// 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_report_ops *ops;
        void *data;
        atomic_t count;
} 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;

        guard(rwsem_write)(&tsm_rwsem);
        if (!provider.ops)
                return -ENXIO;

        /*
         * 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_REPORT_PRIVLEVEL_MAX)
                return -EINVAL;

        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);

        if (!provider.ops)
                return -ENXIO;

        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_REPORT_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);
        if (!provider.ops)
                return -ENXIO;

        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_report_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 -ENXIO;
        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_REPORT_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_REPORT_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_REPORT_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_obj(*state);
        if (!state)
                return ERR_PTR(-ENOMEM);

        atomic_inc(&provider.count);
        config_item_init_type_name(&state->cfg, name, &tsm_report_type);
        return &state->cfg;
}

static void tsm_report_drop_item(struct config_group *group, struct config_item *item)
{
        config_item_put(item);
        atomic_dec(&provider.count);
}

static struct configfs_group_operations tsm_report_group_ops = {
        .make_item = tsm_report_make_item,
        .drop_item = tsm_report_drop_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_report_register(const struct tsm_report_ops *ops, void *priv)
{
        const struct tsm_report_ops *conflict;

        guard(rwsem_write)(&tsm_rwsem);
        conflict = provider.ops;
        if (conflict) {
                pr_err("\"%s\" ops already registered\n", conflict->name);
                return -EBUSY;
        }

        if (atomic_read(&provider.count)) {
                pr_err("configfs/tsm/report not empty\n");
                return -EBUSY;
        }

        provider.ops = ops;
        provider.data = priv;
        return 0;
}
EXPORT_SYMBOL_GPL(tsm_report_register);

int tsm_report_unregister(const struct tsm_report_ops *ops)
{
        guard(rwsem_write)(&tsm_rwsem);
        if (ops != provider.ops)
                return -EBUSY;
        if (atomic_read(&provider.count))
                pr_warn("\"%s\" unregistered with items present in configfs/tsm/report\n",
                        provider.ops->name);
        provider.ops = NULL;
        provider.data = NULL;
        return 0;
}
EXPORT_SYMBOL_GPL(tsm_report_unregister);

static struct config_group *tsm_report_group;

static int __init tsm_report_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_report_init);

static void __exit tsm_report_exit(void)
{
        configfs_unregister_default_group(tsm_report_group);
        configfs_unregister_subsystem(&tsm_configfs);
}
module_exit(tsm_report_exit);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Provide Trusted Security Module attestation reports via configfs");