[PATCH] tools: Use a single target-independent config to enable OpenSSL

Alexandru Gagniuc mr.nuke.me at gmail.com
Mon May 24 22:23:17 CEST 2021

Host tool features, such as mkimage's ability to sign FIT images were
enabled or disabled based on the target configuration. However, this
misses the point of a target-agnostic host tool.

A target's ability to verify FIT signatures is independent of
mkimage's ability to create those signatures. In fact, u-boot's build
system doesn't sign images. The target code can be successfully built
without relying on any ability to sign such code.

Conversely, mkimage's ability to sign images does not require that
those images will only work on targets which support FIT verification.
Linking mkimage cryptographic features to target support for FIT
verification is misguided.

Without loss of generality, we can say that host features are and
should be independent of target features.

While we prefer that a host tool always supports the same feature set,
we recognize the following
  - some users prefer to build u-boot without a dependency on OpenSSL.
  - some distros prefer to ship mkimage without linking to OpenSSL

To allow these use cases, introduce a host-only Kconfig which is used
to select or deselect libcrypto support. Some mkimage features or some
host tools might not be available, but this shouldn't affect the
u-boot build.

I also considered setting the default of this config based on
FIT_SIGNATURE. While it would preserve the old behaviour it's also
contrary to the goals of this change. I decided to enable it by
default, so that the default build yields the most feature-complete

Signed-off-by: Alexandru Gagniuc <mr.nuke.me at gmail.com>

This patch is designed to apply on top of
    [PATCH v2 00/18] image: Reduce #ifdef abuse in image code

 tools/Kconfig  | 11 +++++++++++
 tools/Makefile | 46 ++++++++++++++++++++++++++++++----------------
 2 files changed, 41 insertions(+), 16 deletions(-)

diff --git a/tools/Kconfig b/tools/Kconfig
index b2f5012240..214932ae30 100644
--- a/tools/Kconfig
+++ b/tools/Kconfig
@@ -9,4 +9,15 @@ config MKIMAGE_DTC_PATH
 	  some cases the system dtc may not support all required features
 	  and the path to a different version should be given here.
+	bool "Use OpenSSL's libcrypto library for host tools"
+	default y
+	help
+	  Cryptographic signature, verification, and encryption of images is
+	  provided by host tools using OpenSSL's libcrypto. Select 'n' here if
+	  you wish to build host tools without OpenSSL. mkimage will not have
+	  the ability to sign images.
+	  This selection does not affect target features, such as runtime FIT
+	  signature verification.
diff --git a/tools/Makefile b/tools/Makefile
index 722355e984..1f30a06cce 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -3,6 +3,25 @@
 # (C) Copyright 2000-2006
 # Wolfgang Denk, DENX Software Engineering, wd at denx.de.
+# A note on target vs host configuration:
+# Host tools can be used across multiple targets, or different configurations
+# of the same target. Thus, host tools must be able to handle any combination
+# of target configurations. To prevent having different variations of the same
+# tool, the tool build options may not depend on target configuration.
+# Some linux distributions package these utilities as u-boot-tools, and it
+# would be unmaintainable to have a different tool variation for each
+# arch or configuration.
+# A couple of simple rules:
+# 1) Do not use target CONFIG_* options to enable or disable features in host
+#    tools. Only use the configs from tools/Kconfig
+# 2) It's okay to use target configs to disable building specific tools.
+#    That's as long as the features of those tools aren't modified.
 # Enable all the config-independent tools
 ifneq ($(HOST_TOOLS_ALL),)
@@ -53,30 +72,30 @@ hostprogs-y += mkenvimage
 mkenvimage-objs := mkenvimage.o os_support.o lib/crc32.o
 hostprogs-y += dumpimage mkimage
-hostprogs-$(CONFIG_FIT_SIGNATURE) += fit_info fit_check_sign
+hostprogs-$(CONFIG_TOOLS_USE_LIBCRYPTO) += fit_info fit_check_sign
 hostprogs-$(CONFIG_CMD_BOOTEFI_SELFTEST) += file2include
 FIT_OBJS-$(CONFIG_FIT) := fit_common.o fit_image.o image-host.o common/image-fit.o
-FIT_SIG_OBJS-$(CONFIG_FIT_SIGNATURE) := image-sig-host.o common/image-fit-sig.o
-FIT_CIPHER_OBJS-$(CONFIG_FIT_CIPHER) := common/image-cipher.o
+FIT_SIG_OBJS-$(CONFIG_TOOLS_USE_LIBCRYPTO) := image-sig-host.o common/image-fit-sig.o
 # The following files are synced with upstream DTC.
 # Use synced versions from scripts/dtc/libfdt/.
 LIBFDT_OBJS := $(addprefix libfdt/, fdt.o fdt_ro.o fdt_wip.o fdt_sw.o fdt_rw.o \
 		fdt_strerror.o fdt_empty_tree.o fdt_addresses.o fdt_overlay.o)
-RSA_OBJS-$(CONFIG_FIT_SIGNATURE) := $(addprefix lib/rsa/, \
+RSA_OBJS-$(CONFIG_TOOLS_USE_LIBCRYPTO) := $(addprefix lib/rsa/, \
 					rsa-sign.o rsa-verify.o \
-ECDSA_OBJS-$(CONFIG_FIT_SIGNATURE) := $(addprefix lib/ecdsa/, ecdsa-libcrypto.o)
+ECDSA_OBJS-$(CONFIG_TOOLS_USE_LIBCRYPTO) := $(addprefix lib/ecdsa/, ecdsa-libcrypto.o)
-AES_OBJS-$(CONFIG_FIT_CIPHER) := $(addprefix lib/aes/, \
+AES_OBJS-$(CONFIG_TOOLS_USE_LIBCRYPTO) := $(addprefix lib/aes/, \
 					aes-encrypt.o aes-decrypt.o)
 # Cryptographic helpers that depend on openssl/libcrypto
-LIBCRYPTO_OBJS-$(CONFIG_FIT_SIGNATURE) := $(addprefix lib/, \
 ROCKCHIP_OBS = lib/rc4.o rkcommon.o rkimage.o rksd.o rkspi.o
@@ -136,22 +155,17 @@ fit_info-objs   := $(dumpimage-mkimage-objs) fit_info.o
 fit_check_sign-objs   := $(dumpimage-mkimage-objs) fit_check_sign.o
 file2include-objs := file2include.o
 # Add CONFIG_MXS into host CFLAGS, so we can check whether or not register
 # the mxsimage support within tools/mxsimage.c .
 # This affects include/image.h, but including the board config file
 # is tricky, so manually define this options here.
-# This affects include/image.h, but including the board config file
-# is tricky, so manually define this options here.
@@ -164,7 +178,7 @@ HOSTCFLAGS_kwbimage.o += -DCONFIG_KWB_SECURE
 # MXSImage needs LibSSL
 HOSTCFLAGS_kwbimage.o += \
 	$(shell pkg-config --cflags libssl libcrypto 2> /dev/null || echo "")
 HOSTLDLIBS_mkimage += \

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