Gerd I cannot agree your statement on ordering. Smart attacker can forge the good measurement based upon the severity of vulnerability.
One famous example in 2011: https://invisiblethingslab.com/resources/2011/Attacking_Intel_TXT_via_SINIT_hijacking.pdf Because the attack happens before PCR18 measurement, the PCR18 is forged successfully. > -----Original Message----- > From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Gerd > Hoffmann > Sent: Wednesday, April 20, 2022 4:17 PM > To: Yao, Jiewen <jiewen....@intel.com> > Cc: devel@edk2.groups.io; Xu, Min M <min.m...@intel.com>; Ard Biesheuvel > <ardb+tianoc...@kernel.org>; Justen, Jordan L <jordan.l.jus...@intel.com>; > Brijesh Singh <brijesh.si...@amd.com>; Aktas, Erdem > <erdemak...@google.com>; James Bottomley <j...@linux.ibm.com>; Tom > Lendacky <thomas.lenda...@amd.com> > Subject: Re: [edk2-devel] [PATCH V3 5/9] OvmfPkg/IntelTdx: Measure Td > HobList and Configuration FV > > Hi, > > > > Yes for validation (aka sanity-checking the fields, etc). > > > But for measurement I don't see why the ordering matters. > > > Whenever you do that before or after consuming the TdHob > > > should not make a difference. > > > > [Jiewen] I disagree. The order matters from security perspective. > > If you use it, there is risk that the buggy code will compromise the system > before you have chance to measure it. > > Measurement will only record hashes for verification later on. > It will not prevent running possibly buggy/compromised code. > > So, no matter what the order is, you'll figure the system got > compromised after the fact, when checking the hashes later, and in turn > take actions like refusing to hand out secrets to the compromised > system. > > > There was already known attacks: The measurement was in wrong place, > > which caused the attack can forge the measurement. > > Do you have a link or CVE number for me? > > thanks, > Gerd > > > > > -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#89134): https://edk2.groups.io/g/devel/message/89134 Mute This Topic: https://groups.io/mt/90531017/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
