[RFC PATCH v1 05/11] attestation: Make the evidence-get challenge attribute optional

["Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org>]

The following PCI/TSM integration retrieves cached evidence through
EVIDENCE_GET. A challenge is used when refreshing that evidence, not
when reading the current cache, so requiring evidence.challenge forces
callers to supply an otherwise unused empty attribute.

Make evidence.challenge optional in the common request schema.

Cc: Jiri Pirko <jiri@resnulli.us>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Jonathan Cameron <jic23@kernel.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
 Documentation/ctlv/abi/ctlv-attestation.yaml  |  2 +-
 .../ctlv/specs/ctlv-attestation.yaml          |  2 +-
 Documentation/driver-api/attestation.rst      | 12 ++++++++++
 drivers/attestation/core/ctlv.c               |  7 +++---
 .../generated/ctlv_attestation_gen.c          |  4 ++--
 .../generated/ctlv_attestation_gen.h          | 22 +++++++++----------
 .../selftests/attestation/attestation_test.c  |  4 +---
 .../ctlv_attestation_sim_user_gen.c           | 20 ++++++++---------
 .../ctlv_attestation_tdx_user_gen.c           | 20 ++++++++---------
 .../attestation/ctlv_attestation_user_gen.c   | 20 ++++++++---------
 .../attestation/tdx_attestation_test.c        |  9 ++++++--
 11 files changed, 69 insertions(+), 53 deletions(-)

diff --git a/Documentation/ctlv/abi/ctlv-attestation.yaml b/Documentation/ctlv/abi/ctlv-attestation.yaml
index 018417fe3682..373614f97021 100644
--- a/Documentation/ctlv/abi/ctlv-attestation.yaml
+++ b/Documentation/ctlv/abi/ctlv-attestation.yaml
@@ -172,12 +172,12 @@ ops:
     abi: {id: 2, type: action, availability: dynamic, optional: true}
     request:
       attrs:
-        - evidence.challenge
         - evidence.object:
             attrs: [evidence.blob-class, evidence.format,
                     evidence.representation, evidence.data]
             optional-attrs: [evidence.blob-instance, evidence.hash-algo]
       optional-attrs:
+        - evidence.challenge
         - device.generation
         - evidence.selection: {attrs: [mr.id, evidence.hash-algo]}
         - evidence.privlevel
diff --git a/Documentation/ctlv/specs/ctlv-attestation.yaml b/Documentation/ctlv/specs/ctlv-attestation.yaml
index 98d6753d878f..e2371813ec25 100644
--- a/Documentation/ctlv/specs/ctlv-attestation.yaml
+++ b/Documentation/ctlv/specs/ctlv-attestation.yaml
@@ -320,9 +320,9 @@ attr-sets:
 
   - name: evidence-request
     attrs:
-      - evidence.challenge
       - evidence.object
     optional-attrs:
+      - evidence.challenge
       - device.generation
       - evidence.selection
       - evidence.privlevel
diff --git a/Documentation/driver-api/attestation.rst b/Documentation/driver-api/attestation.rst
index 06af8df23a46..d23b7c65d35b 100644
--- a/Documentation/driver-api/attestation.rst
+++ b/Documentation/driver-api/attestation.rst
@@ -29,6 +29,18 @@ dynamic topology retains handles returned by ``attestation_mr_create()`` and
 passes each handle exactly once to ``attestation_mr_destroy()``.  Property
 storage remains valid for the handle's lifetime.
 
+Evidence retrieval
+==================
+
+``EVIDENCE_GET`` requests may omit ``evidence.challenge``. The core treats
+an omitted challenge as zero bytes and still enforces the provider's minimum
+and maximum challenge lengths. Providers that require a challenge, such as
+TDX, retain that requirement.
+
+Cached-evidence providers such as PCI/TSM can fetch the current evidence
+without a challenge. A challenge for fresh PCI/TSM evidence belongs to the
+separate evidence-refresh operation.
+
 Per-instance features
 =====================
 
diff --git a/drivers/attestation/core/ctlv.c b/drivers/attestation/core/ctlv.c
index f0238c4c4cf2..50aa3cb84ddd 100644
--- a/drivers/attestation/core/ctlv.c
+++ b/drivers/attestation/core/ctlv.c
@@ -350,13 +350,14 @@ static int attestation_evidence_request_decode(struct attestation *att, struct c
 					       struct ctlv_cursor *options)
 {
 	const struct attestation_evidence_caps *caps = att->provider->evidence_caps;
-	u32 challenge_length, guid_length;
+	u32 challenge_length = 0, guid_length;
 	const void *guid;
 	bool service;
 	int ret;
 
-	decoded->challenge =
-		ctlv_attestation_evidence_get_evidence_challenge_get(request, &challenge_length);
+	if (ctlv_attestation_evidence_get_evidence_challenge_present(request))
+		decoded->challenge = ctlv_attestation_evidence_get_evidence_challenge_get(
+			request, &challenge_length);
 	decoded->challenge_length = challenge_length;
 	if (challenge_length < caps->min_challenge_length ||
 	    challenge_length > caps->max_challenge_length)
diff --git a/drivers/attestation/generated/ctlv_attestation_gen.c b/drivers/attestation/generated/ctlv_attestation_gen.c
index a858a84da135..0bd4bc76b718 100644
--- a/drivers/attestation/generated/ctlv_attestation_gen.c
+++ b/drivers/attestation/generated/ctlv_attestation_gen.c
@@ -49,9 +49,9 @@ static const struct ctlv_stub_schema device_get_reply_stub_schemas[] = {
 };
 
 static const struct ctlv_node_schema evidence_get_request_node_schemas[] = {
-	CTLV_NODE_SCHEMA_ROOT(1, 9, 2),
-	CTLV_NODE_SCHEMA_BINARY(CTLV_ATTESTATION_ATTR_EVIDENCE_CHALLENGE, 1, 0, 4096),
+	CTLV_NODE_SCHEMA_ROOT(1, 9, 1),
 	CTLV_NODE_SCHEMA_NEST(CTLV_ATTESTATION_ATTR_EVIDENCE_OBJECT, 16, 10, 6, 4),
+	CTLV_NODE_SCHEMA_BINARY(CTLV_ATTESTATION_ATTR_EVIDENCE_CHALLENGE, 1, 0, 4096),
 	CTLV_NODE_SCHEMA_UINT(CTLV_ATTESTATION_ATTR_DEVICE_GENERATION, 1, 0, U32_MAX),
 	CTLV_NODE_SCHEMA_NEST(CTLV_ATTESTATION_ATTR_EVIDENCE_SELECTION, 256, 16, 2, 2),
 	CTLV_NODE_SCHEMA_UINT(CTLV_ATTESTATION_ATTR_EVIDENCE_PRIVLEVEL, 1, 0, U32_MAX),
diff --git a/drivers/attestation/generated/ctlv_attestation_gen.h b/drivers/attestation/generated/ctlv_attestation_gen.h
index 95cb6a083633..bd55158d8819 100644
--- a/drivers/attestation/generated/ctlv_attestation_gen.h
+++ b/drivers/attestation/generated/ctlv_attestation_gen.h
@@ -81,15 +81,15 @@ CTLV_OP_DISABLE(ctlv_attestation_devsec_state_get, CTLV_ATTESTATION_OP_DEVSEC_ST
 CTLV_OP_PROVIDE(ctlv_attestation_mr_log_get, CTLV_ATTESTATION_OP_MR_LOG_GET)
 
