Introduce the "retpoline" x86 mitigation technique for variant #2 of the speculative execution vulnerabilities disclosed today, specifically identified by CVE-2017-5715, "Branch Target Injection", and is one of the two halves to Spectre..

Summary:
First, we need to explain the core of the vulnerability. Note that this
is a very incomplete description, please see the Project Zero blog post
for details:
https://googleprojectzero.blogspot.com/2018/01/reading-privileged-memory-with-side.html

The basis for branch target injection is to direct speculative execution
of the processor to some "gadget" of executable code by poisoning the
prediction of indirect branches with the address of that gadget. The
gadget in turn contains an operation that provides a side channel for
reading data. Most commonly, this will look like a load of secret data
followed by a branch on the loaded value and then a load of some
predictable cache line. The attacker then uses timing of the processors
cache to determine which direction the branch took *in the speculative
execution*, and in turn what one bit of the loaded value was. Due to the
nature of these timing side channels and the branch predictor on Intel
processors, this allows an attacker to leak data only accessible to
a privileged domain (like the kernel) back into an unprivileged domain.

The goal is simple: avoid generating code which contains an indirect
branch that could have its prediction poisoned by an attacker. In many
cases, the compiler can simply use directed conditional branches and
a small search tree. LLVM already has support for lowering switches in
this way and the first step of this patch is to disable jump-table
lowering of switches and introduce a pass to rewrite explicit indirectbr
sequences into a switch over integers.

However, there is no fully general alternative to indirect calls. We
introduce a new construct we call a "retpoline" to implement indirect
calls in a non-speculatable way. It can be thought of loosely as
a trampoline for indirect calls which uses the RET instruction on x86.
Further, we arrange for a specific call->ret sequence which ensures the
processor predicts the return to go to a controlled, known location. The
retpoline then "smashes" the return address pushed onto the stack by the
call with the desired target of the original indirect call. The result
is a predicted return to the next instruction after a call (which can be
used to trap speculative execution within an infinite loop) and an
actual indirect branch to an arbitrary address.

On 64-bit x86 ABIs, this is especially easily done in the compiler by
using a guaranteed scratch register to pass the target into this device.
For 32-bit ABIs there isn't a guaranteed scratch register and so several
different retpoline variants are introduced to use a scratch register if
one is available in the calling convention and to otherwise use direct
stack push/pop sequences to pass the target address.

This "retpoline" mitigation is fully described in the following blog
post: https://support.google.com/faqs/answer/7625886

We also support a target feature that disables emission of the retpoline
thunk by the compiler to allow for custom thunks if users want them.
These are particularly useful in environments like kernels that
routinely do hot-patching on boot and want to hot-patch their thunk to
different code sequences. They can write this custom thunk and use
`-mretpoline-external-thunk` *in addition* to `-mretpoline`. In this
case, on x86-64 thu thunk names must be:
```
  __llvm_external_retpoline_r11
```
or on 32-bit:
```
  __llvm_external_retpoline_eax
  __llvm_external_retpoline_ecx
  __llvm_external_retpoline_edx
  __llvm_external_retpoline_push
```
And the target of the retpoline is passed in the named register, or in
the case of the `push` suffix on the top of the stack via a `pushl`
instruction.

There is one other important source of indirect branches in x86 ELF
binaries: the PLT. These patches also include support for LLD to
generate PLT entries that perform a retpoline-style indirection.

The only other indirect branches remaining that we are aware of are from
precompiled runtimes (such as crt0.o and similar). The ones we have
found are not really attackable, and so we have not focused on them
here, but eventually these runtimes should also be replicated for
retpoline-ed configurations for completeness.

For kernels or other freestanding or fully static executables, the
compiler switch `-mretpoline` is sufficient to fully mitigate this
particular attack. For dynamic executables, you must compile *all*
libraries with `-mretpoline` and additionally link the dynamic
executable and all shared libraries with LLD and pass `-z retpolineplt`
(or use similar functionality from some other linker). We strongly
recommend also using `-z now` as non-lazy binding allows the
retpoline-mitigated PLT to be substantially smaller.

When manually apply similar transformations to `-mretpoline` to the
Linux kernel we observed very small performance hits to applications
running typical workloads, and relatively minor hits (approximately 2%)
even for extremely syscall-heavy applications. This is largely due to
the small number of indirect branches that occur in performance
sensitive paths of the kernel.

