commands/efi/tpm: Re-enable measurements on confidential computing platforms

The measurements for confidential computing has been introduced in the
commit 4c76565b6 (efi/tpm: Add EFI_CC_MEASUREMENT_PROTOCOL support).
Recently the patch 30708dfe3 (tpm: Disable the tpm verifier if the TPM
device is not present) has been introduced to optimize the memory usage
when a TPM device is not available on platforms. This fix prevents the
tpm module to be loaded on confidential computing platforms, e.g. Intel
machines with TDX enabled, where the TPM device is not available.

In this patch, we propose to load the tpm module for this use case by
generalizing the tpm feature detection in order to cover CC platforms.
Basically, we do it by detecting the availability of the
EFI_CC_MEASUREMENT_PROTOCOL EFI protocol.

Fixes: https://savannah.gnu.org/bugs/?65821
Fixes: 30708dfe3 (tpm: Disable the tpm verifier if the TPM device is not present)
Signed-off-by: Hector Cao <hector.cao@canonical.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

diff --git a/grub-core/commands/efi/tpm.c b/grub-core/commands/efi/tpm.c
index f250c30dbc3068a9f7b7f7e9ad30910e2756f0dd..cbac6986691645711eec5e69dd3f64cab86bdf7f 100644 (file)
--- a/grub-core/commands/efi/tpm.c
+++ b/grub-core/commands/efi/tpm.c
@@ -292,6 +292,15 @@ grub_tpm_present (void)
 {
   grub_efi_handle_t tpm_handle;
   grub_efi_uint8_t protocol_version;
+  grub_efi_cc_protocol_t *cc;
+
+  /*
+   * When confidential computing measurement protocol is enabled
+   * we assume the TPM is present.
+   */
+  cc = grub_efi_locate_protocol (&cc_measurement_guid, NULL);
+  if (cc != NULL)
+    return 1;
 
   if (!grub_tpm_handle_find (&tpm_handle, &protocol_version))
     return 0;