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Date: Mon, 25 Mar 2019 08:10:58 +0100
From: magnum <>
Subject: Re: can other user access secrets in GPU's memory?

On 2019-03-24 23:42, Aleksey Cherepanov wrote:
> I was playing around with OpenCL and it looks like memory is not zeroed
> by default on GPUs, i.e. I can read old values from gpu on another run
> of host program. So I guess it means that other users can read these
> values too, right? Does john clean up memory after work to avoid this?

No. We could add zeroing of allocated buffers before releasing them but 
there'd still be lots of data in other memory where we don't have any 

> Or is it unusual to run john on a shared machine/gpu?

Maybe not (cloud computing eg. AWS) but GPUs doesn't have any protection 
against users reading your memory even *while* you're using it. In my 
view is this is primarily a driver/runtime issue and ultimately even a 
hardware issue (no memory protection in the design).


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