Re: [PATCH] mkimage: use environment variable MKIMAGE_SIGN_PIN to set pin for OpenSSL Engine

[Alex G.]

Hi Marc,

On 7/23/21 3:17 PM, Marc Kleine-Budde wrote:
This patch adds the possibility to pass the PIN the OpenSSL Engine
used during signing via the environment variable MKIMAGE_SIGN_PIN.
This follows the approach used during kernel module
signing ("KBUILD_SIGN_PIN") or UBIFS image
signing ("MKIMAGE_SIGN_PIN").

I think the preferred approach would have been to add a flag to mkimage, 
similar to "-N => openssl engine to use for signing". Environment 
variables are rarely used to talk to tools, and not very intuitive. I 
can only really think of NO_SDL=1 being used by u-boot.

Since this patch already made it, I hope you have the bandwidth to look 
at converting this to a mkimage flag.

Alex

Signed-off-by: Marc Kleine-Budde <m...@pengutronix.de>
---
  doc/uImage.FIT/signature.txt |  4 ++--
  lib/rsa/rsa-sign.c           | 11 +++++++++++
  2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/doc/uImage.FIT/signature.txt b/doc/uImage.FIT/signature.txt
index 7cb1c15e5e15..61a72db3c74f 100644
--- a/doc/uImage.FIT/signature.txt
+++ b/doc/uImage.FIT/signature.txt
@@ -533,8 +533,8 @@ Generic engine key ids:
  or
    "<key-name-hint>"
  
-As mkimage does not at this time support prompting for passwords HSM may need
-key preloading wrapper to be used when invoking mkimage.
+In order to set the pin in the HSM, an environment variable "MKIMAGE_SIGN_PIN"
+can be specified.
  
  The following examples use the Nitrokey Pro using pkcs11 engine. Instructions
  for other devices may vary.
diff --git a/lib/rsa/rsa-sign.c b/lib/rsa/rsa-sign.c
index f4ed11e74a4a..49abec6c83fb 100644
--- a/lib/rsa/rsa-sign.c
+++ b/lib/rsa/rsa-sign.c
@@ -338,6 +338,7 @@ static int rsa_init(void)
  
  static int rsa_engine_init(const char *engine_id, ENGINE **pe)
  {
+       const char *key_pass;
        ENGINE *e;
        int ret;
  
@@ -362,10 +363,20 @@ static int rsa_engine_init(const char *engine_id, ENGINE **pe)
                goto err_set_rsa;
        }
  
+	key_pass = getenv("MKIMAGE_SIGN_PIN");
+       if (key_pass) {
+               if (!ENGINE_ctrl_cmd_string(e, "PIN", key_pass, 0)) {
+                       fprintf(stderr, "Couldn't set PIN\n");
+                       ret = -1;
+                       goto err_set_pin;
+               }
+       }
+
        *pe = e;
  
  	return 0;
  
+err_set_pin:
  err_set_rsa:
        ENGINE_finish(e);
  err_engine_init: