[PATCH] crypto: twofish-avx - remove useless instruction

[PATCH] crypto: twofish-avx - remove useless instruction

[Johannes Goetzfried]

The register %rdx is written, but never read till the end of the encryption
routine. Therefore let's delete the useless instruction.

Signed-off-by: Johannes Goetzfried <Johannes.Goetzfried@informatik.stud.uni-erlangen.de>
---
 arch/x86/crypto/twofish-avx-x86_64-asm_64.S |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/arch/x86/crypto/twofish-avx-x86_64-asm_64.S b/arch/x86/crypto/twofish-avx-x86_64-asm_64.S
index fc31b89..35f4557 100644
--- a/arch/x86/crypto/twofish-avx-x86_64-asm_64.S
+++ b/arch/x86/crypto/twofish-avx-x86_64-asm_64.S
@@ -243,7 +243,6 @@ __twofish_enc_blk_8way:
 	popq %rbx;
 
 	leaq (4*4*4)(%rsi), %rax;
-	leaq (4*4*4)(%rax), %rdx;
 
 	testb %cl, %cl;
 	jnz __enc_xor8;
-- 
1.7.2.5

Re: [PATCH] crypto: twofish-avx - remove useless instruction

[Henrique de Moraes Holschuh]

On Thu, 05 Jul 2012, Johannes Goetzfried wrote:
> The register %rdx is written, but never read till the end of the encryption
> routine. Therefore let's delete the useless instruction.

Is it useless, or is it there to harden against some side-channel
attack?

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh

Re: [PATCH] crypto: twofish-avx - remove useless instruction

[Johannes Goetzfried]

On Thu, Jul 05, 2012 at 08:46:12PM -0300, Henrique de Moraes Holschuh wrote:
> Is it useless, or is it there to harden against some side-channel
> attack?

When writing this implementation, I first had a different approach with more
data getting read in and I just forgot to delete this instruction in the end.
The instruction didn't have any purpose regarding side-channel attacks. In the
decryption routine the instruction has been correctly deleted in the same
place.

Re: [PATCH] crypto: twofish-avx - remove useless instruction

[Herbert Xu]

On Thu, Jul 05, 2012 at 08:43:58PM +0200, Johannes Goetzfried wrote:
> The register %rdx is written, but never read till the end of the encryption
> routine. Therefore let's delete the useless instruction.
> 
> Signed-off-by: Johannes Goetzfried <Johannes.Goetzfried@informatik.stud.uni-erlangen.de>

Patch applied.  Thanks!
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt