Patch "[Variant 2/Spectre-v2] arm64: Add skeleton to harden the branch predictor against aliasing attacks" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

[Variant 2/Spectre-v2] arm64: Add skeleton to harden the branch predictor against aliasing attacks

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
arm64-add-skeleton-to-harden-the-branch-predictor-against-aliasing-attacks.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Will Deacon <[email protected]>
Date: Wed, 3 Jan 2018 11:17:58 +0000
Subject: [Variant 2/Spectre-v2] arm64: Add skeleton to harden the branch predictor against aliasing attacks

From: Will Deacon <[email protected]>

Commit 0f15adbb2861 upstream.

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.

---
 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        |    8 ++--
 arch/arm64/mm/context.c          |    2 +
 arch/arm64/mm/fault.c            |   17 ++++++++
 11 files changed, 215 insertions(+), 4 deletions(-)
 create mode 100644 arch/arm64/kernel/bpi.S

@@ -818,6 +818,23 @@ 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

@@ -41,7 +41,8 @@
 #define ARM64_WORKAROUND_CAVIUM_30115		20
 #define ARM64_HAS_DCPOP				21
 #define ARM64_UNMAP_KERNEL_AT_EL0		23
+#define ARM64_HARDEN_BRANCH_PREDICTOR		24
 
-#define ARM64_NCAPS				24
+#define ARM64_NCAPS				25
 
 #endif /* __ASM_CPUCAPS_H */

@@ -41,6 +41,43 @@ static inline bool arm64_kernel_unmapped
 	       cpus_have_const_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_const_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);

@@ -333,6 +333,7 @@
 
 /* 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

@@ -55,6 +55,10 @@ arm64-obj-$(CONFIG_ARM64_RELOC_TEST)	+=
 arm64-reloc-test-y := reloc_test_core.o reloc_test_syms.o
 arm64-obj-$(CONFIG_CRASH_DUMP)		+= crash_dump.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

@@ -126,6 +126,7 @@ static const struct arm64_ftr_bits ftr_i
 
 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_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_CSV2_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),

@@ -724,13 +724,15 @@ el0_ia:
 	 * Instruction abort handling
 	 */
 	mrs	x26, far_el1
-	// enable interrupts before calling the main handler
-	enable_dbg_and_irq
+	enable_dbg
+#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:
 	/*

@@ -242,6 +242,8 @@ asmlinkage void post_ttbr_update_workaro
 			"ic iallu; dsb nsh; isb",
 			ARM64_WORKAROUND_CAVIUM_27456,
 			CONFIG_CAVIUM_ERRATUM_27456));
+
+	arm64_apply_bp_hardening();
 }
 
 static int asids_init(void)

@@ -751,6 +751,23 @@ asmlinkage void __exception do_mem_abort
 	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.
  */

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/arm64-make-user_ds-an-inclusive-limit.patch queue-4.14/arm64-mm-remove-pre_ttbr0_update_workaround-for-falkor-erratum-e1003.patch queue-4.14/arm64-uaccess-don-t-bother-eliding-access_ok-checks-in-__-get-put-_user.patch queue-4.14/arm64-cpufeature-pass-capability-structure-to-enable-callback.patch queue-4.14/arm64-uaccess-mask-__user-pointers-for-__arch_-clear-copy_-_user.patch queue-4.14/arm64-mm-add-arm64_kernel_unmapped_at_el0-helper.patch queue-4.14/arm64-entry-reword-comment-about-post_ttbr_update_workaround.patch queue-4.14/arm64-kaslr-put-kernel-vectors-address-in-separate-data-page.patch queue-4.14/arm-arm64-smccc-make-function-identifiers-an-unsigned-quantity.patch queue-4.14/arm64-move-bp-hardening-to-check_and_switch_context.patch queue-4.14/arm-arm64-kvm-advertise-smccc-v1.1.patch queue-4.14/arm64-move-post_ttbr_update_workaround-to-c-code.patch queue-4.14/arm64-turn-on-kpti-only-on-cpus-that-need-it.patch queue-4.14/firmware-psci-expose-psci-conduit.patch queue-4.14/arm64-force-kpti-to-be-disabled-on-cavium-thunderx.patch queue-4.14/arm64-entry-apply-bp-hardening-for-high-priority-synchronous-exceptions.patch queue-4.14/arm64-kpti-fix-the-interaction-between-asid-switching-and-software-pan.patch queue-4.14/firmware-psci-expose-smccc-version-through-psci_ops.patch queue-4.14/arm64-mm-permit-transitioning-from-global-to-non-global-without-bbm.patch queue-4.14/arm64-mm-allocate-asids-in-pairs.patch queue-4.14/arm64-tls-avoid-unconditional-zeroing-of-tpidrro_el0-for-native-tasks.patch queue-4.14/arm64-use-ret-instruction-for-exiting-the-trampoline.patch queue-4.14/arm64-futex-mask-__user-pointers-prior-to-dereference.patch queue-4.14/arm64-entry-explicitly-pass-exception-level-to-kernel_ventry-macro.patch queue-4.14/arm64-implement-branch-predictor-hardening-for-affected-cortex-a-cpus.patch queue-4.14/arm64-kpti-make-use-of-ng-dependent-on-arm64_kernel_unmapped_at_el0.patch queue-4.14/arm-arm64-kvm-add-psci_version-helper.patch queue-4.14/arm64-kill-psci_get_version-as-a-variant-2-workaround.patch queue-4.14/arm64-entry-ensure-branch-through-syscall-table-is-bounded-under-speculation.patch queue-4.14/arm64-mm-use-non-global-mappings-for-kernel-space.patch queue-4.14/arm64-entry-apply-bp-hardening-for-suspicious-interrupts-from-el0.patch queue-4.14/arm64-capabilities-handle-duplicate-entries-for-a-capability.patch queue-4.14/arm64-entry-hook-up-entry-trampoline-to-exception-vectors.patch queue-4.14/arm64-branch-predictor-hardening-for-cavium-thunderx2.patch queue-4.14/arm64-uaccess-prevent-speculative-use-of-the-current-addr_limit.patch queue-4.14/.arm64-add-software-workaround-for-falkor-erratum-1041.patch.swp queue-4.14/arm64-use-pointer-masking-to-limit-uaccess-speculation.patch queue-4.14/arm64-add-arm_smccc_arch_workaround_1-bp-hardening-support.patch queue-4.14/arm64-erratum-work-around-falkor-erratum-e1003-in-trampoline-code.patch queue-4.14/arm64-mm-fix-and-re-enable-arm64_sw_ttbr0_pan.patch queue-4.14/arm64-mm-invalidate-both-kernel-and-user-asids-when-performing-tlbi.patch queue-4.14/drivers-firmware-expose-psci_get_version-through-psci_ops-structure.patch queue-4.14/arm64-mm-rename-post_ttbr0_update_workaround.patch queue-4.14/arm64-mm-map-entry-trampoline-into-trampoline-and-kernel-page-tables.patch queue-4.14/arm-arm64-kvm-turn-kvm_psci_version-into-a-static-inline.patch queue-4.14/arm-arm64-kvm-implement-psci-1.0-support.patch queue-4.14/arm64-move-task_-definitions-to-asm-processor.h.patch queue-4.14/arm64-kconfig-reword-unmap_kernel_at_el0-kconfig-entry.patch queue-4.14/arm64-mm-move-asid-from-ttbr0-to-ttbr1.patch queue-4.14/arm64-mm-introduce-ttbr_asid_mask-for-getting-at-the-asid-in-the-ttbr.patch queue-4.14/arm64-kvm-add-smccc_arch_workaround_1-fast-handling.patch queue-4.14/arm64-take-into-account-id_aa64pfr0_el1.csv3.patch queue-4.14/arm64-cputype-add-missing-midr-values-for-cortex-a72-and-cortex-a75.patch queue-4.14/arm64-kvm-report-smccc_arch_workaround_1-bp-hardening-support.patch queue-4.14/arm64-barrier-add-csdb-macros-to-control-data-value-prediction.patch queue-4.14/arm-arm64-smccc-implement-smccc-v1.1-inline-primitive.patch queue-4.14/arm64-implement-branch-predictor-hardening-for-falkor.patch queue-4.14/arm64-kconfig-add-config_unmap_kernel_at_el0.patch queue-4.14/arm64-add-software-workaround-for-falkor-erratum-1041.patch queue-4.14/arm64-idmap-use-awx-flags-for-.idmap.text-.pushsection-directives.patch queue-4.14/arm64-run-enable-method-for-errata-work-arounds-on-late-cpus.patch queue-4.14/arm64-mm-temporarily-disable-arm64_sw_ttbr0_pan.patch queue-4.14/arm64-entry-add-exception-trampoline-page-for-exceptions-from-el0.patch queue-4.14/arm64-kvm-make-psci_version-a-fast-path.patch queue-4.14/arm64-cpufeature-__this_cpu_has_cap-shouldn-t-stop-early.patch queue-4.14/arm64-implement-array_index_mask_nospec.patch queue-4.14/arm64-kpti-add-enable-callback-to-remap-swapper-using-ng-mappings.patch queue-4.14/arm-arm64-kvm-consolidate-the-psci-include-files.patch queue-4.14/arm64-add-skeleton-to-harden-the-branch-predictor-against-aliasing-attacks.patch queue-4.14/arm64-define-cputype-macros-for-falkor-cpu.patch queue-4.14/arm64-cpu_errata-add-kryo-to-falkor-1003-errata.patch queue-4.14/arm-arm64-kvm-add-smccc-accessors-to-psci-code.patch queue-4.14/arm64-entry-add-fake-cpu-feature-for-unmapping-the-kernel-at-el0.patch queue-4.14/arm64-kvm-use-per-cpu-vector-when-bp-hardening-is-enabled.patch queue-4.14/arm64-cputype-add-midr-values-for-cavium-thunderx2-cpus.patch queue-4.14/arm64-kvm-increment-pc-after-handling-an-smc-trap.patch