[RFC PATCH v1] lib: rsa: introduce RSA_SOFTWARE_EXP_TINY

[RFC PATCH v1] lib: rsa: introduce RSA_SOFTWARE_EXP_TINY

[Igor Opaniuk]

From: Igor Opaniuk <igor.opaniuk@foundries.io>

Introduce RSA_SOFTWARE_EXP_TINY Kconfig option, which does not require
DM to be enabled. This can be handy on devices, where SPL + signed
U-Boot FIT image setup is used, where it isn't possible to enable SPL_DM
mainly due to SRAM size constraits.

For example, on iMX8MM with this option enabled and SPL_DM disabled
it's possible to save almost 11Kb:

With RSA_SOFTWARE_EXP_TINY enabled:
spl/u-boot-spl-nodtb.bin 99824

Without:
spl/u-boot-spl-nodtb.bin 111088

Signed-off-by: Igor Opaniuk <igor.opaniuk@foundries.io>
---

 lib/rsa/Kconfig      | 11 ++++++++++-
 lib/rsa/rsa-verify.c |  8 ++++----
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/lib/rsa/Kconfig b/lib/rsa/Kconfig
index a90d67e5a8..03692b73bb 100644
--- a/lib/rsa/Kconfig
+++ b/lib/rsa/Kconfig
@@ -1,7 +1,8 @@
 config RSA
 	bool "Use RSA Library"
 	select RSA_FREESCALE_EXP if FSL_CAAM && !ARCH_MX7 && !ARCH_MX6 && !ARCH_MX5
-	select RSA_SOFTWARE_EXP if !RSA_FREESCALE_EXP
+	select RSA_SOFTWARE_EXP if !RSA_FREESCALE_EXP && DM
+	select RSA_SOFTWARE_EXP_TINY if !RSA_FREESCALE_EXP && !DM
 	help
 	  RSA support. This enables the RSA algorithm used for FIT image
 	  verification in U-Boot.
@@ -45,6 +46,14 @@ config RSA_VERIFY_WITH_PKEY
 	  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_TINY
+	bool "Enable non-DM RSA Modular Exponentiation software implementation"
+	help
+	  Enable modular exponentiation implementation in software, which
+	  does not require Driver Model to be enabled. This is a RSA algorithm
+	  used in FIT image verification. It required RSA Key as input.
+	  See doc/uImage.FIT/signature.txt for more details.
+
 config RSA_SOFTWARE_EXP
 	bool "Enable driver for RSA Modular Exponentiation in software"
 	depends on DM
diff --git a/lib/rsa/rsa-verify.c b/lib/rsa/rsa-verify.c
index aee76f42d5..0162253636 100644
--- a/lib/rsa/rsa-verify.c
+++ b/lib/rsa/rsa-verify.c
@@ -319,7 +319,7 @@ static int rsa_verify_key(struct image_sign_info *info,
 			  const uint32_t key_len)
 {
 	int ret;
-#if !defined(USE_HOSTCC)
+#if !(defined(USE_HOSTCC) || defined(RSA_SOFTWARE_EXP_TINY))
 	struct udevice *mod_exp_dev;
 #endif
 	struct checksum_algo *checksum = info->checksum;
@@ -346,7 +346,9 @@ static int rsa_verify_key(struct image_sign_info *info,
 	uint8_t buf[sig_len];
 	hash_len = checksum->checksum_len;
 
-#if !defined(USE_HOSTCC)
+#if defined(USE_HOSTCC) || defined(RSA_SOFTWARE_EXP_TINY)
+	ret = rsa_mod_exp_sw(sig, sig_len, prop, buf);
+#else
 	ret = uclass_get_device(UCLASS_MOD_EXP, 0, &mod_exp_dev);
 	if (ret) {
 		printf("RSA: Can't find Modular Exp implementation\n");
@@ -354,8 +356,6 @@ static int rsa_verify_key(struct image_sign_info *info,
 	}
 
 	ret = rsa_mod_exp(mod_exp_dev, sig, sig_len, prop, buf);
-#else
-	ret = rsa_mod_exp_sw(sig, sig_len, prop, buf);
 #endif
 	if (ret) {
 		debug("Error in Modular exponentation\n");
-- 
2.25.1

[RFC PATCH v1] lib: rsa: introduce RSA_SOFTWARE_EXP_TINY

[Simon Glass]

Hi Igor,

On Fri, 16 Apr 2021 at 01:10, Igor Opaniuk <igor.opaniuk@foundries.io> wrote:
>
> From: Igor Opaniuk <igor.opaniuk@foundries.io>
>
> Introduce RSA_SOFTWARE_EXP_TINY Kconfig option, which does not require
> DM to be enabled. This can be handy on devices, where SPL + signed
> U-Boot FIT image setup is used, where it isn't possible to enable SPL_DM
> mainly due to SRAM size constraits.
>
> For example, on iMX8MM with this option enabled and SPL_DM disabled
> it's possible to save almost 11Kb:

That seems a lot...do you have OF_PLATDATA enabled?

