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 # Select if arch init_task must go in the __init_task_data section
305 config ARCH_TASK_STRUCT_ON_STACK
308 # Select if arch has its private alloc_task_struct() function
309 config ARCH_TASK_STRUCT_ALLOCATOR
312 config HAVE_ARCH_THREAD_STRUCT_WHITELIST
314 depends on !ARCH_TASK_STRUCT_ALLOCATOR
316 An architecture should select this to provide hardened usercopy
317 knowledge about what region of the thread_struct should be
318 whitelisted for copying to userspace. Normally this is only the
319 FPU registers. Specifically, arch_thread_struct_whitelist()
320 should be implemented. Without this, the entire thread_struct
321 field in task_struct will be left whitelisted.
323 # Select if arch has its private alloc_thread_stack() function
324 config ARCH_THREAD_STACK_ALLOCATOR
327 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
328 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
331 config ARCH_WANTS_NO_INSTR
334 An architecture should select this if the noinstr macro is being used on
335 functions to denote that the toolchain should avoid instrumenting such
336 functions and is required for correctness.
338 config ARCH_32BIT_OFF_T
342 All new 32-bit architectures should have 64-bit off_t type on
343 userspace side which corresponds to the loff_t kernel type. This
344 is the requirement for modern ABIs. Some existing architectures
345 still support 32-bit off_t. This option is enabled for all such
346 architectures explicitly.
348 # Selected by 64 bit architectures which have a 32 bit f_tinode in struct ustat
349 config ARCH_32BIT_USTAT_F_TINODE
352 config HAVE_ASM_MODVERSIONS
355 This symbol should be selected by an architecture if it provides
356 <asm/asm-prototypes.h> to support the module versioning for symbols
357 exported from assembly code.
359 config HAVE_REGS_AND_STACK_ACCESS_API
362 This symbol should be selected by an architecture if it supports
363 the API needed to access registers and stack entries from pt_regs,
364 declared in asm/ptrace.h
365 For example the kprobes-based event tracer needs this API.
369 depends on HAVE_REGS_AND_STACK_ACCESS_API
371 This symbol should be selected by an architecture if it
372 supports an implementation of restartable sequences.
377 This symbol should be selected by an architecture if it
380 config HAVE_FUNCTION_ARG_ACCESS_API
383 This symbol should be selected by an architecture if it supports
384 the API needed to access function arguments from pt_regs,
385 declared in asm/ptrace.h
387 config HAVE_HW_BREAKPOINT
389 depends on PERF_EVENTS
391 config HAVE_MIXED_BREAKPOINTS_REGS
393 depends on HAVE_HW_BREAKPOINT
395 Depending on the arch implementation of hardware breakpoints,
396 some of them have separate registers for data and instruction
397 breakpoints addresses, others have mixed registers to store
398 them but define the access type in a control register.
399 Select this option if your arch implements breakpoints under the
402 config HAVE_USER_RETURN_NOTIFIER
405 config HAVE_PERF_EVENTS_NMI
408 System hardware can generate an NMI using the perf event
409 subsystem. Also has support for calculating CPU cycle events
410 to determine how many clock cycles in a given period.
412 config HAVE_HARDLOCKUP_DETECTOR_PERF
414 depends on HAVE_PERF_EVENTS_NMI
416 The arch chooses to use the generic perf-NMI-based hardlockup
417 detector. Must define HAVE_PERF_EVENTS_NMI.
419 config HAVE_HARDLOCKUP_DETECTOR_ARCH
422 The arch provides its own hardlockup detector implementation instead
425 It uses the same command line parameters, and sysctl interface,
426 as the generic hardlockup detectors.
428 config HAVE_PERF_REGS
431 Support selective register dumps for perf events. This includes
432 bit-mapping of each registers and a unique architecture id.
434 config HAVE_PERF_USER_STACK_DUMP
437 Support user stack dumps for perf event samples. This needs
438 access to the user stack pointer which is not unified across
441 config HAVE_ARCH_JUMP_LABEL
444 config HAVE_ARCH_JUMP_LABEL_RELATIVE
447 config MMU_GATHER_TABLE_FREE
450 config MMU_GATHER_RCU_TABLE_FREE
452 select MMU_GATHER_TABLE_FREE
454 config MMU_GATHER_PAGE_SIZE
457 config MMU_GATHER_NO_RANGE
459 select MMU_GATHER_MERGE_VMAS
461 config MMU_GATHER_NO_FLUSH_CACHE
464 config MMU_GATHER_MERGE_VMAS
467 config MMU_GATHER_NO_GATHER
469 depends on MMU_GATHER_TABLE_FREE
471 config ARCH_WANT_IRQS_OFF_ACTIVATE_MM
474 Temporary select until all architectures can be converted to have
475 irqs disabled over activate_mm. Architectures that do IPI based TLB
476 shootdowns should enable this.
478 # Use normal mm refcounting for MMU_LAZY_TLB kernel thread references.
479 # MMU_LAZY_TLB_REFCOUNT=n can improve the scalability of context switching
480 # to/from kernel threads when the same mm is running on a lot of CPUs (a large
481 # multi-threaded application), by reducing contention on the mm refcount.
483 # This can be disabled if the architecture ensures no CPUs are using an mm as a
484 # "lazy tlb" beyond its final refcount (i.e., by the time __mmdrop frees the mm
485 # or its kernel page tables). This could be arranged by arch_exit_mmap(), or
486 # final exit(2) TLB flush, for example.
488 # To implement this, an arch *must*:
489 # Ensure the _lazy_tlb variants of mmgrab/mmdrop are used when manipulating
490 # the lazy tlb reference of a kthread's ->active_mm (non-arch code has been
491 # converted already).
492 config MMU_LAZY_TLB_REFCOUNT
494 depends on !MMU_LAZY_TLB_SHOOTDOWN
496 # This option allows MMU_LAZY_TLB_REFCOUNT=n. It ensures no CPUs are using an
497 # mm as a lazy tlb beyond its last reference count, by shooting down these
498 # users before the mm is deallocated. __mmdrop() first IPIs all CPUs that may
499 # be using the mm as a lazy tlb, so that they may switch themselves to using
500 # init_mm for their active mm. mm_cpumask(mm) is used to determine which CPUs
501 # may be using mm as a lazy tlb mm.
503 # To implement this, an arch *must*:
504 # - At the time of the final mmdrop of the mm, ensure mm_cpumask(mm) contains
505 # at least all possible CPUs in which the mm is lazy.
506 # - It must meet the requirements for MMU_LAZY_TLB_REFCOUNT=n (see above).
507 config MMU_LAZY_TLB_SHOOTDOWN
510 config ARCH_HAVE_NMI_SAFE_CMPXCHG
513 config ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
516 config HAVE_ALIGNED_STRUCT_PAGE
519 This makes sure that struct pages are double word aligned and that
520 e.g. the SLUB allocator can perform double word atomic operations
521 on a struct page for better performance. However selecting this
522 might increase the size of a struct page by a word.
524 config HAVE_CMPXCHG_LOCAL
527 config HAVE_CMPXCHG_DOUBLE
530 config ARCH_WEAK_RELEASE_ACQUIRE
533 config ARCH_WANT_IPC_PARSE_VERSION
536 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
539 config ARCH_WANT_OLD_COMPAT_IPC
540 select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
543 config HAVE_ARCH_SECCOMP
546 An arch should select this symbol to support seccomp mode 1 (the fixed
547 syscall policy), and must provide an overrides for __NR_seccomp_sigreturn,
548 and compat syscalls if the asm-generic/seccomp.h defaults need adjustment:
549 - __NR_seccomp_read_32
550 - __NR_seccomp_write_32
551 - __NR_seccomp_exit_32
552 - __NR_seccomp_sigreturn_32
554 config HAVE_ARCH_SECCOMP_FILTER
556 select HAVE_ARCH_SECCOMP
558 An arch should select this symbol if it provides all of these things:
559 - all the requirements for HAVE_ARCH_SECCOMP
561 - syscall_get_arguments()
563 - syscall_set_return_value()
564 - SIGSYS siginfo_t support
565 - secure_computing is called from a ptrace_event()-safe context
566 - secure_computing return value is checked and a return value of -1
567 results in the system call being skipped immediately.
568 - seccomp syscall wired up
569 - if !HAVE_SPARSE_SYSCALL_NR, have SECCOMP_ARCH_NATIVE,
570 SECCOMP_ARCH_NATIVE_NR, SECCOMP_ARCH_NATIVE_NAME defined. If
571 COMPAT is supported, have the SECCOMP_ARCH_COMPAT* defines too.
574 prompt "Enable seccomp to safely execute untrusted bytecode"
576 depends on HAVE_ARCH_SECCOMP
578 This kernel feature is useful for number crunching applications
579 that may need to handle untrusted bytecode during their
580 execution. By using pipes or other transports made available
581 to the process as file descriptors supporting the read/write
582 syscalls, it's possible to isolate those applications in their
583 own address space using seccomp. Once seccomp is enabled via
584 prctl(PR_SET_SECCOMP) or the seccomp() syscall, it cannot be
585 disabled and the task is only allowed to execute a few safe
586 syscalls defined by each seccomp mode.
