Am Samstag, 25. März 2017, 08:36:48 CET schrieb Krzysztof Kozlowski: Hi Krzysztof, > On Fri, Mar 24, 2017 at 09:41:59PM +0100, Stephan Müller wrote: > > Am Freitag, 24. März 2017, 19:26:04 CET schrieb Krzysztof Kozlowski: > > > > Hi Krzysztof, > > > > > +static unsigned int exynos_rng_copy_random(struct exynos_rng_dev *rng, > > > + u8 *dst, unsigned int dlen) > > > +{ > > > + unsigned int cnt = 0; > > > + int i, j; > > > + u32 val; > > > + > > > + for (j = 0; j < EXYNOS_RNG_SEED_REGS; j++) { > > > + val = exynos_rng_readl(rng, EXYNOS_RNG_OUT(j)); > > > + > > > + for (i = 0; i < 4; i++) { > > > + dst[cnt] = val & 0xff; > > > + val >>= 8; > > > + if (++cnt >= dlen) > > > + return cnt; > > > + } > > > + rng->seed_save[j] = val; > > > > Just to clarify: is this call right? Shouldn't that be removed? Any RNG > > that is given to a caller is tainted and should not serve as seed. > > In that case I could either re-use RNGs not passed to the caller (like > in the block quoted below) or generate another round of them just for > purpose of next seeding. > > With the first approach the problem is that I might wait for such unused > numbers pretty long. If user is requesting large amount of data, then I > will always give him all five output numbers. I will not have unused > numbers. > > The second approach seems safe, but requires additional engine run which > will slow down some of the generate() calls. Random numbers should never be used twice. > > > > + } > > > + > > > + /* > > > + * Engine filled all output registers, so read the remaining registers > > > + * for storing data as future seed. > > > + */ > > > + for (; j < EXYNOS_RNG_SEED_REGS; j++) > > > + rng->seed_save[j] = exynos_rng_readl(rng, EXYNOS_RNG_OUT(j)); > > > > With this call, I guess the questioned line above could go away, right? > > This is used in combination with the previous line so I will get five > seeds (for five registers). > > Best regards, > Krzysztof Ciao Stephan