From d2704808f24fbc869ba54df82d4b1af49ab496e2 Mon Sep 17 00:00:00 2001 From: AngeloGioacchino Del Regno Date: Fri, 29 Oct 2021 10:09:15 +0200 Subject: tpm: tpm_tis_spi_cr50: Add default RNG quality To allow this device to fill the kernel's entropy pool at boot, setup a default quality for the hwrng found in Cr50. After some testing with rngtest and dieharder it was, in short, discovered that the RNG produces fair quality randomness, giving around 99.93% successes in rngtest FIPS140-2. Notably, though, when testing with dieharder it was noticed that we get 3 WEAK results over 114, which isn't optimal, and also the p-values distribution wasn't uniform in all the cases, so a conservative quality value was chosen by applying an arbitrary penalty to the calculated values. For reference, this is how the values were calculated: The dieharder results were averaged, then normalized (0-1000) and re-averaged with the rngtest result (where the result was given a score of 99.93% of 1000, so 999.3), then aggregated together and averaged again. An arbitrary penalty of -100 was applied due to the retrieved value, which brings us finally to 700. Signed-off-by: AngeloGioacchino Del Regno Reviewed-by: Jarkko Sakkinen Signed-off-by: Jarkko Sakkinen --- drivers/char/tpm/tpm_tis_spi_cr50.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'drivers/char') diff --git a/drivers/char/tpm/tpm_tis_spi_cr50.c b/drivers/char/tpm/tpm_tis_spi_cr50.c index ea759af25634..dae98dbeeeac 100644 --- a/drivers/char/tpm/tpm_tis_spi_cr50.c +++ b/drivers/char/tpm/tpm_tis_spi_cr50.c @@ -36,6 +36,9 @@ #define TPM_CR50_FW_VER(l) (0x0f90 | ((l) << 12)) #define TPM_CR50_MAX_FW_VER_LEN 64 +/* Default quality for hwrng. */ +#define TPM_CR50_DEFAULT_RNG_QUALITY 700 + struct cr50_spi_phy { struct tpm_tis_spi_phy spi_phy; @@ -264,6 +267,7 @@ int cr50_spi_probe(struct spi_device *spi) phy = &cr50_phy->spi_phy; phy->flow_control = cr50_spi_flow_control; phy->wake_after = jiffies; + phy->priv.rng_quality = TPM_CR50_DEFAULT_RNG_QUALITY; init_completion(&phy->ready); cr50_phy->access_delay = CR50_NOIRQ_ACCESS_DELAY; -- cgit