Re: [RFC PATCH v2 2/4] tsm: Add RTMRs to the configfs-tsm hierarchy

[Kuppuswamy Sathyanarayanan]

On 1/28/24 1:25 PM, Samuel Ortiz wrote:
> RTMRs are defined and managed by their corresponding TSM provider. As
> such, they can be configured through the TSM configfs root.
>
> An additional `rtmrs` directory is added by default under the `tsm` one,
> where each supported RTMR can be configured:
>
> mkdir /sys/kernel/config/tsm/rtmrs/rtmr0
> echo 0 > /sys/kernel/config/tsm/rtmrs/rtmr0/index
>
> An RTMR can not be extended nor read before its configured by assigning
> it an index. It is the TSM backend responsibility and choice to map that
> index to a hardware RTMR.
>
> Signed-off-by: Samuel Ortiz <sameo@xxxxxxxxxxxx>
> ---
>  Documentation/ABI/testing/configfs-tsm |  11 ++
>  drivers/virt/coco/tsm.c                | 164 +++++++++++++++++++++++++
>  2 files changed, 175 insertions(+)
>
> diff --git a/Documentation/ABI/testing/configfs-tsm b/Documentation/ABI/testing/configfs-tsm
> index dd24202b5ba5..590e103a9bcd 100644
> --- a/Documentation/ABI/testing/configfs-tsm
> +++ b/Documentation/ABI/testing/configfs-tsm
> @@ -80,3 +80,14 @@ Contact:	linux-coco@xxxxxxxxxxxxxxx
>  Description:
>  		(RO) Indicates the minimum permissible value that can be written
>  		to @privlevel.
> +
> +What:		/sys/kernel/config/tsm/rtmrs/$name/index
> +Date:		January, 2024
> +KernelVersion:	v6.8
v6.9?
> +Contact:	linux-coco@xxxxxxxxxxxxxxx
> +Description:
> +		(RW) A Runtime Measurement Register (RTMR) hardware index.
> +                Once created under /sys/kernel/config/tsm/rtmrs/, an RTMR entry
> +                can be mapped to a hardware RTMR by writing into its index
> +                attribute. The TSM provider will then map the configfs entry to
> +                its corresponding hardware register.
> diff --git a/drivers/virt/coco/tsm.c b/drivers/virt/coco/tsm.c
> index 1a8c3c096120..bb9ed2d2accc 100644
> --- a/drivers/virt/coco/tsm.c
> +++ b/drivers/virt/coco/tsm.c
> @@ -419,6 +419,108 @@ static const struct config_item_type tsm_reports_type = {
>  	.ct_group_ops = &tsm_report_group_ops,
>  };
>  
> +static ssize_t tsm_rtmr_index_store(struct config_item *cfg,
> +				    const char *buf, size_t len)
> +{
> +	struct tsm_rtmr_state *rtmr_state = to_tsm_rtmr_state(cfg);
> +	const struct tsm_ops *ops;
> +	unsigned int val;
> +	int rc;
> +
> +	rc = kstrtouint(buf, 0, &val);
> +	if (rc)
> +		return rc;
> +
> +	guard(rwsem_write)(&tsm_rwsem);
> +
> +	/* Index can only be configured once */
> +	if (is_rtmr_configured(rtmr_state))
> +		return -EBUSY;
> +
> +	/* Check that index stays within the TSM provided capabilities */
> +	ops = provider.ops;
> +	if (!ops)
> +		return -ENOTTY;
> +
> +	if (val > ops->capabilities.num_rtmrs - 1)
> +		return -EINVAL;
> +
> +	/* Check that this index is available */
> +	if (tsm_rtmrs->rtmrs[val])
> +		return -EINVAL;
> +
> +	rtmr_state->index = val;
> +	rtmr_state->alg = ops->capabilities.rtmrs[val].hash_alg;
> +
> +	tsm_rtmrs->rtmrs[val] = rtmr_state;
> +
> +	return len;
> +}
> +
> +static ssize_t tsm_rtmr_index_show(struct config_item *cfg,
> +				   char *buf)
> +{
> +	struct tsm_rtmr_state *rtmr_state = to_tsm_rtmr_state(cfg);
> +
> +	guard(rwsem_read)(&tsm_rwsem);
> +
> +	/* An RTMR is not available if it has not been configured */
> +	if (!is_rtmr_configured(rtmr_state))
> +		return -ENXIO;
> +
> +	return sysfs_emit(buf, "%u\n", rtmr_state->index);
> +}
> +CONFIGFS_ATTR(tsm_rtmr_, index);
> +
> +static struct configfs_attribute *tsm_rtmr_attrs[] = {
> +	&tsm_rtmr_attr_index,
> +	NULL,
> +};
> +
> +static void tsm_rtmr_item_release(struct config_item *cfg)
> +{
> +	struct tsm_rtmr_state *state = to_tsm_rtmr_state(cfg);
> +
> +	kfree(state);

I think you need to clear the index history as well?

