--- /dev/null
+What: /sys/kernel/config/tsm/report/$name/inblob
+Date: September, 2023
+KernelVersion: v6.7
+Contact: linux-coco@lists.linux.dev
+Description:
+ (WO) Up to 64 bytes of user specified binary data. For replay
+ protection this should include a nonce, but the kernel does not
+ place any restrictions on the content.
+
+What: /sys/kernel/config/tsm/report/$name/outblob
+Date: September, 2023
+KernelVersion: v6.7
+Contact: linux-coco@lists.linux.dev
+Description:
+ (RO) Binary attestation report generated from @inblob and other
+ options The format of the report is implementation specific
+ where the implementation is conveyed via the @provider
+ attribute.
+
+What: /sys/kernel/config/tsm/report/$name/auxblob
+Date: October, 2023
+KernelVersion: v6.7
+Contact: linux-coco@lists.linux.dev
+Description:
+ (RO) Optional supplemental data that a TSM may emit, visibility
+ of this attribute depends on TSM, and may be empty if no
+ auxiliary data is available.
+
+ When @provider is "sev_guest" this file contains the
+ "cert_table" from SEV-ES Guest-Hypervisor Communication Block
+ Standardization v2.03 Section 4.1.8.1 MSG_REPORT_REQ.
+ https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/56421.pdf
+
+What: /sys/kernel/config/tsm/report/$name/provider
+Date: September, 2023
+KernelVersion: v6.7
+Contact: linux-coco@lists.linux.dev
+Description:
+ (RO) A name for the format-specification of @outblob like
+ "sev_guest" [1] or "tdx_guest" [2] in the near term, or a
+ common standard format in the future.
+
+ [1]: SEV Secure Nested Paging Firmware ABI Specification
+ Revision 1.55 Table 22
+ https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/56860.pdf
+
+ [2]: Intel® Trust Domain Extensions Data Center Attestation
+ Primitives : Quote Generation Library and Quote Verification
+ Library Revision 0.8 Appendix 4,5
+ https://download.01.org/intel-sgx/latest/dcap-latest/linux/docs/Intel_TDX_DCAP_Quoting_Library_API.pdf
+
+What: /sys/kernel/config/tsm/report/$name/generation
+Date: September, 2023
+KernelVersion: v6.7
+Contact: linux-coco@lists.linux.dev
+Description:
+ (RO) The value in this attribute increments each time @inblob or
+ any option is written. Userspace can detect conflicts by
+ checking generation before writing to any attribute and making
+ sure the number of writes matches expectations after reading
+ @outblob, or it can prevent conflicts by creating a report
+ instance per requesting context.
+
+What: /sys/kernel/config/tsm/report/$name/privlevel
+Date: September, 2023
+KernelVersion: v6.7
+Contact: linux-coco@lists.linux.dev
+Description:
+ (WO) Attribute is visible if a TSM implementation provider
+ supports the concept of attestation reports for TVMs running at
+ different privilege levels, like SEV-SNP "VMPL", specify the
+ privilege level via this attribute. The minimum acceptable
+ value is conveyed via @privlevel_floor and the maximum
+ acceptable value is TSM_PRIVLEVEL_MAX (3).
+
+What: /sys/kernel/config/tsm/report/$name/privlevel_floor
+Date: September, 2023
+KernelVersion: v6.7
+Contact: linux-coco@lists.linux.dev
+Description:
+ (RO) Indicates the minimum permissible value that can be written
+ to @privlevel.
--- /dev/null
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright(c) 2023 Intel Corporation. All rights reserved. */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/tsm.h>
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/rwsem.h>
+#include <linux/string.h>
+#include <linux/module.h>
+#include <linux/cleanup.h>
+#include <linux/configfs.h>
+
+static struct tsm_provider {
+ const struct tsm_ops *ops;
+ const struct config_item_type *type;
+ void *data;
+} provider;
+static DECLARE_RWSEM(tsm_rwsem);
+
+/**
+ * DOC: Trusted Security Module (TSM) Attestation Report Interface
+ *
+ * The TSM report interface is a common provider of blobs that facilitate
+ * attestation of a TVM (confidential computing guest) by an attestation
+ * service. A TSM report combines a user-defined blob (likely a public-key with
+ * a nonce for a key-exchange protocol) with a signed attestation report. That
+ * combined blob is then used to obtain secrets provided by an agent that can
+ * validate the attestation report. The expectation is that this interface is
+ * invoked infrequently, however configfs allows for multiple agents to
+ * own their own report generation instances to generate reports as
+ * often as needed.
+ *
+ * The attestation report format is TSM provider specific, when / if a standard
+ * materializes that can be published instead of the vendor layout. Until then
+ * the 'provider' attribute indicates the format of 'outblob', and optionally
+ * 'auxblob'.
+ */
+
+struct tsm_report_state {
+ struct tsm_report report;
+ unsigned long write_generation;
+ unsigned long read_generation;
+ struct config_item cfg;
+};
+
+enum tsm_data_select {
+ TSM_REPORT,
+ TSM_CERTS,
+};
+
+static struct tsm_report *to_tsm_report(struct config_item *cfg)
+{
+ struct tsm_report_state *state =
+ container_of(cfg, struct tsm_report_state, cfg);
+
+ return &state->report;
+}
+
+static struct tsm_report_state *to_state(struct tsm_report *report)
+{
+ return container_of(report, struct tsm_report_state, report);
+}
+
+static int try_advance_write_generation(struct tsm_report *report)
+{
+ struct tsm_report_state *state = to_state(report);
+
+ lockdep_assert_held_write(&tsm_rwsem);
+
+ /*
+ * Malicious or broken userspace has written enough times for
+ * read_generation == write_generation by modular arithmetic without an
+ * interim read. Stop accepting updates until the current report
+ * configuration is read.
+ */
+ if (state->write_generation == state->read_generation - 1)
+ return -EBUSY;
+ state->write_generation++;
+ return 0;
+}
+
+static ssize_t tsm_report_privlevel_store(struct config_item *cfg,
+ const char *buf, size_t len)
+{
+ struct tsm_report *report = to_tsm_report(cfg);
+ unsigned int val;
+ int rc;
+
+ rc = kstrtouint(buf, 0, &val);
+ if (rc)
+ return rc;
+
+ /*
+ * The valid privilege levels that a TSM might accept, if it accepts a
+ * privilege level setting at all, are a max of TSM_PRIVLEVEL_MAX (see
+ * SEV-SNP GHCB) and a minimum of a TSM selected floor value no less
+ * than 0.
+ */
+ if (provider.ops->privlevel_floor > val || val > TSM_PRIVLEVEL_MAX)
+ return -EINVAL;
+
+ guard(rwsem_write)(&tsm_rwsem);
+ rc = try_advance_write_generation(report);
+ if (rc)
+ return rc;
+ report->desc.privlevel = val;
+
+ return len;
+}
+CONFIGFS_ATTR_WO(tsm_report_, privlevel);
+
+static ssize_t tsm_report_privlevel_floor_show(struct config_item *cfg,
+ char *buf)
+{
+ guard(rwsem_read)(&tsm_rwsem);
+ return sysfs_emit(buf, "%u\n", provider.ops->privlevel_floor);
+}
+CONFIGFS_ATTR_RO(tsm_report_, privlevel_floor);
+
+static ssize_t tsm_report_inblob_write(struct config_item *cfg,
+ const void *buf, size_t count)
+{
+ struct tsm_report *report = to_tsm_report(cfg);
+ int rc;
+
+ guard(rwsem_write)(&tsm_rwsem);
+ rc = try_advance_write_generation(report);
+ if (rc)
+ return rc;
+
+ report->desc.inblob_len = count;
+ memcpy(report->desc.inblob, buf, count);
+ return count;
+}
+CONFIGFS_BIN_ATTR_WO(tsm_report_, inblob, NULL, TSM_INBLOB_MAX);
+
+static ssize_t tsm_report_generation_show(struct config_item *cfg, char *buf)
+{
+ struct tsm_report *report = to_tsm_report(cfg);
+ struct tsm_report_state *state = to_state(report);
+
+ guard(rwsem_read)(&tsm_rwsem);
+ return sysfs_emit(buf, "%lu\n", state->write_generation);
+}
+CONFIGFS_ATTR_RO(tsm_report_, generation);
+
+static ssize_t tsm_report_provider_show(struct config_item *cfg, char *buf)
+{
+ guard(rwsem_read)(&tsm_rwsem);
+ return sysfs_emit(buf, "%s\n", provider.ops->name);
+}
+CONFIGFS_ATTR_RO(tsm_report_, provider);
+
+static ssize_t __read_report(struct tsm_report *report, void *buf, size_t count,
+ enum tsm_data_select select)
+{
+ loff_t offset = 0;
+ ssize_t len;
+ u8 *out;
+
+ if (select == TSM_REPORT) {
+ out = report->outblob;
+ len = report->outblob_len;
+ } else {
+ out = report->auxblob;
+ len = report->auxblob_len;
+ }
+
+ /*
+ * Recall that a NULL @buf is configfs requesting the size of
+ * the buffer.
