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Reply-To: kernel-hardening@lists.openwall.com
Date: Tue, 29 Nov 2016 10:31:59 +0100
From: Peter Zijlstra <peterz@infradead.org>
Message-ID: <20161129093159.GD3092@twins.programming.kicks-ass.net>
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In-Reply-To: <000779ba-0b53-3064-db8a-f309b2c993f5@ozlabs.ru>
Subject: [kernel-hardening] Re: Conversion from atomic_t to refcount_t: summary of issues
To: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: "Reshetova, Elena" <elena.reshetova@intel.com>, "kernel-hardening@lists.openwall.com" <kernel-hardening@lists.openwall.com>, Greg KH <gregkh@linuxfoundation.org>, Kees Cook <keescook@chromium.org>, "will.deacon@arm.com" <will.deacon@arm.com>, Boqun Feng <boqun.feng@gmail.com>, Hans Liljestrand <ishkamiel@gmail.com>, David Windsor <dwindsor@gmail.com>, david@gibson.dropbear.id.au
List-ID: <kernel-hardening.lists.openwall.com>

On Tue, Nov 29, 2016 at 02:19:56PM +1100, Alexey Kardashevskiy wrote:
> On 28/11/16 23:13, Peter Zijlstra wrote:
> > On Mon, Nov 28, 2016 at 11:56:17AM +0000, Reshetova, Elena wrote:
> >> First, about the types. 
> >> We do have a number of instances of atomic_long_t used as refcounters, see below:
> > 
> > Right, those were expected. We could do long_refcount_t I suppose.
> > 
> >> And yes, we *do* have at least one instance (again not 100% finished,
> >> more might show up) of atomic64_t used as refcounter:
> >>
> >> arch/powerpc/mm/mmu_context_iommu.c:
> >> struct mm_iommu_table_group_mem_t {
> >> ...
> >>     atomic64_t mapped;
> >> ...
> >> }
> > 
> > *urgh*, Alexey does that really need to be atomic64_t ? Wouldn't
> > atomic_long_t work for you?
> 
> 
> It would, this code only works in 64bit where long==64bit anyway (in fact
> even 32bit variant would do).
> 

Thanks, we'll convert it to a 32bit refcount then.