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Subject[PATCH 4.9 071/102] arm64: Turn on KPTI only on CPUs that need it
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

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: Alex Shi <alex.shi@linaro.org> [v4.9 backport]
Signed-off-by: Mark Rutland <mark.rutland@arm.com> [v4.9 backport]
Tested-by: Will Deacon <will.deacon@arm.com>
Tested-by: Greg Hackmann <ghackmann@google.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
@@ -766,6 +766,13 @@ 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);

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