Re: [PATCH] mm/vmalloc: randomize vmalloc() allocations

[Topi Miettinen]

On 3.12.2020 8.58, Mike Rapoport wrote:
> On Wed, Dec 02, 2020 at 08:49:06PM +0200, Topi Miettinen wrote:
> > On 1.12.2020 23.45, Topi Miettinen wrote:
> > > Memory mappings inside kernel allocated with vmalloc() are in
> > > predictable order and packed tightly toward the low addresses. With
> > > new kernel boot parameter 'randomize_vmalloc=1', the entire area is
> > > used randomly to make the allocations less predictable and harder to
> > > guess for attackers.
> >
> > This also seems to randomize module addresses. I was going to check that
> > next, so nice surprise!
>
> Heh, that's because module_alloc() uses vmalloc() in that way or another :)

The modules are still allocated from their small (1.5GB) separate area 
instead of the much larger (32TB/12.5PB) vmalloc area, which would 
greatly improve ASLR for the modules. To fix that, I tried to to #define 
MODULES_VADDR to VMALLOC_START etc. like x86_32 does, but then kernel 
dies very early without even any output.

-Topi