[PATCH] efi_loader: explicitly return EFI_UNSUPPORTED for TCG 1.0 compatibility

[Ilias Apalodimas]

In the EFI TCG spec EFI_TCG2_BOOT_SERVICE_CAPABILITY struct is
versioned -- there are 1.0 and 1.1 versions of that struct.
The spec [0] describes:
"Version of the EFI_TCG2_BOOT_SERVICE_CAPABILITY
structure itself. For this version of the protocol, the Major version
SHALL be set to 1 and the Minor version SHALL be set to 1."
which is what we currently support.

The SCT tests perfromed By Arms SIE(Security interface extensions) [1]
perform a check for clients supporting the older 1.0 version of the
spec (Test 30.1.1.4). Given than this spec is 7 years old,  there should
be no need for the older 1.0 version support.  Instead of returning
EFI_BUFFER_TOO_SMALLL switch to EFI_UNSUPPORTED which is more
appropriate.  It's worth noting that the spec doesn't explicitly
describe the return value at the moment.

[0] https://trustedcomputinggroup.org/wp-content/uploads/EFI-Protocol-Specification-rev13-160330final.pdf
[1] https://github.com/stuyod01/edk2-test/blob/master/uefi-sct/Doc/UEFI-SCT-Case-Spec/30_Protocols_TCG2_Test.md

Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
---

Heinrich,  Stuart is investigating the chance of the spec getting updated
adding EFI_UNSUPPORTED.  In any case I think the patch should be aplied since
the new return code makes more sense.  If for some reason the spec change is
rejected, I can go back and add support for 1.0 structure versions.

 lib/efi_loader/efi_tcg2.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/efi_loader/efi_tcg2.c b/lib/efi_loader/efi_tcg2.c
index a83ae7a46cf3..220c442bdf93 100644
--- a/lib/efi_loader/efi_tcg2.c
+++ b/lib/efi_loader/efi_tcg2.c
@@ -750,7 +750,7 @@ efi_tcg2_get_capability(struct efi_tcg2_protocol *this,

 	if (capability->size < sizeof(*capability)) {
 		capability->size = sizeof(*capability);
-		efi_ret = EFI_BUFFER_TOO_SMALL;
+		efi_ret = EFI_UNSUPPORTED;
 		goto out;
 	}

--
2.39.2