[PATCH v4 00/29] Integrate MbedTLS v3.6 LTS with U-Boot

[Tom Rini]

On Tue, Jul 02, 2024 at 11:22:36AM -0700, Raymond Mao wrote:

> Integrate MbedTLS v3.6 LTS (currently v3.6.0-RC1) 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.
> `MBEDTLS_LIB_TLS` is for SSL/TLS (Disabled until LWIP port for MbedTLS is
> ready).
> `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 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.
> 
> Target(QEMU arm64) size-growth when enabling MbedTLS:
> v1: 6.03%
> v2: 4.66%
> v3 & v4: 4.55%
> 
> Please see the latest output of bloat-o-meter for the reference of the
> size-growth on QEMU arm64 target [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.
> 
> [1]: bloat-o-meter output between disabling/enabling MbedTLS (QEMU arm64)
> ```
> add/remove: 206/81 grow/shrink: 19/17 up/down: 55548/-17495 (38053)

bloat-o-meter is a bit off then, since buildman shows:
u-boot: add: 243/-17, grow: 18/-17 bytes: 65723/-8480 (57243)

(Please use buildman for the size comparisons in the future).

And in both cases, there's a pretty big non-removal of code I was
expecting since overall we're replacing a lot of functionality, not just
enabling new functionality? If I'm wrong about that and we're doing
both, please separate out "enables new features" from "feature parity
with legacy" in commit updates to qemu_arm64 since buildman's handy
"show the delta for each commit in a series" is quite helpful in
spotting when we changed more/less than expected. And in this case
perhaps qemu_army64 wasn't fully enabling stuff before? sandbox changes
by only ~16Kib which is much better and I see pkcs7 and x509 related
removals in the size comparison.

Another note is that qemu-x86_64, which should be similar in EFI feature
function only grows by 129 bytes. Which isn't zero, but isn't bad. I
haven't done a for-each-commit build, but if we have generic bugfixes
here, we should split those out.

For example, I do see we're dropping some legacy hash related code, but
I'd want to dig a bit to make sure it's all of it.

And for v4 I'm not doing a world build comparison with mbedTLS being
default rather than legacy since I think the logic there is where some
of the Kconfig issues I mentioned are from and so I'm not confident the
results would look good. But for v5, please pick some arbitrary
platforms and switch them over and check the size change there as well.

Thanks!

-- 
Tom
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