[PATCH resend 2/2] tpm,random: Call add_drbg_randomness after selftest

[Andy Lutomirski]

TPMs contain a DRBG.  Use it.

On some but not all TPMs, this will also call add_drbg_randomness on
resume.  As a future improvement, this could be tweaked to cover all
of them, but I'll leave that to someone more familiar with the
individual drivers.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
---
 drivers/char/tpm/tpm-interface.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index 62e10fd..20516e7 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -28,6 +28,7 @@
 #include <linux/mutex.h>
 #include <linux/spinlock.h>
 #include <linux/freezer.h>
+#include <linux/random.h>
 
 #include "tpm.h"
 #include "tpm_eventlog.h"
@@ -780,10 +781,22 @@ int tpm_do_selftest(struct tpm_chip *chip)
 			return 0;
 		}
 		if (rc != TPM_WARN_DOING_SELFTEST)
-			return rc;
+			break;
 		msleep(delay_msec);
 	} while (--loops > 0);
 
+	if (rc == 0) {
+		/* We're functional and/or we just resumed. */
+		u8 randomness[32];
+		int bytes = tpm_get_random(chip->dev_num,
+					   randomness, sizeof(randomness));
+		if (bytes > 0) {
+			dev_info(chip->dev, "adding %d bits of DRBG data\n",
+				 bytes * 8);
+			add_drbg_randomness(randomness, bytes);
+		}
+	}
+
 	return rc;
 }
 EXPORT_SYMBOL_GPL(tpm_do_selftest);
-- 
1.9.0

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