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

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Date:   Fri, 20 Nov 2020 21:38:10 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Suman Anna <s-anna@...com>
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 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"?

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
>