>
> With RSA_SOFTWARE_EXP_TINY enabled:
> spl/u-boot-spl-nodtb.bin 99824
>
> Without:
> spl/u-boot-spl-nodtb.bin 111088
>
> Signed-off-by: Igor Opaniuk <igor.opaniuk@foundries.io>
> ---
>
>  lib/rsa/Kconfig      | 11 ++++++++++-
>  lib/rsa/rsa-verify.c |  8 ++++----
>  2 files changed, 14 insertions(+), 5 deletions(-)

Regards,
Simon

[RFC PATCH v1] lib: rsa: introduce RSA_SOFTWARE_EXP_TINY

[Igor Opaniuk]

Hi Simon,

On Thu, Apr 29, 2021 at 7:10 PM Simon Glass <sjg@chromium.org> wrote:
>
> Hi Igor,
>
> On Fri, 16 Apr 2021 at 01:10, Igor Opaniuk <igor.opaniuk@foundries.io> wrote:
> >
> > From: Igor Opaniuk <igor.opaniuk@foundries.io>
> >
> > Introduce RSA_SOFTWARE_EXP_TINY Kconfig option, which does not require
> > DM to be enabled. This can be handy on devices, where SPL + signed
> > U-Boot FIT image setup is used, where it isn't possible to enable SPL_DM
> > mainly due to SRAM size constraits.
> >
> > For example, on iMX8MM with this option enabled and SPL_DM disabled
> > it's possible to save almost 11Kb:
>
> That seems a lot...do you have OF_PLATDATA enabled?
Nope, it's not enabled.
I've managed to get these numbers when experimenting with NXP U-Boot fork,
which is based on 2020.04.

I also checked a while ago iMX6ULL mainline U-Boot with this patch, and size
decrease was around 4-5 Kb, which basically is also not bad (considering 64Kb
SPL size limitation for this SoC).

>
> >
> > With RSA_SOFTWARE_EXP_TINY enabled:
> > spl/u-boot-spl-nodtb.bin 99824
> >
> > Without:
> > spl/u-boot-spl-nodtb.bin 111088
> >
> > Signed-off-by: Igor Opaniuk <igor.opaniuk@foundries.io>
> > ---
> >
> >  lib/rsa/Kconfig      | 11 ++++++++++-
> >  lib/rsa/rsa-verify.c |  8 ++++----
> >  2 files changed, 14 insertions(+), 5 deletions(-)
>
> Regards,
> Simon

Thanks

-- 
Best regards - Freundliche Gr?sse - Meilleures salutations

Igor Opaniuk
Embedded Software Engineer
T:  +380 938364067
E: igor.opaniuk at foundries.io
W: www.foundries.io

[RFC PATCH v1] lib: rsa: introduce RSA_SOFTWARE_EXP_TINY

[Simon Glass]

Hi Igor,

On Wed, 5 May 2021 at 06:58, Igor Opaniuk <igor.opaniuk@foundries.io> wrote:
>
> Hi Simon,
>
> On Thu, Apr 29, 2021 at 7:10 PM Simon Glass <sjg@chromium.org> wrote:
> >
> > Hi Igor,
> >
> > On Fri, 16 Apr 2021 at 01:10, Igor Opaniuk <igor.opaniuk@foundries.io> wrote:
> > >
> > > From: Igor Opaniuk <igor.opaniuk@foundries.io>
> > >
> > > Introduce RSA_SOFTWARE_EXP_TINY Kconfig option, which does not require
> > > DM to be enabled. This can be handy on devices, where SPL + signed
> > > U-Boot FIT image setup is used, where it isn't possible to enable SPL_DM
> > > mainly due to SRAM size constraits.
> > >
> > > For example, on iMX8MM with this option enabled and SPL_DM disabled
> > > it's possible to save almost 11Kb:
> >
> > That seems a lot...do you have OF_PLATDATA enabled?
> Nope, it's not enabled.

I think you should look at that first. It is likely to give a much
larger benefit.

> I've managed to get these numbers when experimenting with NXP U-Boot fork,
> which is based on 2020.04.
>
> I also checked a while ago iMX6ULL mainline U-Boot with this patch, and size
> decrease was around 4-5 Kb, which basically is also not bad (considering 64Kb
> SPL size limitation for this SoC).

OK I see, but if we did this with every subsystem won't we end up with
chaos? There will be cases where driver model is impossible, but with
64KB (which I assume you mean) I would hope that we could avoid it.

>
> >
> > >
> > > With RSA_SOFTWARE_EXP_TINY enabled:
> > > spl/u-boot-spl-nodtb.bin 99824
> > >
> > > Without:
> > > spl/u-boot-spl-nodtb.bin 111088
> > >
> > > Signed-off-by: Igor Opaniuk <igor.opaniuk@foundries.io>
> > > ---
> > >
> > >  lib/rsa/Kconfig      | 11 ++++++++++-
> > >  lib/rsa/rsa-verify.c |  8 ++++----
> > >  2 files changed, 14 insertions(+), 5 deletions(-)

Regards,
Simon