1# SPDX-License-Identifier: GPL-2.0 2# 3# General architecture dependent options 4# 5 6# 7# Note: arch/$(SRCARCH)/Kconfig needs to be included first so that it can 8# override the default values in this file. 9# 10source "arch/$(SRCARCH)/Kconfig" 11 12config ARCH_CONFIGURES_CPU_MITIGATIONS 13 bool 14 15if !ARCH_CONFIGURES_CPU_MITIGATIONS 16config CPU_MITIGATIONS 17 def_bool y 18endif 19 20# 21# Selected by architectures that need custom DMA operations for e.g. legacy 22# IOMMUs not handled by dma-iommu. Drivers must never select this symbol. 23# 24config ARCH_HAS_DMA_OPS 25 depends on HAS_DMA 26 select DMA_OPS_HELPERS 27 bool 28 29menu "General architecture-dependent options" 30 31config ARCH_HAS_SUBPAGE_FAULTS 32 bool 33 help 34 Select if the architecture can check permissions at sub-page 35 granularity (e.g. arm64 MTE). The probe_user_*() functions 36 must be implemented. 37 38config HOTPLUG_SMT 39 bool 40 41config SMT_NUM_THREADS_DYNAMIC 42 bool 43 44# Selected by HOTPLUG_CORE_SYNC_DEAD or HOTPLUG_CORE_SYNC_FULL 45config HOTPLUG_CORE_SYNC 46 bool 47 48# Basic CPU dead synchronization selected by architecture 49config HOTPLUG_CORE_SYNC_DEAD 50 bool 51 select HOTPLUG_CORE_SYNC 52 53# Full CPU synchronization with alive state selected by architecture 54config HOTPLUG_CORE_SYNC_FULL 55 bool 56 select HOTPLUG_CORE_SYNC_DEAD if HOTPLUG_CPU 57 select HOTPLUG_CORE_SYNC 58 59config HOTPLUG_SPLIT_STARTUP 60 bool 61 select HOTPLUG_CORE_SYNC_FULL 62 63config HOTPLUG_PARALLEL 64 bool 65 select HOTPLUG_SPLIT_STARTUP 66 67config GENERIC_ENTRY 68 bool 69 70config KPROBES 71 bool "Kprobes" 72 depends on HAVE_KPROBES 73 select KALLSYMS 74 select EXECMEM 75 select NEED_TASKS_RCU 76 help 77 Kprobes allows you to trap at almost any kernel address and 78 execute a callback function. register_kprobe() establishes 79 a probepoint and specifies the callback. Kprobes is useful 80 for kernel debugging, non-intrusive instrumentation and testing. 81 If in doubt, say "N". 82 83config JUMP_LABEL 84 bool "Optimize very unlikely/likely branches" 85 depends on HAVE_ARCH_JUMP_LABEL 86 select OBJTOOL if HAVE_JUMP_LABEL_HACK 87 help 88 This option enables a transparent branch optimization that 89 makes certain almost-always-true or almost-always-false branch 90 conditions even cheaper to execute within the kernel. 91 92 Certain performance-sensitive kernel code, such as trace points, 93 scheduler functionality, networking code and KVM have such 94 branches and include support for this optimization technique. 95 96 If it is detected that the compiler has support for "asm goto", 97 the kernel will compile such branches with just a nop 98 instruction. When the condition flag is toggled to true, the 99 nop will be converted to a jump instruction to execute the 100 conditional block of instructions. 101 102 This technique lowers overhead and stress on the branch prediction 103 of the processor and generally makes the kernel faster. The update 104 of the condition is slower, but those are always very rare. 105 106 ( On 32-bit x86, the necessary options added to the compiler 107 flags may increase the size of the kernel slightly. ) 108 109config STATIC_KEYS_SELFTEST 110 bool "Static key selftest" 111 depends on JUMP_LABEL 112 help 113 Boot time self-test of the branch patching code. 114 115config STATIC_CALL_SELFTEST 116 bool "Static call selftest" 117 depends on HAVE_STATIC_CALL 118 help 119 Boot time self-test of the call patching code. 120 121config OPTPROBES 122 def_bool y 123 depends on KPROBES && HAVE_OPTPROBES 124 select NEED_TASKS_RCU 125 126config KPROBES_ON_FTRACE 127 def_bool y 128 depends on KPROBES && HAVE_KPROBES_ON_FTRACE 129 depends on DYNAMIC_FTRACE_WITH_REGS 130 help 131 If function tracer is enabled and the arch supports full 132 passing of pt_regs to function tracing, then kprobes can 133 optimize on top of function tracing. 134 135config UPROBES 136 def_bool n 137 depends on ARCH_SUPPORTS_UPROBES 138 select TASKS_TRACE_RCU 139 help 140 Uprobes is the user-space counterpart to kprobes: they 141 enable instrumentation applications (such as 'perf probe') 142 to establish unintrusive probes in user-space binaries and 143 libraries, by executing handler functions when the probes 144 are hit by user-space applications. 145 146 ( These probes come in the form of single-byte breakpoints, 147 managed by the kernel and kept transparent to the probed 148 application. ) 149 150config HAVE_64BIT_ALIGNED_ACCESS 151 def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS 152 help 153 Some architectures require 64 bit accesses to be 64 bit 154 aligned, which also requires structs containing 64 bit values 155 to be 64 bit aligned too. This includes some 32 bit 156 architectures which can do 64 bit accesses, as well as 64 bit 157 architectures without unaligned access. 158 159 This symbol should be selected by an architecture if 64 bit 160 accesses are required to be 64 bit aligned in this way even 161 though it is not a 64 bit architecture. 162 163 See Documentation/core-api/unaligned-memory-access.rst for 164 more information on the topic of unaligned memory accesses. 165 166config HAVE_EFFICIENT_UNALIGNED_ACCESS 167 bool 168 help 169 Some architectures are unable to perform unaligned accesses 170 without the use of get_unaligned/put_unaligned. Others are 171 unable to perform such accesses efficiently (e.g. trap on 172 unaligned access and require fixing it up in the exception 173 handler.) 174 175 This symbol should be selected by an architecture if it can 176 perform unaligned accesses efficiently to allow different 177 code paths to be selected for these cases. Some network 178 drivers, for example, could opt to not fix up alignment 179 problems with received packets if doing so would not help 180 much. 181 182 See Documentation/core-api/unaligned-memory-access.rst for more 183 information on the topic of unaligned memory accesses. 184 185config ARCH_USE_BUILTIN_BSWAP 186 bool 187 help 188 Modern versions of GCC (since 4.4) have builtin functions 189 for handling byte-swapping. Using these, instead of the old 190 inline assembler that the architecture code provides in the 191 __arch_bswapXX() macros, allows the compiler to see what's 192 happening and offers more opportunity for optimisation. In 193 particular, the compiler will be able to combine the byteswap 194 with a nearby load or store and use load-and-swap or 195 store-and-swap instructions if the architecture has them. It 196 should almost *never* result in code which is worse than the 197 hand-coded assembler in <asm/swab.h>. But just in case it 198 does, the use of the builtins is optional. 199 200 Any architecture with load-and-swap or store-and-swap 201 instructions should set this. And it shouldn't hurt to set it 202 on architectures that don't have such instructions. 203 204config KRETPROBES 205 def_bool y 206 depends on KPROBES && (HAVE_KRETPROBES || HAVE_RETHOOK) 207 208config KRETPROBE_ON_RETHOOK 209 def_bool y 210 depends on HAVE_RETHOOK 211 depends on KRETPROBES 212 select RETHOOK 213 214config USER_RETURN_NOTIFIER 215 bool 216 depends on HAVE_USER_RETURN_NOTIFIER 217 help 218 Provide a kernel-internal notification when a cpu is about to 219 switch to user mode. 220 221config HAVE_IOREMAP_PROT 222 bool 223 224config HAVE_KPROBES 225 bool 226 227config HAVE_KRETPROBES 228 bool 229 230config HAVE_OPTPROBES 231 bool 232 233config HAVE_KPROBES_ON_FTRACE 234 bool 235 236config ARCH_CORRECT_STACKTRACE_ON_KRETPROBE 237 bool 238 help 239 Since kretprobes modifies return address on the stack, the 240 stacktrace may see the kretprobe trampoline address instead 241 of correct one. If the architecture stacktrace code and 242 unwinder can adjust such entries, select this configuration. 243 244config HAVE_FUNCTION_ERROR_INJECTION 245 bool 246 247config HAVE_NMI 248 bool 249 250config HAVE_FUNCTION_DESCRIPTORS 251 bool 252 253config TRACE_IRQFLAGS_SUPPORT 254 bool 255 256config TRACE_IRQFLAGS_NMI_SUPPORT 257 bool 258 259# 260# An arch should select this if it provides all these things: 261# 262# task_pt_regs() in asm/processor.h or asm/ptrace.h 263# arch_has_single_step() if there is hardware single-step support 264# arch_has_block_step() if there is hardware block-step support 265# asm/syscall.h supplying asm-generic/syscall.h interface 266# linux/regset.h user_regset interfaces 267# CORE_DUMP_USE_REGSET #define'd in linux/elf.h 268# TIF_SYSCALL_TRACE calls ptrace_report_syscall_{entry,exit} 269# TIF_NOTIFY_RESUME calls resume_user_mode_work() 270# 271config HAVE_ARCH_TRACEHOOK 272 bool 273 274config HAVE_DMA_CONTIGUOUS 275 bool 276 277config GENERIC_SMP_IDLE_THREAD 278 bool 279 280config GENERIC_IDLE_POLL_SETUP 281 bool 282 283config ARCH_HAS_FORTIFY_SOURCE 284 bool 285 help 286 An architecture should select this when it can successfully 287 build and run with CONFIG_FORTIFY_SOURCE. 288 289# 290# Select if the arch provides a historic keepinit alias for the retain_initrd 291# command line option 292# 293config ARCH_HAS_KEEPINITRD 294 bool 295 296# Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h 297config ARCH_HAS_SET_MEMORY 298 bool 299 300# Select if arch has all set_direct_map_invalid/default() functions 301config ARCH_HAS_SET_DIRECT_MAP 302 bool 303 304# 305# Select if the architecture provides the arch_dma_set_uncached symbol to 306# either provide an uncached segment alias for a DMA allocation, or 307# to remap the page tables in place. 308# 309config ARCH_HAS_DMA_SET_UNCACHED 310 bool 311 312# 313# Select if the architectures provides the arch_dma_clear_uncached symbol 314# to undo an in-place page table remap for uncached access. 315# 316config ARCH_HAS_DMA_CLEAR_UNCACHED 317 bool 318 319config ARCH_HAS_CPU_FINALIZE_INIT 320 bool 321 322# The architecture has a per-task state that includes the mm's PASID 323config ARCH_HAS_CPU_PASID 324 bool 325 select IOMMU_MM_DATA 326 327config HAVE_ARCH_THREAD_STRUCT_WHITELIST 328 bool 329 help 330 An architecture should select this to provide hardened usercopy 331 knowledge about what region of the thread_struct should be 332 whitelisted for copying to userspace. Normally this is only the 333 FPU registers. Specifically, arch_thread_struct_whitelist() 334 should be implemented. Without this, the entire thread_struct 335 field in task_struct will be left whitelisted. 336 337# Select if arch wants to size task_struct dynamically via arch_task_struct_size: 338config ARCH_WANTS_DYNAMIC_TASK_STRUCT 339 bool 340 341config ARCH_WANTS_NO_INSTR 342 bool 343 help 344 An architecture should select this if the noinstr macro is being used on 345 functions to denote that the toolchain should avoid instrumenting such 346 functions and is required for correctness. 347 348config ARCH_32BIT_OFF_T 349 bool 350 depends on !64BIT 351 help 352 All new 32-bit architectures should have 64-bit off_t type on 353 userspace side which corresponds to the loff_t kernel type. This 354 is the requirement for modern ABIs. Some existing architectures 355 still support 32-bit off_t. This option is enabled for all such 356 architectures explicitly. 357 358# Selected by 64 bit architectures which have a 32 bit f_tinode in struct ustat 359config ARCH_32BIT_USTAT_F_TINODE 360 bool 361 362config HAVE_ASM_MODVERSIONS 363 bool 364 help 365 This symbol should be selected by an architecture if it provides 366 <asm/asm-prototypes.h> to support the module versioning for symbols 367 exported from assembly code. 368 369config HAVE_REGS_AND_STACK_ACCESS_API 370 bool 371 help 372 This symbol should be selected by an architecture if it supports 373 the API needed to access registers and stack entries from pt_regs, 374 declared in asm/ptrace.h 375 For example the kprobes-based event tracer needs this API. 376 377config HAVE_RSEQ 378 bool 379 depends on HAVE_REGS_AND_STACK_ACCESS_API 380 help 381 This symbol should be selected by an architecture if it 382 supports an implementation of restartable sequences. 