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Subject: Re: [PATCH] mm/vmalloc: randomize vmalloc() allocations
To:     Mike Rapoport <rppt@kernel.org>
Cc:     linux-hardening@vger.kernel.org, akpm@linux-foundation.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Andy Lutomirski <luto@kernel.org>,
        Jann Horn <jannh@google.com>,
        Kees Cook <keescook@chromium.org>,
        Linux API <linux-api@vger.kernel.org>,
        Matthew Wilcox <willy@infradead.org>
References: <20201201214547.9721-1-toiwoton@gmail.com>
 <9d34fb0a-7aba-1e84-6426-006ea7c3d9f5@gmail.com>
 <20201203065801.GH751215@kernel.org>
From:   Topi Miettinen <toiwoton@gmail.com>
Message-ID: <26f0c73a-3a81-4ba6-2b6f-c5ca73ea866b@gmail.com>
Date:   Wed, 9 Dec 2020 21:08:23 +0200
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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