llvm-cfi-verify.cpp

//===-- llvm-cfi-verify.cpp - CFI Verification tool for LLVM --------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This tool verifies Control Flow Integrity (CFI) instrumentation by static
// binary anaylsis. See the design document in /docs/CFIVerify.rst for more
// information.
//
// This tool is currently incomplete. It currently only does disassembly for
// object files, and searches through the code for indirect control flow
// instructions, printing them once found.
//
//===----------------------------------------------------------------------===//

#include"lib/FileAnalysis.h"
#include"lib/GraphBuilder.h"

#include"llvm/BinaryFormat/ELF.h"
#include"llvm/Support/CommandLine.h"
#include"llvm/Support/Error.h"
#include"llvm/Support/FormatVariadic.h"
#include"llvm/Support/SpecialCaseList.h"
#include"llvm/Support/VirtualFileSystem.h"

#include<cstdlib>

usingnamespacellvm;
usingnamespacellvm::object;
usingnamespacellvm::cfi_verify;

cl::opt<std::string> InputFilename(cl::Positional, cl::desc("<input file>"),
 cl::Required);
cl::opt<std::string> BlacklistFilename(cl::Positional,
cl::desc("[blacklist file]"),
 cl::init("-"));
cl::opt<bool> PrintGraphs(
"print-graphs",
cl::desc("Print graphs around indirect CF instructions in DOT format."),
 cl::init(false));
cl::opt<unsigned> PrintBlameContext(
"blame-context",
cl::desc("Print the blame context (if possible) for BAD instructions. This "
"specifies the number of lines of context to include, where zero "
"disables this feature."),
 cl::init(0));
cl::opt<unsigned> PrintBlameContextAll(
"blame-context-all",
cl::desc("Prints the blame context (if possible) for ALL instructions. "
"This specifies the number of lines of context for non-BAD "
"instructions (see --blame-context). If --blame-context is "
"unspecified, it prints this number of contextual lines for BAD "
"instructions as well."),
 cl::init(0));
cl::opt<bool> Summarize("summarize", cl::desc("Print the summary only."),
 cl::init(false));

ExitOnError ExitOnErr;

voidprintBlameContext(const DILineInfo &LineInfo, unsigned Context) {
auto FileOrErr = MemoryBuffer::getFile(LineInfo.FileName);
if (!FileOrErr) {
errs() << "Could not open file: " << LineInfo.FileName << "\n";
return;
 }

 std::unique_ptr<MemoryBuffer> File = std::move(FileOrErr.get());
 SmallVector<StringRef, 100> Lines;
 File->getBuffer().split(Lines, '\n');

for (unsigned i = std::max<size_t>(1, LineInfo.Line - Context);
 i <
 std::min<size_t>(Lines.size() + 1, LineInfo.Line + Context + 1);
 ++i) {
if (i == LineInfo.Line)
outs() << ">";
else
outs() << "";

outs() << i << ": " << Lines[i - 1] << "\n";
 }
}

voidprintInstructionInformation(const FileAnalysis &Analysis,
const Instr &InstrMeta,
const GraphResult &Graph,
 CFIProtectionStatus ProtectionStatus) {
outs() << "Instruction: " << format_hex(InstrMeta.VMAddress, 2) << " ("
 << stringCFIProtectionStatus(ProtectionStatus) << "): ";
 Analysis.printInstruction(InstrMeta, outs());
outs() << "\n";

if (PrintGraphs)
 Graph.printToDOT(Analysis, outs());
}

voidprintInstructionStatus(unsigned BlameLine, bool CFIProtected,
const DILineInfo &LineInfo) {
if (BlameLine) {
outs() << "Blacklist Match: " << BlacklistFilename << ":" << BlameLine
 << "\n";
if (CFIProtected)
outs() << "====> Unexpected Protected\n";
else
outs() << "====> Expected Unprotected\n";

if (PrintBlameContextAll)
printBlameContext(LineInfo, PrintBlameContextAll);
 } else {
if (CFIProtected) {
outs() << "====> Expected Protected\n";
if (PrintBlameContextAll)
printBlameContext(LineInfo, PrintBlameContextAll);
 } else {
outs() << "====> Unexpected Unprotected (BAD)\n";
if (PrintBlameContext)
printBlameContext(LineInfo, PrintBlameContext);
 }
 }
}

voidprintIndirectCFInstructions(FileAnalysis &Analysis,
const SpecialCaseList *SpecialCaseList) {
uint64_t ExpectedProtected = 0;
uint64_t UnexpectedProtected = 0;
uint64_t ExpectedUnprotected = 0;
uint64_t UnexpectedUnprotected = 0;

 std::map<unsigned, uint64_t> BlameCounter;

for (object::SectionedAddress Address : Analysis.getIndirectInstructions()) {
constauto &InstrMeta = Analysis.getInstructionOrDie(Address.Address);
 GraphResult Graph = GraphBuilder::buildFlowGraph(Analysis, Address);

 CFIProtectionStatus ProtectionStatus =
 Analysis.validateCFIProtection(Graph);
bool CFIProtected = (ProtectionStatus == CFIProtectionStatus::PROTECTED);

if (!Summarize) {
outs() << "-----------------------------------------------------\n";
printInstructionInformation(Analysis, InstrMeta, Graph, ProtectionStatus);
 }

if (IgnoreDWARFFlag) {
if (CFIProtected)
 ExpectedProtected++;
else
 UnexpectedUnprotected++;
continue;
 }

auto InliningInfo = Analysis.symbolizeInlinedCode(Address);
if (!InliningInfo || InliningInfo->getNumberOfFrames() == 0) {
errs() << "Failed to symbolise " << format_hex(Address.Address, 2)
 << " with line tables from " << InputFilename << "\n";
exit(EXIT_FAILURE);
 }

constauto &LineInfo = InliningInfo->getFrame(0);

// Print the inlining symbolisation of this instruction.
if (!Summarize) {
for (uint32_t i = 0; i < InliningInfo->getNumberOfFrames(); ++i) {
constauto &Line = InliningInfo->getFrame(i);
outs() << "" << format_hex(Address.Address, 2) << " = "
 << Line.FileName << ":" << Line.Line << ":" << Line.Column
 << " (" << Line.FunctionName << ")\n";
 }
 }

if (!SpecialCaseList) {
if (CFIProtected) {
if (PrintBlameContextAll && !Summarize)
printBlameContext(LineInfo, PrintBlameContextAll);
 ExpectedProtected++;
 } else {
if (PrintBlameContext && !Summarize)
printBlameContext(LineInfo, PrintBlameContext);
 UnexpectedUnprotected++;
 }
continue;
 }

unsigned BlameLine = 0;
for (auto &K : {"cfi-icall", "cfi-vcall"}) {
if (!BlameLine)
 BlameLine =
 SpecialCaseList->inSectionBlame(K, "src", LineInfo.FileName);
if (!BlameLine)
 BlameLine =
 SpecialCaseList->inSectionBlame(K, "fun", LineInfo.FunctionName);
 }

if (BlameLine) {
 BlameCounter[BlameLine]++;
if (CFIProtected)
 UnexpectedProtected++;
else
 ExpectedUnprotected++;
 } else {
if (CFIProtected)
 ExpectedProtected++;
else
 UnexpectedUnprotected++;
 }

if (!Summarize)
printInstructionStatus(BlameLine, CFIProtected, LineInfo);
 }

uint64_t IndirectCFInstructions = ExpectedProtected + UnexpectedProtected +
 ExpectedUnprotected + UnexpectedUnprotected;

if (IndirectCFInstructions == 0) {
outs() << "No indirect CF instructions found.\n";
return;
 }

outs() << formatv("\nTotal Indirect CF Instructions: {0}\n"
"Expected Protected: {1} ({2:P})\n"
"Unexpected Protected: {3} ({4:P})\n"
"Expected Unprotected: {5} ({6:P})\n"
"Unexpected Unprotected (BAD): {7} ({8:P})\n",
 IndirectCFInstructions, ExpectedProtected,
 ((double)ExpectedProtected) / IndirectCFInstructions,
 UnexpectedProtected,
 ((double)UnexpectedProtected) / IndirectCFInstructions,
 ExpectedUnprotected,
 ((double)ExpectedUnprotected) / IndirectCFInstructions,
 UnexpectedUnprotected,
 ((double)UnexpectedUnprotected) / IndirectCFInstructions);

if (!SpecialCaseList)
return;

outs() << "\nBlacklist Results:\n";
for (constauto &KV : BlameCounter) {
outs() << "" << BlacklistFilename << ":" << KV.first << " affects "
 << KV.second << " indirect CF instructions.\n";
 }
}

intmain(int argc, char **argv) {
cl::ParseCommandLineOptions(
 argc, argv,
"Identifies whether Control Flow Integrity protects all indirect control "
"flow instructions in the provided object file, DSO or binary.\nNote: "
"Anything statically linked into the provided file *must* be compiled "
"with '-g'. This can be relaxed through the '--ignore-dwarf' flag.");

InitializeAllTargetInfos();
InitializeAllTargetMCs();
InitializeAllAsmParsers();
InitializeAllDisassemblers();

if (PrintBlameContextAll && !PrintBlameContext)
 PrintBlameContext.setValue(PrintBlameContextAll);

 std::unique_ptr<SpecialCaseList> SpecialCaseList;
if (BlacklistFilename != "-") {
 std::string Error;
 SpecialCaseList = SpecialCaseList::create({BlacklistFilename},
 *vfs::getRealFileSystem(), Error);
if (!SpecialCaseList) {
errs() << "Failed to get blacklist: " << Error << "\n";
exit(EXIT_FAILURE);
 }
 }

 FileAnalysis Analysis = ExitOnErr(FileAnalysis::Create(InputFilename));
printIndirectCFInstructions(Analysis, SpecialCaseList.get());

return EXIT_SUCCESS;
}