From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lamorak.hansenpartnership.com (lamorak.hansenpartnership.com [198.37.111.173]) (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 917401F130B; Tue, 30 Sep 2025 14:17:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.37.111.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759241847; cv=none; b=sqtYK+4psImqHmYdqVaK0HMwkaQihGRrsjUhVtJPA/AR8Gv118MeKhZw3mxQCZj2b+xMErUy9AAmIpqSXl17exptcq6cokhKVAwr0/kvEhS9gmiMaucGkPLUgeHLrh9QtvCTUrKxG+vTOBK3NKP6a6DNn9nHgCoqPFzcgLlcock= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759241847; c=relaxed/simple; bh=X52jzvEdaHhj/kDojZhvUNfMXxpYzry+8StGkxPvcJ4=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=noyLeXZ8ftQWBl6lF4e1E411Nb44PiY+DO1i9mVhqB3KkjMdD7vvPR7Wy60JLXInSN4oTPk7bxY1c7JwuN5QD+nZ6sUdK8ZK1bNQ/9KL5IAfdQsOpSNu8bKcmit4+olyBsqzR/YEp8xCzbOwfIX3vkYlxsmAPigUbgGiNImAeUE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=HansenPartnership.com; spf=pass smtp.mailfrom=HansenPartnership.com; dkim=pass (1024-bit key) header.d=hansenpartnership.com header.i=@hansenpartnership.com header.b=gqVUjDUv; arc=none smtp.client-ip=198.37.111.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=HansenPartnership.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=HansenPartnership.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=hansenpartnership.com header.i=@hansenpartnership.com header.b="gqVUjDUv" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=hansenpartnership.com; s=20151216; t=1759241843; bh=X52jzvEdaHhj/kDojZhvUNfMXxpYzry+8StGkxPvcJ4=; h=Message-ID:Subject:From:To:Date:In-Reply-To:References:From; b=gqVUjDUvVGQ+4CEJFSbWPh8xgG8CplOxSdfmtictafAiPlbySmI6XbaKN34rBwLNp DiQc7Roe2S1JlAyIbBPjDxTzXsm4PygtiK8fIvvMaY4uvtLfGNVyqRlZg9mkslTCNl vpIWMUu1YNz4V7Y+LUd/OQOswsVrKRTzk9PUBXR8= Received: from lingrow.int.hansenpartnership.com (unknown [IPv6:2601:5c4:4302:c21::a774]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange x25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lamorak.hansenpartnership.com (Postfix) with ESMTPSA id BFCA71C02E9; Tue, 30 Sep 2025 10:17:22 -0400 (EDT) Message-ID: Subject: Re: [PATCH v3 01/10] tpm: Cap the number of PCR banks From: James Bottomley To: Jarkko Sakkinen , Jonathan McDowell Cc: linux-integrity@vger.kernel.org, dpsmith@apertussolutions.com, ross.philipson@oracle.com, Jarkko Sakkinen , Roberto Sassu , Peter Huewe , Jason Gunthorpe , David Howells , Paul Moore , James Morris , "Serge E. Hallyn" , open list , "open list:KEYS/KEYRINGS" , "open list:SECURITY SUBSYSTEM" Date: Tue, 30 Sep 2025 10:17:22 -0400 In-Reply-To: References: <20250929194832.2913286-1-jarkko@kernel.org> <20250929194832.2913286-2-jarkko@kernel.org> Autocrypt: addr=James.Bottomley@HansenPartnership.com; prefer-encrypt=mutual; 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MAdnPcDVFzaXJdlAAJdjfg/lyJtAyxifflG8NnXJ3elwGqoBso84XBNWWzbc5VKmatzhYLOvXtfzDhu4mNPv/z7S1HTtRguI0NlH5RVBzSvfzybin9hysE3/+r3C0HJ2xiOHzucNAmG03aztzZYDMTbKQW4bQqeD5MJxT68vBYu8MtzfIe41lSLpb/qlwq1qg0iQElBBgBAgAPBQJUdhaZAhsMBQkA7U4AAAoJEIFK5HwhSFTW3YgH/AyJL2rlCvGrkLcas94ND9Pmn0cUlVrPl7wVGcIV+6I4nrw6u49TyqNMmsYam2YpjervJGgbvIbMzoHFCREi6R9XyUsw5w7GCRoWegw2blZYi5A52xe500+/RruG//MKfOtVUotu3N+u7FcXaYAg9gbYeGNZCV70vI+cnFgq0AEJRdjidzfCWVKPjafTo7jHeFxX7Q22kUfWOkMzzhoDbFg0jPhVYNiEXpNyXCwirzvKA7bvFwZPlRkbfihaiXDE7QKIUtQ10i5kw4C9rqDKwx8F0PaWDRF9gGaKd7/IJGHJaac/OcSJ36zxgkNgLsVX5GUroJ2GaZcR7W9Vppj5H+C4UgRkuRyTEwgqhkjOPQMBBwIDBOySomnsW2SkApXv1zUBaD38dFEj0LQeDEMdSE7bm1fnrdjAYt0f/CtbUUiDaPodQk2qeHzOP6wA/2K6rrjwNIWJAT0EGAEIACcDGyAEFiEE1WBuc8i0YnG+rZrfgUrkfCFIVNYFAmWoM/gFCQSxfmUACgkQgUrkfCFIVNZhTgf/VQxtQ5rgu2aoXh2KOH6naGzPKDkYDJ/K7XCJAq3nJYEpYN8G+F8mL/ql0hrihAsHfjmoDOlt+INa3AcG3v0jDZIMEzmcjAlu7g5NcXS3kntcMHgw3dCgE9eYDaKGipUCubdXvBaZWU6AUlTldaB8FE6u7It7+UO+IW4/L+KpLYKs8V5POInu2rqahlm7vgxY5iv4Txz4EvCW2e4dAlG 8mT2Eh9SkH+YVOmaKsajgZgrBxA7fWmGoxXswEVxJIFj3vW7yNc0C5HaUdYa5iGOMs4kg2ht4s7yy7NRQuh7BifWjo6BQ6k4S1H+6axZucxhSV1L6zN9d+lr3Xo/vy1unzA== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2025-09-30 at 15:36 +0300, Jarkko Sakkinen wrote: > On Tue, Sep 30, 2025 at 12:09:15PM +0100, Jonathan McDowell wrote: > > On Mon, Sep 29, 2025 at 10:48:23PM +0300, Jarkko Sakkinen wrote: [...] > > > +#define TPM2_MAX_DIGEST_SIZE SHA512_DIGEST_SIZE > > > +#define TPM2_MAX_BANKS 4 > >=20 > > Where does this max come from? It matches what I see with swtpm by=20 > > default (SHA1, SHA2-256, SHA2-384, SHA-512), so I haven't seen > > anything that exceeds it myself. >=20 > I've never seen hardware TPM that would have more than one or two > banks. We can double it to leave some room. This was tested with > swtpm defaults. I've got a hardware TPM that comes with 3 banks by default (it's a chinese one which has sha1 sha256 and sm2). swtpm isn't a good indicator because it's default allocation is rather pejorative (it disables sha1 whereas most field TPMs don't). However, if you look at how the reference implementation works, the user is allowed to define any number of banks they want, up to the number of supported hashes. The only limitation being there can't be >1 bank for the same hash. Field TPM implementations are allowed to constrain this, but most don't. The question you should be asking here is not how many banks does a particular implementation allow by default, but what's the maximum number a user could configure. Regards, James