[kernel-hardening] Re: [PATCH v9 1/4] syscalls: Verify address limit before returning to user-mode

[Christoph Hellwig]

On Tue, May 09, 2017 at 08:45:22AM +0200, Ingo Molnar wrote:
> We only have ~115 code blocks in the kernel that set/restore KERNEL_DS, it would 
> be a pity to add a runtime check to every system call ...

I think we should simply strive to remove all of them that aren't
in core scheduler / arch code.  Basically evetyytime we do the

	oldfs = get_fs();
	set_fs(KERNEL_DS); 
	..
	set_fs(oldfs);

trick we're doing something wrong, and there should always be better
ways to archive it.  E.g. using iov_iter with a ITER_KVEC type
consistently would already remove most of them.