Add a TPM Passthrough backend driver implementation

This patch is based of off version 9 of Stefan Berger's patch series
  "QEMU Trusted Platform Module (TPM) integration"
and adds a new backend driver for it.

This patch adds a passthrough backend driver for passing commands sent to the
emulated TPM device directly to a TPM device opened on the host machine.
Thus it is possible to use a hardware TPM device in a system running on QEMU,
providing the ability to access a TPM in a special state (e.g. after a Trusted
Boot).

This functionality is being used in the acTvSM Trusted Virtualization Platform
which is available on [1].

Usage example:
  qemu-system-x86_64 -tpmdev passthrough,id=tpm0,path=/dev/tpm0 \
                     -device tpm-tis,tpmdev=tpm0 \
                     -cdrom test.iso -boot d

Some notes about the host TPM:
The TPM needs to be enabled and activated. If that's not the case one
has to go through the BIOS/UEFI and enable and activate that TPM for TPM
commands to work as expected.
It may be necessary to boot the kernel using tpm_tis.force=1 in the boot
command line or 'modprobe tpm_tis force=1' in case of using it as a module.

Regards,
Andreas Niederl, Stefan Berger

[1] http://trustedjava.sourceforge.net/

Signed-off-by: Andreas Niederl <andreas.niederl@iaik.tugraz.at>
Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Reviewed-by: Corey Bryant <coreyb@linux.vnet.ibm.com>
Reviewed-by: Joel Schopp <jschopp@linux.vnet.ibm.com>
Message-id: 1361987275-26289-6-git-send-email-stefanb@linux.vnet.ibm.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/tpm/tpm.c b/tpm/tpm.c
index 02735493c5..ffd24956d7 100644
--- a/tpm/tpm.c
+++ b/tpm/tpm.c
@@ -61,6 +61,20 @@ static bool tpm_model_is_registered(enum TpmModel model)
     return false;
 }
 
+/*
+ * Write an error message in the given output buffer.
+ */
+void tpm_write_fatal_error_response(uint8_t *out, uint32_t out_len)
+{
+    if (out_len >= sizeof(struct tpm_resp_hdr)) {
+        struct tpm_resp_hdr *resp = (struct tpm_resp_hdr *)out;
+
+        resp->tag = cpu_to_be16(TPM_TAG_RSP_COMMAND);
+        resp->len = cpu_to_be32(sizeof(struct tpm_resp_hdr));
+        resp->errcode = cpu_to_be32(TPM_FAIL);
+    }
+}
+
 const TPMDriverOps *tpm_get_backend_driver(const char *type)
 {
     int i;