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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 6C40DEB64DC for ; Sun, 9 Jul 2023 14:06:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-ID:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=+8hmBRGztDryoeNfMVtKVYLi8ylunQ3bBKkRxLvjoVc=; b=AZUfTFINjxMJdl sNHl6ugJzDF4aulK5eSD3CmK+qL/mEG/tNSa7DiySMMkuN1mUkttNP/3VH8QNsDicC7Hn4jl+GRhv hy0vgh+YexnUF2UpRP+PDWXetihCz+u+meVR5Tb7mTu4lceIFJKwpGRNVSHaMKxSnj6aa7sp4Z5Yz ldjh/7GuJLjNCcvfNARwBeWvTEI22zRqEQP6pFKjFpSb1bEXUcCiCrixGoDF0Qc6okNEyxFBUmENv tg7l8fCcUcVQgLU6bPnTPQYDfvqE2qi8rQTNbstbrW9WW0uKLWckpZCzIoZxAsiGDwgDcTiSwWHMW XHNMYoqhfES2rfUr+HfA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qIV3P-009DI0-0i; Sun, 09 Jul 2023 14:06:23 +0000 Received: from gloria.sntech.de ([185.11.138.130]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1qIV3L-009DHO-2e for linux-riscv@lists.infradead.org; Sun, 09 Jul 2023 14:06:21 +0000 Received: from i53875a50.versanet.de ([83.135.90.80] helo=phil.localnet) by gloria.sntech.de with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1qIV3J-0002bh-B1; Sun, 09 Jul 2023 16:06:17 +0200 From: Heiko Stuebner To: Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-riscv@lists.infradead.org Cc: Samuel Ortiz , linux@rivosinc.com, Conor Dooley , Andrew Jones , Anup Patel , linux-kernel@vger.kernel.org, "Hongren (Zenithal) Zheng" , Guo Ren , Atish Patra , =?ISO-8859-1?Q?Bj=F6rn_T=F6pel?= , Evan Green , devicetree@vger.kernel.org, Samuel Ortiz Subject: Re: [PATCH v3 4/4] RISC-V: Implement archrandom when Zkr is available Date: Sun, 09 Jul 2023 16:06:16 +0200 Message-ID: <3566075.R56niFO833@phil> In-Reply-To: <20230709115549.2666557-5-sameo@rivosinc.com> References: <20230709115549.2666557-1-sameo@rivosinc.com> <20230709115549.2666557-5-sameo@rivosinc.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230709_070619_875554_43B8DAA6 X-CRM114-Status: GOOD ( 13.62 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org Am Sonntag, 9. Juli 2023, 13:55:46 CEST schrieb Samuel Ortiz: > The Zkr extension is ratified and provides 16 bits of entropy seed when > reading the SEED CSR. > > We can implement arch_get_random_seed_longs() by doing multiple csrrw to > that CSR and filling an unsigned long with valid entropy bits. > > Acked-by: Conor Dooley > Signed-off-by: Samuel Ortiz > --- > +static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, size_t max_longs) > +{ > + if (!max_longs) > + return 0; > + > + /* > + * If Zkr is supported and csr_seed_long succeeds, we return one long > + * worth of entropy. > + */ > + if (riscv_has_extension_likely(RISCV_ISA_EXT_ZKR) && csr_seed_long(v)) While this whole thing looks really nice, I don't think you can only check the ZKR existence though. To access the seed csr from supervisor-mode, it looks like the SSEED bit in the mseccfg register also needs to be set by firmware. And in the kernel we will likely need to check this setting somehow before enabling access. At least my qemu fails with an illegal instruction otherwise during the early random seed initialization. Heiko _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv