stubdom/vtpm: fix memcmp in TPM_ChangeAuthAsymFinish

gcc8 spotted this error:
error: 'memcmp' reading 20 bytes from a region of size 8 [-Werror=stringop-overflow=]

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
(cherry picked from commit 22bf5be323)

stubdom/Makefile

@@ -229,6 +229,7 @@ tpm_emulator-$(XEN_TARGET_ARCH): tpm_emulator-$(TPMEMU_VERSION).tar.gz
 	patch -d $@ -p1 < vtpm-deepquote-anyloc.patch
 	patch -d $@ -p1 < vtpm-cmake-Wextra.patch
 	patch -d $@ -p1 < vtpm-implicit-fallthrough.patch
+	patch -d $@ -p1 < vtpm_TPM_ChangeAuthAsymFinish.patch
 	mkdir $@/build
 	cd $@/build; CC=${CC} $(CMAKE) .. -DCMAKE_C_FLAGS:STRING="-std=c99 -DTPM_NO_EXTERN $(TARGET_CPPFLAGS) $(TARGET_CFLAGS) -Wno-declaration-after-statement"
 	touch $@

stubdom/vtpm_TPM_ChangeAuthAsymFinish.patch

@@ -0,0 +1,12 @@
+error: 'memcmp' reading 20 bytes from a region of size 8 [-Werror=stringop-overflow=]
+--- a/tpm/tpm_deprecated.c
++++ b/tpm/tpm_deprecated.c
+@@ -434,7 +434,7 @@ TPM_RESULT TPM_ChangeAuthAsymFinish(TPM_
+   tpm_hmac_final(&hmac_ctx, b1.digest);
+   /* 6. The TPM SHALL compare b1 with newAuthLink. The TPM SHALL
+         indicate a failure if the values do not match. */
+-  if (memcmp(&b1, &newAuthLink, sizeof(TPM_HMAC))) {
++  if (memcmp(&b1, newAuthLink, sizeof(TPM_HMAC))) {
+     debug("TPM_ChangeAuthAsymFinish(): newAuthLink value does not match.");
+     return TPM_FAIL;
+   }