Hi Hector, On Tue, Feb 14, 2023 at 8:08 PM Hector Martin <marcan@xxxxxxxxx> wrote: > > On 14/02/2023 18.00, Julian Calaby wrote: > > Hi Arend, > > > > On Tue, Feb 14, 2023 at 7:04 PM Hector Martin <marcan@xxxxxxxxx> wrote: > >> > >> Newer Apple firmwares on chipsets without a hardware RNG require the > >> host to provide a buffer of 256 random bytes to the device on > >> initialization. This buffer is present immediately before NVRAM, > >> suffixed by a footer containing a magic number and the buffer length. > >> > >> This won't affect chips/firmwares that do not use this feature, so do it > >> unconditionally for all Apple platforms (those with an Apple OTP). > > > > Following on from the conversation a year ago, is there a way to > > detect chipsets that need these random bytes? While I'm sure Apple is > > doing their own special thing for special Apple reasons, it seems > > relatively sensible to omit a RNG on lower-cost chipsets, so would > > other chipsets need it? > > I think we could include a list of chips known not to have the RNG (I > think it's only the ones shipped on T2 machines). The main issue is I > don't have access to those machines so it's hard for me to test exactly > which ones need it. IIRC Apple's driver unconditionally provides the > randomness. I could at least test the newer chips on AS platforms and > figure out if they need it to exclude them... but then again, all I can > do is test whether they work without the blob, but they might still want > it (and simply become less secure without it). > > So I guess the answer is "maybe, I don't know, and it's kind of hard to > know for sure"... the joys of reverse engineering hardware without > vendor documentation. > > If you mean whether other chips with non-apple firmware can use this, I > have no idea. That's probably something for Arend to answer. My gut > feeling is Apple added this as part of a hardening mechanism and > non-Apple firmware does not use it (and Broadcom then probably started > shipping chips with a hardware RNG and firmware that uses it directly > across all vendors), in which case the answer is no. Sorry, I should have been more clear, I wasn't expecting you to know, I was asking Arend if he knew. Thanks, -- Julian Calaby Email: julian.calaby@xxxxxxxxx Profile: http://www.google.com/profiles/julian.calaby/
