From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 93D3F1E570D; Mon, 6 Oct 2025 14:18:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759760298; cv=none; b=cWiCH4XjnycdB47ae8Pezd1z7h+m7y8ITybP4HLvdcZmvD74brSXv9OlzNVWVOA2IP333dj1hqmw+vwbISb2QI+q3+9wwcadOIxuFO4+8Qk+U34l8Qlpt6Y8Nl/PyK44q9gooqFhgTvF4uhqBfvzFapJT192OtUnyy+6JqJGAkc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759760298; c=relaxed/simple; bh=nEaSVOanl5k6WKOgap9cfNjneoyL3wULm9rxvYRal6Q=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=WsIgUnrNW4rGXtGp1mhS4sL5f1SPX5b+XsFJ2Z7IJsAA4Tb0cDzAqEGRpXHk0LZLsgRxMiMH0kwr97YwT3tPWqf0k6ddp54/3BI3R9CXM9yPfY9jlP91e17+R1upahRCT/P/oblXXss9rp5GTYzzPzppeyv2OK8pdgCR1is37Lg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cT2DuKTv; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="cT2DuKTv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A5F0AC4CEF5; Mon, 6 Oct 2025 14:18:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1759760297; bh=nEaSVOanl5k6WKOgap9cfNjneoyL3wULm9rxvYRal6Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=cT2DuKTvOPR0iK4HEjUaijCOpM3Zrr5/XNlKH5vpL2zThMJITnjz5KSbvO9saK/zh 3t3UBSvc1VmDexL//Y0tNLIoB1wrMA2ewXr3qxHENWq9TscNLOOFajjrifjS6Mri19 CZ5hEsEPm9BU5cIOJ7Cmfmw1s4EINyGFm4gh2dQ1TouIEIx7fdUxIywzsjwzfL1rJY fGnoibCVylhc+x1kyutTDtOGY832lYqZPH5jbL0cxweBlsjpxWS1szsU0RcYhf5f47 r3DnVQiKVdd/UiCozyg4gtxaZUsg17URUzC2ksy0EGuQCBgDBXI2Bu9RlJbs21CTD2 YRCopNCwtQGbQ== Date: Mon, 6 Oct 2025 17:18:13 +0300 From: Jarkko Sakkinen To: Linus Torvalds Cc: Peter Huewe , Jason Gunthorpe , David Howells , keyrings@vger.kernel.org, linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [GIT PULL] TPM DEVICE DRIVER: tpmdd-next-v6.18 Message-ID: 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=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Oct 06, 2025 at 05:13:02PM +0300, Jarkko Sakkinen wrote: > On Mon, Oct 06, 2025 at 02:58:17PM +0300, Jarkko Sakkinen wrote: > > On Sun, Oct 05, 2025 at 11:09:08AM -0700, Linus Torvalds wrote: > > > On Sun, 5 Oct 2025 at 08:47, Jarkko Sakkinen wrote: > > > > > > > > This pull request disables > > > > TCG_TPM2_HMAC from the default configuration as it does not perform well > > > > enough [1]. > > > > > > > > [1] https://lore.kernel.org/linux-integrity/20250825203223.629515-1-jarkko@kernel.org/ > > > > > > This link is entirely useless, and doesn't explain what the problem > > > was and *why* TPM2_TCG_HMAC shouldn't be on by default. > > > > > > I think a much better link is > > > > > > https://lore.kernel.org/linux-integrity/20250814162252.3504279-1-cfenn@google.com/ > > > > > > which talks about the problems that TPM2_TCG_HMAC causes. > > > > > > Which weren't just about "not performing well enough", but actually > > > about how it breaks TPM entirely for some cases. > > > > Fair enough. I'll also enumerate the issues, and also roadmap > > to heal the feature. > > So some of the arguments in Chris' email are debatable, such as > this list: > > - TPM_RH_NULL > - TPM2_CreatePrimary > - TPM2_ContextSave > - ECDH-P256 > - AES-128-CFB > > > We've never encountered a TPM chip without those TPM commands, and e.g. > /dev/tpmrm0 heavily relies on TPM2_ContextSave, and has been in the > mainline since 2017. And further, this has been the case on ARM too. > > So using all of the arguments as rationale for the change that according > to Chris' email are broken because I cannnot objectively on all of the > arguments. > > E.g. I have to assume to this day that all known TPM chips have those > commands because no smoking gun exists. And if DID exist, then I'd > assume someone would fixed /dev/tpmrm0 ages ago. > > That said, I do agree on disabling the feature for the time being: > we have consensus on actions but not really on stimulus tbh. > And if there is stimulus I would postpone this patch to create > fix also for /dev/tpmrm0. > > Argument where I meet with Chris suggestion are: > > 1. Performance. The key generation during boot is extremely bad > idea and depending on the deployment the encryption cost is > too much (e.g. with my laptop having fTPM it does not really > matter). > 2. Null seed was extremely bad idea. The way I'm planning to actually > fix this is to parametrize the primary key to a persistent key handle > stored into nvram of the chip instead of genration. This will address > also ambiguity and can be linked directly to vendor ceritifcate > for e.g. to perfom remote attesttion. > > Things don't go broken by saying that they are broken and nothing > elsewhere in the mainline has supporting evidence that those commands > would be optional. I cannot agree on argument which I have zero > means to measure in any possible way. > > This is exactly also the root reason why I wrote my own commit instead > with the same change: I could have never signed off the commit that > I don't believe is true in its storyline. > > So if I write cover for the pull request where I use the subset of > arguments with shared consensus would that be enough to get this > through? As for primary key handle fix I rather do that with > time and proper care. I had to use few hours to remind why I did my commit instead of acking the original and this is the root. We've never had e.g. a bug in the wild that would /dev/tpmrm0 to be broken because ContextSave is not available, and it is *widely* used device across all major platforms. BR, Jarkko