linux-ext4 - Re: [PATCH] fscrypt: don't use hardware offload Crypto API drivers

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Message-ID: <8f4c2f36-71af-4c84-bcee-2554cea991d0@foss.st.com>
Date: Fri, 13 Jun 2025 11:01:03 +0200
From: Maxime MERE <maxime.mere@...s.st.com>
To: Eric Biggers <ebiggers@...nel.org>, <linux-fscrypt@...r.kernel.org>
CC: <linux-crypto@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-mtd@...ts.infradead.org>, <linux-ext4@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>, <ceph-devel@...r.kernel.org>
Subject: Re: [PATCH] fscrypt: don't use hardware offload Crypto API drivers

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