From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.alien8.de (mail.alien8.de [65.109.113.108]) (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 A078D3750CA for ; Wed, 10 Jun 2026 20:01:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=65.109.113.108 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781121674; cv=none; b=rF5F6+cfwSELL2vxEcddKCSWsddSy+JzFfsZopu/uHcezLtwJrz7LbhS/46VHggpxLLF+dJPdTrE/npsN4tmmQ2pbonfh5LTVmgRXcsLOemPuE/Wl3K9HJocgVcqQGZ7St7mfKdr21YCYK1YbXqbGIuEr+QGFcDZToIq1kl+1Uc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781121674; c=relaxed/simple; bh=qk3K557+IKqIQAu0hRMQhlV/TXLIR6eH147f3tik4kQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=eNWWkFgvnPU7lGDh1V6L9HNMr7WtWTeGlXTHLnpfRdVwqj389BRVoI/tzDnCl0ocAq+hB/htQdshmF4DNpnW4r3dg3wGbI75nCcykIqMhFHPL3QoPgc1q7jHA1b4ML6Vgi34bx8qYIQ9QGC5WgrtwLVW5rVso9mLngOEsaSs/fY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=alien8.de; spf=pass smtp.mailfrom=alien8.de; dkim=fail (4096-bit key) header.d=alien8.de header.i=@alien8.de header.b=UH6Xwvar reason="signature verification failed"; arc=none smtp.client-ip=65.109.113.108 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=alien8.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=alien8.de Authentication-Results: smtp.subspace.kernel.org; dkim=fail reason="signature verification failed" (4096-bit key) header.d=alien8.de header.i=@alien8.de header.b="UH6Xwvar" Received: from localhost (localhost.localdomain [127.0.0.1]) by mail.alien8.de (SuperMail on ZX Spectrum 128k) with ESMTP id 0994B40E0215; Wed, 10 Jun 2026 20:01:11 +0000 (UTC) X-Virus-Scanned: Debian amavisd-new at mail.alien8.de Authentication-Results: mail.alien8.de (amavisd-new); dkim=fail (4096-bit key) reason="fail (body has been altered)" header.d=alien8.de Received: from mail.alien8.de ([127.0.0.1]) by localhost (mail.alien8.de [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id JrJRTKDPj6pN; Wed, 10 Jun 2026 20:01:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=alien8; t=1781121661; bh=6Cqaf648edAaOTO3z2erAabcP5hKj2ZUlqQL78FVwZk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=UH6XwvarsW6TpWiMH+QbxZ4wl87UsRH/uyHnQtmftpMpz0ERFLVhyxzAyP5p+3rFm QCHqC2VhXHLiwyDWaxD/TRFbpQDWMzbMrBFUSLTBWoznXu58jat9mECMnHRo9l8irt EPYMKXPo6sS9yHip3JFD+j6E2LPUSA/5stvYnGVveQQJ9S+j7bx2s29bJv/p7wu8l5 ZZlQHKRhjYDzbY3Q9yX417x3x+zpw5W58/5np4HhSGiyCwh6DIU8fSuInf6Eo9xrGK KLq2R3TPA6a5NXwDoo8PlfmLb1xkL1X9NY0Or6cRXCgvM6pTe6KsFZQ5sY7iVnMhY+ iByn0rqJuWwp4EP+aJBypFzT0YH6up/yPdKgLaDlf9RMpFhwK0ijBaRzBbycbpc7Eh uDXr2u8mtXl7EjixWtrWL0OWjl67f0lzIOeS7niXR75ZkhlQc1v64xBVd1yXv53aUX c8ztQjPTi7HeXaKwqfhSfXP7Dia0p+1qM98Dy2/EDa3qcnwvHHVI1d2nu3xYVf18TK j9WHOJxirjuZ1IExdFlqIMZeCMOo8CnFY02JxJKpOH20hF+R0bGkw8hCEZGtstpnd3 ZjaqBvoP1B3FJeT45QUeLNYFsWFd8BXm2H9RhoIMY250yWkpPxMEdHLg2cFoHrSlTt nzPId3PNaDAi4ZhgP4M+b1Vw= Received: from stx.tnic (unknown [IPv6:2600:1700:38ca:c00::1a]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature ECDSA (P-256) server-digest SHA256) (No client certificate requested) by mail.alien8.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 6BCC040E01B5; Wed, 10 Jun 2026 20:00:57 +0000 (UTC) Date: Wed, 10 Jun 2026 13:00:54 -0700 From: Borislav Petkov To: Ronan Pigott Cc: linux-kernel@vger.kernel.org, x86@kernel.org Subject: Re: UMIP and clearcpuid= Message-ID: <20260610200054.GDainCdpF585khK77w@fat_crate.local> References: 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=utf-8 Content-Disposition: inline In-Reply-To: Content-Transfer-Encoding: quoted-printable On Wed, Jun 10, 2026 at 07:46:11PM +0000, Ronan Pigott wrote: > In [1] the clearcpuid=3D flag was hidden, but afaik this remains the on= ly way to > disable UMIP. The reason for wanting to disable it being? > At the time UMIP was enabled, clearcpuid was apparently determined to b= e the > appropriate method of disablement in [2], Don't confuse "appropriate" with "might be good enough" ;) > and it remains recommended by the documentation in [3]. That doc says: "DO NOT USE this cmdline option in production - it is meant to be used on= ly as a quick=E2=80=99n=E2=80=99dirty debugging aid to rule out a feature-enabl= ing code is the culprit. If you use it, it=E2=80=99ll taint the kernel." > If clearcpuid is no good, can we have a sanctioned method to disable UM= IP > protections instead then? Let's figure out the use case first pls. Thx. --=20 Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette