Messages in this thread | | | Subject | Re: [PATCH 0/4] aarch64: avoid mprotect(PROT_BTI|PROT_EXEC) [BZ #26831] | From | Jeremy Linton <> | Date | Tue, 3 Nov 2020 23:41:42 -0600 |
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Hi,
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.
Thanks,
> reason we went with having the dynamic linker enable PROT_BTI in the > first place was to give us more flexibility to handle any unforseen > consequences of enabling BTI that we run into. We are going to have > similar issues with other features like MTE so we need to make sure that > whatever we're doing works with them too. > > Also updated to Will's current e-mail address - Will, do you have > thoughts on what we should do here? >
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