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SubjectRe: [PATCH v2] nvmem: core: Set no-read-write provider to avoid userspace read/write

On 3/20/2019 9:56 PM, Srinivas Kandagatla wrote:
> On 20/03/2019 15:50, Gaurav Kohli wrote:
>> On 3/20/2019 8:04 PM, Srinivas Kandagatla wrote:
>>> On 17/03/2019 14:12, Gaurav Kohli wrote:
>>>> Current nvmem framework allows user space to read all register space
>>>> populated by nvmem binary file, In case we don't want to expose value
>>>> of registers to userspace and only want kernel space to read cell
>>>> value from nvmem_cell_read_u32.
>>>> To protect the same, Add no-read-write property to prevent read
>>>> from userspace.
>>> Can you explain the real need of this?
>>> Is there any issue you are noticing while reading nvmem content from
>>> userspace?
>> Hi Srinivas,
>> No, We are not observing any issue, nvmem is dumping the data properly.
>> But there are certain register, which we don't want to expose to user
>> space and want kernel space can only read via nvmem_cell_read.
> Am guessing these are some kind of keys or something that you do not
> want user to see.
Hi Srinivas,


Yes exactly, there are certain keys or even certain bit that we don't
want to expose to user.

> Is root only option not helping you in this case?
Yes we want to protect at root level as well, i mean it is better if we
can avoid exposing to userspace at all.
> We could go down the route of adding new config option something like
> CONFIG_NVMEM_NO_SYSFS_ENTRY to prevent adding nvmem entry in userspace.
> Let me know if you are happy to create a patch for this change?

I am happy with either way config option or dt binding(seems easy),
please let me know we will post new patch for the same.

In config option, do i have to remove all binary creation code of nvmem
, correct? or simply put a check like dt binding option

so user cannot read it.



> Thanks,
> srini
>> In existing design, even if we read cell from kernel space, nvmem
>> binary files is still populated to user space unconditionally.
>> Regards
>> Gaurav

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