From: "Jarkko Sakkinen" <jarkko@kernel.org>
To: "Eric Biggers" <ebiggers@kernel.org>,
"Andy Lutomirski" <luto@kernel.org>
Cc: "Andrew Cooper" <andrew.cooper3@citrix.com>,
"Ard Biesheuvel" <ardb@kernel.org>,
"Ross Philipson" <ross.philipson@oracle.com>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"the arch/x86 maintainers" <x86@kernel.org>,
<linux-integrity@vger.kernel.org>, <linux-doc@vger.kernel.org>,
"Linux Crypto Mailing List" <linux-crypto@vger.kernel.org>,
<kexec@lists.infradead.org>, <linux-efi@vger.kernel.org>,
<dpsmith@apertussolutions.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>,
"Borislav Petkov" <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
"Matthew Garrett" <mjg59@srcf.ucam.org>,
<James.Bottomley@hansenpartnership.com>, <peterhuewe@gmx.de>,
"Jason Gunthorpe" <jgg@ziepe.ca>,
"luto@amacapital.net" <luto@amacapital.net>,
"Arvind Sankar" <nivedita@alum.mit.edu>,
"Herbert Xu" <herbert@gondor.apana.org.au>, <davem@davemloft.net>,
<kanth.ghatraju@oracle.com>, <trenchboot-devel@googlegroups.com>
Subject: Re: [PATCH v8 06/15] x86: Add early SHA support for Secure Launch early measurements
Date: Thu, 04 Apr 2024 17:55:22 +0300 [thread overview]
Message-ID: <D0BFBFRVGG47.FXCTWETKP7H4@kernel.org> (raw)
In-Reply-To: <20240403235635.GA24248@quark.localdomain>
On Thu Apr 4, 2024 at 2:56 AM EEST, Eric Biggers wrote:
> On Wed, Apr 03, 2024 at 09:32:02AM -0700, Andy Lutomirski wrote:
> > On Fri, Feb 23, 2024, at 10:30 AM, Eric Biggers wrote:
> > > On Fri, Feb 23, 2024 at 06:20:27PM +0000, Andrew Cooper wrote:
> > >> On 23/02/2024 5:54 pm, Eric Biggers wrote:
> > >> > On Fri, Feb 23, 2024 at 04:42:11PM +0000, Andrew Cooper wrote:
> > >> >> Yes, and I agree. We're not looking to try and force this in with
> > >> >> underhand tactics.
> > >> >>
> > >> >> But a blind "nack to any SHA-1" is similarly damaging in the opposite
> > >> >> direction.
> > >> >>
> > >> > Well, reviewers have said they'd prefer that SHA-1 not be included and given
> > >> > some thoughtful reasons for that. But also they've given suggestions on how to
> > >> > make the SHA-1 support more palatable, such as splitting it into a separate
> > >> > patch and giving it a proper justification.
> > >> >
> > >> > All suggestions have been ignored.
> > >>
> > >> The public record demonstrates otherwise.
> > >>
> > >> But are you saying that you'd be happy if the commit message read
> > >> something more like:
> > >>
> > >> ---8<---
> > >> For better or worse, Secure Launch needs SHA-1 and SHA-256.
> > >>
> > >> The choice of hashes used lie with the platform firmware, not with
> > >> software, and is often outside of the users control.
> > >>
> > >> Even if we'd prefer to use SHA-256-only, if firmware elected to start us
> > >> with the SHA-1 and SHA-256 backs active, we still need SHA-1 to parse
> > >> the TPM event log thus far, and deliberately cap the SHA-1 PCRs in order
> > >> to safely use SHA-256 for everything else.
> > >> ---
> > >
> > > Please take some time to read through the comments that reviewers have left on
> > > previous versions of the patchset.
> >
> > So I went and read through the old comments, and I'm lost. In brief summary:
> >
> > If the hardware+firmware only supports SHA-1, then some reviewers would prefer
> > Linux not to support DRTM. I personally think this is a bit silly, but it's
> > not entirely unreasonable. Maybe it should be a config option?
> >
> > If the hardware+firmware does support SHA-256, then it sounds (to me, reading
> > this -- I haven't dug into the right spec pages) that, for optimal security,
> > something still needs to effectively turn SHA-1 *off* at runtime by capping
> > the event log properly. And that requires computing a SHA-1 hash. And, to be
> > clear, (a) this is only on systems that already support SHA-256 and that we
> > should support and (b) *not* doing so leaves us potentially more vulnerable to
> > SHA-1 attacks than doing so. And no SHA-256-supporting tooling will actually
> > be compromised by a SHA-1 compromise if we cap the event log.
> >
> > So is there a way forward? Just saying "read through the comments" seems like
> > a dead end.