When using these patches on statically linked applications, especially
C++ applications, you should expect to see a much more dramatic
performance hit. For microbenchmarks that are switch, indirect-, or
virtual-call heavy we have seen overheads ranging from 10% to 50%.

However, real-world workloads exhibit substantially lower performance
impact. Notably, techniques such as PGO and ThinLTO dramatically reduce
the impact of hot indirect calls (by speculatively promoting them to
direct calls) and allow optimized search trees to be used to lower
switches. If you need to deploy these techniques in C++ applications, we
*strongly* recommend that you ensure all hot call targets are statically
linked (avoiding PLT indirection) and use both PGO and ThinLTO. Well
tuned servers using all of these techniques saw 5% - 10% overhead from
the use of retpoline.

We will add detailed documentation covering these components in
subsequent patches, but wanted to make the core functionality available
as soon as possible. Happy for more code review, but we'd really like to
get these patches landed and backported ASAP for obvious reasons. We're
planning to backport this to both 6.0 and 5.0 release streams and get
a 5.0 release with just this cherry picked ASAP for distros and vendors.

This patch is the work of a number of people over the past month: Eric, Reid,
Rui, and myself. I'm mailing it out as a single commit due to the time
sensitive nature of landing this and the need to backport it. Huge thanks to
everyone who helped out here, and everyone at Intel who helped out in
discussions about how to craft this. Also, credit goes to Paul Turner (at
Google, but not an LLVM contributor) for much of the underlying retpoline
design.

Reviewers: echristo, rnk, ruiu, craig.topper, DavidKreitzer

Subscribers: sanjoy, emaste, mcrosier, mgorny, mehdi_amini, hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D41723

llvm-svn: 323155

Author: chandlerc

Diff for: clang/include/clang/Driver/Options.td

@@ -2594,6 +2594,10 @@ def mshstk : Flag<["-"], "mshstk">, Group<m_x86_Features_Group>;
 def mno_shstk : Flag<["-"], "mno-shstk">, Group<m_x86_Features_Group>;
 def mibt : Flag<["-"], "mibt">, Group<m_x86_Features_Group>;
 def mno_ibt : Flag<["-"], "mno-ibt">, Group<m_x86_Features_Group>;
+def mretpoline : Flag<["-"], "mretpoline">, Group<m_x86_Features_Group>;
+def mno_retpoline : Flag<["-"], "mno-retpoline">, Group<m_x86_Features_Group>;
+def mretpoline_external_thunk : Flag<["-"], "mretpoline-external-thunk">, Group<m_x86_Features_Group>;
+def mno_retpoline_external_thunk : Flag<["-"], "mno-retpoline-external-thunk">, Group<m_x86_Features_Group>;
 
 // These are legacy user-facing driver-level option spellings. They are always
 // aliases for options that are spelled using the more common Unix / GNU flag

Diff for: clang/lib/Basic/Targets/X86.cpp

@@ -787,6 +787,10 @@ bool X86TargetInfo::handleTargetFeatures(std::vector<std::string> &Features,
       HasCLZERO = true;
     } else if (Feature == "+rdpid") {
       HasRDPID = true;
+    } else if (Feature == "+retpoline") {
+      HasRetpoline = true;
+    } else if (Feature == "+retpoline-external-thunk") {
+      HasRetpolineExternalThunk = true;
     }
 
     X86SSEEnum Level = llvm::StringSwitch<X86SSEEnum>(Feature)
@@ -1333,6 +1337,8 @@ bool X86TargetInfo::hasFeature(StringRef Feature) const {
       .Case("rdpid", HasRDPID)
       .Case("rdrnd", HasRDRND)
       .Case("rdseed", HasRDSEED)
+      .Case("retpoline", HasRetpoline)
+      .Case("retpoline-external-thunk", HasRetpolineExternalThunk)
       .Case("rtm", HasRTM)
       .Case("sgx", HasSGX)
       .Case("sha", HasSHA)

Diff for: clang/lib/Basic/Targets/X86.h

@@ -97,6 +97,8 @@ class LLVM_LIBRARY_VISIBILITY X86TargetInfo : public TargetInfo {
   bool HasMOVBE = false;
   bool HasPREFETCHWT1 = false;
   bool HasRDPID = false;
+  bool HasRetpoline = false;
+  bool HasRetpolineExternalThunk = false;
 
