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Date:   Wed, 9 Dec 2020 21:08:23 +0200
From:   Topi Miettinen <>
To:     Mike Rapoport <>
        Andy Lutomirski <>,
        Jann Horn <>,
        Kees Cook <>,
        Linux API <>,
        Matthew Wilcox <>
Subject: Re: [PATCH] mm/vmalloc: randomize vmalloc() allocations

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.


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