Am Fri, Nov 04, 2022 at 04:42:30PM +0100 schrieb Jason A. Donenfeld: > Most hw_random devices return entropy which is assumed to be of full > quality, but driver authors don't bother setting the quality knob. Some > hw_random devices return less than full quality entropy, and then driver > authors set the quality knob. Therefore, the entropy crediting should be > opt-out rather than opt-in per-driver, to reflect the actual reality on > the ground. > > For example, the two Raspberry Pi RNG drivers produce full entropy > randomness, and both EDK2 and U-Boot's drivers for these treat them as > such. The result is that EFI then uses these numbers and passes the to > Linux, and Linux credits them as boot, thereby initializing the RNG. > Yet, in Linux, the quality knob was never set to anything, and so on the > chance that Linux is booted without EFI, nothing is ever credited. > That's annoying. > > The same pattern appears to repeat itself throughout various drivers. In > fact, very very few drivers have bothered setting quality=1024. > > So let's invert this logic. A hw_random struct's quality knob now > controls the maximum quality a driver can produce, or 0 to specify 1024. > Then, the module-wide switch called "default_quality" is changed to > represent the maximum quality of any driver. By default it's 1024, and > the quality of any particular driver is then given by: > > min(default_quality, rng->quality ?: 1024); > > This way, the user can still turn this off for weird reasons, yet we get > proper crediting for relevant RNGs. Hm. Wouldn't we need to verify that 1024 is appropriate for all drivers where the quality currently is not set? Thanks, Dominik
