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Date:   Fri, 20 Nov 2020 21:44:44 -0600
From:   Suman Anna <s-anna@...com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
CC:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Arnaud Pouliquen <arnaud.pouliquen@...com>,
        Loic Pallardy <loic.pallardy@...com>,
        Grzegorz Jaszczyk <grzegorz.jaszczyk@...aro.org>,
        Tony Lindgren <tony@...mide.com>,
        <linux-remoteproc@...r.kernel.org>, <linux-omap@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] remoteproc: Introduce deny_sysfs_ops flag

On 11/20/20 9:38 PM, Bjorn Andersson wrote:
> On Fri 20 Nov 21:01 CST 2020, Suman Anna wrote:
> 
>> The remoteproc framework provides sysfs interfaces for changing
>> the firmware name and for starting/stopping a remote processor
>> through the sysfs files 'state' and 'firmware'. The 'recovery'
>> sysfs file can also be used similarly to control the error recovery
>> state machine of a remoteproc. These interfaces are currently
>> allowed irrespective of how the remoteprocs were booted (like
>> remoteproc self auto-boot, remoteproc client-driven boot etc).
>> These interfaces can adversely affect a remoteproc and its clients
>> especially when a remoteproc is being controlled by a remoteproc
>> client driver(s). Also, not all remoteproc drivers may want to
>> support the sysfs interfaces by default.
>>
>> Add support to deny the sysfs state/firmware/recovery change by
>> introducing a state flag 'deny_sysfs_ops' that the individual
>> remoteproc drivers can set based on their usage needs. The default
>> behavior is to allow the sysfs operations as before.
>>
> 
> This makes sense, but can't we implement attribute_group->is_visible to
> simply hide these entries from userspace instead of leaving them
> "broken"?

I would have to look into that, but can that be changed dynamically?
Also, note that the enforcement is only on the writes/stores which impact
the state-machine, but not the reads/shows.

For PRU usecases, we will be setting this dynamically.

regards
Suman

> 
> Regards,
> Bjorn
> 
>> Signed-off-by: Suman Anna <s-anna@...com>
>> ---
>> v2: revised to account for the 'recovery' sysfs file as well, patch
>>     description updated accordingly
>> v1: https://patchwork.kernel.org/project/linux-remoteproc/patch/20180915003725.17549-5-s-anna@ti.com/
>>
>>  drivers/remoteproc/remoteproc_sysfs.c | 12 ++++++++++++
>>  include/linux/remoteproc.h            |  2 ++
>>  2 files changed, 14 insertions(+)
>>
>> diff --git a/drivers/remoteproc/remoteproc_sysfs.c b/drivers/remoteproc/remoteproc_sysfs.c
>> index bd2950a246c9..3fd18a71c188 100644
>> --- a/drivers/remoteproc/remoteproc_sysfs.c
>> +++ b/drivers/remoteproc/remoteproc_sysfs.c
>> @@ -49,6 +49,10 @@ static ssize_t recovery_store(struct device *dev,
>>  {
>>  	struct rproc *rproc = to_rproc(dev);
>>  
>> +	/* restrict sysfs operations if not allowed by remoteproc drivers */
>> +	if (rproc->deny_sysfs_ops)
>> +		return -EPERM;
>> +
>>  	if (sysfs_streq(buf, "enabled")) {
>>  		/* change the flag and begin the recovery process if needed */
>>  		rproc->recovery_disabled = false;
>> @@ -158,6 +162,10 @@ static ssize_t firmware_store(struct device *dev,
>>  	char *p;
>>  	int err, len = count;
>>  
>> +	/* restrict sysfs operations if not allowed by remoteproc drivers */
>> +	if (rproc->deny_sysfs_ops)
>> +		return -EPERM;
>> +
>>  	err = mutex_lock_interruptible(&rproc->lock);
>>  	if (err) {
>>  		dev_err(dev, "can't lock rproc %s: %d\n", rproc->name, err);
>> @@ -225,6 +233,10 @@ static ssize_t state_store(struct device *dev,
>>  	struct rproc *rproc = to_rproc(dev);
>>  	int ret = 0;
>>  
>> +	/* restrict sysfs operations if not allowed by remoteproc drivers */
>> +	if (rproc->deny_sysfs_ops)
>> +		return -EPERM;
>> +
>>  	if (sysfs_streq(buf, "start")) {
>>  		if (rproc->state == RPROC_RUNNING)
>>  			return -EBUSY;
>> diff --git a/include/linux/remoteproc.h b/include/linux/remoteproc.h
>> index 3fa3ba6498e8..dbc3767f7d0e 100644
>> --- a/include/linux/remoteproc.h
>> +++ b/include/linux/remoteproc.h
>> @@ -508,6 +508,7 @@ struct rproc_dump_segment {
>>   * @has_iommu: flag to indicate if remote processor is behind an MMU
>>   * @auto_boot: flag to indicate if remote processor should be auto-started
>>   * @autonomous: true if an external entity has booted the remote processor
>> + * @deny_sysfs_ops: flag to not permit sysfs operations on state, firmware and recovery
>>   * @dump_segments: list of segments in the firmware
>>   * @nb_vdev: number of vdev currently handled by rproc
>>   * @char_dev: character device of the rproc
>> @@ -545,6 +546,7 @@ struct rproc {
>>  	bool has_iommu;
>>  	bool auto_boot;
>>  	bool autonomous;
>> +	bool deny_sysfs_ops;
>>  	struct list_head dump_segments;
>>  	int nb_vdev;
>>  	u8 elf_class;
>> -- 
>> 2.28.0
>>

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