[PATCH v4 5/5] virt: tdx-guest: Expose TDX MRs as sysfs attributes

From: Cedric Xing
Date: Mon Apr 14 2025 - 17:59:43 EST

Expose the most commonly used TDX MRs (Measurement Registers) as sysfs
attributes. Use the ioctl() interface of /dev/tdx_guest to request a full
TDREPORT for access to other TD measurements.

Directory structure of TDX MRs inside a TDVM is as follows:

/sys/class/misc/tdx_guest
└── mr
├── mrconfigid
├── mrowner
├── mrownerconfig
├── mrtd:sha384
├── rtmr0:sha384
├── rtmr1:sha384
├── rtmr2:sha384
└── rtmr3:sha384

Read the file/attribute to retrieve the current value of an MR. Write to
the file/attribute (if writable) to extend the corresponding RTMR. Refer to
Documentation/ABI/testing/sysfs-devices-virtual-misc-tdx_guest-mr for more
information.

Signed-off-by: Cedric Xing <cedric.xing@xxxxxxxxx>
---
.../testing/sysfs-devices-virtual-misc-tdx_guest | 60 +++++
MAINTAINERS | 1 +
drivers/virt/coco/tdx-guest/Kconfig | 1 +
drivers/virt/coco/tdx-guest/tdx-guest.c | 291 +++++++++++++--------
4 files changed, 250 insertions(+), 103 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-devices-virtual-misc-tdx_guest b/Documentation/ABI/testing/sysfs-devices-virtual-misc-tdx_guest
new file mode 100644
index 000000000000..fb7b27ae0b74
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-devices-virtual-misc-tdx_guest
@@ -0,0 +1,60 @@
+What: /sys/devices/virtual/misc/tdx_guest/mr/MRNAME[:HASH]
+Date: April, 2025
+KernelVersion: v6.16
+Contact: linux-coco@xxxxxxxxxxxxxxx
+Description:
+ Value of a TDX measurement register (MR). MRNAME and HASH above
+ are placeholders. The optional suffix :HASH is used for MRs
+ that have associated hash algorithms. See below for a complete
+ list of TDX MRs exposed via sysfs. Refer to Intel TDX Module
+ ABI Specification for the definition of TDREPORT and the full
+ list of TDX measurements.
+
+ Intel TDX Module ABI Specification can be found at:
+ https://www.intel.com/content/www/us/en/developer/tools/trust-domain-extensions/documentation.html#architecture
+
+What: /sys/devices/virtual/misc/tdx_guest/mr/mrconfigid
+Date: April, 2025
+KernelVersion: v6.16
+Contact: linux-coco@xxxxxxxxxxxxxxx
+Description:
+ (RO) MRCONFIGID - 48-byte immutable storage typically used for
+ software-defined ID for non-owner-defined configuration of the
+ guest TD – e.g., run-time or OS configuration.
+
+What: /sys/devices/virtual/misc/tdx_guest/mr/mrowner
+Date: April, 2025
+KernelVersion: v6.16
+Contact: linux-coco@xxxxxxxxxxxxxxx
+Description:
+ (RO) MROWNER - 48-byte immutable storage typically used for
+ software-defined ID for the guest TD’s owner.
+
+What: /sys/devices/virtual/misc/tdx_guest/mr/mrownerconfig
+Date: April, 2025
+KernelVersion: v6.16
+Contact: linux-coco@xxxxxxxxxxxxxxx
+Description:
+ (RO) MROWNERCONFIG - 48-byte immutable storage typically used
+ for software-defined ID for owner-defined configuration of the
+ guest TD – e.g., specific to the workload rather than the
+ run-time or OS.
+
+What: /sys/devices/virtual/misc/tdx_guest/mr/mrtd:sha384
+Date: April, 2025
+KernelVersion: v6.16
+Contact: linux-coco@xxxxxxxxxxxxxxx
+Description:
+ (RO) MRTD - Measurement of the initial contents of the TD.
+
+What: /sys/devices/virtual/misc/tdx_guest/mr/rtmr[0123]:sha384
+Date: April, 2025
+KernelVersion: v6.16
+Contact: linux-coco@xxxxxxxxxxxxxxx
+Description:
+ (RW) RTMR[0123] - 4 Run-Time extendable Measurement Registers.
+ Read from any of these returns the current value of the
+ corresponding RTMR. Write extends the written buffer to the
+ RTMR. All writes must start at offset 0 and be 48 bytes in
+ size. Partial writes will result in EINVAL returned by the
+ write() syscall.
diff --git a/MAINTAINERS b/MAINTAINERS
index 870b34190de7..1632dfb0051d 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -26228,6 +26228,7 @@ L: x86@xxxxxxxxxx
L: linux-coco@xxxxxxxxxxxxxxx
S: Supported
T: git git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/tdx
+F: Documentation/ABI/testing/sysfs-devices-virtual-misc-tdx_guest-mr
F: arch/x86/boot/compressed/tdx*
F: arch/x86/coco/tdx/
F: arch/x86/include/asm/shared/tdx.h
diff --git a/drivers/virt/coco/tdx-guest/Kconfig b/drivers/virt/coco/tdx-guest/Kconfig
index 22dd59e19431..dbbdc14383b1 100644
--- a/drivers/virt/coco/tdx-guest/Kconfig
+++ b/drivers/virt/coco/tdx-guest/Kconfig
@@ -2,6 +2,7 @@ config TDX_GUEST_DRIVER
tristate "TDX Guest driver"
depends on INTEL_TDX_GUEST
select TSM_REPORTS
+ select TSM_MEASUREMENTS
help
The driver provides userspace interface to communicate with
the TDX module to request the TDX guest details like attestation
diff --git a/drivers/virt/coco/tdx-guest/tdx-guest.c b/drivers/virt/coco/tdx-guest/tdx-guest.c
index 224e7dde9cde..e76810d89e0b 100644
--- a/drivers/virt/coco/tdx-guest/tdx-guest.c
+++ b/drivers/virt/coco/tdx-guest/tdx-guest.c
@@ -5,6 +5,8 @@
* Copyright (C) 2022 Intel Corporation
*/

