Gold Linker Patch: Introduce the "retpoline" x86 mitigation technique for variant #2 of the speculative execution vulnerabilities disclosed today, specifically identified by CVE-2017-5715 and in some places called "spectre".
Sriraman Tallam via binutils
binutils@sourceware.org
Fri Jan 5 00:35:00 GMT 2018
Hi Cary,
Thanks for reviewing.
On Thu, Jan 4, 2018 at 3:08 PM, Cary Coutant <ccoutant@gmail.com> wrote:
>> * options.h (retpolineplt): New -z option to use retpoline PLT.
>> * x86_64.cc (Output_data_plt_x86_64_retpoline): New class.
>> (Target_x86_64<64>::do_make_data_plt): Create retpoline PLT when
>> the option is used.
>> * testsuite/Makefile.am (retpoline_plt_1.sh): New test.
>> * testsuite/Makefile.in: Regenerate.
>> * testsuite/retpoline_plt_1.sh: New test script.
>> * testsuite/retpoline_plt_1.s: New test source.
>
> This makes the -z bndplt and -z retpolineplt options mutually
> exclusive. Please add a check in options.cc
> (General_options::finalize) for this.
Done and new patch attached.
* options.h (retpolineplt): New -z option to use retpoline PLT.
* options.cc (General_options::finalize): Check if both retpolineplt
and bndplt are turned on.
* x86_64.cc (Output_data_plt_x86_64_retpoline): New class.
(Target_x86_64<64>::do_make_data_plt): Create retpoline PLT when
the option is used.
* testsuite/Makefile.am (retpoline_plt_1.sh): New test.
* testsuite/Makefile.in: Regenerate.
* testsuite/retpoline_plt_1.sh: New test script.
* testsuite/retpoline_plt_1.s: New test source.
>
> Will we be seeing an aarch64 patch along these same lines soon? As I
> understand it, 64-bit ARM is susceptible to Spectre, but 32-bit ARM is
> not (because 32-bit chips don't do any OOO execution). I haven't seen
> a clear statement about other architectures like Sparc and PPC.
retpoline is currently an x86-specific mitigation. Other architectural
mitigations may be forthcoming, but I'm not actively working on them.
Thanks
Sri
>
> -cary
-------------- next part --------------
* options.h (retpolineplt): New -z option to use retpoline PLT.
* options.cc (General_options::finalize): Check if both retpolineplt
and bndplt are turned on.
* x86_64.cc (Output_data_plt_x86_64_retpoline): New class.
(Target_x86_64<64>::do_make_data_plt): Create retpoline PLT when
the option is used.
* testsuite/Makefile.am (retpoline_plt_1.sh): New test.
* testsuite/Makefile.in: Regenerate.
* testsuite/retpoline_plt_1.sh: New test script.
* testsuite/retpoline_plt_1.s: New test source.
diff --git a/gold/options.cc b/gold/options.cc
index f511ba1e79..a33fa31420 100644
--- a/gold/options.cc
+++ b/gold/options.cc
@@ -1367,6 +1367,11 @@ General_options::finalize()
if (this->user_set_rosegment_gap())
this->set_rosegment(true);
+ if (this->bndplt() && this->retpolineplt())
+ {
+ gold_fatal(_("-z,bndplt and -z,retpolineplt are mutually exclusive"));
+ }
+
// FIXME: we can/should be doing a lot more sanity checking here.
