1 # SPDX-License-Identifier: GPL-2.0
2 #
3 # General architecture dependent options
4 #
5
6 #
7 # Note: arch/$(SRCARCH)/Kconfig needs to be included first so that it can
8 # override the default values in this file.
9 #
10 source "arch/$(SRCARCH)/Kconfig"
11
12 config ARCH_CONFIGURES_CPU_MITIGATIONS
13 bool
14
15 if !ARCH_CONFIGURES_CPU_MITIGATIONS
16 config CPU_MITIGATIONS
17 def_bool y
18 endif
19
20 menu "General architecture-dependent options"
21
22 config ARCH_HAS_SUBPAGE_FAULTS
23 bool
24 help
25 Select if the architecture can check permissions at sub-page
26 granularity (e.g. arm64 MTE). The probe_user_*() functions
27 must be implemented.
28
29 config HOTPLUG_SMT
30 bool
31
32 config SMT_NUM_THREADS_DYNAMIC
33 bool
34
35 # Selected by HOTPLUG_CORE_SYNC_DEAD or HOTPLUG_CORE_SYNC_FULL
36 config HOTPLUG_CORE_SYNC
37 bool
38
39 # Basic CPU dead synchronization selected by architecture
40 config HOTPLUG_CORE_SYNC_DEAD
41 bool
42 select HOTPLUG_CORE_SYNC
43
44 # Full CPU synchronization with alive state selected by architecture
45 config HOTPLUG_CORE_SYNC_FULL
46 bool
47 select HOTPLUG_CORE_SYNC_DEAD if HOTPLUG_CPU
48 select HOTPLUG_CORE_SYNC
49
50 config HOTPLUG_SPLIT_STARTUP
51 bool
52 select HOTPLUG_CORE_SYNC_FULL
53
54 config HOTPLUG_PARALLEL
55 bool
56 select HOTPLUG_SPLIT_STARTUP
57
58 config GENERIC_ENTRY
59 bool
60
61 config KPROBES
62 bool "Kprobes"
63 depends on HAVE_KPROBES
64 select KALLSYMS
65 select EXECMEM
66 select NEED_TASKS_RCU
67 help
68 Kprobes allows you to trap at almost any kernel address and
69 execute a callback function. register_kprobe() establishes
70 a probepoint and specifies the callback. Kprobes is useful
71 for kernel debugging, non-intrusive instrumentation and testing.
72 If in doubt, say "N".
73
74 config JUMP_LABEL
75 bool "Optimize very unlikely/likely branches"
76 depends on HAVE_ARCH_JUMP_LABEL
77 select OBJTOOL if HAVE_JUMP_LABEL_HACK
78 help
79 This option enables a transparent branch optimization that
80 makes certain almost-always-true or almost-always-false branch
81 conditions even cheaper to execute within the kernel.
82
83 Certain performance-sensitive kernel code, such as trace points,
84 scheduler functionality, networking code and KVM have such
85 branches and include support for this optimization technique.
86
87 If it is detected that the compiler has support for "asm goto",
88 the kernel will compile such branches with just a nop
89 instruction. When the condition flag is toggled to true, the
90 nop will be converted to a jump instruction to execute the
91 conditional block of instructions.
92
93 This technique lowers overhead and stress on the branch prediction
94 of the processor and generally makes the kernel faster. The update
95 of the condition is slower, but those are always very rare.
96
97 ( On 32-bit x86, the necessary options added to the compiler
98 flags may increase the size of the kernel slightly. )
99
100 config STATIC_KEYS_SELFTEST
101 bool "Static key selftest"
102 depends on JUMP_LABEL
103 help
104 Boot time self-test of the branch patching code.
105
106 config STATIC_CALL_SELFTEST
107 bool "Static call selftest"
108 depends on HAVE_STATIC_CALL
109 help
110 Boot time self-test of the call patching code.
111
112 config OPTPROBES
113 def_bool y
114 depends on KPROBES && HAVE_OPTPROBES
115 select NEED_TASKS_RCU
116
117 config KPROBES_ON_FTRACE
118 def_bool y
119 depends on KPROBES && HAVE_KPROBES_ON_FTRACE
120 depends on DYNAMIC_FTRACE_WITH_REGS
121 help
122 If function tracer is enabled and the arch supports full
123 passing of pt_regs to function tracing, then kprobes can
124 optimize on top of function tracing.
125
126 config UPROBES
127 def_bool n
128 depends on ARCH_SUPPORTS_UPROBES
129 help
130 Uprobes is the user-space counterpart to kprobes: they
131 enable instrumentation applications (such as 'perf probe')
132 to establish unintrusive probes in user-space binaries and
133 libraries, by executing handler functions when the probes
134 are hit by user-space applications.
135
136 ( These probes come in the form of single-byte breakpoints,
137 managed by the kernel and kept transparent to the probed
138 application. )
139
140 config HAVE_64BIT_ALIGNED_ACCESS
141 def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
142 help
143 Some architectures require 64 bit accesses to be 64 bit
144 aligned, which also requires structs containing 64 bit values
145 to be 64 bit aligned too. This includes some 32 bit
146 architectures which can do 64 bit accesses, as well as 64 bit
147 architectures without unaligned access.
148
149 This symbol should be selected by an architecture if 64 bit
150 accesses are required to be 64 bit aligned in this way even
151 though it is not a 64 bit architecture.
152
153 See Documentation/core-api/unaligned-memory-access.rst for
154 more information on the topic of unaligned memory accesses.
155
156 config HAVE_EFFICIENT_UNALIGNED_ACCESS
157 bool
158 help
159 Some architectures are unable to perform unaligned accesses
160 without the use of get_unaligned/put_unaligned. Others are
161 unable to perform such accesses efficiently (e.g. trap on
162 unaligned access and require fixing it up in the exception
163 handler.)
164
165 This symbol should be selected by an architecture if it can
166 perform unaligned accesses efficiently to allow different
167 code paths to be selected for these cases. Some network
168 drivers, for example, could opt to not fix up alignment
169 problems with received packets if doing so would not help
170 much.
171
172 See Documentation/core-api/unaligned-memory-access.rst for more
173 information on the topic of unaligned memory accesses.
174
175 config ARCH_USE_BUILTIN_BSWAP
176 bool
177 help
178 Modern versions of GCC (since 4.4) have builtin functions
179 for handling byte-swapping. Using these, instead of the old
180 inline assembler that the architecture code provides in the
181 __arch_bswapXX() macros, allows the compiler to see what's
182 happening and offers more opportunity for optimisation. In
183 particular, the compiler will be able to combine the byteswap
184 with a nearby load or store and use load-and-swap or
185 store-and-swap instructions if the architecture has them. It
186 should almost *never* result in code which is worse than the
187 hand-coded assembler in <asm/swab.h>. But just in case it
188 does, the use of the builtins is optional.
189
190 Any architecture with load-and-swap or store-and-swap
191 instructions should set this. And it shouldn't hurt to set it
192 on architectures that don't have such instructions.
