| Advisory TFV-5 (CVE-2017-15031) |
| =============================== |
| |
| +----------------+-------------------------------------------------------------+ |
| | Title | Not initializing or saving/restoring ``PMCR_EL0`` can leak | |
| | | secure world timing information | |
| +================+=============================================================+ |
| | CVE ID | `CVE-2017-15031`_ | |
| +----------------+-------------------------------------------------------------+ |
| | Date | 02 Oct 2017 | |
| +----------------+-------------------------------------------------------------+ |
| | Versions | All, up to and including v1.4 | |
| | Affected | | |
| +----------------+-------------------------------------------------------------+ |
| | Configurations | All | |
| | Affected | | |
| +----------------+-------------------------------------------------------------+ |
| | Impact | Leakage of sensitive secure world timing information | |
| +----------------+-------------------------------------------------------------+ |
| | Fix Version | `Pull Request #1127`_ (merged on 18 October 2017) | |
| +----------------+-------------------------------------------------------------+ |
| | Credit | Arm | |
| +----------------+-------------------------------------------------------------+ |
| |
| The ``PMCR_EL0`` (Performance Monitors Control Register) provides details of the |
| Performance Monitors implementation, including the number of counters |
| implemented, and configures and controls the counters. If the ``PMCR_EL0.DP`` |
| bit is set to zero, the cycle counter (when enabled) counts during secure world |
| execution, even when prohibited by the debug signals. |
| |
| Since Arm TF does not save and restore ``PMCR_EL0`` when switching between the |
| normal and secure worlds, normal world code can set ``PMCR_EL0.DP`` to zero to |
| cause leakage of secure world timing information. This register should be added |
| to the list of saved/restored registers. |
| |
| Furthermore, ``PMCR_EL0.DP`` has an architecturally ``UNKNOWN`` reset value. |
| Since Arm TF does not initialize this register, it's possible that on at least |
| some implementations, ``PMCR_EL0.DP`` is set to zero by default. This and other |
| bits with an architecturally UNKNOWN reset value should be initialized to |
| sensible default values in the secure context. |
| |
| The same issue exists for the equivalent AArch32 register, ``PMCR``, except that |
| here ``PMCR_EL0.DP`` architecturally resets to zero. |
| |
| .. _CVE-2017-15031: http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-15031 |
| .. _Pull Request #1127: https://github.com/ARM-software/arm-trusted-firmware/pull/1127 |
