Re: [systemd-devel] BTI interaction between seccomp filters in systemd and... | linux-arm-kernel

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On Do, 22.10.20 09:29, Szabolcs Nagy (szabolcs.nagy@arm.com) wrote:

The dynamic loader has to process the LOAD segments to get to the ELF
note that says to enable BTI.  Maybe we could do a first pass and load
only the segments that cover notes.  But that requires lots of changes
to generic code in the loader.
What if the loader always enabled BTI for PROT_EXEC pages, but then when
discovering that this was a mistake, mprotect() the pages without BTI? Then
both BTI and MDWX would work and the penalty of not getting MDWX would fall
to non-BTI programs. What's the expected proportion of BTI enabled code vs.
disabled in the future, is it perhaps expected that a distro would enable
the flag globally so eventually only a few legacy programs might be
unprotected?
i thought mprotect(PROT_EXEC) would get filtered
with or without bti, is that not the case?
We can adjust the filter in systemd to match any combination of
flags to allow and to deny.

Lennart

--
Lennart Poettering, Berlin

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Re: [systemd-devel] BTI interaction between seccomp filters in systemd and glibc mprotect calls, causing service failures

Possibly related (same subject, not in this thread)