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authorThomas Gleixner <tglx@linutronix.de>2019-02-18 22:04:08 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-05-16 19:45:14 +0200
commit8c7398befdf1ecb163b5d0f6f5ba27b45c63211e (patch)
tree92a8e5f9351e5c38532a233867eea0f8688860ad /Documentation
parentd4c1e6cbbcdca0f4688a58092ecbb81a58fe4421 (diff)
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x86/speculation/mds: Add mitigation control for MDS
commit bc1241700acd82ec69fde98c5763ce51086269f8 upstream. Now that the mitigations are in place, add a command line parameter to control the mitigation, a mitigation selector function and a SMT update mechanism. This is the minimal straight forward initial implementation which just provides an always on/off mode. The command line parameter is: mds=[full|off] This is consistent with the existing mitigations for other speculative hardware vulnerabilities. The idle invocation is dynamically updated according to the SMT state of the system similar to the dynamic update of the STIBP mitigation. The idle mitigation is limited to CPUs which are only affected by MSBDS and not any other variant, because the other variants cannot be mitigated on SMT enabled systems. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Borislav Petkov <bp@suse.de> Reviewed-by: Jon Masters <jcm@redhat.com> Tested-by: Jon Masters <jcm@redhat.com> [bwh: Backported to 4.4: - Drop " __ro_after_init" - Adjust filename, context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/kernel-parameters.txt22
1 files changed, 22 insertions, 0 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 47a8916e4cd4..9786b4bd039b 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2035,6 +2035,28 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
Format: <first>,<last>
Specifies range of consoles to be captured by the MDA.
+ mds= [X86,INTEL]
+ Control mitigation for the Micro-architectural Data
+ Sampling (MDS) vulnerability.
+
+ Certain CPUs are vulnerable to an exploit against CPU
+ internal buffers which can forward information to a
+ disclosure gadget under certain conditions.
+
+ In vulnerable processors, the speculatively
+ forwarded data can be used in a cache side channel
+ attack, to access data to which the attacker does
+ not have direct access.
+
+ This parameter controls the MDS mitigation. The
+ options are:
+
+ full - Enable MDS mitigation on vulnerable CPUs
+ off - Unconditionally disable MDS mitigation
+
+ Not specifying this option is equivalent to
+ mds=full.
+
mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
Amount of memory to be used when the kernel is not able
to see the whole system memory or for test.