Make RAM dataspaces read-only (sth similar to mprotect in Linux)

[David]

Dear Genode community,


I've joined Denis Huber's project on developing a real-time 
checkpoint/restore component for Genode.

( https://sourceforge.net/p/genode/mailman/message/35211808/ )


In order to improve our process of memory checkpointing we would like to 
distinguish reading memory accesses from writing memory accesses.
While we do not care about reading, we are highly interested in 
detecting the occurrence of writing accesses.

At the moment our way to detect the access to a specific memory region 
is to detach the corresponding dataspace and handle
the pagefault which is produced when the component tries to access the 
dataspace.


We are aware that it is possible to determine whether a writing or a 
reading access triggered a pagefault but we don't want to increase
the amount of pagefaults by detaching dataspaces after every time they 
were only read. It would be cool if writing would cause an error
which is is not produced by reading.


As a solution to this we thought of adding the possibility to make a RAM 
dataspace read-only, something which is similar to „mprotect“ in Linux.
With this feature we would not need to detach dataspaces but writing 
accesses would still produce faults which we could track in order to 
detect them.


Is such an alteration of RAM dataspaces possible? If yes, how would you 
do it?

What kind of fault would be triggered if someone tries to write to a 
read-only memory?

Are we able to get information about such a fault in Genode?


We are using Genode on top of the Fiasco.OC.


Thanks in advance!


Kind Regards,

David

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