Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> writes: > On Wed, 2018-05-02 at 09:45 -0500, Eric W. Biederman wrote: >> Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> 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 > verification. 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 parameter. 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. Eric
