Re: [PATCH] efi: move some sysfs files to be read-only by root

[Greg Kroah-Hartman]

On Tue, Dec 05, 2017 at 10:16:56AM +0000, Ard Biesheuvel wrote:
> On 5 December 2017 at 10:13, Greg Kroah-Hartman
> <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > Thanks to the scripts/leaking_addresses.pl script, it was found that
> > some EFI values should not be readable by non-root users.
> >
> > So make them root-only, and to do that, add a __ATTR_RO_MODE() macro to
> > make this easier, and use it in other places at the same time.
> >
> > Reported-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > Tested-by: Dave Young <dyoung@xxxxxxxxxx>
> > Cc: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>
> > Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> > Cc: stable <stable@xxxxxxxxxxxxxxx>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> >
> > ---
> >  drivers/firmware/efi/efi.c         |    3 +--
> >  drivers/firmware/efi/esrt.c        |   15 ++++++---------
> >  drivers/firmware/efi/runtime-map.c |   10 +++++-----
> >  include/linux/sysfs.h              |    5 +++++
> >  4 files changed, 17 insertions(+), 16 deletions(-)
> >
> > --- a/drivers/firmware/efi/efi.c
> > +++ b/drivers/firmware/efi/efi.c
> > @@ -143,8 +143,7 @@ static ssize_t systab_show(struct kobjec
> >         return str - buf;
> >  }
> >
> > -static struct kobj_attribute efi_attr_systab =
> > -                       __ATTR(systab, 0400, systab_show, NULL);
> > +static struct kobj_attribute efi_attr_systab = __ATTR_RO_MODE(systab, 0400);
> >
> >  #define EFI_FIELD(var) efi.var
> >
> > --- a/drivers/firmware/efi/esrt.c
> > +++ b/drivers/firmware/efi/esrt.c
> > @@ -106,7 +106,7 @@ static const struct sysfs_ops esre_attr_
> >  };
> >
> >  /* Generic ESRT Entry ("ESRE") support. */
> > -static ssize_t esre_fw_class_show(struct esre_entry *entry, char *buf)
> > +static ssize_t fw_class_show(struct esre_entry *entry, char *buf)
> >  {
> >         char *str = buf;
> >
> > @@ -117,18 +117,16 @@ static ssize_t esre_fw_class_show(struct
> >         return str - buf;
> >  }
> >
> > -static struct esre_attribute esre_fw_class = __ATTR(fw_class, 0400,
> > -       esre_fw_class_show, NULL);
> > +static struct esre_attribute esre_fw_class = __ATTR_RO_MODE(fw_class, 0400);
> >
> >  #define esre_attr_decl(name, size, fmt) \
> > -static ssize_t esre_##name##_show(struct esre_entry *entry, char *buf) \
> > +static ssize_t name##_show(struct esre_entry *entry, char *buf) \
> >  { \
> >         return sprintf(buf, fmt "\n", \
> >                        le##size##_to_cpu(entry->esre.esre1->name)); \
> >  } \
> >  \
> > -static struct esre_attribute esre_##name = __ATTR(name, 0400, \
> > -       esre_##name##_show, NULL)
> > +static struct esre_attribute esre_##name = __ATTR_RO_MODE(name, 0400)
> >
> >  esre_attr_decl(fw_type, 32, "%u");
> >  esre_attr_decl(fw_version, 32, "%u");
> > @@ -193,14 +191,13 @@ static int esre_create_sysfs_entry(void
> >
> >  /* support for displaying ESRT fields at the top level */
> >  #define esrt_attr_decl(name, size, fmt) \
> > -static ssize_t esrt_##name##_show(struct kobject *kobj, \
> > +static ssize_t name##_show(struct kobject *kobj, \
> >                                   struct kobj_attribute *attr, char *buf)\
> >  { \
> >         return sprintf(buf, fmt "\n", le##size##_to_cpu(esrt->name)); \
> >  } \
> >  \
> > -static struct kobj_attribute esrt_##name = __ATTR(name, 0400, \
> > -       esrt_##name##_show, NULL)
> > +static struct kobj_attribute esrt_##name = __ATTR_RO_MODE(name, 0400)
> >
> >  esrt_attr_decl(fw_resource_count, 32, "%u");
> >  esrt_attr_decl(fw_resource_count_max, 32, "%u");
> > --- a/drivers/firmware/efi/runtime-map.c
> > +++ b/drivers/firmware/efi/runtime-map.c
> > @@ -63,11 +63,11 @@ static ssize_t map_attr_show(struct kobj
> >         return map_attr->show(entry, buf);
> >  }
> >
> > -static struct map_attribute map_type_attr = __ATTR_RO(type);
> > -static struct map_attribute map_phys_addr_attr   = __ATTR_RO(phys_addr);
> > -static struct map_attribute map_virt_addr_attr  = __ATTR_RO(virt_addr);
> > -static struct map_attribute map_num_pages_attr  = __ATTR_RO(num_pages);
> > -static struct map_attribute map_attribute_attr  = __ATTR_RO(attribute);
> > +static struct map_attribute map_type_attr = __ATTR_RO_MODE(type, 0400);
> > +static struct map_attribute map_phys_addr_attr = __ATTR_RO_MODE(phys_addr, 0400);
> > +static struct map_attribute map_virt_addr_attr = __ATTR_RO_MODE(virt_addr, 0400);
> > +static struct map_attribute map_num_pages_attr = __ATTR_RO_MODE(num_pages, 0400);
> > +static struct map_attribute map_attribute_attr = __ATTR_RO_MODE(attribute, 0400);
> >
> >  /*
> >   * These are default attributes that are added for every memmap entry.
> > --- a/include/linux/sysfs.h
> > +++ b/include/linux/sysfs.h
> > @@ -117,6 +117,11 @@ struct attribute_group {
> >         .show   = _name##_show,                                         \
> >  }
> >
> > +#define __ATTR_RO_MODE(_name, _mode) {                                 \
> > +       .attr   = { .name = __stringify(_name), .mode = _mode },        \
> > +       .show   = _name##_show,                                         \
> > +}
> > +
> >  #define __ATTR_WO(_name) {                                             \
> >         .attr   = { .name = __stringify(_name), .mode = S_IWUSR },      \
> >         .store  = _name##_store,                                        \
> >
> 
> Thanks Greg.
> 
> Do we need the VERIFY_OCTAL_PERMISSION() thing here as well?

Ah, totally missed that, let me go add it now, good catch...

greg k-h