+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
#include <linux/kernel.h>
#include <linux/miscdevice.h>
#include <linux/mm.h>
@@ -15,8 +17,9 @@
#include <linux/set_memory.h>
#include <linux/io.h>
#include <linux/delay.h>
+#include <linux/sockptr.h>
#include <linux/tsm.h>
-#include <linux/sizes.h>
+#include <linux/tsm-mr.h>

#include <uapi/linux/tdx-guest.h>

@@ -66,39 +69,144 @@ static DEFINE_MUTEX(quote_lock);
*/
static u32 getquote_timeout = 30;

-static long tdx_get_report0(struct tdx_report_req __user *req)
+/* Buffers for TDREPORT and RTMR extension */
+static u8 *tdx_report_buf, *tdx_extend_buf;
+
+/* Lock to serialize TDG.MR.REPORT & TDG.MR.RTMR.EXTEND requests */
+static DEFINE_MUTEX(mr_lock);
+
+/* TDREPORT fields */
+enum {
+ TDREPORT_reportdata = 128,
+ TDREPORT_tee_tcb_info = 256,
+ TDREPORT_tdinfo = TDREPORT_tee_tcb_info + 256,
+ TDREPORT_attributes = TDREPORT_tdinfo,
+ TDREPORT_xfam = TDREPORT_attributes + sizeof(u64),
+ TDREPORT_mrtd = TDREPORT_xfam + sizeof(u64),
+ TDREPORT_mrconfigid = TDREPORT_mrtd + SHA384_DIGEST_SIZE,
+ TDREPORT_mrowner = TDREPORT_mrconfigid + SHA384_DIGEST_SIZE,
+ TDREPORT_mrownerconfig = TDREPORT_mrowner + SHA384_DIGEST_SIZE,
+ TDREPORT_rtmr0 = TDREPORT_mrownerconfig + SHA384_DIGEST_SIZE,
+ TDREPORT_rtmr1 = TDREPORT_rtmr0 + SHA384_DIGEST_SIZE,
+ TDREPORT_rtmr2 = TDREPORT_rtmr1 + SHA384_DIGEST_SIZE,
+ TDREPORT_rtmr3 = TDREPORT_rtmr2 + SHA384_DIGEST_SIZE,
+ TDREPORT_servtd_hash = TDREPORT_rtmr3 + SHA384_DIGEST_SIZE,
+};
+
+static inline int tdx_mr_report_locked(sockptr_t data, sockptr_t tdreport)
{
- u8 *reportdata, *tdreport;
- long ret;
+ scoped_cond_guard(mutex_intr, return -EINTR, &mr_lock) {
+ u8 *p = tdx_report_buf + TDREPORT_reportdata;
+ int ret;