193
194 config KRETPROBES
195 def_bool y
196 depends on KPROBES && (HAVE_KRETPROBES || HAVE_RETHOOK)
197
198 config KRETPROBE_ON_RETHOOK
199 def_bool y
200 depends on HAVE_RETHOOK
201 depends on KRETPROBES
202 select RETHOOK
203
204 config USER_RETURN_NOTIFIER
205 bool
206 depends on HAVE_USER_RETURN_NOTIFIER
207 help
208 Provide a kernel-internal notification when a cpu is about to
209 switch to user mode.
210
211 config HAVE_IOREMAP_PROT
212 bool
213
214 config HAVE_KPROBES
215 bool
216
217 config HAVE_KRETPROBES
218 bool
219
220 config HAVE_OPTPROBES
221 bool
222
223 config HAVE_KPROBES_ON_FTRACE
224 bool
225
226 config ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
227 bool
228 help
229 Since kretprobes modifies return address on the stack, the
230 stacktrace may see the kretprobe trampoline address instead
231 of correct one. If the architecture stacktrace code and
232 unwinder can adjust such entries, select this configuration.
233
234 config HAVE_FUNCTION_ERROR_INJECTION
235 bool
236
237 config HAVE_NMI
238 bool
239
240 config HAVE_FUNCTION_DESCRIPTORS
241 bool
242
243 config TRACE_IRQFLAGS_SUPPORT
244 bool
245
246 config TRACE_IRQFLAGS_NMI_SUPPORT
247 bool
248
249 #
250 # An arch should select this if it provides all these things:
251 #
252 # task_pt_regs() in asm/processor.h or asm/ptrace.h
253 # arch_has_single_step() if there is hardware single-step support
254 # arch_has_block_step() if there is hardware block-step support
255 # asm/syscall.h supplying asm-generic/syscall.h interface
256 # linux/regset.h user_regset interfaces
257 # CORE_DUMP_USE_REGSET #define'd in linux/elf.h
258 # TIF_SYSCALL_TRACE calls ptrace_report_syscall_{entry,exit}
259 # TIF_NOTIFY_RESUME calls resume_user_mode_work()
260 #
261 config HAVE_ARCH_TRACEHOOK
262 bool
263
264 config HAVE_DMA_CONTIGUOUS
265 bool
266
267 config GENERIC_SMP_IDLE_THREAD
268 bool
269
270 config GENERIC_IDLE_POLL_SETUP
271 bool
272
273 config ARCH_HAS_FORTIFY_SOURCE
274 bool
275 help
276 An architecture should select this when it can successfully
277 build and run with CONFIG_FORTIFY_SOURCE.
278
279 #
280 # Select if the arch provides a historic keepinit alias for the retain_initrd
281 # command line option
282 #
283 config ARCH_HAS_KEEPINITRD
284 bool
285
286 # Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
287 config ARCH_HAS_SET_MEMORY
288 bool
289
290 # Select if arch has all set_direct_map_invalid/default() functions
291 config ARCH_HAS_SET_DIRECT_MAP
292 bool
293
294 #
295 # Select if the architecture provides the arch_dma_set_uncached symbol to
296 # either provide an uncached segment alias for a DMA allocation, or
297 # to remap the page tables in place.
298 #
299 config ARCH_HAS_DMA_SET_UNCACHED
300 bool
301
302 #
303 # Select if the architectures provides the arch_dma_clear_uncached symbol
304 # to undo an in-place page table remap for uncached access.
305 #
306 config ARCH_HAS_DMA_CLEAR_UNCACHED
307 bool
308
309 config ARCH_HAS_CPU_FINALIZE_INIT
310 bool
311
312 # The architecture has a per-task state that includes the mm's PASID
313 config ARCH_HAS_CPU_PASID
314 bool
315 select IOMMU_MM_DATA
316
317 config HAVE_ARCH_THREAD_STRUCT_WHITELIST
318 bool
319 help
320 An architecture should select this to provide hardened usercopy
321 knowledge about what region of the thread_struct should be
322 whitelisted for copying to userspace. Normally this is only the
323 FPU registers. Specifically, arch_thread_struct_whitelist()
324 should be implemented. Without this, the entire thread_struct
325 field in task_struct will be left whitelisted.
326
327 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
328 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
329 bool
330
331 config ARCH_WANTS_NO_INSTR
332 bool
333 help
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.
337
338 config ARCH_32BIT_OFF_T
339 bool
340 depends on !64BIT
341 help
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.
347
348 # Selected by 64 bit architectures which have a 32 bit f_tinode in struct ustat
349 config ARCH_32BIT_USTAT_F_TINODE
350 bool
351
352 config HAVE_ASM_MODVERSIONS
353 bool
354 help
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.
358
359 config HAVE_REGS_AND_STACK_ACCESS_API
360 bool
361 help
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.
366
367 config HAVE_RSEQ
368 bool
369 depends on HAVE_REGS_AND_STACK_ACCESS_API
370 help
371 This symbol should be selected by an architecture if it
372 supports an implementation of restartable sequences.
373
374 config HAVE_RUST
375 bool
376 help
377 This symbol should be selected by an architecture if it
378 supports Rust.
379
380 config HAVE_FUNCTION_ARG_ACCESS_API
381 bool
382 help
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
386
387 config HAVE_HW_BREAKPOINT
388 bool
389 depends on PERF_EVENTS
390
391 config HAVE_MIXED_BREAKPOINTS_REGS
392 bool
393 depends on HAVE_HW_BREAKPOINT
394 help
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
400 latter fashion.
401
402 config HAVE_USER_RETURN_NOTIFIER
403 bool
404
405 config HAVE_PERF_EVENTS_NMI
406 bool
407 help
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.
411
412 config HAVE_HARDLOCKUP_DETECTOR_PERF
413 bool
414 depends on HAVE_PERF_EVENTS_NMI
415 help
416 The arch chooses to use the generic perf-NMI-based hardlockup
417 detector. Must define HAVE_PERF_EVENTS_NMI.
418
419 config HAVE_HARDLOCKUP_DETECTOR_ARCH
420 bool
421 help
422 The arch provides its own hardlockup detector implementation instead
423 of the generic ones.
424
425 It uses the same command line parameters, and sysctl interface,
426 as the generic hardlockup detectors.
427
428 config HAVE_PERF_REGS
429 bool
430 help
431 Support selective register dumps for perf events. This includes
432 bit-mapping of each registers and a unique architecture id.
433
434 config HAVE_PERF_USER_STACK_DUMP
435 bool
436 help
437 Support user stack dumps for perf event samples. This needs
438 access to the user stack pointer which is not unified across
439 architectures.
440
441 config HAVE_ARCH_JUMP_LABEL
442 bool
443
444 config HAVE_ARCH_JUMP_LABEL_RELATIVE
445 bool
446
447 config MMU_GATHER_TABLE_FREE
448 bool
449
450 config MMU_GATHER_RCU_TABLE_FREE
451 bool
452 select MMU_GATHER_TABLE_FREE
453
454 config MMU_GATHER_PAGE_SIZE
455 bool
456
457 config MMU_GATHER_NO_RANGE
458 bool
459 select MMU_GATHER_MERGE_VMAS
460
461 config MMU_GATHER_NO_FLUSH_CACHE
462 bool
463
464 config MMU_GATHER_MERGE_VMAS
465 bool
466
467 config MMU_GATHER_NO_GATHER
468 bool
469 depends on MMU_GATHER_TABLE_FREE
470
471 config ARCH_WANT_IRQS_OFF_ACTIVATE_MM
472 bool
473 help
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.
477
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.
482 #
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.
487 #
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
493 def_bool y
494 depends on !MMU_LAZY_TLB_SHOOTDOWN
495
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.
502 #
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
508 bool
509
510 config ARCH_HAVE_NMI_SAFE_CMPXCHG
511 bool
512
513 config ARCH_HAVE_EXTRA_ELF_NOTES
514 bool
515 help
516 An architecture should select this in order to enable adding an
517 arch-specific ELF note section to core files. It must provide two
518 functions: elf_coredump_extra_notes_size() and
519 elf_coredump_extra_notes_write() which are invoked by the ELF core
520 dumper.
521
522 config ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
523 bool
524
525 config HAVE_ALIGNED_STRUCT_PAGE
526 bool
527 help
528 This makes sure that struct pages are double word aligned and that
529 e.g. the SLUB allocator can perform double word atomic operations
530 on a struct page for better performance. However selecting this
531 might increase the size of a struct page by a word.
532
533 config HAVE_CMPXCHG_LOCAL
534 bool
535
536 config HAVE_CMPXCHG_DOUBLE
537 bool
538
539 config ARCH_WEAK_RELEASE_ACQUIRE
540 bool
541
542 config ARCH_WANT_IPC_PARSE_VERSION
543 bool
544
545 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
546 bool
547
548 config ARCH_WANT_OLD_COMPAT_IPC
549 select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
550 bool
551
552 config HAVE_ARCH_SECCOMP
553 bool
554 help
555 An arch should select this symbol to support seccomp mode 1 (the fixed
556 syscall policy), and must provide an overrides for __NR_seccomp_sigreturn,
557 and compat syscalls if the asm-generic/seccomp.h defaults need adjustment:
558 - __NR_seccomp_read_32
559 - __NR_seccomp_write_32
560 - __NR_seccomp_exit_32
561 - __NR_seccomp_sigreturn_32
562
563 config HAVE_ARCH_SECCOMP_FILTER
564 bool
565 select HAVE_ARCH_SECCOMP
566 help
567 An arch should select this symbol if it provides all of these things:
568 - all the requirements for HAVE_ARCH_SECCOMP
569 - syscall_get_arch()
570 - syscall_get_arguments()
571 - syscall_rollback()
572 - syscall_set_return_value()
573 - SIGSYS siginfo_t support
574 - secure_computing is called from a ptrace_event()-safe context
575 - secure_computing return value is checked and a return value of -1
576 results in the system call being skipped immediately.
577 - seccomp syscall wired up
578 - if !HAVE_SPARSE_SYSCALL_NR, have SECCOMP_ARCH_NATIVE,
579 SECCOMP_ARCH_NATIVE_NR, SECCOMP_ARCH_NATIVE_NAME defined. If
580 COMPAT is supported, have the SECCOMP_ARCH_COMPAT* defines too.
581
582 config SECCOMP
583 prompt "Enable seccomp to safely execute untrusted bytecode"
584 def_bool y
585 depends on HAVE_ARCH_SECCOMP
586 help
587 This kernel feature is useful for number crunching applications
588 that may need to handle untrusted bytecode during their
589 execution. By using pipes or other transports made available
590 to the process as file descriptors supporting the read/write
591 syscalls, it's possible to isolate those applications in their
592 own address space using seccomp. Once seccomp is enabled via
593 prctl(PR_SET_SECCOMP) or the seccomp() syscall, it cannot be
594 disabled and the task is only allowed to execute a few safe
595 syscalls defined by each seccomp mode.
596
597 If unsure, say Y.
598
599 config SECCOMP_FILTER
600 def_bool y
601 depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
602 help
603 Enable tasks to build secure computing environments defined
604 in terms of Berkeley Packet Filter programs which implement
605 task-defined system call filtering polices.
606
607 See Documentation/userspace-api/seccomp_filter.rst for details.
608
609 config SECCOMP_CACHE_DEBUG
610 bool "Show seccomp filter cache status in /proc/pid/seccomp_cache"
611 depends on SECCOMP_FILTER && !HAVE_SPARSE_SYSCALL_NR
612 depends on PROC_FS
613 help
614 This enables the /proc/pid/seccomp_cache interface to monitor
615 seccomp cache data. The file format is subject to change. Reading
616 the file requires CAP_SYS_ADMIN.
617
618 This option is for debugging only. Enabling presents the risk that
619 an adversary may be able to infer the seccomp filter logic.
620
621 If unsure, say N.
622
623 config HAVE_ARCH_STACKLEAK
624 bool
625 help
626 An architecture should select this if it has the code which
627 fills the used part of the kernel stack with the STACKLEAK_POISON
628 value before returning from system calls.
629
630 config HAVE_STACKPROTECTOR
631 bool
632 help
633 An arch should select this symbol if:
634 - it has implemented a stack canary (e.g. __stack_chk_guard)
635
636 config STACKPROTECTOR
637 bool "Stack Protector buffer overflow detection"
638 depends on HAVE_STACKPROTECTOR
639 depends on $(cc-option,-fstack-protector)
640 default y
641 help
642 This option turns on the "stack-protector" GCC feature. This
643 feature puts, at the beginning of functions, a canary value on
644 the stack just before the return address, and validates
645 the value just before actually returning. Stack based buffer
646 overflows (that need to overwrite this return address) now also
647 overwrite the canary, which gets detected and the attack is then
648 neutralized via a kernel panic.
649
650 Functions will have the stack-protector canary logic added if they
651 have an 8-byte or larger character array on the stack.
652
653 This feature requires gcc version 4.2 or above, or a distribution
654 gcc with the feature backported ("-fstack-protector").
655
656 On an x86 "defconfig" build, this feature adds canary checks to
657 about 3% of all kernel functions, which increases kernel code size
658 by about 0.3%.
659
660 config STACKPROTECTOR_STRONG
661 bool "Strong Stack Protector"
662 depends on STACKPROTECTOR
663 depends on $(cc-option,-fstack-protector-strong)
664 default y
665 help
666 Functions will have the stack-protector canary logic added in any
667 of the following conditions:
668
669 - local variable's address used as part of the right hand side of an
670 assignment or function argument
671 - local variable is an array (or union containing an array),
672 regardless of array type or length
673 - uses register local variables
674
675 This feature requires gcc version 4.9 or above, or a distribution
676 gcc with the feature backported ("-fstack-protector-strong").
677
678 On an x86 "defconfig" build, this feature adds canary checks to
679 about 20% of all kernel functions, which increases the kernel code
680 size by about 2%.
