Hi Andre, On Friday 20 February 2015 10:07 AM, Andre Wolokita wrote: > In omap4_rng_init(), a check of bit 10 of the RNG_CONFIG_REG is done to determine > whether the RNG is running. This is suspicious firstly due to the use of > RNG_CONTROL_ENABLE_TRNG_MASK and secondly because the same mask is written to > RNG_CONTROL_REG after configuration of the FROs. Similar suspicious logic is > repeated in omap4_rng_cleanup() when RNG_CONTROL_REG masked with > RNG_CONTROL_ENABLE_TRNG_MASK is read, the same mask bit is cleared, and then > written to RNG_CONFIG_REG. Unless the TRNG is enabled with one bit in RNG_CONTROL > and disabled with another in RNG_CONFIG and these bits are mirrored in some way, > I believe that the TRNG is not really shutting off, leaving the FROs running > indefinitely which, in an extreme case, could lead to degredation of the > hardware and potentially reduce the level of entropy generated. Yes you are correct. Patch looks good to me. It should be RNG_CONTROL_REG Acked-by: Lokesh Vutla <lokeshvutla@xxxxxx> Thanks and regards, Lokesh > > Apart from the strange logic, I have reason to suspect that the OMAP4 related > code in this driver is driving an Inside Secure IP hardware RNG and strongly > suspect that bit 10 of RNG_CONFIG_REG is one of the bits configuring the > sampling rate of the FROs. This option is by default set to 0 and is not being > set anywhere in omap-rng.c. Reading this bit during omap4_rng_init() will > always return 0. It will remain 0 because ~(value of TRNG_MASK in control) will > always be 0, because the TRNG is never shut off. This is of course presuming > that the OMAP4 features the Inside Secure IP, which I strongly suspect. > > I'm interested in knowing what the guys at TI think about this, as only they > can confirm or deny the detailed structure of these registers. > > Signed-off-by: Andre Wolokita <Andre.Wolokita@xxxxxxxxxx> > --- > drivers/char/hw_random/omap-rng.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/char/hw_random/omap-rng.c b/drivers/char/hw_random/omap-rng.c > index d14dcf7..67151cb 100644 > --- a/drivers/char/hw_random/omap-rng.c > +++ b/drivers/char/hw_random/omap-rng.c > @@ -236,7 +236,7 @@ static int omap4_rng_init(struct omap_rng_dev *priv) > u32 val; > > /* Return if RNG is already running. */ > - if (omap_rng_read(priv, RNG_CONFIG_REG) & RNG_CONTROL_ENABLE_TRNG_MASK) > + if (omap_rng_read(priv, RNG_CONTROL_REG) & RNG_CONTROL_ENABLE_TRNG_MASK) > return 0; > > val = RNG_CONFIG_MIN_REFIL_CYCLES << RNG_CONFIG_MIN_REFIL_CYCLES_SHIFT; > @@ -262,7 +262,7 @@ static void omap4_rng_cleanup(struct omap_rng_dev *priv) > > val = omap_rng_read(priv, RNG_CONTROL_REG); > val &= ~RNG_CONTROL_ENABLE_TRNG_MASK; > - omap_rng_write(priv, RNG_CONFIG_REG, val); > + omap_rng_write(priv, RNG_CONTROL_REG, val); > } > > static irqreturn_t omap4_rng_irq(int irq, void *dev_id) > -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