- reportdata = kmalloc(TDX_REPORTDATA_LEN, GFP_KERNEL);
- if (!reportdata)
- return -ENOMEM;
+ if (!sockptr_is_null(data) &&
+ copy_from_sockptr(p, data, TDX_REPORTDATA_LEN))
+ return -EFAULT;

- tdreport = kzalloc(TDX_REPORT_LEN, GFP_KERNEL);
- if (!tdreport) {
- ret = -ENOMEM;
- goto out;
+ ret = tdx_mcall_get_report0(p, tdx_report_buf);
+ if (WARN(ret, "tdx_mcall_get_report0() failed: %d", ret))
+ return ret;
+
+ if (!sockptr_is_null(tdreport) &&
+ copy_to_sockptr(tdreport, tdx_report_buf, TDX_REPORT_LEN))
+ return -EFAULT;
}
+ return 0;
+}

- if (copy_from_user(reportdata, req->reportdata, TDX_REPORTDATA_LEN)) {
- ret = -EFAULT;
- goto out;
+static inline int tdx_mr_extend_locked(ptrdiff_t mr_ind, const u8 *data)
+{
+ scoped_cond_guard(mutex_intr, return -EINTR, &mr_lock) {
+ int ret;
+
+ memcpy(tdx_extend_buf, data, SHA384_DIGEST_SIZE);
+
+ ret = tdx_mcall_extend_rtmr(mr_ind, tdx_extend_buf);
+ if (WARN(ret, "tdx_mcall_extend_rtmr(%ld) failed: %d", mr_ind, ret))
+ return ret;
}
+ return 0;
+}
+
+#define TDX_MR_(r) .mr_value = (void *)TDREPORT_##r, TSM_MR_(r, SHA384)
+static struct tsm_measurement_register tdx_mrs[] = {
+ { TDX_MR_(rtmr0) | TSM_MR_F_RTMR },
+ { TDX_MR_(rtmr1) | TSM_MR_F_RTMR },
+ { TDX_MR_(rtmr2) | TSM_MR_F_RTMR },
+ { TDX_MR_(rtmr3) | TSM_MR_F_RTMR },
+ { TDX_MR_(mrtd) },
+ { TDX_MR_(mrconfigid) | TSM_MR_F_NOHASH },
+ { TDX_MR_(mrowner) | TSM_MR_F_NOHASH },
+ { TDX_MR_(mrownerconfig) | TSM_MR_F_NOHASH },
+};
+#undef TDX_MR_
+
+static int tdx_mr_refresh(const struct tsm_measurements *tm,
+ const struct tsm_measurement_register *mr)
+{
+ return tdx_mr_report_locked(KERNEL_SOCKPTR(NULL), KERNEL_SOCKPTR(NULL));
+}

- /* Generate TDREPORT0 using "TDG.MR.REPORT" TDCALL */
- ret = tdx_mcall_get_report0(reportdata, tdreport);
+static int tdx_mr_extend(const struct tsm_measurements *tm,
+ const struct tsm_measurement_register *mr,
+ const u8 *data)
+{
+ return tdx_mr_extend_locked(mr - tm->mrs, data);
+}
+
+static struct tsm_measurements tdx_measurements = {
+ .mrs = tdx_mrs,
+ .nr_mrs = ARRAY_SIZE(tdx_mrs),
+ .refresh = tdx_mr_refresh,
+ .write = tdx_mr_extend,
+};
+
+/* attribute groups of tdx_misc_dev */
+static const struct attribute_group *tdx_attr_groups[] = {
+ NULL,
+ NULL,
+};
+
+static int tdx_mr_init(void)
+{
+ int ret;
+
+ u8 *report_buf __free(kfree) = kzalloc(TDX_REPORT_LEN, GFP_KERNEL);
+
+ /* TDG.MR.RTMR.EXTEND requires 64-byte aligned input */
+ u8 *extend_buf __free(kfree) = kmalloc(64, GFP_KERNEL);
+
+ if (!report_buf || !extend_buf)
+ return -ENOMEM;
+
+ tdx_report_buf = report_buf;
+ ret = tdx_mr_refresh(&tdx_measurements, NULL);
if (ret)
- goto out;
+ return ret;

