Re: [PATCH v3 03/25] mbedtls: add mbedtls into the build system

[Tom Rini <trini@konsulko.com>]

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On Wed, May 29, 2024 at 03:42:04PM -0400, Raymond Mao wrote:
> Hi Tom,
> 
> On Wed, 29 May 2024 at 14:43, Tom Rini <trini@konsulko.com> wrote:
> 
> > On Wed, May 29, 2024 at 02:38:10PM -0400, Raymond Mao wrote:
> > > Hi Tom,
> > >
> > > On Wed, 29 May 2024 at 14:01, Tom Rini <trini@konsulko.com> wrote:
> > >
> > > > On Wed, May 29, 2024 at 01:42:16PM -0400, Raymond Mao wrote:
> > > > > Hi Tom,
> > > > >
> > > > > On Wed, 29 May 2024 at 12:58, Tom Rini <trini@konsulko.com> wrote:
> > > > >
> > > > > > On Tue, May 28, 2024 at 07:09:14AM -0700, Raymond Mao wrote:
> > > > > >
> > > > > > > Port mbedtls with dummy libc header files.
> > > > > > > Add mbedtls default config header file.
> > > > > > > Optimize mbedtls default config by disabling unused features to
> > > > > > > reduce the target size.
> > > > > > > Add mbedtls kbuild makefile.
> > > > > > > Add Kconfig and mbedtls config submenu.
> > > > > > [snip]
> > > > > > > diff --git a/lib/mbedtls/Kconfig b/lib/mbedtls/Kconfig
> > > > > > > new file mode 100644
> > > > > > > index 00000000000..d6e77d56871
> > > > > > > --- /dev/null
> > > > > > > +++ b/lib/mbedtls/Kconfig
> > > > > > > @@ -0,0 +1,25 @@
> > > > > > > +menuconfig MBEDTLS_LIB
> > > > > > > +     bool "Use mbedtls libraries"
> > > > > > > +     select MBEDTLS_LIB_CRYPTO
> > > > > > > +     select MBEDTLS_LIB_X509
> > > > > > > +     help
> > > > > > > +       Enable mbedtls libraries
> > > > > > > +
> > > > > > > +if MBEDTLS_LIB
> > > > > > > +
> > > > > > > +config MBEDTLS_LIB_CRYPTO
> > > > > > > +     bool "Crypto library"
> > > > > > > +     help
> > > > > > > +       Enable mbedtls crypto library
> > > > > > > +
> > > > > > > +config MBEDTLS_LIB_X509
> > > > > > > +     bool "X509 library"
> > > > > > > +     help
> > > > > > > +       Enable mbedtls X509 library
> > > > > > > +
> > > > > > > +config MBEDTLS_LIB_TLS
> > > > > > > +     bool "TLS library"
> > > > > > > +     help
> > > > > > > +       Enable mbedtls TLS library
> > > > > > > +
> > > > > > > +endif # MBEDTLS_LIB
> > > > > >
> > > > > > We need much more granularity here, and to re-think some existing
> > > > > > symbols too perhaps. What we should be able to do is pick mbedTLS
> > or
> > > > > > "legacy SW implementation" or "HW implementation" for the various
> > > > > > algorithms, and that in turn can have some higher level grouping
> > to it.
> > > > > > This should then negate a bunch of the Makefile work you're doing
> > as we
> > > > > > won't have CONFIG_SHA256 enabled as we'll have
> > > > CONFIG_MBEDTLS_LIB_SHA256
> > > > > > or whatever enabled.
> > > > > >
> > > > >
> > > > > I think we should use CONFIG_MBEDTLS_LIB_[CRYPTO,X509,TLS] for
> > high-level
> > > > > grouping.
> > > > > Underneath, the CONFIG_SHA[1,256,512] switches (and other crypto
> > options)
> > > > > can be
> > > > > used as sub build options in both MbedTLS and "legacy libs".
> > > > >
> > > > > Take hash as an example, if the users prefer to use MbedTLS other
> > than
> > > > > "legacy libs" for
> > > > > hash operation, CONFIG_MBEDTLS_LIB_CRYPTO should be defined as the
> > main
> > > > > switch
> > > > > (the users can still prefer to use "legacy libs" for X509 by
> > > > > keeping  CONFIG_MBEDTLS_LIB_X509
> > > > > disabled).