}
diff --git a/gold/options.h b/gold/options.h
index d5b8fe43ac..035e48110f 100644
--- a/gold/options.h
+++ b/gold/options.h
@@ -1426,6 +1426,9 @@ class General_options
DEFINE_bool(bndplt, options::DASH_Z, '\0', false,
N_("(x86-64 only) Generate a BND PLT for Intel MPX"),
N_("Generate a regular PLT"));
+ DEFINE_bool(retpolineplt, options::DASH_Z, '\0', false,
+ N_("(x86-64 only) Generate a retpoline PLT"),
+ N_("Generate a regular PLT"));
DEFINE_bool(combreloc, options::DASH_Z, '\0', true,
N_("Sort dynamic relocs"),
N_("Do not sort dynamic relocs"));
diff --git a/gold/testsuite/Makefile.am b/gold/testsuite/Makefile.am
index 16cae8004c..8c04091c8d 100644
--- a/gold/testsuite/Makefile.am
+++ b/gold/testsuite/Makefile.am
@@ -3219,6 +3219,15 @@ split_x86_64_r.stdout: split_x86_64_1.o split_x86_64_n.o ../ld-new
MOSTLYCLEANFILES += split_x86_64_1 split_x86_64_2 split_x86_64_3 \
split_x86_64_4 split_x86_64_r
+check_SCRIPTS += retpoline_plt_1.sh
+check_DATA += retpoline_plt_1.stdout
+retpoline_plt_1.o: retpoline_plt_1.s
+ $(TEST_AS) --64 -o $@ $<
+retpoline_plt_1.so: retpoline_plt_1.o ../ld-new
+ ../ld-new -shared -z retpolineplt retpoline_plt_1.o -o $@
+retpoline_plt_1.stdout: retpoline_plt_1.so
+ $(TEST_OBJDUMP) -dw $< > $@
+
check_SCRIPTS += bnd_plt_1.sh
check_DATA += bnd_plt_1.stdout
bnd_plt_1.o: bnd_plt_1.s
diff --git a/gold/testsuite/retpoline_plt_1.s b/gold/testsuite/retpoline_plt_1.s
index e69de29bb2..0aa1be0228 100644
--- a/gold/testsuite/retpoline_plt_1.s
+++ b/gold/testsuite/retpoline_plt_1.s
@@ -0,0 +1,4 @@
+ .text
+ .globl _start
+_start:
+ call foo1@plt
diff --git a/gold/testsuite/retpoline_plt_1.sh b/gold/testsuite/retpoline_plt_1.sh
index e69de29bb2..28be2034cb 100755
--- a/gold/testsuite/retpoline_plt_1.sh
+++ b/gold/testsuite/retpoline_plt_1.sh
@@ -0,0 +1,33 @@
+#!/bin/sh
+
+# retpoline_plt_1.sh -- test -z retpolineplt for x86_64
+
+# Copyright (C) 2016-2017 Free Software Foundation, Inc.
+# Written by Sriraman Tallam <tmsriram@google.com>.
+
+# This file is part of gold.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
+# MA 02110-1301, USA.
+
+noindirectjump()
+{
+ if egrep "$1" "$2" >/dev/null 2>&1; then
+ echo 1>&2 "Found indirect jump '$1' in $2"
+ exit 1
+ fi
+}
+
+noindirectjump 'jmpq[ ]*\*0x[0-9a-f]*\(%rip\)' retpoline_plt_1.stdout
diff --git a/gold/x86_64.cc b/gold/x86_64.cc
index a8140602b0..2eefe5d93e 100644
--- a/gold/x86_64.cc
+++ b/gold/x86_64.cc
@@ -542,6 +542,84 @@ class Output_data_plt_x86_64_bnd : public Output_data_plt_x86_64<64>
static const unsigned char plt_eh_frame_fde[plt_eh_frame_fde_size];
};
+template<int size>
+class Output_data_plt_x86_64_retpoline : public Output_data_plt_x86_64<size>
+{
+ public:
+ Output_data_plt_x86_64_retpoline(Layout* layout,
+ Output_data_got<64, false>* got,
+ Output_data_got_plt_x86_64* got_plt,
+ Output_data_space* got_irelative)
+ : Output_data_plt_x86_64<size>(layout, plt_entry_size,
+ got, got_plt, got_irelative)
+ { }
+
+ Output_data_plt_x86_64_retpoline(Layout* layout,
+ Output_data_got<64, false>* got,