- if (copy_to_user(req->tdreport, tdreport, TDX_REPORT_LEN))
- ret = -EFAULT;
+ for (size_t i = 0; i < ARRAY_SIZE(tdx_mrs); ++i)
+ *(long *)&tdx_mrs[i].mr_value += (long)report_buf;

-out:
- kfree(reportdata);
- kfree(tdreport);
+ tdx_attr_groups[0] = tsm_mr_create_attribute_group(&tdx_measurements);
+ if (IS_ERR(tdx_attr_groups[0]))
+ return PTR_ERR(tdx_attr_groups[0]);

- return ret;
+ tdx_report_buf = no_free_ptr(report_buf);
+ tdx_extend_buf = no_free_ptr(extend_buf);
+ return 0;
+}
+
+static void tdx_mr_deinit(void)
+{
+ tsm_mr_free_attribute_group(tdx_attr_groups[0]);
+ kfree(tdx_extend_buf);
+ kfree(tdx_report_buf);
+}
+
+static long tdx_get_report0(struct tdx_report_req __user *req)
+{
+ return tdx_mr_report_locked(USER_SOCKPTR(req->reportdata),
+ USER_SOCKPTR(req->tdreport));
}

static void free_quote_buf(void *buf)
@@ -159,91 +267,60 @@ static int wait_for_quote_completion(struct tdx_quote_buf *quote_buf, u32 timeou

static int tdx_report_new(struct tsm_report *report, void *data)
{
- u8 *buf, *reportdata = NULL, *tdreport = NULL;
+ u8 *buf;
struct tdx_quote_buf *quote_buf = quote_data;
struct tsm_desc *desc = &report->desc;
int ret;
u64 err;

