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//===--- SanitizerMetadata.cpp - Ignored entities for sanitizers ----------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Class which emits metadata consumed by sanitizer instrumentation passes.
//
//===----------------------------------------------------------------------===//
#include "SanitizerMetadata.h"
#include "CodeGenModule.h"
#include "clang/AST/Attr.h"
#include "clang/AST/Type.h"
using namespace clang;
using namespace CodeGen;
SanitizerMetadata::SanitizerMetadata(CodeGenModule &CGM) : CGM(CGM) {}
static bool isAsanHwasanMemTagOrTysan(const SanitizerSet &SS) {
return SS.hasOneOf(SanitizerKind::Address | SanitizerKind::KernelAddress |
SanitizerKind::HWAddress | SanitizerKind::MemTag |
SanitizerKind::Type);
}
static SanitizerMask expandKernelSanitizerMasks(SanitizerMask Mask) {
if (Mask & (SanitizerKind::Address | SanitizerKind::KernelAddress))
Mask |= SanitizerKind::Address | SanitizerKind::KernelAddress;
// Note: KHWASan doesn't support globals.
return Mask;
}
static bool shouldTagGlobal(const llvm::GlobalVariable &G) {
// For now, don't instrument constant data, as it'll be in .rodata anyway. It
// may be worth instrumenting these in future to stop them from being used as
// gadgets.
if (G.getName().starts_with("llvm.") || G.isThreadLocal() || G.isConstant())
return false;
// Globals can be placed implicitly or explicitly in sections. There's two
// different types of globals that meet this criteria that cause problems:
// 1. Function pointers that are going into various init arrays (either
// explicitly through `__attribute__((section(<foo>)))` or implicitly
// through `__attribute__((constructor)))`, such as ".(pre)init(_array)",
// ".fini(_array)", ".ctors", and ".dtors". These function pointers end up
// overaligned and overpadded, making iterating over them problematic, and
// each function pointer is individually tagged (so the iteration over
// them causes SIGSEGV/MTE[AS]ERR).
// 2. Global variables put into an explicit section, where the section's name
// is a valid C-style identifier. The linker emits a `__start_<name>` and
// `__stop_<name>` symbol for the section, so that you can iterate over
// globals within this section. Unfortunately, again, these globals would
// be tagged and so iteration causes SIGSEGV/MTE[AS]ERR.
//
// To mitigate both these cases, and because specifying a section is rare
// outside of these two cases, disable MTE protection for globals in any
// section.
if (G.hasSection())
return false;
return true;
}
void SanitizerMetadata::reportGlobal(llvm::GlobalVariable *GV,
SourceLocation Loc, StringRef Name,
QualType Ty,
SanitizerMask NoSanitizeAttrMask,
bool IsDynInit) {
SanitizerSet FsanitizeArgument = CGM.getLangOpts().Sanitize;
if (!isAsanHwasanMemTagOrTysan(FsanitizeArgument))
return;
FsanitizeArgument.Mask = expandKernelSanitizerMasks(FsanitizeArgument.Mask);
NoSanitizeAttrMask = expandKernelSanitizerMasks(NoSanitizeAttrMask);
SanitizerSet NoSanitizeAttrSet = {NoSanitizeAttrMask &
FsanitizeArgument.Mask};
llvm::GlobalVariable::SanitizerMetadata Meta;
if (GV->hasSanitizerMetadata())
Meta = GV->getSanitizerMetadata();
Meta.NoAddress |= NoSanitizeAttrSet.hasOneOf(SanitizerKind::Address);
Meta.NoAddress |= CGM.isInNoSanitizeList(
FsanitizeArgument.Mask & SanitizerKind::Address, GV, Loc, Ty);
Meta.NoHWAddress |= NoSanitizeAttrSet.hasOneOf(SanitizerKind::HWAddress);
Meta.NoHWAddress |= CGM.isInNoSanitizeList(
FsanitizeArgument.Mask & SanitizerKind::HWAddress, GV, Loc, Ty);
if (shouldTagGlobal(*GV)) {
Meta.Memtag |= static_cast<bool>(FsanitizeArgument.Mask &
SanitizerKind::MemtagGlobals);
Meta.Memtag &= !NoSanitizeAttrSet.hasOneOf(SanitizerKind::MemTag);
Meta.Memtag &= !CGM.isInNoSanitizeList(
FsanitizeArgument.Mask & SanitizerKind::MemTag, GV, Loc, Ty);
} else {
Meta.Memtag = false;
}
Meta.IsDynInit = IsDynInit && !Meta.NoAddress &&
FsanitizeArgument.has(SanitizerKind::Address) &&
!CGM.isInNoSanitizeList(SanitizerKind::Address |
SanitizerKind::KernelAddress,
GV, Loc, Ty, "init");
GV->setSanitizerMetadata(Meta);
if (Ty.isNull() || !CGM.getLangOpts().Sanitize.has(SanitizerKind::Type) ||
NoSanitizeAttrMask & SanitizerKind::Type)
return;
llvm::MDNode *TBAAInfo = CGM.getTBAATypeInfo(Ty);
if (!TBAAInfo || TBAAInfo == CGM.getTBAATypeInfo(CGM.getContext().CharTy))
return;
llvm::Metadata *GlobalMetadata[] = {llvm::ConstantAsMetadata::get(GV),
TBAAInfo};
// Metadata for the global already registered.
if (llvm::MDNode::getIfExists(CGM.getLLVMContext(), GlobalMetadata))
return;
llvm::MDNode *ThisGlobal =
llvm::MDNode::get(CGM.getLLVMContext(), GlobalMetadata);
llvm::NamedMDNode *TysanGlobals =
CGM.getModule().getOrInsertNamedMetadata("llvm.tysan.globals");
TysanGlobals->addOperand(ThisGlobal);
}
void SanitizerMetadata::reportGlobal(llvm::GlobalVariable *GV, const VarDecl &D,
bool IsDynInit) {
if (!isAsanHwasanMemTagOrTysan(CGM.getLangOpts().Sanitize))
return;
std::string QualName;
llvm::raw_string_ostream OS(QualName);
D.printQualifiedName(OS);
auto getNoSanitizeMask = [](const VarDecl &D) {
if (D.hasAttr<DisableSanitizerInstrumentationAttr>())
return SanitizerKind::All;
SanitizerMask NoSanitizeMask;
for (auto *Attr : D.specific_attrs<NoSanitizeAttr>())
NoSanitizeMask |= Attr->getMask();
// External definitions and incomplete types get handled at the place they
// are defined.
if (D.hasExternalStorage() || D.getType()->isIncompleteType())
NoSanitizeMask |= SanitizerKind::Type;
return NoSanitizeMask;
};
reportGlobal(GV, D.getLocation(), QualName, D.getType(), getNoSanitizeMask(D),
IsDynInit);
}
void SanitizerMetadata::disableSanitizerForGlobal(llvm::GlobalVariable *GV) {
reportGlobal(GV, SourceLocation(), "", QualType(), SanitizerKind::All);
}
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