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

[Gaurav Kohli]

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,

Thanks.

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

Gaurav

> 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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