+ */
+ if (!buf)
+ return len;
+ return memory_read_from_buffer(buf, count, &offset, out, len);
+}
+
+static ssize_t read_cached_report(struct tsm_report *report, void *buf,
+ size_t count, enum tsm_data_select select)
+{
+ struct tsm_report_state *state = to_state(report);
+
+ guard(rwsem_read)(&tsm_rwsem);
+ if (!report->desc.inblob_len)
+ return -EINVAL;
+
+ /*
+ * A given TSM backend always fills in ->outblob regardless of
+ * whether the report includes an auxblob or not.
+ */
+ if (!report->outblob ||
+ state->read_generation != state->write_generation)
+ return -EWOULDBLOCK;
+
+ return __read_report(report, buf, count, select);
+}
+
+static ssize_t tsm_report_read(struct tsm_report *report, void *buf,
+ size_t count, enum tsm_data_select select)
+{
+ struct tsm_report_state *state = to_state(report);
+ const struct tsm_ops *ops;
+ ssize_t rc;
+
+ /* try to read from the existing report if present and valid... */
+ rc = read_cached_report(report, buf, count, select);
+ if (rc >= 0 || rc != -EWOULDBLOCK)
+ return rc;
+
+ /* slow path, report may need to be regenerated... */
+ guard(rwsem_write)(&tsm_rwsem);
+ ops = provider.ops;
+ if (!ops)
+ return -ENOTTY;
+ if (!report->desc.inblob_len)
+ return -EINVAL;
+
+ /* did another thread already generate this report? */
+ if (report->outblob &&
+ state->read_generation == state->write_generation)
+ goto out;
+
+ kvfree(report->outblob);
+ kvfree(report->auxblob);
+ report->outblob = NULL;
+ report->auxblob = NULL;
+ rc = ops->report_new(report, provider.data);
+ if (rc < 0)
+ return rc;
+ state->read_generation = state->write_generation;
+out:
+ return __read_report(report, buf, count, select);
+}
+
+static ssize_t tsm_report_outblob_read(struct config_item *cfg, void *buf,
+ size_t count)
+{
+ struct tsm_report *report = to_tsm_report(cfg);
+
+ return tsm_report_read(report, buf, count, TSM_REPORT);
+}
+CONFIGFS_BIN_ATTR_RO(tsm_report_, outblob, NULL, TSM_OUTBLOB_MAX);
+
+static ssize_t tsm_report_auxblob_read(struct config_item *cfg, void *buf,
+ size_t count)
+{
+ struct tsm_report *report = to_tsm_report(cfg);
+
+ return tsm_report_read(report, buf, count, TSM_CERTS);
+}
+CONFIGFS_BIN_ATTR_RO(tsm_report_, auxblob, NULL, TSM_OUTBLOB_MAX);
+
+#define TSM_DEFAULT_ATTRS() \
+ &tsm_report_attr_generation, \
+ &tsm_report_attr_provider
+
+static struct configfs_attribute *tsm_report_attrs[] = {
+ TSM_DEFAULT_ATTRS(),
+ NULL,
+};
+
+static struct configfs_attribute *tsm_report_extra_attrs[] = {
+ TSM_DEFAULT_ATTRS(),
+ &tsm_report_attr_privlevel,
+ &tsm_report_attr_privlevel_floor,
+ NULL,
+};
+
+#define TSM_DEFAULT_BIN_ATTRS() \
+ &tsm_report_attr_inblob, \
+ &tsm_report_attr_outblob
+
+static struct configfs_bin_attribute *tsm_report_bin_attrs[] = {
+ TSM_DEFAULT_BIN_ATTRS(),
+ NULL,
+};
+
+static struct configfs_bin_attribute *tsm_report_bin_extra_attrs[] = {
+ TSM_DEFAULT_BIN_ATTRS(),
+ &tsm_report_attr_auxblob,
+ NULL,
+};
+
+static void tsm_report_item_release(struct config_item *cfg)
+{
+ struct tsm_report *report = to_tsm_report(cfg);
+ struct tsm_report_state *state = to_state(report);
+
+ kvfree(report->auxblob);
+ kvfree(report->outblob);
+ kfree(state);
+}
+
