From: James Morse <james.morse@xxxxxxx> commit 228a26b912287934789023b4132ba76065d9491c upstream. Future CPUs may implement a clearbhb instruction that is sufficient to mitigate SpectreBHB. CPUs that implement this instruction, but not CSV2.3 must be affected by Spectre-BHB. Add support to use this instruction as the BHB mitigation on CPUs that support it. The instruction is in the hint space, so it will be treated by a NOP as older CPUs. Reviewed-by: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx> Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx> [ modified for stable: Use a KVM vector template instead of alternatives ] Signed-off-by: James Morse <james.morse@xxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/arm64/include/asm/assembler.h | 7 +++++++ arch/arm64/include/asm/cpufeature.h | 13 +++++++++++++ arch/arm64/include/asm/sysreg.h | 3 +++ arch/arm64/include/asm/vectors.h | 7 +++++++ arch/arm64/kernel/bpi.S | 5 +++++ arch/arm64/kernel/cpu_errata.c | 14 ++++++++++++++ arch/arm64/kernel/cpufeature.c | 1 + arch/arm64/kernel/entry.S | 8 ++++++++ 8 files changed, 58 insertions(+) --- a/arch/arm64/include/asm/assembler.h +++ b/arch/arm64/include/asm/assembler.h @@ -104,6 +104,13 @@ .endm /* + * Clear Branch History instruction + */ + .macro clearbhb + hint #22 + .endm + +/* * Sanitise a 64-bit bounded index wrt speculation, returning zero if out * of bounds. */ --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -471,6 +471,19 @@ static inline bool supports_csv2p3(int s return csv2_val == 3; } +static inline bool supports_clearbhb(int scope) +{ + u64 isar2; + + if (scope == SCOPE_LOCAL_CPU) + isar2 = read_sysreg_s(SYS_ID_AA64ISAR2_EL1); + else + isar2 = read_sanitised_ftr_reg(SYS_ID_AA64ISAR2_EL1); + + return cpuid_feature_extract_unsigned_field(isar2, + ID_AA64ISAR2_CLEARBHB_SHIFT); +} + static inline bool system_supports_32bit_el0(void) { return cpus_have_const_cap(ARM64_HAS_32BIT_EL0); --- a/arch/arm64/include/asm/sysreg.h +++ b/arch/arm64/include/asm/sysreg.h @@ -404,6 +404,9 @@ #define ID_AA64ISAR1_JSCVT_SHIFT 12 #define ID_AA64ISAR1_DPB_SHIFT 0 +/* id_aa64isar2 */ +#define ID_AA64ISAR2_CLEARBHB_SHIFT 28 + /* id_aa64pfr0 */ #define ID_AA64PFR0_CSV3_SHIFT 60 #define ID_AA64PFR0_CSV2_SHIFT 56 --- a/arch/arm64/include/asm/vectors.h +++ b/arch/arm64/include/asm/vectors.h @@ -33,6 +33,12 @@ enum arm64_bp_harden_el1_vectors { * canonical vectors. */ EL1_VECTOR_BHB_FW, + + /* + * Use the ClearBHB instruction, before branching to the canonical + * vectors. + */ + EL1_VECTOR_BHB_CLEAR_INSN, #endif /* CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY */ /* @@ -44,6 +50,7 @@ enum arm64_bp_harden_el1_vectors { #ifndef CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY #define EL1_VECTOR_BHB_LOOP -1 #define EL1_VECTOR_BHB_FW -1 +#define EL1_VECTOR_BHB_CLEAR_INSN -1 #endif /* !CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY */ /* The vectors to use on return from EL0. e.g. to remap the kernel */ --- a/arch/arm64/kernel/bpi.S +++ b/arch/arm64/kernel/bpi.S @@ -116,3 +116,8 @@ ENTRY(__spectre_bhb_loop_k32_start) ldp x0, x1, [sp, #(8 * 0)] add sp, sp, #(8 * 2) ENTRY(__spectre_bhb_loop_k32_end) + +ENTRY(__spectre_bhb_clearbhb_start) + hint #22 /* aka clearbhb */ + isb +ENTRY(__spectre_bhb_clearbhb_end) --- a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c @@ -94,6 +94,8 @@ extern char __spectre_bhb_loop_k24_start extern char __spectre_bhb_loop_k24_end[]; extern char __spectre_bhb_loop_k32_start[]; extern char __spectre_bhb_loop_k32_end[]; +extern char __spectre_bhb_clearbhb_start[]; +extern char __spectre_bhb_clearbhb_end[]; static void __copy_hyp_vect_bpi(int slot, const char *hyp_vecs_start, const char *hyp_vecs_end) @@ -826,6 +828,7 @@ static void update_mitigation_state(enum * - Mitigated by a branchy loop a CPU specific number of times, and listed * in our "loop mitigated list". * - Mitigated in software by the firmware Spectre v2 call. + * - Has the ClearBHB instruction to perform the mitigation. * - Has the 'Exception Clears Branch History Buffer' (ECBHB) feature, so no * software mitigation in the vectors is needed. * - Has CSV2.3, so is unaffected. @@ -965,6 +968,9 @@ bool is_spectre_bhb_affected(const struc if (supports_csv2p3(scope)) return false; + if (supports_clearbhb(scope)) + return true; + if (spectre_bhb_loop_affected(scope)) return true; @@ -1005,6 +1011,8 @@ static const char *kvm_bhb_get_vecs_end( return __spectre_bhb_loop_k24_end; else if (start == __spectre_bhb_loop_k32_start) return __spectre_bhb_loop_k32_end; + else if (start == __spectre_bhb_clearbhb_start) + return __spectre_bhb_clearbhb_end; return NULL; } @@ -1046,6 +1054,7 @@ static void kvm_setup_bhb_slot(const cha #define __spectre_bhb_loop_k8_start NULL #define __spectre_bhb_loop_k24_start NULL #define __spectre_bhb_loop_k32_start NULL +#define __spectre_bhb_clearbhb_start NULL static void kvm_setup_bhb_slot(const char *hyp_vecs_start) { }; #endif @@ -1065,6 +1074,11 @@ void spectre_bhb_enable_mitigation(const pr_info_once("spectre-bhb mitigation disabled by command line option\n"); } else if (supports_ecbhb(SCOPE_LOCAL_CPU)) { state = SPECTRE_MITIGATED; + } else if (supports_clearbhb(SCOPE_LOCAL_CPU)) { + kvm_setup_bhb_slot(__spectre_bhb_clearbhb_start); + this_cpu_set_vectors(EL1_VECTOR_BHB_CLEAR_INSN); + + state = SPECTRE_MITIGATED; } else if (spectre_bhb_loop_affected(SCOPE_LOCAL_CPU)) { switch (spectre_bhb_loop_affected(SCOPE_SYSTEM)) { case 8: --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -135,6 +135,7 @@ static const struct arm64_ftr_bits ftr_i }; static const struct arm64_ftr_bits ftr_id_aa64isar2[] = { + ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_HIGHER_SAFE, ID_AA64ISAR2_CLEARBHB_SHIFT, 4, 0), ARM64_FTR_END, }; --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -1033,6 +1033,7 @@ alternative_else_nop_endif #define BHB_MITIGATION_NONE 0 #define BHB_MITIGATION_LOOP 1 #define BHB_MITIGATION_FW 2 +#define BHB_MITIGATION_INSN 3 .macro tramp_ventry, vector_start, regsize, kpti, bhb .align 7 @@ -1049,6 +1050,11 @@ alternative_else_nop_endif __mitigate_spectre_bhb_loop x30 .endif // \bhb == BHB_MITIGATION_LOOP + .if \bhb == BHB_MITIGATION_INSN + clearbhb + isb + .endif // \bhb == BHB_MITIGATION_INSN + .if \kpti == 1 /* * Defend against branch aliasing attacks by pushing a dummy @@ -1125,6 +1131,7 @@ ENTRY(tramp_vectors) #ifdef CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY generate_tramp_vector kpti=1, bhb=BHB_MITIGATION_LOOP generate_tramp_vector kpti=1, bhb=BHB_MITIGATION_FW + generate_tramp_vector kpti=1, bhb=BHB_MITIGATION_INSN #endif /* CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY */ generate_tramp_vector kpti=1, bhb=BHB_MITIGATION_NONE END(tramp_vectors) @@ -1187,6 +1194,7 @@ ENTRY(__bp_harden_el1_vectors) #ifdef CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY generate_el1_vector bhb=BHB_MITIGATION_LOOP generate_el1_vector bhb=BHB_MITIGATION_FW + generate_el1_vector bhb=BHB_MITIGATION_INSN #endif /* CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY */ END(__bp_harden_el1_vectors) .popsection Patches currently in stable-queue which might be from james.morse@xxxxxxx are queue-4.14/arm64-entry-add-macro-for-reading-symbol-addresses-from-the-trampoline.patch queue-4.14/arm64-use-the-clearbhb-instruction-in-mitigations.patch queue-4.14/arm64-add-percpu-vectors-for-el1.patch queue-4.14/arm64-arch_timer-add-workaround-for-arm-erratum-1188873.patch queue-4.14/arm64-entry-free-up-another-register-on-kpti-s-tramp_exit-path.patch queue-4.14/arm64-entry-don-t-assume-tramp_vectors-is-the-start-of-the-vectors.patch queue-4.14/arm64-entry-make-the-trampoline-cleanup-optional.patch queue-4.14/arm64-add-silicon-errata.txt-entry-for-arm-erratum-1188873.patch queue-4.14/kvm-arm64-add-templates-for-bhb-mitigation-sequences.patch queue-4.14/arm64-entry-add-non-kpti-__bp_harden_el1_vectors-for-mitigations.patch queue-4.14/arm64-add-id_aa64isar2_el1-sys-register.patch queue-4.14/kvm-arm64-allow-smccc_arch_workaround_3-to-be-discovered-and-migrated.patch queue-4.14/arm64-add-neoverse-n2-cortex-a710-cpu-part-definition.patch queue-4.14/arm64-arch_timer-avoid-unused-function-warning.patch queue-4.14/arm64-entry-move-trampoline-macros-out-of-ifdef-d-section.patch queue-4.14/arm64-entry-allow-tramp_alias-to-access-symbols-after-the-4k-boundary.patch queue-4.14/arm64-add-part-number-for-arm-cortex-a77.patch queue-4.14/arm64-entry-move-the-trampoline-data-page-before-the-text-page.patch queue-4.14/arm64-entry.s-add-ventry-overflow-sanity-checks.patch queue-4.14/arm64-add-part-number-for-neoverse-n1.patch queue-4.14/arm64-entry-add-vectors-that-have-the-bhb-mitigation-sequences.patch queue-4.14/arm64-make-arm64_erratum_1188873-depend-on-compat.patch queue-4.14/arm64-mitigate-spectre-style-branch-history-side-channels.patch queue-4.14/arm64-entry-allow-the-trampoline-text-to-occupy-multiple-pages.patch queue-4.14/arm64-proton-pack-report-spectre-bhb-vulnerabilities-as-part-of-spectre-v2.patch queue-4.14/arm64-add-cortex-x2-cpu-part-definition.patch queue-4.14/arm64-entry-make-the-kpti-trampoline-s-kpti-sequence-optional.patch