[AArch64][GCS][LLD] Introduce -z gcs-report-dynamic option

When GCS was introduced to LLD, the gcs-report option allowed
for a user to gain information relating to if their relocatable objects
supported the feature. For an executable or shared-library to support
GCS, all relocatable objects must declare that they support GCS.

The gcs-report checks were only done on relocatable object files,
however for a program to enable GCS, the executable and all
shared libraries that it loads must enable GCS.
gcs-report-dynamic enables checks to be performed on all shared
objects loaded by LLD, and in cases where GCS is not supported,
a warning or error will be emitted.

It should be noted that only shared files directly passed to LLD
are checked for GCS support. Files that are noted in the `DT_NEEDED`
tags are assumed to have had their GCS support checked when they
were created.

The behaviour of the -zgcs-dynamic-report option matches that of
GNU ld. The behaviour is as follows unless the user explicitly
sets the value:
* -zgcs-report=warning or -zgcs-report=error implies
-zgcs-report-dynamic=warning.

This approach avoids inheriting an error level if the
user wishes to continue building a module without rebuilding all
the shared libraries. The same approach was taken for the GNU ld
linker, so behaviour is identical across the toolchains.

This implementation matches the error message and command
line interface used within the GNU ld Linker. See here:
https://inbox.sourceware.org/binutils/[email protected]/

To enable the checking of the GNU GCS Attributes when linking together
an application, LLD needs to be able to parse a Shared Files program
headers. This will enable a new option, allowing the user to output
diagnostic information relating to if there are shared files being
used that do not support the GCS extension.

To define if a shared file support GCS, the GNU GCS Attribute will
be stored within the Program Header, so this is parsed and, if
found, the `andFeatures` value updated to reflect the support level.

Author: Stylie777

lld/ELF/Config.h

@@ -232,6 +232,7 @@ struct Config {
   ReportPolicy zCetReport = ReportPolicy::None;
   ReportPolicy zPauthReport = ReportPolicy::None;
   ReportPolicy zGcsReport = ReportPolicy::None;
+  ReportPolicy zGcsReportDynamic = ReportPolicy::None;
   ReportPolicy zExecuteOnlyReport = ReportPolicy::None;
   bool ltoBBAddrMap;
   llvm::StringRef ltoBasicBlockSections;
@@ -749,6 +750,18 @@ uint64_t errCount(Ctx &ctx);
 
 ELFSyncStream InternalErr(Ctx &ctx, const uint8_t *buf);
 
+inline StringRef gcsReportPolicytoString(GcsReportPolicy value) {
+  StringRef ret;
+  if (value == GcsReportPolicy::Warning)
+    ret = "warning";
+  else if (value == GcsReportPolicy::Error)
+    ret = "error";
+  else
+    ret = "none";
+
+  return ret;
+}
+
 #define CHECK2(E, S) lld::check2((E), [&] { return toStr(ctx, S); })
 
 inline DiagLevel toDiagLevel(ReportPolicy policy) {

lld/ELF/Driver.cpp

@@ -56,13 +56,13 @@
 #include "llvm/Object/IRObjectFile.h"
 #include "llvm/Remarks/HotnessThresholdParser.h"
 #include "llvm/Support/CommandLine.h"
-#include "llvm/Support/SaveAndRestore.h"
 #include "llvm/Support/Compression.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/GlobPattern.h"
 #include "llvm/Support/LEB128.h"
 #include "llvm/Support/Parallel.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/SaveAndRestore.h"
 #include "llvm/Support/TarWriter.h"
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/TimeProfiler.h"
@@ -402,6 +402,8 @@ static void checkOptions(Ctx &ctx) {
       ErrAlways(ctx) << "-z pauth-report only supported on AArch64";
     if (ctx.arg.zGcsReport != ReportPolicy::None)
       ErrAlways(ctx) << "-z gcs-report only supported on AArch64";
+    if (ctx.arg.zGcsReportDynamic != ReportPolicy::None)
+      ErrAlways(ctx) << "-z gcs-report-dynamic only supported on AArch64";
     if (ctx.arg.zGcs != GcsPolicy::Implicit)
       ErrAlways(ctx) << "-z gcs only supported on AArch64";
   }
@@ -574,25 +576,35 @@ static GcsPolicy getZGcs(Ctx &ctx, opt::InputArgList &args) {
   return ret;
 }
 
-static ReportPolicy getZGcsReport(Ctx &ctx, opt::InputArgList &args) {
-  ReportPolicy ret = ReportPolicy::None;
+static void getZGcsReport(Ctx &ctx, opt::InputArgList &args) {
+  bool reportDynamicDefined = false;
 
   for (auto *arg : args.filtered(OPT_z)) {
     std::pair<StringRef, StringRef> kv = StringRef(arg->getValue()).split('=');
-    if (kv.first == "gcs-report") {
+    if ((kv.first == "gcs-report") || kv.first == "gcs-report-dynamic") {
       arg->claim();
-      if (kv.second == "none")
-        ret = ReportPolicy::None;
-      else if (kv.second == "warning")
-        ret = ReportPolicy::Warning;
-      else if (kv.second == "error")
-        ret = ReportPolicy::Error;
-      else
-        ErrAlways(ctx) << "unknown -z gcs-report= value: " << kv.second;
+      ReportPolicy value = StringSwitch<ReportPolicy>(kv.second)
+                                  .Case("none", ReportPolicy::None)
+                                  .Case("warning", ReportPolicy::Warning)
+                                  .Case("error", ReportPolicy::Error);
+
+      if (kv.first == "gcs-report")
+        ctx.arg.zGcsReport = value;
+      else if (kv.first == "gcs-report-dynamic") {
+        ctx.arg.zGcsReportDynamic = value;
+        reportDynamicDefined = true;
+      }
     }
   }
 
-  return ret;
+  // The behaviour of -zgnu-report-dynamic matches that of GNU ld. When
+  // -zgcs-report is set to `warning` or `error`, -zgcs-report-dynamic will
+  // inherit this value if there is no user set value. This detects shared
+  // libraries without the GCS property but does not the shared-libraries to be
+  // rebuilt for successful linking
+  if (!reportDynamicDefined && ctx.arg.zGcsReport != ReportPolicy::None &&
+      ctx.arg.zGcsReportDynamic == ReportPolicy::None)
+    ctx.arg.zGcsReportDynamic = ReportPolicy::Warning;
 }
 
 // Report a warning for an unknown -z option.
@@ -1569,7 +1581,10 @@ static void readConfigs(Ctx &ctx, opt::InputArgList &args) {
   ctx.arg.zForceBti = hasZOption(args, "force-bti");
   ctx.arg.zForceIbt = hasZOption(args, "force-ibt");
   ctx.arg.zGcs = getZGcs(ctx, args);
-  ctx.arg.zGcsReport = getZGcsReport(ctx, args);
+  // getZGcsReport assings the values for `ctx.arg.zGcsReport` and
+  // `ctx.arg.zGcsReportDynamic within the function. By doing this, it saves
+  // calling the function twice, as both values can be parsed at once.
+  getZGcsReport(ctx, args);
   ctx.arg.zGlobal = hasZOption(args, "global");
   ctx.arg.zGnustack = getZGnuStack(args);
   ctx.arg.zHazardplt = hasZOption(args, "hazardplt");
@@ -1642,10 +1657,11 @@ static void readConfigs(Ctx &ctx, opt::InputArgList &args) {
       ErrAlways(ctx) << errPrefix << pat.takeError() << ": " << kv.first;
   }
 
-  auto reports = {std::make_pair("bti-report", &ctx.arg.zBtiReport),
-                  std::make_pair("cet-report", &ctx.arg.zCetReport),
-                  std::make_pair("execute-only-report", &ctx.arg.zExecuteOnlyReport),
-                  std::make_pair("pauth-report", &ctx.arg.zPauthReport)};
+  auto reports = {
+      std::make_pair("bti-report", &ctx.arg.zBtiReport),
+      std::make_pair("cet-report", &ctx.arg.zCetReport),
+      std::make_pair("execute-only-report", &ctx.arg.zExecuteOnlyReport),
+      std::make_pair("pauth-report", &ctx.arg.zPauthReport)};
   for (opt::Arg *arg : args.filtered(OPT_z)) {
     std::pair<StringRef, StringRef> option =
         StringRef(arg->getValue()).split('=');
@@ -2927,6 +2943,22 @@ static void readSecurityNotes(Ctx &ctx) {
     ctx.arg.andFeatures |= GNU_PROPERTY_AARCH64_FEATURE_1_GCS;
   else if (ctx.arg.zGcs == GcsPolicy::Never)
     ctx.arg.andFeatures &= ~GNU_PROPERTY_AARCH64_FEATURE_1_GCS;
+
+  // If we are utilising GCS at any stage, the sharedFiles should be checked to
+  // ensure they also support this feature. The gcs-report-dynamic option is
+  // used to indicate if the user wants information relating to this, and will
+  // be set depending on the user's input, or warning if gcs-report is set to
+  // either `warning` or `error`.
+  if (ctx.arg.andFeatures & GNU_PROPERTY_AARCH64_FEATURE_1_GCS)
+    for (SharedFile *f : ctx.sharedFiles)
+      reportUnless(ctx.arg.zGcsReportDynamic,
+                   f->andFeatures & GNU_PROPERTY_AARCH64_FEATURE_1_GCS)
+          << f
+          << ": GCS is required by -z gcs, but this shared library lacks the "
+             "necessary property note. The "
+          << "dynamic loader might not enable GCS or refuse to load the "
+             "program unless all shared library "
+          << "dependencies have the GCS marking.";
 }
 
 static void initSectionsAndLocalSyms(ELFFileBase *file, bool ignoreComdats) {

lld/ELF/InputFiles.cpp

@@ -918,6 +918,60 @@ void ObjFile<ELFT>::initializeSections(bool ignoreComdats,
     handleSectionGroup<ELFT>(this->sections, entries);
 }
 
+template <typename ELFT>
+static void parseGnuPropertyNote(Ctx &ctx, uint32_t &featureAndType,
+                                 ArrayRef<uint8_t> &desc, ELFFileBase *f,
+                                 const uint8_t *base,
+                                 ArrayRef<uint8_t> *data = nullptr) {
+  auto err = [&](const uint8_t *place) -> ELFSyncStream {
+    auto diag = Err(ctx);
+    diag << f->getName() << ":(" << ".note.gnu.property+0x"
+         << Twine::utohexstr(place - base) << "): ";
+    return diag;
+  };
+
+  while (!desc.empty()) {
+    const uint8_t *place = desc.data();
+    if (desc.size() < 8)
+      return void(err(place) << "program property is too short");
+    uint32_t type = read32<ELFT::Endianness>(desc.data());
+    uint32_t size = read32<ELFT::Endianness>(desc.data() + 4);
+    desc = desc.slice(8);
+    if (desc.size() < size)
+      return void(err(place) << "program property is too short");
+
+    if (type == featureAndType) {
+      // We found a FEATURE_1_AND field. There may be more than one of these
+      // in a .note.gnu.property section, for a relocatable object we
+      // accumulate the bits set.
+      if (size < 4)
+        return void(err(place) << "FEATURE_1_AND entry is too short");
+      f->andFeatures |= read32<ELFT::Endianness>(desc.data());
+    } else if (ctx.arg.emachine == EM_AARCH64 &&
+               type == GNU_PROPERTY_AARCH64_FEATURE_PAUTH) {
+      // If the file being parsed is a SharedFile, we cannot pass in
+      // the data variable as there is no InputSection to collect the
+      // data from. As such, these are ignored. They are needed either
+      // when loading a shared library oject.
+      ArrayRef<uint8_t> contents = data ? *data : desc;
+      if (!f->aarch64PauthAbiCoreInfo.empty()) {
+        return void(
+            err(contents.data())
+            << "multiple GNU_PROPERTY_AARCH64_FEATURE_PAUTH entries are "
+               "not supported");
+      } else if (size != 16) {
+        return void(err(contents.data())
+                    << "GNU_PROPERTY_AARCH64_FEATURE_PAUTH entry "
+                       "is invalid: expected 16 bytes, but got "
+                    << size);
+      }
+      f->aarch64PauthAbiCoreInfo = desc;
+    }
+
+    // Padding is present in the note descriptor, if necessary.
+    desc = desc.slice(alignTo<(ELFT::Is64Bits ? 8 : 4)>(size));
+  }
+}
 // Read the following info from the .note.gnu.property section and write it to
 // the corresponding fields in `ObjFile`:
 // - Feature flags (32 bits) representing x86 or AArch64 features for
@@ -955,42 +1009,8 @@ static void readGnuProperty(Ctx &ctx, const InputSection &sec,
 
