Hi,
There is a problem with glibc+systemd on BTI enabled systems. Systemd
has a service flag "MemoryDenyWriteExecute" which uses seccomp to deny
PROT_EXEC changes. Glibc enables BTI only on segments which are marked
as being BTI compatible by calling mprotect PROT_EXEC|PROT_BTI. That
call is caught by the seccomp filter, resulting in service failures.
So, at the moment one has to pick either denying PROT_EXEC changes, or
BTI. This is obviously not desirable.
Various changes have been suggested, replacing the mprotect with mmap
calls having PROT_BTI set on the original mapping, re-mmapping the
segments, implying PROT_EXEC on mprotect PROT_BTI calls when VM_EXEC is
already set, and various modification to seccomp to allow particular
mprotect cases to bypass the filters. In each case there seems to be an
undesirable attribute to the solution.
So, whats the best solution?
Thanks everyone,
PS: There is a fedora bug about this here:
https://bugzilla.redhat.com/show_bug.cgi?id=1888842 which is also
tracking a systemd issue of the same subject.
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