383 384config HAVE_RUST 385 bool 386 help 387 This symbol should be selected by an architecture if it 388 supports Rust. 389 390config HAVE_FUNCTION_ARG_ACCESS_API 391 bool 392 help 393 This symbol should be selected by an architecture if it supports 394 the API needed to access function arguments from pt_regs, 395 declared in asm/ptrace.h 396 397config HAVE_HW_BREAKPOINT 398 bool 399 depends on PERF_EVENTS 400 401config HAVE_MIXED_BREAKPOINTS_REGS 402 bool 403 depends on HAVE_HW_BREAKPOINT 404 help 405 Depending on the arch implementation of hardware breakpoints, 406 some of them have separate registers for data and instruction 407 breakpoints addresses, others have mixed registers to store 408 them but define the access type in a control register. 409 Select this option if your arch implements breakpoints under the 410 latter fashion. 411 412config HAVE_USER_RETURN_NOTIFIER 413 bool 414 415config HAVE_PERF_EVENTS_NMI 416 bool 417 help 418 System hardware can generate an NMI using the perf event 419 subsystem. Also has support for calculating CPU cycle events 420 to determine how many clock cycles in a given period. 421 422config HAVE_HARDLOCKUP_DETECTOR_PERF 423 bool 424 depends on HAVE_PERF_EVENTS_NMI 425 help 426 The arch chooses to use the generic perf-NMI-based hardlockup 427 detector. Must define HAVE_PERF_EVENTS_NMI. 428 429config HAVE_HARDLOCKUP_DETECTOR_ARCH 430 bool 431 help 432 The arch provides its own hardlockup detector implementation instead 433 of the generic ones. 434 435 It uses the same command line parameters, and sysctl interface, 436 as the generic hardlockup detectors. 437 438config HAVE_PERF_REGS 439 bool 440 help 441 Support selective register dumps for perf events. This includes 442 bit-mapping of each registers and a unique architecture id. 443 444config HAVE_PERF_USER_STACK_DUMP 445 bool 446 help 447 Support user stack dumps for perf event samples. This needs 448 access to the user stack pointer which is not unified across 449 architectures. 450 451config HAVE_ARCH_JUMP_LABEL 452 bool 453 454config HAVE_ARCH_JUMP_LABEL_RELATIVE 455 bool 456 457config MMU_GATHER_TABLE_FREE 458 bool 459 460config MMU_GATHER_RCU_TABLE_FREE 461 bool 462 select MMU_GATHER_TABLE_FREE 463 464config MMU_GATHER_PAGE_SIZE 465 bool 466 467config MMU_GATHER_NO_RANGE 468 bool 469 select MMU_GATHER_MERGE_VMAS 470 471config MMU_GATHER_NO_FLUSH_CACHE 472 bool 473 474config MMU_GATHER_MERGE_VMAS 475 bool 476 477config MMU_GATHER_NO_GATHER 478 bool 479 depends on MMU_GATHER_TABLE_FREE 480 481config ARCH_WANT_IRQS_OFF_ACTIVATE_MM 482 bool 483 help 484 Temporary select until all architectures can be converted to have 485 irqs disabled over activate_mm. Architectures that do IPI based TLB 486 shootdowns should enable this. 487 488# Use normal mm refcounting for MMU_LAZY_TLB kernel thread references. 489# MMU_LAZY_TLB_REFCOUNT=n can improve the scalability of context switching 490# to/from kernel threads when the same mm is running on a lot of CPUs (a large 491# multi-threaded application), by reducing contention on the mm refcount. 492# 493# This can be disabled if the architecture ensures no CPUs are using an mm as a 494# "lazy tlb" beyond its final refcount (i.e., by the time __mmdrop frees the mm 495# or its kernel page tables). This could be arranged by arch_exit_mmap(), or 496# final exit(2) TLB flush, for example. 497# 498# To implement this, an arch *must*: 499# Ensure the _lazy_tlb variants of mmgrab/mmdrop are used when manipulating 500# the lazy tlb reference of a kthread's ->active_mm (non-arch code has been 501# converted already). 502config MMU_LAZY_TLB_REFCOUNT 503 def_bool y 504 depends on !MMU_LAZY_TLB_SHOOTDOWN 505 506# This option allows MMU_LAZY_TLB_REFCOUNT=n. It ensures no CPUs are using an 507# mm as a lazy tlb beyond its last reference count, by shooting down these 508# users before the mm is deallocated. __mmdrop() first IPIs all CPUs that may 509# be using the mm as a lazy tlb, so that they may switch themselves to using 510# init_mm for their active mm. mm_cpumask(mm) is used to determine which CPUs 511# may be using mm as a lazy tlb mm. 512# 513# To implement this, an arch *must*: 514# - At the time of the final mmdrop of the mm, ensure mm_cpumask(mm) contains 515# at least all possible CPUs in which the mm is lazy. 516# - It must meet the requirements for MMU_LAZY_TLB_REFCOUNT=n (see above). 517config MMU_LAZY_TLB_SHOOTDOWN 518 bool 519 520config ARCH_HAVE_NMI_SAFE_CMPXCHG 521 bool 522 523config ARCH_HAVE_EXTRA_ELF_NOTES 524 bool 525 help 526 An architecture should select this in order to enable adding an 527 arch-specific ELF note section to core files. It must provide two 528 functions: elf_coredump_extra_notes_size() and 529 elf_coredump_extra_notes_write() which are invoked by the ELF core 530 dumper. 531 532config ARCH_HAS_NMI_SAFE_THIS_CPU_OPS 533 bool 534 535config HAVE_ALIGNED_STRUCT_PAGE 536 bool 537 help 538 This makes sure that struct pages are double word aligned and that 539 e.g. the SLUB allocator can perform double word atomic operations 540 on a struct page for better performance. However selecting this 541 might increase the size of a struct page by a word. 542 543config HAVE_CMPXCHG_LOCAL 544 bool 545 546config HAVE_CMPXCHG_DOUBLE 547 bool 548 549config ARCH_WEAK_RELEASE_ACQUIRE 550 bool 551 552config ARCH_WANT_IPC_PARSE_VERSION 553 bool 554 555config ARCH_WANT_COMPAT_IPC_PARSE_VERSION 556 bool 557 558config ARCH_WANT_OLD_COMPAT_IPC 559 select ARCH_WANT_COMPAT_IPC_PARSE_VERSION 560 bool 561 562config HAVE_ARCH_SECCOMP 563 bool 564 help 565 An arch should select this symbol to support seccomp mode 1 (the fixed 566 syscall policy), and must provide an overrides for __NR_seccomp_sigreturn, 567 and compat syscalls if the asm-generic/seccomp.h defaults need adjustment: 568 - __NR_seccomp_read_32 569 - __NR_seccomp_write_32 570 - __NR_seccomp_exit_32 571 - __NR_seccomp_sigreturn_32 572 573config HAVE_ARCH_SECCOMP_FILTER 574 bool 575 select HAVE_ARCH_SECCOMP 576 help 577 An arch should select this symbol if it provides all of these things: 578 - all the requirements for HAVE_ARCH_SECCOMP 579 - syscall_get_arch() 580 - syscall_get_arguments() 581 - syscall_rollback() 582 - syscall_set_return_value() 583 - SIGSYS siginfo_t support 584 - secure_computing is called from a ptrace_event()-safe context 585 - secure_computing return value is checked and a return value of -1 586 results in the system call being skipped immediately. 587 - seccomp syscall wired up 588 - if !HAVE_SPARSE_SYSCALL_NR, have SECCOMP_ARCH_NATIVE, 589 SECCOMP_ARCH_NATIVE_NR, SECCOMP_ARCH_NATIVE_NAME defined. If 590 COMPAT is supported, have the SECCOMP_ARCH_COMPAT* defines too. 591 592config SECCOMP 593 prompt "Enable seccomp to safely execute untrusted bytecode" 594 def_bool y 595 depends on HAVE_ARCH_SECCOMP 596 help 597 This kernel feature is useful for number crunching applications 598 that may need to handle untrusted bytecode during their 599 execution. By using pipes or other transports made available 600 to the process as file descriptors supporting the read/write 601 syscalls, it's possible to isolate those applications in their 602 own address space using seccomp. Once seccomp is enabled via 603 prctl(PR_SET_SECCOMP) or the seccomp() syscall, it cannot be 604 disabled and the task is only allowed to execute a few safe 605 syscalls defined by each seccomp mode. 606 607 If unsure, say Y. 608 609config SECCOMP_FILTER 610 def_bool y 611 depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET 612 help 613 Enable tasks to build secure computing environments defined 614 in terms of Berkeley Packet Filter programs which implement 615 task-defined system call filtering polices. 616 617 See Documentation/userspace-api/seccomp_filter.rst for details. 618 619config SECCOMP_CACHE_DEBUG 620 bool "Show seccomp filter cache status in /proc/pid/seccomp_cache" 621 depends on SECCOMP_FILTER && !HAVE_SPARSE_SYSCALL_NR 622 depends on PROC_FS 623 help 624 This enables the /proc/pid/seccomp_cache interface to monitor 625 seccomp cache data. The file format is subject to change. Reading 626 the file requires CAP_SYS_ADMIN. 627 628 This option is for debugging only. Enabling presents the risk that 629 an adversary may be able to infer the seccomp filter logic. 630 631 If unsure, say N. 632 633config HAVE_ARCH_STACKLEAK 634 bool 635 help 636 An architecture should select this if it has the code which 637 fills the used part of the kernel stack with the STACKLEAK_POISON 638 value before returning from system calls. 639 640config HAVE_STACKPROTECTOR 641 bool 642 help 643 An arch should select this symbol if: 644 - it has implemented a stack canary (e.g. __stack_chk_guard) 645 646config STACKPROTECTOR 647 bool "Stack Protector buffer overflow detection" 648 depends on HAVE_STACKPROTECTOR 649 depends on $(cc-option,-fstack-protector) 650 default y 651 help 652 This option turns on the "stack-protector" GCC feature. This 653 feature puts, at the beginning of functions, a canary value on 654 the stack just before the return address, and validates 655 the value just before actually returning. Stack based buffer 656 overflows (that need to overwrite this return address) now also 657 overwrite the canary, which gets detected and the attack is then 658 neutralized via a kernel panic. 659 660 Functions will have the stack-protector canary logic added if they 661 have an 8-byte or larger character array on the stack. 662 663 This feature requires gcc version 4.2 or above, or a distribution 664 gcc with the feature backported ("-fstack-protector"). 665 666 On an x86 "defconfig" build, this feature adds canary checks to 667 about 3% of all kernel functions, which increases kernel code size 668 by about 0.3%. 669 670config STACKPROTECTOR_STRONG 671 bool "Strong Stack Protector" 672 depends on STACKPROTECTOR 673 depends on $(cc-option,-fstack-protector-strong) 674 default y 675 help 676 Functions will have the stack-protector canary logic added in any 677 of the following conditions: 678 679 - local variable's address used as part of the right hand side of an 680 assignment or function argument 681 - local variable is an array (or union containing an array), 682 regardless of array type or length 683 - uses register local variables 684 685 This feature requires gcc version 4.9 or above, or a distribution 686 gcc with the feature backported ("-fstack-protector-strong"). 687 688 On an x86 "defconfig" build, this feature adds canary checks to 689 about 20% of all kernel functions, which increases the kernel code 690 size by about 2%. 691 692config ARCH_SUPPORTS_SHADOW_CALL_STACK 693 bool 694 help 695 An architecture should select this if it supports the compiler's 696 Shadow Call Stack and implements runtime support for shadow stack 697 switching. 698 699config SHADOW_CALL_STACK 700 bool "Shadow Call Stack" 701 depends on ARCH_SUPPORTS_SHADOW_CALL_STACK 702 depends on DYNAMIC_FTRACE_WITH_ARGS || DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER 703 depends on MMU 704 help 705 This option enables the compiler's Shadow Call Stack, which 706 uses a shadow stack to protect function return addresses from 707 being overwritten by an attacker. More information can be found 708 in the compiler's documentation: 709 710 - Clang: https://clang.llvm.org/docs/ShadowCallStack.html 711 - GCC: https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html#Instrumentation-Options 712 713 Note that security guarantees in the kernel differ from the 714 ones documented for user space. The kernel must store addresses 715 of shadow stacks in memory, which means an attacker capable of 716 reading and writing arbitrary memory may be able to locate them 717 and hijack control flow by modifying the stacks. 718 719config DYNAMIC_SCS 720 bool 721 help 722 Set by the arch code if it relies on code patching to insert the 723 shadow call stack push and pop instructions rather than on the 724 compiler. 