> +}
> +
> +static struct configfs_item_operations tsm_rtmr_item_ops = {
> +	.release = tsm_rtmr_item_release,
> +};
> +
> +const struct config_item_type tsm_rtmr_type = {
> +	.ct_owner = THIS_MODULE,
> +	.ct_attrs = tsm_rtmr_attrs,
> +	.ct_item_ops = &tsm_rtmr_item_ops,
> +};
> +
> +static struct config_item *tsm_rtmrs_make_item(struct config_group *group,
> +					       const char *name)
> +{
> +	struct tsm_rtmr_state *state;
> +
> +	guard(rwsem_read)(&tsm_rwsem);
> +	if (!(provider.ops && (provider.ops->capabilities.num_rtmrs > 0)))
> +		return ERR_PTR(-ENXIO);
> +
> +	state = kzalloc(sizeof(*state), GFP_KERNEL);
> +	if (!state)
> +		return ERR_PTR(-ENOMEM);
> +	state->index = U32_MAX;
> +
> +	config_item_init_type_name(&state->cfg, name, &tsm_rtmr_type);
> +	return &state->cfg;
> +}
> +
> +static struct configfs_group_operations tsm_rtmrs_group_ops = {
> +	.make_item = tsm_rtmrs_make_item,
> +};
> +
> +static const struct config_item_type tsm_rtmrs_type = {
> +	.ct_owner = THIS_MODULE,
> +	.ct_group_ops = &tsm_rtmrs_group_ops,
> +};
> +
>  static const struct config_item_type tsm_root_group_type = {
>  	.ct_owner = THIS_MODULE,
>  };
> @@ -433,10 +535,48 @@ static struct configfs_subsystem tsm_configfs = {
>  	.su_mutex = __MUTEX_INITIALIZER(tsm_configfs.su_mutex),
>  };
>  
> +static int tsm_rtmr_register(const struct tsm_ops *ops)
> +{
> +	struct config_group *rtmrs_group;
> +
> +	lockdep_assert_held_write(&tsm_rwsem);
> +
> +	if (!ops || !ops->capabilities.num_rtmrs)
> +		return 0;
> +
> +	if (ops->capabilities.num_rtmrs > TSM_MAX_RTMR)
> +		return -EINVAL;
> +
> +	tsm_rtmrs = kzalloc(sizeof(struct tsm_rtmrs_state), GFP_KERNEL);
> +	if (!tsm_rtmrs)
> +		return -ENOMEM;
> +
> +	tsm_rtmrs->rtmrs = kcalloc(ops->capabilities.num_rtmrs,
> +				   sizeof(struct tsm_rtmr_state *),
> +				   GFP_KERNEL);
> +	if (!tsm_rtmrs->rtmrs) {
> +		kfree(tsm_rtmrs);
> +		return -ENOMEM;
> +	}
> +
> +	rtmrs_group = configfs_register_default_group(&tsm_configfs.su_group, "rtmrs",
> +						      &tsm_rtmrs_type);
> +	if (IS_ERR(rtmrs_group)) {
> +		kfree(tsm_rtmrs->rtmrs);
> +		kfree(tsm_rtmrs);
> +		return PTR_ERR(rtmrs_group);
> +	}
> +
> +	tsm_rtmrs->group = rtmrs_group;
> +
> +	return 0;
> +}
> +
>  int tsm_register(const struct tsm_ops *ops, void *priv,
>  		 const struct config_item_type *type)
>  {
>  	const struct tsm_ops *conflict;
> +	int rc;
>  
>  	if (!type)
>  		type = &tsm_report_default_type;
> @@ -450,6 +590,10 @@ int tsm_register(const struct tsm_ops *ops, void *priv,
>  		return -EBUSY;
>  	}
>  
> +	rc = tsm_rtmr_register(ops);
> +	if (rc < 0)
> +		return rc;
> +
>  	provider.ops = ops;
>  	provider.data = priv;
>  	provider.type = type;
> @@ -457,11 +601,31 @@ int tsm_register(const struct tsm_ops *ops, void *priv,
>  }
>  EXPORT_SYMBOL_GPL(tsm_register);
>  
> +static int tsm_rtmr_unregister(const struct tsm_ops *ops)
> +{
> +	lockdep_assert_held_write(&tsm_rwsem);
> +
> +	if ((ops) && (ops->capabilities.num_rtmrs > 0)) {
This check is used in multiple places. May you can add a helper function
for it. is_valid_rtmr()?
> +		configfs_unregister_default_group(tsm_rtmrs->group);
> +		kfree(tsm_rtmrs->rtmrs);
> +		kfree(tsm_rtmrs);
> +	}
> +
> +	return 0;
> +}
> +
>  int tsm_unregister(const struct tsm_ops *ops)
>  {
> +	int rc;
> +
>  	guard(rwsem_write)(&tsm_rwsem);
>  	if (ops != provider.ops)
>  		return -EBUSY;
> +
> +	rc = tsm_rtmr_unregister(ops);
> +	if (rc < 0)
> +		return rc;
> +
>  	provider.ops = NULL;
>  	provider.data = NULL;
>  	provider.type = NULL;

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer