BTI interaction between seccomp filters in systemd and glibc mprotect calls, causing service failures

[Florian Weimer]

* Dave Martin via Libc-alpha:

> Would it now help to add something like:
>
> int mchangeprot(void *addr, size_t len, int old_flags, int new_flags)
> {
> 	int ret = -EINVAL;
> 	mmap_write_lock(current->mm);
> 	if (all vmas in [addr .. addr + len) have
> 			their mprotect flags set to old_flags) {
>
> 		ret = mprotect(addr, len, new_flags);
> 	}
> 	
> 	mmap_write_unlock(current->mm);
> 	return ret;
> }

I suggested something similar as well.  Ideally, the interface would
subsume pkey_mprotect, though, and have a separate flags argument from
the protection flags.  But then we run into argument list length limits.

Thanks,
Florian
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