On 19 June 2017 at 11:51, Herbert Xu <[email protected]> wrote:
> On Sun, Jun 18, 2017 at 10:00:17PM -0700, Mike Frysinger wrote:
>>
>> in order to make tpm-rng react in the way you're implying, the TPM
>> subsystem would need to add a notification chain for transitions from
>> none<->some devices, then tpm-rng could subscribe to that, and during
>> those transition points, it would call hwrng_register/hwrng_unregister
>> to make itself visible accordingly to the hwrng subsystem. maybe
>> someone on the TPM side would be interested in writing all that logic,
>> but it sounds excessive for this minor usage. the current tpm-rng
>> driver is *extremely* simple -- it's 3 funcs, each of which are 1
>> line.
>
> It's simple and it's broken, as far as the way it hooks into the
> hwrng is concerned.
*********************************************************************************************
diff --git a/drivers/char/hw_random/tpm-rng.c b/drivers/char/hw_random/tpm-rng.c
index d6d4482..4861b35 100644
--- a/drivers/char/hw_random/tpm-rng.c
+++ b/drivers/char/hw_random/tpm-rng.c
@@ -22,6 +22,10 @@
#include <linux/tpm.h>
#define MODULE_NAME "tpm-rng"
+#define MAX_RETRIES 30
+
+static struct delayed_work check_tpm_work;
+static int retry_count;
static int tpm_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
{
@@ -33,9 +37,27 @@ static struct hwrng tpm_rng = {
.read = tpm_rng_read,
};
+static void check_tpm_presence(struct work_struct *work)
+{
+ u8 data = 0;
+ if (tpm_get_random(TPM_ANY_NUM, &data, 1) > 0) {
+ hwrng_register(&tpm_rng);
+ } else {
+ if (retry_count < MAX_RETRIES) {
+ retry_count++;
+ schedule_delayed_work(&check_tpm_work, HZ * 10);
+ } else {
+ pr_err("Could not find any TPM chip, not
registering rng");
+ }
+ }
+}
+
static int __init rng_init(void)
{
- return hwrng_register(&tpm_rng);
+ INIT_DELAYED_WORK(&check_tpm_work, check_tpm_presence);
+ check_tpm_presence(NULL);
+
+ return 0;
}
module_init(rng_init);
*********************************************************************************************
Why not something like this? Patch is completely untested. If this
idea seems useful I can clean the code but would require help in
testing.
Regards,
PrasannaKumar
