On Thu, Oct 22, 2020 at 01:39:07PM +0300, Topi Miettinen wrote: > But I think SELinux has a more complete solution (execmem) which can track > the pages better than is possible with seccomp solution which has a very > narrow field of view. Maybe this facility could be made available to > non-SELinux systems, for example with prctl()? Then the in-kernel MDWX could > allow mprotect(PROT_EXEC | PROT_BTI) in case the backing file hasn't been > modified, the source filesystem isn't writable for the calling process and > the file descriptor isn't created with memfd_create(). Right. The problem here is that systemd is attempting to mediate a state change using only syscall details (i.e. with seccomp) instead of a stateful analysis. Using a MAC is likely the only sane way to do that. SELinux is a bit difficult to adjust "on the fly" the way systemd would like to do things, and the more dynamic approach seen with SARA[1] isn't yet in the kernel. Trying to enforce memory W^X protection correctly via seccomp isn't really going to work well, as far as I can see. Regardless, it makes sense to me to have the kernel load the executable itself with BTI enabled by default. I prefer gaining Catalin's suggested patch[2]. :) [1] https://lore.kernel.org/kernel-hardening/1562410493-8661-1-git-send-email-s.mesoraca16@xxxxxxxxx/ [2] https://lore.kernel.org/linux-arm-kernel/20201022093104.GB1229@gaia/ -- Kees Cook
