tlcl: move open retry into Tlcl

Make sure all Tlcl users benefit from the new retry logic.

BUG=None
TEST=daisy build, manual testing of racing tpmc loops
BRANCH=None

Change-Id: I8e9656a65b5d6b45694c1c8bceb95f54f7c751bb
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/39525
Reviewed-by: Luigi Semenzato <semenzato@chromium.org>

1 files changed, 24 insertions, 6 deletions

diff --git a/firmware/stub/tpm_lite_stub.c b/firmware/stub/tpm_lite_stub.c
index a60d6507..60065e64 100644
--- a/firmware/stub/tpm_lite_stub.c
+++ b/firmware/stub/tpm_lite_stub.c
@@ -21,9 +21,13 @@
 #include <sys/time.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <time.h>
 #include <unistd.h>
 
 #define TPM_DEVICE_PATH "/dev/tpm0"
+/* Retry failed open()s for 5 seconds in 10ms polling intervals. */
+#define OPEN_RETRY_DELAY_NS (10 * 1000 * 1000)
+#define OPEN_RETRY_MAX_NUM  500
 
 /* TODO: these functions should pass errors back rather than returning void */
 /* TODO: if the only callers to these are just wrappers, should just
@@ -143,6 +147,8 @@ VbError_t VbExTpmClose(void) {
 
 VbError_t VbExTpmOpen(void) {
   char* device_path;
+  struct timespec delay;
+  int retries, saved_errno;
 
   if (tpm_fd >= 0)
     return VBERROR_SUCCESS;  /* Already open */
@@ -152,13 +158,25 @@ VbError_t VbExTpmOpen(void) {
     device_path = TPM_DEVICE_PATH;
   }
 
-  tpm_fd = open(device_path, O_RDWR);
-  if (tpm_fd < 0) {
-    return DoError(TPM_E_NO_DEVICE, "TPM: Cannot open TPM device %s: %s\n",
-                   device_path, strerror(errno));
+  /* Retry TPM opens on EBUSY failures. */
+  for (retries = 0; retries < OPEN_RETRY_MAX_NUM; ++ retries) {
+    errno = 0;
+    tpm_fd = open(device_path, O_RDWR);
+    saved_errno = errno;
+    if (tpm_fd >= 0)
+      return VBERROR_SUCCESS;
+    if (saved_errno != EBUSY)
+      break;
+
+    VBDEBUG(("TPM: retrying %s: %s\n", device_path, strerror(errno)));
+
+     /* Stall until TPM comes back. */
+     delay.tv_sec = 0;
+     delay.tv_nsec = OPEN_RETRY_DELAY_NS;
+     nanosleep(&delay, NULL);
   }
-
-  return VBERROR_SUCCESS;
+  return DoError(TPM_E_NO_DEVICE, "TPM: Cannot open TPM device %s: %s\n",
+                 device_path, strerror(saved_errno));
 }