENSE("GPL");
> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index 03deb4d6920d..2a79ca92a52d 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -11,10 +11,12 @@
> #include <asm/insn.h>
> #include <asm/insn-eval.h>
> #include <asm/pgtable.h>
> +#include <asm/io.h>
>
> /* TDX module Call Leaf IDs */
> #define TDX_GET_INFO 1
> #define TDX_GET_VEINFO 3
> +#define TDX_GET_REPORT 4
> #define TDX_ACCEPT_PAGE 6
>
> /* TDX hypercall Leaf IDs */
> @@ -34,6 +36,10 @@
> #define VE_GET_PORT_NUM(e) ((e) >> 16)
> #define VE_IS_IO_STRING(e) ((e) & BIT(4))
>
> +/* TDX Module call error codes */
> +#define TDCALL_RETURN_CODE_MASK 0xffffffff00000000
> +#define TDCALL_RETURN_CODE(a) ((a) & TDCALL_RETURN_CODE_MASK)
> +
> /*
> * Wrapper for standard use of __tdx_hypercall with no output aside from
> * return code.
> @@ -98,6 +104,45 @@ static inline void tdx_module_call(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
> panic("TDCALL %lld failed (Buggy TDX module!)\n", fn);
> }
>
> +/*
> + * tdx_mcall_tdreport() - Generate TDREPORT_STRUCT using TDCALL.
> + *
> + * @data : Address of 1024B aligned data to store
> + * TDREPORT_STRUCT.
> + * @reportdata : Address of 64B aligned report data
> + *
> + * return 0 on success or failure error number.

Is "failure error number" TDX status code? not -Evalue?

> + */
> +long tdx_mcall_tdreport(void *data, void *reportdata)
> +{
> + u64 ret;
> +
> + /*
> + * Check for a valid TDX guest to ensure this API is only
> + * used by TDX guest platform. Also make sure "data" and
> + * "reportdata" pointers are valid.
> + */
> + if (!data || !reportdata || !cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
> + return -EINVAL;
> +
> + /*
> + * Pass the physical address of user generated report data
> + * and the physical address of output buffer to the TDX module
> + * to generate the TD report. Generated data contains
> + * measurements/configuration data of the TD guest. More info
> + * about ABI can be found in TDX 1.0 Module specification, sec
> + * titled "TDG.MR.REPORT".
> + */
> + ret = __tdx_module_call(TDX_GET_REPORT, virt_to_phys(data),
> + virt_to_phys(reportdata), 0, 0, NULL);
> +
> + if (ret)
> + return TDCALL_RETURN_CODE(ret);

Why is status code masked?

> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(tdx_mcall_tdreport);

Can this function be put into attest.c. Instead, wecan export __tdx_module_call.

> static u64 get_cc_mask(void)
> {
> struct tdx_module_output out;
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index 020c81a7c729..a151f69dd6ef 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -67,6 +67,8 @@ void tdx_safe_halt(void);
>
> bool tdx_early_handle_ve(struct pt_regs *regs);
>
> +long tdx_mcall_tdreport(void *data, void *reportdata);
> +
> #else
>
> static inline void tdx_early_init(void) { };
> diff --git a/arch/x86/include/uapi/asm/tdx.h b/arch/x86/include/uapi/asm/tdx.h
> new file mode 100644
> index 000000000000..c21f9d6fe88b
> --- /dev/null
> +++ b/arch/x86/include/uapi/asm/tdx.h
> @@ -0,0 +1,23 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +#ifndef _UAPI_ASM_X86_TDX_H
> +#define _UAPI_ASM_X86_TDX_H
> +
> +#include <linux/types.h>
> +#include <linux/ioctl.h>
> +
> +/* Input report data length for TDX_CMD_GET_TDREPORT IOCTL request */
> +#define TDX_REPORT_DATA_LEN 64
> +
> +/* Output TD report data length after TDX_CMD_GET_TDREPORT IOCTL execution */
> +#define TDX_TDREPORT_LEN 1024
> +
> +/*
> + * TDX_CMD_GET_TDREPORT IOCTL is used to get TDREPORT data from the TDX
> + * Module. Users should pass report data of size TDX_REPORT_DATA_LEN bytes
> + * via user input buffer of size TDX_TDREPORT_LEN. Once IOCTL is successful
> + * TDREPORT data is copied to the user buffer. On failure, TDCALL error
> + * code is copied back to the user buffer.
> + */
> +#define TDX_CMD_GET_TDREPORT _IOWR('T', 0x01, __u64)
> +
> +#endif /* _UAPI_ASM_X86_TDX_H */
> --
> 2.25.1
>

--
Isaku Yamahata <isaku.yamahata@gmail.com>