[PATCH v4 2/2] binman: add fast authentication method for i.MX8M signing

[Brian Ruley]

Using the PKI tree with SRKs as intermediate CA isn't necessary or even
desirable in some situations (boot time, for example). Add the possibility
to use the "fast authentication" method where the image and CSF are both
signed using the SRK [1, p.63].

[1] https://community.nxp.com/pwmxy87654/attachments/pwmxy87654/imx-processors/202591/1/CST_UG.pdf

Signed-off-by: Brian Ruley <brian.ruley at gehealthcare.com>
Cc: Marek Vasut <marex at denx.de>
---
Changes for v2:
- fixed default key length (s/2048/4096) for srk-crt node
Changes for v3:
- code formatting
Changes for v4:
- fix spelling in commit message
- code formatting

 tools/binman/etype/nxp_imx8mcst.py | 34 +++++++++++++++++++++++-------
 1 file changed, 26 insertions(+), 8 deletions(-)

diff --git a/tools/binman/etype/nxp_imx8mcst.py b/tools/binman/etype/nxp_imx8mcst.py
index bd5a5d805f..a7d8db4eec 100644
--- a/tools/binman/etype/nxp_imx8mcst.py
+++ b/tools/binman/etype/nxp_imx8mcst.py
@@ -38,6 +38,9 @@ CSF_CONFIG_TEMPLATE = f'''
   File = "SRK_1_2_3_4_table.bin"
   Source index = 0
 
+[Install NOCAK]
+  File = "SRK1_{KEY_NAME}.pem"
+
 [Install CSFK]
   File = "CSF1_1_{KEY_NAME}.pem"
 
@@ -74,12 +77,19 @@ class Entry_nxp_imx8mcst(Entry_mkimage):
         self.srk_table = os.getenv(
             'SRK_TABLE', fdt_util.GetString(self._node, 'nxp,srk-table',
                                             'SRK_1_2_3_4_table.bin'))
-        self.csf_crt = os.getenv(
-            'CSF_KEY', fdt_util.GetString(self._node, 'nxp,csf-crt',
-                                          f'CSF1_1_{KEY_NAME}.pem'))
-        self.img_crt = os.getenv(
-            'IMG_KEY', fdt_util.GetString(self._node, 'nxp,img-crt',
-                                          f'IMG1_1_{KEY_NAME}.pem'))
+        self.fast_auth = fdt_util.GetBool(self._node, 'nxp,fast-auth')
+        if not self.fast_auth:
+            self.csf_crt = os.getenv(
+                'CSF_KEY', fdt_util.GetString(self._node, 'nxp,csf-crt',
+                                              f'CSF1_1_{KEY_NAME}.pem'))
+            self.img_crt = os.getenv(
+                'IMG_KEY', fdt_util.GetString(self._node, 'nxp,img-crt',
+                                              f'IMG1_1_{KEY_NAME}.pem'))
+        else:
+            self.srk_crt = os.getenv(
+                'SRK_KEY', fdt_util.GetString(self._node, 'nxp,srk-crt',
+                                              f'SRK1_{KEY_NAME}.pem'))
+
         self.unlock = fdt_util.GetBool(self._node, 'nxp,unlock')
         self.ReadEntries()
 
@@ -133,8 +143,16 @@ class Entry_nxp_imx8mcst(Entry_mkimage):
         # Load configuration template and modify keys of interest
         config.read_string(CSF_CONFIG_TEMPLATE)
         config['Install SRK']['File']  = f'"{self.srk_table}"'
-        config['Install CSFK']['File'] = f'"{self.csf_crt}"'
-        config['Install Key']['File']  = f'"{self.img_crt}"'
+        if not self.fast_auth:
+            config.remove_section('Install NOCAK')
+            config['Install CSFK']['File'] = f'"{self.csf_crt}"'
+            config['Install Key']['File']  = f'"{self.img_crt}"'
+        else:
+            config.remove_section('Install CSFK')
+            config.remove_section('Install Key')
+            config['Install NOCAK']['File'] = f'"{self.srk_crt}"'
+            config['Authenticate Data']['Verification index'] = '0'
+
         config['Authenticate Data']['Blocks'] = \
             f'{signbase:#x} 0 {len(data):#x} "{output_dname}"'
 
-- 
2.39.5