   /// \brief Enumeration of all of the X86 CPUs supported by Clang.
   ///

Diff for: clang/test/Driver/x86-target-features.c

@@ -129,3 +129,13 @@
 // RUN: %clang -target i386-unknown-linux-gnu -march=i386 -mno-rdpid %s -### -o %t.o 2>&1 | FileCheck -check-prefix=NO-RDPID %s
 // RDPID: "-target-feature" "+rdpid"
 // NO-RDPID: "-target-feature" "-rdpid"
+
+// RUN: %clang -target i386-linux-gnu -mretpoline %s -### -o %t.o 2>&1 | FileCheck -check-prefix=RETPOLINE %s
+// RUN: %clang -target i386-linux-gnu -mno-retpoline %s -### -o %t.o 2>&1 | FileCheck -check-prefix=NO-RETPOLINE %s
+// RETPOLINE: "-target-feature" "+retpoline"
+// NO-RETPOLINE: "-target-feature" "-retpoline"
+
+// RUN: %clang -target i386-linux-gnu -mretpoline -mretpoline-external-thunk %s -### -o %t.o 2>&1 | FileCheck -check-prefix=RETPOLINE-EXTERNAL-THUNK %s
+// RUN: %clang -target i386-linux-gnu -mretpoline -mno-retpoline-external-thunk %s -### -o %t.o 2>&1 | FileCheck -check-prefix=NO-RETPOLINE-EXTERNAL-THUNK %s
+// RETPOLINE-EXTERNAL-THUNK: "-target-feature" "+retpoline-external-thunk"
+// NO-RETPOLINE-EXTERNAL-THUNK: "-target-feature" "-retpoline-external-thunk"

Diff for: lld/ELF/Arch/X86.cpp

@@ -21,7 +21,7 @@ using namespace lld;
 using namespace lld::elf;
 
 namespace {
-class X86 final : public TargetInfo {
+class X86 : public TargetInfo {
 public:
   X86();
   RelExpr getRelExpr(RelType Type, const Symbol &S,
@@ -399,7 +399,145 @@ void X86::relaxTlsLdToLe(uint8_t *Loc, RelType Type, uint64_t Val) const {
   memcpy(Loc - 2, Inst, sizeof(Inst));
 }
 
