@@ -1421,6 +1421,21 @@ config ARM64_PTR_AUTH
endmenu
+menu "ARMv8.5 architectural features"
+
+config ARM64_E0PD
+ bool "Enable support for E0PD"
+ default y
+ help
+ E0PD (part of the ARMv8.5 extensions) allows us to ensure
+ that EL0 accesses made via TTBR1 always fault in constant time,
+ providing benefits to KPTI with lower overhead and without
+ disrupting legitimate access to kernel memory such as SPE.
+
+ This option enables E0PD for TTBR1 where available.
+
+endmenu
+
config ARM64_SVE
bool "ARM Scalable Vector Extension support"
default y
@@ -52,7 +52,8 @@
#define ARM64_HAS_IRQ_PRIO_MASKING 42
#define ARM64_HAS_DCPODP 43
#define ARM64_WORKAROUND_1463225 44
+#define ARM64_HAS_E0PD 45
-#define ARM64_NCAPS 45
+#define ARM64_NCAPS 46
#endif /* __ASM_CPUCAPS_H */
@@ -292,6 +292,8 @@
#define TCR_HD (UL(1) << 40)
#define TCR_NFD0 (UL(1) << 53)
#define TCR_NFD1 (UL(1) << 54)
+#define TCR_E0PD0 (UL(1) << 55)
+#define TCR_E0PD1 (UL(1) << 56)
/*
* TTBR.
@@ -655,6 +655,7 @@
#define ID_AA64MMFR1_VMIDBITS_16 2
/* id_aa64mmfr2 */
+#define ID_AA64MMFR2_E0PD_SHIFT 60
#define ID_AA64MMFR2_FWB_SHIFT 40
#define ID_AA64MMFR2_AT_SHIFT 32
#define ID_AA64MMFR2_LVA_SHIFT 16
@@ -220,6 +220,7 @@ static const struct arm64_ftr_bits ftr_id_aa64mmfr1[] = {
};
static const struct arm64_ftr_bits ftr_id_aa64mmfr2[] = {
+ ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64MMFR2_E0PD_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64MMFR2_FWB_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64MMFR2_AT_SHIFT, 4, 0),
ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64MMFR2_LVA_SHIFT, 4, 0),
@@ -1245,6 +1246,19 @@ static void cpu_enable_address_auth(struct arm64_cpu_capabilities const *cap)
}
#endif /* CONFIG_ARM64_PTR_AUTH */
+#ifdef CONFIG_ARM64_E0PD
+static void cpu_enable_e0pd(struct arm64_cpu_capabilities const *cap)
+{
+ /*
+ * The cpu_enable() callback gets called even on CPUs that
+ * don't detect the feature so we need to verify if we can
+ * enable.
+ */
+ if (this_cpu_has_cap(ARM64_HAS_E0PD))
+ sysreg_clear_set(tcr_el1, 0, TCR_E0PD1);
+}
+#endif /* CONFIG_ARM64_E0PD */
+
#ifdef CONFIG_ARM64_PSEUDO_NMI
static bool enable_pseudo_nmi;
@@ -1560,6 +1574,19 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.sign = FTR_UNSIGNED,
.min_field_value = 1,
},
+#endif
+#ifdef CONFIG_ARM64_E0PD
+ {
+ .desc = "E0PD",
+ .capability = ARM64_HAS_E0PD,
+ .type = ARM64_CPUCAP_SYSTEM_FEATURE,
+ .sys_reg = SYS_ID_AA64MMFR2_EL1,
+ .sign = FTR_UNSIGNED,
+ .field_pos = ID_AA64MMFR2_E0PD_SHIFT,
+ .matches = has_cpuid_feature,
+ .min_field_value = 1,
+ .cpu_enable = cpu_enable_e0pd,
+ },
#endif
{},
};
Kernel Page Table Isolation (KPTI) is used to mitigate some speculation based security issues by ensuring that the kernel is not mapped when userspace is running but this approach is expensive and is incompatible with SPE. E0PD, introduced in the ARMv8.5 extensions, provides an alternative to this which ensures that accesses from userspace to the kernel's half of the memory map to always fault with constant time, preventing timing attacks without requiring constant unmapping and remapping or preventing legitimate accesses. Currently this feature will only be enabled if all CPUs in the system support E0PD, if some CPUs do not support the feature at boot time then the feature will not be enabled and in the unlikely event that a late CPU is the first CPU to lack the feature then we will reject that CPU. This initial patch does not yet integrate with KPTI, this will be dealt with in followup patches. Ideally we could ensure that by default we don't use KPTI on CPUs where E0PD is present. Signed-off-by: Mark Brown <broonie@kernel.org> --- arch/arm64/Kconfig | 15 ++++++++++++++ arch/arm64/include/asm/cpucaps.h | 3 ++- arch/arm64/include/asm/pgtable-hwdef.h | 2 ++ arch/arm64/include/asm/sysreg.h | 1 + arch/arm64/kernel/cpufeature.c | 27 ++++++++++++++++++++++++++ 5 files changed, 47 insertions(+), 1 deletion(-)