Comment by l1k
10 hours ago
It does enable address space separation of secret keys from user space, which some people love:
https://blog.cloudflare.com/the-linux-kernel-key-retention-s...
https://www.youtube.com/watch?v=7djRRjxaCKk
https://www.youtube.com/watch?v=lvZaDE578yc
So it's not as simple as "should not exist". I agree though that there doesn't seem to be a valid need to expose authencesn to user space.
Disclosure: I'm co-maintaining crypto/asymmetric_keys/ in the kernel and the author/presenter in the first two links is another co-maintainer.
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...
can you please give me a real-life example of an application, on a typical linux laptop or typical linux server, which userspace application would use this CRYPTO_USER_API ? None that I looked at seem to use it: openssl, pgp, sha256sum
As Eric has correctly stated above, we believe iwd (Intel Wireless Daemon), or rather the ell library it relies on (Embedded Linux Library) is the only relatively widespread user space application relying on it.
Isn't the better argument to ask whether there'd be benefit if all those things did?
A lack of adoption isn't apriori a good argument against an interface, and serious bugs can happen anywhere.
My personal opinion for a while has been that crypto operations should be in the kernel so we can end the madness that is every application shipping it's own crypto and trust system which has only gotten worse since containers were invented.
> My personal opinion for a while has been that crypto operations should be in the kernel so we can end the madness that is every application shipping it's own crypto and trust system which has only gotten worse since containers were invented.
There’s a valid argument here but I think that’d devolve into the DNSSec trap without both a very well-designed API and a stable way to ship updates for older kernels. If people can’t get good user experience or have to force kernel upgrades to improve security, most applications will avoid it. Things like Chrome shipping their own crypto mean that they can very quickly ship things like PQC without waiting years or having to deal with issues like kernel n+1 having unrelated driver or performance issues which force things into a security vs. functionality fight.
> A lack of adoption isn't apriori a good argument against an interface
I mean it kind of is (perhaps not a priori, but why is that relavent?). If something is not being used, its not meeting needs, so its just increasing attack surfaces without benefit.