+static struct configfs_item_operations tsm_report_item_ops = {
+ .release = tsm_report_item_release,
+};
+
+const struct config_item_type tsm_report_default_type = {
+ .ct_owner = THIS_MODULE,
+ .ct_bin_attrs = tsm_report_bin_attrs,
+ .ct_attrs = tsm_report_attrs,
+ .ct_item_ops = &tsm_report_item_ops,
+};
+EXPORT_SYMBOL_GPL(tsm_report_default_type);
+
+const struct config_item_type tsm_report_extra_type = {
+ .ct_owner = THIS_MODULE,
+ .ct_bin_attrs = tsm_report_bin_extra_attrs,
+ .ct_attrs = tsm_report_extra_attrs,
+ .ct_item_ops = &tsm_report_item_ops,
+};
+EXPORT_SYMBOL_GPL(tsm_report_extra_type);
+
+static struct config_item *tsm_report_make_item(struct config_group *group,
+ const char *name)
+{
+ struct tsm_report_state *state;
+
+ guard(rwsem_read)(&tsm_rwsem);
+ if (!provider.ops)
+ return ERR_PTR(-ENXIO);
+
+ state = kzalloc(sizeof(*state), GFP_KERNEL);
+ if (!state)
+ return ERR_PTR(-ENOMEM);
+
+ config_item_init_type_name(&state->cfg, name, provider.type);
+ return &state->cfg;
+}
+
+static struct configfs_group_operations tsm_report_group_ops = {
+ .make_item = tsm_report_make_item,
+};
+
+static const struct config_item_type tsm_reports_type = {
+ .ct_owner = THIS_MODULE,
+ .ct_group_ops = &tsm_report_group_ops,
+};
+
+static const struct config_item_type tsm_root_group_type = {
+ .ct_owner = THIS_MODULE,
+};
+
+static struct configfs_subsystem tsm_configfs = {
+ .su_group = {
+ .cg_item = {
+ .ci_namebuf = "tsm",
+ .ci_type = &tsm_root_group_type,
+ },
+ },
+ .su_mutex = __MUTEX_INITIALIZER(tsm_configfs.su_mutex),
+};
+
+int tsm_register(const struct tsm_ops *ops, void *priv,
+ const struct config_item_type *type)
+{
+ const struct tsm_ops *conflict;
+
+ if (!type)
+ type = &tsm_report_default_type;
+ if (!(type == &tsm_report_default_type || type == &tsm_report_extra_type))
+ return -EINVAL;
+
+ guard(rwsem_write)(&tsm_rwsem);
+ conflict = provider.ops;
+ if (conflict) {
+ pr_err("\"%s\" ops already registered\n", conflict->name);
+ return -EBUSY;
+ }
+
+ provider.ops = ops;
+ provider.data = priv;
+ provider.type = type;
+ return 0;
+}
+EXPORT_SYMBOL_GPL(tsm_register);
+
+int tsm_unregister(const struct tsm_ops *ops)
+{
+ guard(rwsem_write)(&tsm_rwsem);
+ if (ops != provider.ops)
+ return -EBUSY;
+ provider.ops = NULL;
+ provider.data = NULL;
+ provider.type = NULL;
+ return 0;
+}
+EXPORT_SYMBOL_GPL(tsm_unregister);
+
+static struct config_group *tsm_report_group;
+
+static int __init tsm_init(void)
+{
+ struct config_group *root = &tsm_configfs.su_group;
+ struct config_group *tsm;
+ int rc;
+
+ config_group_init(root);
+ rc = configfs_register_subsystem(&tsm_configfs);
+ if (rc)
+ return rc;
+
+ tsm = configfs_register_default_group(root, "report",
+ &tsm_reports_type);
+ if (IS_ERR(tsm)) {
+ configfs_unregister_subsystem(&tsm_configfs);
+ return PTR_ERR(tsm);
+ }
+ tsm_report_group = tsm;
+
+ return 0;
+}
+module_init(tsm_init);
+
+static void __exit tsm_exit(void)
+{
+ configfs_unregister_default_group(tsm_report_group);
+ configfs_unregister_subsystem(&tsm_configfs);
+}
+module_exit(tsm_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Provide Trusted Security Module attestation reports via configfs");
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