On Wed, Nov 04, 2020 at 08:57:05AM +0000, Szabolcs Nagy wrote: > The 11/03/2020 23:41, Jeremy Linton wrote: > > On 11/3/20 11:34 AM, Mark Brown wrote: > > > On Tue, Nov 03, 2020 at 10:25:37AM +0000, Szabolcs Nagy wrote: > > > > > > > Re-mmap executable segments instead of mprotecting them in > > > > case mprotect is seccomp filtered. > > > > > > > For the kernel mapped main executable we don't have the fd > > > > for re-mmap so linux needs to be updated to add BTI. (In the > > > > presence of seccomp filters for mprotect(PROT_EXEC) the libc > > > > cannot change BTI protection at runtime based on user space > > > > policy so it is better if the kernel maps BTI compatible > > > > binaries with PROT_BTI by default.) > > > > > > Given that there were still some ongoing discussions on a more robust > > > kernel interface here and there seem to be a few concerns with this > > > series should we perhaps just take a step back and disable this seccomp > > > filter in systemd on arm64, at least for the time being? That seems > > > safer than rolling out things that set ABI quickly, a big part of the > > > > So, that's a bigger hammer than I think is needed and punishes !BTI > > machines. I'm going to suggest that if we need to carry a temp patch its > > more like the glibc patch I mentioned in the Fedora defect. That patch > > simply logs a message, on the mprotect failures rather than aborting. Its > > fairly non-intrusive. > > > > That leaves seccomp functional, and BTI generally functional except when > > seccomp is restricting it. I've also been asked that if a patch like that is > > needed, its (temporary?) merged to the glibc trunk, rather than just being > > carried by the distro's. > > note that changing mprotect into mmap in glibc works > even if the kernel or systemd decides to do things > differently: currently the only wart is that on the > main exe we have to use mprotect and silently ignore > the failures. Can the dynamic loader mmap() the main exe again while munmap'ing the original one? (sorry if it was already discussed) -- Catalin
