On Mon Jan 13 20, Mimi Zohar wrote:
On Mon, 2020-01-13 at 17:06 -0700, Jerry Snitselaar wrote:
We had a report of messages from ima saying "Error communicating with
TPM". Looking into it a bit, it looks like with some Dell systems
(possibly others as well) in the bios they can set the hash algorithm
being used. In this case with that set to sha256 the messages
appear. Flipping the system to using sha1 makes them disappear.
Looking at the ima code, ima_calc_boot_aggregate_tfm hard codes using
sha1. Should that be changed to use whatever the default is in the
config, or possibly find out from the tpm what algorithm is being used?
The ima-ng template contains two digests. The first digest is the
value being extended into the TPM, while the second digest is either
the boot aggregate or file data hash. It sounds like the problem is
with the first digest. Changing the boot-aggregate to use sha256
might be a good idea, but probably won't fix the problem.
Mimi
The error message is coming from ima_pcrread, and the tpm_digest that gets passed
by ima_calc_boot_aggregate_tfm to ima_pcrread is declared:
struct tpm_digest d = { .alg_id = TPM_ALG_SHA1, .digest = {0} };
According to Dell their default BIOS setting is to use sha256. What they see with that
setting is:
[ 5.475036] ima: Error Communicating to TPM chip
[ 5.475083] tsc: Refined TSC clocksource calibration: 3311.999 MHz
[ 5.475092] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x2fbd936b72f, max_idle_ns: 440795283163 ns
[ 5.475118] ima: Error Communicating to TPM chip
[ 5.475165] ima: Error Communicating to TPM chip
[ 5.475235] clocksource: Switched to clocksource tsc
[ 5.475266] ima: Error Communicating to TPM chip
[ 5.475311] ima: Error Communicating to TPM chip
[ 5.475341] ima: Error Communicating to TPM chip
[ 5.475371] ima: Error Communicating to TPM chip
[ 5.475402] ima: Error Communicating to TPM chip
[ 5.489049] ima: No architecture policies found