 /* Reading a validated message. A blob has a resolver instead of a getter. */
+CTLV_IN_REF(ctlv_attestation_evidence_get_evidence_object, &ctlv_attestation_op_schemas[1].request,
+	    CTLV_ATTESTATION_ATTR_EVIDENCE_OBJECT, 0, 0, CTLV_SCHEMA_NEST)
+#define ctlv_attestation_evidence_get_evidence_object_for_each(_attr, _nest) \
+	CTLV_IN_FOR_EACH(ctlv_attestation_evidence_get_evidence_object, _attr, _nest)
 CTLV_IN_REF(ctlv_attestation_evidence_get_evidence_challenge,
-	    &ctlv_attestation_op_schemas[1].request, CTLV_ATTESTATION_ATTR_EVIDENCE_CHALLENGE, 0, 0,
+	    &ctlv_attestation_op_schemas[1].request, CTLV_ATTESTATION_ATTR_EVIDENCE_CHALLENGE, 0, 1,
 	    CTLV_SCHEMA_BINARY)
 CTLV_IN_HAS(ctlv_attestation_evidence_get_evidence_challenge)
 CTLV_IN_BINARY(ctlv_attestation_evidence_get_evidence_challenge)
-CTLV_IN_REF(ctlv_attestation_evidence_get_evidence_object, &ctlv_attestation_op_schemas[1].request,
-	    CTLV_ATTESTATION_ATTR_EVIDENCE_OBJECT, 0, 1, CTLV_SCHEMA_NEST)
-#define ctlv_attestation_evidence_get_evidence_object_for_each(_attr, _nest) \
-	CTLV_IN_FOR_EACH(ctlv_attestation_evidence_get_evidence_object, _attr, _nest)
 CTLV_IN_REF(ctlv_attestation_evidence_get_device_generation,
 	    &ctlv_attestation_op_schemas[1].request, CTLV_ATTESTATION_ATTR_DEVICE_GENERATION, 0, 2,
 	    CTLV_SCHEMA_UINT)
@@ -125,32 +125,32 @@ CTLV_IN_REF(ctlv_attestation_evidence_get_evidence_options, &ctlv_attestation_op
 CTLV_IN_HAS(ctlv_attestation_evidence_get_evidence_options)
 CTLV_IN_NEST(ctlv_attestation_evidence_get_evidence_options)
 CTLV_IN_REF(ctlv_attestation_evidence_get_object_evidence_blob_class,
-	    &ctlv_attestation_op_schemas[1].request, CTLV_ATTESTATION_ATTR_EVIDENCE_BLOB_CLASS, 2,
+	    &ctlv_attestation_op_schemas[1].request, CTLV_ATTESTATION_ATTR_EVIDENCE_BLOB_CLASS, 1,
 	    0, CTLV_SCHEMA_ENUM)
 CTLV_IN_HAS(ctlv_attestation_evidence_get_object_evidence_blob_class)
 CTLV_IN_U64(ctlv_attestation_evidence_get_object_evidence_blob_class)
 CTLV_IN_REF(ctlv_attestation_evidence_get_object_evidence_format,
-	    &ctlv_attestation_op_schemas[1].request, CTLV_ATTESTATION_ATTR_EVIDENCE_FORMAT, 2, 1,
+	    &ctlv_attestation_op_schemas[1].request, CTLV_ATTESTATION_ATTR_EVIDENCE_FORMAT, 1, 1,
 	    CTLV_SCHEMA_STRING)
 CTLV_IN_HAS(ctlv_attestation_evidence_get_object_evidence_format)
 CTLV_IN_STRING(ctlv_attestation_evidence_get_object_evidence_format)
 CTLV_IN_REF(ctlv_attestation_evidence_get_object_evidence_representation,
 	    &ctlv_attestation_op_schemas[1].request, CTLV_ATTESTATION_ATTR_EVIDENCE_REPRESENTATION,
-	    2, 2, CTLV_SCHEMA_ENUM)
+	    1, 2, CTLV_SCHEMA_ENUM)
 CTLV_IN_HAS(ctlv_attestation_evidence_get_object_evidence_representation)
 CTLV_IN_U64(ctlv_attestation_evidence_get_object_evidence_representation)
 CTLV_IN_REF(ctlv_attestation_evidence_get_object_evidence_data,
-	    &ctlv_attestation_op_schemas[1].request, CTLV_ATTESTATION_ATTR_EVIDENCE_DATA, 2, 3,
+	    &ctlv_attestation_op_schemas[1].request, CTLV_ATTESTATION_ATTR_EVIDENCE_DATA, 1, 3,
 	    CTLV_SCHEMA_BLOB)
 CTLV_IN_HAS(ctlv_attestation_evidence_get_object_evidence_data)
 CTLV_IN_BLOB(ctlv_attestation_evidence_get_object_evidence_data)
 CTLV_IN_REF(ctlv_attestation_evidence_get_object_evidence_blob_instance,
 	    &ctlv_attestation_op_schemas[1].request, CTLV_ATTESTATION_ATTR_EVIDENCE_BLOB_INSTANCE,
-	    2, 4, CTLV_SCHEMA_UINT)
+	    1, 4, CTLV_SCHEMA_UINT)
 CTLV_IN_HAS(ctlv_attestation_evidence_get_object_evidence_blob_instance)
 CTLV_IN_U64(ctlv_attestation_evidence_get_object_evidence_blob_instance)
 CTLV_IN_REF(ctlv_attestation_evidence_get_object_evidence_hash_algo,
-	    &ctlv_attestation_op_schemas[1].request, CTLV_ATTESTATION_ATTR_EVIDENCE_HASH_ALGO, 2, 5,
+	    &ctlv_attestation_op_schemas[1].request, CTLV_ATTESTATION_ATTR_EVIDENCE_HASH_ALGO, 1, 5,
 	    CTLV_SCHEMA_UINT)
 CTLV_IN_HAS(ctlv_attestation_evidence_get_object_evidence_hash_algo)
 CTLV_IN_U64(ctlv_attestation_evidence_get_object_evidence_hash_algo)
diff --git a/tools/testing/selftests/attestation/attestation_test.c b/tools/testing/selftests/attestation/attestation_test.c
index bd831b0ef14f..40be7fd0c492 100644
--- a/tools/testing/selftests/attestation/attestation_test.c
+++ b/tools/testing/selftests/attestation/attestation_test.c
@@ -374,15 +374,13 @@ TEST_F(attestation, extension_record_log_and_event)
 static int evidence_get(struct ctlv_dev *dev, void *output, size_t output_length,
 			struct ctlv_reply **reply, struct ctlv_error *error)
 {
-	static const unsigned char challenge[] = "freshness";
 	struct ctlv_msg *request;
 	int ret;
 
