Commit 5ab1ff2e authored by Eric Biggers's avatar Eric Biggers
Browse files

crypto: x86/aes-gcm - optimize AVX512 precomputation of H^2 from H^1 



Squaring in GF(2^128) requires fewer instructions than a generic
multiplication in GF(2^128).  Take advantage of this when computing H^2
from H^1 in aes_gcm_precompute_vaes_avx512().

Note that aes_gcm_precompute_vaes_avx2() already uses this optimization.

Acked-by: default avatarArd Biesheuvel <ardb@kernel.org>
Tested-by: default avatarArd Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20251002023117.37504-8-ebiggers@kernel.org


Signed-off-by: default avatarEric Biggers <ebiggers@kernel.org>
parent e0abd005

arch/x86/crypto/aes-gcm-vaes-avx512.S

+14 −2
Original line number Diff line number Diff line
@@ -260,6 +260,19 @@ 
	vpternlogd	$0x96, \t0, \mi, \hi

.endm



// This is a specialized version of _ghash_mul that computes \a * \a, i.e. it

// squares \a.  It skips computing MI = (a_L * a_H) + (a_H * a_L) = 0.

.macro	_ghash_square	a, dst, gfpoly, t0, t1

	vpclmulqdq	$0x00, \a, \a, \t0	  // LO = a_L * a_L

	vpclmulqdq	$0x11, \a, \a, \dst	  // HI = a_H * a_H

	vpclmulqdq	$0x01, \t0, \gfpoly, \t1  // LO_L*(x^63 + x^62 + x^57)

	vpshufd		$0x4e, \t0, \t0		  // Swap halves of LO

	vpxord		\t0, \t1, \t1		  // Fold LO into MI

	vpclmulqdq	$0x01, \t1, \gfpoly, \t0  // MI_L*(x^63 + x^62 + x^57)

	vpshufd		$0x4e, \t1, \t1		  // Swap halves of MI

	vpternlogd	$0x96, \t0, \t1, \dst	  // Fold MI into HI

.endm



// void aes_gcm_precompute_vaes_avx512(struct aes_gcm_key_vaes_avx512 *key);

//

// Given the expanded AES key |key->base.aes_key|, derive the GHASH subkey and
@@ -337,8 +350,7 @@ SYM_FUNC_START(aes_gcm_precompute_vaes_avx512) 
	// special needs to be done to make this happen, though: H^1 * H^1 would

	// end up with two factors of x^-1, but the multiplication consumes one.

	// So the product H^2 ends up with the desired one factor of x^-1.

	_ghash_mul	H_CUR_XMM, H_CUR_XMM, H_INC_XMM, GFPOLY_XMM, \

			%xmm0, %xmm1, %xmm2

	_ghash_square	H_CUR_XMM, H_INC_XMM, GFPOLY_XMM, %xmm0, %xmm1



	// Create H_CUR_YMM = [H^2, H^1] and H_INC_YMM = [H^2, H^2].

	vinserti128	$1, H_CUR_XMM, H_INC_YMM, H_CUR_YMM