Re: [PATCH] fscrypt: don't use hardware offload Crypto API drivers

Maxime MERE
2025-06-13T09:02:38Z

Hello,

On 6/11/25 22:58, Eric Biggers wrote:
> To protect users from these buggy and seemingly unhelpful drivers that I
> have no way of testing, let's make fscrypt not use them. Unfortunately
> there is no direct support for doing so in the Crypto API, but we can
> achieve something very close to it by disallowing algorithms that have
> ASYNC, ALLOCATES_MEMORY, or KERN_DRIVER_ONLY set.

I agree that software drivers are more efficient and less prone to bugs
than hardware drivers. However, I would like to highlight the fact that
certain ST products (the STM32MP2x series) have features that allow the
loading of a secret key via an internal bus from a Secure OS to the CRYP
peripheral (usable by the kernel). This enables cryptographic operations
to be delegated to the non-secure side (the kernel) without exposing the
key.

If fscrypt no longer supports hardware drivers, then this type of
functionality could not be used, which I find unfortunate because it is
something that might interest users.

cheers,

Maxime