From Daniel's cover letter:
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 patch series flushes the L1 cache on kernel entry (patch 2) and after the
kernel performs any user accesses (patch 3). It also adds a self-test and
performs some related cleanups.
-----BEGIN PGP SIGNATURE-----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=Yibq
-----END PGP SIGNATURE-----
Merge tag 'powerpc-cve-2020-4788' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux
Pull powerpc fixes from Michael Ellerman:
"Fixes for CVE-2020-4788.
From Daniel's cover letter:
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 patch series flushes the L1 cache on kernel entry (patch 2) and
after the kernel performs any user accesses (patch 3). It also adds a
self-test and performs some related cleanups"
* tag 'powerpc-cve-2020-4788' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux:
powerpc/64s: rename pnv|pseries_setup_rfi_flush to _setup_security_mitigations
selftests/powerpc: refactor entry and rfi_flush tests
selftests/powerpc: entry flush test
powerpc: Only include kup-radix.h for 64-bit Book3S
powerpc/64s: flush L1D after user accesses
powerpc/64s: flush L1D on kernel entry
selftests/powerpc: rfi_flush: disable entry flush if present
dda3f4252e