590 config SECCOMP_FILTER
592 depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
594 Enable tasks to build secure computing environments defined
595 in terms of Berkeley Packet Filter programs which implement
596 task-defined system call filtering polices.
598 See Documentation/userspace-api/seccomp_filter.rst for details.
600 config SECCOMP_CACHE_DEBUG
601 bool "Show seccomp filter cache status in /proc/pid/seccomp_cache"
602 depends on SECCOMP_FILTER && !HAVE_SPARSE_SYSCALL_NR
605 This enables the /proc/pid/seccomp_cache interface to monitor
606 seccomp cache data. The file format is subject to change. Reading
607 the file requires CAP_SYS_ADMIN.
609 This option is for debugging only. Enabling presents the risk that
610 an adversary may be able to infer the seccomp filter logic.
614 config HAVE_ARCH_STACKLEAK
617 An architecture should select this if it has the code which
618 fills the used part of the kernel stack with the STACKLEAK_POISON
619 value before returning from system calls.
621 config HAVE_STACKPROTECTOR
624 An arch should select this symbol if:
625 - it has implemented a stack canary (e.g. __stack_chk_guard)
627 config STACKPROTECTOR
628 bool "Stack Protector buffer overflow detection"
629 depends on HAVE_STACKPROTECTOR
630 depends on $(cc-option,-fstack-protector)
633 This option turns on the "stack-protector" GCC feature. This
634 feature puts, at the beginning of functions, a canary value on
635 the stack just before the return address, and validates
636 the value just before actually returning. Stack based buffer
637 overflows (that need to overwrite this return address) now also
638 overwrite the canary, which gets detected and the attack is then
639 neutralized via a kernel panic.
641 Functions will have the stack-protector canary logic added if they
642 have an 8-byte or larger character array on the stack.
644 This feature requires gcc version 4.2 or above, or a distribution
645 gcc with the feature backported ("-fstack-protector").
647 On an x86 "defconfig" build, this feature adds canary checks to
648 about 3% of all kernel functions, which increases kernel code size
651 config STACKPROTECTOR_STRONG
652 bool "Strong Stack Protector"
653 depends on STACKPROTECTOR
654 depends on $(cc-option,-fstack-protector-strong)
657 Functions will have the stack-protector canary logic added in any
658 of the following conditions:
660 - local variable's address used as part of the right hand side of an
661 assignment or function argument
662 - local variable is an array (or union containing an array),
663 regardless of array type or length
664 - uses register local variables
666 This feature requires gcc version 4.9 or above, or a distribution
667 gcc with the feature backported ("-fstack-protector-strong").
669 On an x86 "defconfig" build, this feature adds canary checks to
670 about 20% of all kernel functions, which increases the kernel code
673 config ARCH_SUPPORTS_SHADOW_CALL_STACK
676 An architecture should select this if it supports the compiler's
677 Shadow Call Stack and implements runtime support for shadow stack
680 config SHADOW_CALL_STACK
681 bool "Shadow Call Stack"
682 depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
683 depends on DYNAMIC_FTRACE_WITH_ARGS || DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
685 This option enables the compiler's Shadow Call Stack, which
686 uses a shadow stack to protect function return addresses from
687 being overwritten by an attacker. More information can be found
688 in the compiler's documentation:
690 - Clang: https://clang.llvm.org/docs/ShadowCallStack.html
691 - GCC: https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html#Instrumentation-Options
693 Note that security guarantees in the kernel differ from the
694 ones documented for user space. The kernel must store addresses
695 of shadow stacks in memory, which means an attacker capable of
696 reading and writing arbitrary memory may be able to locate them
697 and hijack control flow by modifying the stacks.
702 Set by the arch code if it relies on code patching to insert the
703 shadow call stack push and pop instructions rather than on the
709 Selected if the kernel will be built using the compiler's LTO feature.
715 Selected if the kernel will be built using Clang's LTO feature.
717 config ARCH_SUPPORTS_LTO_CLANG
720 An architecture should select this option if it supports:
721 - compiling with Clang,
722 - compiling inline assembly with Clang's integrated assembler,
723 - and linking with LLD.
725 config ARCH_SUPPORTS_LTO_CLANG_THIN
728 An architecture should select this option if it can support Clang's
733 depends on CC_IS_CLANG && LD_IS_LLD && AS_IS_LLVM
734 depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
735 depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
736 depends on ARCH_SUPPORTS_LTO_CLANG
737 depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT
738 # https://github.com/ClangBuiltLinux/linux/issues/1721
739 depends on (!KASAN || KASAN_HW_TAGS || CLANG_VERSION >= 170000) || !DEBUG_INFO
740 depends on (!KCOV || CLANG_VERSION >= 170000) || !DEBUG_INFO
741 depends on !GCOV_KERNEL
743 The compiler and Kconfig options support building with Clang's
747 prompt "Link Time Optimization (LTO)"
750 This option enables Link Time Optimization (LTO), which allows the
751 compiler to optimize binaries globally.
753 If unsure, select LTO_NONE. Note that LTO is very resource-intensive
754 so it's disabled by default.
759 Build the kernel normally, without Link Time Optimization (LTO).
761 config LTO_CLANG_FULL
762 bool "Clang Full LTO (EXPERIMENTAL)"
763 depends on HAS_LTO_CLANG
764 depends on !COMPILE_TEST
767 This option enables Clang's full Link Time Optimization (LTO), which
768 allows the compiler to optimize the kernel globally. If you enable
769 this option, the compiler generates LLVM bitcode instead of ELF
770 object files, and the actual compilation from bitcode happens at
771 the LTO link step, which may take several minutes depending on the
772 kernel configuration. More information can be found from LLVM's
775 https://llvm.org/docs/LinkTimeOptimization.html
777 During link time, this option can use a large amount of RAM, and
778 may take much longer than the ThinLTO option.
780 config LTO_CLANG_THIN
781 bool "Clang ThinLTO (EXPERIMENTAL)"
782 depends on HAS_LTO_CLANG && ARCH_SUPPORTS_LTO_CLANG_THIN
785 This option enables Clang's ThinLTO, which allows for parallel
786 optimization and faster incremental compiles compared to the
787 CONFIG_LTO_CLANG_FULL option. More information can be found
788 from Clang's documentation:
790 https://clang.llvm.org/docs/ThinLTO.html
795 config ARCH_SUPPORTS_CFI_CLANG
798 An architecture should select this option if it can support Clang's
799 Control-Flow Integrity (CFI) checking.
801 config ARCH_USES_CFI_TRAPS
805 bool "Use Clang's Control Flow Integrity (CFI)"
806 depends on ARCH_SUPPORTS_CFI_CLANG
807 depends on $(cc-option,-fsanitize=kcfi)
809 This option enables Clang’s forward-edge Control Flow Integrity
810 (CFI) checking, where the compiler injects a runtime check to each
811 indirect function call to ensure the target is a valid function with
812 the correct static type. This restricts possible call targets and
813 makes it more difficult for an attacker to exploit bugs that allow
814 the modification of stored function pointers. More information can be
815 found from Clang's documentation:
817 https://clang.llvm.org/docs/ControlFlowIntegrity.html
819 config CFI_PERMISSIVE
820 bool "Use CFI in permissive mode"
823 When selected, Control Flow Integrity (CFI) violations result in a
824 warning instead of a kernel panic. This option should only be used
825 for finding indirect call type mismatches during development.
829 config HAVE_ARCH_WITHIN_STACK_FRAMES
832 An architecture should select this if it can walk the kernel stack
833 frames to determine if an object is part of either the arguments
834 or local variables (i.e. that it excludes saved return addresses,
835 and similar) by implementing an inline arch_within_stack_frames(),
836 which is used by CONFIG_HARDENED_USERCOPY.
838 config HAVE_CONTEXT_TRACKING_USER
841 Provide kernel/user boundaries probes necessary for subsystems
842 that need it, such as userspace RCU extended quiescent state.
843 Syscalls need to be wrapped inside user_exit()-user_enter(), either
844 optimized behind static key or through the slow path using TIF_NOHZ
845 flag. Exceptions handlers must be wrapped as well. Irqs are already
846 protected inside ct_irq_enter/ct_irq_exit() but preemption or signal
847 handling on irq exit still need to be protected.
849 config HAVE_CONTEXT_TRACKING_USER_OFFSTACK
852 Architecture neither relies on exception_enter()/exception_exit()
853 nor on schedule_user(). Also preempt_schedule_notrace() and
854 preempt_schedule_irq() can't be called in a preemptible section
855 while context tracking is CONTEXT_USER. This feature reflects a sane
856 entry implementation where the following requirements are met on
857 critical entry code, ie: before user_exit() or after user_enter():
859 - Critical entry code isn't preemptible (or better yet:
861 - No use of RCU read side critical sections, unless ct_nmi_enter()
863 - No use of instrumentation, unless instrumentation_begin() got
869 Arch relies on TIF_NOHZ and syscall slow path to implement context
870 tracking calls to user_enter()/user_exit().
872 config HAVE_VIRT_CPU_ACCOUNTING
875 config HAVE_VIRT_CPU_ACCOUNTING_IDLE
878 Architecture has its own way to account idle CPU time and therefore
879 doesn't implement vtime_account_idle().
881 config ARCH_HAS_SCALED_CPUTIME
884 config HAVE_VIRT_CPU_ACCOUNTING_GEN
888 With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
889 Before enabling this option, arch code must be audited
890 to ensure there are no races in concurrent read/write of
891 cputime_t. For example, reading/writing 64-bit cputime_t on
892 some 32-bit arches may require multiple accesses, so proper
893 locking is needed to protect against concurrent accesses.
895 config HAVE_IRQ_TIME_ACCOUNTING
898 Archs need to ensure they use a high enough resolution clock to
899 support irq time accounting and then call enable_sched_clock_irqtime().
904 Architectures that select this are able to move page tables at the
905 PUD level. If there are only 3 page table levels, the move effectively
906 happens at the PGD level.
911 Archs that select this are able to move page tables at the PMD level.
913 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
916 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
919 config HAVE_ARCH_HUGE_VMAP
923 # Archs that select this would be capable of PMD-sized vmaps (i.e.,
924 # arch_vmap_pmd_supported() returns true). The VM_ALLOW_HUGE_VMAP flag
925 # must be used to enable allocations to use hugepages.
927 config HAVE_ARCH_HUGE_VMALLOC
928 depends on HAVE_ARCH_HUGE_VMAP
931 config ARCH_WANT_HUGE_PMD_SHARE
934 # Archs that want to use pmd_mkwrite on kernel memory need it defined even
935 # if there are no userspace memory management features that use it
936 config ARCH_WANT_KERNEL_PMD_MKWRITE
939 config ARCH_WANT_PMD_MKWRITE
940 def_bool TRANSPARENT_HUGEPAGE || ARCH_WANT_KERNEL_PMD_MKWRITE
942 config HAVE_ARCH_SOFT_DIRTY
945 config HAVE_MOD_ARCH_SPECIFIC
948 The arch uses struct mod_arch_specific to store data. Many arches
949 just need a simple module loader without arch specific data - those
950 should not enable this.
952 config MODULES_USE_ELF_RELA
955 Modules only use ELF RELA relocations. Modules with ELF REL
956 relocations will give an error.
958 config MODULES_USE_ELF_REL
961 Modules only use ELF REL relocations. Modules with ELF RELA
962 relocations will give an error.
964 config ARCH_WANTS_MODULES_DATA_IN_VMALLOC
967 For architectures like powerpc/32 which have constraints on module
968 allocation and need to allocate module data outside of module area.
970 config HAVE_IRQ_EXIT_ON_IRQ_STACK
973 Architecture doesn't only execute the irq handler on the irq stack
974 but also irq_exit(). This way we can process softirqs on this irq
975 stack instead of switching to a new one when we call __do_softirq()
976 in the end of an hardirq.
977 This spares a stack switch and improves cache usage on softirq
980 config HAVE_SOFTIRQ_ON_OWN_STACK
983 Architecture provides a function to run __do_softirq() on a
986 config SOFTIRQ_ON_OWN_STACK
987 def_bool HAVE_SOFTIRQ_ON_OWN_STACK && !PREEMPT_RT
989 config ALTERNATE_USER_ADDRESS_SPACE
992 Architectures set this when the CPU uses separate address
993 spaces for kernel and user space pointers. In this case, the
994 access_ok() check on a __user pointer is skipped.
996 config PGTABLE_LEVELS
1000 config ARCH_HAS_ELF_RANDOMIZE
1003 An architecture supports choosing randomized locations for
1004 stack, mmap, brk, and ET_DYN. Defined functions:
1006 - arch_randomize_brk()
1008 config HAVE_ARCH_MMAP_RND_BITS
1011 An arch should select this symbol if it supports setting a variable
1012 number of bits for use in establishing the base address for mmap
1013 allocations, has MMU enabled and provides values for both:
1014 - ARCH_MMAP_RND_BITS_MIN
1015 - ARCH_MMAP_RND_BITS_MAX
1017 config HAVE_EXIT_THREAD
1020 An architecture implements exit_thread.
1022 config ARCH_MMAP_RND_BITS_MIN
1025 config ARCH_MMAP_RND_BITS_MAX
1028 config ARCH_MMAP_RND_BITS_DEFAULT
1031 config ARCH_MMAP_RND_BITS
1032 int "Number of bits to use for ASLR of mmap base address" if EXPERT
1033 range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
1034 default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
1035 default ARCH_MMAP_RND_BITS_MIN
1036 depends on HAVE_ARCH_MMAP_RND_BITS
1038 This value can be used to select the number of bits to use to
1039 determine the random offset to the base address of vma regions
1040 resulting from mmap allocations. This value will be bounded
1041 by the architecture's minimum and maximum supported values.
1043 This value can be changed after boot using the
1044 /proc/sys/vm/mmap_rnd_bits tunable
1046 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
1049 An arch should select this symbol if it supports running applications
1050 in compatibility mode, supports setting a variable number of bits for
1051 use in establishing the base address for mmap allocations, has MMU
1052 enabled and provides values for both:
1053 - ARCH_MMAP_RND_COMPAT_BITS_MIN
1054 - ARCH_MMAP_RND_COMPAT_BITS_MAX
1056 config ARCH_MMAP_RND_COMPAT_BITS_MIN
1059 config ARCH_MMAP_RND_COMPAT_BITS_MAX
1062 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
1065 config ARCH_MMAP_RND_COMPAT_BITS
1066 int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
1067 range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
1068 default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
1069 default ARCH_MMAP_RND_COMPAT_BITS_MIN
1070 depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
1072 This value can be used to select the number of bits to use to
1073 determine the random offset to the base address of vma regions
1074 resulting from mmap allocations for compatible applications This
1075 value will be bounded by the architecture's minimum and maximum
1078 This value can be changed after boot using the
1079 /proc/sys/vm/mmap_rnd_compat_bits tunable
1081 config HAVE_ARCH_COMPAT_MMAP_BASES
1084 This allows 64bit applications to invoke 32-bit mmap() syscall
1085 and vice-versa 32-bit applications to call 64-bit mmap().
1086 Required for applications doing different bitness syscalls.
1088 config PAGE_SIZE_LESS_THAN_64KB
1090 depends on !ARM64_64K_PAGES
1091 depends on !IA64_PAGE_SIZE_64KB
1092 depends on !PAGE_SIZE_64KB
1093 depends on !PARISC_PAGE_SIZE_64KB
1094 depends on PAGE_SIZE_LESS_THAN_256KB
1096 config PAGE_SIZE_LESS_THAN_256KB
1098 depends on !PAGE_SIZE_256KB
1100 # This allows to use a set of generic functions to determine mmap base
1101 # address by giving priority to top-down scheme only if the process
1102 # is not in legacy mode (compat task, unlimited stack size or
1103 # sysctl_legacy_va_layout).
1104 # Architecture that selects this option can provide its own version of:
1106 config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
1109 select ARCH_HAS_ELF_RANDOMIZE
1114 config HAVE_JUMP_LABEL_HACK
1117 config HAVE_NOINSTR_HACK
1120 config HAVE_NOINSTR_VALIDATION
1123 config HAVE_UACCESS_VALIDATION
1127 config HAVE_STACK_VALIDATION
1130 Architecture supports objtool compile-time frame pointer rule
1133 config HAVE_RELIABLE_STACKTRACE
1136 Architecture has either save_stack_trace_tsk_reliable() or
1137 arch_stack_walk_reliable() function which only returns a stack trace
1138 if it can guarantee the trace is reliable.
1140 config HAVE_ARCH_HASH
1144 If this is set, the architecture provides an <asm/hash.h>
1145 file which provides platform-specific implementations of some
1146 functions in <linux/hash.h> or fs/namei.c.
1148 config HAVE_ARCH_NVRAM_OPS
1157 config CLONE_BACKWARDS
1160 Architecture has tls passed as the 4th argument of clone(2),
1163 config CLONE_BACKWARDS2
1166 Architecture has the first two arguments of clone(2) swapped.
1168 config CLONE_BACKWARDS3
1171 Architecture has tls passed as the 3rd argument of clone(2),
1174 config ODD_RT_SIGACTION
1177 Architecture has unusual rt_sigaction(2) arguments
1179 config OLD_SIGSUSPEND
1182 Architecture has old sigsuspend(2) syscall, of one-argument variety
1184 config OLD_SIGSUSPEND3
1187 Even weirder antique ABI - three-argument sigsuspend(2)
1189 config OLD_SIGACTION
1192 Architecture has old sigaction(2) syscall. Nope, not the same
1193 as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
1194 but fairly different variant of sigaction(2), thanks to OSF/1
1197 config COMPAT_OLD_SIGACTION
1200 config COMPAT_32BIT_TIME
1201 bool "Provide system calls for 32-bit time_t"
1202 default !64BIT || COMPAT
1204 This enables 32 bit time_t support in addition to 64 bit time_t support.
1205 This is relevant on all 32-bit architectures, and 64-bit architectures
1206 as part of compat syscall handling.
1208 config ARCH_NO_PREEMPT
1211 config ARCH_SUPPORTS_RT
1214 config CPU_NO_EFFICIENT_FFS
1217 config HAVE_ARCH_VMAP_STACK
1220 An arch should select this symbol if it can support kernel stacks
1221 in vmalloc space. This means:
1223 - vmalloc space must be large enough to hold many kernel stacks.