725 726config LTO 727 bool 728 help 729 Selected if the kernel will be built using the compiler's LTO feature. 730 731config LTO_CLANG 732 bool 733 select LTO 734 help 735 Selected if the kernel will be built using Clang's LTO feature. 736 737config ARCH_SUPPORTS_LTO_CLANG 738 bool 739 help 740 An architecture should select this option if it supports: 741 - compiling with Clang, 742 - compiling inline assembly with Clang's integrated assembler, 743 - and linking with LLD. 744 745config ARCH_SUPPORTS_LTO_CLANG_THIN 746 bool 747 help 748 An architecture should select this option if it can support Clang's 749 ThinLTO mode. 750 751config HAS_LTO_CLANG 752 def_bool y 753 depends on CC_IS_CLANG && LD_IS_LLD && AS_IS_LLVM 754 depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm) 755 depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm) 756 depends on ARCH_SUPPORTS_LTO_CLANG 757 depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT 758 # https://github.com/ClangBuiltLinux/linux/issues/1721 759 depends on (!KASAN || KASAN_HW_TAGS || CLANG_VERSION >= 170000) || !DEBUG_INFO 760 depends on (!KCOV || CLANG_VERSION >= 170000) || !DEBUG_INFO 761 depends on !GCOV_KERNEL 762 help 763 The compiler and Kconfig options support building with Clang's 764 LTO. 765 766choice 767 prompt "Link Time Optimization (LTO)" 768 default LTO_NONE 769 help 770 This option enables Link Time Optimization (LTO), which allows the 771 compiler to optimize binaries globally. 772 773 If unsure, select LTO_NONE. Note that LTO is very resource-intensive 774 so it's disabled by default. 775 776config LTO_NONE 777 bool "None" 778 help 779 Build the kernel normally, without Link Time Optimization (LTO). 780 781config LTO_CLANG_FULL 782 bool "Clang Full LTO (EXPERIMENTAL)" 783 depends on HAS_LTO_CLANG 784 depends on !COMPILE_TEST 785 select LTO_CLANG 786 help 787 This option enables Clang's full Link Time Optimization (LTO), which 788 allows the compiler to optimize the kernel globally. If you enable 789 this option, the compiler generates LLVM bitcode instead of ELF 790 object files, and the actual compilation from bitcode happens at 791 the LTO link step, which may take several minutes depending on the 792 kernel configuration. More information can be found from LLVM's 793 documentation: 794 795 https://llvm.org/docs/LinkTimeOptimization.html 796 797 During link time, this option can use a large amount of RAM, and 798 may take much longer than the ThinLTO option. 799 800config LTO_CLANG_THIN 801 bool "Clang ThinLTO (EXPERIMENTAL)" 802 depends on HAS_LTO_CLANG && ARCH_SUPPORTS_LTO_CLANG_THIN 803 select LTO_CLANG 804 help 805 This option enables Clang's ThinLTO, which allows for parallel 806 optimization and faster incremental compiles compared to the 807 CONFIG_LTO_CLANG_FULL option. More information can be found 808 from Clang's documentation: 809 810 https://clang.llvm.org/docs/ThinLTO.html 811 812 If unsure, say Y. 813endchoice 814 815config ARCH_SUPPORTS_AUTOFDO_CLANG 816 bool 817 818config AUTOFDO_CLANG 819 bool "Enable Clang's AutoFDO build (EXPERIMENTAL)" 820 depends on ARCH_SUPPORTS_AUTOFDO_CLANG 821 depends on CC_IS_CLANG && CLANG_VERSION >= 170000 822 help 823 This option enables Clang’s AutoFDO build. When 824 an AutoFDO profile is specified in variable 825 CLANG_AUTOFDO_PROFILE during the build process, 826 Clang uses the profile to optimize the kernel. 827 828 If no profile is specified, AutoFDO options are 829 still passed to Clang to facilitate the collection 830 of perf data for creating an AutoFDO profile in 831 subsequent builds. 832 833 If unsure, say N. 834 835config ARCH_SUPPORTS_PROPELLER_CLANG 836 bool 837 838config PROPELLER_CLANG 839 bool "Enable Clang's Propeller build" 840 depends on ARCH_SUPPORTS_PROPELLER_CLANG 841 depends on CC_IS_CLANG && CLANG_VERSION >= 190000 842 help 843 This option enables Clang’s Propeller build. When the Propeller 844 profiles is specified in variable CLANG_PROPELLER_PROFILE_PREFIX 845 during the build process, Clang uses the profiles to optimize 846 the kernel. 847 848 If no profile is specified, Propeller options are still passed 849 to Clang to facilitate the collection of perf data for creating 850 the Propeller profiles in subsequent builds. 851 852 If unsure, say N. 853 854config ARCH_SUPPORTS_CFI_CLANG 855 bool 856 help 857 An architecture should select this option if it can support Clang's 858 Control-Flow Integrity (CFI) checking. 859 860config ARCH_USES_CFI_TRAPS 861 bool 862 863config CFI_CLANG 864 bool "Use Clang's Control Flow Integrity (CFI)" 865 depends on ARCH_SUPPORTS_CFI_CLANG 866 depends on $(cc-option,-fsanitize=kcfi) 867 help 868 This option enables Clang's forward-edge Control Flow Integrity 869 (CFI) checking, where the compiler injects a runtime check to each 870 indirect function call to ensure the target is a valid function with 871 the correct static type. This restricts possible call targets and 872 makes it more difficult for an attacker to exploit bugs that allow 873 the modification of stored function pointers. More information can be 874 found from Clang's documentation: 875 876 https://clang.llvm.org/docs/ControlFlowIntegrity.html 877 878config CFI_ICALL_NORMALIZE_INTEGERS 879 bool "Normalize CFI tags for integers" 880 depends on CFI_CLANG 881 depends on HAVE_CFI_ICALL_NORMALIZE_INTEGERS_CLANG 882 help 883 This option normalizes the CFI tags for integer types so that all 884 integer types of the same size and signedness receive the same CFI 885 tag. 886 887 The option is separate from CONFIG_RUST because it affects the ABI. 888 When working with build systems that care about the ABI, it is 889 convenient to be able to turn on this flag first, before Rust is 890 turned on. 891 892 This option is necessary for using CFI with Rust. If unsure, say N. 893 894config HAVE_CFI_ICALL_NORMALIZE_INTEGERS_CLANG 895 def_bool y 896 depends on $(cc-option,-fsanitize=kcfi -fsanitize-cfi-icall-experimental-normalize-integers) 897 # With GCOV/KASAN we need this fix: https://github.com/llvm/llvm-project/pull/104826 898 depends on CLANG_VERSION >= 190103 || (!GCOV_KERNEL && !KASAN_GENERIC && !KASAN_SW_TAGS) 899 900config HAVE_CFI_ICALL_NORMALIZE_INTEGERS_RUSTC 901 def_bool y 902 depends on HAVE_CFI_ICALL_NORMALIZE_INTEGERS_CLANG 903 depends on RUSTC_VERSION >= 107900 904 # With GCOV/KASAN we need this fix: https://github.com/rust-lang/rust/pull/129373 905 depends on (RUSTC_LLVM_VERSION >= 190103 && RUSTC_VERSION >= 108200) || \ 906 (!GCOV_KERNEL && !KASAN_GENERIC && !KASAN_SW_TAGS) 907 908config CFI_PERMISSIVE 909 bool "Use CFI in permissive mode" 910 depends on CFI_CLANG 911 help 912 When selected, Control Flow Integrity (CFI) violations result in a 913 warning instead of a kernel panic. This option should only be used 914 for finding indirect call type mismatches during development. 