 	ret = ctlv_attestation_evidence_get_request_new(&request);
 	if (ret)
 		return ret;
-	ctlv_attestation_evidence_challenge_put(
-		request, challenge, sizeof(challenge) - 1);
+	/* Providers with a zero minimum accept an omitted challenge. */
 	ctlv_attestation_evidence_object_start(request);
 	ctlv_attestation_evidence_blob_class_put(
 		request, CTLV_ATTESTATION_EVIDENCE_BLOB_CLASS_PRIMARY);
diff --git a/tools/testing/selftests/attestation/ctlv_attestation_sim_user_gen.c b/tools/testing/selftests/attestation/ctlv_attestation_sim_user_gen.c
index 795cf514c761..89b7db4df55b 100644
--- a/tools/testing/selftests/attestation/ctlv_attestation_sim_user_gen.c
+++ b/tools/testing/selftests/attestation/ctlv_attestation_sim_user_gen.c
@@ -279,14 +279,6 @@ static const struct ctlv_node_schema evidence_get_request_selection_attr_node_sc
 
 /* root, attrs */
 static const struct ctlv_node_schema evidence_get_request_attr_node_schemas[] = {
-	{
-		.attr_id = CTLV_ATTESTATION_ATTR_EVIDENCE_CHALLENGE,
-		.kind = CTLV_SCHEMA_BINARY,
-		.max_occurrences = 1,
-		.present = CTLV_NODE_SCHEMA_HAS_MIN_LENGTH | CTLV_NODE_SCHEMA_HAS_MAX_LENGTH,
-		.min_length = 0,
-		.max_length = 4096,
-	},
 	{
 		.attr_id = CTLV_ATTESTATION_ATTR_EVIDENCE_OBJECT,
 		.kind = CTLV_SCHEMA_NEST,
@@ -300,6 +292,14 @@ static const struct ctlv_node_schema evidence_get_request_attr_node_schemas[] =
 
