Messages in this thread |  | | Date | Mon, 10 Oct 2016 07:59:25 +0300 | From | Jarkko Sakkinen <> | Subject | Re: [tpmdd-devel] [PATCH RFC 1/3] tpm_crb: expand struct crb_control_area to struct crb_regs |
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On Mon, Oct 10, 2016 at 12:25:11AM +0000, Winkler, Tomas wrote: > > > > -----Original Message----- > > From: Jason Gunthorpe [mailto:jgunthorpe@obsidianresearch.com] > > Sent: Monday, October 10, 2016 02:08 > > To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> > > Cc: moderated list:TPM DEVICE DRIVER <tpmdd-devel@lists.sourceforge.net>; > > open list <linux-kernel@vger.kernel.org> > > Subject: Re: [tpmdd-devel] [PATCH RFC 1/3] tpm_crb: expand struct > > crb_control_area to struct crb_regs > > > > 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. > > I addition I believe it should be always on offset FED4_0xxxh by the > Spec, so all this arithmetic is a bit of overkill.
It's all done to workaround ACPI start. Even if CRB start devices would always be in that offset it still would be needed.
> Thanks > Tomas
/Jarkko
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