firmware: dmi-sysfs: why is the access mode of dmi sysfs entries restricted to 0400?

firmware: dmi-sysfs: why is the access mode of dmi sysfs entries restricted to 0400?

[Guoheyi]

Hi,

Why is the access mode of dmi sysfs entries restricted to 0400? Is it 
for security concern? If it is, which information do we consider as privacy?

We would like to fetch CPU information from non-root application, is 
there feasible way to do that?

Any advice is appreciated.

Thanks,

Heyi

Re: firmware: dmi-sysfs: why is the access mode of dmi sysfs entries restricted to 0400?

[Greg Kroah-Hartman]

On Wed, Dec 04, 2019 at 03:31:22PM +0800, Guoheyi wrote:
> Hi,
> 
> Why is the access mode of dmi sysfs entries restricted to 0400? Is it for
> security concern? If it is, which information do we consider as privacy?

There's lots of "interesting" information in dmi entries that you
probably do not want all processes reading, which is why they are
restricted.

> We would like to fetch CPU information from non-root application, is there
> feasible way to do that?

What specific CPU information is not currently exported in /proc/cpuinfo
that only shows up in DMI entries that you are interested in?

You can always have root change the permissions of a sysfs file if you
have a service that wants to allow non-root programs to read specific
entries.

thanks,

greg k-h

Re: firmware: dmi-sysfs: why is the access mode of dmi sysfs entries restricted to 0400?

[Guoheyi]

在 2019/12/4 15:41, Greg Kroah-Hartman 写道:
> On Wed, Dec 04, 2019 at 03:31:22PM +0800, Guoheyi wrote:
>> Hi,
>>
>> Why is the access mode of dmi sysfs entries restricted to 0400? Is it for
>> security concern? If it is, which information do we consider as privacy?
> There's lots of "interesting" information in dmi entries that you
> probably do not want all processes reading, which is why they are
> restricted.
>
>> We would like to fetch CPU information from non-root application, is there
>> feasible way to do that?
> What specific CPU information is not currently exported in /proc/cpuinfo
> that only shows up in DMI entries that you are interested in?

We'd like to get processor manufacturer, speed and version, and pass the 
information to qemu virtual machine, for users of VM might be happy to 
see this instead of "unknown xxx", while qemu may run as non-root.

>
> You can always have root change the permissions of a sysfs file if you
> have a service that wants to allow non-root programs to read specific
> entries.

Thanks; we'll try it.

Heyi

>
> thanks,
>
> greg k-h
>
> .

Re: firmware: dmi-sysfs: why is the access mode of dmi sysfs entries restricted to 0400?

[Greg Kroah-Hartman]

On Wed, Dec 04, 2019 at 05:01:06PM +0800, Guoheyi wrote:
> 
> 在 2019/12/4 15:41, Greg Kroah-Hartman 写道:
> > On Wed, Dec 04, 2019 at 03:31:22PM +0800, Guoheyi wrote:
> > > Hi,
> > > 
> > > Why is the access mode of dmi sysfs entries restricted to 0400? Is it for
> > > security concern? If it is, which information do we consider as privacy?
> > There's lots of "interesting" information in dmi entries that you
> > probably do not want all processes reading, which is why they are
> > restricted.
> > 
> > > We would like to fetch CPU information from non-root application, is there
> > > feasible way to do that?
> > What specific CPU information is not currently exported in /proc/cpuinfo
> > that only shows up in DMI entries that you are interested in?
> 
> We'd like to get processor manufacturer, speed and version, and pass the
> information to qemu virtual machine, for users of VM might be happy to see
> this instead of "unknown xxx", while qemu may run as non-root.

Careful about this as if you move that virtual machine around, those
values will change and if userspace was depending on them being static
(set up at program start time), then you might have problems.

good luck!

greg k-h

Re: firmware: dmi-sysfs: why is the access mode of dmi sysfs entries restricted to 0400?

[Guoheyi]

在 2019/12/4 17:29, Greg Kroah-Hartman 写道:
> On Wed, Dec 04, 2019 at 05:01:06PM +0800, Guoheyi wrote:
>> 在 2019/12/4 15:41, Greg Kroah-Hartman 写道:
>>> On Wed, Dec 04, 2019 at 03:31:22PM +0800, Guoheyi wrote:
>>>> Hi,
>>>>
>>>> Why is the access mode of dmi sysfs entries restricted to 0400? Is it for
>>>> security concern? If it is, which information do we consider as privacy?
>>> There's lots of "interesting" information in dmi entries that you
>>> probably do not want all processes reading, which is why they are
>>> restricted.
>>>
>>>> We would like to fetch CPU information from non-root application, is there
>>>> feasible way to do that?
>>> What specific CPU information is not currently exported in /proc/cpuinfo
>>> that only shows up in DMI entries that you are interested in?
>> We'd like to get processor manufacturer, speed and version, and pass the
>> information to qemu virtual machine, for users of VM might be happy to see
>> this instead of "unknown xxx", while qemu may run as non-root.
> Careful about this as if you move that virtual machine around, those
> values will change and if userspace was depending on them being static
> (set up at program start time), then you might have problems.
>
> good luck!

The information will be used as VM DMI/SMBIOS as well, so it will be 
read only once during VM boot. I guess we will be OK :)

Thanks a lot.

Heyi

>
> greg k-h
>
> .