linux-kernel - Re: [PATCH v2 2/3] remoteproc: Introduce deny_sysfs

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Message-ID: <1930fba4-70bd-f602-6dbd-f1cc8071da10@ti.com>
Date:   Sun, 22 Nov 2020 11:48:43 -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 11/21/20 11:33 PM, Bjorn Andersson wrote:
> On Fri 20 Nov 21:44 CST 2020, Suman Anna wrote:
> 
>> 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.
>>
> 
> It looks to be dynamic, but I don't know if there's any "caching"
> involved. Please have a look and let me know.

OK, will do. I can only check the week after though.

regards
Suman

> 
> Regards,
> Bjorn
> 
>> 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
>>>>
>>