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authorNicholas Piggin <npiggin@gmail.com>2020-11-17 16:59:12 +1100
committerMichael Ellerman <mpe@ellerman.id.au>2020-11-19 23:47:15 +1100
commitf79643787e0a0762d2409b7b8334e83f22d85695 (patch)
treeed004d08dce4f9fa4a8f42024d63cf376adb5a9f /Documentation
parentfcb48454c23c5679d1a2e252f127642e91b05cbe (diff)
powerpc/64s: flush L1D on kernel entry
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: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt3
1 files changed, 3 insertions, 0 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 526d65d8573a..383889fe771f 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2858,6 +2858,7 @@
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
@@ -3186,6 +3187,8 @@
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]