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 4C6732AF1D; Sun, 23 Mar 2025 21:18:47 +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=1742764730; cv=none; b=hkkd6I9cemw7ww9IZ2P9agc52Gz3Y+F6+9Mn2kURZe+JpLWOs909tW10LMQypTj4f5UR71NduZTurhWDFlBU33z6ktMdStClWwX1S7WsbD+7kWTl9hKVC8LEfWod2Cj+kRNvjk4u4hnScmMZNKJM5Qv9Itt8bQO2NiEXUufyJKU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742764730; c=relaxed/simple; bh=VfcdpQnzSD1rS34uOpu8qcqXqndjkR9Po1lWFaGQxAc=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; 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linux-kernel@vger.kernel.org Date: Sun, 23 Mar 2025 17:18:45 -0400 In-Reply-To: <20250323140911.226137-4-nstange@suse.de> References: <20250323140911.226137-1-nstange@suse.de> <20250323140911.226137-4-nstange@suse.de> Autocrypt: addr=James.Bottomley@HansenPartnership.com; prefer-encrypt=mutual; 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 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 Sun, 2025-03-23 at 15:09 +0100, Nicolai Stange wrote: > Normally IMA would extend a template hash of each bank's associated > algorithm into a PCR. However, if a bank's hash algorithm is > unavailable to the kernel at IMA init time, it would fallback to > extending padded SHA1 hashes instead. >=20 > That is, if e.g. SHA-256 was missing at IMA init, it would extend > padded SHA1 template hashes into a PCR's SHA-256 bank. >=20 > The ima_measurement command (marked as experimental) from ima-evm- > utils would accordingly try both variants when attempting to verify a > measurement list against PCRs. keylime OTOH doesn't seem to -- it > expects the template hash type to match the PCR bank algorithm. I > would argue that for the latter case, the fallback scheme could > potentially cause hard to debug verification failures. >=20 > There's another problem with the fallback scheme: right now, SHA-1 > availability is a hard requirement for IMA, and it would be good for > a number of reasons to get rid of that. However, if SHA-1 is not > available to the kernel, it can hardly provide padded SHA-1 template > hashes for PCR banks with unsupported algos. I think this was done against the day IMA only supported sha1 and the TPM sha256 and beyond so there'd at least be a record that could be replayed. I think today with most distros defaulting IMAs hash to sha256 that's much less of a problem. > There are several more or less reasonable alternatives possible, > among them are: > a.) Instead of padded SHA-1, use padded/truncated ima_hash template > =C2=A0=C2=A0=C2=A0 hashes. > b.) Don't extend unsupported banks at all. > c.) Record every event as a violation, i.e. extend unsupported banks > =C2=A0=C2=A0=C2=A0 with 0xffs. > d.) Invalidate unsupported banks at least once by extending with a > unique > =C2=A0=C2=A0=C2=A0 constant (e.g. with 0xfes). Instead of any of that, why not do what the TCG tells us to do for unsupported banks and simply cap them with 0xffffffff record EV_SEPARATOR and stop extending to them? (note this would probably require defining a separator event for IMA) Regards, James