I have three separate but related questions. Perhaps they belong in Programming, but it is Linux- and security- specific, so I thought here would be a good place.

Is there any way for an application to request that it's memory space never be sent to swap. For instance, say I write an encryption-related application that must store plaintext in memory. I wouldn't want that to get swapped, as that leaves it somewhat vulnerable. In this case I would rather the kernel rudely kill my process than swap it.

The second question is, does the kernel ever swap any part of itself? I would imagine not, but I suppose what I'm asking is, would it work as a dirty hack to simply move the code into kernel-space?

And the final question: assuming that an application can't request to be swapped, how difficult would it be to implement that into the kernel? I'm imagining that would require digging into the guts of the kernel's memory management and process management, so pretty difficult. However, I have never even touched kernel development, so could someone clue me in to exactly the level of impracticality in implementing that?

I would look at the mlock() call. It does exactly what you want. Be careful not to lock too much memory, of course... I would only lock parts that MUST be secure.

Thank you greatly. I *knew* I couldn't be the first to want that.

Nope... it's commonly used by processes like gpg, gpg-agent, ssh-agent, and other encryption apps.

Of course you could also just encrypt the swap space.

Always more than one answer.

A friend who's a computer security academic suggested that both (i) locking memory and (ii) encrypting swap space were problematic: (i) because any selfish program could make itself run faster by preventing itself swapping at the expense of forcing others to swap more and (ii) because you have the possibility of accidentally encrypting the swap space key and therefore losing the ability to decrypt swap. Perhaps he was being too pessimistic...

I was about to make a few choice comments re academics, but decided to resist.
Sufficed to note that he offerred no solution.

Sheesh ...