[PATCH v3 2/2] arm64: Turn on KPTI only on CPUs that need it

Jayachandran C
2018-01-19T12:22:48Z

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>
---
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 647d44b..fb698ca 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -866,6 +866,13 @@ 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);
--
2.7.4