linux-kernel - [PATCH 10/16] arm64: Make KPTI strict CPU local feature

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Date:   Tue, 23 Jan 2018 12:28:03 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, ard.biesheuvel@...aro.org,
        will.deacon@....com, mark.rutland@....com, marc.zyngier@....com,
        catalin.marinas@....com, ckadabi@...eaurora.org,
        jnair@...iumnetworks.com, Suzuki K Poulose <suzuki.poulose@....com>
Subject: [PATCH 10/16] arm64: Make KPTI strict CPU local feature

KPTI capability is a security feature which should be enabled
when at least one CPU on the system needs it. Any late CPU
which needs the kernel support, should be prevented from
booting (and thus making the system unsecure) if the feature
was not already enabled.

Cc: Will Deacon <will.deacon@....com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
---
 arch/arm64/kernel/cpufeature.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 111f6c4b4cd7..2627a836e99d 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -862,9 +862,8 @@ static bool has_no_fpsimd(const struct arm64_cpu_capabilities *entry, int __unus
 static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */
 
 static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
-				int __unused)
+				int scope)
 {
-	u64 pfr0 = read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1);
 
 	/* Forced on command line? */
 	if (__kpti_forced) {
@@ -878,8 +877,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
 		return true;
 
 	/* Defer to CPU feature registers */
-	return !cpuid_feature_extract_unsigned_field(pfr0,
-						     ID_AA64PFR0_CSV3_SHIFT);
+	return !has_cpuid_feature(entry, scope);
 }
 
 static int __init parse_kpti(char *str)
@@ -1003,7 +1001,10 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 	{
 		.desc = "Kernel page table isolation (KPTI)",
 		.capability = ARM64_UNMAP_KERNEL_AT_EL0,
-		.type = ARM64_CPUCAP_BOOT_SYSTEM_FEATURE,
+		.type = ARM64_CPUCAP_STRICT_CPU_LOCAL_FEATURE,
+		.sys_reg = SYS_ID_AA64PFR0_EL1,
+		.field_pos = ID_AA64PFR0_CSV3_SHIFT,
+		.min_field_value = 1,
 		.matches = unmap_kernel_at_el0,
 	},
 #endif
-- 
2.13.6