On Mon, 15 Jun 2015 17:11:00 +0800 Dave Young <dyoung at redhat.com> wrote: > On 06/14/15 at 11:50pm, Theodore Ts'o wrote: > > From experimentation and from looking at the sources, it appears that > > the signature checking is only done in the kexec_file_load(2) system > > all, and not in the kexec_load(2) system call. And I understand why > > -- the signature is not sent from userspace to the kernel in the older > > kexec_load(2) system call. > > > > The problem is that if you use an old version of kexec, it will use > > the old kexec_load(2) system call, and even though > > CONFIG_KEXEC_VERIFY_SIG is enabled, kexec_load(2) will happily load an > > unsigned kernel, and then "kexec -e" will happily boot into it. > > > > Correct me if I am wrong, but this appears to be a hole in Secure Boot > > you could drive a Mack Truck through. > > > > (I noticed this because Debian is still using a kexec-tools from the > > stone ages, version 2.0.7, and I was wondering **why** I was able to > > kexec boot completely unsigned kernels.) > > > > It would appear to me that if CONFIG_KEXEC_VERIFY_SIG is enabled, the > > old kexec_load(2) system call should be disabled (and a warning be > > placed in the Kconfig help that the user should have at least verision > > 2.X of kexec-tools if they enable this kernel option). > > IMO it is fine to disable old syscall incase CONFIG_KEXEC_VERIFY=y Definitely. It is not possible to to sign all code passed through kexec_load(2), at least not without giving kexec-tools the private part of the key (which would effectively destroy the goal of Secure Boot). Whenever signature verification is required, kexec_load(2) must be disabled. Petr Tesarik
