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

[Russell Currey]

On Thu, 2023-01-05 at 18:28 +1100, Andrew Donnellan wrote:
> 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@xxxxxxxxxx>
> 
> Minor comments below, but regardless:
> 
> Reviewed-by: Andrew Donnellan <ajd@xxxxxxxxxxxxx>
> 
> > ---
> > 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.

Yeah we should fix that for all of them, good catch.

> 
> > +               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);
>