681
682 config ARCH_SUPPORTS_SHADOW_CALL_STACK
683 bool
684 help
685 An architecture should select this if it supports the compiler's
686 Shadow Call Stack and implements runtime support for shadow stack
687 switching.
688
689 config SHADOW_CALL_STACK
690 bool "Shadow Call Stack"
691 depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
692 depends on DYNAMIC_FTRACE_WITH_ARGS || DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
693 depends on MMU
694 help
695 This option enables the compiler's Shadow Call Stack, which
696 uses a shadow stack to protect function return addresses from
697 being overwritten by an attacker. More information can be found
698 in the compiler's documentation:
699
700 - Clang: https://clang.llvm.org/docs/ShadowCallStack.html
701 - GCC: https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html#Instrumentation-Options
702
703 Note that security guarantees in the kernel differ from the
704 ones documented for user space. The kernel must store addresses
705 of shadow stacks in memory, which means an attacker capable of
706 reading and writing arbitrary memory may be able to locate them
707 and hijack control flow by modifying the stacks.
708
709 config DYNAMIC_SCS
710 bool
711 help
712 Set by the arch code if it relies on code patching to insert the
713 shadow call stack push and pop instructions rather than on the
714 compiler.
715
716 config LTO
717 bool
718 help
719 Selected if the kernel will be built using the compiler's LTO feature.
720
721 config LTO_CLANG
722 bool
723 select LTO
724 help
725 Selected if the kernel will be built using Clang's LTO feature.
726
727 config ARCH_SUPPORTS_LTO_CLANG
728 bool
729 help
730 An architecture should select this option if it supports:
731 - compiling with Clang,
732 - compiling inline assembly with Clang's integrated assembler,
733 - and linking with LLD.
734
735 config ARCH_SUPPORTS_LTO_CLANG_THIN
736 bool
737 help
738 An architecture should select this option if it can support Clang's
739 ThinLTO mode.
740
741 config HAS_LTO_CLANG
742 def_bool y
743 depends on CC_IS_CLANG && LD_IS_LLD && AS_IS_LLVM
744 depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
745 depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
746 depends on ARCH_SUPPORTS_LTO_CLANG
747 depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT
748 # https://github.com/ClangBuiltLinux/linux/issues/1721
749 depends on (!KASAN || KASAN_HW_TAGS || CLANG_VERSION >= 170000) || !DEBUG_INFO
750 depends on (!KCOV || CLANG_VERSION >= 170000) || !DEBUG_INFO
751 depends on !GCOV_KERNEL
752 help
753 The compiler and Kconfig options support building with Clang's
754 LTO.
755
756 choice
757 prompt "Link Time Optimization (LTO)"
758 default LTO_NONE
759 help
760 This option enables Link Time Optimization (LTO), which allows the
761 compiler to optimize binaries globally.
762
763 If unsure, select LTO_NONE. Note that LTO is very resource-intensive
764 so it's disabled by default.
765
766 config LTO_NONE
767 bool "None"
768 help
769 Build the kernel normally, without Link Time Optimization (LTO).
770
771 config LTO_CLANG_FULL
772 bool "Clang Full LTO (EXPERIMENTAL)"
773 depends on HAS_LTO_CLANG
774 depends on !COMPILE_TEST
775 select LTO_CLANG
776 help
777 This option enables Clang's full Link Time Optimization (LTO), which
778 allows the compiler to optimize the kernel globally. If you enable
779 this option, the compiler generates LLVM bitcode instead of ELF
780 object files, and the actual compilation from bitcode happens at
781 the LTO link step, which may take several minutes depending on the
782 kernel configuration. More information can be found from LLVM's
783 documentation:
784
785 https://llvm.org/docs/LinkTimeOptimization.html
786
787 During link time, this option can use a large amount of RAM, and
788 may take much longer than the ThinLTO option.
789
790 config LTO_CLANG_THIN
791 bool "Clang ThinLTO (EXPERIMENTAL)"
792 depends on HAS_LTO_CLANG && ARCH_SUPPORTS_LTO_CLANG_THIN
793 select LTO_CLANG
794 help
795 This option enables Clang's ThinLTO, which allows for parallel
796 optimization and faster incremental compiles compared to the
797 CONFIG_LTO_CLANG_FULL option. More information can be found
798 from Clang's documentation:
799
800 https://clang.llvm.org/docs/ThinLTO.html
801
802 If unsure, say Y.
803 endchoice
804
805 config ARCH_SUPPORTS_CFI_CLANG
806 bool
807 help
808 An architecture should select this option if it can support Clang's
809 Control-Flow Integrity (CFI) checking.
810
811 config ARCH_USES_CFI_TRAPS
812 bool
813
814 config CFI_CLANG
815 bool "Use Clang's Control Flow Integrity (CFI)"
816 depends on ARCH_SUPPORTS_CFI_CLANG
817 depends on $(cc-option,-fsanitize=kcfi)
818 help
819 This option enables Clang's forward-edge Control Flow Integrity
820 (CFI) checking, where the compiler injects a runtime check to each
821 indirect function call to ensure the target is a valid function with
822 the correct static type. This restricts possible call targets and
823 makes it more difficult for an attacker to exploit bugs that allow
824 the modification of stored function pointers. More information can be
825 found from Clang's documentation:
826
827 https://clang.llvm.org/docs/ControlFlowIntegrity.html
828
829 config CFI_PERMISSIVE
830 bool "Use CFI in permissive mode"
831 depends on CFI_CLANG
832 help
833 When selected, Control Flow Integrity (CFI) violations result in a
834 warning instead of a kernel panic. This option should only be used
835 for finding indirect call type mismatches during development.
836
837 If unsure, say N.
838
839 config HAVE_ARCH_WITHIN_STACK_FRAMES
840 bool
841 help
842 An architecture should select this if it can walk the kernel stack
843 frames to determine if an object is part of either the arguments
844 or local variables (i.e. that it excludes saved return addresses,
845 and similar) by implementing an inline arch_within_stack_frames(),
846 which is used by CONFIG_HARDENED_USERCOPY.
847
848 config HAVE_CONTEXT_TRACKING_USER
849 bool
850 help
851 Provide kernel/user boundaries probes necessary for subsystems
852 that need it, such as userspace RCU extended quiescent state.
853 Syscalls need to be wrapped inside user_exit()-user_enter(), either
854 optimized behind static key or through the slow path using TIF_NOHZ
855 flag. Exceptions handlers must be wrapped as well. Irqs are already
856 protected inside ct_irq_enter/ct_irq_exit() but preemption or signal
857 handling on irq exit still need to be protected.
858
859 config HAVE_CONTEXT_TRACKING_USER_OFFSTACK
860 bool
861 help
862 Architecture neither relies on exception_enter()/exception_exit()
863 nor on schedule_user(). Also preempt_schedule_notrace() and
864 preempt_schedule_irq() can't be called in a preemptible section
865 while context tracking is CONTEXT_USER. This feature reflects a sane
866 entry implementation where the following requirements are met on
867 critical entry code, ie: before user_exit() or after user_enter():
868
869 - Critical entry code isn't preemptible (or better yet:
870 not interruptible).
871 - No use of RCU read side critical sections, unless ct_nmi_enter()
872 got called.
873 - No use of instrumentation, unless instrumentation_begin() got
874 called.
875
876 config HAVE_TIF_NOHZ
877 bool
878 help
879 Arch relies on TIF_NOHZ and syscall slow path to implement context
880 tracking calls to user_enter()/user_exit().
881
882 config HAVE_VIRT_CPU_ACCOUNTING
883 bool
884
885 config HAVE_VIRT_CPU_ACCOUNTING_IDLE
886 bool
887 help
888 Architecture has its own way to account idle CPU time and therefore
889 doesn't implement vtime_account_idle().
890
891 config ARCH_HAS_SCALED_CPUTIME
892 bool
893
894 config HAVE_VIRT_CPU_ACCOUNTING_GEN
895 bool
896 default y if 64BIT
897 help
898 With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
899 Before enabling this option, arch code must be audited
900 to ensure there are no races in concurrent read/write of
901 cputime_t. For example, reading/writing 64-bit cputime_t on
902 some 32-bit arches may require multiple accesses, so proper
903 locking is needed to protect against concurrent accesses.
904
905 config HAVE_IRQ_TIME_ACCOUNTING
906 bool
907 help
908 Archs need to ensure they use a high enough resolution clock to
909 support irq time accounting and then call enable_sched_clock_irqtime().
910
911 config HAVE_MOVE_PUD
912 bool
913 help
914 Architectures that select this are able to move page tables at the
915 PUD level. If there are only 3 page table levels, the move effectively
916 happens at the PGD level.
917
918 config HAVE_MOVE_PMD
919 bool
920 help
921 Archs that select this are able to move page tables at the PMD level.
922
923 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
924 bool
925
926 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
927 bool
928
929 config HAVE_ARCH_HUGE_VMAP
930 bool
931
932 #
933 # Archs that select this would be capable of PMD-sized vmaps (i.e.,
934 # arch_vmap_pmd_supported() returns true). The VM_ALLOW_HUGE_VMAP flag
935 # must be used to enable allocations to use hugepages.
936 #
937 config HAVE_ARCH_HUGE_VMALLOC
938 depends on HAVE_ARCH_HUGE_VMAP
939 bool
940
941 config ARCH_WANT_HUGE_PMD_SHARE
942 bool
943
944 # Archs that want to use pmd_mkwrite on kernel memory need it defined even
945 # if there are no userspace memory management features that use it
946 config ARCH_WANT_KERNEL_PMD_MKWRITE
947 bool
948
949 config ARCH_WANT_PMD_MKWRITE
950 def_bool TRANSPARENT_HUGEPAGE || ARCH_WANT_KERNEL_PMD_MKWRITE
951
952 config HAVE_ARCH_SOFT_DIRTY
953 bool
954
955 config HAVE_MOD_ARCH_SPECIFIC
956 bool
957 help
958 The arch uses struct mod_arch_specific to store data. Many arches
959 just need a simple module loader without arch specific data - those
960 should not enable this.
961
962 config MODULES_USE_ELF_RELA
963 bool
964 help
965 Modules only use ELF RELA relocations. Modules with ELF REL
966 relocations will give an error.
967
968 config MODULES_USE_ELF_REL
969 bool
970 help
971 Modules only use ELF REL relocations. Modules with ELF RELA
972 relocations will give an error.
973
974 config ARCH_WANTS_MODULES_DATA_IN_VMALLOC
975 bool
976 help
977 For architectures like powerpc/32 which have constraints on module
978 allocation and need to allocate module data outside of module area.
979
980 config ARCH_WANTS_EXECMEM_LATE
981 bool
982 help
983 For architectures that do not allocate executable memory early on
984 boot, but rather require its initialization late when there is
985 enough entropy for module space randomization, for instance
986 arm64.
987
988 config HAVE_IRQ_EXIT_ON_IRQ_STACK
989 bool
990 help
991 Architecture doesn't only execute the irq handler on the irq stack
992 but also irq_exit(). This way we can process softirqs on this irq
993 stack instead of switching to a new one when we call __do_softirq()
994 in the end of an hardirq.
995 This spares a stack switch and improves cache usage on softirq
996 processing.
997
998 config HAVE_SOFTIRQ_ON_OWN_STACK
999 bool
1000 help
1001 Architecture provides a function to run __do_softirq() on a
1002 separate stack.
1003
1004 config SOFTIRQ_ON_OWN_STACK
1005 def_bool HAVE_SOFTIRQ_ON_OWN_STACK && !PREEMPT_RT
1006
1007 config ALTERNATE_USER_ADDRESS_SPACE
1008 bool
1009 help
1010 Architectures set this when the CPU uses separate address
1011 spaces for kernel and user space pointers. In this case, the
1012 access_ok() check on a __user pointer is skipped.
1013
1014 config PGTABLE_LEVELS
1015 int
1016 default 2
1017
1018 config ARCH_HAS_ELF_RANDOMIZE
1019 bool
1020 help
1021 An architecture supports choosing randomized locations for
1022 stack, mmap, brk, and ET_DYN. Defined functions:
1023 - arch_mmap_rnd()
1024 - arch_randomize_brk()
1025
1026 config HAVE_ARCH_MMAP_RND_BITS
1027 bool
1028 help
1029 An arch should select this symbol if it supports setting a variable
1030 number of bits for use in establishing the base address for mmap
1031 allocations, has MMU enabled and provides values for both:
1032 - ARCH_MMAP_RND_BITS_MIN
1033 - ARCH_MMAP_RND_BITS_MAX
1034
1035 config HAVE_EXIT_THREAD
1036 bool
1037 help
1038 An architecture implements exit_thread.
1039
1040 config ARCH_MMAP_RND_BITS_MIN
1041 int
1042
1043 config ARCH_MMAP_RND_BITS_MAX
1044 int
1045
1046 config ARCH_MMAP_RND_BITS_DEFAULT
1047 int
1048
1049 config ARCH_MMAP_RND_BITS
1050 int "Number of bits to use for ASLR of mmap base address" if EXPERT
1051 range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
1052 default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
1053 default ARCH_MMAP_RND_BITS_MIN
1054 depends on HAVE_ARCH_MMAP_RND_BITS
1055 help
1056 This value can be used to select the number of bits to use to
1057 determine the random offset to the base address of vma regions
1058 resulting from mmap allocations. This value will be bounded
1059 by the architecture's minimum and maximum supported values.
1060
1061 This value can be changed after boot using the
1062 /proc/sys/vm/mmap_rnd_bits tunable
1063
1064 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
1065 bool
1066 help
1067 An arch should select this symbol if it supports running applications
1068 in compatibility mode, supports setting a variable number of bits for
1069 use in establishing the base address for mmap allocations, has MMU
1070 enabled and provides values for both:
1071 - ARCH_MMAP_RND_COMPAT_BITS_MIN
1072 - ARCH_MMAP_RND_COMPAT_BITS_MAX
1073
1074 config ARCH_MMAP_RND_COMPAT_BITS_MIN
1075 int
1076
1077 config ARCH_MMAP_RND_COMPAT_BITS_MAX
1078 int
1079
1080 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
1081 int
1082
1083 config ARCH_MMAP_RND_COMPAT_BITS
1084 int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
1085 range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
1086 default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
1087 default ARCH_MMAP_RND_COMPAT_BITS_MIN
1088 depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
1089 help
1090 This value can be used to select the number of bits to use to
1091 determine the random offset to the base address of vma regions
1092 resulting from mmap allocations for compatible applications This
1093 value will be bounded by the architecture's minimum and maximum
1094 supported values.
1095
1096 This value can be changed after boot using the
1097 /proc/sys/vm/mmap_rnd_compat_bits tunable
1098
1099 config HAVE_ARCH_COMPAT_MMAP_BASES
1100 bool
1101 help
1102 This allows 64bit applications to invoke 32-bit mmap() syscall
1103 and vice-versa 32-bit applications to call 64-bit mmap().
1104 Required for applications doing different bitness syscalls.
1105
1106 config HAVE_PAGE_SIZE_4KB
1107 bool
1108
1109 config HAVE_PAGE_SIZE_8KB
1110 bool
1111
1112 config HAVE_PAGE_SIZE_16KB
1113 bool
1114
1115 config HAVE_PAGE_SIZE_32KB
1116 bool
1117
1118 config HAVE_PAGE_SIZE_64KB
1119 bool
1120
1121 config HAVE_PAGE_SIZE_256KB
1122 bool
1123
1124 choice
1125 prompt "MMU page size"
1126
1127 config PAGE_SIZE_4KB
1128 bool "4KiB pages"
1129 depends on HAVE_PAGE_SIZE_4KB
1130 help
1131 This option select the standard 4KiB Linux page size and the only
1132 available option on many architectures. Using 4KiB page size will
1133 minimize memory consumption and is therefore recommended for low
1134 memory systems.
1135 Some software that is written for x86 systems makes incorrect
1136 assumptions about the page size and only runs on 4KiB pages.
1137
1138 config PAGE_SIZE_8KB
1139 bool "8KiB pages"
1140 depends on HAVE_PAGE_SIZE_8KB
1141 help
1142 This option is the only supported page size on a few older
1143 processors, and can be slightly faster than 4KiB pages.
1144
1145 config PAGE_SIZE_16KB
1146 bool "16KiB pages"
1147 depends on HAVE_PAGE_SIZE_16KB
1148 help
1149 This option is usually a good compromise between memory
1150 consumption and performance for typical desktop and server
1151 workloads, often saving a level of page table lookups compared
1152 to 4KB pages as well as reducing TLB pressure and overhead of
1153 per-page operations in the kernel at the expense of a larger
1154 page cache.
1155
1156 config PAGE_SIZE_32KB
1157 bool "32KiB pages"
1158 depends on HAVE_PAGE_SIZE_32KB
1159 help
1160 Using 32KiB page size will result in slightly higher performance
1161 kernel at the price of higher memory consumption compared to
1162 16KiB pages. This option is available only on cnMIPS cores.
1163 Note that you will need a suitable Linux distribution to
1164 support this.
1165
1166 config PAGE_SIZE_64KB
1167 bool "64KiB pages"
1168 depends on HAVE_PAGE_SIZE_64KB
1169 help
1170 Using 64KiB page size will result in slightly higher performance
1171 kernel at the price of much higher memory consumption compared to
1172 4KiB or 16KiB pages.
1173 This is not suitable for general-purpose workloads but the
1174 better performance may be worth the cost for certain types of
1175 supercomputing or database applications that work mostly with
1176 large in-memory data rather than small files.
1177
1178 config PAGE_SIZE_256KB
1179 bool "256KiB pages"
1180 depends on HAVE_PAGE_SIZE_256KB
1181 help
1182 256KiB pages have little practical value due to their extreme
1183 memory usage. The kernel will only be able to run applications
1184 that have been compiled with '-zmax-page-size' set to 256KiB
1185 (the default is 64KiB or 4KiB on most architectures).
1186
1187 endchoice
1188
1189 config PAGE_SIZE_LESS_THAN_64KB
1190 def_bool y
1191 depends on !PAGE_SIZE_64KB
1192 depends on PAGE_SIZE_LESS_THAN_256KB
1193
1194 config PAGE_SIZE_LESS_THAN_256KB
1195 def_bool y
1196 depends on !PAGE_SIZE_256KB
1197
1198 config PAGE_SHIFT
1199 int
1200 default 12 if PAGE_SIZE_4KB
1201 default 13 if PAGE_SIZE_8KB
1202 default 14 if PAGE_SIZE_16KB
1203 default 15 if PAGE_SIZE_32KB
1204 default 16 if PAGE_SIZE_64KB
1205 default 18 if PAGE_SIZE_256KB
1206
1207 # This allows to use a set of generic functions to determine mmap base
1208 # address by giving priority to top-down scheme only if the process
1209 # is not in legacy mode (compat task, unlimited stack size or
1210 # sysctl_legacy_va_layout).
1211 # Architecture that selects this option can provide its own version of:
1212 # - STACK_RND_MASK
1213 config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
1214 bool
1215 depends on MMU
1216 select ARCH_HAS_ELF_RANDOMIZE
1217
1218 config HAVE_OBJTOOL
1219 bool
1220
1221 config HAVE_JUMP_LABEL_HACK
1222 bool
1223
1224 config HAVE_NOINSTR_HACK
1225 bool
1226
1227 config HAVE_NOINSTR_VALIDATION
1228 bool
1229
1230 config HAVE_UACCESS_VALIDATION
1231 bool
1232 select OBJTOOL
1233
1234 config HAVE_STACK_VALIDATION
1235 bool
1236 help
1237 Architecture supports objtool compile-time frame pointer rule
1238 validation.
1239
1240 config HAVE_RELIABLE_STACKTRACE
1241 bool
1242 help
1243 Architecture has either save_stack_trace_tsk_reliable() or
1244 arch_stack_walk_reliable() function which only returns a stack trace
1245 if it can guarantee the trace is reliable.
1246
1247 config HAVE_ARCH_HASH
1248 bool
1249 default n
1250 help
1251 If this is set, the architecture provides an <asm/hash.h>
1252 file which provides platform-specific implementations of some
1253 functions in <linux/hash.h> or fs/namei.c.
1254
1255 config HAVE_ARCH_NVRAM_OPS
1256 bool
1257
1258 config ISA_BUS_API
1259 def_bool ISA
1260
1261 #
1262 # ABI hall of shame
1263 #
1264 config CLONE_BACKWARDS
1265 bool
1266 help
1267 Architecture has tls passed as the 4th argument of clone(2),
1268 not the 5th one.
