Patch "[Variant 3/Meltdown] arm64: Turn on KPTI only on CPUs that need it" has been added to the 4.15-stable tree

Patch "[Variant 3/Meltdown] arm64: Turn on KPTI only on CPUs that need it" has been added to the 4.15-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    [Variant 3/Meltdown] arm64: Turn on KPTI only on CPUs that need it

to the 4.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     arm64-turn-on-kpti-only-on-cpus-that-need-it.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Tue Feb 13 17:25:10 CET 2018
From: Jayachandran C <jnair@caviumnetworks.com>
Date: Fri, 19 Jan 2018 04:22:48 -0800
Subject: [Variant 3/Meltdown] arm64: Turn on KPTI only on CPUs that need it

From: Jayachandran C <jnair@caviumnetworks.com>


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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/arm64/kernel/cpufeature.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -866,6 +866,13 @@ static bool unmap_kernel_at_el0(const st
 	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);


Patches currently in stable-queue which might be from jnair@caviumnetworks.com are

queue-4.15/arm64-turn-on-kpti-only-on-cpus-that-need-it.patch
queue-4.15/arm64-branch-predictor-hardening-for-cavium-thunderx2.patch
queue-4.15/arm64-cputype-add-midr-values-for-cavium-thunderx2-cpus.patch