From 3e6c69a058deaa50d33c3dac36cde80b4ce590e8 Mon Sep 17 00:00:00 2001 From: Mark Brown Date: Mon, 9 Dec 2019 18:12:14 +0000 Subject: [PATCH] arm64: Add initial support for E0PD 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 Reviewed-by: Suzuki K Poulose [will: Fixed typo in Kconfig text] Signed-off-by: Will Deacon --- arch/arm64/Kconfig | 16 ++++++++++++++++ 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 | 22 ++++++++++++++++++++++ 5 files changed, 43 insertions(+), 1 deletion(-) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index b1b4476ddb83..9cee2008ea9e 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -1484,6 +1484,22 @@ 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 similar benefits to KASLR as those provided by KPTI, but + 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 diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h index b92683871119..33ff25c1ab1b 100644 --- a/arch/arm64/include/asm/cpucaps.h +++ b/arch/arm64/include/asm/cpucaps.h @@ -56,7 +56,8 @@ #define ARM64_WORKAROUND_CAVIUM_TX2_219_PRFM 46 #define ARM64_WORKAROUND_1542419 47 #define ARM64_WORKAROUND_1319367 48 +#define ARM64_HAS_E0PD 49 -#define ARM64_NCAPS 49 +#define ARM64_NCAPS 50 #endif /* __ASM_CPUCAPS_H */ diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h index d9fbd433cc17..378566f4882e 100644 --- a/arch/arm64/include/asm/pgtable-hwdef.h +++ b/arch/arm64/include/asm/pgtable-hwdef.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. diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h index 6e919fafb43d..b085258cfe4e 100644 --- a/arch/arm64/include/asm/sysreg.h +++ b/arch/arm64/include/asm/sysreg.h @@ -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 diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 04cf64e9f0c9..9d578e720168 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -225,6 +225,7 @@ 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), @@ -1251,6 +1252,14 @@ 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) +{ + 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; @@ -1566,6 +1575,19 @@ 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 {}, }; -- 2.30.2