[PATCH v6 00/28] Integrate MbedTLS v3.6 LTS with U-Boot

[Raymond Mao]

Hi Simon,

On Sat, 17 Aug 2024 at 11:58, Simon Glass <sjg at chromium.org> wrote:

> Hi Raymond,
>
> On Fri, 16 Aug 2024 at 15:44, Raymond Mao <raymond.mao at linaro.org> wrote:
> >
> > Integrate MbedTLS v3.6 LTS (currently v3.6.0) with U-Boot.
> >
> > Motivations:
> > ------------
> >
> > 1. MbedTLS is well maintained with LTS versions.
> > 2. LWIP is integrated with MbedTLS and easily to enable HTTPS.
> > 3. MbedTLS recently switched license back to GPLv2.
> >
> > Prerequisite:
> > -------------
> >
> > This patch series requires mbedtls git repo to be added as a
> > subtree to the main U-Boot repo via:
> >     $ git subtree add --prefix lib/mbedtls/external/mbedtls \
> >           https://github.com/Mbed-TLS/mbedtls.git \
> >           v3.6.0 --squash
> > Moreover, due to the Windows-style files from mbedtls git repo,
> > we need to convert the CRLF endings to LF and do a commit manually:
> >     $ git add --renormalize .
> >     $ git commit
> >
> > New Kconfig options:
> > --------------------
> >
> > `MBEDTLS_LIB` is for MbedTLS general switch.
> > `MBEDTLS_LIB_CRYPTO` is for replacing original digest and crypto libs
> with
> > MbedTLS.
> > `MBEDTLS_LIB_X509` is for replacing original X509, PKCS7, MSCode, ASN1,
> > and Pubkey parser with MbedTLS.
> > `LEGACY_CRYPTO` is introduced as a main switch for legacy crypto library.
> > `LEGACY_CRYPTO_BASIC` is for the basic crypto functionalities and
> > `LEGACY_CRYPTO_CERT` is for the certificate related functionalities.
> > For each of the algorithm, a pair of `<alg>_LEGACY` and `<alg>_MBEDTLS`
> > Kconfig options are introduced. Meanwhile, `SPL_` Kconfig options are
> > introduced.
> >
> > In this patch set, MBEDTLS_LIB, MBEDTLS_LIB_CRYPTO and MBEDTLS_LIB_X509
> > are by default enabled in qemu_arm64_defconfig and sandbox_defconfig
> > for testing purpose.
> >
> > Patches for external MbedTLS project:
> > -------------------------------------
> >
> > Since U-Boot uses Microsoft Authentication Code to verify PE/COFFs
> > executables which is not supported by MbedTLS at the moment,
> > addtional patches for MbedTLS are created to adapt with the EFI loader:
> > 1. Decoding of Microsoft Authentication Code.
> > 2. Decoding of PKCS#9 Authenticate Attributes.
> > 3. Extending MbedTLS PKCS#7 lib to support multiple signer's
> certificates.
> > 4. MbedTLS native test suites for PKCS#7 signer's info.
> >
> > All above 4 patches (tagged with `mbedtls/external`) are submitted to
> > MbedTLS project and being reviewed, eventually they should be part of
> > MbedTLS LTS release.
> > But before that, please merge them into U-Boot, otherwise the building
> > will be broken when MBEDTLS_LIB_X509 is enabled.
> >
> > See below PR link for the reference:
> > https://github.com/Mbed-TLS/mbedtls/pull/9001
> >
> > Miscellaneous:
> > --------------
> >
> > Optimized MbedTLS library size by tailoring the config file
> > and disabling all unnecessary features for EFI loader.
> > From v2, original libs (rsa, asn1_decoder, rsa_helper, md5, sha1, sha256,
> > sha512) are completely replaced when MbedTLS is enabled.
> > From v3, the size-growth is slightly reduced by refactoring Hash
> functions.
> > From v6, smaller implementations for SHA256 and SHA512 are enabled and
> > target size reduce significantly.
> > Target(QEMU arm64) size-growth when enabling MbedTLS:
> > v1: 6.03%
> > v2: 4.66%
> > v3 - v5: 4.55%
> > v6: 2.90%
> >
> > Please see the latest output from buildman for size-growth on QEMU arm64,
> > Sandbox and Nanopi A64. [1]
> >
> > Tests done:
> > -----------
> >
> > EFI Secure Boot test (EFI variables loading and verifying, EFI signed
> image
> > verifying and booting) via U-Boot console.
> > EFI Secure Boot and Capsule sandbox test passed.
> >
> > Known issues:
> > -------------
> >
> > None.
>
> I wonder if we could leave out the SHA stuff? The algorithms are
> stable and this would seem to avoid much of the size growth, and all
> the pain of trying to integrate another yet another hashing layer (we
> already have normal, progressive and h/w acceleration, plus
> UCLASS_HASH which h/w acceleration should use but that migration never
> happened). I struggle to see any benefit in replacing U-Boot's very
> solid hashing infra with something else, particularly as this series
> adds yet another. Better to invest the time to refactor it. I asked
> about this before and was told that it would happen 'later'. Let's
> just not change it at all, then it is more likely someone will sort it
> out.
>
> Unfortunately, MbedTLS depends on its own digest layer. Unless we patch
MbedTLS
to allow an external digest library from U-Boot ...


> Also, if MbedTLS is wanting to be a general library for TLS (I assume
> transport-local security, not thread-local storage) perhaps it might
> consider changing to non-Windows newlines, or perhaps even kernel code
> style?
>
> We can feedback this to the MbedTLS project when the first series are
accepted.

Regards,
Raymond