arm64: Turn on KPTI only on CPUs that need it

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.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Jayachandran C <jnair@caviumnetworks.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 5612d6f46331..4b6f9051cf0c 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -868,6 +868,13 @@ 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);