Re: [PATCH 29/33] bpf: crypto: Use AES-CBC and AES-ECB libraries

[Vadim Fedorenko <vadim.fedorenko@linux.dev>]

On 07/07/2026 19:20, Eric Biggers wrote:
> On Tue, Jul 07, 2026 at 04:01:13PM +0100, Vadim Fedorenko wrote:
>> cc +bpf
>>
>> On 07/07/2026 06:34, Eric Biggers wrote:
>>> BPF crypto was implemented using the lskcipher API, which doesn't seem
>>> to be going anywhere.  It supports only "arc4", "cbc(aes)", "ecb(aes)",
>>> and only with unoptimized implementations.
>>>
>>> Library APIs also have been found to be a much better approach, for a
>>> variety of reasons, including reduced overhead, greater flexibility, and
>>> having to be explicit about the crypto algorithms that are supported.
>>>
>>> We can safely ignore the theoretical "arc4" support in BPF crypto as
>>> unused, which leaves "cbc(aes)" and "ecb(aes)".  Why these algorithms
>>> were chosen, it's unclear.  Regardless, I'll assume that "cbc(aes)" and
>>> "ecb(aes)" need to continue to be supported for backwards compatibility.
>>
>> That was done for single use case of decrypting small blocks in TC
>> layer with "cbc(aes)", with assumption of extending it later.
> 
> What protocol is using AES-CBC?  And is the kernel encrypting or
> decrypting the data elsewhere, or it is just routing an encrypted packet
> and only the BPF program decrypts it?

That's a "home-made" part of UDP encapsulation, the kernel routes it
further based on the info collected by BPF decrypt program.

> Does this mean the AES-ECB support is unnecessary and can be dropped?

Let's keep it if it doesn't hurt.

>> This change looks great, but it would be great to CC bpf folks just to
>> be aware of the refactoring.
> 
> Sure.  I'm only looking to apply patches 1-13 for now; the rest (bpf,
> fscrypt, keyrings, libceph, mac80211, macsec, mac802154, smb, ksmbd,
> tipc) are proof of concept, showing how the library APIs can be used in
> a wide range of kernel subsystems.  I didn't want to spam the entire
> series to 20 mailing lists.  I'll resend them individually later.

Ok, cool. But you can keep my Rb anyways - I checked the code and run
tests.

> 
> Thanks!
> 
> - Eric