     // Read a body of a NOTE record, which consists of type-length-value fields.
     ArrayRef<uint8_t> desc = note.getDesc(sec.addralign);
-    while (!desc.empty()) {
-      const uint8_t *place = desc.data();
-      if (desc.size() < 8)
-        return void(err(place) << "program property is too short");
-      uint32_t type = read32<ELFT::Endianness>(desc.data());
-      uint32_t size = read32<ELFT::Endianness>(desc.data() + 4);
-      desc = desc.slice(8);
-      if (desc.size() < size)
-        return void(err(place) << "program property is too short");
-
-      if (type == featureAndType) {
-        // We found a FEATURE_1_AND field. There may be more than one of these
-        // in a .note.gnu.property section, for a relocatable object we
-        // accumulate the bits set.
-        if (size < 4)
-          return void(err(place) << "FEATURE_1_AND entry is too short");
-        f.andFeatures |= read32<ELFT::Endianness>(desc.data());
-      } else if (ctx.arg.emachine == EM_AARCH64 &&
-                 type == GNU_PROPERTY_AARCH64_FEATURE_PAUTH) {
-        if (!f.aarch64PauthAbiCoreInfo.empty()) {
-          return void(
-              err(data.data())
-              << "multiple GNU_PROPERTY_AARCH64_FEATURE_PAUTH entries are "
-                 "not supported");
-        } else if (size != 16) {
-          return void(err(data.data())
-                      << "GNU_PROPERTY_AARCH64_FEATURE_PAUTH entry "
-                         "is invalid: expected 16 bytes, but got "
-                      << size);
-        }
-        f.aarch64PauthAbiCoreInfo = desc;
-      }
-
-      // Padding is present in the note descriptor, if necessary.
-      desc = desc.slice(alignTo<(ELFT::Is64Bits ? 8 : 4)>(size));
-    }
+    const uint8_t *base = sec.content().data();
+    parseGnuPropertyNote<ELFT>(ctx, featureAndType, desc, &f, base, &data);
 
     // Go to next NOTE record to look for more FEATURE_1_AND descriptions.
     data = data.slice(nhdr->getSize(sec.addralign));
@@ -1418,6 +1438,37 @@ std::vector<uint32_t> SharedFile::parseVerneed(const ELFFile<ELFT> &obj,
   return verneeds;
 }
 
+// To determine if a shared file can support any of the GNU Attributes,
+// the .note.gnu.properties section need to be read. The appropriate
+// location in memory is located then the GnuPropertyNote can be parsed.
+// This is the same process as is used for readGnuProperty, however we
+// do not pass the data variable as, without an InputSection, its value
+// is unknown in a SharedFile. This is ok as the information that would
+// be collected from this is irrelevant for a dynamic object.
+template <typename ELFT>
+void SharedFile::parseGnuAndFeatures(const uint8_t *base,
+                                     const typename ELFT::PhdrRange headers) {
+  if (headers.size() == 0)
+    return;
+  uint32_t featureAndType = ctx.arg.emachine == EM_AARCH64
+                                ? GNU_PROPERTY_AARCH64_FEATURE_1_AND
+                                : GNU_PROPERTY_X86_FEATURE_1_AND;
+
+  for (unsigned i = 0; i < headers.size(); i++) {
+    if (headers[i].p_type != PT_GNU_PROPERTY)
+      continue;
+    const typename ELFT::Note note(
+        *reinterpret_cast<const typename ELFT::Nhdr *>(base +
+                                                       headers[i].p_offset));
+    if (note.getType() != NT_GNU_PROPERTY_TYPE_0 || note.getName() != "GNU")
+      continue;
+
+    // Read a body of a NOTE record, which consists of type-length-value fields.
+    ArrayRef<uint8_t> desc = note.getDesc(headers[i].p_align);
+    parseGnuPropertyNote<ELFT>(ctx, featureAndType, desc, this, base);
+  }
+}
+
 // We do not usually care about alignments of data in shared object
 // files because the loader takes care of it. However, if we promote a
 // DSO symbol to point to .bss due to copy relocation, we need to keep
@@ -1454,10 +1505,12 @@ template <class ELFT> void SharedFile::parse() {
   using Elf_Sym = typename ELFT::Sym;
   using Elf_Verdef = typename ELFT::Verdef;
   using Elf_Versym = typename ELFT::Versym;
+  using Elf_Phdr = typename ELFT::Phdr;
 