1224 This may rule out many 32-bit architectures.
1226 - Stacks in vmalloc space need to work reliably. For example, if
1227 vmap page tables are created on demand, either this mechanism
1228 needs to work while the stack points to a virtual address with
1229 unpopulated page tables or arch code (switch_to() and switch_mm(),
1230 most likely) needs to ensure that the stack's page table entries
1231 are populated before running on a possibly unpopulated stack.
1233 - If the stack overflows into a guard page, something reasonable
1234 should happen. The definition of "reasonable" is flexible, but
1235 instantly rebooting without logging anything would be unfriendly.
1239 bool "Use a virtually-mapped stack"
1240 depends on HAVE_ARCH_VMAP_STACK
1241 depends on !KASAN || KASAN_HW_TAGS || KASAN_VMALLOC
1243 Enable this if you want the use virtually-mapped kernel stacks
1244 with guard pages. This causes kernel stack overflows to be
1245 caught immediately rather than causing difficult-to-diagnose
1248 To use this with software KASAN modes, the architecture must support
1249 backing virtual mappings with real shadow memory, and KASAN_VMALLOC
1252 config HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
1255 An arch should select this symbol if it can support kernel stack
1256 offset randomization with calls to add_random_kstack_offset()
1257 during syscall entry and choose_random_kstack_offset() during
1258 syscall exit. Careful removal of -fstack-protector-strong and
1259 -fstack-protector should also be applied to the entry code and
1260 closely examined, as the artificial stack bump looks like an array
1261 to the compiler, so it will attempt to add canary checks regardless
1262 of the static branch state.
1264 config RANDOMIZE_KSTACK_OFFSET
1265 bool "Support for randomizing kernel stack offset on syscall entry" if EXPERT
1267 depends on HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
1268 depends on INIT_STACK_NONE || !CC_IS_CLANG || CLANG_VERSION >= 140000
1270 The kernel stack offset can be randomized (after pt_regs) by
1271 roughly 5 bits of entropy, frustrating memory corruption
1272 attacks that depend on stack address determinism or
1273 cross-syscall address exposures.
1275 The feature is controlled via the "randomize_kstack_offset=on/off"
1276 kernel boot param, and if turned off has zero overhead due to its use
1277 of static branches (see JUMP_LABEL).
1281 config RANDOMIZE_KSTACK_OFFSET_DEFAULT
1282 bool "Default state of kernel stack offset randomization"
1283 depends on RANDOMIZE_KSTACK_OFFSET
1285 Kernel stack offset randomization is controlled by kernel boot param
1286 "randomize_kstack_offset=on/off", and this config chooses the default
1289 config ARCH_OPTIONAL_KERNEL_RWX
1292 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1295 config ARCH_HAS_STRICT_KERNEL_RWX
1298 config STRICT_KERNEL_RWX
1299 bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
1300 depends on ARCH_HAS_STRICT_KERNEL_RWX
1301 default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1303 If this is set, kernel text and rodata memory will be made read-only,
1304 and non-text memory will be made non-executable. This provides
1305 protection against certain security exploits (e.g. executing the heap
1308 These features are considered standard security practice these days.
1309 You should say Y here in almost all cases.
1311 config ARCH_HAS_STRICT_MODULE_RWX
1314 config STRICT_MODULE_RWX
1315 bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
1316 depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
1317 default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1319 If this is set, module text and rodata memory will be made read-only,
1320 and non-text memory will be made non-executable. This provides
1321 protection against certain security exploits (e.g. writing to text)
1323 # select if the architecture provides an asm/dma-direct.h header
1324 config ARCH_HAS_PHYS_TO_DMA
1327 config HAVE_ARCH_COMPILER_H
1330 An architecture can select this if it provides an
1331 asm/compiler.h header that should be included after
1332 linux/compiler-*.h in order to override macro definitions that those
1333 headers generally provide.
1335 config HAVE_ARCH_PREL32_RELOCATIONS
1338 May be selected by an architecture if it supports place-relative
1339 32-bit relocations, both in the toolchain and in the module loader,
1340 in which case relative references can be used in special sections
1341 for PCI fixup, initcalls etc which are only half the size on 64 bit
1342 architectures, and don't require runtime relocation on relocatable
1345 config ARCH_USE_MEMREMAP_PROT
1348 config LOCK_EVENT_COUNTS
1349 bool "Locking event counts collection"
1352 Enable light-weight counting of various locking related events
1353 in the system with minimal performance impact. This reduces
1354 the chance of application behavior change because of timing
1355 differences. The counts are reported via debugfs.
1357 # Select if the architecture has support for applying RELR relocations.
1358 config ARCH_HAS_RELR
1362 bool "Use RELR relocation packing"
1363 depends on ARCH_HAS_RELR && TOOLS_SUPPORT_RELR
1366 Store the kernel's dynamic relocations in the RELR relocation packing
1367 format. Requires a compatible linker (LLD supports this feature), as
1368 well as compatible NM and OBJCOPY utilities (llvm-nm and llvm-objcopy
1371 config ARCH_HAS_MEM_ENCRYPT
1374 config ARCH_HAS_CC_PLATFORM
1377 config HAVE_SPARSE_SYSCALL_NR
1380 An architecture should select this if its syscall numbering is sparse
1381 to save space. For example, MIPS architecture has a syscall array with
1382 entries at 4000, 5000 and 6000 locations. This option turns on syscall
1383 related optimizations for a given architecture.
1385 config ARCH_HAS_VDSO_DATA
1388 config HAVE_STATIC_CALL
1391 config HAVE_STATIC_CALL_INLINE
1393 depends on HAVE_STATIC_CALL
1396 config HAVE_PREEMPT_DYNAMIC
1399 config HAVE_PREEMPT_DYNAMIC_CALL
1401 depends on HAVE_STATIC_CALL
1402 select HAVE_PREEMPT_DYNAMIC
1404 An architecture should select this if it can handle the preemption
1405 model being selected at boot time using static calls.
1407 Where an architecture selects HAVE_STATIC_CALL_INLINE, any call to a
1408 preemption function will be patched directly.
1410 Where an architecture does not select HAVE_STATIC_CALL_INLINE, any
1411 call to a preemption function will go through a trampoline, and the
1412 trampoline will be patched.
1414 It is strongly advised to support inline static call to avoid any
1417 config HAVE_PREEMPT_DYNAMIC_KEY
1419 depends on HAVE_ARCH_JUMP_LABEL
1420 select HAVE_PREEMPT_DYNAMIC
1422 An architecture should select this if it can handle the preemption
1423 model being selected at boot time using static keys.
1425 Each preemption function will be given an early return based on a
1426 static key. This should have slightly lower overhead than non-inline
1427 static calls, as this effectively inlines each trampoline into the
1428 start of its callee. This may avoid redundant work, and may
1429 integrate better with CFI schemes.
1431 This will have greater overhead than using inline static calls as
1432 the call to the preemption function cannot be entirely elided.
1434 config ARCH_WANT_LD_ORPHAN_WARN
1437 An arch should select this symbol once all linker sections are explicitly
1438 included, size-asserted, or discarded in the linker scripts. This is
1439 important because we never want expected sections to be placed heuristically
1440 by the linker, since the locations of such sections can change between linker
1443 config HAVE_ARCH_PFN_VALID
1446 config ARCH_SUPPORTS_DEBUG_PAGEALLOC
1449 config ARCH_SUPPORTS_PAGE_TABLE_CHECK
1452 config ARCH_SPLIT_ARG64
1455 If a 32-bit architecture requires 64-bit arguments to be split into
1456 pairs of 32-bit arguments, select this option.
1458 config ARCH_HAS_ELFCORE_COMPAT
1461 config ARCH_HAS_PARANOID_L1D_FLUSH
1464 config ARCH_HAVE_TRACE_MMIO_ACCESS
1467 config DYNAMIC_SIGFRAME
1470 # Select, if arch has a named attribute group bound to NUMA device nodes.
1471 config HAVE_ARCH_NODE_DEV_GROUP
1474 config ARCH_HAS_NONLEAF_PMD_YOUNG
1477 Architectures that select this option are capable of setting the
1478 accessed bit in non-leaf PMD entries when using them as part of linear
1479 address translations. Page table walkers that clear the accessed bit
1480 may use this capability to reduce their search space.
1482 source "kernel/gcov/Kconfig"
1484 source "scripts/gcc-plugins/Kconfig"
1486 config FUNCTION_ALIGNMENT_4B
1489 config FUNCTION_ALIGNMENT_8B
1492 config FUNCTION_ALIGNMENT_16B
1495 config FUNCTION_ALIGNMENT_32B
1498 config FUNCTION_ALIGNMENT_64B
1501 config FUNCTION_ALIGNMENT
1503 default 64 if FUNCTION_ALIGNMENT_64B
1504 default 32 if FUNCTION_ALIGNMENT_32B
1505 default 16 if FUNCTION_ALIGNMENT_16B
1506 default 8 if FUNCTION_ALIGNMENT_8B
1507 default 4 if FUNCTION_ALIGNMENT_4B