- /* TODO: switch to guard(mutex_intr) */
- if (mutex_lock_interruptible(&quote_lock))
- return -EINTR;
-
- /*
- * If the previous request is timedout or interrupted, and the
- * Quote buf status is still in GET_QUOTE_IN_FLIGHT (owned by
- * VMM), don't permit any new request.
- */
- if (quote_buf->status == GET_QUOTE_IN_FLIGHT) {
- ret = -EBUSY;
- goto done;
- }
-
- if (desc->inblob_len != TDX_REPORTDATA_LEN) {
- ret = -EINVAL;
- goto done;
- }
-
- reportdata = kmalloc(TDX_REPORTDATA_LEN, GFP_KERNEL);
- if (!reportdata) {
- ret = -ENOMEM;
- goto done;
- }
-
- tdreport = kzalloc(TDX_REPORT_LEN, GFP_KERNEL);
- if (!tdreport) {
- ret = -ENOMEM;
- goto done;
- }
-
- memcpy(reportdata, desc->inblob, desc->inblob_len);
-
- /* Generate TDREPORT0 using "TDG.MR.REPORT" TDCALL */
- ret = tdx_mcall_get_report0(reportdata, tdreport);
- if (ret) {
- pr_err("GetReport call failed\n");
- goto done;
+ scoped_cond_guard(mutex_intr, ret = -EINTR, &quote_lock) {
+ /*
+ * If the previous request is timedout or interrupted, and the
+ * Quote buf status is still in GET_QUOTE_IN_FLIGHT (owned by
+ * VMM), don't permit any new request.
+ */
+ if (quote_buf->status == GET_QUOTE_IN_FLIGHT)
+ return -EBUSY;
+
+ if (desc->inblob_len != TDX_REPORTDATA_LEN)
+ return -EINVAL;
+
+ memset(quote_data, 0, GET_QUOTE_BUF_SIZE);
+
+ /* Update Quote buffer header */
+ quote_buf->version = GET_QUOTE_CMD_VER;
+ quote_buf->in_len = TDX_REPORT_LEN;
+
+ /* Generate TDREPORT0 using "TDG.MR.REPORT" TDCALL */
+ ret = tdx_mr_report_locked(KERNEL_SOCKPTR(desc->inblob),
+ KERNEL_SOCKPTR(quote_buf->data));
+ if (ret)
+ break;
+
+ err = tdx_hcall_get_quote(quote_data, GET_QUOTE_BUF_SIZE);
+ if (err) {
+ pr_err("GetQuote hypercall failed, status:%llx\n", err);
+ return -EIO;
+ }
+
+ ret = wait_for_quote_completion(quote_buf, getquote_timeout);
+ if (ret) {
+ pr_err("GetQuote request timedout\n");
+ break;
+ }
+
+ buf = kvmemdup(quote_buf->data, quote_buf->out_len, GFP_KERNEL);
+ if (!buf)
+ return -ENOMEM;
+
+ report->outblob = buf;
+ report->outblob_len = quote_buf->out_len;
+
+ /*
+ * TODO: parse the PEM-formatted cert chain out of the quote
+ * buffer when provided
+ */
}
-
- memset(quote_data, 0, GET_QUOTE_BUF_SIZE);
-
- /* Update Quote buffer header */
- quote_buf->version = GET_QUOTE_CMD_VER;
- quote_buf->in_len = TDX_REPORT_LEN;
-
- memcpy(quote_buf->data, tdreport, TDX_REPORT_LEN);
-
- err = tdx_hcall_get_quote(quote_data, GET_QUOTE_BUF_SIZE);
- if (err) {
- pr_err("GetQuote hypercall failed, status:%llx\n", err);
- ret = -EIO;
- goto done;
- }
-
- ret = wait_for_quote_completion(quote_buf, getquote_timeout);
- if (ret) {
- pr_err("GetQuote request timedout\n");
- goto done;
- }
-
- buf = kvmemdup(quote_buf->data, quote_buf->out_len, GFP_KERNEL);
- if (!buf) {
- ret = -ENOMEM;
- goto done;
- }
-
- report->outblob = buf;
- report->outblob_len = quote_buf->out_len;
-
- /*
- * TODO: parse the PEM-formatted cert chain out of the quote buffer when
- * provided
- */
-done:
- mutex_unlock(&quote_lock);
- kfree(reportdata);
- kfree(tdreport);
-
return ret;
}

@@ -289,6 +366,7 @@ static struct miscdevice tdx_misc_dev = {
.name = KBUILD_MODNAME,
.minor = MISC_DYNAMIC_MINOR,
.fops = &tdx_guest_fops,
+ .groups = tdx_attr_groups,
};

static const struct x86_cpu_id tdx_guest_ids[] = {
@@ -311,10 +389,14 @@ static int __init tdx_guest_init(void)
if (!x86_match_cpu(tdx_guest_ids))
return -ENODEV;

- ret = misc_register(&tdx_misc_dev);
+ ret = tdx_mr_init();
if (ret)
return ret;

+ ret = misc_register(&tdx_misc_dev);
+ if (ret)
+ goto free_tsm_mr;
+
quote_data = alloc_quote_buf();
if (!quote_data) {
pr_err("Failed to allocate Quote buffer\n");
@@ -332,6 +414,8 @@ static int __init tdx_guest_init(void)
free_quote_buf(quote_data);
free_misc:
misc_deregister(&tdx_misc_dev);
+free_tsm_mr:
+ tdx_mr_deinit();

return ret;
}
@@ -342,6 +426,7 @@ static void __exit tdx_guest_exit(void)
tsm_unregister(&tdx_tsm_ops);
free_quote_buf(quote_data);
misc_deregister(&tdx_misc_dev);
+ tdx_mr_deinit();
}
module_exit(tdx_guest_exit);


--
2.43.0