From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 39D1F2E1F10 for ; Tue, 2 Sep 2025 19:57:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756843061; cv=none; b=srY/jhSDihikJRbvwzHqJeuhtvZAJzM20N4aYHt42XY5D4E96cavh762TJoplrHJ26GvYe+OCSKRalNARIBQQrMkzKhNx+sgsvekjKw1tn3dAsNKJZS4ezp3oNVTVYngKXJ/hNHb7pIsFeQQ3juF7kMyIs+GLZQrV9N7hDLvby8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756843061; c=relaxed/simple; bh=h17LMsILj8e0VSgRn5q9BxKODp6LJ0WmzZ/Aulwk0SE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ejsLjsFio8uy5kWtVYicyojaXy6tWhtpvmQSYiadC90e4HJb38whVSGRFm1G2T6DQxgvTpF5l9ALuJXCS0ewIk5p37gmE6FUqZcfguf8SiVg4oRTsbUp5N5j3UfuoYs+GXpZpQ5BdkFIKYIhvOj97hKGThdU0Qhed4Cv+u4UmOw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=MLFllj3q; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="MLFllj3q" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=o1WxhFDj4HDK+ojytAfPZg3U0Olh8tYi2Vi91RLUHzQ=; b=MLFllj3qoftsytYU2YiXF5Xxqs Xd5xFaBxVoU8TS1flxQERkB5QOuF+iKUSHWKDpqh5t526P0/teZsxD7rgzXqPAGUYini22Ptiz5b0 fOFS458Hh1PqJYpVG+y+ZLADXK1d/J62NgocdpAZP2bD/4fW49bzBTyaaNdzu8/+oBAOog9X8w6/4 FwhJOiFWlgcayJI9i7H9WpY3+P3s+ik9Lo1rhTKVIzk1EZEpMPx4RS9nnnngzp1SfRz6oFpigVzrn vCzc+yfX8WC3qogFXJ3BvB4tXki16YCIWNfPXQSjC0SwnINw9zKjoyWhBfyJogEZbtYnzn30CKOBv zFA8RPuQ==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1utX8K-0000000AuIy-0CIJ; Tue, 02 Sep 2025 19:57:36 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id CC52230039F; Tue, 02 Sep 2025 21:57:35 +0200 (CEST) Date: Tue, 2 Sep 2025 21:57:35 +0200 From: Peter Zijlstra To: Alexei Starovoitov Cc: X86 ML , "H. Peter Anvin" , Kees Cook , alyssa.milburn@intel.com, scott.d.constable@intel.com, Joao Moreira , Andrew Cooper , Sami Tolvanen , Nathan Chancellor , Masami Hiramatsu , ojeda@kernel.org, LKML Subject: Re: [PATCH v2] x86,ibt: Use UDB instead of 0xEA Message-ID: <20250902195735.GM3245006@noisy.programming.kicks-ass.net> References: <20250901191307.GI4067720@noisy.programming.kicks-ass.net> <20250902081915.GK3245006@noisy.programming.kicks-ass.net> <20250902192609.GL3245006@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Sep 02, 2025 at 12:37:26PM -0700, Alexei Starovoitov wrote: > Well, I mean all these tricky changes are allegedly because > "Intel/AMD have not blessed using this instruction, it is on > their 'reserved' opcode list for future use" > > I suspect that 'reserved' opcode will not be used any time soon. > If 10 years from now the opcode is used in some future CPU that CPU > is better to be not vulnerable and CFI, FineIBT things will be > gone from the kernel by then. > So I would do absolutely nothing and just ignore the lack of blessing. Ah. CFI is not only about speculation, it is also very much a protection against pointer hijacking. Note how kCFI was not brought in because of speculation, but as a hardening against pointer hijacking. Yes, my interest in Intel CET-IBT is mostly from the speculation avoidance angle, but CFI as a whole has wider applicability. Even a 'fixed' CPU would want to use CFI. I would also love AMD to grow support for CET-IBT; they already implemented CET-SS. Also, Intel pays me, if they say make it use 0xD6, this is what we do :-)