[PATCH v2] Add support for OpenSSL Provider API
Eddie Kovsky
ekovsky at redhat.com
Mon Dec 22 18:38:05 CET 2025
On 12/11/25, Mattijs Korpershoek wrote:
> Hi Eddie,
>
> Thank you for working on this. It would be really nice if we could build
> U-Boot on more recent Linux distros without bridge packages such as
> openssl-devel-engine.
>
>
> I also don't linke this double negative.
> As you already shared, Linux solved this via:
>
> #if OPENSSL_VERSION_MAJOR >= 3
>
> Why can't we have something similar?
> See: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=558bdc45dfb2669e1741384a0c80be9c82fa052c
>
Hi Mattijs
Yes, we could also implement it this way with the extra USE_PKCS11_XXX
symbol. Jan's original patch I based my work on does something similar,
and I perhaps oversimplified it.
> >
> > [4] https://docs.openssl.org/3.0/man7/openssl_user_macros/
> >
> >> > Provider API while continuing to use the existing Engine API on distros
> >> > shipping older releases of OpenSSL.
> >> >
> >>
> >> One can use org.openssl.engine: as prefix for provider arguments when one
> >> wants to use an engine still.
> >>
> >
> > Sorry, but it's not clear what you are referring to here.
> >
> >> > This is based on similar work contributed by Jan Stancek updating Linux
> >> > to use the Provider interface.
> >> >
> >> > commit 558bdc45dfb2669e1741384a0c80be9c82fa052c
> >> > Author: Jan Stancek <jstancek at redhat.com>
> >> > Date: Fri Sep 20 19:52:48 2024 +0300
> >> >
> >> > sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3
> >> >
> >> > The changes have been tested with the FIT signature verification vboot
> >> > tests on Fedora 42 and Debian 13. All 30 tests pass with both the legacy
> >> > Engine library installed and with the Provider API.
> >> >
> >>
> >> Are there actually tests using an OpenSSL engine? Because otherwise it's
> >> simply checking that local keys are still working... which isn't that much
> >> different from what we currently have with engines when not using engines.
> >>
> >> I'm implementing FIT images signing with OpenSSL engines, and it'd be nice
> >> if we could have something that doesn't require changes to support providers
> >> (or if it does, not in a confusing manner for example).
> >>
> >> https://lore.kernel.org/u-boot/20251031-binman-engine-v1-0-c13c1b5dac43@cherry.de/T/#t
> >> for the v1, I'll soon (next hours or tomorrow) post a v2 and Cc you if you
> >> don't mind.
> >>
> >> [...]
> >>
> >
> > As mentioned above, the motivation for this patch is that the Engine
> > API has already been deprecated. Projects that depend on OpenSSL will
> > need to move to the new Provider API in order to continue to function.
> >
> > The FIT Signature Verification tests I used to exercise both APIs are
> > documented here.[5]
> >
> > [5] https://docs.u-boot.org/en/latest/usage/fit/signature.html#u-boot-fit-signature-verification
> >
> >
> >> > diff --git a/lib/rsa/Kconfig b/lib/rsa/Kconfig
> >> > index 9033384e60a3..1bf0ac96d598 100644
> >> > --- a/lib/rsa/Kconfig
> >> > +++ b/lib/rsa/Kconfig
> >> > @@ -20,6 +20,13 @@ config SPL_RSA
> >> > bool "Use RSA Library within SPL"
> >> > depends on SPL
> >> >
> >> > +config OPENSSL_NO_DEPRECATED
> >> > + bool "Build U-Boot without support for OpenSSL Engine"
> >> > + help
> >> > + Add support for the OpenSSL Provider API, which is the officially
> >> > + supported mechanism in OpenSSL 3.x and later releases for accessing
> >> > + hardware and software cryptography.
> >> > +
> >>
> >> mmmm Cannot we use providers for something else than RSA? In which case it's
> >> a bit odd to have it in lib/rsa/Kconfig (but I have no better suggestion).
> >>
> >
> > To the best of my knowledge, the only areas in the U-Boot source that
> > are using the Engine API are the RSA and AES libraries. All other uses
> > in U-Boot are clients of these two libraries.