> > > > > Then enable the algorithms they need (e.g. CONFIG_SHA256) - the
> > algorithm
> > > > > options works
> > > > > for both MbedTLS and "legacy libs".
> > > > >
> > > > > HW implementations with MbedTLS (aka, Alternative algorithms in
> > MbedTLS)
> > > > is
> > > > > another
> > > > > topic which is not covered in this patch set (It needs to migrate
> > each
> > > > > vendor's solution under
> > > > > MbedTLS alternative algorithm).
> > > > > Current patch set is focused on SW implementation with MbedTLS.
> > > >
> > > > The "easy" problem with what's in v3 is that X509 and CRYPTO are
> > > > select'd under the main heading.
> > >
> > > Not sure if I get what you mentioned, currently all MbedTLS options are
> > > under
> > > Library routines > Security support
> > > Do you think we should keep them in other places?
> > >
> > >
> > > > The harder problem is that we
> > > > intentionally have granularity for SHA256, SHA512, etc, etc and all of
> > > > that goes away with the current Kconfig option if you select mbedTLS.
> > We
> > > > need to bring that back. And we shouldn't need to have all of the ifneq
> > > > statements in Makefiles because both CONFIG_SHA256 and
> > > > CONFIG_MBEDLTS_LIB_CRYPTO_SHA256 will not be true (Or possibly,
> > > > CONFIG_SHA256 gates things U-Boot's internal API for sha256'ing
> > > > something and CONFIG_LEGACY_SHA256 controls building lib/sha256.c).
> > > >
> > > > I think we should not introduce new ones like CONFIG_LEGACY_,
> > > CONFIG_SHA[1,256,512] should be used no matter whether MbedTLS is
> > > enabled or not.
> > > I understand your concern, I will bring CONFIG_SHA[1,256,512] back when
> > > MbedTLS is enabled. Those options should control the options in the
> > MbedTLS
> > > default config file.
> >
> > My concern is that we do not have the correct level of granularity, and
> > that can partly be seen by the number of ifneq(...) statements being
> > added around already conditional logic. We should have almost none of
> > those, in the end, is what I'm saying. We have a mechanism for
> > configuring the build, Kconfig, and that should drive the decisions as
> > much as possible.
>
> The `ifneq(ONFIG_MBEDTLS_LIB_*)` statements are due to the fact that we
> still
> need lib/Makefile and lib/crypto/Makefile when building hash and x509
> stuffs with
> MbedTLS enabled.
> To address this, I guess we have to first refactor all "legacy libs" that
> will be replaced
> by MbedTLS:
> Move md5, sha* from lib to to a new dir lib/hash and move public_key,
> rsapubkey*,
> rsa_helper, x509*, pkcs7*,mscode* from lib/crypto to a new dir lib/x509.
> When they are all independent modules with separated Makefile, we can remove
> `ifneq(ONFIG_MBEDTLS_LIB_*)` and all can be driven in lib/Makefile.
> 
> Is that something you expect?
> If yes I can do this for v4, or put it into another prerequisite/refactor
> series.

We should not need to do that because we should not have CONFIG_SHA256
set if we are not building lib/sha256.c at that stage, is what I'm
saying. CONFIG_LEGACY_SHA256 should control it and CONFIG_SHA256 should
control the API and CONFIG_MBEDTLS_LIB_CRYPTO_SHA256 should control the
mbedTLS version, and this should either expand on, or if needed
update/rework, the mechanism that lets us also have say
CONFIG_ARMV8_CE_SHA256 for using that HW based version of the support.

-- 
Tom

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