Commit fba4ceaa authored by Dan Williams's avatar Dan Williams
Browse files

configfs-tsm-report: Fix NULL dereference of tsm_ops 



Unlike sysfs, the lifetime of configfs objects is controlled by
userspace. There is no mechanism for the kernel to find and delete all
created config-items. Instead, the configfs-tsm-report mechanism has an
expectation that tsm_unregister() can happen at any time and cause
established config-item access to start failing.

That expectation is not fully satisfied. While tsm_report_read(),
tsm_report_{is,is_bin}_visible(), and tsm_report_make_item() safely fail
if tsm_ops have been unregistered, tsm_report_privlevel_store()
tsm_report_provider_show() fail to check for ops registration. Add the
missing checks for tsm_ops having been removed.

Now, in supporting the ability for tsm_unregister() to always succeed,
it leaves the problem of what to do with lingering config-items. The
expectation is that the admin that arranges for the ->remove() (unbind)
of the ${tsm_arch}-guest driver is also responsible for deletion of all
open config-items. Until that deletion happens, ->probe() (reload /
bind) of the ${tsm_arch}-guest driver fails.

This allows for emergency shutdown / revocation of attestation
interfaces, and requires coordinated restart.

Fixes: 70e6f7e2 ("configfs-tsm: Introduce a shared ABI for attestation reports")
Cc: stable@vger.kernel.org
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Steven Price <steven.price@arm.com>
Cc: Sami Mujawar <sami.mujawar@arm.com>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: default avatarKuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reported-by: default avatarCedric Xing <cedric.xing@intel.com>
Reviewed-by: default avatarKai Huang <kai.huang@intel.com>
Link: https://patch.msgid.link/20250430203331.1177062-1-dan.j.williams@intel.com


Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
parent 8ffd015d

drivers/virt/coco/tsm.c

+29 −2
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ 
static struct tsm_provider {

	const struct tsm_ops *ops;

	void *data;

	atomic_t count;

} provider;

static DECLARE_RWSEM(tsm_rwsem);
@@ -92,6 +93,10 @@ static ssize_t tsm_report_privlevel_store(struct config_item *cfg, 
	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
@@ -101,7 +106,6 @@ static ssize_t tsm_report_privlevel_store(struct config_item *cfg, 
	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;
@@ -115,6 +119,10 @@ 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);
@@ -217,6 +225,9 @@ 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);
@@ -284,7 +295,7 @@ static ssize_t tsm_report_read(struct tsm_report *report, void *buf, 
	guard(rwsem_write)(&tsm_rwsem);

	ops = provider.ops;

	if (!ops)

		return -ENOTTY;

		return -ENXIO;

	if (!report->desc.inblob_len)

		return -EINVAL;
@@ -421,12 +432,20 @@ static struct config_item *tsm_report_make_item(struct config_group *group, 
	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 = {
@@ -459,6 +478,11 @@ int tsm_register(const struct tsm_ops *ops, void *priv) 
		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;
@@ -470,6 +494,9 @@ int tsm_unregister(const struct tsm_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;