 /* root, optional attrs */
 static const struct ctlv_node_schema evidence_get_request_optional_attr_node_schemas[] = {
+	{
+		.attr_id = CTLV_ATTESTATION_ATTR_EVIDENCE_CHALLENGE,
+		.kind = CTLV_SCHEMA_BINARY,
+		.max_occurrences = 1,
+		.present = CTLV_NODE_SCHEMA_HAS_MIN_LENGTH | CTLV_NODE_SCHEMA_HAS_MAX_LENGTH,
+		.min_length = 0,
+		.max_length = 4096,
+	},
 	{
 		.attr_id = CTLV_ATTESTATION_ATTR_DEVICE_GENERATION,
 		.kind = CTLV_SCHEMA_UINT,
@@ -359,9 +359,9 @@ static const struct ctlv_node_schema evidence_get_request_node_schema = {
 	.kind = CTLV_SCHEMA_NEST,
 	.max_occurrences = 1,
 	.attrs = evidence_get_request_attr_node_schemas,
-	.attrs_count = 2,
+	.attrs_count = 1,
 	.optional_attrs = evidence_get_request_optional_attr_node_schemas,
-	.optional_attrs_count = 7,
+	.optional_attrs_count = 8,
 };
 
 /* root, attrs */
diff --git a/tools/testing/selftests/attestation/ctlv_attestation_tdx_user_gen.c b/tools/testing/selftests/attestation/ctlv_attestation_tdx_user_gen.c
index 787edd7d8ce4..cdf54af49a81 100644
--- a/tools/testing/selftests/attestation/ctlv_attestation_tdx_user_gen.c
+++ b/tools/testing/selftests/attestation/ctlv_attestation_tdx_user_gen.c
@@ -295,14 +295,6 @@ static const struct ctlv_node_schema evidence_get_request_selection_attr_node_sc
 
 /* root, attrs */
 static const struct ctlv_node_schema evidence_get_request_attr_node_schemas[] = {
-	{
-		.attr_id = CTLV_ATTESTATION_ATTR_EVIDENCE_CHALLENGE,
-		.kind = CTLV_SCHEMA_BINARY,
-		.max_occurrences = 1,
-		.present = CTLV_NODE_SCHEMA_HAS_MIN_LENGTH | CTLV_NODE_SCHEMA_HAS_MAX_LENGTH,
-		.min_length = 0,
-		.max_length = 4096,
-	},
 	{
 		.attr_id = CTLV_ATTESTATION_ATTR_EVIDENCE_OBJECT,
 		.kind = CTLV_SCHEMA_NEST,
@@ -316,6 +308,14 @@ static const struct ctlv_node_schema evidence_get_request_attr_node_schemas[] =
 
 /* root, optional attrs */
 static const struct ctlv_node_schema evidence_get_request_optional_attr_node_schemas[] = {
+	{
+		.attr_id = CTLV_ATTESTATION_ATTR_EVIDENCE_CHALLENGE,
+		.kind = CTLV_SCHEMA_BINARY,
+		.max_occurrences = 1,
+		.present = CTLV_NODE_SCHEMA_HAS_MIN_LENGTH | CTLV_NODE_SCHEMA_HAS_MAX_LENGTH,
+		.min_length = 0,
+		.max_length = 4096,
+	},
 	{
 		.attr_id = CTLV_ATTESTATION_ATTR_DEVICE_GENERATION,
 		.kind = CTLV_SCHEMA_UINT,
@@ -375,9 +375,9 @@ static const struct ctlv_node_schema evidence_get_request_node_schema = {
 	.kind = CTLV_SCHEMA_NEST,
 	.max_occurrences = 1,
 	.attrs = evidence_get_request_attr_node_schemas,
-	.attrs_count = 2,
+	.attrs_count = 1,
 	.optional_attrs = evidence_get_request_optional_attr_node_schemas,
-	.optional_attrs_count = 7,
+	.optional_attrs_count = 8,
 };
 
