tpm: Move tpm_get_random api into the TPM device driver

Move the tpm_get_random api from the trusted keys code into the TPM
device driver itself so that other callers can make use of it. Also,
change the api slightly so that the number of bytes read is returned in
the call, since the TPM command can potentially return fewer bytes than
requested.

Acked-by: David Safford <safford@linux.vnet.ibm.com>
Reviewed-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Kent Yoder <key@linux.vnet.ibm.com>

2 files changed, 76 insertions, 6 deletions

diff --git a/drivers/char/tpm/tpm.c b/drivers/char/tpm/tpm.c
index 677c6e2..36e43e5 100644
--- a/drivers/char/tpm/tpm.c
+++ b/drivers/char/tpm/tpm.c
@@ -32,12 +32,6 @@
 #include "tpm.h"
 #include "tpm_eventlog.h"
 
-enum tpm_const {
-	TPM_MINOR = 224,	/* officially assigned */
-	TPM_BUFSIZE = 4096,
-	TPM_NUM_DEVICES = 256,
-};
-
 enum tpm_duration {
 	TPM_SHORT = 0,
 	TPM_MEDIUM = 1,
@@ -483,6 +477,7 @@ static ssize_t transmit_cmd(struct tpm_chip *chip, struct tpm_cmd_t *cmd,
 #define TPM_INTERNAL_RESULT_SIZE 200
 #define TPM_TAG_RQU_COMMAND cpu_to_be16(193)
 #define TPM_ORD_GET_CAP cpu_to_be32(101)
+#define TPM_ORD_GET_RANDOM cpu_to_be32(70)
 
 static const struct tpm_input_header tpm_getcap_header = {
 	.tag = TPM_TAG_RQU_COMMAND,
@@ -1327,6 +1322,58 @@ int tpm_pm_resume(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(tpm_pm_resume);
 
+#define TPM_GETRANDOM_RESULT_SIZE	18
+static struct tpm_input_header tpm_getrandom_header = {
+	.tag = TPM_TAG_RQU_COMMAND,
+	.length = cpu_to_be32(14),
+	.ordinal = TPM_ORD_GET_RANDOM
+};
+
+/**
+ * tpm_get_random() - Get random bytes from the tpm's RNG
+ * @chip_num: A specific chip number for the request or TPM_ANY_NUM
+ * @out: destination buffer for the random bytes
+ * @max: the max number of bytes to write to @out
+ *
+ * Returns < 0 on error and the number of bytes read on success
+ */
+int tpm_get_random(u32 chip_num, u8 *out, size_t max)
+{
+	struct tpm_chip *chip;
+	struct tpm_cmd_t tpm_cmd;
+	u32 recd, num_bytes = min_t(u32, max, TPM_MAX_RNG_DATA);
+	int err, total = 0, retries = 5;
+	u8 *dest = out;
+
+	chip = tpm_chip_find_get(chip_num);
+	if (chip == NULL)
+		return -ENODEV;
+
+	if (!out || !num_bytes || max > TPM_MAX_RNG_DATA)
+		return -EINVAL;
+
+	do {
+		tpm_cmd.header.in = tpm_getrandom_header;
+		tpm_cmd.params.getrandom_in.num_bytes = cpu_to_be32(num_bytes);
+
+		err = transmit_cmd(chip, &tpm_cmd,
+				   TPM_GETRANDOM_RESULT_SIZE + num_bytes,
+				   "attempting get random");
+		if (err)
+			break;
+
+		recd = be32_to_cpu(tpm_cmd.params.getrandom_out.rng_data_len);
+		memcpy(dest, tpm_cmd.params.getrandom_out.rng_data, recd);
+
+		dest += recd;
+		total += recd;
+		num_bytes -= recd;
+	} while (retries-- && total < max);
+
+	return total ? total : -EIO;
+}
+EXPORT_SYMBOL_GPL(tpm_get_random);
+
 /* In case vendor provided release function, call it too.*/
 
 void tpm_dev_vendor_release(struct tpm_chip *chip)
diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
index 917f727..645136e 100644
--- a/drivers/char/tpm/tpm.h
+++ b/drivers/char/tpm/tpm.h
@@ -28,6 +28,12 @@
 #include <linux/io.h>
 #include <linux/tpm.h>
 
+enum tpm_const {
+	TPM_MINOR = 224,	/* officially assigned */
+	TPM_BUFSIZE = 4096,
+	TPM_NUM_DEVICES = 256,
+};
+
 enum tpm_timeout {
 	TPM_TIMEOUT = 5,	/* msecs */
 };
@@ -269,6 +275,21 @@ struct tpm_pcrextend_in {
 	u8	hash[TPM_DIGEST_SIZE];
 }__attribute__((packed));
 
+/* 128 bytes is an arbitrary cap. This could be as large as TPM_BUFSIZE - 18
+ * bytes, but 128 is still a relatively large number of random bytes and
+ * anything much bigger causes users of struct tpm_cmd_t to start getting
+ * compiler warnings about stack frame size. */
+#define TPM_MAX_RNG_DATA	128
+
+struct tpm_getrandom_out {
+	__be32 rng_data_len;
+	u8     rng_data[TPM_MAX_RNG_DATA];
+}__attribute__((packed));
+
+struct tpm_getrandom_in {
+	__be32 num_bytes;
+}__attribute__((packed));
+
 typedef union {
 	struct	tpm_getcap_params_out getcap_out;
 	struct	tpm_readpubek_params_out readpubek_out;
@@ -277,6 +298,8 @@ typedef union {
 	struct	tpm_pcrread_in	pcrread_in;
 	struct	tpm_pcrread_out	pcrread_out;
 	struct	tpm_pcrextend_in pcrextend_in;
+	struct	tpm_getrandom_in getrandom_in;
+	struct	tpm_getrandom_out getrandom_out;
 } tpm_cmd_params;
 
 struct tpm_cmd_t {