On Thu, Nov 08, 2018 at 10:29:53AM -0500, Mimi Zohar wrote: > On Thu, 2018-11-08 at 17:21 +0200, Jarkko Sakkinen wrote: > > On Thu, Nov 08, 2018 at 07:20:51PM +0530, Nayna Jain wrote: > > > Based on a discussion with Ken, the count in the TPML_PCR_SELECTION returns > > > the number of possible algorithms supported. In the example below, two > > > possible algorithms - SHA1 and SHA256 - are returned. > > > > > > # /usr/local/bin/tssgetcapability -cap 5 > > > 2 PCR selections > > > hash TPM_ALG_SHA1 > > > TPMS_PCR_SELECTION length 3 > > > ff ff ff > > > hash TPM_ALG_SHA256 > > > TPMS_PCR_SELECTION length 3 > > > 00 00 00 > > > > > > The pcr_select fields - "ff ff ff" and "00 00 00" - are bit masks for the > > > enabled PCRs. The SHA1 bank is enabled for all PCRs (0-23), while the SHA256 > > > bank is not enabled. > > > > > > The current code works, but it unnecessarily extends some banks. Instead of > > > basing the number of active banks on the number of algorithms returned, it > > > should be based on the pcr_select field. > > > > > > - Mimi & Nayna > > > > I would just allocate array of the size of possible banks and grow > > nr_active_banks for active algorithms to keep the code simple because > > we are talking about insignificant amount of wasted space (might be > > even zero bytes given how kernel allocators works)> > > That's fine. Remember the memory is just one concern, but the other > concerns are the performance of calculating the unneeded hash and the > TPM performance of including it in the PCR extend. The driver would initialize only as many entries as are active array and set nr_active_banks accordingly. /Jarkko