1269
1270 config CLONE_BACKWARDS2
1271 bool
1272 help
1273 Architecture has the first two arguments of clone(2) swapped.
1274
1275 config CLONE_BACKWARDS3
1276 bool
1277 help
1278 Architecture has tls passed as the 3rd argument of clone(2),
1279 not the 5th one.
1280
1281 config ODD_RT_SIGACTION
1282 bool
1283 help
1284 Architecture has unusual rt_sigaction(2) arguments
1285
1286 config OLD_SIGSUSPEND
1287 bool
1288 help
1289 Architecture has old sigsuspend(2) syscall, of one-argument variety
1290
1291 config OLD_SIGSUSPEND3
1292 bool
1293 help
1294 Even weirder antique ABI - three-argument sigsuspend(2)
1295
1296 config OLD_SIGACTION
1297 bool
1298 help
1299 Architecture has old sigaction(2) syscall. Nope, not the same
1300 as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
1301 but fairly different variant of sigaction(2), thanks to OSF/1
1302 compatibility...
1303
1304 config COMPAT_OLD_SIGACTION
1305 bool
1306
1307 config COMPAT_32BIT_TIME
1308 bool "Provide system calls for 32-bit time_t"
1309 default !64BIT || COMPAT
1310 help
1311 This enables 32 bit time_t support in addition to 64 bit time_t support.
1312 This is relevant on all 32-bit architectures, and 64-bit architectures
1313 as part of compat syscall handling.
1314
1315 config ARCH_NO_PREEMPT
1316 bool
1317
1318 config ARCH_SUPPORTS_RT
1319 bool
1320
1321 config CPU_NO_EFFICIENT_FFS
1322 def_bool n
1323
1324 config HAVE_ARCH_VMAP_STACK
1325 def_bool n
1326 help
1327 An arch should select this symbol if it can support kernel stacks
1328 in vmalloc space. This means:
1329
1330 - vmalloc space must be large enough to hold many kernel stacks.
1331 This may rule out many 32-bit architectures.
1332
1333 - Stacks in vmalloc space need to work reliably. For example, if
1334 vmap page tables are created on demand, either this mechanism
1335 needs to work while the stack points to a virtual address with
1336 unpopulated page tables or arch code (switch_to() and switch_mm(),
1337 most likely) needs to ensure that the stack's page table entries
1338 are populated before running on a possibly unpopulated stack.
1339
1340 - If the stack overflows into a guard page, something reasonable
1341 should happen. The definition of "reasonable" is flexible, but
1342 instantly rebooting without logging anything would be unfriendly.
1343
1344 config VMAP_STACK
1345 default y
1346 bool "Use a virtually-mapped stack"
1347 depends on HAVE_ARCH_VMAP_STACK
1348 depends on !KASAN || KASAN_HW_TAGS || KASAN_VMALLOC
1349 help
1350 Enable this if you want the use virtually-mapped kernel stacks
1351 with guard pages. This causes kernel stack overflows to be
1352 caught immediately rather than causing difficult-to-diagnose
1353 corruption.
1354
1355 To use this with software KASAN modes, the architecture must support
1356 backing virtual mappings with real shadow memory, and KASAN_VMALLOC
1357 must be enabled.
1358
1359 config HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
1360 def_bool n
1361 help
1362 An arch should select this symbol if it can support kernel stack
1363 offset randomization with calls to add_random_kstack_offset()
1364 during syscall entry and choose_random_kstack_offset() during
1365 syscall exit. Careful removal of -fstack-protector-strong and
1366 -fstack-protector should also be applied to the entry code and
1367 closely examined, as the artificial stack bump looks like an array
1368 to the compiler, so it will attempt to add canary checks regardless
1369 of the static branch state.
1370
1371 config RANDOMIZE_KSTACK_OFFSET
1372 bool "Support for randomizing kernel stack offset on syscall entry" if EXPERT
1373 default y
1374 depends on HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
1375 depends on INIT_STACK_NONE || !CC_IS_CLANG || CLANG_VERSION >= 140000
1376 help
1377 The kernel stack offset can be randomized (after pt_regs) by
1378 roughly 5 bits of entropy, frustrating memory corruption
1379 attacks that depend on stack address determinism or
1380 cross-syscall address exposures.
1381
1382 The feature is controlled via the "randomize_kstack_offset=on/off"
1383 kernel boot param, and if turned off has zero overhead due to its use
1384 of static branches (see JUMP_LABEL).
1385
1386 If unsure, say Y.
1387
1388 config RANDOMIZE_KSTACK_OFFSET_DEFAULT
1389 bool "Default state of kernel stack offset randomization"
1390 depends on RANDOMIZE_KSTACK_OFFSET
1391 help
1392 Kernel stack offset randomization is controlled by kernel boot param
1393 "randomize_kstack_offset=on/off", and this config chooses the default
1394 boot state.
1395
1396 config ARCH_OPTIONAL_KERNEL_RWX
1397 def_bool n
1398
1399 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1400 def_bool n
1401
1402 config ARCH_HAS_STRICT_KERNEL_RWX
1403 def_bool n
1404
1405 config STRICT_KERNEL_RWX
1406 bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
1407 depends on ARCH_HAS_STRICT_KERNEL_RWX
1408 default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1409 help
1410 If this is set, kernel text and rodata memory will be made read-only,
1411 and non-text memory will be made non-executable. This provides
1412 protection against certain security exploits (e.g. executing the heap
1413 or modifying text)
1414
1415 These features are considered standard security practice these days.
1416 You should say Y here in almost all cases.
1417
1418 config ARCH_HAS_STRICT_MODULE_RWX
1419 def_bool n
1420
1421 config STRICT_MODULE_RWX
1422 bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
1423 depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
1424 default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1425 help
1426 If this is set, module text and rodata memory will be made read-only,
1427 and non-text memory will be made non-executable. This provides
1428 protection against certain security exploits (e.g. writing to text)
1429
1430 # select if the architecture provides an asm/dma-direct.h header
1431 config ARCH_HAS_PHYS_TO_DMA
1432 bool
1433
1434 config HAVE_ARCH_COMPILER_H
1435 bool
1436 help
1437 An architecture can select this if it provides an
1438 asm/compiler.h header that should be included after
1439 linux/compiler-*.h in order to override macro definitions that those
1440 headers generally provide.
1441
1442 config HAVE_ARCH_PREL32_RELOCATIONS
1443 bool
1444 help
1445 May be selected by an architecture if it supports place-relative
1446 32-bit relocations, both in the toolchain and in the module loader,
1447 in which case relative references can be used in special sections
1448 for PCI fixup, initcalls etc which are only half the size on 64 bit
1449 architectures, and don't require runtime relocation on relocatable
1450 kernels.
1451
1452 config ARCH_USE_MEMREMAP_PROT
1453 bool
1454
1455 config LOCK_EVENT_COUNTS
1456 bool "Locking event counts collection"
1457 depends on DEBUG_FS
1458 help
1459 Enable light-weight counting of various locking related events
1460 in the system with minimal performance impact. This reduces
1461 the chance of application behavior change because of timing
1462 differences. The counts are reported via debugfs.