> >
> >> > config SPL_RSA_VERIFY
> >> > bool
> >> > depends on SPL_RSA
> >>
> >> [...]
> >>
> >> > @@ -207,6 +247,37 @@ static int rsa_pem_get_priv_key(const char *keydir, const char *name,
> >> > return -ENOENT;
> >> > }
> >> >
> >> > +#ifdef CONFIG_OPENSSL_NO_DEPRECATED
> >> > + EVP_PKEY *private_key = NULL;
> >> > + OSSL_STORE_CTX *store;
> >> > +
> >> > + if (!OSSL_PROVIDER_try_load(NULL, "pkcs11", true))
> >> > + ERR(1, "OSSL_PROVIDER_try_load(pkcs11)");
> >> > + if (!OSSL_PROVIDER_try_load(NULL, "default", true))
> >> > + ERR(1, "OSSL_PROVIDER_try_load(default)");
> >> > +
> >> > + store = OSSL_STORE_open(path, NULL, NULL, NULL, NULL);
> >> > + ERR(!store, "OSSL_STORE_open");
> >> > +
> >> > + while (!OSSL_STORE_eof(store)) {
> >> > + OSSL_STORE_INFO *info = OSSL_STORE_load(store);
> >> > +
> >> > + if (!info) {
> >> > + drain_openssl_errors(__LINE__, 0);
> >> > + continue;
> >> > + }
> >> > + if (OSSL_STORE_INFO_get_type(info) == OSSL_STORE_INFO_PKEY) {
> >> > + private_key = OSSL_STORE_INFO_get1_PKEY(info);
> >> > + ERR(!private_key, "OSSL_STORE_INFO_get1_PKEY");
> >> > + }
> >> > + OSSL_STORE_INFO_free(info);
> >> > + if (private_key)
> >> > + break;
> >> > + }
> >> > + OSSL_STORE_close(store);
> >> > +
> >> > + *evpp = private_key;
> >> > +#else
> >>
> >> Wondering if it really makes sense to have the provider API implemented as
> >> an #ifdef to save like 10 common lines between key-based and provider-based
> >> implems.
> >>
> >> On another topic, my first reading of the code makes me a bit worried by the
> >> fact that there's seemingly no way to select whether we want to use a local
> >> key or a provider key. Also, I see "pkcs11" and "default" here, but how do I
> >> select which provider I want to use (e.g. my custom one). If I somehow
> >> manage to have a key named the same locally and in one or more providers,
> >> how do I make sure the proper one is selected? I'm wondering whether we
> >> should be reusing the engine parameter to select a provider?
> >>
> >> I have 0 security or crypto background, don't hesitate to be verbose in your
> >> answer.
> >>
> >> Cheers,
> >> Quentin
> >>
> >
> > It's not the prettiest code. But I'm trying to be very conservative
> > in making these changes so that no one's workflow is disrupted.
> > Developers should be able to build U-Boot with the latest OpenSSL
> > without impacting developers who are in environments utilizing the
> > Engine API. The goal here is to preserve feature parity between the two
> > APIs. Adding support for custom Providers is outside the scope of this
> > change, but could certainly be added later.
>
> I'd be in favor to drop CONFIG_OPENSSL_NO_DEPRECATED all together and
> just use "#if OPENSSL_VERSION_MAJOR >= 3".
>
> Tom, or anyone else, is there a particular` reason for gating this in a
> Kconfig ?
>
> The oldest Ubuntu version that seems supported (22.04) already has
> OpenSSL version 3:
>
> $ podman run -it /bin/bash ubuntu:22.04
> root at 6dc347676b8a:~# apt update && apt install -y openssl
> root at 6dc347676b8a:~# openssl version
> OpenSSL 3.0.2 15 Mar 2022 (Library: OpenSSL 3.0.2 15 Mar 2022)
>
I assumed that we would want this to be an explicit config option, but
logically there is no reason that it has to be. I'd be happy to spin up
a v3 if there's agreement that the Kconfig isn't needed.
Eddie
More information about the U-Boot
mailing list