| Message ID | 20200727124552.4336-1-ceggers@arri.de (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Herbert Xu |
| Headers | show |
| Series | hwrng: imx-rngc - setup default RNG quality | expand |
Hi Christian, On 20-07-27 14:45, Christian Eggers wrote: > When hw_random device's quality is non-zero, it will automatically fill > the kernel's entropy pool at boot. For this purpose, one conservative > quality value is being picked up as the default value. IMHO your value is not conservative enough and the commit message should explain why we should use 900. Unfortunately I had not enough time to send my patch addressing this. However please check my commit message why 900 is not good: 8<------------------------------------------------------------------------ From 9f047eee5e4ce8353c9b764a47e7f584b2013347 Mon Sep 17 00:00:00 2001 From: Marco Felsch <m.felsch@pengutronix.de> Date: Thu, 7 May 2020 12:01:28 +0200 Subject: [PATCH] hwrng: imx-rngc - add quality to use it as kernel entropy pool The RM describes the RNGB as follow: 8<---------------------------------------------------------------- The RNGB uses the True Random Number Generator (TRNG) and a Pseudo-Random Number Generator (PRNG) to achieve a true randomness and cryptographic strength. 8<---------------------------------------------------------------- The RNGB has 3 operation modes: self-test, seed-generation and the final 'random number generation' mode. Befor we can retrieve random numbers from the RNGB we need to generate the seed pool: 8<---------------------------------------------------------------- During the seed generation, the RNGB adds the entropy generated in the TRNG to the 256-bit XKEY register. The PRNG algorithm executes 20.000 entropy samples from the TRNG to create an initial seed for the random number generation. 8<---------------------------------------------------------------- The RNGB can generate 2^20 words (4byte) of 'random' data after the seed pool was initialized. The pool needs to be reseeded if more words are required. The reseeding is done automatically since commit 3acd9ea9331c ("hwrng: imx-rngc - use automatic seeding"). We can't retrieve the TRNG values directly so we need a other way to get the quality level. We know that the PRNG uses 20.000 entropy samples from the TRNG to generate 2^20 words (1MiB) and the quality level is defined as (in bits of entropy per 1024 bits of input). So the quality level can be calculated by: 20.000 * 1024 ------------- = ~ 19.5 2^20 Signed-off-by: Marco Felsch <m.felsch@pengutronix.de> --- drivers/char/hw_random/imx-rngc.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/char/hw_random/imx-rngc.c b/drivers/char/hw_random/imx-rngc.c index 9c47e431ce90..61c844baf26e 100644 --- a/drivers/char/hw_random/imx-rngc.c +++ b/drivers/char/hw_random/imx-rngc.c @@ -285,6 +285,7 @@ static int imx_rngc_probe(struct platform_device *pdev) rngc->rng.init = imx_rngc_init; rngc->rng.read = imx_rngc_read; rngc->rng.cleanup = imx_rngc_cleanup; + rngc->rng.quality = 19; rngc->dev = &pdev->dev; platform_set_drvdata(pdev, rngc);
Hi Marco, On Tuesday, 28 July 2020, 09:48:17 CEST, Marco Felsch wrote: > Hi Christian, > > On 20-07-27 14:45, Christian Eggers wrote: > > When hw_random device's quality is non-zero, it will automatically fill > > the kernel's entropy pool at boot. For this purpose, one conservative > > quality value is being picked up as the default value. > > IMHO your value is not conservative enough and the commit message should > explain why we should use 900. Unfortunately I had not enough time to > send my patch addressing this. However please check my commit message > why 900 is not good: ok, you caught me. I found the value of 900 in several other drivers and simply took it. Even parts of my commit message were simply copied... As I have no real idea about determining the right quality, I will leave this task for you :-) Thanks Christian
diff --git a/drivers/char/hw_random/imx-rngc.c b/drivers/char/hw_random/imx-rngc.c index f9c5ddd0276b..a62ff78bd7ea 100644 --- a/drivers/char/hw_random/imx-rngc.c +++ b/drivers/char/hw_random/imx-rngc.c @@ -285,6 +285,7 @@ static int imx_rngc_probe(struct platform_device *pdev) rngc->rng.init = imx_rngc_init; rngc->rng.read = imx_rngc_read; rngc->rng.cleanup = imx_rngc_cleanup; + rngc->rng.quality = 900; rngc->dev = &pdev->dev; platform_set_drvdata(pdev, rngc);
When hw_random device's quality is non-zero, it will automatically fill the kernel's entropy pool at boot. For this purpose, one conservative quality value is being picked up as the default value. Signed-off-by: Christian Eggers <ceggers@arri.de> --- drivers/char/hw_random/imx-rngc.c | 1 + 1 file changed, 1 insertion(+)