1 # SPDX-License-Identifier: GPL-2.0
3 # General architecture dependent options
7 # Note: arch/$(SRCARCH)/Kconfig needs to be included first so that it can
8 # override the default values in this file.
10 source "arch/$(SRCARCH)/Kconfig"
12 menu "General architecture-dependent options"
14 config ARCH_HAS_SUBPAGE_FAULTS
17 Select if the architecture can check permissions at sub-page
18 granularity (e.g. arm64 MTE). The probe_user_*() functions
24 config SMT_NUM_THREADS_DYNAMIC
27 # Selected by HOTPLUG_CORE_SYNC_DEAD or HOTPLUG_CORE_SYNC_FULL
28 config HOTPLUG_CORE_SYNC
31 # Basic CPU dead synchronization selected by architecture
32 config HOTPLUG_CORE_SYNC_DEAD
34 select HOTPLUG_CORE_SYNC
36 # Full CPU synchronization with alive state selected by architecture
37 config HOTPLUG_CORE_SYNC_FULL
39 select HOTPLUG_CORE_SYNC_DEAD if HOTPLUG_CPU
40 select HOTPLUG_CORE_SYNC
42 config HOTPLUG_SPLIT_STARTUP
44 select HOTPLUG_CORE_SYNC_FULL
46 config HOTPLUG_PARALLEL
48 select HOTPLUG_SPLIT_STARTUP
56 depends on HAVE_KPROBES
58 select TASKS_RCU if PREEMPTION
60 Kprobes allows you to trap at almost any kernel address and
61 execute a callback function. register_kprobe() establishes
62 a probepoint and specifies the callback. Kprobes is useful
63 for kernel debugging, non-intrusive instrumentation and testing.
67 bool "Optimize very unlikely/likely branches"
68 depends on HAVE_ARCH_JUMP_LABEL
69 select OBJTOOL if HAVE_JUMP_LABEL_HACK
71 This option enables a transparent branch optimization that
72 makes certain almost-always-true or almost-always-false branch
73 conditions even cheaper to execute within the kernel.
75 Certain performance-sensitive kernel code, such as trace points,
76 scheduler functionality, networking code and KVM have such
77 branches and include support for this optimization technique.
79 If it is detected that the compiler has support for "asm goto",
80 the kernel will compile such branches with just a nop
81 instruction. When the condition flag is toggled to true, the
82 nop will be converted to a jump instruction to execute the
83 conditional block of instructions.
85 This technique lowers overhead and stress on the branch prediction
86 of the processor and generally makes the kernel faster. The update
87 of the condition is slower, but those are always very rare.
89 ( On 32-bit x86, the necessary options added to the compiler
90 flags may increase the size of the kernel slightly. )
92 config STATIC_KEYS_SELFTEST
93 bool "Static key selftest"
96 Boot time self-test of the branch patching code.
98 config STATIC_CALL_SELFTEST
99 bool "Static call selftest"
100 depends on HAVE_STATIC_CALL
102 Boot time self-test of the call patching code.
106 depends on KPROBES && HAVE_OPTPROBES
107 select TASKS_RCU if PREEMPTION
109 config KPROBES_ON_FTRACE
111 depends on KPROBES && HAVE_KPROBES_ON_FTRACE
112 depends on DYNAMIC_FTRACE_WITH_REGS
114 If function tracer is enabled and the arch supports full
115 passing of pt_regs to function tracing, then kprobes can
116 optimize on top of function tracing.
120 depends on ARCH_SUPPORTS_UPROBES
122 Uprobes is the user-space counterpart to kprobes: they
123 enable instrumentation applications (such as 'perf probe')
124 to establish unintrusive probes in user-space binaries and
125 libraries, by executing handler functions when the probes
126 are hit by user-space applications.
128 ( These probes come in the form of single-byte breakpoints,
129 managed by the kernel and kept transparent to the probed
132 config HAVE_64BIT_ALIGNED_ACCESS
133 def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
135 Some architectures require 64 bit accesses to be 64 bit
136 aligned, which also requires structs containing 64 bit values
137 to be 64 bit aligned too. This includes some 32 bit
138 architectures which can do 64 bit accesses, as well as 64 bit
139 architectures without unaligned access.
141 This symbol should be selected by an architecture if 64 bit
142 accesses are required to be 64 bit aligned in this way even
143 though it is not a 64 bit architecture.
145 See Documentation/core-api/unaligned-memory-access.rst for
146 more information on the topic of unaligned memory accesses.
148 config HAVE_EFFICIENT_UNALIGNED_ACCESS
151 Some architectures are unable to perform unaligned accesses
152 without the use of get_unaligned/put_unaligned. Others are
153 unable to perform such accesses efficiently (e.g. trap on
154 unaligned access and require fixing it up in the exception
157 This symbol should be selected by an architecture if it can
158 perform unaligned accesses efficiently to allow different
159 code paths to be selected for these cases. Some network
160 drivers, for example, could opt to not fix up alignment
161 problems with received packets if doing so would not help
164 See Documentation/core-api/unaligned-memory-access.rst for more
165 information on the topic of unaligned memory accesses.
167 config ARCH_USE_BUILTIN_BSWAP
170 Modern versions of GCC (since 4.4) have builtin functions
171 for handling byte-swapping. Using these, instead of the old
172 inline assembler that the architecture code provides in the
173 __arch_bswapXX() macros, allows the compiler to see what's
174 happening and offers more opportunity for optimisation. In
175 particular, the compiler will be able to combine the byteswap
176 with a nearby load or store and use load-and-swap or
177 store-and-swap instructions if the architecture has them. It
178 should almost *never* result in code which is worse than the
179 hand-coded assembler in <asm/swab.h>. But just in case it
180 does, the use of the builtins is optional.
182 Any architecture with load-and-swap or store-and-swap
183 instructions should set this. And it shouldn't hurt to set it
184 on architectures that don't have such instructions.
188 depends on KPROBES && (HAVE_KRETPROBES || HAVE_RETHOOK)
190 config KRETPROBE_ON_RETHOOK
192 depends on HAVE_RETHOOK
193 depends on KRETPROBES
196 config USER_RETURN_NOTIFIER
198 depends on HAVE_USER_RETURN_NOTIFIER
200 Provide a kernel-internal notification when a cpu is about to
203 config HAVE_IOREMAP_PROT
209 config HAVE_KRETPROBES
212 config HAVE_OPTPROBES
215 config HAVE_KPROBES_ON_FTRACE
218 config ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
221 Since kretprobes modifies return address on the stack, the
222 stacktrace may see the kretprobe trampoline address instead
223 of correct one. If the architecture stacktrace code and
224 unwinder can adjust such entries, select this configuration.
226 config HAVE_FUNCTION_ERROR_INJECTION
232 config HAVE_FUNCTION_DESCRIPTORS
235 config TRACE_IRQFLAGS_SUPPORT
238 config TRACE_IRQFLAGS_NMI_SUPPORT
242 # An arch should select this if it provides all these things:
244 # task_pt_regs() in asm/processor.h or asm/ptrace.h
245 # arch_has_single_step() if there is hardware single-step support
246 # arch_has_block_step() if there is hardware block-step support
247 # asm/syscall.h supplying asm-generic/syscall.h interface
248 # linux/regset.h user_regset interfaces
249 # CORE_DUMP_USE_REGSET #define'd in linux/elf.h
250 # TIF_SYSCALL_TRACE calls ptrace_report_syscall_{entry,exit}
251 # TIF_NOTIFY_RESUME calls resume_user_mode_work()
253 config HAVE_ARCH_TRACEHOOK
256 config HAVE_DMA_CONTIGUOUS
259 config GENERIC_SMP_IDLE_THREAD
262 config GENERIC_IDLE_POLL_SETUP
265 config ARCH_HAS_FORTIFY_SOURCE
268 An architecture should select this when it can successfully
269 build and run with CONFIG_FORTIFY_SOURCE.
272 # Select if the arch provides a historic keepinit alias for the retain_initrd
273 # command line option
275 config ARCH_HAS_KEEPINITRD
278 # Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
279 config ARCH_HAS_SET_MEMORY
282 # Select if arch has all set_direct_map_invalid/default() functions
283 config ARCH_HAS_SET_DIRECT_MAP
287 # Select if the architecture provides the arch_dma_set_uncached symbol to
288 # either provide an uncached segment alias for a DMA allocation, or
289 # to remap the page tables in place.
291 config ARCH_HAS_DMA_SET_UNCACHED
295 # Select if the architectures provides the arch_dma_clear_uncached symbol
296 # to undo an in-place page table remap for uncached access.
298 config ARCH_HAS_DMA_CLEAR_UNCACHED
301 config ARCH_HAS_CPU_FINALIZE_INIT
304 # The architecture has a per-task state that includes the mm's PASID
305 config ARCH_HAS_CPU_PASID
309 config HAVE_ARCH_THREAD_STRUCT_WHITELIST
312 An architecture should select this to provide hardened usercopy
313 knowledge about what region of the thread_struct should be
314 whitelisted for copying to userspace. Normally this is only the
315 FPU registers. Specifically, arch_thread_struct_whitelist()
316 should be implemented. Without this, the entire thread_struct
317 field in task_struct will be left whitelisted.
319 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
320 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
323 config ARCH_WANTS_NO_INSTR
326 An architecture should select this if the noinstr macro is being used on
327 functions to denote that the toolchain should avoid instrumenting such
328 functions and is required for correctness.
330 config ARCH_32BIT_OFF_T
334 All new 32-bit architectures should have 64-bit off_t type on
335 userspace side which corresponds to the loff_t kernel type. This
336 is the requirement for modern ABIs. Some existing architectures
337 still support 32-bit off_t. This option is enabled for all such
338 architectures explicitly.
340 # Selected by 64 bit architectures which have a 32 bit f_tinode in struct ustat
341 config ARCH_32BIT_USTAT_F_TINODE
344 config HAVE_ASM_MODVERSIONS
347 This symbol should be selected by an architecture if it provides
348 <asm/asm-prototypes.h> to support the module versioning for symbols
349 exported from assembly code.
351 config HAVE_REGS_AND_STACK_ACCESS_API
354 This symbol should be selected by an architecture if it supports
355 the API needed to access registers and stack entries from pt_regs,
356 declared in asm/ptrace.h
357 For example the kprobes-based event tracer needs this API.
361 depends on HAVE_REGS_AND_STACK_ACCESS_API
363 This symbol should be selected by an architecture if it
364 supports an implementation of restartable sequences.
369 This symbol should be selected by an architecture if it
372 config HAVE_FUNCTION_ARG_ACCESS_API
375 This symbol should be selected by an architecture if it supports
376 the API needed to access function arguments from pt_regs,
377 declared in asm/ptrace.h
379 config HAVE_HW_BREAKPOINT
381 depends on PERF_EVENTS
383 config HAVE_MIXED_BREAKPOINTS_REGS
385 depends on HAVE_HW_BREAKPOINT
387 Depending on the arch implementation of hardware breakpoints,
388 some of them have separate registers for data and instruction
389 breakpoints addresses, others have mixed registers to store
390 them but define the access type in a control register.
391 Select this option if your arch implements breakpoints under the
394 config HAVE_USER_RETURN_NOTIFIER
397 config HAVE_PERF_EVENTS_NMI
400 System hardware can generate an NMI using the perf event
401 subsystem. Also has support for calculating CPU cycle events
402 to determine how many clock cycles in a given period.
404 config HAVE_HARDLOCKUP_DETECTOR_PERF
406 depends on HAVE_PERF_EVENTS_NMI
408 The arch chooses to use the generic perf-NMI-based hardlockup
409 detector. Must define HAVE_PERF_EVENTS_NMI.
411 config HAVE_HARDLOCKUP_DETECTOR_ARCH
414 The arch provides its own hardlockup detector implementation instead
417 It uses the same command line parameters, and sysctl interface,
418 as the generic hardlockup detectors.
420 config HAVE_PERF_REGS
423 Support selective register dumps for perf events. This includes
424 bit-mapping of each registers and a unique architecture id.
426 config HAVE_PERF_USER_STACK_DUMP
429 Support user stack dumps for perf event samples. This needs
430 access to the user stack pointer which is not unified across
433 config HAVE_ARCH_JUMP_LABEL
436 config HAVE_ARCH_JUMP_LABEL_RELATIVE
439 config MMU_GATHER_TABLE_FREE
442 config MMU_GATHER_RCU_TABLE_FREE
444 select MMU_GATHER_TABLE_FREE
446 config MMU_GATHER_PAGE_SIZE
449 config MMU_GATHER_NO_RANGE
451 select MMU_GATHER_MERGE_VMAS
453 config MMU_GATHER_NO_FLUSH_CACHE
456 config MMU_GATHER_MERGE_VMAS
459 config MMU_GATHER_NO_GATHER
461 depends on MMU_GATHER_TABLE_FREE
463 config ARCH_WANT_IRQS_OFF_ACTIVATE_MM
466 Temporary select until all architectures can be converted to have
467 irqs disabled over activate_mm. Architectures that do IPI based TLB
468 shootdowns should enable this.
470 # Use normal mm refcounting for MMU_LAZY_TLB kernel thread references.
471 # MMU_LAZY_TLB_REFCOUNT=n can improve the scalability of context switching
472 # to/from kernel threads when the same mm is running on a lot of CPUs (a large
473 # multi-threaded application), by reducing contention on the mm refcount.
475 # This can be disabled if the architecture ensures no CPUs are using an mm as a
476 # "lazy tlb" beyond its final refcount (i.e., by the time __mmdrop frees the mm
477 # or its kernel page tables). This could be arranged by arch_exit_mmap(), or
478 # final exit(2) TLB flush, for example.
480 # To implement this, an arch *must*:
481 # Ensure the _lazy_tlb variants of mmgrab/mmdrop are used when manipulating
482 # the lazy tlb reference of a kthread's ->active_mm (non-arch code has been
483 # converted already).
484 config MMU_LAZY_TLB_REFCOUNT
486 depends on !MMU_LAZY_TLB_SHOOTDOWN
488 # This option allows MMU_LAZY_TLB_REFCOUNT=n. It ensures no CPUs are using an
489 # mm as a lazy tlb beyond its last reference count, by shooting down these
490 # users before the mm is deallocated. __mmdrop() first IPIs all CPUs that may
491 # be using the mm as a lazy tlb, so that they may switch themselves to using
492 # init_mm for their active mm. mm_cpumask(mm) is used to determine which CPUs
493 # may be using mm as a lazy tlb mm.
495 # To implement this, an arch *must*:
496 # - At the time of the final mmdrop of the mm, ensure mm_cpumask(mm) contains
497 # at least all possible CPUs in which the mm is lazy.
498 # - It must meet the requirements for MMU_LAZY_TLB_REFCOUNT=n (see above).
499 config MMU_LAZY_TLB_SHOOTDOWN
502 config ARCH_HAVE_NMI_SAFE_CMPXCHG
505 config ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
508 config HAVE_ALIGNED_STRUCT_PAGE
511 This makes sure that struct pages are double word aligned and that
512 e.g. the SLUB allocator can perform double word atomic operations
513 on a struct page for better performance. However selecting this
514 might increase the size of a struct page by a word.
516 config HAVE_CMPXCHG_LOCAL
519 config HAVE_CMPXCHG_DOUBLE
522 config ARCH_WEAK_RELEASE_ACQUIRE
525 config ARCH_WANT_IPC_PARSE_VERSION
528 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
531 config ARCH_WANT_OLD_COMPAT_IPC
532 select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
535 config HAVE_ARCH_SECCOMP
538 An arch should select this symbol to support seccomp mode 1 (the fixed
539 syscall policy), and must provide an overrides for __NR_seccomp_sigreturn,
540 and compat syscalls if the asm-generic/seccomp.h defaults need adjustment:
541 - __NR_seccomp_read_32
542 - __NR_seccomp_write_32
543 - __NR_seccomp_exit_32
544 - __NR_seccomp_sigreturn_32
546 config HAVE_ARCH_SECCOMP_FILTER
548 select HAVE_ARCH_SECCOMP
550 An arch should select this symbol if it provides all of these things:
551 - all the requirements for HAVE_ARCH_SECCOMP
553 - syscall_get_arguments()
555 - syscall_set_return_value()
556 - SIGSYS siginfo_t support
557 - secure_computing is called from a ptrace_event()-safe context
558 - secure_computing return value is checked and a return value of -1
559 results in the system call being skipped immediately.
560 - seccomp syscall wired up
561 - if !HAVE_SPARSE_SYSCALL_NR, have SECCOMP_ARCH_NATIVE,
562 SECCOMP_ARCH_NATIVE_NR, SECCOMP_ARCH_NATIVE_NAME defined. If
563 COMPAT is supported, have the SECCOMP_ARCH_COMPAT* defines too.
566 prompt "Enable seccomp to safely execute untrusted bytecode"
568 depends on HAVE_ARCH_SECCOMP
570 This kernel feature is useful for number crunching applications
571 that may need to handle untrusted bytecode during their
572 execution. By using pipes or other transports made available
573 to the process as file descriptors supporting the read/write
574 syscalls, it's possible to isolate those applications in their
575 own address space using seccomp. Once seccomp is enabled via
576 prctl(PR_SET_SECCOMP) or the seccomp() syscall, it cannot be
577 disabled and the task is only allowed to execute a few safe
578 syscalls defined by each seccomp mode.
582 config SECCOMP_FILTER
584 depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
586 Enable tasks to build secure computing environments defined
587 in terms of Berkeley Packet Filter programs which implement
588 task-defined system call filtering polices.
590 See Documentation/userspace-api/seccomp_filter.rst for details.
592 config SECCOMP_CACHE_DEBUG
593 bool "Show seccomp filter cache status in /proc/pid/seccomp_cache"
594 depends on SECCOMP_FILTER && !HAVE_SPARSE_SYSCALL_NR
597 This enables the /proc/pid/seccomp_cache interface to monitor
598 seccomp cache data. The file format is subject to change. Reading
599 the file requires CAP_SYS_ADMIN.
601 This option is for debugging only. Enabling presents the risk that
602 an adversary may be able to infer the seccomp filter logic.
606 config HAVE_ARCH_STACKLEAK
609 An architecture should select this if it has the code which
610 fills the used part of the kernel stack with the STACKLEAK_POISON
611 value before returning from system calls.
613 config HAVE_STACKPROTECTOR
616 An arch should select this symbol if:
617 - it has implemented a stack canary (e.g. __stack_chk_guard)
619 config STACKPROTECTOR
620 bool "Stack Protector buffer overflow detection"
621 depends on HAVE_STACKPROTECTOR
622 depends on $(cc-option,-fstack-protector)
625 This option turns on the "stack-protector" GCC feature. This
626 feature puts, at the beginning of functions, a canary value on
627 the stack just before the return address, and validates
628 the value just before actually returning. Stack based buffer
629 overflows (that need to overwrite this return address) now also
630 overwrite the canary, which gets detected and the attack is then
631 neutralized via a kernel panic.
633 Functions will have the stack-protector canary logic added if they
634 have an 8-byte or larger character array on the stack.
636 This feature requires gcc version 4.2 or above, or a distribution
637 gcc with the feature backported ("-fstack-protector").
639 On an x86 "defconfig" build, this feature adds canary checks to
640 about 3% of all kernel functions, which increases kernel code size
643 config STACKPROTECTOR_STRONG
644 bool "Strong Stack Protector"
645 depends on STACKPROTECTOR
646 depends on $(cc-option,-fstack-protector-strong)
649 Functions will have the stack-protector canary logic added in any
650 of the following conditions:
652 - local variable's address used as part of the right hand side of an
653 assignment or function argument
654 - local variable is an array (or union containing an array),
655 regardless of array type or length
656 - uses register local variables
658 This feature requires gcc version 4.9 or above, or a distribution
659 gcc with the feature backported ("-fstack-protector-strong").
661 On an x86 "defconfig" build, this feature adds canary checks to
662 about 20% of all kernel functions, which increases the kernel code
665 config ARCH_SUPPORTS_SHADOW_CALL_STACK
668 An architecture should select this if it supports the compiler's
669 Shadow Call Stack and implements runtime support for shadow stack
672 config SHADOW_CALL_STACK
673 bool "Shadow Call Stack"
674 depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
675 depends on DYNAMIC_FTRACE_WITH_ARGS || DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
677 This option enables the compiler's Shadow Call Stack, which
678 uses a shadow stack to protect function return addresses from
679 being overwritten by an attacker. More information can be found
680 in the compiler's documentation:
682 - Clang: https://clang.llvm.org/docs/ShadowCallStack.html
683 - GCC: https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html#Instrumentation-Options
685 Note that security guarantees in the kernel differ from the
686 ones documented for user space. The kernel must store addresses
687 of shadow stacks in memory, which means an attacker capable of
688 reading and writing arbitrary memory may be able to locate them
689 and hijack control flow by modifying the stacks.
694 Set by the arch code if it relies on code patching to insert the
695 shadow call stack push and pop instructions rather than on the
701 Selected if the kernel will be built using the compiler's LTO feature.
707 Selected if the kernel will be built using Clang's LTO feature.
709 config ARCH_SUPPORTS_LTO_CLANG
712 An architecture should select this option if it supports:
713 - compiling with Clang,
714 - compiling inline assembly with Clang's integrated assembler,
715 - and linking with LLD.
717 config ARCH_SUPPORTS_LTO_CLANG_THIN
720 An architecture should select this option if it can support Clang's
725 depends on CC_IS_CLANG && LD_IS_LLD && AS_IS_LLVM
726 depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
727 depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
728 depends on ARCH_SUPPORTS_LTO_CLANG
729 depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT
730 # https://github.com/ClangBuiltLinux/linux/issues/1721
731 depends on (!KASAN || KASAN_HW_TAGS || CLANG_VERSION >= 170000) || !DEBUG_INFO
732 depends on (!KCOV || CLANG_VERSION >= 170000) || !DEBUG_INFO
733 depends on !GCOV_KERNEL
735 The compiler and Kconfig options support building with Clang's
739 prompt "Link Time Optimization (LTO)"
742 This option enables Link Time Optimization (LTO), which allows the
743 compiler to optimize binaries globally.
745 If unsure, select LTO_NONE. Note that LTO is very resource-intensive
746 so it's disabled by default.
751 Build the kernel normally, without Link Time Optimization (LTO).
753 config LTO_CLANG_FULL
754 bool "Clang Full LTO (EXPERIMENTAL)"
755 depends on HAS_LTO_CLANG
756 depends on !COMPILE_TEST
759 This option enables Clang's full Link Time Optimization (LTO), which
760 allows the compiler to optimize the kernel globally. If you enable
761 this option, the compiler generates LLVM bitcode instead of ELF
762 object files, and the actual compilation from bitcode happens at
763 the LTO link step, which may take several minutes depending on the
764 kernel configuration. More information can be found from LLVM's
767 https://llvm.org/docs/LinkTimeOptimization.html
769 During link time, this option can use a large amount of RAM, and
770 may take much longer than the ThinLTO option.
772 config LTO_CLANG_THIN
773 bool "Clang ThinLTO (EXPERIMENTAL)"
774 depends on HAS_LTO_CLANG && ARCH_SUPPORTS_LTO_CLANG_THIN
777 This option enables Clang's ThinLTO, which allows for parallel
778 optimization and faster incremental compiles compared to the
779 CONFIG_LTO_CLANG_FULL option. More information can be found
780 from Clang's documentation:
782 https://clang.llvm.org/docs/ThinLTO.html
787 config ARCH_SUPPORTS_CFI_CLANG
790 An architecture should select this option if it can support Clang's
791 Control-Flow Integrity (CFI) checking.
793 config ARCH_USES_CFI_TRAPS
797 bool "Use Clang's Control Flow Integrity (CFI)"
798 depends on ARCH_SUPPORTS_CFI_CLANG
799 depends on $(cc-option,-fsanitize=kcfi)
801 This option enables Clang’s forward-edge Control Flow Integrity
802 (CFI) checking, where the compiler injects a runtime check to each
803 indirect function call to ensure the target is a valid function with
804 the correct static type. This restricts possible call targets and
805 makes it more difficult for an attacker to exploit bugs that allow
806 the modification of stored function pointers. More information can be
807 found from Clang's documentation:
809 https://clang.llvm.org/docs/ControlFlowIntegrity.html
811 config CFI_PERMISSIVE
812 bool "Use CFI in permissive mode"
815 When selected, Control Flow Integrity (CFI) violations result in a
816 warning instead of a kernel panic. This option should only be used
817 for finding indirect call type mismatches during development.
821 config HAVE_ARCH_WITHIN_STACK_FRAMES
824 An architecture should select this if it can walk the kernel stack
825 frames to determine if an object is part of either the arguments
826 or local variables (i.e. that it excludes saved return addresses,
827 and similar) by implementing an inline arch_within_stack_frames(),
828 which is used by CONFIG_HARDENED_USERCOPY.
830 config HAVE_CONTEXT_TRACKING_USER
833 Provide kernel/user boundaries probes necessary for subsystems
834 that need it, such as userspace RCU extended quiescent state.
835 Syscalls need to be wrapped inside user_exit()-user_enter(), either
836 optimized behind static key or through the slow path using TIF_NOHZ
837 flag. Exceptions handlers must be wrapped as well. Irqs are already
838 protected inside ct_irq_enter/ct_irq_exit() but preemption or signal
839 handling on irq exit still need to be protected.
841 config HAVE_CONTEXT_TRACKING_USER_OFFSTACK
844 Architecture neither relies on exception_enter()/exception_exit()
845 nor on schedule_user(). Also preempt_schedule_notrace() and
846 preempt_schedule_irq() can't be called in a preemptible section
847 while context tracking is CONTEXT_USER. This feature reflects a sane
848 entry implementation where the following requirements are met on
849 critical entry code, ie: before user_exit() or after user_enter():
851 - Critical entry code isn't preemptible (or better yet:
853 - No use of RCU read side critical sections, unless ct_nmi_enter()
855 - No use of instrumentation, unless instrumentation_begin() got
861 Arch relies on TIF_NOHZ and syscall slow path to implement context
862 tracking calls to user_enter()/user_exit().
864 config HAVE_VIRT_CPU_ACCOUNTING
867 config HAVE_VIRT_CPU_ACCOUNTING_IDLE
870 Architecture has its own way to account idle CPU time and therefore
871 doesn't implement vtime_account_idle().
873 config ARCH_HAS_SCALED_CPUTIME
876 config HAVE_VIRT_CPU_ACCOUNTING_GEN
880 With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
881 Before enabling this option, arch code must be audited
882 to ensure there are no races in concurrent read/write of
883 cputime_t. For example, reading/writing 64-bit cputime_t on
884 some 32-bit arches may require multiple accesses, so proper
885 locking is needed to protect against concurrent accesses.
887 config HAVE_IRQ_TIME_ACCOUNTING
890 Archs need to ensure they use a high enough resolution clock to
891 support irq time accounting and then call enable_sched_clock_irqtime().
896 Architectures that select this are able to move page tables at the
897 PUD level. If there are only 3 page table levels, the move effectively
898 happens at the PGD level.
903 Archs that select this are able to move page tables at the PMD level.
905 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
908 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
911 config HAVE_ARCH_HUGE_VMAP
915 # Archs that select this would be capable of PMD-sized vmaps (i.e.,
916 # arch_vmap_pmd_supported() returns true). The VM_ALLOW_HUGE_VMAP flag
917 # must be used to enable allocations to use hugepages.
919 config HAVE_ARCH_HUGE_VMALLOC
920 depends on HAVE_ARCH_HUGE_VMAP
923 config ARCH_WANT_HUGE_PMD_SHARE
926 # Archs that want to use pmd_mkwrite on kernel memory need it defined even
927 # if there are no userspace memory management features that use it
928 config ARCH_WANT_KERNEL_PMD_MKWRITE
931 config ARCH_WANT_PMD_MKWRITE
932 def_bool TRANSPARENT_HUGEPAGE || ARCH_WANT_KERNEL_PMD_MKWRITE
934 config HAVE_ARCH_SOFT_DIRTY
937 config HAVE_MOD_ARCH_SPECIFIC
940 The arch uses struct mod_arch_specific to store data. Many arches
941 just need a simple module loader without arch specific data - those
942 should not enable this.
944 config MODULES_USE_ELF_RELA
947 Modules only use ELF RELA relocations. Modules with ELF REL
948 relocations will give an error.
950 config MODULES_USE_ELF_REL
953 Modules only use ELF REL relocations. Modules with ELF RELA
954 relocations will give an error.
956 config ARCH_WANTS_MODULES_DATA_IN_VMALLOC
959 For architectures like powerpc/32 which have constraints on module
960 allocation and need to allocate module data outside of module area.
962 config HAVE_IRQ_EXIT_ON_IRQ_STACK
965 Architecture doesn't only execute the irq handler on the irq stack
966 but also irq_exit(). This way we can process softirqs on this irq
967 stack instead of switching to a new one when we call __do_softirq()
968 in the end of an hardirq.
969 This spares a stack switch and improves cache usage on softirq
972 config HAVE_SOFTIRQ_ON_OWN_STACK
975 Architecture provides a function to run __do_softirq() on a
978 config SOFTIRQ_ON_OWN_STACK
979 def_bool HAVE_SOFTIRQ_ON_OWN_STACK && !PREEMPT_RT
981 config ALTERNATE_USER_ADDRESS_SPACE
984 Architectures set this when the CPU uses separate address
985 spaces for kernel and user space pointers. In this case, the
986 access_ok() check on a __user pointer is skipped.
988 config PGTABLE_LEVELS
992 config ARCH_HAS_ELF_RANDOMIZE
995 An architecture supports choosing randomized locations for
996 stack, mmap, brk, and ET_DYN. Defined functions:
998 - arch_randomize_brk()
1000 config HAVE_ARCH_MMAP_RND_BITS
1003 An arch should select this symbol if it supports setting a variable
1004 number of bits for use in establishing the base address for mmap
1005 allocations, has MMU enabled and provides values for both:
1006 - ARCH_MMAP_RND_BITS_MIN
1007 - ARCH_MMAP_RND_BITS_MAX
1009 config HAVE_EXIT_THREAD
1012 An architecture implements exit_thread.
1014 config ARCH_MMAP_RND_BITS_MIN
1017 config ARCH_MMAP_RND_BITS_MAX
1020 config ARCH_MMAP_RND_BITS_DEFAULT
1023 config ARCH_MMAP_RND_BITS
1024 int "Number of bits to use for ASLR of mmap base address" if EXPERT
1025 range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
1026 default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
1027 default ARCH_MMAP_RND_BITS_MIN
1028 depends on HAVE_ARCH_MMAP_RND_BITS
1030 This value can be used to select the number of bits to use to
1031 determine the random offset to the base address of vma regions
1032 resulting from mmap allocations. This value will be bounded
1033 by the architecture's minimum and maximum supported values.
1035 This value can be changed after boot using the
1036 /proc/sys/vm/mmap_rnd_bits tunable
1038 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
1041 An arch should select this symbol if it supports running applications
1042 in compatibility mode, supports setting a variable number of bits for
1043 use in establishing the base address for mmap allocations, has MMU
1044 enabled and provides values for both:
1045 - ARCH_MMAP_RND_COMPAT_BITS_MIN
1046 - ARCH_MMAP_RND_COMPAT_BITS_MAX
1048 config ARCH_MMAP_RND_COMPAT_BITS_MIN
1051 config ARCH_MMAP_RND_COMPAT_BITS_MAX
1054 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
1057 config ARCH_MMAP_RND_COMPAT_BITS
1058 int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
1059 range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
1060 default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
1061 default ARCH_MMAP_RND_COMPAT_BITS_MIN
1062 depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
1064 This value can be used to select the number of bits to use to
1065 determine the random offset to the base address of vma regions
1066 resulting from mmap allocations for compatible applications This
1067 value will be bounded by the architecture's minimum and maximum
1070 This value can be changed after boot using the
1071 /proc/sys/vm/mmap_rnd_compat_bits tunable
1073 config HAVE_ARCH_COMPAT_MMAP_BASES
1076 This allows 64bit applications to invoke 32-bit mmap() syscall
1077 and vice-versa 32-bit applications to call 64-bit mmap().
1078 Required for applications doing different bitness syscalls.
1080 config PAGE_SIZE_LESS_THAN_64KB
1082 depends on !ARM64_64K_PAGES
1083 depends on !PAGE_SIZE_64KB
1084 depends on !PARISC_PAGE_SIZE_64KB
1085 depends on PAGE_SIZE_LESS_THAN_256KB
1087 config PAGE_SIZE_LESS_THAN_256KB
1089 depends on !PAGE_SIZE_256KB
1091 # This allows to use a set of generic functions to determine mmap base
1092 # address by giving priority to top-down scheme only if the process
1093 # is not in legacy mode (compat task, unlimited stack size or
1094 # sysctl_legacy_va_layout).
1095 # Architecture that selects this option can provide its own version of:
1097 config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
1100 select ARCH_HAS_ELF_RANDOMIZE
1105 config HAVE_JUMP_LABEL_HACK
1108 config HAVE_NOINSTR_HACK
1111 config HAVE_NOINSTR_VALIDATION
1114 config HAVE_UACCESS_VALIDATION
1118 config HAVE_STACK_VALIDATION
1121 Architecture supports objtool compile-time frame pointer rule
1124 config HAVE_RELIABLE_STACKTRACE
1127 Architecture has either save_stack_trace_tsk_reliable() or
1128 arch_stack_walk_reliable() function which only returns a stack trace
1129 if it can guarantee the trace is reliable.
