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| author | Nicholas Piggin <npiggin@gmail.com> | 2020-11-20 10:35:13 +1100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-11-22 10:14:10 +0100 |
| commit | b65458b6be8032c5179d4f562038575d7b3a6be3 (patch) | |
| tree | a275f567b813f5cc4f3971954349eea40725f4bf /Documentation | |
| parent | bcf7f2d3fcec8a47ddfee6d8801ab57162922480 (diff) | |
| download | linux-stable-b65458b6be8032c5179d4f562038575d7b3a6be3.tar.gz linux-stable-b65458b6be8032c5179d4f562038575d7b3a6be3.tar.bz2 linux-stable-b65458b6be8032c5179d4f562038575d7b3a6be3.zip | |
powerpc/64s: flush L1D on kernel entry
commit f79643787e0a0762d2409b7b8334e83f22d85695 upstream.
[backporting note: we need to mark some exception handlers as out-of-line
because the flushing makes them take too much space -- dja]
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 flushes the L1 cache on kernel entry.
This is part of the fix for CVE-2020-4788.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 5b4753e602de..e1036ff037e6 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2667,6 +2667,7 @@ mds=off [X86] tsx_async_abort=off [X86] kvm.nx_huge_pages=off [X86] + no_entry_flush [PPC] Exceptions: This does not have any effect on @@ -2989,6 +2990,8 @@ noefi Disable EFI runtime services support. + no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel. + noexec [IA-64] noexec [X86] |