[PATCH 2/3] kexec: call LSM hook for kexec_load syscall
Eric W. Biederman
ebiederm at xmission.com
Thu May 3 08:51:38 PDT 2018
Mimi Zohar <zohar at linux.vnet.ibm.com> writes:
> On Wed, 2018-05-02 at 09:45 -0500, Eric W. Biederman wrote:
>> Mimi Zohar <zohar at linux.vnet.ibm.com> writes:
>> > Allow LSMs and IMA to differentiate between the kexec_load and
>> > kexec_file_load syscalls by adding an "unnecessary" call to
>> > security_kernel_read_file() in kexec_load. This would be similar to the
>> > existing init_module syscall calling security_kernel_read_file().
>> Given the reasonable desire to load a policy that ensures everything
>> has a signature I don't have fundamental objections.
>> security_kernel_read_file as a hook seems an odd choice. At the very
>> least it has a bad name because there is no file reading going on here.
>> I am concerned that I don't see CONFIG_KEXEC_VERIFY_SIG being tested
>> anywhere. Which means I could have a kernel compiled without that and I
>> would be allowed to use kexec_file_load without signature checking.
>> While kexec_load would be denied.
>> Am I missing something here?
> The kexec_file_load() calls kernel_read_file_from_fd(), which in turn
> calls security_kernel_read_file(). So kexec_file_load and kexec_load
> syscall would be using the same method for enforcing signature
Having looked at your patches and the kernel a little more I think
this should be a separate security hook that does not take a file
Right now every other security module assumes !file is init_module.
So I think this change has the potential to confuse other security
modules, with the result of unintended policy being applied.
So just for good security module hygeine I think this needs a dedicated
kexec_load security hook.
> This is independent of the architecture specific method for verifying
> signatures. The coordination between these two methods was included
> in the lockdown patch set, but is being removed, as well the gating of
> kexec_load syscall. Instead of being based on the lockdown flag, I
> assume the coordination between the two methods will reappear based on
> a secure boot flag of some sort.
I was blind there for a moment. Yes this is all about the ima xattrs
allowing a file to be loaded.
More information about the kexec