Hi, On 27 April 2016 at 09:14, Andreas Dannenberg <[email protected]> wrote: > On Wed, Apr 27, 2016 at 08:34:50AM -0600, Simon Glass wrote: >> Hi Andreas, >> >> On 14 April 2016 at 17:07, Andreas Dannenberg <[email protected]> wrote: >> > >> > Hi Simon, thanks for the feedback. Additional comments inlined... >> > >> > On Mon, Apr 04, 2016 at 06:04:15PM -0600, Simon Glass wrote: >> > > Hi Andreas, >> > > >> > > On 28 March 2016 at 14:19, Andreas Dannenberg <[email protected]> wrote: >> > > > On Mon, Mar 28, 2016 at 03:32:40PM -0400, Tom Rini wrote: >> > > >> I'm interested in getting secure device support going, but it seems >> > > >> like we should need more than that, ie something to keep the chain of >> > > >> trust going. >> > > > >> > > > Tom et al., >> > > > I just saw your reply to Vitaly's email and I'm actually just looking >> > > > into something along the lines you brought up but I didn't want to >> > > > hijack that discussion so here's a new thread. >> > > > >> > > > As for the chain of trust for ARMv7, my understanding is that when >> > > > using a combination of SPL and U-Boot there will always be a vendor- >> > > > specific initial boot (ROM) code that authenticates SPL, and then there >> > > > will need to be some code inserted into SPL that authenticates U-Boot >> > > > after it's loaded (for example by using some secure ROM API call and >> > > > such). >> > > > >> > > > So I was looking into if there is already some generic framework for >> > > > this in U-Boot but didn't see anything obvious. One "easy" way would be >> > > > to add a simple call to an authentication routine to board_init_r >> > > > (u-boot/common/spl/spl.c) but let's say we add such a call for TI or >> > > > other vendor's stuff I suppose this would not scale very well. >> > > > >> > > > But what about adding one generic call to a default authentication >> > > > function declared as __weak for spl_image that doesn't do anything, but >> > > > can be overwritten in vendor-specific files to provide means of >> > > > authenticating spl_image. Would this be a good approach? >> > > > >> > > > >> > > > >> > > > Beyond that I was reviewing some of the awesome work from the Chromium >> > > > team and I think on ARMv7 after we get MLO to authenticate U-Boot >> > > > everything beyond that is already looking very solid and thorough (with >> > > > FIT, DTB/Kernel and initramfs authentication). >> > > >> > > It should be possible to use this from SPL, if you can enable FIT in >> > > SPL. The current implementation does not support verification, and is >> > > deliberately cut down. See common/spl/spl_fit.c. >> > >> > Oh, I just noticed this file after doing a pull, that's really one step >> > ahead of the U-Boot versions I've worked with so far. Upon further >> > digging I found that the general SPL FIT approach is actually something >> > we are trying to enable for our own customers moving forward. So adding/ >> > enabling FIT auth in SPL would really help connecting the dots and >> > closing the current authentication gap not just for us but actually for >> > all U-Boot users. >> >> Agreed. >> >> > >> > Will look at this more closely and see how much overhead this would >> > involve since for SPL memory can be of an issue, as using SPL >> > authenticated FIT will probably mean pulling in the U-Boot crypto stuff >> > as in such case we would be using U-Boot tooling to generate the signed >> > FIT image (as opposed to a vendor-specific signing tool generating an >> > image compatible with a simple SoC ROM API auth call). But looking at >> > the already memory-optimized U-Boot RSA verification code in >> > rsa-verify.c and rsa-checksum.c I would hope the impact would not be too >> > bad. I'd guess maybe 10-20KB total with SHA256, RSA, and the needed code >> > changes to spl_fit.c. >> >> The overhead for U-Boot itself is covered in the 'Verified Boot on >> Chrome OS and How to do it yourself' talk here: >> >> http://elinux.org/ELC_Europe_2013_Presentations >> >> Verified boot itself is about 6KB on Thumb 2, on top of the FIT overhead. > > Hi Simon, > I had actually seen/reviewed this presentation earlier and thought it was > very helpful to get started so thanks for pointing this out again. > >> > > but you could perhaps >> > > provide an option to use the full U-Boot implementation instead. >> > >> > ...which would mean that the entire U-Boot would need to be loaded >> > initially as one piece which wouldn't work on some of our SoCs due to >> > memory constraints (hence the SPL approach). >> >> No I don't mean that. I mean use the full U-Boot FIT implementation, >> i.e. just the same code. It would still run in FIT. > > Ok understood, that would seem to make it easier/cleaner from an > implementation POV. Still, I've concerns specifically with one of our > SoCs of which its high-security device variant apparently only has > something to the order of 45KB for SPL use, which folks had to make a > lot of effort to strip down/squeeze in a custom SPL, even going as far > as trimming down strings (and that's using a proprietary authentication > scheme for U-Boot that almost doesn't take any space at all). I need to > find some time to dig deeper and play with the bits and bytes but my > current thinking is to try to pursue the SPL-based FIT approach you > suggested for the general use case, but have one exception for that > particular one SoC using a vendor-specific authentication approach since > there might not be another way due to the memory constraints. > >> Much of the bloat >> is messages which can be dropped. I did an experiment on this a while >> ago and already have it on my list to see if I can find any remnants >> of it. > > Yeah please let me/us know if there is something you have that could be > recycled.
I just sent a patch referring to this. I didn't find anything but in fact it is pretty easy now as a lot of the work is done. Or at least he hard part is now the logic of which image to load, not the code building. http://patchwork.ozlabs.org/patch/617228/ Also see Teddy's version: http://patchwork.ozlabs.org/patch/617229/ Regards, Simon _______________________________________________ U-Boot mailing list [email protected] http://lists.denx.de/mailman/listinfo/u-boot