915 916 If unsure, say N. 917 918config HAVE_ARCH_WITHIN_STACK_FRAMES 919 bool 920 help 921 An architecture should select this if it can walk the kernel stack 922 frames to determine if an object is part of either the arguments 923 or local variables (i.e. that it excludes saved return addresses, 924 and similar) by implementing an inline arch_within_stack_frames(), 925 which is used by CONFIG_HARDENED_USERCOPY. 926 927config HAVE_CONTEXT_TRACKING_USER 928 bool 929 help 930 Provide kernel/user boundaries probes necessary for subsystems 931 that need it, such as userspace RCU extended quiescent state. 932 Syscalls need to be wrapped inside user_exit()-user_enter(), either 933 optimized behind static key or through the slow path using TIF_NOHZ 934 flag. Exceptions handlers must be wrapped as well. Irqs are already 935 protected inside ct_irq_enter/ct_irq_exit() but preemption or signal 936 handling on irq exit still need to be protected. 937 938config HAVE_CONTEXT_TRACKING_USER_OFFSTACK 939 bool 940 help 941 Architecture neither relies on exception_enter()/exception_exit() 942 nor on schedule_user(). Also preempt_schedule_notrace() and 943 preempt_schedule_irq() can't be called in a preemptible section 944 while context tracking is CT_STATE_USER. This feature reflects a sane 945 entry implementation where the following requirements are met on 946 critical entry code, ie: before user_exit() or after user_enter(): 947 948 - Critical entry code isn't preemptible (or better yet: 949 not interruptible). 950 - No use of RCU read side critical sections, unless ct_nmi_enter() 951 got called. 952 - No use of instrumentation, unless instrumentation_begin() got 953 called. 954 955config HAVE_TIF_NOHZ 956 bool 957 help 958 Arch relies on TIF_NOHZ and syscall slow path to implement context 959 tracking calls to user_enter()/user_exit(). 960 961config HAVE_VIRT_CPU_ACCOUNTING 962 bool 963 964config HAVE_VIRT_CPU_ACCOUNTING_IDLE 965 bool 966 help 967 Architecture has its own way to account idle CPU time and therefore 968 doesn't implement vtime_account_idle(). 969 970config ARCH_HAS_SCALED_CPUTIME 971 bool 972 973config HAVE_VIRT_CPU_ACCOUNTING_GEN 974 bool 975 default y if 64BIT 976 help 977 With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit. 978 Before enabling this option, arch code must be audited 979 to ensure there are no races in concurrent read/write of 980 cputime_t. For example, reading/writing 64-bit cputime_t on 981 some 32-bit arches may require multiple accesses, so proper 982 locking is needed to protect against concurrent accesses. 983 984config HAVE_IRQ_TIME_ACCOUNTING 985 bool 986 help 987 Archs need to ensure they use a high enough resolution clock to 988 support irq time accounting and then call enable_sched_clock_irqtime(). 989 990config HAVE_MOVE_PUD 991 bool 992 help 993 Architectures that select this are able to move page tables at the 994 PUD level. If there are only 3 page table levels, the move effectively 995 happens at the PGD level. 996 997config HAVE_MOVE_PMD 998 bool 999 help 1000 Archs that select this are able to move page tables at the PMD level. 1001 1002config HAVE_ARCH_TRANSPARENT_HUGEPAGE 1003 bool 1004 1005config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD 1006 bool 1007 1008config HAVE_ARCH_HUGE_VMAP 1009 bool 1010 1011# 1012# Archs that select this would be capable of PMD-sized vmaps (i.e., 1013# arch_vmap_pmd_supported() returns true). The VM_ALLOW_HUGE_VMAP flag 1014# must be used to enable allocations to use hugepages. 1015# 1016config HAVE_ARCH_HUGE_VMALLOC 1017 depends on HAVE_ARCH_HUGE_VMAP 1018 bool 1019 1020config ARCH_WANT_HUGE_PMD_SHARE 1021 bool 1022 1023# Archs that want to use pmd_mkwrite on kernel memory need it defined even 1024# if there are no userspace memory management features that use it 1025config ARCH_WANT_KERNEL_PMD_MKWRITE 1026 bool 1027 1028config ARCH_WANT_PMD_MKWRITE 1029 def_bool TRANSPARENT_HUGEPAGE || ARCH_WANT_KERNEL_PMD_MKWRITE 1030 1031config HAVE_ARCH_SOFT_DIRTY 1032 bool 1033 1034config HAVE_MOD_ARCH_SPECIFIC 1035 bool 1036 help 1037 The arch uses struct mod_arch_specific to store data. Many arches 1038 just need a simple module loader without arch specific data - those 1039 should not enable this. 1040 1041config MODULES_USE_ELF_RELA 1042 bool 1043 help 1044 Modules only use ELF RELA relocations. Modules with ELF REL 1045 relocations will give an error. 1046 1047config MODULES_USE_ELF_REL 1048 bool 1049 help 1050 Modules only use ELF REL relocations. Modules with ELF RELA 1051 relocations will give an error. 1052 1053config ARCH_WANTS_MODULES_DATA_IN_VMALLOC 1054 bool 1055 help 1056 For architectures like powerpc/32 which have constraints on module 1057 allocation and need to allocate module data outside of module area. 1058 1059config ARCH_WANTS_EXECMEM_LATE 1060 bool 1061 help 1062 For architectures that do not allocate executable memory early on 1063 boot, but rather require its initialization late when there is 1064 enough entropy for module space randomization, for instance 1065 arm64. 1066 1067config ARCH_HAS_EXECMEM_ROX 1068 bool 1069 depends on MMU && !HIGHMEM 1070 help 1071 For architectures that support allocations of executable memory 1072 with read-only execute permissions. Architecture must implement 1073 execmem_fill_trapping_insns() callback to enable this. 1074 1075config HAVE_IRQ_EXIT_ON_IRQ_STACK 1076 bool 1077 help 1078 Architecture doesn't only execute the irq handler on the irq stack 1079 but also irq_exit(). This way we can process softirqs on this irq 1080 stack instead of switching to a new one when we call __do_softirq() 1081 in the end of an hardirq. 1082 This spares a stack switch and improves cache usage on softirq 1083 processing. 1084 1085config HAVE_SOFTIRQ_ON_OWN_STACK 1086 bool 1087 help 1088 Architecture provides a function to run __do_softirq() on a 1089 separate stack. 1090 1091config SOFTIRQ_ON_OWN_STACK 1092 def_bool HAVE_SOFTIRQ_ON_OWN_STACK && !PREEMPT_RT 1093 1094config ALTERNATE_USER_ADDRESS_SPACE 1095 bool 1096 help 1097 Architectures set this when the CPU uses separate address 1098 spaces for kernel and user space pointers. In this case, the 1099 access_ok() check on a __user pointer is skipped. 1100 1101config PGTABLE_LEVELS 1102 int 1103 default 2 1104 1105config ARCH_HAS_ELF_RANDOMIZE 1106 bool 1107 help 1108 An architecture supports choosing randomized locations for 1109 stack, mmap, brk, and ET_DYN. Defined functions: 1110 - arch_mmap_rnd() 1111 - arch_randomize_brk() 1112 1113config HAVE_ARCH_MMAP_RND_BITS 1114 bool 1115 help 1116 An arch should select this symbol if it supports setting a variable 1117 number of bits for use in establishing the base address for mmap 1118 allocations, has MMU enabled and provides values for both: 1119 - ARCH_MMAP_RND_BITS_MIN 1120 - ARCH_MMAP_RND_BITS_MAX 1121 1122config HAVE_EXIT_THREAD 1123 bool 1124 help 1125 An architecture implements exit_thread. 1126 1127config ARCH_MMAP_RND_BITS_MIN 1128 int 1129 1130config ARCH_MMAP_RND_BITS_MAX 1131 int 1132 1133config ARCH_MMAP_RND_BITS_DEFAULT 1134 int 1135 1136config ARCH_MMAP_RND_BITS 1137 int "Number of bits to use for ASLR of mmap base address" if EXPERT 1138 range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX 1139 default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT 1140 default ARCH_MMAP_RND_BITS_MIN 1141 depends on HAVE_ARCH_MMAP_RND_BITS 1142 help 1143 This value can be used to select the number of bits to use to 1144 determine the random offset to the base address of vma regions 1145 resulting from mmap allocations. This value will be bounded 1146 by the architecture's minimum and maximum supported values. 1147 1148 This value can be changed after boot using the 1149 /proc/sys/vm/mmap_rnd_bits tunable 1150 1151config HAVE_ARCH_MMAP_RND_COMPAT_BITS 1152 bool 1153 help 1154 An arch should select this symbol if it supports running applications 1155 in compatibility mode, supports setting a variable number of bits for 1156 use in establishing the base address for mmap allocations, has MMU 1157 enabled and provides values for both: 1158 - ARCH_MMAP_RND_COMPAT_BITS_MIN 1159 - ARCH_MMAP_RND_COMPAT_BITS_MAX 1160 1161config ARCH_MMAP_RND_COMPAT_BITS_MIN 1162 int 1163 1164config ARCH_MMAP_RND_COMPAT_BITS_MAX 1165 int 1166 1167config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT 1168 int 1169 1170config ARCH_MMAP_RND_COMPAT_BITS 1171 int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT 1172 range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX 1173 default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT 1174 default ARCH_MMAP_RND_COMPAT_BITS_MIN 1175 depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS 1176 help 1177 This value can be used to select the number of bits to use to 1178 determine the random offset to the base address of vma regions 1179 resulting from mmap allocations for compatible applications This 1180 value will be bounded by the architecture's minimum and maximum 1181 supported values. 1182 1183 This value can be changed after boot using the 1184 /proc/sys/vm/mmap_rnd_compat_bits tunable 1185 1186config HAVE_ARCH_COMPAT_MMAP_BASES 1187 bool 1188 help 1189 This allows 64bit applications to invoke 32-bit mmap() syscall 1190 and vice-versa 32-bit applications to call 64-bit mmap(). 1191 Required for applications doing different bitness syscalls. 1192 1193config HAVE_PAGE_SIZE_4KB 1194 bool 1195 1196config HAVE_PAGE_SIZE_8KB 1197 bool 1198 1199config HAVE_PAGE_SIZE_16KB 1200 bool 1201 1202config HAVE_PAGE_SIZE_32KB 1203 bool 1204 1205config HAVE_PAGE_SIZE_64KB 1206 bool 1207 1208config HAVE_PAGE_SIZE_256KB 1209 bool 1210 1211choice 1212 prompt "MMU page size" 1213 1214config PAGE_SIZE_4KB 1215 bool "4KiB pages" 1216 depends on HAVE_PAGE_SIZE_4KB 1217 help 1218 This option select the standard 4KiB Linux page size and the only 1219 available option on many architectures. Using 4KiB page size will 1220 minimize memory consumption and is therefore recommended for low 1221 memory systems. 1222 Some software that is written for x86 systems makes incorrect 1223 assumptions about the page size and only runs on 4KiB pages. 1224 1225config PAGE_SIZE_8KB 1226 bool "8KiB pages" 1227 depends on HAVE_PAGE_SIZE_8KB 1228 help 1229 This option is the only supported page size on a few older 1230 processors, and can be slightly faster than 4KiB pages. 1231 1232config PAGE_SIZE_16KB 1233 bool "16KiB pages" 1234 depends on HAVE_PAGE_SIZE_16KB 1235 help 1236 This option is usually a good compromise between memory 1237 consumption and performance for typical desktop and server 1238 workloads, often saving a level of page table lookups compared 1239 to 4KB pages as well as reducing TLB pressure and overhead of 1240 per-page operations in the kernel at the expense of a larger 1241 page cache. 1242 1243config PAGE_SIZE_32KB 1244 bool "32KiB pages" 1245 depends on HAVE_PAGE_SIZE_32KB 1246 help 1247 Using 32KiB page size will result in slightly higher performance 1248 kernel at the price of higher memory consumption compared to 1249 16KiB pages. This option is available only on cnMIPS cores. 