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linux/drivers/virt/coco/tsm.c
Tom Lendacky 627dc67151 x86/sev: Extend the config-fs attestation support for an SVSM
When an SVSM is present, the guest can also request attestation reports
from it. These SVSM attestation reports can be used to attest the SVSM
and any services running within the SVSM.

Extend the config-fs attestation support to provide such. This involves
creating four new config-fs attributes:

  - 'service-provider' (input)
    This attribute is used to determine whether the attestation request
    should be sent to the specified service provider or to the SEV
    firmware. The SVSM service provider is represented by the value
    'svsm'.

  - 'service_guid' (input)
    Used for requesting the attestation of a single service within the
    service provider. A null GUID implies that the SVSM_ATTEST_SERVICES
    call should be used to request the attestation report. A non-null
    GUID implies that the SVSM_ATTEST_SINGLE_SERVICE call should be used.

  - 'service_manifest_version' (input)
    Used with the SVSM_ATTEST_SINGLE_SERVICE call, the service version
    represents a specific service manifest version be used for the
    attestation report.

  - 'manifestblob' (output)
    Used to return the service manifest associated with the attestation
    report.

Only display these new attributes when running under an SVSM.

  [ bp: Massage.
   - s/svsm_attestation_call/svsm_attest_call/g ]

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/965015dce3c76bb8724839d50c5dea4e4b5d598f.1717600736.git.thomas.lendacky@amd.com
2024-06-17 20:42:57 +02:00

513 lines
13 KiB
C

// 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;
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' and 'manifestblob'.
*/
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,
TSM_MANIFEST,
};
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_service_provider_store(struct config_item *cfg,
const char *buf, size_t len)
{
struct tsm_report *report = to_tsm_report(cfg);
size_t sp_len;
char *sp;
int rc;
guard(rwsem_write)(&tsm_rwsem);
rc = try_advance_write_generation(report);
if (rc)
return rc;
sp_len = (buf[len - 1] != '\n') ? len : len - 1;
sp = kstrndup(buf, sp_len, GFP_KERNEL);
if (!sp)
return -ENOMEM;
kfree(report->desc.service_provider);
report->desc.service_provider = sp;
return len;
}
CONFIGFS_ATTR_WO(tsm_report_, service_provider);
static ssize_t tsm_report_service_guid_store(struct config_item *cfg,
const char *buf, size_t len)
{
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.service_guid = guid_null;
rc = guid_parse(buf, &report->desc.service_guid);
if (rc)
return rc;
return len;
}
CONFIGFS_ATTR_WO(tsm_report_, service_guid);
static ssize_t tsm_report_service_manifest_version_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;
guard(rwsem_write)(&tsm_rwsem);
rc = try_advance_write_generation(report);
if (rc)
return rc;
report->desc.service_manifest_version = val;
return len;
}
CONFIGFS_ATTR_WO(tsm_report_, service_manifest_version);
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 if (select == TSM_MANIFEST) {
out = report->manifestblob;
len = report->manifestblob_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/manifestblob 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);
kvfree(report->manifestblob);
report->outblob = NULL;
report->auxblob = NULL;
report->manifestblob = 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);
static ssize_t tsm_report_manifestblob_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_MANIFEST);
}
CONFIGFS_BIN_ATTR_RO(tsm_report_, manifestblob, NULL, TSM_OUTBLOB_MAX);
static struct configfs_attribute *tsm_report_attrs[] = {
[TSM_REPORT_GENERATION] = &tsm_report_attr_generation,
[TSM_REPORT_PROVIDER] = &tsm_report_attr_provider,
[TSM_REPORT_PRIVLEVEL] = &tsm_report_attr_privlevel,
[TSM_REPORT_PRIVLEVEL_FLOOR] = &tsm_report_attr_privlevel_floor,
[TSM_REPORT_SERVICE_PROVIDER] = &tsm_report_attr_service_provider,
[TSM_REPORT_SERVICE_GUID] = &tsm_report_attr_service_guid,
[TSM_REPORT_SERVICE_MANIFEST_VER] = &tsm_report_attr_service_manifest_version,
NULL,
};
static struct configfs_bin_attribute *tsm_report_bin_attrs[] = {
[TSM_REPORT_INBLOB] = &tsm_report_attr_inblob,
[TSM_REPORT_OUTBLOB] = &tsm_report_attr_outblob,
[TSM_REPORT_AUXBLOB] = &tsm_report_attr_auxblob,
[TSM_REPORT_MANIFESTBLOB] = &tsm_report_attr_manifestblob,
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->manifestblob);
kvfree(report->auxblob);
kvfree(report->outblob);
kfree(report->desc.service_provider);
kfree(state);
}
static struct configfs_item_operations tsm_report_item_ops = {
.release = tsm_report_item_release,
};
static bool tsm_report_is_visible(struct config_item *item,
struct configfs_attribute *attr, int n)
{
guard(rwsem_read)(&tsm_rwsem);
if (!provider.ops)
return false;
if (!provider.ops->report_attr_visible)
return true;
return provider.ops->report_attr_visible(n);
}
static bool tsm_report_is_bin_visible(struct config_item *item,
struct configfs_bin_attribute *attr, int n)
{
guard(rwsem_read)(&tsm_rwsem);
if (!provider.ops)
return false;
if (!provider.ops->report_bin_attr_visible)
return true;
return provider.ops->report_bin_attr_visible(n);
}
static struct configfs_group_operations tsm_report_attr_group_ops = {
.is_visible = tsm_report_is_visible,
.is_bin_visible = tsm_report_is_bin_visible,
};
static const struct config_item_type tsm_report_type = {
.ct_owner = THIS_MODULE,
.ct_bin_attrs = tsm_report_bin_attrs,
.ct_attrs = tsm_report_attrs,
.ct_item_ops = &tsm_report_item_ops,
.ct_group_ops = &tsm_report_attr_group_ops,
};
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, &tsm_report_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 tsm_ops *conflict;
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;
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;
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");