 /* root, attrs */
diff --git a/tools/testing/selftests/attestation/ctlv_attestation_user_gen.c b/tools/testing/selftests/attestation/ctlv_attestation_user_gen.c
index b278511f5776..077f8c7fbc81 100644
--- a/tools/testing/selftests/attestation/ctlv_attestation_user_gen.c
+++ b/tools/testing/selftests/attestation/ctlv_attestation_user_gen.c
@@ -265,14 +265,6 @@ static const struct ctlv_node_schema evidence_get_request_selection_attr_node_sc
 
 /* root, attrs */
 static const struct ctlv_node_schema evidence_get_request_attr_node_schemas[] = {
-	{
-		.attr_id = CTLV_ATTESTATION_ATTR_EVIDENCE_CHALLENGE,
-		.kind = CTLV_SCHEMA_BINARY,
-		.max_occurrences = 1,
-		.present = CTLV_NODE_SCHEMA_HAS_MIN_LENGTH | CTLV_NODE_SCHEMA_HAS_MAX_LENGTH,
-		.min_length = 0,
-		.max_length = 4096,
-	},
 	{
 		.attr_id = CTLV_ATTESTATION_ATTR_EVIDENCE_OBJECT,
 		.kind = CTLV_SCHEMA_NEST,
@@ -286,6 +278,14 @@ static const struct ctlv_node_schema evidence_get_request_attr_node_schemas[] =
 
 /* root, optional attrs */
 static const struct ctlv_node_schema evidence_get_request_optional_attr_node_schemas[] = {
+	{
+		.attr_id = CTLV_ATTESTATION_ATTR_EVIDENCE_CHALLENGE,
+		.kind = CTLV_SCHEMA_BINARY,
+		.max_occurrences = 1,
+		.present = CTLV_NODE_SCHEMA_HAS_MIN_LENGTH | CTLV_NODE_SCHEMA_HAS_MAX_LENGTH,
+		.min_length = 0,
+		.max_length = 4096,
+	},
 	{
 		.attr_id = CTLV_ATTESTATION_ATTR_DEVICE_GENERATION,
 		.kind = CTLV_SCHEMA_UINT,
@@ -345,9 +345,9 @@ static const struct ctlv_node_schema evidence_get_request_node_schema = {
 	.kind = CTLV_SCHEMA_NEST,
 	.max_occurrences = 1,
 	.attrs = evidence_get_request_attr_node_schemas,
-	.attrs_count = 2,
+	.attrs_count = 1,
 	.optional_attrs = evidence_get_request_optional_attr_node_schemas,
-	.optional_attrs_count = 7,
+	.optional_attrs_count = 8,
 };
 
 /* root, attrs */
diff --git a/tools/testing/selftests/attestation/tdx_attestation_test.c b/tools/testing/selftests/attestation/tdx_attestation_test.c
index a06315af2021..1a370a529f50 100644
--- a/tools/testing/selftests/attestation/tdx_attestation_test.c
+++ b/tools/testing/selftests/attestation/tdx_attestation_test.c
@@ -165,8 +165,9 @@ static int tdx_evidence_get(struct ctlv_dev *dev, const char *format,
 	ret = ctlv_attestation_evidence_get_request_new(&request);
 	if (ret)
 		return ret;
-	ctlv_attestation_evidence_challenge_put(request, challenge,
-						challenge_length);
+	if (challenge)
+		ctlv_attestation_evidence_challenge_put(request, challenge,
+							challenge_length);
 	ctlv_attestation_evidence_object_start(request);
 	ctlv_attestation_evidence_blob_class_put(request,
 						 CTLV_ATTESTATION_EVIDENCE_BLOB_CLASS_PRIMARY);
@@ -244,6 +245,10 @@ TEST_F(tdx_attestation, common_validation_precedes_native_calls)
 	struct ctlv_reply *reply;
 	struct ctlv_msg *request;
 
+	EXPECT_EQ(-EINVAL,
+		  tdx_evidence_get(self->dev, "tdx-tdreport-1.0", NULL, 0,
+				   report.bytes, sizeof(report.bytes), &reply,
+				   &self->error));
 	EXPECT_EQ(-EINVAL,
 		  tdx_evidence_get(self->dev, "tdx-tdreport-1.0", challenge,
 				   sizeof(challenge) - 1, report.bytes,
-- 
2.43.0