linux-kernel - Re: [PATCH v2 6/7] powerpc/secvar: Extend sysfs to include config vars

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Message-ID: <20729da992c608ed40f5f037a7314395075a4254.camel@linux.ibm.com>
Date:   Thu, 05 Jan 2023 18:28:16 +1100
From:   Andrew Donnellan <ajd@...ux.ibm.com>
To:     Russell Currey <ruscur@...sell.cc>, linuxppc-dev@...ts.ozlabs.org
Cc:     gregkh@...uxfoundation.org, gcwilson@...ux.ibm.com,
        linux-kernel@...r.kernel.org, nayna@...ux.ibm.com,
        zohar@...ux.ibm.com, mpe@...erman.id.au
Subject: Re: [PATCH v2 6/7] powerpc/secvar: Extend sysfs to include config
 vars

On Fri, 2022-12-30 at 15:20 +1100, Russell Currey wrote:
> The forthcoming pseries consumer of the secvar API wants to expose a
> number of config variables.  Allowing secvar implementations to
> provide
> their own sysfs attributes makes it easy for consumers to expose what
> they need to.
> 
> This is not being used by the OPAL secvar implementation at present,
> and
> the config directory will not be created if no attributes are set.
> 
> Signed-off-by: Russell Currey <ruscur@...sell.cc>

Minor comments below, but regardless:

Reviewed-by: Andrew Donnellan <ajd@...ux.ibm.com>

> ---
> I played around with adding an API call to facilitate a more generic
> key/value interface for config variables and it seemed like
> unnecessary
> complexity.  I think this is cleaner.  If there was ever a secvar
> interface other than sysfs we'd have to rework it, though.

I concur, this can be dealt with if/when the secvar interface is
exposed by some other means than sysfs.

> 
>  arch/powerpc/include/asm/secvar.h  |  3 +++
>  arch/powerpc/kernel/secvar-sysfs.c | 40 ++++++++++++++++++++++++++--
> --
>  2 files changed, 38 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/secvar.h
> b/arch/powerpc/include/asm/secvar.h
> index 92d2c051918b..250e7066b6da 100644
> --- a/arch/powerpc/include/asm/secvar.h
> +++ b/arch/powerpc/include/asm/secvar.h
> @@ -10,6 +10,7 @@
>  
>  #include <linux/types.h>
>  #include <linux/errno.h>
> +#include <linux/sysfs.h>
>  
>  extern const struct secvar_operations *secvar_ops;
>  
> @@ -27,10 +28,12 @@ struct secvar_operations {
>  #ifdef CONFIG_PPC_SECURE_BOOT
>  
>  extern void set_secvar_ops(const struct secvar_operations *ops);
> +extern void set_secvar_config_attrs(const struct attribute **attrs);
>  
>  #else
>  
>  static inline void set_secvar_ops(const struct secvar_operations
> *ops) { }
> +static inline void set_secvar_config_attrs(const struct attribute
> **attrs) { }
>  
>  #endif
>  
> diff --git a/arch/powerpc/kernel/secvar-sysfs.c
> b/arch/powerpc/kernel/secvar-sysfs.c
> index aa1daec480e1..ad1e1d72d2ae 100644
> --- a/arch/powerpc/kernel/secvar-sysfs.c
> +++ b/arch/powerpc/kernel/secvar-sysfs.c
> @@ -15,9 +15,17 @@
>  
>  #define NAME_MAX_SIZE     1024
>  
> +const struct attribute **secvar_config_attrs __ro_after_init = NULL;
> +
>  static struct kobject *secvar_kobj;
>  static struct kset *secvar_kset;
>  
> +void set_secvar_config_attrs(const struct attribute **attrs)
> +{
> +       WARN_ON_ONCE(secvar_config_attrs);
> +       secvar_config_attrs = attrs;
> +}
> +
>  static ssize_t format_show(struct kobject *kobj, struct
> kobj_attribute *attr,
>                            char *buf)
>  {
> @@ -134,6 +142,16 @@ static int update_kobj_size(void)
>         return 0;
>  }
>  
> +static int secvar_sysfs_config(struct kobject *kobj)
> +{
> +       struct attribute_group config_group = {
> +               .name = "config",
> +               .attrs = (struct attribute **)secvar_config_attrs,
> +       };

I was slightly concerned that you're putting this on the stack, but it
doesn't appear that sysfs_create_group() keeps any references to the
group around after it creates all the files, so I think this is fine.

> +
> +       return sysfs_create_group(kobj, &config_group);
> +}
> +
>  static int secvar_sysfs_load(void)
>  {
>         char *name;
> @@ -196,26 +214,38 @@ static int secvar_sysfs_init(void)
>  
>         rc = sysfs_create_file(secvar_kobj, &format_attr.attr);
>         if (rc) {
> -               kobject_put(secvar_kobj);
> -               return -ENOMEM;
> +               pr_err("secvar: Failed to create format object\n");

This file defines pr_fmt, so the secvar: prefix here can go away,
though I notice that is the case for all the existing prints in this
function too.

> +               rc = -ENOMEM;
> +               goto err;
>         }
>  
>         secvar_kset = kset_create_and_add("vars", NULL, secvar_kobj);
>         if (!secvar_kset) {
>                 pr_err("secvar: sysfs kobject registration
> failed.\n");
> -               kobject_put(secvar_kobj);
> -               return -ENOMEM;
> +               rc = -ENOMEM;
> +               goto err;
>         }
>  
>         rc = update_kobj_size();
>         if (rc) {
>                 pr_err("Cannot read the size of the attribute\n");
> -               return rc;
> +               goto err;
> +       }
> +
> +       if (secvar_config_attrs) {
> +               rc = secvar_sysfs_config(secvar_kobj);
> +               if (rc) {
> +                       pr_err("secvar: Failed to create config
> directory\n");

Same comment as above

> +                       goto err;
> +               }
>         }
>  
>         secvar_sysfs_load();
>  
>         return 0;
> +err:
> +       kobject_put(secvar_kobj);
> +       return rc;
>  }
>  
>  late_initcall(secvar_sysfs_init);

-- 
Andrew Donnellan    OzLabs, ADL Canberra
ajd@...ux.ibm.com   IBM Australia Limited