Re: [PATCH v2 2/3] remoteproc: Introduce deny_sysfs_ops flag

Suman Anna
2020-11-21T03:45:04Z

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@ti.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
>>