Aliasing attacks against CPU branch predictors can allow an attacker to redirect speculative control flow on some CPUs and potentially divulge information from one context to another.
This patch adds initial skeleton code behind a new Kconfig option to enable implementation-specific mitigations against these attacks for CPUs that are affected.
Co-developed-by: Marc Zyngier marc.zyngier@arm.com Signed-off-by: Will Deacon will.deacon@arm.com (cherry picked from commit 7bd293b6845d003ab087faa6515a626c8703b8da) Signed-off-by: Alex Shi alex.shi@linaro.org
Conflicts: expand enable_da_f in entry.S use 5 parameters ARM64_FTR_BITS() add percpu.h in mm_types.h for percpu functions use cpus_have_cap instead of cpus_have_const_cap arch/arm64/include/asm/cpucaps.h arch/arm64/include/asm/sysreg.h arch/arm64/kernel/cpufeature.c arch/arm64/kernel/entry.S arch/arm64/mm/context.c arch/arm64/mm/fault.c --- arch/arm64/Kconfig | 17 +++++++++ arch/arm64/include/asm/cpucaps.h | 3 +- arch/arm64/include/asm/mmu.h | 37 ++++++++++++++++++++ arch/arm64/include/asm/sysreg.h | 1 + arch/arm64/kernel/Makefile | 4 +++ arch/arm64/kernel/bpi.S | 55 +++++++++++++++++++++++++++++ arch/arm64/kernel/cpu_errata.c | 74 ++++++++++++++++++++++++++++++++++++++++ arch/arm64/kernel/cpufeature.c | 1 + arch/arm64/kernel/entry.S | 7 ++-- arch/arm64/mm/context.c | 2 ++ arch/arm64/mm/fault.c | 16 +++++++++ include/linux/mm_types.h | 1 + 12 files changed, 215 insertions(+), 3 deletions(-) create mode 100644 arch/arm64/kernel/bpi.S
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index d7a516c..7c2d5ea 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -745,6 +745,23 @@ config UNMAP_KERNEL_AT_EL0
If unsure, say Y.
+config HARDEN_BRANCH_PREDICTOR + bool "Harden the branch predictor against aliasing attacks" if EXPERT + default y + help + Speculation attacks against some high-performance processors rely on + being able to manipulate the branch predictor for a victim context by + executing aliasing branches in the attacker context. Such attacks + can be partially mitigated against by clearing internal branch + predictor state and limiting the prediction logic in some situations. + + This config option will take CPU-specific actions to harden the + branch predictor against aliasing attacks and may rely on specific + instruction sequences or control bits being set by the system + firmware. + + If unsure, say Y. + menuconfig ARMV8_DEPRECATED bool "Emulate deprecated/obsolete ARMv8 instructions" depends on COMPAT diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h index ec601db2..bb99b7f 100644 --- a/arch/arm64/include/asm/cpucaps.h +++ b/arch/arm64/include/asm/cpucaps.h @@ -35,6 +35,7 @@ #define ARM64_HYP_OFFSET_LOW 14 #define ARM64_MISMATCHED_CACHE_LINE_SIZE 15 #define ARM64_UNMAP_KERNEL_AT_EL0 16 -#define ARM64_NCAPS 17 +#define ARM64_HARDEN_BRANCH_PREDICTOR 17 +#define ARM64_NCAPS 18
#endif /* __ASM_CPUCAPS_H */ diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h index 32d3a6f..57cdbce 100644 --- a/arch/arm64/include/asm/mmu.h +++ b/arch/arm64/include/asm/mmu.h @@ -38,6 +38,43 @@ static inline bool arm64_kernel_unmapped_at_el0(void) cpus_have_cap(ARM64_UNMAP_KERNEL_AT_EL0); }
