[PATCH v4 2/6] rsa: add CONFIG_RSA_VERIFY_WITH_PKEY config

[AKASHI Takahiro <takahiro.akashi@linaro.org>]

On Wed, Jan 08, 2020 at 01:35:13PM +0100, Heinrich Schuchardt wrote:
> On 11/21/19 1:11 AM, AKASHI Takahiro wrote:
> >In the next couple of commits, under new CONFIG_RSA_VERIFY_WITH_PKEY,
> >rsa_verify() will be extended to be able to perform RSA decryption without
> >additional RSA key properties from FIT image, i.e. rr and n0inv.
> >
> >Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> >Reviewed-by: Simon Glass <sjg@chromium.org>
> 
> The patch series does not build for some configurations.
> 
> >---
> >  lib/rsa/Kconfig | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> >
> >diff --git a/lib/rsa/Kconfig b/lib/rsa/Kconfig
> >index 03ffa2969048..71e4c06bf883 100644
> >--- a/lib/rsa/Kconfig
> >+++ b/lib/rsa/Kconfig
> >@@ -30,6 +30,20 @@ config RSA_VERIFY
> >  	help
> >  	  Add RSA signature verification support.
> >
> >+config RSA_VERIFY_WITH_PKEY
> 
> For CONFIG_RSA_VERIFY_WITH_PKEY=y and CONFIG_RSA_PUBLIC_KEY_PARSER=n
> I get an error:

This error is inevitable as both RSA_VERIFY_WITH_PKEY and
RSA_PUBLIC_KEY_PARSER are "select"able configurations with
visible prompts and then
we should generally avoid potential illegal configurations;
The one should NOT forcibly select the other as the kernel kconfig
document suggests.

#  Note:
#        select should be used with care. select will force
#        a symbol to a value without visiting the dependencies.
#        By abusing select you are able to select a symbol FOO even
#        if FOO depends on BAR that is not set.
#        In general use select only for non-visible symbols
#        (no prompts anywhere) and for symbols with no dependencies.
#        That will limit the usefulness but on the other hand avoid
#        the illegal configurations all over.

-Takahiro Akashi


> lib/rsa/rsa-keyprop.c:669: undefined reference to `rsa_parse_pub_key'
> 
> RSA_PUBLIC_KEY_PARSER depends on
> ASYMMETRIC_KEY_TYPE [=n] && ASYMMETRIC_PUBLIC_KEY_SUBTYPE [=n]
> 
> Please, fix the dependencies.
> 
> Best regards
> 
> Heinrich
> 
> >+	bool "Execute RSA verification without key parameters from FDT"
> >+	depends on RSA
> >+	help
> >+	  The standard RSA-signature verification code (FIT_SIGNATURE) uses
> >+	  pre-calculated key properties, that are stored in fdt blob, in
> >+	  decrypting a signature.
> >+	  This does not suit the use case where there is no way defined to
> >+	  provide such additional key properties in standardized form,
> >+	  particularly UEFI secure boot.
> >+	  This options enables RSA signature verification with a public key
> >+	  directly specified in image_sign_info, where all the necessary
> >+	  key properties will be calculated on the fly in verification code.
> >+
> >  config RSA_SOFTWARE_EXP
> >  	bool "Enable driver for RSA Modular Exponentiation in software"
> >  	depends on DM
> >