Vivek Goyal <vgoyal at redhat.com> writes: > On Fri, Nov 22, 2013 at 07:39:14PM -0800, Eric W. Biederman wrote: > > [..] >> > Hmm..., I am running out of ideas here. This is what I understand. >> > >> > - If I sign the bzImage (using PKCS1.5 signature), and later it is signed >> > with authenticode format signatures, then PKCS1.5 signatures will not be >> > valid as PE/COFF signing will do some modification to PE/COFF header in >> > bzImage. And another problem is that then I don't have a way to find >> > PKCS1.5 signature. >> > >> > - If bzImage is first signed with authenticode format signature and then >> > signed using PKCS1.5 signature, then authenticode format signature >> > will become invalid as it will also hash the data appened at the end >> > of file. >> > >> > So looks like both signatures can't co-exist on same file. That means >> > one signature has to be detached. >> > >> > I am beginning to think that create a kernel option which allows to choose >> > between attached and detached signatures. Extend kexec syscall to allow >> > a parameter to pass in detached signatures. If detached signatures are >> > not passed, then look for signatures at the end of file. That way, those >> > who are signing kernels using platform specific format (authenticode) in >> > this case, they can generate detached signature while others can just >> > use attached signatures. >> > >> > Any thoughts on how this should be handled? >> >> Inside of a modern bzImage there is an embedded ELF image. How about in >> userspace we just strip out the embedded ELF image and write that to a >> file. Then we can use the same signature checking scheme as we do for >> kernel modules. And you only have to support one file format. > > I think there is a problem with that. And that we lose the additional > metadata info present in bzImage which is important. > > For example, knowing how much memory kernel will consume before it > sets up its own GDT and page tables (init_size) is very important. That > gives image loader lot of flexibility in figuring out where to place rest > of the components safely (initrd, GDT, page tables, ELF header segment, > backup region etc). The init_size should be reflected in the .bss of the ELF segments. If not it is a bug when generating the kernel ELF headers and should be fixed. For use by kexec I don't see any issues with just signing the embedded ELF image. Eric
