[PATCH v2 6/7] ima: Define new template evm-sig

Roberto Sassu roberto.sassu at huawei.com
Fri May 28 07:38:11 UTC 2021

With the recent introduction of the evmsig template field, remote verifiers
can obtain the EVM portable signature instead of the IMA signature, to
verify file metadata.

After introducing the new fields to include file metadata in the
measurement list, this patch finally defines the evm-sig template, whose
format is:


xattrnames, xattrlengths and xattrvalues are populated only from defined
EVM protected xattrs, i.e. the ones that EVM considers to verify the
portable signature. xattrnames and xattrlengths are populated only if the
xattr is present.

xattrnames and xattrlengths are not necessary for verifying the EVM
portable signature, but they are included for completeness of information,
if a remote verifier wants to infer more from file metadata.

Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
 Documentation/security/IMA-templates.rst | 1 +
 security/integrity/ima/ima_template.c    | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/Documentation/security/IMA-templates.rst b/Documentation/security/IMA-templates.rst
index 6a58760a0a35..5adc22f99496 100644
--- a/Documentation/security/IMA-templates.rst
+++ b/Documentation/security/IMA-templates.rst
@@ -91,6 +91,7 @@ Below, there is the list of defined template descriptors:
  - "ima-sig": its format is ``d-ng|n-ng|sig``;
  - "ima-buf": its format is ``d-ng|n-ng|buf``;
  - "ima-modsig": its format is ``d-ng|n-ng|sig|d-modsig|modsig``;
+ - "evm-sig": its format is ``d-ng|n-ng|evmsig|xattrnames|xattrlengths|xattrvalues|iuid|igid|imode``;
diff --git a/security/integrity/ima/ima_template.c b/security/integrity/ima/ima_template.c
index 159a31d2fcdf..be435efe6122 100644
--- a/security/integrity/ima/ima_template.c
+++ b/security/integrity/ima/ima_template.c
@@ -22,6 +22,9 @@ static struct ima_template_desc builtin_templates[] = {
 	{.name = "ima-sig", .fmt = "d-ng|n-ng|sig"},
 	{.name = "ima-buf", .fmt = "d-ng|n-ng|buf"},
 	{.name = "ima-modsig", .fmt = "d-ng|n-ng|sig|d-modsig|modsig"},
+	{.name = "evm-sig",
+	 .fmt = "d-ng|n-ng|evmsig|"
+		"xattrnames|xattrlengths|xattrvalues|iuid|igid|imode"},
 	{.name = "", .fmt = ""},	/* placeholder for a custom format */

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