From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.skyhub.de (mail.skyhub.de [5.9.137.197]) (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 2F34E2FAE for ; Fri, 1 Oct 2021 11:06:14 +0000 (UTC) Received: from zn.tnic (p200300ec2f0e8e0006425ffdb1062ac0.dip0.t-ipconnect.de [IPv6:2003:ec:2f0e:8e00:642:5ffd:b106:2ac0]) (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 7CBB61EC0419; Fri, 1 Oct 2021 13:06:12 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1633086372; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=JCBAeXE9Fm2/4A8nfF4qlTElC4omNaQJNghTb8YDddM=; b=kTtfe1X/X1Cm8CiF7sqgmxJbnYSVBHwhUxmVIQWx22i7VqsRKC6EEWMxmDVCD+9RF7VzG5 QJBTrSVvQeE27As7XeJBpiyoxWoEGP1nFgkKyx5GnB9alDDmJT1lAjv2TqZFpTt2XpnmBK KSzCimg6oBTl41PghKnK15OZssLqRMo= Date: Fri, 1 Oct 2021 13:06:08 +0200 From: Borislav Petkov To: Brijesh Singh Cc: x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-crypto@vger.kernel.org, Thomas Gleixner , Ingo Molnar , Joerg Roedel , Tom Lendacky , "H. Peter Anvin" , Ard Biesheuvel , Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Andy Lutomirski , Dave Hansen , Sergio Lopez , Peter Gonda , Peter Zijlstra , Srinivas Pandruvada , David Rientjes , Dov Murik , Tobin Feldman-Fitzthum , Michael Roth , Vlastimil Babka , "Kirill A . Shutemov" , Andi Kleen , tony.luck@intel.com, marcorr@google.com, sathyanarayanan.kuppuswamy@linux.intel.com Subject: Re: [PATCH Part2 v5 06/45] x86/sev: Invalid pages from direct map when adding it to RMP table Message-ID: References: <20210820155918.7518-1-brijesh.singh@amd.com> <20210820155918.7518-7-brijesh.singh@amd.com> <60d6a70d-22ab-9e17-b243-7f5669b4b70d@amd.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <60d6a70d-22ab-9e17-b243-7f5669b4b70d@amd.com> On Thu, Sep 30, 2021 at 09:19:52AM -0700, Brijesh Singh wrote: > . The thought process is if in the future  > set_direct_map_default_noflush() is improved to restore the large > mapping then it will all work transparently. That's only scratching the surface of the *why* this is done so please explain why this dance is being done in a comment above the code so that it is clear. It is not really obvious why that hiding from the direct map is being done. Good reason from that memfd_secret mail are: "* Prevent cross-process secret userspace memory exposures. Once the secret memory is allocated, the user can't accidentally pass it into the kernel to be transmitted somewhere. The secreremem pages cannot be accessed via the direct map and they are disallowed in GUP." and in general hiding RMP pages from the direct map is a nice additional protection. Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette