From bbbb65770bf44d3eaec5b7784028756b58ea08db Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Mon, 16 Oct 2023 11:24:39 +0100 Subject: [PATCH] arm64: Avoid cpus_have_const_cap() for ARM64_HAS_BTI In system_supports_bti() we use cpus_have_const_cap() to check for ARM64_HAS_BTI, but this is not necessary and alternative_has_cap_*() or cpus_have_final_*cap() would be preferable. For historical reasons, cpus_have_const_cap() is more complicated than it needs to be. Before cpucaps are finalized, it will perform a bitmap test of the system_cpucaps bitmap, and once cpucaps are finalized it will use an alternative branch. This used to be necessary to handle some race conditions in the window between cpucap detection and the subsequent patching of alternatives and static branches, where different branches could be out-of-sync with one another (or w.r.t. alternative sequences). Now that we use alternative branches instead of static branches, these are all patched atomically w.r.t. one another, and there are only a handful of cases that need special care in the window between cpucap detection and alternative patching. Due to the above, it would be nice to remove cpus_have_const_cap(), and migrate callers over to alternative_has_cap_*(), cpus_have_final_cap(), or cpus_have_cap() depending on when their requirements. This will remove redundant instructions and improve code generation, and will make it easier to determine how each callsite will behave before, during, and after alternative patching. When CONFIG_ARM64_BTI_KERNEL=y, the ARM64_HAS_BTI cpucap is a strict boot cpu feature which is detected and patched early on the boot cpu. All uses guarded by CONFIG_ARM64_BTI_KERNEL happen after the boot CPU has detected ARM64_HAS_BTI and patched boot alternatives, and hence can safely use alternative_has_cap_*() or cpus_have_final_boot_cap(). Regardless of CONFIG_ARM64_BTI_KERNEL, all other uses of ARM64_HAS_BTI happen after system capabilities have been finalized and alternatives have been patched. Hence these can safely use alternative_has_cap_*) or cpus_have_final_cap(). This patch splits system_supports_bti() into system_supports_bti() and system_supports_bti_kernel(), with the former handling where the cpucap affects userspace functionality, and ther latter handling where the cpucap affects kernel functionality. The use of cpus_have_const_cap() is replaced by cpus_have_final_cap() in cpus_have_const_cap, and cpus_have_final_boot_cap() in system_supports_bti_kernel(). This will avoid generating code to test the system_cpucaps bitmap and should be better for all subsequent calls at runtime. The use of cpus_have_final_cap() and cpus_have_final_boot_cap() will make it easier to spot if code is chaanged such that these run before the ARM64_HAS_BTI cpucap is guaranteed to have been finalized. Signed-off-by: Mark Rutland Reviewed-by: Mark Brown Cc: Ard Biesheuvel Cc: Suzuki K Poulose Cc: Will Deacon Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/cpufeature.h | 8 +++++++- arch/arm64/include/asm/pgtable-prot.h | 6 +----- arch/arm64/kernel/efi.c | 3 +-- arch/arm64/kernel/vdso.c | 2 +- arch/arm64/kvm/hyp/pgtable.c | 2 +- 5 files changed, 11 insertions(+), 10 deletions(-) diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index dfdedbdcc115..caa54ddf0bcd 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -837,7 +837,13 @@ static inline bool system_has_prio_mask_debugging(void) static inline bool system_supports_bti(void) { - return cpus_have_const_cap(ARM64_BTI); + return cpus_have_final_cap(ARM64_BTI); +} + +static inline bool system_supports_bti_kernel(void) +{ + return IS_ENABLED(CONFIG_ARM64_BTI_KERNEL) && + cpus_have_final_boot_cap(ARM64_BTI); } static inline bool system_supports_tlb_range(void) diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h index eed814b00a38..e9624f6326dd 100644 --- a/arch/arm64/include/asm/pgtable-prot.h +++ b/arch/arm64/include/asm/pgtable-prot.h @@ -75,11 +75,7 @@ extern bool arm64_use_ng_mappings; * If we have userspace only BTI we don't want to mark kernel pages * guarded even if the system does support BTI. */ -#ifdef CONFIG_ARM64_BTI_KERNEL -#define PTE_MAYBE_GP (system_supports_bti() ? PTE_GP : 0) -#else -#define PTE_MAYBE_GP 0 -#endif +#define PTE_MAYBE_GP (system_supports_bti_kernel() ? PTE_GP : 0) #define PAGE_KERNEL __pgprot(_PAGE_KERNEL) #define PAGE_KERNEL_RO __pgprot(_PAGE_KERNEL_RO) diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c index 2b478ca356b0..3f8c9c143552 100644 --- a/arch/arm64/kernel/efi.c +++ b/arch/arm64/kernel/efi.c @@ -113,8 +113,7 @@ static int __init set_permissions(pte_t *ptep, unsigned long addr, void *data) pte = set_pte_bit(pte, __pgprot(PTE_RDONLY)); if (md->attribute & EFI_MEMORY_XP) pte = set_pte_bit(pte, __pgprot(PTE_PXN)); - else if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL) && - system_supports_bti() && spd->has_bti) + else if (system_supports_bti_kernel() && spd->has_bti) pte = set_pte_bit(pte, __pgprot(PTE_GP)); set_pte(ptep, pte); return 0; diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c index d9e1355730ef..5562daf38a22 100644 --- a/arch/arm64/kernel/vdso.c +++ b/arch/arm64/kernel/vdso.c @@ -212,7 +212,7 @@ static int __setup_additional_pages(enum vdso_abi abi, if (IS_ERR(ret)) goto up_fail; - if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL) && system_supports_bti()) + if (system_supports_bti_kernel()) gp_flags = VM_ARM64_BTI; vdso_base += VVAR_NR_PAGES * PAGE_SIZE; diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index 799d2c204bb8..77fb330c7bf4 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -401,7 +401,7 @@ static int hyp_set_prot_attr(enum kvm_pgtable_prot prot, kvm_pte_t *ptep) if (device) return -EINVAL; - if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL) && system_supports_bti()) + if (system_supports_bti_kernel()) attr |= KVM_PTE_LEAF_ATTR_HI_S1_GP; } else { attr |= KVM_PTE_LEAF_ATTR_HI_S1_XN; -- 2.25.1