Re: [PATCHv3 1/3] x86/mm: Move LDT remap out of KASLR region on 5-level paging

Andy Lutomirski
2018-11-02T21:08:00Z

On Fri, Oct 26, 2018 at 5:29 AM Kirill A. Shutemov
<kirill.shutemov@linux.intel.com> wrote:
>
> On 5-level paging LDT remap area is placed in the middle of
> KASLR randomization region and it can overlap with direct mapping,
> vmalloc or vmap area.
>
> Let's move LDT just before direct mapping which makes it safe for KASLR.
> This also allows us to unify layout between 4- and 5-level paging.
>
> We don't touch 4 pgd slot gap just before the direct mapping reserved
> for a hypervisor, but move direct mapping by one slot instead.
>
> The LDT mapping is per-mm, so we cannot move it into P4D page table next
> to CPU_ENTRY_AREA without complicating PGD table allocation for 5-level
> paging.

Reviewed-by: Andy Lutomirski <luto@kernel.org>

(assuming it passes tests with 4-level and 5-level. my test setup is
current busted, and i'm bisecting it.)