From 2ccb89d411f0382059a5ec4c382b4ce633906335 Mon Sep 17 00:00:00 2001
From: Will Deacon <will.deacon@arm.com>
Date: Mon, 27 Nov 2017 18:29:30 +0000
Subject: [PATCH 08/24] arm64: Take into account ID_AA64PFR0_EL1.CSV3

Git-commit: 179a56f6f9fbda28f6ca07db1fc3dfad6bc7343c
Patch-mainline: Queued
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
References: bsc#1068032

For non-KASLR kernels where the KPTI behaviour has not been overridden
on the command line we can use ID_AA64PFR0_EL1.CSV3 to determine whether
or not we should unmap the kernel whilst running at EL0.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@suse.com>
---
 arch/arm64/include/asm/sysreg.h | 1 +
 arch/arm64/kernel/cpufeature.c  | 8 +++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index b4d13d9267ff..1849f621b397 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -314,6 +314,7 @@
 #define ID_AA64ISAR1_JSCVT_SHIFT	12
 
 /* id_aa64pfr0 */
+#define ID_AA64PFR0_CSV3_SHIFT		60
 #define ID_AA64PFR0_GIC_SHIFT		24
 #define ID_AA64PFR0_ASIMD_SHIFT		20
 #define ID_AA64PFR0_FP_SHIFT		16
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 188fd56d0da6..aa7c79c30531 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -105,6 +105,7 @@ static const struct arm64_ftr_bits ftr_id_aa64isar1[] = {
 };
 
 static const struct arm64_ftr_bits ftr_id_aa64pfr0[] = {
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_CSV3_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64PFR0_GIC_SHIFT, 4, 0),
 	S_ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_ASIMD_SHIFT, 4, ID_AA64PFR0_ASIMD_NI),
 	S_ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_FP_SHIFT, 4, ID_AA64PFR0_FP_NI),
@@ -780,6 +781,8 @@ 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)
 {
+	u64 pfr0 = read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1);
+
 	/* Forced on command line? */
 	if (__kpti_forced) {
 		pr_info_once("kernel page table isolation forced %s by command line option\n",
@@ -791,7 +794,9 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
 	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE))
 		return true;
 
-	return false;
+	/* Defer to CPU feature registers */
+	return !cpuid_feature_extract_unsigned_field(pfr0,
+						     ID_AA64PFR0_CSV3_SHIFT);
 }
 
 static int __init parse_kpti(char *str)
@@ -896,6 +901,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 	},
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
 	{
+		.desc = "Kernel page table isolation (KPTI)",
 		.capability = ARM64_UNMAP_KERNEL_AT_EL0,
 		.def_scope = SCOPE_SYSTEM,
 		.matches = unmap_kernel_at_el0,
-- 
2.11.0