spectre-bhb mitigation is enabled by default on ARM32, which may
cause performance regression. To offer an option to turn off the
mitigation, here expand an existing cmdline parameter 'nospectre_bhb'
to ARM32, which sets up a switch to skip the mitigation code entry
and bhb workarounds in mitigation method handler.
Signed-off-by: Chen Jiahao <chenjiahao16@xxxxxxxxxx>
---
Documentation/admin-guide/kernel-parameters.txt | 2 +-
arch/arm/mm/proc-v7-bugs.c | 14 ++++++++++++++
2 files changed, 15 insertions(+), 1 deletion(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 0a1731a0f0ef..856edb4403fb 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3902,7 +3902,7 @@
nospec_store_bypass_disable
[HW] Disable all mitigations for the Speculative Store Bypass vulnerability
- nospectre_bhb [ARM64] Disable all mitigations for Spectre-BHB (branch
+ nospectre_bhb [ARM,ARM64] Disable all mitigations for Spectre-BHB (branch
history injection) vulnerability. System may allow data leaks
with this option.
diff --git a/arch/arm/mm/proc-v7-bugs.c b/arch/arm/mm/proc-v7-bugs.c
index 8bc7a2d6d6c7..dd2ddece714f 100644
--- a/arch/arm/mm/proc-v7-bugs.c
+++ b/arch/arm/mm/proc-v7-bugs.c
@@ -9,6 +9,15 @@
#include <asm/spectre.h>
#include <asm/system_misc.h>
+static int nospectre_bhb __read_mostly;
+
+static int __init nospectre_bhb_setup(char *str)
+{
+ nospectre_bhb = 1;
+ return 0;
+}
+early_param("nospectre_bhb", nospectre_bhb_setup);
+
#ifdef CONFIG_ARM_PSCI
static int __maybe_unused spectre_v2_get_cpu_fw_mitigation_state(void)
{
@@ -226,6 +235,11 @@ static void cpu_v7_spectre_bhb_init(void)
{
unsigned int state, method = 0;
+ if (nospectre_bhb) {
+ pr_info_once("Spectre bhb: hardening is disabled\n");
+ return;
+ }
+
switch (read_cpuid_part()) {
case ARM_CPU_PART_CORTEX_A15:
case ARM_CPU_PART_BRAHMA_B15:
--
2.34.1
