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

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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: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20251002023117.37504-8-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
This commit is contained in:
Eric Biggers
2025-10-01 19:31:16 -07:00
parent e0abd0053f
commit 5ab1ff2e0f
1 changed files with 14 additions and 2 deletions
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16
arch/x86/crypto/aes-gcm-vaes-avx512.S
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@@ -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