Re: [PATCH v2 8/8] x86/kaslr: Don't use 64-bit mem_vector for 32-bit kernel

From: Arvind Sankar
Date: Tue Jul 28 2020 - 16:08:15 EST

On Tue, Jul 28, 2020 at 12:37:12PM -0700, Kees Cook wrote:
> On Mon, Jul 27, 2020 at 07:08:01PM -0400, Arvind Sankar wrote:
> > Commit
> > f28442497b5c ("x86/boot: Fix KASLR and memmap= collision")
> > converted mem_vector type to use 64-bit on the 32-bit kernel as well,
> > based on Thomas's review [0]. However:
> > - the code still doesn't consistently use 64-bit types. For instance,
> > mem_avoid_overlap uses 32-bit types when checking for overlaps. This
> > is actually okay, as the passed in memory range will have been clipped
> > to below 4G, but it is difficult to reason about the safety of the
> > code.
> > - KASLR on 32-bit can't use memory above 4G anyway, so it's pointless
> > to keep track of ranges above 4G.
> >
> > Switch the type back to unsigned long, and use a helper function to clip
> > regions to 4G on 32-bit, when storing mem_avoid, immovable_mem, EFI,
> > E820 and command-line memory regions.
> The reason for long long is to avoid having to check for overflows in
> any of the offset calculations. Why not just leave this as-is?

The first bullet: there are still unsigned long's in the code that get
assigned mem_vector.start etc. Taking into account Ingo's review as
well, I'm planning to just make all those u64 as well in v3, instead of
this patch.