kexec_load(2) bypasses signature verification
dyoung at redhat.com
Mon Jun 15 02:11:00 PDT 2015
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
Add Vivek to the loop.
More information about the kexec