Date: Sun, 13 Jun 2010 10:07:15 +0200 From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no> To: ticso@cicely.de Cc: current@freebsd.org Subject: Re: Cleanup for cryptographic algorithms vs. compiler optimizations Message-ID: <86wru3we30.fsf@ds4.des.no> In-Reply-To: <20100612225216.GT87112@cicely7.cicely.de> (Bernd Walter's message of "Sun, 13 Jun 2010 00:52:16 %2B0200") References: <20100611162118.GR39829@acme.spoerlein.net> <867hm5tl6u.fsf@ds4.des.no> <20100612153526.GA3632@acme.spoerlein.net> <20100612163208.GS87112@cicely7.cicely.de> <864oh86tnl.fsf@ds4.des.no> <20100612225216.GT87112@cicely7.cicely.de>
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Bernd Walter <ticso@cicely7.cicely.de> writes: > Dag-Erling Sm=C3=B8rgrav <des@des.no> writes: > > Bernd Walter <ticso@cicely7.cicely.de> writes: > > > I'm not sure when removing a memset is allowed. > > Always, if the compiler can determine that the data will not be used > > later. > I'm at least sure that the compiler can't if it is linked from another > object file. When running in hosted mode, the compiler can *always* inline a memset() call or eliminate it if it can determine that the result is not used. > The problem with memset is that the compiler has an internal > implementation. That's a feature, not a problem. > On the other hand I wonder what the deep sense is to clear memory > which is unused later. I know that crypto code can be tricky > sometimes, but if someone is willing to explain the specific reason my > curiosity would be satified. You always overwrite passphrases, keys etc. as soon as you're done with them so they don't end up in a crash dump or on a swap disk or something. DES --=20 Dag-Erling Sm=C3=B8rgrav - des@des.no
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