From: Jayachandran C <jnair@caviumnetworks.com>
Date: Fri, 19 Jan 2018 12:22:48 +0000 (-0800)
Subject: arm64: Turn on KPTI only on CPUs that need it
X-Git-Tag: C0P2-H0.0--20200415~132
X-Git-Url: https://git.somdevices.com/?a=commitdiff_plain;h=bd80461a1f3564249e61534bcc3eb71c27d36b58;p=linux.git

arm64: Turn on KPTI only on CPUs that need it

commit 0ba2e29c7fc1 upstream.

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>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Alex Shi <alex.shi@linaro.org>
---

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 6200b81de034..e62583d3abd6 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -766,6 +766,13 @@ 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);