[llvm-dev] "compiler-rt" - DataFlowSanitizer

[Bekket McClane via llvm-dev]

I haven’t used DFS yet, but I don’t think you need to write a pass.

You just need to include <sanitizer/dfsan_interface.h> and insert dfsan_* functions in the source code you want to inspect, following instructions in https://clang.llvm.org/docs/DataFlowSanitizer.html <https://clang.llvm.org/docs/DataFlowSanitizer.html>  or Sam’s instructions in previous email of this thread.

Bekket
> On Apr 18, 2019, at 7:00 AM, dareen khalid via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> I'm new to llvm passes. I wonder if I can use the pass to dynamically analyze a program. 
> Let me explain what I want to do in the following example .
> 
> 
> 
> //"Result" is an object that doesn't have a fixed length like int and float.
> 
> //The program is as follows.
> Result retrieve_data_fun (){
>  //the function retrieves some sensitive data from  files/DB
>  
>  return result_info;
> } 
> 
> void main(){
> ...
> Result var1, var2, var3l
> var1 = retrieve_data_fun();
> ...
> Result var2 = retrieve_data_fun();
> 
> printf (var1); 
> var3 = var2+'xxx';
> print (var3);
> 
> }
> 
> My goal is to track all the returned data from "retrieve_data_fun" and monitor actions on them. 
> So, whenever the data is used (e.g., printed) , I want to detect that; maybe by printing a statement or anything. 
> Could you please help me to do that ? 
> 
> Thanks, 
> Daren
> 
> 
> From: llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of Sam Kerner via llvm-dev <llvm-dev at lists.llvm.org>
> Sent: Wednesday, April 17, 2019 5:56 PM
> To: llvm-dev at lists.llvm.org
> Subject: Re: [llvm-dev] "compiler-rt" - DataFlowSanitizer
>  
> On Tue, Apr 16, 2019 at 3:44 PM dareen khalid via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> >
> > Hi all,
> >
> > I have some questions about "DataFlowSanitizer" from "compiler-rt".
> > I want to know how I can test the "DataFlowSanitizer"?
> 
> This document is a good reference for DataFlowSanitizer:
>   https://clang.llvm.org/docs/DataFlowSanitizer.html <https://clang.llvm.org/docs/DataFlowSanitizer.html>
> 
> > Can I configure it to label only some values,
> 
> The section named "Example" in the document above shows a simple
> program that sets and tests for labels.
> 
> dfsan_create_label() creates a label.
> 
> dfsan_set_label() applies a label to the memory holding a variable.
> 
> > i.e, the return values from specific functions?
> 
> To label the return value of a function, add a call to
> dfsan_set_label() on the return value of the function:
> 
>   // Outside the function:
>   dfsan_label return_label = dfsan_create_label("return_label", 0);
> 
>   // An example function:
>   int MyFunction(int a, int b) {
>     ...
>     int result = ...;
> 
>     // Set a label on the returned value:
>     dfsan_set_label(return_label, &result, sizeof(result));
> 
>     return result;
>   }
> 
> > Also, how can I print these labels?
> 
> To discover the label on a variable, you can test for it and print the result:
> 
>   int var = ...;
> 
>   // Does 'var' have label 'return_label'?
>   dfsan_label var_label = dfsan_get_label(var);
>   if (dfsan_has_label(var_label, return_label)) {
>     printf("'var' has the label ''return_label");
>   }
> 
> To see the state of all labels at the time the program exits set, set
> the shell variable DFSAN_OPTIONS to "dump_labels_at_exit=<file path>".
> For example, suppose the example program in the document is in a file
> named "dfsan.c".  Here are the commands I ran to see the state of all
> labels when it exits:
> 
>   # Compile dfsan.c into a binary named "dfsan":
>   $ clang -g -fsanitize=dataflow dfsan.c -o dfsan
> 
>   # Run it.  There is no output because all assertions pass:
>   $ ./dfsan
> 
>   # Run it again with shell variable DFSAN_OPTIONS set to export label
> state to standard out on exit:
>   $ env DFSAN_OPTIONS=dump_labels_at_exit=/dev/stdout ./dfsan
>   ==21994==INFO: DataFlowSanitizer: dumping labels to /dev/stdout
>   1 0 0 i
>   2 0 0 j
>   3 0 0 k
>   4 1 2
>   5 3 4
> 
> If you tell us more about what you are trying to accomplish with
> DataFlowSanitizer, we may be able to give more specific advice.
> 
> >
> > Thanks,
> > Dareen
> > _______________________________________________
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