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Re: [PATCH RFC] explicit_bzero, again

On Fri, Aug 21, 2015 at 2:37 AM, Florian Weimer <> wrote:
> On 08/16/2015 06:43 PM, Zack Weinberg wrote:
>> +@strong{Warning:} The compiler is free to make additional copies of
>> +any object, or parts of it, in temporary storage areas (such as
>> +registers and ``scratch'' stack space).  @code{explicit_bzero} does
>> +not guarantee that temporary copies of sensitive data are destroyed.
> Perhaps you should add that explicit_bzero can create the copy which it
> is about to overwrite, leaving the original untouched.  A partial
> countermeasure could be a barrier with register clobbers for as many
> caller-saved registers as possible.

I'm not doubting you, but that's surprising enough that if I am going
to put it in the manual, it needs an example of the situation where it
can happen, and I am failing to think of one; what do you have in

Also, are you saying that this barrier should be part of
explicit_bzero itself, or something the application needs to do?


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