Re: x86: PIE support and option to extend KASLR randomization

On Wed, Aug 16, 2017 at 05:12:35PM +0200, Ingo Molnar wrote:

Unfortunately mcmodel=large looks pretty heavy too AFAICS, at the machine 
instruction level.

Function calls look like this:

 -mcmodel=medium:

   757:   e8 98 ff ff ff          callq  6f4 <test_code>

 -mcmodel=large

   77b:   48 b8 10 f7 df ff ff    movabs $0xffffffffffdff710,%rax
   782:   ff ff ff 
   785:   48 8d 04 03             lea    (%rbx,%rax,1),%rax
   789:   ff d0                   callq  *%rax

And we'd do this for _EVERY_ function call in the kernel. That kind of crap is 
totally unacceptable.

So why does this need to be computed for every single call? How often
will we move the kernel around at runtime?

Why can't we process the relocation at load time and then discard the
relocation tables along with the rest of __init ?