From 24ea8003a49dbbcdfbbf2e5969c4bf8002063b86 Mon Sep 17 00:00:00 2001
From: Zach Koopmans <zkoopmans@google.com>
Date: Mon, 22 Feb 2021 16:00:33 -0800
Subject: Only detect mds for mitigate.

Only detect and mitigate on mds for the mitigate command.

PiperOrigin-RevId: 358924466
---
 runsc/mitigate/cpu.go      | 34 +++++++---------------------------
 runsc/mitigate/mitigate.go |  6 +-----
 2 files changed, 8 insertions(+), 32 deletions(-)

diff --git a/runsc/mitigate/cpu.go b/runsc/mitigate/cpu.go
index ae4ce9579..38f9b787a 100644
--- a/runsc/mitigate/cpu.go
+++ b/runsc/mitigate/cpu.go
@@ -23,15 +23,10 @@ import (
 )
 
 const (
-	// constants of coomm
-	meltdown = "cpu_meltdown"
-	l1tf     = "l1tf"
-	mds      = "mds"
-	swapgs   = "swapgs"
-	taa      = "taa"
-)
+	// mds is the only bug we care about.
+	mds = "mds"
 
-const (
+	// Constants for parsing /proc/cpuinfo.
 	processorKey  = "processor"
 	vendorIDKey   = "vendor_id"
 	cpuFamilyKey  = "cpu family"
@@ -39,9 +34,8 @@ const (
 	physicalIDKey = "physical id"
 	coreIDKey     = "core id"
 	bugsKey       = "bugs"
-)
 
-const (
+	// Path to shutdown a CPU.
 	cpuOnlineTemplate = "/sys/devices/system/cpu/cpu%d/online"
 )
 
@@ -249,24 +243,10 @@ func (t *thread) shutdown() error {
 	return ioutil.WriteFile(cpuPath, []byte{'0'}, 0644)
 }
 
-// List of pertinent side channel vulnerablilites.
-// For mds, see: https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/mds.html.
-var vulnerabilities = []string{
-	meltdown,
-	l1tf,
-	mds,
-	swapgs,
-	taa,
-}
-
-// isVulnerable checks if a CPU is vulnerable to pertinent bugs.
+// isVulnerable checks if a CPU is vulnerable to mds.
 func (t *thread) isVulnerable() bool {
-	for _, bug := range vulnerabilities {
-		if _, ok := t.bugs[bug]; ok {
-			return true
-		}
-	}
-	return false
+	_, ok := t.bugs[mds]
+	return ok
 }
 
 // isActive checks if a CPU is active from /sys/devices/system/cpu/cpu{N}/online
diff --git a/runsc/mitigate/mitigate.go b/runsc/mitigate/mitigate.go
index 5be66f5f3..3ea58454f 100644
--- a/runsc/mitigate/mitigate.go
+++ b/runsc/mitigate/mitigate.go
@@ -36,11 +36,7 @@ type Mitigate struct {
 func (m Mitigate) Usage() string {
 	usageString := `mitigate [flags]
 
-This command mitigates an underlying system against side channel attacks.
-The command checks /proc/cpuinfo for cpus having key vulnerablilities (meltdown,
-l1tf, mds, swapgs, taa). If cpus are found to have one of the vulnerabilities,
-all but one cpu is shutdown on each core via
-/sys/devices/system/cpu/cpu{N}/online.
+Mitigate mitigates a system to the "MDS" vulnerability by implementing a manual shutdown of SMT. The command checks /proc/cpuinfo for cpus having the MDS vulnerability, and if found, shutdown all but one CPU per hyperthread pair via /sys/devices/system/cpu/cpu{N}/online. CPUs can be restored by writing "2" to each file in /sys/devices/system/cpu/cpu{N}/online or performing a system reboot.
 `
 	return usageString + m.other.usage()
 }
-- 
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