From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jarkko Sakkinen Subject: Re: [PATCH RFC 1/3] tpm_crb: expand struct crb_control_area to struct crb_regs Date: Mon, 10 Oct 2016 07:45:08 +0300 Message-ID: <20161010044508.GA5920@intel.com> References: <1475972112-2819-1-git-send-email-jarkko.sakkinen@linux.intel.com> <1475972112-2819-2-git-send-email-jarkko.sakkinen@linux.intel.com> <20161009014256.GA8210@obsidianresearch.com> <20161009093818.GG31891@intel.com> <20161009164905.GA12551@obsidianresearch.com> <20161009183232.GA27764@intel.com> <20161009183358.GB27764@intel.com> <20161009230737.GA23823@obsidianresearch.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20161009230737.GA23823-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: tpmdd-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: Jason Gunthorpe Cc: "moderated list:TPM DEVICE DRIVER" , open list List-Id: tpmdd-devel@lists.sourceforge.net On Sun, Oct 09, 2016 at 05:07:37PM -0600, Jason Gunthorpe wrote: > On Sun, Oct 09, 2016 at 09:33:58PM +0300, Jarkko Sakkinen wrote: > > > > Sorry I missed this part. > > > > > > Here are the constraints for existing hardware: > > > > > > 1. All the existing CRB start only hardware has the iomem covering the > > > control area and registers for multiple localities. > > > 2. All the existing ACPI start hardware has only the control area. > > > > > > If you assume that SSDT does not have malicous behavior caused by either > > > a BIOS bug or maybe a rootkit, then the current patch works for all the > > > existing hardware. > > > > > > To counter-measure for unexpected behavior in non-existing hardware and > > > buggy or malicious firmware it probably make sense to use crb_map_res to > > > validate the part of the CRB registers that is not part of the control > > > area. > > I don't know how much I'd assume BIOS authors do what you think - the > spec I saw for this seems very vauge. > > Certainly checking that locality region falls within the acpi mapping > seems essential. > > > > Doing it in the way you proposed does not work for ACPI start devices. > > > > > > For them it should be done in the same way as I'm doing in the existing > > > patch as for ACPI start devices the address below the control area are > > > never accessed. Having a separate crb_map_res for CRB start only devices > > > is sane thing to do for validation. > > > > Alternative is to do two structures crb_regs_head and crb_regs_tail, > > which might be cleaner. I'm fine with going either route. > > Since the iomem doesn't actually exist for a configuration having two > pointers is the better choice. Make sure one is null for the > configuration that does not support it. > > The negative offset thing is way too subtle. Yeah, I do agree with you on this. Even if it was functionalliy correct, it is hard to understand if you don't proactively work on the driver. > Jason /Jarkko ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot