[PATCH v2] tpm: Disable tpm verifier if tpm is not present

[Michael Chang]

This helps to prevent out of memory error when reading large files via disabling
tpm device as verifier has to read all content into memory in one chunk to
measure the hash and extend to tpm.

Signed-off-by: Michael Chang <mchang@suse.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
---
 grub-core/commands/efi/tpm.c | 37 ++++++++++++++++++++++++++++++++++++
 grub-core/commands/tpm.c     |  4 ++++
 include/grub/tpm.h           |  1 +
 3 files changed, 42 insertions(+)

diff --git a/grub-core/commands/efi/tpm.c b/grub-core/commands/efi/tpm.c
index ae09c1bf8..e1f343fea 100644
--- a/grub-core/commands/efi/tpm.c
+++ b/grub-core/commands/efi/tpm.c
@@ -287,3 +287,40 @@ grub_tpm_measure (unsigned char *buf, grub_size_t size, 
grub_uint8_t pcr,
   else
     return grub_tpm2_log_event (tpm_handle, buf, size, pcr, description);
 }
+
+int
+grub_tpm_present (void)
+{
+  grub_efi_handle_t tpm_handle;
+  grub_efi_uint8_t protocol_version;
+
+  if (!grub_tpm_handle_find (&tpm_handle, &protocol_version))
+    return 0;
+
+  if (protocol_version == 1)
+    {
+      grub_efi_tpm_protocol_t *tpm;
+
+      tpm = grub_efi_open_protocol (tpm_handle, &tpm_guid,
+                                   GRUB_EFI_OPEN_PROTOCOL_GET_PROTOCOL);
+      if (!tpm)
+       {
+         grub_dprintf ("tpm", "Cannot open TPM protocol\n");
+         return 0;
+       }
+      return grub_tpm1_present (tpm);
+    }
+  else
+    {
+      grub_efi_tpm2_protocol_t *tpm;
+
+      tpm = grub_efi_open_protocol (tpm_handle, &tpm2_guid,
+                                   GRUB_EFI_OPEN_PROTOCOL_GET_PROTOCOL);
+      if (!tpm)
+       {
+         grub_dprintf ("tpm", "Cannot open TPM protocol\n");
+         return 0;
+       }
+      return grub_tpm2_present (tpm);
+    }
+}
diff --git a/grub-core/commands/tpm.c b/grub-core/commands/tpm.c
index 2052c36ea..cb8ed6b94 100644
--- a/grub-core/commands/tpm.c
+++ b/grub-core/commands/tpm.c
@@ -86,10 +86,14 @@ struct grub_file_verifier grub_tpm_verifier = {
 
 GRUB_MOD_INIT (tpm)
 {
+  if (!grub_tpm_present())
+    return;
   grub_verifier_register (&grub_tpm_verifier);
 }
 
 GRUB_MOD_FINI (tpm)
 {
+  if (!grub_tpm_present())
+    return;
   grub_verifier_unregister (&grub_tpm_verifier);
 }
diff --git a/include/grub/tpm.h b/include/grub/tpm.h
index 5c285cbc5..c19fcbd0a 100644
--- a/include/grub/tpm.h
+++ b/include/grub/tpm.h
@@ -36,4 +36,5 @@
 
 grub_err_t grub_tpm_measure (unsigned char *buf, grub_size_t size,
                             grub_uint8_t pcr, const char *description);
+int grub_tpm_present (void);
 #endif
-- 
2.35.3