+ Output_data_got_plt_x86_64* got_plt,
+ Output_data_space* got_irelative,
+ unsigned int plt_count)
+ : Output_data_plt_x86_64<size>(layout, plt_entry_size,
+ got, got_plt, got_irelative,
+ plt_count)
+ { }
+
+ protected:
+ virtual unsigned int
+ do_get_plt_entry_size() const
+ { return plt_entry_size; }
+
+ virtual void
+ do_add_eh_frame(Layout* layout)
+ {
+ layout->add_eh_frame_for_plt(this,
+ this->plt_eh_frame_cie,
+ this->plt_eh_frame_cie_size,
+ plt_eh_frame_fde,
+ plt_eh_frame_fde_size);
+ }
+
+ virtual void
+ do_fill_first_plt_entry(unsigned char* pov,
+ typename elfcpp::Elf_types<size>::Elf_Addr got_addr,
+ typename elfcpp::Elf_types<size>::Elf_Addr plt_addr);
+
+ virtual unsigned int
+ do_fill_plt_entry(unsigned char* pov,
+ typename elfcpp::Elf_types<size>::Elf_Addr got_address,
+ typename elfcpp::Elf_types<size>::Elf_Addr plt_address,
+ unsigned int got_offset,
+ unsigned int plt_offset,
+ unsigned int plt_index);
+
+ virtual void
+ do_fill_tlsdesc_entry(unsigned char* pov,
+ typename elfcpp::Elf_types<size>::Elf_Addr got_address,
+ typename elfcpp::Elf_types<size>::Elf_Addr plt_address,
+ typename elfcpp::Elf_types<size>::Elf_Addr got_base,
+ unsigned int tlsdesc_got_offset,
+ unsigned int plt_offset);
+
+ private:
+ // The size of an entry in the PLT.
+ static const int plt_entry_size = 32;
+
+ // The first entry in the PLT.
+ // From the AMD64 ABI: "Unlike Intel386 ABI, this ABI uses the same
+ // procedure linkage table for both programs and shared objects."
+ static const unsigned char first_plt_entry[plt_entry_size];
+
+ // Other entries in the PLT for an executable.
+ static const unsigned char plt_entry[plt_entry_size];
+
+ // The reserved TLSDESC entry in the PLT for an executable.
+ static const unsigned char tlsdesc_plt_entry[plt_entry_size];
+
+ // The .eh_frame unwind information for the PLT.
+ static const int plt_eh_frame_fde_size = 32;
+ static const unsigned char plt_eh_frame_fde[plt_eh_frame_fde_size];
+};
+
template<int size>
class Lazy_view
{
@@ -1814,6 +1892,129 @@ Output_data_plt_x86_64_standard<size>::do_fill_tlsdesc_entry(
+ 12)));
}
+// The first entry in the PLT for an executable.
+
+template<int size>
+const unsigned char
+Output_data_plt_x86_64_retpoline<size>::first_plt_entry[plt_entry_size] =
+{
+ // Retpoline first PLT entry code sequence.
+ 0xff, 0x35, // pushq contents of memory address
+ 0, 0, 0, 0, // replaced with address of .got + 8
+ 0x4c, 0x8b, 0x1d, // mov GOT(%rip), %r11
+ 0, 0, 0, 0,
+ 0xe8, 0x04, 0, 0, 0, // callq next
+ 0xf3, 0x90, // loop: pause
+ 0xeb, 0xfc, // jmp loop
+ 0x4c, 0x89, 0x1c, 0x24, // next: mov r11, %(rsp)
+ 0xc3, // ret
+ 0xcc, 0xcc, 0xcc, 0xcc, 0xcc // 5 extra bytes
+};
+
+template<int size>
+void
+Output_data_plt_x86_64_retpoline<size>::do_fill_first_plt_entry(
+ unsigned char* pov,
+ typename elfcpp::Elf_types<size>::Elf_Addr got_address,
+ typename elfcpp::Elf_types<size>::Elf_Addr plt_address)
+{
+ memcpy(pov, first_plt_entry, plt_entry_size);
+ // We do a jmp relative to the PC at the end of this instruction.
