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

[Simon Glass]

Hi Raymond,

On Tue, 3 Sept 2024 at 08:59, Raymond Mao <raymond.mao at linaro.org> wrote:
>
> 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 ...

Yes that sounds best. It looks like only a few call sites, so it
should be a matter of leaving out the MbedTLS code and adding some
static inlines.

>
>>
>> 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.

OK.

Regards,
Simon