+namespace {
+class RetpolinePic : public X86 {
+public:
+  RetpolinePic();
+  void writeGotPlt(uint8_t *Buf, const Symbol &S) const override;
+  void writePltHeader(uint8_t *Buf) const override;
+  void writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr, uint64_t PltEntryAddr,
+                int32_t Index, unsigned RelOff) const override;
+};
+
+class RetpolineNoPic : public X86 {
+public:
+  RetpolineNoPic();
+  void writeGotPlt(uint8_t *Buf, const Symbol &S) const override;
+  void writePltHeader(uint8_t *Buf) const override;
+  void writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr, uint64_t PltEntryAddr,
+                int32_t Index, unsigned RelOff) const override;
+};
+} // namespace
+
+RetpolinePic::RetpolinePic() {
+  PltHeaderSize = 48;
+  PltEntrySize = 32;
+}
+
+void RetpolinePic::writeGotPlt(uint8_t *Buf, const Symbol &S) const {
+  write32le(Buf, S.getPltVA() + 17);
+}
+
+void RetpolinePic::writePltHeader(uint8_t *Buf) const {
+  const uint8_t Insn[] = {
+      0xff, 0xb3, 0,    0,    0,    0,          // 0:    pushl GOTPLT+4(%ebx)
+      0x50,                                     // 6:    pushl %eax
+      0x8b, 0x83, 0,    0,    0,    0,          // 7:    mov GOTPLT+8(%ebx), %eax
+      0xe8, 0x0e, 0x00, 0x00, 0x00,             // d:    call next
+      0xf3, 0x90,                               // 12: loop: pause
+      0x0f, 0xae, 0xe8,                         // 14:   lfence
+      0xeb, 0xf9,                               // 17:   jmp loop
+      0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, // 19:   int3; .align 16
+      0x89, 0x0c, 0x24,                         // 20: next: mov %ecx, (%esp)
+      0x8b, 0x4c, 0x24, 0x04,                   // 23:   mov 0x4(%esp), %ecx
+      0x89, 0x44, 0x24, 0x04,                   // 27:   mov %eax ,0x4(%esp)
+      0x89, 0xc8,                               // 2b:   mov %ecx, %eax
+      0x59,                                     // 2d:   pop %ecx
+      0xc3,                                     // 2e:   ret
+  };
+  memcpy(Buf, Insn, sizeof(Insn));
+
+  uint32_t Ebx = InX::Got->getVA() + InX::Got->getSize();
+  uint32_t GotPlt = InX::GotPlt->getVA() - Ebx;
+  write32le(Buf + 2, GotPlt + 4);
+  write32le(Buf + 9, GotPlt + 8);
+}
+
+void RetpolinePic::writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr,
+                            uint64_t PltEntryAddr, int32_t Index,
+                            unsigned RelOff) const {
+  const uint8_t Insn[] = {
+      0x50,                   // pushl %eax
+      0x8b, 0x83, 0, 0, 0, 0, // mov foo@GOT(%ebx), %eax
+      0xe8, 0,    0, 0, 0,    // call plt+0x20
+      0xe9, 0,    0, 0, 0,    // jmp plt+0x12
+      0x68, 0,    0, 0, 0,    // pushl $reloc_offset
+      0xe9, 0,    0, 0, 0,    // jmp plt+0
+  };
+  memcpy(Buf, Insn, sizeof(Insn));
+
+  uint32_t Ebx = InX::Got->getVA() + InX::Got->getSize();
+  write32le(Buf + 3, GotPltEntryAddr - Ebx);
+  write32le(Buf + 8, -Index * PltEntrySize - PltHeaderSize - 12 + 32);
+  write32le(Buf + 13, -Index * PltEntrySize - PltHeaderSize - 17 + 18);
+  write32le(Buf + 18, RelOff);
+  write32le(Buf + 23, -Index * PltEntrySize - PltHeaderSize - 27);
+}
+
+RetpolineNoPic::RetpolineNoPic() {
+  PltHeaderSize = 64;
+  PltEntrySize = 32;
+}
+
+void RetpolineNoPic::writeGotPlt(uint8_t *Buf, const Symbol &S) const {
+  write32le(Buf, S.getPltVA() + 16);
+}
+
+void RetpolineNoPic::writePltHeader(uint8_t *Buf) const {
+  const uint8_t PltData[] = {
+      0xff, 0x35, 0,    0,    0,    0, // 0:    pushl GOTPLT+4
+      0x50,                            // 6:    pushl %eax
+      0xa1, 0,    0,    0,    0,       // 7:    mov GOTPLT+8, %eax
+      0xe8, 0x0f, 0x00, 0x00, 0x00,    // c:    call next
+      0xf3, 0x90,                      // 11: loop: pause
+      0x0f, 0xae, 0xe8,                // 13:   lfence
+      0xeb, 0xf9,                      // 16:   jmp loop
+      0xcc, 0xcc, 0xcc, 0xcc, 0xcc,    // 18:   int3
+      0xcc, 0xcc, 0xcc,                // 1f:   int3; .align 16
+      0x89, 0x0c, 0x24,                // 20: next: mov %ecx, (%esp)
+      0x8b, 0x4c, 0x24, 0x04,          // 23:   mov 0x4(%esp), %ecx
+      0x89, 0x44, 0x24, 0x04,          // 27:   mov %eax ,0x4(%esp)
+      0x89, 0xc8,                      // 2b:   mov %ecx, %eax
+      0x59,                            // 2d:   pop %ecx
+      0xc3,                            // 2e:   ret
+  };
+  memcpy(Buf, PltData, sizeof(PltData));
+
+  uint32_t GotPlt = InX::GotPlt->getVA();
+  write32le(Buf + 2, GotPlt + 4);
+  write32le(Buf + 8, GotPlt + 8);
+}
+
+void RetpolineNoPic::writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr,
+                              uint64_t PltEntryAddr, int32_t Index,
+                              unsigned RelOff) const {
+  const uint8_t Insn[] = {
+      0x50,             // 0:  pushl %eax
+      0xa1, 0, 0, 0, 0, // 1:  mov foo_in_GOT, %eax
+      0xe8, 0, 0, 0, 0, // 6:  call plt+0x20
+      0xe9, 0, 0, 0, 0, // b:  jmp plt+0x11
+      0x68, 0, 0, 0, 0, // 10: pushl $reloc_offset
+      0xe9, 0, 0, 0, 0, // 15: jmp plt+0
+  };
+  memcpy(Buf, Insn, sizeof(Insn));
+
+  write32le(Buf + 2, GotPltEntryAddr);
+  write32le(Buf + 7, -Index * PltEntrySize - PltHeaderSize - 11 + 32);
+  write32le(Buf + 12, -Index * PltEntrySize - PltHeaderSize - 16 + 17);
+  write32le(Buf + 17, RelOff);
+  write32le(Buf + 22, -Index * PltEntrySize - PltHeaderSize - 26);
+}
+
 TargetInfo *elf::getX86TargetInfo() {
-  static X86 Target;
-  return &Target;
+  if (Config->ZRetpolineplt) {
+    if (Config->Pic) {
+      static RetpolinePic T;
+      return &T;
+    }
+    static RetpolineNoPic T;
+    return &T;
+  }
+
+  static X86 T;
+  return &T;
 }

