From mboxrd@z Thu Jan 1 00:00:00 1970 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 B1AE4C433EF for ; Fri, 27 May 2022 11:49:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238607AbiE0Lt0 (ORCPT ); Fri, 27 May 2022 07:49:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56322 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1352038AbiE0LpR (ORCPT ); Fri, 27 May 2022 07:45:17 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 20E2413FD72; Fri, 27 May 2022 04:41:48 -0700 (PDT) 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 ams.source.kernel.org (Postfix) with ESMTPS id 408E7B824D8; Fri, 27 May 2022 11:41:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8FEB4C385A9; Fri, 27 May 2022 11:41:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1653651705; bh=1gYXjOiQ/z90nRzb8U321OxJ4EeK2vYVDyO9CPVnJcY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UlUf2fYsROZXikyjxEsaUndw/nCbTy5JdQz4emaM/MA2dl+EKIyMlOOv3gi1DJ3Sy wRcOIJW74D3cDhWs2ag0KcDlGI0GWdlEopzj1SgV7K1z3t5f/RO4PXjSxQ9Hcv/9wa kVIQIliEGZJadH4omyaHskquXJc8W4cOJNAnZpkw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Dominik Brodowski , "Jason A. Donenfeld" Subject: [PATCH 5.15 031/145] random: cleanup fractional entropy shift constants Date: Fri, 27 May 2022 10:48:52 +0200 Message-Id: <20220527084854.599461457@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220527084850.364560116@linuxfoundation.org> References: <20220527084850.364560116@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Jason A. Donenfeld" commit 18263c4e8e62f7329f38f5eadc568751242ca89c upstream. The entropy estimator is calculated in terms of 1/8 bits, which means there are various constants where things are shifted by 3. Move these into our pool info enum with the other relevant constants. While we're at it, move an English assertion about sizes into a proper BUILD_BUG_ON so that the compiler can ensure this invariant. Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld Signed-off-by: Greg Kroah-Hartman --- drivers/char/random.c | 28 +++++++++++++--------------- 1 file changed, 13 insertions(+), 15 deletions(-) --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -359,16 +359,6 @@ /* #define ADD_INTERRUPT_BENCH */ /* - * To allow fractional bits to be tracked, the entropy_count field is - * denominated in units of 1/8th bits. - * - * 2*(POOL_ENTROPY_SHIFT + poolbitshift) must <= 31, or the multiply in - * credit_entropy_bits() needs to be 64 bits wide. - */ -#define POOL_ENTROPY_SHIFT 3 -#define POOL_ENTROPY_BITS() (input_pool.entropy_count >> POOL_ENTROPY_SHIFT) - -/* * If the entropy count falls under this number of bits, then we * should wake up processes which are selecting or polling on write * access to /dev/random. @@ -425,8 +415,13 @@ enum poolinfo { POOL_WORDMASK = POOL_WORDS - 1, POOL_BYTES = POOL_WORDS * sizeof(u32), POOL_BITS = POOL_BYTES * 8, - POOL_BITSHIFT = ilog2(POOL_WORDS) + 5, - POOL_FRACBITS = POOL_WORDS << (POOL_ENTROPY_SHIFT + 5), + POOL_BITSHIFT = ilog2(POOL_BITS), + + /* To allow fractional bits to be tracked, the entropy_count field is + * denominated in units of 1/8th bits. */ + POOL_ENTROPY_SHIFT = 3, +#define POOL_ENTROPY_BITS() (input_pool.entropy_count >> POOL_ENTROPY_SHIFT) + POOL_FRACBITS = POOL_BITS << POOL_ENTROPY_SHIFT, /* x^128 + x^104 + x^76 + x^51 +x^25 + x + 1 */ POOL_TAP1 = 104, @@ -652,6 +647,9 @@ static void credit_entropy_bits(int nbit int entropy_count, entropy_bits, orig; int nfrac = nbits << POOL_ENTROPY_SHIFT; + /* Ensure that the multiplication can avoid being 64 bits wide. */ + BUILD_BUG_ON(2 * (POOL_ENTROPY_SHIFT + POOL_BITSHIFT) > 31); + if (!nbits) return; @@ -687,13 +685,13 @@ retry: /* The +2 corresponds to the /4 in the denominator */ do { - unsigned int anfrac = min(pnfrac, POOL_FRACBITS/2); + unsigned int anfrac = min(pnfrac, POOL_FRACBITS / 2); unsigned int add = - ((POOL_FRACBITS - entropy_count)*anfrac*3) >> s; + ((POOL_FRACBITS - entropy_count) * anfrac * 3) >> s; entropy_count += add; pnfrac -= anfrac; - } while (unlikely(entropy_count < POOL_FRACBITS-2 && pnfrac)); + } while (unlikely(entropy_count < POOL_FRACBITS - 2 && pnfrac)); } if (WARN_ON(entropy_count < 0)) {