Testing BIOS Interrupt 0x13 Based Software Write Blockers James R. Lyle and Paul E. Black

1. 1. Disk access via BIOS Int 0x13 2. Disk access with SWB tool 3. Flow to test SWB tool Application program Application program Test harness issue 0x13 cmd query result SWB tool SWB tool block block return return allow allow Int 0x13 monitor block report count count allow BIOS Int 0x13 BIOS Int 0x13 BIOS Int 0x13 issue cmd to drive issue cmd to drive issue cmd to drive return return return 4. The test cases 5. Results of testing SWB tools Class of Commands Disks Used Disks Protected Return Status • Seven SWB tools tested: 4 versions of one tool and 3 version of another. Small differences in all of them. • Advice: use auxiliary scripts and programs • Reduces chance of tester error • Easier to rerun (always needed) • But masks some tester mistakes 6. Validating the test tools • How do we know that the test tools behave properly, that is, that they test the SWB according to the test plan? • Write new test tools, test SWB’s, and compare results • Not independent • Run tools against disks • Not all commands effect disks • Disks may be destroyed • Review code & write mini-testers • Reviews and tests only found unimportant anomalies. Testing BIOS Interrupt 0x13 Based Software Write Blockers James R. Lyle and Paul E. Black U.S. National Institute of Standards and Technology (NIST) //www.cftt.nist.gov/