Vivek Goyal <vgoyal at redhat.com> writes: > On Tue, Jun 16, 2015 at 02:38:31PM -0500, Eric W. Biederman wrote: >> >> Adding Vivek as he is the one who implemented kexec_file_load. >> I was hoping he would respond to this thread, and it looks like he >> simply has not ever been Cc'd. >> >> Theodore Ts'o <tytso at mit.edu> writes: >> >> > On Mon, Jun 15, 2015 at 09:37:05AM -0400, Josh Boyer wrote: >> >> The bits that actually read Secure Boot state out of the UEFI >> >> variables, and apply protections to the machine to avoid compromise >> >> under the SB threat model. Things like disabling the old kexec... >> > >> > I don't have any real interest in using Secure Boot, but I *am* >> > interested in using CONFIG_KEXEC_VERIFY_SIG[1]. So perhaps we need to >> > have something similar to what we have with signed modules in terms of >> > CONFIG_MODULE_SIG_FORCE and module/sig_enforce, but for >> > KEXEC_VERIFY_SIG. This would mean creating a separate flag >> > independent of the one Linus suggested for Secure Boot, but since we >> > have one for signed modules, we do have precedent for this sort of >> > thing. >> >> My overall request with respect to kexec has been that we implement >> things that make sense outside of the bizarre threat model of the Linux >> folks who were talking about secure boot. >> >> nI have not navigated the labyrinth of config options but having a way to >> only boot signed things with kexec seems a completely sensible way to >> operate in the context of signed images. >> >> I don't know how much that will help given that actors with sufficient >> resources have demonstrated the ability to steal private keys, but >> assuming binary signing is an effective technique (or why else do it) >> then having an option to limit kexec to only loading signed images seems >> sensible. > > I went through the mail chain on web and here are my thoughts. > > - So yes, upstream does not have the logic which automatically disables > the old syscall (kexec_load()) on secureboot systems. Distributions > carry those patches. > > - This KEXEC_VERIFY_SIG option only cotrols the behavior for > kexec_file_load() syscall and is not meant to directly affect any > behavior of old syscall (kexec_load()). I think I should have named > it KEXEC_FILE_VERIFY_SIG. Though help text makes it clear. > "Verify kernel signature during kexec_file_load() syscall". > > - I think disabling old system call if KEXEC_VERIFY_SIG() is set > will break existing setup which use old system call by default, except > the case of secureboot system. And old syscall path is well tested > and new syscall might not be in a position to support all the corner > cases, atleast as of now. > > Ted, > > So looks like you are looking for a system/option where you just want to > always make use of kexec_file_load() and disable kexec_load(). This sounds > like you want a kernel where kexec_load() is compiled out and you want > only kexec_file_load() in. > > Right now one can't do that becase kexec_file_load() depends on > CONFIG_KEXEC option. > > I am wondering that how about making CONFIG_KEXEC_FILE_LOAD independent > of CONFIG_KEXEC. That way one can set CONFIG_KEXEC_VERIFY_SIG=y, and > only signed kernel can be kexeced on that system. > > This should gel well with long term strategy of deprecating kexec_load() > at some point of time when kexec_file_load() is ready to completely > replace it. Interesting. I suspect that what we want is to have CONFIG_KEXEC for the core and additional CONFIG_KEXEC_LOAD option that covers that kexec_load call. That should make it trivially easy to disable the kexec_load system call in cases where people care. Eric
