[cfe-dev] Tainting adjacent variables

cmp xchg8b f00fbugx86 at gmail.com
Mon Apr 22 08:33:24 PDT 2013


I'm new to LLVM and am trying to build a checker for clang. In a program

void foo()
int a;
int b;
int c;
int d;

If doSomeThingWith(c) detects a problem with the value c, I want to taint
variables beyond c (aka c, b and a) so that when calling
doSomeThingWith(a), the function says "hey, this value is tainted but it

I did something like :

const StackLocalsSpaceRegion *stackFrame =


in checkLocation to say "hey, I want to taint the entire stack frame". And
then, I do the check in checkPreCall with :

if (State->isTainted(dyn_cast<MemRegion>(stackFrame)))
 // bad


if (R && State->isTainted(dyn_cast<MemRegion>(R)))
std::cout << "Corrupted stack" << std::endl;



But when I test my checker on a buggy program, the taint checking doesn't
work. Stack frames are note the same. If I only taint MemRegions, I
actually only taint a chunk of a variable. (like a byte of a buffer) I
can't taint adjacent data. I can't say for example "I can overflow a buffer
from up to 12 bytes so I will taint the 12 bytes that follow that buffer
aka the 3 4-bytes integers that are above the buffer in the code".

Could you please give me some help doing that? What is the proper way to
taint / checker the taint of the stack frame? How can I find adjacent
variables? (didn't find anything that fits in the doxygene doc)

Thank you in advance!
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