[PATCH 0/7] CVE-2020-4788: Speculation on incompletely validated data on IBM Power9

[Daniel Axtens]

IBM Power9 processors can speculatively operate on data in the L1
cache before it has been completely validated, via a way-prediction
mechanism. It is not possible for an attacker to determine the
contents of impermissible memory using this method, since these
systems implement a combination of hardware and software security
measures to prevent scenarios where protected data could be leaked.

However these measures don't address the scenario where an attacker
induces the operating system to speculatively execute instructions
using data that the attacker controls. This can be used for example to
speculatively bypass "kernel user access prevention" techniques, as
discovered by Anthony Steinhauser of Google's Safeside Project. This
is not an attack by itself, but there is a possibility it could be
used in conjunction with side-channels or other weaknesses in the
privileged code to construct an attack.

This issue can be mitigated by flushing the L1 cache between privilege
boundaries of concern. This series flushes the cache on kernel entry and
after kernel user accesses.

Thanks to Nick Piggin, Russell Currey, Christopher M. Riedl, Michael
Ellerman and Spoorthy S for their work in developing, optimising,
testing and backporting these fixes, and to the many others who helped
behind the scenes.

Daniel Axtens (3):
  selftests/powerpc: entry flush test
  selftests/powerpc: refactor entry and rfi_flush tests
  powerpc/64s: rename pnv|pseries_setup_rfi_flush to
    _setup_security_mitigations

Michael Ellerman (1):
  powerpc: Only include kup-radix.h for 64-bit Book3S

Nicholas Piggin (2):
  powerpc/64s: flush L1D on kernel entry
  powerpc/64s: flush L1D after user accesses

Russell Currey (1):
  selftests/powerpc: rfi_flush: disable entry flush if present

 .../admin-guide/kernel-parameters.txt         |   7 +
 .../powerpc/include/asm/book3s/64/kup-radix.h |  66 ++++++---
 arch/powerpc/include/asm/exception-64s.h      |  12 +-
 arch/powerpc/include/asm/feature-fixups.h     |  19 +++
 arch/powerpc/include/asm/kup.h                |  26 +++-
 arch/powerpc/include/asm/security_features.h  |   7 +
 arch/powerpc/include/asm/setup.h              |   4 +
 arch/powerpc/kernel/exceptions-64s.S          |  80 +++++-----
 arch/powerpc/kernel/setup_64.c                | 122 ++++++++++++++-
 arch/powerpc/kernel/syscall_64.c              |   2 +-
 arch/powerpc/kernel/vmlinux.lds.S             |  14 ++
 arch/powerpc/lib/feature-fixups.c             | 104 +++++++++++++
 arch/powerpc/platforms/powernv/setup.c        |  24 ++-
 arch/powerpc/platforms/pseries/mobility.c     |   4 +-
 arch/powerpc/platforms/pseries/pseries.h      |   2 +-
 arch/powerpc/platforms/pseries/setup.c        |  15 +-
 .../testing/selftests/powerpc/include/utils.h |   5 +
 .../selftests/powerpc/security/.gitignore     |   1 +
 .../selftests/powerpc/security/Makefile       |   4 +-
 .../selftests/powerpc/security/entry_flush.c  | 139 ++++++++++++++++++
 .../selftests/powerpc/security/flush_utils.c  |  70 +++++++++
 .../selftests/powerpc/security/flush_utils.h  |  17 +++
 .../selftests/powerpc/security/rfi_flush.c    |  96 ++++--------
 23 files changed, 693 insertions(+), 147 deletions(-)
 create mode 100644 tools/testing/selftests/powerpc/security/entry_flush.c
 create mode 100644 tools/testing/selftests/powerpc/security/flush_utils.c
 create mode 100644 tools/testing/selftests/powerpc/security/flush_utils.h

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2.25.1