[shaded-enmity]

> I believe the concern is that the attackers gain root access on system A but hide their presence/activity - even in the presence of logs to remote, more trusted server B.

That's generally called pivoting and has nothing to do with method of persistence of the malicious code.

OP makes a point that certain systems move or have moved away from giving root user the ability to extend/modify kernel code at runtime via kernel modules, my argument is that none of that matters since root user can still extend/modify kernel code at runtime via binary patching.

[rollcat]

> my argument is that none of that matters since root user can still extend/modify kernel code at runtime via binary patching.

OpenBSD restricts that ability as well[1]. Neither /dev/mem nor /dev/kmem can be opened (read or write) during normal multi-user operation; you have to enter single-user mode (which requires serial console or physical access to achieve anything useful). Raw disk devices of mounted partitions can't be altered, immutable/append-only files can't be altered, etc.

You can also choose to completely prohibit access to raw disk devices, although that gets annoying when you e.g. need to format an external drive. There is of course still a lot of potential to do harm as root, but it's not as easy to create a persistent threat or resist in-system analysis by an administrator.

[1]: https://man.openbsd.org/securelevel

[shaded-enmity]

From your link:

> securelevel may no longer be lowered except by init

> The list of securelevel's effects may not be comprehensive.

So yes, it's a nice sandbox that can help prevent accidents, but doesn't sound like something you should rely on for actual defense.

[rollcat]

You sound like you're dismissing it, but even if it wasn't all that useful on its own, it's a part of defense in depth strategy - it's just one layer in a carefully thought out system. Pledge/unveil is another, so is privsep+imsg, W^X, (K)ASLR, syscall origin verification, boot-time libc/kernel relinking, and a couple dozen other features I can't even recall now.

Most importantly, all of these features and mitigations are enabled by default, and are pretty much invisible to the end user or administrator; and actually easy to use for a developer. Contrast this with e.g. seccomp or SELinux. Google is even hinting "selinux permissive" and "selinux disable" in top 3 suggestions...

[cb321]

Ah. I misunderstood your "persistence" to mean "persistence of logs" not "of code/illicit powers". Sorry - I read too quickly.

I do think the defense mentality, as evidenced by many comments in this thread, remains a bit too much about "how challenging to make things" rather than the "in theory possibility". Besides binary patching a static kernel as you say, for example, you could have remote hashes of all relevant files a la tripwire, and remote access and programs to check said hashes. If the attacker can detect and adapt to a hash checking pattern then they can "provide the old file" for some purposes/etc. to hide their presence. To do so they have to also write the code to detect/conditionalize. The rationale of this defense mentality seems to hope for a "distribution of attacker laziness" that may at least "help", but sure - it is just a higher, finite bar. And once the work has been done..game over. But I do not mean to belabor the obvious. Anyway, thanks for clarifying your argument.

[shaded-enmity]

Aye, I think what you're describing is "security by obscurity" - i.e. the capability is still there, I'm just counting on the attacker not knowing that it is because I've hidden it so well. It can work really well in combination with actual security practices, but it absolutely shouldn't be considered one.