Re: [PATCH 2/2] x86/ldt: Unmap PTEs for the slow before freeing LDT
From: Andy Lutomirski
Date: Wed Oct 24 2018 - 14:49:33 EST
On Tue, Oct 23, 2018 at 9:32 AM Kirill A. Shutemov
> modify_ldt(2) leaves old LDT mapped after we switch over to the new one.
> Memory for the old LDT gets freed and the pages can be re-used.
> Leaving the mapping in place can have security implications. The mapping
> is present in userspace copy of page tables and Meltdown-like attack can
> read these freed and possibly reused pages.
Code looks okay. But:
> - /*
> - * Did we already have the top level entry allocated? We can't
> - * use pgd_none() for this because it doens't do anything on
> - * 4-level page table kernels.
> - */
> - pgd = pgd_offset(mm, LDT_BASE_ADDR);
This looks like an unrelated cleanup. Can it be its own patch?