1463
1464 # Select if the architecture has support for applying RELR relocations.
1465 config ARCH_HAS_RELR
1466 bool
1467
1468 config RELR
1469 bool "Use RELR relocation packing"
1470 depends on ARCH_HAS_RELR && TOOLS_SUPPORT_RELR
1471 default y
1472 help
1473 Store the kernel's dynamic relocations in the RELR relocation packing
1474 format. Requires a compatible linker (LLD supports this feature), as
1475 well as compatible NM and OBJCOPY utilities (llvm-nm and llvm-objcopy
1476 are compatible).
1477
1478 config ARCH_HAS_MEM_ENCRYPT
1479 bool
1480
1481 config ARCH_HAS_CC_PLATFORM
1482 bool
1483
1484 config HAVE_SPARSE_SYSCALL_NR
1485 bool
1486 help
1487 An architecture should select this if its syscall numbering is sparse
1488 to save space. For example, MIPS architecture has a syscall array with
1489 entries at 4000, 5000 and 6000 locations. This option turns on syscall
1490 related optimizations for a given architecture.
1491
1492 config ARCH_HAS_VDSO_DATA
1493 bool
1494
1495 config HAVE_STATIC_CALL
1496 bool
1497
1498 config HAVE_STATIC_CALL_INLINE
1499 bool
1500 depends on HAVE_STATIC_CALL
1501 select OBJTOOL
1502
1503 config HAVE_PREEMPT_DYNAMIC
1504 bool
1505
1506 config HAVE_PREEMPT_DYNAMIC_CALL
1507 bool
1508 depends on HAVE_STATIC_CALL
1509 select HAVE_PREEMPT_DYNAMIC
1510 help
1511 An architecture should select this if it can handle the preemption
1512 model being selected at boot time using static calls.
1513
1514 Where an architecture selects HAVE_STATIC_CALL_INLINE, any call to a
1515 preemption function will be patched directly.
1516
1517 Where an architecture does not select HAVE_STATIC_CALL_INLINE, any
1518 call to a preemption function will go through a trampoline, and the
1519 trampoline will be patched.
1520
1521 It is strongly advised to support inline static call to avoid any
1522 overhead.
1523
1524 config HAVE_PREEMPT_DYNAMIC_KEY
1525 bool
1526 depends on HAVE_ARCH_JUMP_LABEL
1527 select HAVE_PREEMPT_DYNAMIC
1528 help
1529 An architecture should select this if it can handle the preemption
1530 model being selected at boot time using static keys.
1531
1532 Each preemption function will be given an early return based on a
1533 static key. This should have slightly lower overhead than non-inline
1534 static calls, as this effectively inlines each trampoline into the
1535 start of its callee. This may avoid redundant work, and may
1536 integrate better with CFI schemes.
1537
1538 This will have greater overhead than using inline static calls as
1539 the call to the preemption function cannot be entirely elided.
1540
1541 config ARCH_WANT_LD_ORPHAN_WARN
1542 bool
1543 help
1544 An arch should select this symbol once all linker sections are explicitly
1545 included, size-asserted, or discarded in the linker scripts. This is
1546 important because we never want expected sections to be placed heuristically
1547 by the linker, since the locations of such sections can change between linker
1548 versions.
1549
1550 config HAVE_ARCH_PFN_VALID
1551 bool
1552
1553 config ARCH_SUPPORTS_DEBUG_PAGEALLOC
1554 bool
1555
1556 config ARCH_SUPPORTS_PAGE_TABLE_CHECK
1557 bool
1558
1559 config ARCH_SPLIT_ARG64
1560 bool
1561 help
1562 If a 32-bit architecture requires 64-bit arguments to be split into
1563 pairs of 32-bit arguments, select this option.
1564
1565 config ARCH_HAS_ELFCORE_COMPAT
1566 bool
1567
1568 config ARCH_HAS_PARANOID_L1D_FLUSH
1569 bool
1570
1571 config ARCH_HAVE_TRACE_MMIO_ACCESS
1572 bool
1573
1574 config DYNAMIC_SIGFRAME
1575 bool
1576
1577 # Select, if arch has a named attribute group bound to NUMA device nodes.
1578 config HAVE_ARCH_NODE_DEV_GROUP
1579 bool
1580
1581 config ARCH_HAS_HW_PTE_YOUNG
1582 bool
1583 help
1584 Architectures that select this option are capable of setting the
1585 accessed bit in PTE entries when using them as part of linear address
1586 translations. Architectures that require runtime check should select
1587 this option and override arch_has_hw_pte_young().
1588
1589 config ARCH_HAS_NONLEAF_PMD_YOUNG
1590 bool
1591 help
1592 Architectures that select this option are capable of setting the
1593 accessed bit in non-leaf PMD entries when using them as part of linear
1594 address translations. Page table walkers that clear the accessed bit
1595 may use this capability to reduce their search space.
1596
1597 config ARCH_HAS_KERNEL_FPU_SUPPORT
1598 bool
1599 help
1600 Architectures that select this option can run floating-point code in
1601 the kernel, as described in Documentation/core-api/floating-point.rst.
1602
1603 source "kernel/gcov/Kconfig"
1604
1605 source "scripts/gcc-plugins/Kconfig"
1606
1607 config FUNCTION_ALIGNMENT_4B
1608 bool
1609
1610 config FUNCTION_ALIGNMENT_8B
1611 bool
1612
1613 config FUNCTION_ALIGNMENT_16B
1614 bool
1615
1616 config FUNCTION_ALIGNMENT_32B
1617 bool
1618
1619 config FUNCTION_ALIGNMENT_64B
1620 bool
1621
1622 config FUNCTION_ALIGNMENT
1623 int
1624 default 64 if FUNCTION_ALIGNMENT_64B
1625 default 32 if FUNCTION_ALIGNMENT_32B
1626 default 16 if FUNCTION_ALIGNMENT_16B
1627 default 8 if FUNCTION_ALIGNMENT_8B
1628 default 4 if FUNCTION_ALIGNMENT_4B
1629 default 0
1630
1631 config CC_HAS_MIN_FUNCTION_ALIGNMENT
1632 # Detect availability of the GCC option -fmin-function-alignment which
1633 # guarantees minimal alignment for all functions, unlike
1634 # -falign-functions which the compiler ignores for cold functions.
1635 def_bool $(cc-option, -fmin-function-alignment=8)
1636
1637 config CC_HAS_SANE_FUNCTION_ALIGNMENT
1638 # Set if the guaranteed alignment with -fmin-function-alignment is
1639 # available or extra care is required in the kernel. Clang provides
1640 # strict alignment always, even with -falign-functions.
1641 def_bool CC_HAS_MIN_FUNCTION_ALIGNMENT || CC_IS_CLANG
1642
1643 config ARCH_NEED_CMPXCHG_1_EMU
1644 bool
1645
1646 endmenu
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