[PATCH v6 00/10] Retpoline: Avoid speculative indirect calls in kernel

[David Woodhouse]

This is a mitigation for the 'variant 2' attack described in
https://googleprojectzero.blogspot.com/2018/01/reading-privileged-memory-with-side.html

Using GCC patches available from the hjl/indirect/gcc-7-branch/master
branch of https://github.com/hjl-tools/gcc/commits/hjl and by manually
patching assembler code, all vulnerable indirect branches (that occur
after userspace first runs) are eliminated from the kernel.

They are replaced with a 'retpoline' call sequence which deliberately
prevents speculation.

Fedora 27 packages of the updated compiler are available at
https://koji.fedoraproject.org/koji/taskinfo?taskID=24065739


v1: Initial post.
v2: Add CONFIG_RETPOLINE to build kernel without it.
    Change warning messages.
    Hide modpost warning message
v3: Update to the latest CET-capable retpoline version
    Reinstate ALTERNATIVE support
v4: Finish reconciling Andi's and my patch sets, bug fixes.
    Exclude objtool support for now
    Add 'noretpoline' boot option
    Add AMD retpoline alternative
v5: Silence MODVERSIONS warnings
    Use pause;jmp loop instead of lfence;jmp
    Switch to X86_FEATURE_RETPOLINE positive feature logic
    Emit thunks inline from assembler macros
    Merge AMD support into initial patch
v6: Update to latest GCC patches with no dots in symbols
    Fix MODVERSIONS properly(ish)
    Fix typo breaking 32-bit, introduced in V5
    Never set X86_FEATURE_RETPOLINE_AMD yet, pending confirmation

Andi Kleen (3):
  x86/retpoline/irq32: Convert assembler indirect jumps
  x86/retpoline: Add boot time option to disable retpoline
  x86/retpoline: Exclude objtool with retpoline

David Woodhouse (7):
  x86/retpoline: Add initial retpoline support
  x86/retpoline/crypto: Convert crypto assembler indirect jumps
  x86/retpoline/entry: Convert entry assembler indirect jumps
  x86/retpoline/ftrace: Convert ftrace assembler indirect jumps
  x86/retpoline/hyperv: Convert assembler indirect jumps
  x86/retpoline/xen: Convert Xen hypercall indirect jumps
  x86/retpoline/checksum32: Convert assembler indirect jumps

 Documentation/admin-guide/kernel-parameters.txt |  3 +
 arch/x86/Kconfig                                | 17 ++++-
 arch/x86/Kconfig.debug                          |  6 +-
 arch/x86/Makefile                               | 10 +++
 arch/x86/crypto/aesni-intel_asm.S               |  5 +-
 arch/x86/crypto/camellia-aesni-avx-asm_64.S     |  3 +-
 arch/x86/crypto/camellia-aesni-avx2-asm_64.S    |  3 +-
 arch/x86/crypto/crc32c-pcl-intel-asm_64.S       |  3 +-
 arch/x86/entry/entry_32.S                       |  5 +-
 arch/x86/entry/entry_64.S                       | 12 +++-
 arch/x86/include/asm/asm-prototypes.h           | 25 +++++++
 arch/x86/include/asm/cpufeatures.h              |  2 +
 arch/x86/include/asm/mshyperv.h                 | 18 ++---
 arch/x86/include/asm/nospec-branch.h            | 92 +++++++++++++++++++++++++
 arch/x86/include/asm/xen/hypercall.h            |  5 +-
 arch/x86/kernel/cpu/common.c                    |  3 +
 arch/x86/kernel/cpu/intel.c                     | 11 +++
 arch/x86/kernel/ftrace_32.S                     |  6 +-
 arch/x86/kernel/ftrace_64.S                     |  8 +--
 arch/x86/kernel/irq_32.c                        |  9 +--
 arch/x86/lib/Makefile                           |  1 +
 arch/x86/lib/checksum_32.S                      |  7 +-
 arch/x86/lib/retpoline.S                        | 48 +++++++++++++
 23 files changed, 264 insertions(+), 38 deletions(-)
 create mode 100644 arch/x86/include/asm/nospec-branch.h
 create mode 100644 arch/x86/lib/retpoline.S

-- 
2.7.4