Comment by ebiggers
10 hours ago
That can be done in userspace too -- different userspace processes have different address spaces too.
The fact that the first link recommends using keyctl() for RSA private keys is also "interesting", given that the kernel's implementation of RSA isn't hardened against timing attacks (but userspace implementations of RSA typically are).
The CloudFlare blog discusses that idea when they talk about having an "agent process" to hold cryptographic material, but they list drawbacks like having to develop two processes, implement a well-defined interface, and enforce ACLs. I'm not convinced that "developing two processes" is a reason not to do it, since the kernel is effectively just the second process now, but everything else makes sense.
It's unfortunate though since this is one thing I think Windows does decently well. The Windows crypto and TLS APIs do use a key isolation process by default (LSASS) and have a stable interface for other processes to use it [0]. I imagine systemd could implement something similar, but I also know that there are very strong opinions about adding more surface area to systemd.
[0] https://blackhat.com/docs/us-16/materials/us-16-Kambic-Cunni...
TBH LSASS is privileged enough to be a good target for exploits.
> the kernel's implementation of RSA isn't hardened against timing attacks
Cloudflare is using custom BoringSSL-based crypto code in the kernel:
https://lore.kernel.org/all/CALrw=nEyTeP=6QcdEvaeMLZEq_pYB9W...