Diff for: lld/ELF/Arch/X86_64.cpp

@@ -23,7 +23,7 @@ using namespace lld;
 using namespace lld::elf;
 
 namespace {
-template <class ELFT> class X86_64 final : public TargetInfo {
+template <class ELFT> class X86_64 : public TargetInfo {
 public:
   X86_64();
   RelExpr getRelExpr(RelType Type, const Symbol &S,
@@ -460,12 +460,125 @@ void X86_64<ELFT>::relaxGot(uint8_t *Loc, uint64_t Val) const {
   write32le(Loc - 1, Val + 1);
 }
 
-TargetInfo *elf::getX32TargetInfo() {
-  static X86_64<ELF32LE> Target;
-  return &Target;
+namespace {
+template <class ELFT> class Retpoline : public X86_64<ELFT> {
+public:
+  Retpoline();
+  void writeGotPlt(uint8_t *Buf, const Symbol &S) const override;
+  void writePltHeader(uint8_t *Buf) const override;
+  void writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr, uint64_t PltEntryAddr,
+                int32_t Index, unsigned RelOff) const override;
+};
+
+template <class ELFT> class RetpolineZNow : public X86_64<ELFT> {
+public:
+  RetpolineZNow();
+  void writeGotPlt(uint8_t *Buf, const Symbol &S) const override {}
+  void writePltHeader(uint8_t *Buf) const override;
+  void writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr, uint64_t PltEntryAddr,
+                int32_t Index, unsigned RelOff) const override;
+};
+} // namespace
+
+template <class ELFT> Retpoline<ELFT>::Retpoline() {
+  TargetInfo::PltHeaderSize = 48;
+  TargetInfo::PltEntrySize = 32;
+}
+
+template <class ELFT>
+void Retpoline<ELFT>::writeGotPlt(uint8_t *Buf, const Symbol &S) const {
+  write32le(Buf, S.getPltVA() + 17);
+}
+
+template <class ELFT> void Retpoline<ELFT>::writePltHeader(uint8_t *Buf) const {
+  const uint8_t Insn[] = {
+      0xff, 0x35, 0,    0,    0,    0,          // 0:    pushq GOTPLT+8(%rip)
+      0x4c, 0x8b, 0x1d, 0,    0,    0,    0,    // 6:    mov GOTPLT+16(%rip), %r11
+      0xe8, 0x0e, 0x00, 0x00, 0x00,             // d:    callq next
+      0xf3, 0x90,                               // 12: loop: pause
+      0x0f, 0xae, 0xe8,                         // 14:   lfence
+      0xeb, 0xf9,                               // 17:   jmp loop
+      0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, // 19:   int3; .align 16
+      0x4c, 0x89, 0x1c, 0x24,                   // 20: next: mov %r11, (%rsp)
+      0xc3,                                     // 24:   ret
+  };
+  memcpy(Buf, Insn, sizeof(Insn));
+
+  uint64_t GotPlt = InX::GotPlt->getVA();
+  uint64_t Plt = InX::Plt->getVA();
+  write32le(Buf + 2, GotPlt - Plt - 6 + 8);
+  write32le(Buf + 9, GotPlt - Plt - 13 + 16);
+}
+
+template <class ELFT>
+void Retpoline<ELFT>::writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr,
+                               uint64_t PltEntryAddr, int32_t Index,
+                               unsigned RelOff) const {
+  const uint8_t Insn[] = {
+      0x4c, 0x8b, 0x1d, 0, 0, 0, 0, // 0:  mov foo@GOTPLT(%rip), %r11
+      0xe8, 0,    0,    0, 0,       // 7:  callq plt+0x20
+      0xe9, 0,    0,    0, 0,       // c:  jmp plt+0x12
+      0x68, 0,    0,    0, 0,       // 11: pushq <relocation index>
+      0xe9, 0,    0,    0, 0,       // 16: jmp plt+0
+  };
+  memcpy(Buf, Insn, sizeof(Insn));
+
+  uint64_t Off = TargetInfo::PltHeaderSize + TargetInfo::PltEntrySize * Index;
+
+  write32le(Buf + 3, GotPltEntryAddr - PltEntryAddr - 7);
+  write32le(Buf + 8, -Off - 12 + 32);
+  write32le(Buf + 13, -Off - 17 + 18);
+  write32le(Buf + 18, Index);
+  write32le(Buf + 23, -Off - 27);
+}
+
+template <class ELFT> RetpolineZNow<ELFT>::RetpolineZNow() {
+  TargetInfo::PltHeaderSize = 32;
+  TargetInfo::PltEntrySize = 16;
+}
+
+template <class ELFT>
+void RetpolineZNow<ELFT>::writePltHeader(uint8_t *Buf) const {
+  const uint8_t Insn[] = {
+      0xe8, 0x0b, 0x00, 0x00, 0x00, // 0:    call next
+      0xf3, 0x90,                   // 5:  loop: pause
+      0x0f, 0xae, 0xe8,             // 7:    lfence
+      0xeb, 0xf9,                   // a:    jmp loop
+      0xcc, 0xcc, 0xcc, 0xcc,       // c:    int3; .align 16
+      0x4c, 0x89, 0x1c, 0x24,       // 10: next: mov %r11, (%rsp)
+      0xc3,                         // 14:   ret
+  };
+  memcpy(Buf, Insn, sizeof(Insn));
 }
 
