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 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.

-- 
Tom

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