   ArrayRef<Elf_Dyn> dynamicTags;
   const ELFFile<ELFT> obj = this->getObj<ELFT>();
   ArrayRef<Elf_Shdr> sections = getELFShdrs<ELFT>();
+  ArrayRef<Elf_Phdr> pHeaders = CHECK2(obj.program_headers(), this);
 
   const Elf_Shdr *versymSec = nullptr;
   const Elf_Shdr *verdefSec = nullptr;
@@ -1528,6 +1581,7 @@ template <class ELFT> void SharedFile::parse() {
 
   verdefs = parseVerdefs<ELFT>(obj.base(), verdefSec);
   std::vector<uint32_t> verneeds = parseVerneed<ELFT>(obj, verneedSec);
+  parseGnuAndFeatures<ELFT>(obj.base(), pHeaders);
 
   // Parse ".gnu.version" section which is a parallel array for the symbol
   // table. If a given file doesn't have a ".gnu.version" section, we use

lld/ELF/InputFiles.h

@@ -364,6 +364,9 @@ class SharedFile : public ELFFileBase {
   template <typename ELFT>
   std::vector<uint32_t> parseVerneed(const llvm::object::ELFFile<ELFT> &obj,
                                      const typename ELFT::Shdr *sec);
+  template <typename ELFT>
+  void parseGnuAndFeatures(const uint8_t *base,
+                           const typename ELFT::PhdrRange headers);
 };
 
 class BinaryFile : public InputFile {

lld/docs/ReleaseNotes.rst

@@ -25,6 +25,11 @@ Non-comprehensive list of changes in this release
 
 ELF Improvements
 ----------------
+* For AArch64, support for the ``-zgcs-report-dynamic`` option has been added. This will provide users with
+  the ability to check any Dynamic Objects explicitly passed to LLD for the GNU GCS Attribute Flag. This is
+  required for all files when linking with GCS enabled. Unless defined by the user, ``-zgcs-report-dynamic``
+  inherits its value from the ``-zgcs-report`` option, capped at the ``warning`` level to ensure that a users
+  module can still compile. This behaviour is designed to match the GNU ld Linker.
 
 Breaking changes
 ----------------

lld/test/ELF/aarch64-feature-gcs.s

@@ -49,15 +49,34 @@
 # REPORT-WARN: warning: func2.o: -z gcs-report: file does not have GNU_PROPERTY_AARCH64_FEATURE_1_GCS property
 # REPORT-ERROR: error: func3.o: -z gcs-report: file does not have GNU_PROPERTY_AARCH64_FEATURE_1_GCS property
 
