Introduction to software vulnerability analysis (I)

Mixed assembly and inline assembly

Prepare to take notes of some knowledge points about software security from this article , Make a series , I hope I can stick to it . Limited ability , The knowledge point is also relatively simple , If there are omissions in your notes, please forgive me .

Because the notes focus on the analysis and practical operation of software vulnerabilities , Some basic knowledge of compilation is not included in this series , By default, you already have a certain assembly foundation , Therefore, the author will not add comments next to all sentences .

adopt VS2022 Conduct C and x86 Assembly mixed programming

Why not use more convenient VS2010 Well , One is that many software security textbooks are relatively old , Can't keep up with the new era , And if you are VS2022 The latest version can be debugged successfully , Then many previous versions can be debugged successfully in this way

;func.asm

.model	flat  ; Pseudo instruction   Determine the working mode 
PUBLIC	_TestDemo ;extern int TestDemo();   
_TEXT	SEGMENT ; Code segment 
_TestDemo PROC
		MOV EAX, 2222  ;
		RET
_TestDemo ENDP
_TEXT	ENDS
END

//main.c

#include <stdio.h>
int TestDemo(void);
int main()
{
    
	int c = TestDemo();
	printf("%d\n",c);
}

You can see , In the project file main.c Inside , It's not TestDemo The definition of function , TestDemo Is defined in another func.asm In the assembly statement , In order for the main code to know TestDemo The content of , You need a linker to link and compile the two files to generate an executable program

Add two files to VS2022 In the project , Because it needs links asm Assembly files , Therefore, the following settings are required:

Right click project --> Generation dependency --> Generate custom

Check masm

Right click func.asm choice attribute , Item type selection Microsoft Macro Assembler Give Way IDE distinguish

Item properties , The subsystem setting under the linker should be changed to console

Because the experiment is x86 assembly , Therefore, the generated compiled file must be x86 Format

Compile operation

adopt VS2022 Conduct X86 Embedded assembly programming

Now we embed the assembly code main.c Inline execution
Compared with the above code , This is a small improvement , Added the input part , Make it a normal adder
Compared with hybrid assembly , This inline assembly does not require link compilation , Because the assembled code is main.c Inside , As long as it contains dependencies that recognize assembly , You can directly compile and run

//main.c

#include <stdio.h>
#include <stdlib.h>
int TestDemo(int a, int b)
{
    
    // Assembly part 
  __asm{
    
   mov eax, a    ; Get first argument
   mov ecx, b  	 ; Get second argument
   add eax, ecx  ;  take eax,ecx Value added to eax On 
  };
}
int main()
{
    
	int a,b,c;
	scanf("%d %d",&a,&b);
	c = TestDemo(a,b);
	printf("%d\n",c);
	system("pause");
}

In order to make the code work properly , It also needs to be set

Same as before , You also need to add dependencies masm

subsystem The setting should also be changed to console

Compile operation

The above two are the most common assembly code calls , After completing the compilation and generation of a program , You can start to disassemble and analyze its executable file