On Thu, Mar 21, 2013 at 10:58:23AM -0500, Serge E. Hallyn wrote: > Quoting Vivek Goyal (vgoyal@xxxxxxxxxx): > > On Thu, Mar 21, 2013 at 10:37:25AM -0500, Serge E. Hallyn wrote: > > > Quoting Vivek Goyal (vgoyal@xxxxxxxxxx): > > > ... > > > > Giving CAP_MODIFY_KERNEL to processess upon signature verification > > > > will simplify things a bit. > > > > > > > > Only thing is that signature verification alone is not sufficient. We > > > > also need to make sure after signature verification executable can > > > > not be modified in memory in any way. So that means atleast couple of > > > > things. > > > > > > Also what about context? If I construct a mounts namespace a certain > > > way, can I trick this executable into loading an old singed bzImage that > > > I had laying around? > > > > We were thinking that /sbin/kexec will need to verify bzImage signature > > before loading it. > > > > Key for verification is in kernel so idea was to take kernel's help > > in verifying signature. > > > > Not sure how exactly the interface should look like. > > > > - I was thinking may be process can mmap() the bzImage with MAP_LOCKED. > > We can create additional flag say MAP_VERIFY_SIG_POST, which tries > > to verify signature/integrity of mapped region of file after mapping and > > locking pages and mmap() fails if signature verification fails. > > > > There have been suggestions about creating new system call altogether. > > > > > > > > ISTM the only sane thing to do, if you're going down this road, > > > is to have CAP_MODIFIY_KERNEL pulled from bounding set for everyone > > > except a getty started by init on ttyS0. Then log in on serial > > > to update. Or run a damon with CAP_MODIFIY_KERNEL which listens > > > to a init_net_ns netlink socket for very basic instructions, like > > > "find and install latest signed bzImage in /boot". Then you can > > > at least trust that /boot for that daemon is not faked. > > > > daemon does not have the key and can't verify signature of signed > > bzImage. Even if it had the key, it can't trust the crypto code for > > signature verification as none of that is signed. > > I'm not saying not to use the kernel to verify the signature. Ok. So why can't /sbin/kexec can do the verification of bzImage with kernel's help. Due to crafted /boot/ it might load old signed bzImage, but it can't load unsigned/untrusted code on secureboot system at ring 0. I am hoping I did not miss your point entirely. Thanks Vivek -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