+typedef void (*bp_hardening_cb_t)(void); + +struct bp_hardening_data { + int hyp_vectors_slot; + bp_hardening_cb_t fn; +}; + +#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR +extern char __bp_harden_hyp_vecs_start[], __bp_harden_hyp_vecs_end[]; + +DECLARE_PER_CPU_READ_MOSTLY(struct bp_hardening_data, bp_hardening_data); + +static inline struct bp_hardening_data *arm64_get_bp_hardening_data(void) +{ + return this_cpu_ptr(&bp_hardening_data); +} + +static inline void arm64_apply_bp_hardening(void) +{ + struct bp_hardening_data *d; + + if (!cpus_have_cap(ARM64_HARDEN_BRANCH_PREDICTOR)) + return; + + d = arm64_get_bp_hardening_data(); + if (d->fn) + d->fn(); +} +#else +static inline struct bp_hardening_data *arm64_get_bp_hardening_data(void) +{ + return NULL; +} + +static inline void arm64_apply_bp_hardening(void) { } +#endif /* CONFIG_HARDEN_BRANCH_PREDICTOR */ + extern void paging_init(void); extern void bootmem_init(void); extern void __iomem *early_io_map(phys_addr_t phys, unsigned long virt); diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h index 7cb7f7c..a692209 100644 --- a/arch/arm64/include/asm/sysreg.h +++ b/arch/arm64/include/asm/sysreg.h @@ -118,6 +118,7 @@
/* id_aa64pfr0 */ #define ID_AA64PFR0_CSV3_SHIFT 60 +#define ID_AA64PFR0_CSV2_SHIFT 56 #define ID_AA64PFR0_GIC_SHIFT 24 #define ID_AA64PFR0_ASIMD_SHIFT 20 #define ID_AA64PFR0_FP_SHIFT 16 diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index 7d66bba..74b8fd8 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -51,6 +51,10 @@ arm64-obj-$(CONFIG_HIBERNATION) += hibernate.o hibernate-asm.o arm64-obj-$(CONFIG_KEXEC) += machine_kexec.o relocate_kernel.o \ cpu-reset.o
+ifeq ($(CONFIG_KVM),y) +arm64-obj-$(CONFIG_HARDEN_BRANCH_PREDICTOR) += bpi.o +endif + obj-y += $(arm64-obj-y) vdso/ probes/ obj-m += $(arm64-obj-m) head-y := head.o diff --git a/arch/arm64/kernel/bpi.S b/arch/arm64/kernel/bpi.S new file mode 100644 index 0000000..06a931e --- /dev/null +++ b/arch/arm64/kernel/bpi.S @@ -0,0 +1,55 @@ +/* + * Contains CPU specific branch predictor invalidation sequences + * + * Copyright (C) 2018 ARM Ltd. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program. If not, see http://www.gnu.org/licenses/. + */ + +#include <linux/linkage.h> + +.macro ventry target + .rept 31 + nop + .endr + b \target +.endm + +.macro vectors target + ventry \target + 0x000 + ventry \target + 0x080 + ventry \target + 0x100 + ventry \target + 0x180 + + ventry \target + 0x200 + ventry \target + 0x280 + ventry \target + 0x300 + ventry \target + 0x380 + + ventry \target + 0x400 + ventry \target + 0x480 + ventry \target + 0x500 + ventry \target + 0x580 + + ventry \target + 0x600 + ventry \target + 0x680 + ventry \target + 0x700 + ventry \target + 0x780 +.endm + + .align 11 +ENTRY(__bp_harden_hyp_vecs_start) + .rept 4 + vectors __kvm_hyp_vector + .endr +ENTRY(__bp_harden_hyp_vecs_end) diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c index c66a673c..75ad384 100644 --- a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c @@ -46,6 +46,80 @@ static int cpu_enable_trap_ctr_access(void *__unused) return 0; }
+#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR +#include <asm/mmu_context.h> +#include <asm/cacheflush.h> + +DEFINE_PER_CPU_READ_MOSTLY(struct bp_hardening_data, bp_hardening_data); + +#ifdef CONFIG_KVM +static void __copy_hyp_vect_bpi(int slot, const char *hyp_vecs_start, + const char *hyp_vecs_end) +{ + void *dst = lm_alias(__bp_harden_hyp_vecs_start + slot * SZ_2K); + int i; + + for (i = 0; i < SZ_2K; i += 0x80) + memcpy(dst + i, hyp_vecs_start, hyp_vecs_end - hyp_vecs_start); + + flush_icache_range((uintptr_t)dst, (uintptr_t)dst + SZ_2K); +} + +static void __install_bp_hardening_cb(bp_hardening_cb_t fn, + const char *hyp_vecs_start, + const char *hyp_vecs_end) +{ + static int last_slot = -1; + static DEFINE_SPINLOCK(bp_lock); + int cpu, slot = -1; + + spin_lock(&bp_lock); + for_each_possible_cpu(cpu) { + if (per_cpu(bp_hardening_data.fn, cpu) == fn) { + slot = per_cpu(bp_hardening_data.hyp_vectors_slot, cpu); + break; + } + } + + if (slot == -1) { + last_slot++; + BUG_ON(((__bp_harden_hyp_vecs_end - __bp_harden_hyp_vecs_start) + / SZ_2K) <= last_slot); + slot = last_slot; + __copy_hyp_vect_bpi(slot, hyp_vecs_start, hyp_vecs_end); + } + + __this_cpu_write(bp_hardening_data.hyp_vectors_slot, slot); + __this_cpu_write(bp_hardening_data.fn, fn); + spin_unlock(&bp_lock); +} +#else +static void __install_bp_hardening_cb(bp_hardening_cb_t fn, + const char *hyp_vecs_start, + const char *hyp_vecs_end) +{ + __this_cpu_write(bp_hardening_data.fn, fn); +} +#endif /* CONFIG_KVM */ + +static void install_bp_hardening_cb(const struct arm64_cpu_capabilities *entry, + bp_hardening_cb_t fn, + const char *hyp_vecs_start, + const char *hyp_vecs_end) +{ + u64 pfr0; + + if (!entry->matches(entry, SCOPE_LOCAL_CPU)) + return; + + pfr0 = read_cpuid(ID_AA64PFR0_EL1); + if (cpuid_feature_extract_unsigned_field(pfr0, ID_AA64PFR0_CSV2_SHIFT)) + return; + + __install_bp_hardening_cb(fn, hyp_vecs_start, hyp_vecs_end); +} +#endif /* CONFIG_HARDEN_BRANCH_PREDICTOR */ + #define MIDR_RANGE(model, min, max) \ .def_scope = SCOPE_LOCAL_CPU, \ .matches = is_affected_midr_range, \ diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index a77fb5b..fbbf65f 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -99,6 +99,7 @@ static const struct arm64_ftr_bits ftr_id_aa64pfr0[] = { S_ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_ASIMD_SHIFT, 4, ID_AA64PFR0_ASIMD_NI), S_ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_FP_SHIFT, 4, ID_AA64PFR0_FP_NI), ARM64_FTR_BITS(FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_CSV3_SHIFT, 4, 0), + ARM64_FTR_BITS(FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_CSV2_SHIFT, 4, 0), /* Linux doesn't care about the EL3 */ ARM64_FTR_BITS(FTR_NONSTRICT, FTR_EXACT, ID_AA64PFR0_EL3_SHIFT, 4, 0), ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64PFR0_EL2_SHIFT, 4, 0), diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 074c402..bd39713 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -589,12 +589,15 @@ el0_ia: */ mrs x26, far_el1 // enable interrupts before calling the main handler - enable_dbg_and_irq + msr daifclr, #(8 | 4 | 1) +#ifdef CONFIG_TRACE_IRQFLAGS + bl trace_hardirqs_off +#endif ct_user_exit mov x0, x26 mov x1, x25 mov x2, sp - bl do_mem_abort + bl do_el0_ia_bp_hardening b ret_to_user el0_fpsimd_acc: /* diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c index b9b0875..accf7ea 100644 --- a/arch/arm64/mm/context.c +++ b/arch/arm64/mm/context.c @@ -240,6 +240,8 @@ asmlinkage void post_ttbr_update_workaround(void) "ic iallu; dsb nsh; isb", ARM64_WORKAROUND_CAVIUM_27456, CONFIG_CAVIUM_ERRATUM_27456)); + + arm64_apply_bp_hardening(); }
static int asids_init(void) diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 403fe9e..8e7e54d 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -590,6 +590,22 @@ asmlinkage void __exception do_mem_abort(unsigned long addr, unsigned int esr, arm64_notify_die("", regs, &info, esr); }
+asmlinkage void __exception do_el0_ia_bp_hardening(unsigned long addr, + unsigned int esr, + struct pt_regs *regs) +{ + /* + * We've taken an instruction abort from userspace and not yet + * re-enabled IRQs. If the address is a kernel address, apply + * BP hardening prior to enabling IRQs and pre-emption. + */ + if (addr > TASK_SIZE) + arm64_apply_bp_hardening(); + + local_irq_enable(); + do_mem_abort(addr, esr, regs); +} + /* * Handle stack alignment exceptions. */ diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index e8471c2..15a82f3 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -13,6 +13,7 @@ #include <linux/uprobes.h> #include <linux/page-flags-layout.h> #include <linux/workqueue.h> +#include <linux/percpu.h> #include <asm/page.h> #include <asm/mmu.h>