tpmc: add PCR reading function

Add ability to report a single PCR value via the tpmc utility. Using
/sys/devices/platform/tpm_tis/pcrs is too slow, since it reads all
PCRs before returning. Anything wanting to read PCR0 on a time-critical
path needs maximum speed.

BUG=chromium-os:22172
TEST=install and test x86-alex.

Change-Id: I2d450961d33fa314d54b909135a74aa756279ec6
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/13891
Reviewed-by: Luigi Semenzato <semenzato@chromium.org>

2 files changed, 28 insertions, 0 deletions

diff --git a/firmware/lib/tpm_lite/include/tlcl_structures.h b/firmware/lib/tpm_lite/include/tlcl_structures.h
index a53e2baa..e0a7a46b 100644
--- a/firmware/lib/tpm_lite/include/tlcl_structures.h
+++ b/firmware/lib/tpm_lite/include/tlcl_structures.h
@@ -94,6 +94,12 @@ const struct s_tpm_ppassert_cmd{
 } tpm_ppassert_cmd = {{0x0, 0xc1, 0x0, 0x0, 0x0, 0xc, 0x40, 0x0, 0x0, 0xa, 0x0, 0x8, },
 };
 
+const struct s_tpm_pcr_read_cmd{
+  uint8_t buffer[14];
+  uint16_t pcrNum;
+} tpm_pcr_read_cmd = {{0x0, 0xc1, 0x0, 0x0, 0x0, 0xe, 0x0, 0x0, 0x0, 0x15, },
+10, };
+
 const struct s_tpm_nv_read_cmd{
   uint8_t buffer[22];
   uint16_t index;
diff --git a/firmware/lib/tpm_lite/tlcl.c b/firmware/lib/tpm_lite/tlcl.c
index fc820b55..42739904 100644
--- a/firmware/lib/tpm_lite/tlcl.c
+++ b/firmware/lib/tpm_lite/tlcl.c
@@ -214,6 +214,28 @@ uint32_t TlclRead(uint32_t index, void* data, uint32_t length) {
   return result;
 }
 
+uint32_t TlclPCRRead(uint32_t index, void* data, uint32_t length) {
+  struct s_tpm_nv_read_cmd cmd;
+  uint8_t response[TPM_LARGE_ENOUGH_COMMAND_SIZE];
+  uint32_t result_length;
+  uint32_t result;
+
+  VBDEBUG(("TPM: TlclPCRRead(0x%x, %d)\n", index, length));
+  if (length < kPcrDigestLength) {
+    return TPM_E_IOERROR;
+  }
+  Memcpy(&cmd, &tpm_pcr_read_cmd, sizeof(cmd));
+  ToTpmUint32(cmd.buffer + tpm_pcr_read_cmd.pcrNum, index);
+
+  result = TlclSendReceive(cmd.buffer, response, sizeof(response));
+  if (result == TPM_SUCCESS) {
+    uint8_t* pcr_read_cursor = response + kTpmResponseHeaderLength;
+    Memcpy(data, pcr_read_cursor, kPcrDigestLength);
+  }
+
+  return result;
+}
+
 uint32_t TlclWriteLock(uint32_t index) {
   VBDEBUG(("TPM: Write lock 0x%x\n", index));
   return TlclWrite(index, NULL, 0);