Messages in this thread | | | From | Nicholas Johnson <> | Subject | Re: [PATCH v1 1/3] nvmem: Add support for write-only instances | Date | Tue, 25 Feb 2020 15:30:22 +0000 |
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On Tue, Feb 25, 2020 at 02:51:41PM +0200, Mika Westerberg wrote: > On Mon, Feb 24, 2020 at 05:42:33PM +0000, Nicholas Johnson wrote: > > Mika Westerberg requires write-only nvmem for the Thunderbolt driver. > > Refer to 03cd45d2e219 ("thunderbolt: Prevent crash if non-active NVMem > > file is read"). Hence, there is at least one real-world use for > > write-only nvmem instances. > > Well, I don't require anything ;-) It is the thunderbolt driver that has > one nvmem device that is write-only and it may take advantage of this. Sorry, I will re-word it to be more accurate. I need to work on saying what I actually mean.
> > > Add support for write-only nvmem instances by changing the nvmem attrs > > to 0222 if the .reg_read callback is not populated. > > > > Add a WARN_ON in case a driver populates neither .reg_read nor > > .reg_write because this behaviour should clearly never occur. > > > > Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au> > > --- > > drivers/nvmem/nvmem-sysfs.c | 77 +++++++++++++++++++++++++++++++++---- > > 1 file changed, 70 insertions(+), 7 deletions(-) > > > > diff --git a/drivers/nvmem/nvmem-sysfs.c b/drivers/nvmem/nvmem-sysfs.c > > index 9e0c429cd..be3b94f0b 100644 > > --- a/drivers/nvmem/nvmem-sysfs.c > > +++ b/drivers/nvmem/nvmem-sysfs.c > > @@ -147,6 +147,30 @@ static const struct attribute_group *nvmem_ro_dev_groups[] = { > > NULL, > > }; > > > > +/* write only permission */ > > +static struct bin_attribute bin_attr_wo_nvmem = { > > + .attr = { > > + .name = "nvmem", > > + .mode = 0222, > > I would say no sysfs attribute should ever be writable by the world. I cannot think of an argument against this, nor can I rule out one existing. But I would be inclined to agree.
> > Actually I think maybe we make this one only writeable by root, in other > words it would always require ->root_only to be set. There is a world-accessible rw entry already, which would, if anything, be even more dangerous than a world writable entry. However, there could be a hypothetical use case. I agree it is unlikely to be required, but who knows?
Based on your statement that no sysfs should ever be world-writable, should I be trying to remove the world-accessible rw as well? > > > + }, > > + .write = bin_attr_nvmem_write, > > +}; > > + > > +static struct bin_attribute *nvmem_bin_wo_attributes[] = { > > + &bin_attr_wo_nvmem, > > + NULL, > > +}; > > + > > +static const struct attribute_group nvmem_bin_wo_group = { > > + .bin_attrs = nvmem_bin_wo_attributes, > > + .attrs = nvmem_attrs, > > +}; > > + > > +static const struct attribute_group *nvmem_wo_dev_groups[] = { > > + &nvmem_bin_wo_group, > > + NULL, > > +}; > > + > > /* default read/write permissions, root only */ > > static struct bin_attribute bin_attr_rw_root_nvmem = { > > .attr = { > > @@ -196,16 +220,50 @@ static const struct attribute_group *nvmem_ro_root_dev_groups[] = { > > NULL, > > }; > > > > +/* write only permission, root only */ > > +static struct bin_attribute bin_attr_wo_root_nvmem = { > > + .attr = { > > + .name = "nvmem", > > + .mode = 0200, > > + }, > > + .write = bin_attr_nvmem_write, > > +}; > > + > > +static struct bin_attribute *nvmem_bin_wo_root_attributes[] = { > > + &bin_attr_wo_root_nvmem, > > + NULL, > > +}; > > + > > +static const struct attribute_group nvmem_bin_wo_root_group = { > > + .bin_attrs = nvmem_bin_wo_root_attributes, > > + .attrs = nvmem_attrs, > > +}; > > + > > +static const struct attribute_group *nvmem_wo_root_dev_groups[] = { > > + &nvmem_bin_wo_root_group, > > + NULL, > > +}; > > + > > const struct attribute_group **nvmem_sysfs_get_groups( > > struct nvmem_device *nvmem, > > const struct nvmem_config *config) > > { > > - if (config->root_only) > > - return nvmem->read_only ? > > - nvmem_ro_root_dev_groups : > > - nvmem_rw_root_dev_groups; > > - > > - return nvmem->read_only ? nvmem_ro_dev_groups : nvmem_rw_dev_groups; > > + /* > > + * If neither reg_read nor reg_write are provided, we cannot use this > > + * nvmem entry, as any operation will cause kernel mode NULL reference. > > + */ > > + WARN_ON(!nvmem->reg_read && !nvmem->reg_write); > > This should also be documented in kernel-doc of struct nvmem_config. Roger.
> > > + > > + if (nvmem->reg_read && nvmem->reg_write) > > + return config->root_only ? > > + nvmem_rw_root_dev_groups : nvmem_rw_dev_groups; > > + > > + if (nvmem->reg_read && !nvmem->reg_write) > > + return config->root_only ? > > + nvmem_ro_root_dev_groups : nvmem_ro_dev_groups; > > + > > + return config->root_only ? > > + nvmem_wo_root_dev_groups : nvmem_wo_dev_groups; > > } > > > > /* > > @@ -224,11 +282,16 @@ int nvmem_sysfs_setup_compat(struct nvmem_device *nvmem, > > if (!config->base_dev) > > return -EINVAL; > > > > - if (nvmem->read_only) { > > + if (nvmem->reg_read && !nvmem->reg_write) { > > if (config->root_only) > > nvmem->eeprom = bin_attr_ro_root_nvmem; > > else > > nvmem->eeprom = bin_attr_ro_nvmem; > > + } else if (!nvmem->reg_read && nvmem->reg_write) { > > + if (config->root_only) > > + nvmem->eeprom = bin_attr_wo_root_nvmem; > > + else > > + nvmem->eeprom = bin_attr_wo_nvmem; > > } else { > > if (config->root_only) > > nvmem->eeprom = bin_attr_rw_root_nvmem; > > -- > > 2.25.1
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