[PATCH v4 04/12] arm64: remove the ability to build a kernel without hardened branch predictors

[Jeremy Linton <jeremy.linton@arm.com>]

Buried behind EXPERT is the ability to build a kernel without
hardened branch predictors, this needlessly clutters up the
code as well as creates the opportunity for bugs. It also
removes the kernel's ability to determine if the machine its
running on is vulnerable.

Since its also possible to disable it at boot time, lets remove
the config option.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Cc: Christoffer Dall <christoffer.dall@arm.com>
Cc: kvmarm@lists.cs.columbia.edu
---
 arch/arm64/Kconfig               | 17 -----------------
 arch/arm64/include/asm/kvm_mmu.h | 12 ------------
 arch/arm64/include/asm/mmu.h     | 12 ------------
 arch/arm64/kernel/cpu_errata.c   | 19 -------------------
 arch/arm64/kernel/entry.S        |  2 --
 arch/arm64/kvm/Kconfig           |  3 ---
 arch/arm64/kvm/hyp/hyp-entry.S   |  2 --
 7 files changed, 67 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 0baa632bf0a8..6b4c6d3fdf4d 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1005,23 +1005,6 @@ 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.
-
 config HARDEN_EL2_VECTORS
 	bool "Harden EL2 vector mapping against system register leak" if EXPERT
 	default y
diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index a5c152d79820..9dd680194db9 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -444,7 +444,6 @@ static inline int kvm_read_guest_lock(struct kvm *kvm,
 	return ret;
 }
 
-#ifdef CONFIG_KVM_INDIRECT_VECTORS
 /*
  * EL2 vectors can be mapped and rerouted in a number of ways,
  * depending on the kernel configuration and CPU present:
@@ -529,17 +528,6 @@ static inline int kvm_map_vectors(void)
 
 	return 0;
 }
-#else
-static inline void *kvm_get_hyp_vector(void)
-{
-	return kern_hyp_va(kvm_ksym_ref(__kvm_hyp_vector));
-}
-
-static inline int kvm_map_vectors(void)
-{
-	return 0;
-}
-#endif
 
 DECLARE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required);
 
diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
index 3e8063f4f9d3..20fdf71f96c3 100644
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -95,13 +95,9 @@ struct bp_hardening_data {
 	bp_hardening_cb_t	fn;
 };
 
-#if (defined(CONFIG_HARDEN_BRANCH_PREDICTOR) ||	\
-     defined(CONFIG_HARDEN_EL2_VECTORS))
 extern char __bp_harden_hyp_vecs_start[], __bp_harden_hyp_vecs_end[];
 extern atomic_t arm64_el2_vector_last_slot;
-#endif  /* CONFIG_HARDEN_BRANCH_PREDICTOR || CONFIG_HARDEN_EL2_VECTORS */
 
-#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
 DECLARE_PER_CPU_READ_MOSTLY(struct bp_hardening_data, bp_hardening_data);
 
 static inline struct bp_hardening_data *arm64_get_bp_hardening_data(void)
@@ -120,14 +116,6 @@ static inline void arm64_apply_bp_hardening(void)
 	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);
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 934d50788ca3..de09a3537cd4 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -109,13 +109,11 @@ cpu_enable_trap_ctr_access(const struct arm64_cpu_capabilities *__unused)
 
 atomic_t arm64_el2_vector_last_slot = ATOMIC_INIT(-1);
 
-#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_INDIRECT_VECTORS
 extern char __smccc_workaround_1_smc_start[];
 extern char __smccc_workaround_1_smc_end[];
 
@@ -165,17 +163,6 @@ static void __install_bp_hardening_cb(bp_hardening_cb_t fn,
 	__this_cpu_write(bp_hardening_data.fn, fn);
 	raw_spin_unlock(&bp_lock);
 }
-#else
-#define __smccc_workaround_1_smc_start		NULL
-#define __smccc_workaround_1_smc_end		NULL
-
-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_INDIRECT_VECTORS */
 
 static void  install_bp_hardening_cb(const struct arm64_cpu_capabilities *entry,
 				     bp_hardening_cb_t fn,
@@ -279,7 +266,6 @@ enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
 
 	return;
 }
-#endif	/* CONFIG_HARDEN_BRANCH_PREDICTOR */
 
 DEFINE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required);
 
@@ -516,7 +502,6 @@ cpu_enable_cache_maint_trap(const struct arm64_cpu_capabilities *__unused)
 	.type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM,			\
 	CAP_MIDR_RANGE_LIST(midr_list)
 
-#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
 
 /*
  * List of CPUs where we need to issue a psci call to
@@ -535,8 +520,6 @@ static const struct midr_range arm64_bp_harden_smccc_cpus[] = {
 	{},
 };
 
-#endif
-
 #ifdef CONFIG_HARDEN_EL2_VECTORS
 
 static const struct midr_range arm64_harden_el2_vectors[] = {
@@ -710,13 +693,11 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 		ERRATA_MIDR_ALL_VERSIONS(MIDR_CORTEX_A73),
 	},
 #endif
-#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
 	{
 		.capability = ARM64_HARDEN_BRANCH_PREDICTOR,
 		.cpu_enable = enable_smccc_arch_workaround_1,
 		ERRATA_MIDR_RANGE_LIST(arm64_bp_harden_smccc_cpus),
 	},
-#endif
 #ifdef CONFIG_HARDEN_EL2_VECTORS
 	{
 		.desc = "EL2 vector hardening",
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index bee54b7d17b9..3f0eaaf704c8 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -842,11 +842,9 @@ el0_irq_naked:
 #endif
 
 	ct_user_exit
-#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
 	tbz	x22, #55, 1f
 	bl	do_el0_irq_bp_hardening
 1:
-#endif
 	irq_handler
 
 #ifdef CONFIG_TRACE_IRQFLAGS
diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
index a3f85624313e..402bcfb85f25 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig
@@ -58,9 +58,6 @@ config KVM_ARM_PMU
 	  Adds support for a virtual Performance Monitoring Unit (PMU) in
 	  virtual machines.
 
-config KVM_INDIRECT_VECTORS
-       def_bool KVM && (HARDEN_BRANCH_PREDICTOR || HARDEN_EL2_VECTORS)
-
 source "drivers/vhost/Kconfig"
 
 endif # VIRTUALIZATION
diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index 53c9344968d4..e02ddf40f113 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -272,7 +272,6 @@ ENTRY(__kvm_hyp_vector)
 	valid_vect	el1_error		// Error 32-bit EL1
 ENDPROC(__kvm_hyp_vector)
 
-#ifdef CONFIG_KVM_INDIRECT_VECTORS
 .macro hyp_ventry
 	.align 7
 1:	.rept 27
@@ -331,4 +330,3 @@ ENTRY(__smccc_workaround_1_smc_start)
 	ldp	x0, x1, [sp, #(8 * 2)]
 	add	sp, sp, #(8 * 4)
 ENTRY(__smccc_workaround_1_smc_end)
-#endif
-- 
2.17.2