From nobody Wed Sep 17 11:57:09 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 622F3C4332F for ; Tue, 20 Dec 2022 05:42:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233066AbiLTFmN (ORCPT ); Tue, 20 Dec 2022 00:42:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52128 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232853AbiLTFmC (ORCPT ); Tue, 20 Dec 2022 00:42:02 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 701AA10B56; Mon, 19 Dec 2022 21:42:01 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 099F561284; Tue, 20 Dec 2022 05:42:01 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3059AC433A0; Tue, 20 Dec 2022 05:41:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1671514920; bh=dsBT80rMbHb7evBtDRzv5PT3ZA7g7MTpg/OO26ExzF0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jYOojsuBCSLHGr8TW6ECUwgWw+LEvw+PHi3nql2vBWzBzEq7MyKtVOLJ/b2Kiu4gS oMG/dlg3OnMmVJmrdSv2oL97DF/CUUglF7nDPoQjrR1EUjWMzPIKMXZdHUPv8l8Sjd UXS+WUfMJ0NGEcylNFSYCWZt2yo1UQq4aV3vPbfVoQuD+Qp8TbeWtUxBsxReFPOxlA zfs32JevZlz+K+Uv5duClJslwi2mYsu29ttlLiM4znIDXOp4GXmEIq6usK1oiCT/rX LwdwbARx6KolYJUmb/r6mqXzDaBmbWq87tBtJKhhILBQJc9wo5CJtT/46YobC23TXN w7YoOtqqwQbVA== From: Eric Biggers To: linux-crypto@vger.kernel.org Cc: Peter Zijlstra , corbet@lwn.net, will@kernel.org, boqun.feng@gmail.com, mark.rutland@arm.com, catalin.marinas@arm.com, dennis@kernel.org, tj@kernel.org, cl@linux.com, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, Herbert Xu , davem@davemloft.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, joro@8bytes.org, suravee.suthikulpanit@amd.com, robin.murphy@arm.com, dwmw2@infradead.org, baolu.lu@linux.intel.com, Arnd Bergmann , penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, Andrew Morton , vbabka@suse.cz, roman.gushchin@linux.dev, 42.hyeyoo@gmail.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-s390@vger.kernel.org, iommu@lists.linux.dev, linux-arch@vger.kernel.org Subject: [PATCH 3/3] crypto: x86/ghash - add comment and fix broken link Date: Mon, 19 Dec 2022 21:40:42 -0800 Message-Id: <20221220054042.188537-4-ebiggers@kernel.org> X-Mailer: git-send-email 2.39.0 In-Reply-To: <20221220054042.188537-1-ebiggers@kernel.org> References: <20221220054042.188537-1-ebiggers@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Eric Biggers Add a comment that explains what ghash_setkey() is doing, as it's hard to understand otherwise. Also fix a broken hyperlink. Signed-off-by: Eric Biggers --- arch/x86/crypto/ghash-clmulni-intel_asm.S | 2 +- arch/x86/crypto/ghash-clmulni-intel_glue.c | 27 ++++++++++++++++++---- 2 files changed, 24 insertions(+), 5 deletions(-) diff --git a/arch/x86/crypto/ghash-clmulni-intel_asm.S b/arch/x86/crypto/gh= ash-clmulni-intel_asm.S index 9dfeb4d31b92..257ed9446f3e 100644 --- a/arch/x86/crypto/ghash-clmulni-intel_asm.S +++ b/arch/x86/crypto/ghash-clmulni-intel_asm.S @@ -4,7 +4,7 @@ * instructions. This file contains accelerated part of ghash * implementation. More information about PCLMULQDQ can be found at: * - * http://software.intel.com/en-us/articles/carry-less-multiplication-and-= its-usage-for-computing-the-gcm-mode/ + * https://www.intel.com/content/dam/develop/external/us/en/documents/clmu= l-wp-rev-2-02-2014-04-20.pdf * * Copyright (c) 2009 Intel Corp. * Author: Huang Ying diff --git a/arch/x86/crypto/ghash-clmulni-intel_glue.c b/arch/x86/crypto/g= hash-clmulni-intel_glue.c index 9453b094bb3b..700ecaee9a08 100644 --- a/arch/x86/crypto/ghash-clmulni-intel_glue.c +++ b/arch/x86/crypto/ghash-clmulni-intel_glue.c @@ -60,16 +60,35 @@ static int ghash_setkey(struct crypto_shash *tfm, if (keylen !=3D GHASH_BLOCK_SIZE) return -EINVAL; =20 - /* perform multiplication by 'x' in GF(2^128) */ + /* + * GHASH maps bits to polynomial coefficients backwards, which makes it + * hard to implement. But it can be shown that the GHASH multiplication + * + * D * K (mod x^128 + x^7 + x^2 + x + 1) + * + * (where D is a data block and K is the key) is equivalent to: + * + * bitreflect(D) * bitreflect(K) * x^(-127) + * (mod x^128 + x^127 + x^126 + x^121 + 1) + * + * So, the code below precomputes: + * + * bitreflect(K) * x^(-127) (mod x^128 + x^127 + x^126 + x^121 + 1) + * + * ... but in Montgomery form (so that Montgomery multiplication can be + * used), i.e. with an extra x^128 factor, which means actually: + * + * bitreflect(K) * x (mod x^128 + x^127 + x^126 + x^121 + 1) + * + * The within-a-byte part of bitreflect() cancels out GHASH's built-in + * reflection, and thus bitreflect() is actually a byteswap. + */ a =3D get_unaligned_be64(key); b =3D get_unaligned_be64(key + 8); - ctx->shash.a =3D cpu_to_le64((a << 1) | (b >> 63)); ctx->shash.b =3D cpu_to_le64((b << 1) | (a >> 63)); - if (a >> 63) ctx->shash.a ^=3D cpu_to_le64((u64)0xc2 << 56); - return 0; } =20 --=20 2.39.0