linux-kernel - Re: [PATCH v4] mm/vmalloc: randomize vmalloc() allocations

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Date:   Mon, 15 Mar 2021 09:16:26 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Uladzislau Rezki <urezki@...il.com>
Cc:     Topi Miettinen <toiwoton@...il.com>,
        linux-hardening@...r.kernel.org, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Jann Horn <jannh@...gle.com>,
        Linux API <linux-api@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Mike Rapoport <rppt@...nel.org>
Subject: Re: [PATCH v4] mm/vmalloc: randomize vmalloc() allocations

On Mon, Mar 15, 2021 at 01:24:10PM +0100, Uladzislau Rezki wrote:
> On Mon, Mar 15, 2021 at 11:04:42AM +0200, Topi Miettinen wrote:
> > What's the problem with that? It seems to me that nothing relies on specific
> > addresses of the chunks, so it should be possible to randomize these too.
> > Also the alignment is honored.
> > 
> My concern are:
> 
> - it is not a vmalloc allocator;
> - per-cpu allocator allocates chunks, thus it might be it happens only once. It does not allocate it often;

That's actually the reason to randomize it: if it always ends up in the
same place at every boot, it becomes a stable target for attackers.

> - changing it will likely introduce issues you are not aware of;
> - it is not supposed to be interacting with vmalloc allocator. Read the
>   comment under pcpu_get_vm_areas();
> 
> Therefore i propose just not touch it.

How about splitting it from this patch instead? Then it can get separate
testing, etc.

-- 
Kees Cook