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[2a01:4f8:190:11c2::b:1457]) by mx.google.com with ESMTPS id b1si3297299wrx.350.2019.03.07.09.06.27 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 07 Mar 2019 09:06:27 -0800 (PST) Received-SPF: pass (google.com: domain of bp@alien8.de designates 2a01:4f8:190:11c2::b:1457 as permitted sender) client-ip=2a01:4f8:190:11c2::b:1457; Authentication-Results: mx.google.com; dkim=pass header.i=@alien8.de header.s=dkim header.b=ATn+ZtuV; spf=pass (google.com: domain of bp@alien8.de designates 2a01:4f8:190:11c2::b:1457 as permitted sender) smtp.mailfrom=bp@alien8.de; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=alien8.de Received: from zn.tnic (unknown [IPv6:2003:ec:2f08:1c00:329c:23ff:fea6:a903]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 79C761EC066F; Thu, 7 Mar 2019 18:06:26 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1551978386; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=l8cTM4Q9P0s3RXZNsCWcgbO0ogkOlG4bqVEytx8DQK0=; b=ATn+ZtuVU+ClpyQgBAKOuZpfBSy9/Dx5UMED9ml4h113elugzb1qFn7lbGNrpfnfie8mmC aoP9aXiU+zgnRgI9OpXbhrqrFnO3PsdxLF9jaXXCA2oBndyvQzd6FYW3H78uhFnwXocnhf XncZ0ieSiRYL2PGhG+PbQZvyAnmQfM8= Date: Thu, 7 Mar 2019 18:06:29 +0100 From: Borislav Petkov To: hpa@zytor.com Cc: Nadav Amit , Rick Edgecombe , Andy Lutomirski , Ingo Molnar , LKML , X86 ML , Thomas Gleixner , Dave Hansen , Peter Zijlstra , Damian Tometzki , linux-integrity , LSM List , Andrew Morton , Kernel Hardening , Linux-MM , Will Deacon , Ard Biesheuvel , Kristen Carlson Accardi , "Dock, Deneen T" , Kees Cook , Dave Hansen , Masami Hiramatsu Subject: Re: [PATCH v2 10/20] x86: avoid W^X being broken during modules loading Message-ID: <20190307170629.GG26566@zn.tnic> References: <20190129003422.9328-11-rick.p.edgecombe@intel.com> <20190211182956.GN19618@zn.tnic> <1533F2BB-2284-499B-9912-6D74D0B87BC1@gmail.com> <20190211190108.GP19618@zn.tnic> <20190211191059.GR19618@zn.tnic> <3996E3F9-92D2-4561-84E9-68B43AC60F43@gmail.com> <20190211194251.GS19618@zn.tnic> <20190307072947.GA26566@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Mar 07, 2019 at 08:53:34AM -0800, hpa@zytor.com wrote: > If we *do*, what is the issue here? Although boot_cpu_has() isn't > slow (it should in general be possible to reduce to one testb > instruction followed by a conditional jump) it seems that "avoiding an > alternatives slot" *should* be a *very* weak reason, and seems to me > to look like papering over some other problem. Forget the current thread: this is simply trying to document when to use static_cpu_has() and when to use boot_cpu_has(). I get asked about it at least once a month. And then it is replacing clear slow paths using static_cpu_has() with boot_cpu_has() because there's purely no need to patch there. And having a RIP-relative MOV and a JMP is good enough for slow paths. Makes sense? -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.