Re: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function

[Yu-cheng Yu]

On Mon, 2019-06-10 at 15:59 -0700, Dave Hansen wrote:
> On 6/10/19 3:40 PM, Yu-cheng Yu wrote:
> > Ok, we will go back to do_mmap() with MAP_PRIVATE, MAP_NORESERVE and
> > VM_DONTDUMP.  The bitmap will cover only 48-bit address space.
> 
> Could you make sure to discuss the downsides of only doing a 48-bit
> address space?

The downside is that we cannot load legacy lib's above 48-bit address space, but
currently ld-linux does not do that.  Should ld-linux do that in the future,
dlopen() fails.  Considering CRIU migration, we probably need to do this anyway?

> What are the reasons behind and implications of VM_DONTDUMP?

The bitmap is very big.

In GDB, it should be easy to tell why a control-protection fault occurred
without the bitmap.

Yu-cheng