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authorPawan Gupta <pawan.kumar.gupta@linux.intel.com>2024-03-11 18:57:09 +0300
committerThomas Gleixner <tglx@linutronix.de>2024-04-08 20:27:06 +0300
commit95a6ccbdc7199a14b71ad8901cb788ba7fb5167b (patch)
tree2756d1354b90ff94be54ba551fbe6570365d2bf7 /Documentation
parentec9404e40e8f36421a2b66ecb76dc2209fe7f3ef (diff)
downloadlinux-95a6ccbdc7199a14b71ad8901cb788ba7fb5167b.tar.xz
x86/bhi: Mitigate KVM by default
BHI mitigation mode spectre_bhi=auto does not deploy the software mitigation by default. In a cloud environment, it is a likely scenario where userspace is trusted but the guests are not trusted. Deploying system wide mitigation in such cases is not desirable. Update the auto mode to unconditionally mitigate against malicious guests. Deploy the software sequence at VMexit in auto mode also, when hardware mitigation is not available. Unlike the force =on mode, software sequence is not deployed at syscalls in auto mode. Suggested-by: Alexandre Chartre <alexandre.chartre@oracle.com> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com> Signed-off-by: Daniel Sneddon <daniel.sneddon@linux.intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com> Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/admin-guide/hw-vuln/spectre.rst7
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt5
2 files changed, 8 insertions, 4 deletions
diff --git a/Documentation/admin-guide/hw-vuln/spectre.rst b/Documentation/admin-guide/hw-vuln/spectre.rst
index 7cb99b09827c..b70b1d8bd8e6 100644
--- a/Documentation/admin-guide/hw-vuln/spectre.rst
+++ b/Documentation/admin-guide/hw-vuln/spectre.rst
@@ -439,10 +439,12 @@ The possible values in this file are:
- System is protected by retpoline
* - BHI: BHI_DIS_S
- System is protected by BHI_DIS_S
- * - BHI: SW loop
+ * - BHI: SW loop; KVM SW loop
- System is protected by software clearing sequence
* - BHI: Syscall hardening
- Syscalls are hardened against BHI
+ * - BHI: Syscall hardening; KVM: SW loop
+ - System is protected from userspace attacks by syscall hardening; KVM is protected by software clearing sequence
Full mitigation might require a microcode update from the CPU
vendor. When the necessary microcode is not available, the kernel will
@@ -669,7 +671,8 @@ kernel command line.
unconditionally disable.
auto
enable if hardware mitigation
- control(BHI_DIS_S) is available.
+ control(BHI_DIS_S) is available, otherwise
+ enable alternate mitigation in KVM.
For spectre_v2_user see Documentation/admin-guide/kernel-parameters.txt
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2dbe60c1db22..4fa46302f436 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6071,8 +6071,9 @@
on - unconditionally enable.
off - unconditionally disable.
- auto - (default) enable only if hardware mitigation
- control(BHI_DIS_S) is available.
+ auto - (default) enable hardware mitigation
+ (BHI_DIS_S) if available, otherwise enable
+ alternate mitigation in KVM.
spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2
(indirect branch speculation) vulnerability.