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.
Andrew Donnellan (1):
powerpc: Fix __clear_user() with KUAP enabled
Christophe Leroy (2):
powerpc: Add a framework for user access tracking
powerpc: Implement user_access_begin and friends
Daniel Axtens (1):
powerpc/64s: move some exception handlers out of line
Nicholas Piggin (3):
powerpc/64s: flush L1D on kernel entry
powerpc/uaccess: Evaluate macro arguments once, before user access is
allowed
powerpc/64s: flush L1D after user accesses
.../admin-guide/kernel-parameters.txt | 7 +
.../powerpc/include/asm/book3s/64/kup-radix.h | 22 +++
arch/powerpc/include/asm/exception-64s.h | 9 +-
arch/powerpc/include/asm/feature-fixups.h | 19 +++
arch/powerpc/include/asm/futex.h | 4 +
arch/powerpc/include/asm/kup.h | 40 +++++
arch/powerpc/include/asm/security_features.h | 7 +
arch/powerpc/include/asm/setup.h | 4 +
arch/powerpc/include/asm/uaccess.h | 147 ++++++++++++++----
arch/powerpc/kernel/exceptions-64s.S | 96 +++++++-----
arch/powerpc/kernel/setup_64.c | 122 ++++++++++++++-
arch/powerpc/kernel/vmlinux.lds.S | 14 ++
arch/powerpc/lib/checksum_wrappers.c | 4 +
arch/powerpc/lib/feature-fixups.c | 104 +++++++++++++
arch/powerpc/lib/string_32.S | 4 +-
arch/powerpc/lib/string_64.S | 6 +-
arch/powerpc/platforms/powernv/setup.c | 17 ++
arch/powerpc/platforms/pseries/setup.c | 8 +
18 files changed, 553 insertions(+), 81 deletions(-)
create mode 100644 arch/powerpc/include/asm/book3s/64/kup-radix.h
create mode 100644 arch/powerpc/include/asm/kup.h
--
2.25.1
