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Smith" , "Thomas Gleixner" , "Eric W. Biederman" , "Eric Biggers" Cc: "Ross Philipson" , linux-kernel@vger.kernel.org, x86@kernel.org, linux-integrity@vger.kernel.org, linux-doc@vger.kernel.org, linux-crypto@vger.kernel.org, kexec@lists.infradead.org, linux-efi@vger.kernel.org, iommu@lists.linux-foundation.org, "Ingo Molnar" , "Borislav Petkov" , "H . Peter Anvin" , dave.hansen@linux.intel.com, "Matthew Garrett" , "James Bottomley" , peterhuewe@gmx.de, "Jarkko Sakkinen" , jgg@ziepe.ca, "Andy Lutomirski" , nivedita@alum.mit.edu, "Herbert Xu" , davem@davemloft.net, corbet@lwn.net, dwmw2@infradead.org, baolu.lu@linux.intel.com, kanth.ghatraju@oracle.com, "Andrew Cooper" , trenchboot-devel@googlegroups.com Message-Id: In-Reply-To: <281c3bb3-13f6-47a2-9a9a-134e397bf686@apertussolutions.com> References: <20240531010331.134441-1-ross.philipson@oracle.com> <20240531010331.134441-7-ross.philipson@oracle.com> <20240531021656.GA1502@sol.localdomain> <874jaegk8i.fsf@email.froward.int.ebiederm.org> <5b1ce8d3-516d-4dfd-a976-38e5cee1ef4e@apertussolutions.com> <87ttflli09.ffs@tglx> <281c3bb3-13f6-47a2-9a9a-134e397bf686@apertussolutions.com> Subject: Re: [PATCH v9 06/19] x86: Add early SHA-1 support for Secure Launch early measurements Content-Type: text/plain Content-Transfer-Encoding: 7bit Coming back to this old thread after having spent some time playing with the code: On Thu, 22 Aug 2024, at 20:29, Daniel P. Smith wrote: > Another fact to consider is that the current Intel's TXT MLE > specification dictates SHA1 as a valid configuration. Secure Launch's > use of SHA1 is therefore to comply with Intel's specification for TXT. As I understand the Intel TXT spec and the code: - TPM 1.2 is no longer supported by the TXT spec (since 2023) - TPM 1.2 is not supported by your GRUB implementation - in TPM 2.0 mode, SHA1 is only supported by the TXT spec if it is the /only/ algo supported by the TPM - the proposed kernel implementation ignores any SHA-384 and SM3-256 PCR banks if they are active, and caps them using a { 1, 0, ... } fake digest. So apologies for being slow, but I still struggle to understand why it is so important to have a SHA-1 implementation to cap those PCRs. Is it just to support systems with a TPM 2.0 that only has SHA-1 banks enabled? Assuming that this code will get merged this year, it will be in a LTS branch by 2027, by which time distros like Debian will pick it up. I fully understand that this code has lived out-of-tree for more than a decade, and you likely prefer to get everything upstream that your current users may be relying on. But for Linux, this is a new feature, and merging code now that is basically obsolete on day 1 is not something we should entertain imo. (and apologies for re-opening yet another can of worms - I assure you I am trying to be constructive here) -- Ard.