> >
>
> It seems there may be a justification for some form of SHA-1 support in this
> feature. As I've said, the problem is that it's not explained in the patchset
> itself. Rather, it just talks about "SHA" and pretends like SHA-1 and SHA-2 are
> basically the same. In fact, SHA-1 differs drastically from SHA-2 in terms of
> security. SHA-1 support should be added in a separate patch, with a clearly
> explained rationale *in the patch itself* for the SHA-1 support *specifically*.
Yeah, this is important so that we don't end up deleting that support
by accident. Just adding to denote that this more than just a "process
issue".
> - Eric
BR, Jarkko
next prev parent reply other threads:[~2024-04-04 14:55 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-14 22:18 [PATCH v8 00/15] x86: Trenchboot secure dynamic launch Linux kernel support Ross Philipson
2024-02-14 22:18 ` [PATCH v8 01/15] x86/boot: Place kernel_info at a fixed offset Ross Philipson
2024-02-15 7:56 ` Ard Biesheuvel
2024-02-15 10:56 ` Daniel Kiper
2024-03-21 13:45 ` Daniel P. Smith
2024-03-22 14:18 ` H. Peter Anvin
2024-03-23 1:33 ` Daniel P. Smith
2024-02-14 22:18 ` [PATCH v8 02/15] Documentation/x86: Secure Launch kernel documentation Ross Philipson
2024-02-14 22:18 ` [PATCH v8 03/15] x86: Secure Launch Kconfig Ross Philipson
2024-02-15 7:59 ` Ard Biesheuvel
2024-02-15 22:20 ` ross.philipson
2024-02-14 22:18 ` [PATCH v8 04/15] x86: Secure Launch Resource Table header file Ross Philipson
2024-02-15 8:08 ` Ard Biesheuvel
2024-02-22 2:03 ` Andrew Cooper
2024-02-22 2:10 ` ross.philipson
2024-02-22 17:49 ` ross.philipson
2024-03-29 22:38 ` Kim Phillips
2024-03-29 22:38 ` Kim Phillips
2024-03-29 22:38 ` Kim Phillips
2024-04-01 18:25 ` ross.philipson
2024-02-14 22:18 ` [PATCH v8 05/15] x86: Secure Launch main " Ross Philipson
2024-02-14 22:18 ` [PATCH v8 06/15] x86: Add early SHA support for Secure Launch early measurements Ross Philipson
2024-02-15 8:17 ` Ard Biesheuvel
2024-02-22 3:04 ` Andrew Cooper
2024-02-22 9:34 ` Ard Biesheuvel
2024-02-22 12:30 ` Andrew Cooper
2024-02-23 9:27 ` Ard Biesheuvel
2024-02-23 16:42 ` Andrew Cooper
2024-02-23 17:54 ` Eric Biggers
2024-02-23 18:20 ` Andrew Cooper
2024-02-23 18:30 ` Eric Biggers
2024-04-03 16:32 ` Andy Lutomirski
2024-04-03 23:56 ` Eric Biggers
2024-04-04 4:55 ` ross.philipson
2024-04-04 14:55 ` Jarkko Sakkinen [this message]
2024-02-14 22:18 ` [PATCH v8 07/15] x86: Secure Launch kernel early boot stub Ross Philipson
2024-02-15 8:29 ` Ard Biesheuvel
2024-02-15 22:26 ` ross.philipson
2024-02-14 22:18 ` [PATCH v8 08/15] x86: Secure Launch kernel late " Ross Philipson
2024-02-14 22:18 ` [PATCH v8 09/15] x86: Secure Launch SMP bringup support Ross Philipson
2024-02-14 22:18 ` [PATCH v8 10/15] kexec: Secure Launch kexec SEXIT support Ross Philipson
2024-02-14 22:18 ` [PATCH v8 11/15] reboot: Secure Launch SEXIT support on reboot paths Ross Philipson
2024-02-14 22:18 ` [PATCH v8 12/15] tpm: Add ability to set the preferred locality the TPM chip uses Ross Philipson
2024-02-14 22:18 ` [PATCH v8 13/15] tpm: Add sysfs interface to allow setting and querying the preferred locality Ross Philipson
2024-02-14 22:18 ` [PATCH v8 14/15] x86: Secure Launch late initcall platform module Ross Philipson
2024-02-15 8:40 ` Ard Biesheuvel
2024-02-22 13:57 ` Daniel P. Smith
2024-02-23 9:36 ` Ard Biesheuvel
2024-03-21 14:11 ` Daniel P. Smith
2024-02-16 1:53 ` kernel test robot
2024-02-17 7:53 ` kernel test robot
2024-02-14 22:18 ` [PATCH v8 15/15] x86: EFI stub DRTM launch support for Secure Launch Ross Philipson
2024-02-15 9:01 ` Ard Biesheuvel
2024-02-21 20:17 ` ross.philipson
2024-02-21 20:37 ` H. Peter Anvin
2024-02-21 23:24 ` Ard Biesheuvel
2024-02-17 7:31 ` kernel test robot
2024-02-17 20:06 ` kernel test robot
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