From 32891668e8ec84c15289992d4154707ae1322ae5 Mon Sep 17 00:00:00 2001
From: Jayachandran C <jnair@caviumnetworks.com>
Date: Fri, 19 Jan 2018 04:22:48 -0800
Subject: [PATCH 24/24] arm64: Turn on KPTI only on CPUs that need it
Git-commit: 0ba2e29c7fc1d58a90fab614d41bf487e28e3840
Patch-mainline: v4.16-rc1
References: bsc#1076187
Whitelist Broadcom Vulcan/Cavium ThunderX2 processors in
unmap_kernel_at_el0(). These CPUs are not vulnerable to
CVE-2017-5754 and do not need KPTI when KASLR is off.
Signed-off-by: Jayachandran C <jnair@caviumnetworks.com>
Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@suse.com>
---
arch/arm64/kernel/cpufeature.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index afc0b093554a..ac99515700c6 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -795,6 +795,13 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
if (IS_ENABLED(CONFIG_RANDOMIZE_BASE))
return true;
+ /* Don't force KPTI for CPUs that are not vulnerable */
+ switch (read_cpuid_id() & MIDR_CPU_MODEL_MASK) {
+ case MIDR_CAVIUM_THUNDERX2:
+ case MIDR_BRCM_VULCAN:
+ return false;
+ }
+
/* Defer to CPU feature registers */
return !cpuid_feature_extract_unsigned_field(pfr0,
ID_AA64PFR0_CSV3_SHIFT);
--
2.11.0