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author | AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> | 2021-10-29 10:09:15 +0200 |
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committer | Jarkko Sakkinen <jarkko@kernel.org> | 2022-01-09 00:18:38 +0200 |
commit | d2704808f24fbc869ba54df82d4b1af49ab496e2 (patch) | |
tree | 655b9e7ae49e3af557b311c27e91caa2aa217dc6 | |
parent | f04510f26f82aa7cd0bf932760f01b01a010869f (diff) | |
download | linux-d2704808f24fbc869ba54df82d4b1af49ab496e2.tar.bz2 |
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 <angelogioacchino.delregno@collabora.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
-rw-r--r-- | drivers/char/tpm/tpm_tis_spi_cr50.c | 4 |
1 files changed, 4 insertions, 0 deletions
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; |