SR 3.6: Deterministic Output I S A 6 CR 3.5: Input ValidationĬR 3. a multi-level structure, we add a level of indirection through the use of the page directory, which points to pieces of the page table that indirection. The Unix operating system and its derivatives treat all input and output sources uniformly. This level of indirection is used for another purpose. Technique: T0836 – Modify Parameter I S A 6 SR 3.5: Input Validation On modern multithreaded, multi-core processors, ensuring data consistency by maintaining one mutual exclusion lock for all critical operating system structures. References Standard/framework Mapp i n g M IT R E ATT&CK for ICS Tactic: TA010 – Impair Process Control Now, we can divide the virtual address intothree parts: say 10 bits for the level-0 index, 10 bits for the level-1 index, and again 12 bits for the o setwithin a page. As an example, consider a two-level pagetable, again on a 32-bit architecture with 212 4 kbyte pages. Reliability Identifies non-malicious human errors in programming. Multi-level page tables are tree-like structures to hold page tables. They can be caused by human error but also be inserted maliciously. In both cases, indirection errors can be hard to spot and can have serious impacts. Second, if a wrong indirection leads to writing to the wrong register, the program overwrites code or values you want to keep. There are two potentially dangerous scenarios that can stem from indirection mistakes:įirst, if an indirection leads to reading from the wrong register, the program executes using the wrong values. W hy? B ene ficial for…? Wh y ? Se c u ri t y Most PLCs do not have any feature to handle out-of-bounds indices for arrays. e.g., if you have a need for 5 registers (not binary-sized): If it is not binary-sized, create a mask to the next size up on a binary scale. Create array maskĬheck if the array is binary-sized. The approach can be turned into a few function blocks and possibly even reused for other applications. PLCs do not typically have an “end of an array” flag so it’s a good idea to create it in software the goal is to avoid unusual/unplanned PLC operations.Įxample Instruction List (IL) Programming To decide which pump to start running first based on their current run times.Variable frequency drives (VFDs) that trigger different actions for different frequencies using lookup tables.There are many reasons to use indirections. Se c u ri t y Objective T a rg e t Group The integrity of PLC variables Product Supplier Integration / Maintenance Service Provider PLC Validate indirectionsĪn indirection is the use of the value of a register in another register. PLC best practices – Validate indirections by poisoning array ends to catch fence-post errors.
0 Comments
Leave a Reply. |