Re: Question: a module for wiping userspace RAM before shutdown/reboot/halt

[Danill Klimuk <daniil.klimuk@3mdeb.com>]

Hi Christophe, thank you for the answer.

 > What do you mean by 'wiping', do you mean 'clearing' ?

Yes, by 'wiping' I mean 'clearing'.

 > Can you explain the reason this is needed?

Some of our clients want to clear user space RAM during 
shutdown/reboot/halt sequences of Linux kernel, so the process data or 
any other leftovers do not leak outside current Linux kernel session 
(that is to firmware, or the next boot software, etc.). The reason for 
it to be a module that will execute in a specific moment of the 
sequences is to make it more predictable.

I thought that if the clients want to use it, maybe it will be useful 
for others too :).

On 5/17/25 7:25 PM, Christophe Leroy wrote:
>
>
> Le 15/05/2025 à 15:30, Danill Klimuk a écrit :
>
>> Hello everyone. I have received a request to write a Linux kernel module
>> that will wipe any processes leftovers from userspace RAM during/before
>> Linux kernel shutdown/reboot/halt sequences. The reason I am going to do
>> it inside a module is to do it in a more deterministic way that does not
>> depend on any processes. AFAIK Linux kernel does not have any other
>> functionalities to wipe leftovers from RAM apart from the command line
>> arguments "init_on_free" and "init_on_alloc" that results in memory
>> poisoning only during memory allocation and memory deallocation. These
>> arguments cause the kernel to clean processes memory several times
>> during runtime, that is not deterministic because of processes
>> non-deterministic behavior. Hence, I want to bring the memory wiping
>> mechanism in one place and make it more deterministic. The question is:
>>
>> Maybe the Linux kernel already have such functionalities implemented?
>
> Linux memory management topics should be sent to linux-mm@kvack.org
>
>>
>> Currently I am planning to implement the wiping process to be triggered
>> by "reboot_notifier_callback", so to wipe RAM after PID 1 process
>> finishes and no other processes are executing. I am looking forward to
>> merging the module into Linux kernel upstream too.
>
> What do you mean by 'wiping', do you mean 'clearing' ?
>
> Can you explain the reason this is needed ?
>
> Christophe
>
>
-- 
Best regards, Daniil.
3mdeb Zarhus team leader.