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

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Message-ID: <20210315174742.GA2038@pc638.lan>
Date:   Mon, 15 Mar 2021 18:47:42 +0100
From:   Uladzislau Rezki <urezki@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Uladzislau Rezki <urezki@...il.com>,
        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 09:16:26AM -0700, Kees Cook wrote:
> 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.
> 
Probably we can randomize a base address only once when pcpu-allocator
allocates a fist chunk during the boot.

> > - 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.
> 
It should be split as well as tested.

--
Vlad Rezki