-## An invalid gcs option should give an error
-# RUN: not ld.lld func1-gcs.o func2-gcs.o func3-gcs.o -z gcs=nonsense 2>&1 | FileCheck --check-prefix=INVALID %s
-
-# INVALID: error: unknown -z gcs= value: nonsense
+## gcs-report-dynamic should report any dynamic objects that does not have the gcs property. This also ensures the inhertance from gcs-report is working correctly.
+
+# RUN: ld.lld func1-gcs.o func3-gcs.o no-gcs.so force-gcs.so -z gcs-report=warning -z gcs=always 2>&1 | FileCheck --check-prefix=REPORT-WARN-DYNAMIC %s
+# RUN: ld.lld func1-gcs.o func3-gcs.o no-gcs.so force-gcs.so -z gcs-report-dynamic=warning -z gcs-report=warning -z gcs=always 2>&1 | FileCheck --check-prefix=REPORT-WARN-DYNAMIC %s
+# RUN: ld.lld func1-gcs.o func3-gcs.o no-gcs.so force-gcs.so -z gcs-report=error -z gcs=always 2>&1 | FileCheck --check-prefix=REPORT-WARN-DYNAMIC %s
+# RUN: ld.lld func1-gcs.o func3-gcs.o no-gcs.so force-gcs.so -z gcs-report=error -z gcs-report-dynamic=warning -z gcs=always 2>&1 | FileCheck --check-prefix=REPORT-WARN-DYNAMIC %s
+# RUN: ld.lld func1-gcs.o func3-gcs.o no-gcs.so force-gcs.so -z gcs-report-dynamic=warning -z gcs=always 2>&1 | FileCheck --check-prefix=REPORT-WARN-DYNAMIC %s
+# RUN: ld.lld func1-gcs.o func3-gcs.o no-gcs.so force-gcs.so -z gcs-report=error -z gcs-report-dynamic=warning -z gcs=always 2>&1 | FileCheck --check-prefix=REPORT-WARN-DYNAMIC %s
+# RUN: not ld.lld func1-gcs.o func3-gcs.o no-gcs.so force-gcs.so -z gcs-report-dynamic=error -z gcs-report=error -z gcs=always 2>&1 | FileCheck --check-prefix=REPORT-ERROR-DYNAMIC %s
+# RUN: not ld.lld func1-gcs.o func3-gcs.o no-gcs.so force-gcs.so -z gcs-report-dynamic=error -z gcs=always 2>&1 | FileCheck --check-prefix=REPORT-ERROR-DYNAMIC %s
+# RUN: ld.lld func1-gcs.o func3-gcs.o force-gcs.so -z gcs-report-dynamic=error -z gcs-report=error -z gcs=always 2>&1 | count 0
+# RUN: ld.lld func1-gcs.o func3-gcs.o force-gcs.so -z gcs-report-dynamic=warning -z gcs-report=error -z gcs=always 2>&1 | count 0
+# RUN: ld.lld func1-gcs.o func3-gcs.o force-gcs.so -z gcs-report=warning -z gcs=always 2>&1 | count 0
+# RUN: ld.lld func1-gcs.o func3-gcs.o force-gcs.so -z gcs-report=error -z gcs=always 2>&1 | count 0
+# RUN: ld.lld func1-gcs.o func3-gcs.o force-gcs.so -z gcs-report-dynamic=warning -z gcs=always 2>&1 | count 0
+# RUN: ld.lld func1-gcs.o func3-gcs.o force-gcs.so -z gcs-report-dynamic=error -z gcs=always 2>&1 | count 0
+
+# REPORT-WARN-DYNAMIC: warning: no-gcs.so: GCS is required by -z gcs, but this shared library lacks the necessary property note. The dynamic loader might not enable GCS or refuse to load the program unless all shared library dependencies have the GCS marking.
+# REPORT-WARN-DYNAMIC-NOT: warning: force-gcs.so: GCS is required by -z gcs, but this shared library lacks the necessary property note. The dynamic loader might not enable GCS or refuse to load the program unless all shared library dependencies have the GCS marking.
+# REPORT-ERROR-DYNAMIC: error: no-gcs.so: GCS is required by -z gcs, but this shared library lacks the necessary property note. The dynamic loader might not enable GCS or refuse to load the program unless all shared library dependencies have the GCS marking.
+# REPORT-ERROR-DYNAMIC-NOT: error: force-gcs.so: GCS is required by -z gcs, but this shared library lacks the necessary property note. The dynamic loader might not enable GCS or refuse to load the program unless all shared library dependencies have the GCS marking.
 
 ## An invalid gcs option should give an error
-# RUN: not ld.lld func1-gcs.o func2-gcs.o func3-gcs.o -z gcs-report=nonsense 2>&1 | FileCheck --check-prefix=INVALID-GCS-REPORT %s
+# RUN: not ld.lld func1-gcs.o func2-gcs.o func3-gcs.o -z gcs=nonsense -z gcs-report=nonsense -z gcs-report-dynamic=nonsense 2>&1 | FileCheck --check-prefix=INVALID %s
 
-# INVALID-GCS-REPORT: error: unknown -z gcs-report= value: nonsense
+# INVALID: error: unknown -z gcs= value: nonsense
+# INVALID: error: unknown -z gcs-report= value: nonsense
+# INVALID: error: unknown -z gcs-report-dynamic= value: nonsense
 
 #--- func1-gcs.s
 .section ".note.gnu.property", "a"