-TargetInfo *elf::getX86_64TargetInfo() {
-  static X86_64<ELF64LE> Target;
-  return &Target;
+template <class ELFT>
+void RetpolineZNow<ELFT>::writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr,
+                                   uint64_t PltEntryAddr, int32_t Index,
+                                   unsigned RelOff) const {
+  const uint8_t Insn[] = {
+      0x4c, 0x8b, 0x1d, 0, 0, 0, 0, // mov foo@GOTPLT(%rip), %r11
+      0xe9, 0,    0,    0, 0,       // jmp plt+0
+  };
+  memcpy(Buf, Insn, sizeof(Insn));
+
+  write32le(Buf + 3, GotPltEntryAddr - PltEntryAddr - 7);
+  write32le(Buf + 8,
+            -Index * TargetInfo::PltEntrySize - TargetInfo::PltHeaderSize - 12);
 }
+
+template <class ELFT> TargetInfo *getTargetInfo() {
+  if (Config->ZRetpolineplt) {
+    if (Config->ZNow) {
+      static RetpolineZNow<ELFT> T;
+      return &T;
+    }
+    static Retpoline<ELFT> T;
+    return &T;
+  }
+
+  static X86_64<ELFT> T;
+  return &T;
+}
+
+TargetInfo *elf::getX32TargetInfo() { return getTargetInfo<ELF32LE>(); }
+TargetInfo *elf::getX86_64TargetInfo() { return getTargetInfo<ELF64LE>(); }

Diff for: lld/ELF/Config.h

@@ -160,6 +160,7 @@ struct Configuration {
   bool ZRelro;
   bool ZRodynamic;
   bool ZText;
+  bool ZRetpolineplt;
   bool ExitEarly;
   bool ZWxneeded;
   DiscardPolicy Discard;

Diff for: lld/ELF/Driver.cpp

@@ -678,6 +678,7 @@ void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   Config->ZNow = hasZOption(Args, "now");
   Config->ZOrigin = hasZOption(Args, "origin");
   Config->ZRelro = !hasZOption(Args, "norelro");
+  Config->ZRetpolineplt = hasZOption(Args, "retpolineplt");
   Config->ZRodynamic = hasZOption(Args, "rodynamic");
   Config->ZStackSize = args::getZOptionValue(Args, OPT_z, "stack-size", 0);
   Config->ZText = !hasZOption(Args, "notext");