+ elfcpp::Swap_unaligned<32, false>::writeval(pov + 2,
+ (got_address + 8
+ - (plt_address + 6)));
+ elfcpp::Swap<32, false>::writeval(pov + 9,
+ (got_address + 16
+ - (plt_address + 13)));
+}
+
+// The retpoline entries in the PLT for an executable.
+
+template<int size>
+const unsigned char
+Output_data_plt_x86_64_retpoline<size>::plt_entry[plt_entry_size] =
+{
+ // Retpoline PLT code sequence.
+ 0x4c, 0x8b, 0x1d, 0, 0, 0, 0, // mov sym@GOTPLT(%rip), r11
+ 0xe8, 0x04, 0, 0, 0, // callq next
+ 0xf3, 0x90, // loop: pause
+ 0xeb, 0xfc, // jmp loop
+ 0x4c, 0x89, 0x1c, 0x24, // next: mov r11, %(rsp)
+ 0xc3, // ret
+ 0x68, // pushq immediate
+ 0, 0, 0, 0, // replaced with offset into relocation table
+ 0xe9, // jmpq relative
+ 0, 0, 0, 0, // replaced with offset to start of .plt
+ 0xcc // extra byte
+};
+
+template<int size>
+unsigned int
+Output_data_plt_x86_64_retpoline<size>::do_fill_plt_entry(
+ unsigned char* pov,
+ typename elfcpp::Elf_types<size>::Elf_Addr got_address,
+ typename elfcpp::Elf_types<size>::Elf_Addr plt_address,
+ unsigned int got_offset,
+ unsigned int plt_offset,
+ unsigned int plt_index)
+{
+ // Check PC-relative offset overflow in PLT entry.
+ uint64_t plt_got_pcrel_offset = (got_address + got_offset
+ - (plt_address + plt_offset + 7));
+ if (Bits<32>::has_overflow(plt_got_pcrel_offset))
+ gold_error(_("PC-relative offset overflow in PLT entry %d"),
+ plt_index + 1);
+
+ memcpy(pov, plt_entry, plt_entry_size);
+ elfcpp::Swap_unaligned<32, false>::writeval(pov + 3,
+ plt_got_pcrel_offset);
+
+ elfcpp::Swap_unaligned<32, false>::writeval(pov + 22, plt_index);
+ elfcpp::Swap<32, false>::writeval(pov + 27,
+ - (plt_offset + plt_entry_size - 1));
+
+ return 21;
+
+}
+
+// The reserved TLSDESC entry in the PLT for an executable.
+
+template<int size>
+const unsigned char
+Output_data_plt_x86_64_retpoline<size>::tlsdesc_plt_entry[plt_entry_size] =
+{
+ // From Alexandre Oliva, "Thread-Local Storage Descriptors for IA32
+ // and AMD64/EM64T", Version 0.9.4 (2005-10-10).
+ 0xff, 0x35, // pushq x(%rip)
+ 0, 0, 0, 0, // replaced with address of linkmap GOT entry (at PLTGOT + 8)
+ 0xff, 0x25, // jmpq *y(%rip)
+ 0, 0, 0, 0, // replaced with offset of reserved TLSDESC_GOT entry
+ 0x0f, 0x1f, // nop
+ 0x40, 0
+};
+
+template<int size>
+void
+Output_data_plt_x86_64_retpoline<size>::do_fill_tlsdesc_entry(
+ unsigned char* pov,
+ typename elfcpp::Elf_types<size>::Elf_Addr got_address,
+ typename elfcpp::Elf_types<size>::Elf_Addr plt_address,
+ typename elfcpp::Elf_types<size>::Elf_Addr got_base,
+ unsigned int tlsdesc_got_offset,
+ unsigned int plt_offset)
+{
+ memcpy(pov, tlsdesc_plt_entry, plt_entry_size);
+ elfcpp::Swap_unaligned<32, false>::writeval(pov + 2,
+ (got_address + 8
+ - (plt_address + plt_offset
+ + 6)));
+ elfcpp::Swap_unaligned<32, false>::writeval(pov + 8,
+ (got_base
+ + tlsdesc_got_offset
+ - (plt_address + plt_offset
+ + 12)));
+}
+
// Return the APLT address to use for a global symbol (for -z bndplt).
