[cryptography] Just how bad is OpenSSL ?

Jeffrey Walton noloader at gmail.com
Mon Oct 29 19:47:29 EDT 2012


Hi Alexander,

Sorry to go offlist.

On Mon, Oct 29, 2012 at 7:31 PM, Solar Designer <solar at openwall.com> wrote:
> On Mon, Oct 29, 2012 at 04:06:58PM -0400, Jeffrey Walton wrote:
>> On Sun, Oct 28, 2012 at 3:01 PM, Solar Designer <solar at openwall.com> wrote:
>> > [SNIP, SNIP, SNIP]

>> GCC uses volatile strictly for memory mapped hardware
>> (http://gcc.gnu.org/ml/gcc-help/2012-03/msg00251.html), so its an
>> abuse that the value is changed by software.
>
> <offtopic>
> This thread on gcc-help talks about two possible uses of volatile: for
> memory-mapped I/O (correct) and for communication between threads (wrong
> unless memory barriers are also used).  However, these are not the only
> possible uses.  volatile is also useful for communication within one
> process (one thread), typically when the main program wants to check
> whether one of its signal handlers has been called.  The signal handler
> updates a variable and returns.  The main program reads the volatile
> variable from inside a loop and becomes aware of the event.  Without the
> volatile keyword, it would potentially be reading a cached copy of the
> variable (usually a register), so it would not learn of the event until
> much later (likely until exiting/re-entering the function), if at all.
> </offtopic>
According to GCC's interpretation, I believe this is an abuse since
volatile only applies to memory mapped hardware.

>> The OpenSSL cleanse() function will likely fail on BIOs created from
>> storage and memory mapped files when used on SSDs due to write
>> leveling and on-controller compression. If write leveling goes away,
>> it looks like cleanse() will still fail due to compression. Hence the
>> need for random, non-compressible data.
>
> Not overwriting the same location may also happen due to journaling
> filesystems.
This is a tough problem, and I have not figured out how to solve it
short of using an encrypted drive (not available on all hardware, such
as Mac Books). Risk Acceptance to the rescue!

Jeff



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