netdev - RE: [PATCH 2/3] sha512: reduce stack usage to safe number

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Message-ID: <1326709382.2255.4.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Mon, 16 Jan 2012 11:23:02 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	linux-crypto@...r.kernel.org, netdev@...r.kernel.org,
	ken@...elabs.ch, Steffen Klassert <steffen.klassert@...unet.com>,
	security@...nel.org
Subject: RE: [PATCH 2/3] sha512: reduce stack usage to safe number

Le lundi 16 janvier 2012 à 09:56 +0000, David Laight a écrit :
> Doesn't this badly overflow W[] ..
>  
> > +#define SHA512_0_15(i, a, b, c, d, e, f, g, h) \
> > +	t1 = h + e1(e) + Ch(e, f, g) + sha512_K[i] + W[i];	\
> ...
> > +	for (i = 0; i < 16; i += 8) {
> ...
> > +		SHA512_0_15(i + 7, b, c, d, e, f, g, h, a);
> > +	}
> 
> 	David
> 
> 

No overflow since loop is done for only i=0 and i=8

By the way, I suspect previous code was chosen years ago because this
version uses less stack but adds much more code bloat.


size crypto/sha512_generic.o crypto/sha512_generic_old.o
   text	   data	    bss	    dec	    hex	filename
  17369	    704	      0	  18073	   4699	crypto/sha512_generic.o
   8249	    704	      0	   8953	   22f9	crypto/sha512_generic_old.o



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