1131 config HAVE_ARCH_HASH
1135 If this is set, the architecture provides an <asm/hash.h>
1136 file which provides platform-specific implementations of some
1137 functions in <linux/hash.h> or fs/namei.c.
1139 config HAVE_ARCH_NVRAM_OPS
1148 config CLONE_BACKWARDS
1151 Architecture has tls passed as the 4th argument of clone(2),
1154 config CLONE_BACKWARDS2
1157 Architecture has the first two arguments of clone(2) swapped.
1159 config CLONE_BACKWARDS3
1162 Architecture has tls passed as the 3rd argument of clone(2),
1165 config ODD_RT_SIGACTION
1168 Architecture has unusual rt_sigaction(2) arguments
1170 config OLD_SIGSUSPEND
1173 Architecture has old sigsuspend(2) syscall, of one-argument variety
1175 config OLD_SIGSUSPEND3
1178 Even weirder antique ABI - three-argument sigsuspend(2)
1180 config OLD_SIGACTION
1183 Architecture has old sigaction(2) syscall. Nope, not the same
1184 as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
1185 but fairly different variant of sigaction(2), thanks to OSF/1
1188 config COMPAT_OLD_SIGACTION
1191 config COMPAT_32BIT_TIME
1192 bool "Provide system calls for 32-bit time_t"
1193 default !64BIT || COMPAT
1195 This enables 32 bit time_t support in addition to 64 bit time_t support.
1196 This is relevant on all 32-bit architectures, and 64-bit architectures
1197 as part of compat syscall handling.
1199 config ARCH_NO_PREEMPT
1202 config ARCH_SUPPORTS_RT
1205 config CPU_NO_EFFICIENT_FFS
1208 config HAVE_ARCH_VMAP_STACK
1211 An arch should select this symbol if it can support kernel stacks
1212 in vmalloc space. This means:
1214 - vmalloc space must be large enough to hold many kernel stacks.
1215 This may rule out many 32-bit architectures.
1217 - Stacks in vmalloc space need to work reliably. For example, if
1218 vmap page tables are created on demand, either this mechanism
1219 needs to work while the stack points to a virtual address with
1220 unpopulated page tables or arch code (switch_to() and switch_mm(),
1221 most likely) needs to ensure that the stack's page table entries
1222 are populated before running on a possibly unpopulated stack.
1224 - If the stack overflows into a guard page, something reasonable
1225 should happen. The definition of "reasonable" is flexible, but
1226 instantly rebooting without logging anything would be unfriendly.
1230 bool "Use a virtually-mapped stack"
1231 depends on HAVE_ARCH_VMAP_STACK
1232 depends on !KASAN || KASAN_HW_TAGS || KASAN_VMALLOC
1234 Enable this if you want the use virtually-mapped kernel stacks
1235 with guard pages. This causes kernel stack overflows to be
1236 caught immediately rather than causing difficult-to-diagnose
1239 To use this with software KASAN modes, the architecture must support
1240 backing virtual mappings with real shadow memory, and KASAN_VMALLOC
1243 config HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
1246 An arch should select this symbol if it can support kernel stack
1247 offset randomization with calls to add_random_kstack_offset()
1248 during syscall entry and choose_random_kstack_offset() during
1249 syscall exit. Careful removal of -fstack-protector-strong and
1250 -fstack-protector should also be applied to the entry code and
1251 closely examined, as the artificial stack bump looks like an array
1252 to the compiler, so it will attempt to add canary checks regardless
1253 of the static branch state.
1255 config RANDOMIZE_KSTACK_OFFSET
1256 bool "Support for randomizing kernel stack offset on syscall entry" if EXPERT
1258 depends on HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
1259 depends on INIT_STACK_NONE || !CC_IS_CLANG || CLANG_VERSION >= 140000
1261 The kernel stack offset can be randomized (after pt_regs) by
1262 roughly 5 bits of entropy, frustrating memory corruption
1263 attacks that depend on stack address determinism or
1264 cross-syscall address exposures.
1266 The feature is controlled via the "randomize_kstack_offset=on/off"
1267 kernel boot param, and if turned off has zero overhead due to its use
1268 of static branches (see JUMP_LABEL).
1272 config RANDOMIZE_KSTACK_OFFSET_DEFAULT
1273 bool "Default state of kernel stack offset randomization"
1274 depends on RANDOMIZE_KSTACK_OFFSET
1276 Kernel stack offset randomization is controlled by kernel boot param
1277 "randomize_kstack_offset=on/off", and this config chooses the default
1280 config ARCH_OPTIONAL_KERNEL_RWX
1283 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1286 config ARCH_HAS_STRICT_KERNEL_RWX
1289 config STRICT_KERNEL_RWX
1290 bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
1291 depends on ARCH_HAS_STRICT_KERNEL_RWX
1292 default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1294 If this is set, kernel text and rodata memory will be made read-only,
1295 and non-text memory will be made non-executable. This provides
1296 protection against certain security exploits (e.g. executing the heap
1299 These features are considered standard security practice these days.
1300 You should say Y here in almost all cases.
1302 config ARCH_HAS_STRICT_MODULE_RWX
1305 config STRICT_MODULE_RWX
1306 bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
1307 depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
1308 default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1310 If this is set, module text and rodata memory will be made read-only,
1311 and non-text memory will be made non-executable. This provides
1312 protection against certain security exploits (e.g. writing to text)
1314 # select if the architecture provides an asm/dma-direct.h header
1315 config ARCH_HAS_PHYS_TO_DMA
1318 config HAVE_ARCH_COMPILER_H
1321 An architecture can select this if it provides an
1322 asm/compiler.h header that should be included after
1323 linux/compiler-*.h in order to override macro definitions that those
1324 headers generally provide.
