Edward Tomasz Napierała
2017-Apr-08 11:52 UTC
Proposal for a design for signed kernel/modules/etc
On 0408T0803, Eric McCorkle wrote:> On 04/08/2017 07:11, Edward Tomasz Napiera?a wrote: > > On 0327T1354, Eric McCorkle wrote: > >> Hello everyone, > >> > >> The following is a design proposal for signed kernel and kernel module > >> loading, both at boot- and runtime (with the possibility open for signed > >> executables and libraries if someone wanted to go that route). I'm > >> interested in feedback on the idea before I start actually writing code > >> for it. > > > > I see two potential problems with this. > > > > First, our current loader(8) depends heavily on Forth code. By making > > it load modified 4th files, you can do absolutely anything you want; > > AFAIK they have unrestricted access to hardware. So you should preferably > > be able to sign them as well. You _might_ (not sure on this one) also > > want to be able to restrict access to some of the loader configuration > > variables. > > Loader is handled by the UEFI secure boot framework, though the concerns > about the 4th code are still valid. In a secure system, you'd want to > do something about that, but the concerns are different enough (and it's > isolated enough) that it could be done separately.Unless the way to address those ends up being a signature mechanism that doesn't depend on the format of the files being signed.> > Second - given OpenSSL track record, moving signature verification > > and the x.509 stuff into the kernel (to verify userland) and loader > > (to verify the kernel and modules)... well, it just doesn't seem > > to be a good idea. > > Integrating all of OpenSSL would be massively overkill. All you need is > RSA/Ed25519 signature verification and parsing a subset of PKCS#7. > > My thoughts here are to grab the RSA/Ed25519 implementations from > libsodium and just write a minimal PKCS#7 parser.Ok, that seems to be a reasonable idea.> > Also: do you know about veriexec? > > > > https://reviews.freebsd.org/D8575 > > Is there some documentation of this other than a code review?Not sure; it might be best to just ask the author. Note that there are some manual pages in there, and also that it's not a single review - follow the chain of "Depends on", there's a lot of stuff there.
On 04/08/2017 07:52, Edward Tomasz Napiera?a wrote:> On 0408T0803, Eric McCorkle wrote: >> On 04/08/2017 07:11, Edward Tomasz Napiera?a wrote: >>> On 0327T1354, Eric McCorkle wrote: >>>> Hello everyone, >>>> >>>> The following is a design proposal for signed kernel and kernel module >>>> loading, both at boot- and runtime (with the possibility open for signed >>>> executables and libraries if someone wanted to go that route). I'm >>>> interested in feedback on the idea before I start actually writing code >>>> for it. >>> >>> I see two potential problems with this. >>> >>> First, our current loader(8) depends heavily on Forth code. By making >>> it load modified 4th files, you can do absolutely anything you want; >>> AFAIK they have unrestricted access to hardware. So you should preferably >>> be able to sign them as well. You _might_ (not sure on this one) also >>> want to be able to restrict access to some of the loader configuration >>> variables. >> >> Loader is handled by the UEFI secure boot framework, though the concerns >> about the 4th code are still valid. In a secure system, you'd want to >> do something about that, but the concerns are different enough (and it's >> isolated enough) that it could be done separately. > > Unless the way to address those ends up being a signature mechanism > that doesn't depend on the format of the files being signed.I explored the idea of wrapped or detached signatures in the previous discussion. Envelopes or detached signatures could make sense for the 4th files. It's a small, obscure set of code that probably isn't changed very often. Envelopes or detached signatures for kernel modules and especially signed executables and libraries both have extensive, far-reaching consequences for system administration, packaging, tooling, the ports collection, and so on, whereas signing the executable with an additional section has no such consequences. Config files (and the 4th files really are more like config files) have a different set of constraints, and detached signatures are probably the way to go there. So loader should probably support detached PKCS#7 signature checks. -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 228 bytes Desc: OpenPGP digital signature URL: <http://lists.freebsd.org/pipermail/freebsd-security/attachments/20170409/b690a133/attachment.sig>