uint64_t
@@ -2036,6 +2237,34 @@ Output_data_plt_x86_64_standard<size>::plt_eh_frame_fde[plt_eh_frame_fde_size] =
elfcpp::DW_CFA_nop
};
+template<int size>
+const unsigned char
+Output_data_plt_x86_64_retpoline<size>::plt_eh_frame_fde[plt_eh_frame_fde_size] =
+{
+ 0, 0, 0, 0, // Replaced with offset to .plt.
+ 0, 0, 0, 0, // Replaced with size of .plt.
+ 0, // Augmentation size.
+ elfcpp::DW_CFA_def_cfa_offset, 16, // DW_CFA_def_cfa_offset: 16.
+ elfcpp::DW_CFA_advance_loc + 6, // Advance 6 to __PLT__ + 6.
+ elfcpp::DW_CFA_def_cfa_offset, 24, // DW_CFA_def_cfa_offset: 24.
+ elfcpp::DW_CFA_advance_loc + 10, // Advance 10 to __PLT__ + 16.
+ elfcpp::DW_CFA_def_cfa_expression, // DW_CFA_def_cfa_expression.
+ 11, // Block length.
+ elfcpp::DW_OP_breg7, 8, // Push %rsp + 8.
+ elfcpp::DW_OP_breg16, 0, // Push %rip.
+ elfcpp::DW_OP_lit15, // Push 0xf.
+ elfcpp::DW_OP_and, // & (%rip & 0xf).
+ elfcpp::DW_OP_lit11, // Push 0xb.
+ elfcpp::DW_OP_ge, // >= ((%rip & 0xf) >= 0xb)
+ elfcpp::DW_OP_lit3, // Push 3.
+ elfcpp::DW_OP_shl, // << (((%rip & 0xf) >= 0xb) << 3)
+ elfcpp::DW_OP_plus, // + ((((%rip&0xf)>=0xb)<<3)+%rsp+8
+ elfcpp::DW_CFA_nop, // Align to 32 bytes.
+ elfcpp::DW_CFA_nop,
+ elfcpp::DW_CFA_nop,
+ elfcpp::DW_CFA_nop
+};
+
// The .eh_frame unwind information for the BND PLT.
const unsigned char
Output_data_plt_x86_64_bnd::plt_eh_frame_fde[plt_eh_frame_fde_size] =
@@ -2287,6 +2516,9 @@ Target_x86_64<64>::do_make_data_plt(Layout* layout,
if (parameters->options().bndplt())
return new Output_data_plt_x86_64_bnd(layout, got, got_plt,
got_irelative);
+ else if (parameters->options().retpolineplt())
+ return new Output_data_plt_x86_64_retpoline<64>(layout, got, got_plt,
+ got_irelative);
else
return new Output_data_plt_x86_64_standard<64>(layout, got, got_plt,
got_irelative);
@@ -2316,6 +2548,9 @@ Target_x86_64<64>::do_make_data_plt(Layout* layout,
if (parameters->options().bndplt())
return new Output_data_plt_x86_64_bnd(layout, got, got_plt,
got_irelative, plt_count);
+ else if (parameters->options().retpolineplt())
+ return new Output_data_plt_x86_64_retpoline<64>(layout, got, got_plt,
+ got_irelative, plt_count);
else
return new Output_data_plt_x86_64_standard<64>(layout, got, got_plt,
got_irelative,
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