1326 config HAVE_ARCH_PREL32_RELOCATIONS
1329 May be selected by an architecture if it supports place-relative
1330 32-bit relocations, both in the toolchain and in the module loader,
1331 in which case relative references can be used in special sections
1332 for PCI fixup, initcalls etc which are only half the size on 64 bit
1333 architectures, and don't require runtime relocation on relocatable
1336 config ARCH_USE_MEMREMAP_PROT
1339 config LOCK_EVENT_COUNTS
1340 bool "Locking event counts collection"
1343 Enable light-weight counting of various locking related events
1344 in the system with minimal performance impact. This reduces
1345 the chance of application behavior change because of timing
1346 differences. The counts are reported via debugfs.
1348 # Select if the architecture has support for applying RELR relocations.
1349 config ARCH_HAS_RELR
1353 bool "Use RELR relocation packing"
1354 depends on ARCH_HAS_RELR && TOOLS_SUPPORT_RELR
1357 Store the kernel's dynamic relocations in the RELR relocation packing
1358 format. Requires a compatible linker (LLD supports this feature), as
1359 well as compatible NM and OBJCOPY utilities (llvm-nm and llvm-objcopy
1362 config ARCH_HAS_MEM_ENCRYPT
1365 config ARCH_HAS_CC_PLATFORM
1368 config HAVE_SPARSE_SYSCALL_NR
1371 An architecture should select this if its syscall numbering is sparse
1372 to save space. For example, MIPS architecture has a syscall array with
1373 entries at 4000, 5000 and 6000 locations. This option turns on syscall
1374 related optimizations for a given architecture.
1376 config ARCH_HAS_VDSO_DATA
1379 config HAVE_STATIC_CALL
1382 config HAVE_STATIC_CALL_INLINE
1384 depends on HAVE_STATIC_CALL
1387 config HAVE_PREEMPT_DYNAMIC
1390 config HAVE_PREEMPT_DYNAMIC_CALL
1392 depends on HAVE_STATIC_CALL
1393 select HAVE_PREEMPT_DYNAMIC
1395 An architecture should select this if it can handle the preemption
1396 model being selected at boot time using static calls.
1398 Where an architecture selects HAVE_STATIC_CALL_INLINE, any call to a
1399 preemption function will be patched directly.
1401 Where an architecture does not select HAVE_STATIC_CALL_INLINE, any
1402 call to a preemption function will go through a trampoline, and the
1403 trampoline will be patched.
1405 It is strongly advised to support inline static call to avoid any
1408 config HAVE_PREEMPT_DYNAMIC_KEY
1410 depends on HAVE_ARCH_JUMP_LABEL
1411 select HAVE_PREEMPT_DYNAMIC
1413 An architecture should select this if it can handle the preemption
1414 model being selected at boot time using static keys.
1416 Each preemption function will be given an early return based on a
1417 static key. This should have slightly lower overhead than non-inline
1418 static calls, as this effectively inlines each trampoline into the
1419 start of its callee. This may avoid redundant work, and may
1420 integrate better with CFI schemes.
1422 This will have greater overhead than using inline static calls as
1423 the call to the preemption function cannot be entirely elided.
1425 config ARCH_WANT_LD_ORPHAN_WARN
1428 An arch should select this symbol once all linker sections are explicitly
1429 included, size-asserted, or discarded in the linker scripts. This is
1430 important because we never want expected sections to be placed heuristically
1431 by the linker, since the locations of such sections can change between linker
1434 config HAVE_ARCH_PFN_VALID
1437 config ARCH_SUPPORTS_DEBUG_PAGEALLOC
1440 config ARCH_SUPPORTS_PAGE_TABLE_CHECK
1443 config ARCH_SPLIT_ARG64
1446 If a 32-bit architecture requires 64-bit arguments to be split into
1447 pairs of 32-bit arguments, select this option.
1449 config ARCH_HAS_ELFCORE_COMPAT
1452 config ARCH_HAS_PARANOID_L1D_FLUSH
1455 config ARCH_HAVE_TRACE_MMIO_ACCESS
1458 config DYNAMIC_SIGFRAME
1461 # Select, if arch has a named attribute group bound to NUMA device nodes.
1462 config HAVE_ARCH_NODE_DEV_GROUP
1465 config ARCH_HAS_HW_PTE_YOUNG
1468 Architectures that select this option are capable of setting the
1469 accessed bit in PTE entries when using them as part of linear address
1470 translations. Architectures that require runtime check should select
1471 this option and override arch_has_hw_pte_young().
1473 config ARCH_HAS_NONLEAF_PMD_YOUNG
1476 Architectures that select this option are capable of setting the
1477 accessed bit in non-leaf PMD entries when using them as part of linear
1478 address translations. Page table walkers that clear the accessed bit
1479 may use this capability to reduce their search space.
1481 source "kernel/gcov/Kconfig"
1483 source "scripts/gcc-plugins/Kconfig"
1485 config FUNCTION_ALIGNMENT_4B
1488 config FUNCTION_ALIGNMENT_8B
1491 config FUNCTION_ALIGNMENT_16B
1494 config FUNCTION_ALIGNMENT_32B
1497 config FUNCTION_ALIGNMENT_64B
1500 config FUNCTION_ALIGNMENT
1502 default 64 if FUNCTION_ALIGNMENT_64B
1503 default 32 if FUNCTION_ALIGNMENT_32B
1504 default 16 if FUNCTION_ALIGNMENT_16B
1505 default 8 if FUNCTION_ALIGNMENT_8B
1506 default 4 if FUNCTION_ALIGNMENT_4B