[PATCH v7 00/11] 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
v7: Further bikeshedding on macro names
    Stuff RSB on kernel entry
    Implement 'spectre_v2=' command line option for IBRS/IBPB too
    Revert to precisely the asm sequences from the Google paper

Andi Kleen (3):
  x86/retpoline: Temporarily disable objtool when CONFIG_RETPOLINE=y
  x86/retpoline/irq32: Convert assembler indirect jumps
  x86/retpoline: Avoid return buffer underflows on context switch

David Woodhouse (8):
  x86/retpoline: Add initial retpoline support
  x86/spectre: Add boot time option to select Spectre v2 mitigation
  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 |  28 +++++
 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                       |  22 +++-
 arch/x86/entry/entry_64.S                       |  29 ++++-
 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            | 158 ++++++++++++++++++++++++
 arch/x86/include/asm/xen/hypercall.h            |   5 +-
 arch/x86/kernel/cpu/bugs.c                      | 122 +++++++++++++++++-
 arch/x86/kernel/ftrace_32.S                     |   6 +-
 arch/x86/kernel/ftrace_64.S                     |   8 +-
 arch/x86/kernel/irq_32.c                        |   9 +-
 arch/x86/kernel/setup.c                         |   3 +
 arch/x86/lib/Makefile                           |   1 +
 arch/x86/lib/checksum_32.S                      |   7 +-
 arch/x86/lib/retpoline.S                        |  48 +++++++
 23 files changed, 499 insertions(+), 39 deletions(-)
 create mode 100644 arch/x86/include/asm/nospec-branch.h
 create mode 100644 arch/x86/lib/retpoline.S

-- 
2.7.4