1250 Note that you will need a suitable Linux distribution to 1251 support this. 1252 1253config PAGE_SIZE_64KB 1254 bool "64KiB pages" 1255 depends on HAVE_PAGE_SIZE_64KB 1256 help 1257 Using 64KiB page size will result in slightly higher performance 1258 kernel at the price of much higher memory consumption compared to 1259 4KiB or 16KiB pages. 1260 This is not suitable for general-purpose workloads but the 1261 better performance may be worth the cost for certain types of 1262 supercomputing or database applications that work mostly with 1263 large in-memory data rather than small files. 1264 1265config PAGE_SIZE_256KB 1266 bool "256KiB pages" 1267 depends on HAVE_PAGE_SIZE_256KB 1268 help 1269 256KiB pages have little practical value due to their extreme 1270 memory usage. The kernel will only be able to run applications 1271 that have been compiled with '-zmax-page-size' set to 256KiB 1272 (the default is 64KiB or 4KiB on most architectures). 1273 1274endchoice 1275 1276config PAGE_SIZE_LESS_THAN_64KB 1277 def_bool y 1278 depends on !PAGE_SIZE_64KB 1279 depends on PAGE_SIZE_LESS_THAN_256KB 1280 1281config PAGE_SIZE_LESS_THAN_256KB 1282 def_bool y 1283 depends on !PAGE_SIZE_256KB 1284 1285config PAGE_SHIFT 1286 int 1287 default 12 if PAGE_SIZE_4KB 1288 default 13 if PAGE_SIZE_8KB 1289 default 14 if PAGE_SIZE_16KB 1290 default 15 if PAGE_SIZE_32KB 1291 default 16 if PAGE_SIZE_64KB 1292 default 18 if PAGE_SIZE_256KB 1293 1294# This allows to use a set of generic functions to determine mmap base 1295# address by giving priority to top-down scheme only if the process 1296# is not in legacy mode (compat task, unlimited stack size or 1297# sysctl_legacy_va_layout). 1298# Architecture that selects this option can provide its own version of: 1299# - STACK_RND_MASK 1300config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT 1301 bool 1302 depends on MMU 1303 select ARCH_HAS_ELF_RANDOMIZE 1304 1305config HAVE_OBJTOOL 1306 bool 1307 1308config HAVE_JUMP_LABEL_HACK 1309 bool 1310 1311config HAVE_NOINSTR_HACK 1312 bool 1313 1314config HAVE_NOINSTR_VALIDATION 1315 bool 1316 1317config HAVE_UACCESS_VALIDATION 1318 bool 1319 select OBJTOOL 1320 1321config HAVE_STACK_VALIDATION 1322 bool 1323 help 1324 Architecture supports objtool compile-time frame pointer rule 1325 validation. 1326 1327config HAVE_RELIABLE_STACKTRACE 1328 bool 1329 help 1330 Architecture has either save_stack_trace_tsk_reliable() or 1331 arch_stack_walk_reliable() function which only returns a stack trace 1332 if it can guarantee the trace is reliable. 1333 1334config HAVE_ARCH_HASH 1335 bool 1336 default n 1337 help 1338 If this is set, the architecture provides an <asm/hash.h> 1339 file which provides platform-specific implementations of some 1340 functions in <linux/hash.h> or fs/namei.c. 1341 1342config HAVE_ARCH_NVRAM_OPS 1343 bool 1344 1345config ISA_BUS_API 1346 def_bool ISA 1347 1348# 1349# ABI hall of shame 1350# 1351config CLONE_BACKWARDS 1352 bool 1353 help 1354 Architecture has tls passed as the 4th argument of clone(2), 1355 not the 5th one. 1356 1357config CLONE_BACKWARDS2 1358 bool 1359 help 1360 Architecture has the first two arguments of clone(2) swapped. 1361 1362config CLONE_BACKWARDS3 1363 bool 1364 help 1365 Architecture has tls passed as the 3rd argument of clone(2), 1366 not the 5th one. 1367 1368config ODD_RT_SIGACTION 1369 bool 1370 help 1371 Architecture has unusual rt_sigaction(2) arguments 1372 1373config OLD_SIGSUSPEND 1374 bool 1375 help 1376 Architecture has old sigsuspend(2) syscall, of one-argument variety 1377 1378config OLD_SIGSUSPEND3 1379 bool 1380 help 1381 Even weirder antique ABI - three-argument sigsuspend(2) 1382 1383config OLD_SIGACTION 1384 bool 1385 help 1386 Architecture has old sigaction(2) syscall. Nope, not the same 1387 as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2), 1388 but fairly different variant of sigaction(2), thanks to OSF/1 1389 compatibility... 1390 1391config COMPAT_OLD_SIGACTION 1392 bool 1393 1394config COMPAT_32BIT_TIME 1395 bool "Provide system calls for 32-bit time_t" 1396 default !64BIT || COMPAT 1397 help 1398 This enables 32 bit time_t support in addition to 64 bit time_t support. 1399 This is relevant on all 32-bit architectures, and 64-bit architectures 1400 as part of compat syscall handling. 1401 1402config ARCH_NO_PREEMPT 1403 bool 1404 1405config ARCH_SUPPORTS_RT 1406 bool 1407 1408config CPU_NO_EFFICIENT_FFS 1409 def_bool n 1410 1411config HAVE_ARCH_VMAP_STACK 1412 def_bool n 1413 help 1414 An arch should select this symbol if it can support kernel stacks 1415 in vmalloc space. This means: 1416 1417 - vmalloc space must be large enough to hold many kernel stacks. 1418 This may rule out many 32-bit architectures. 1419 1420 - Stacks in vmalloc space need to work reliably. For example, if 1421 vmap page tables are created on demand, either this mechanism 1422 needs to work while the stack points to a virtual address with 1423 unpopulated page tables or arch code (switch_to() and switch_mm(), 1424 most likely) needs to ensure that the stack's page table entries 1425 are populated before running on a possibly unpopulated stack. 1426 1427 - If the stack overflows into a guard page, something reasonable 1428 should happen. The definition of "reasonable" is flexible, but 1429 instantly rebooting without logging anything would be unfriendly. 1430 1431config VMAP_STACK 1432 default y 1433 bool "Use a virtually-mapped stack" 1434 depends on HAVE_ARCH_VMAP_STACK 1435 depends on !KASAN || KASAN_HW_TAGS || KASAN_VMALLOC 1436 help 1437 Enable this if you want the use virtually-mapped kernel stacks 1438 with guard pages. This causes kernel stack overflows to be 1439 caught immediately rather than causing difficult-to-diagnose 1440 corruption. 1441 1442 To use this with software KASAN modes, the architecture must support 1443 backing virtual mappings with real shadow memory, and KASAN_VMALLOC 1444 must be enabled. 1445 1446config HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET 1447 def_bool n 1448 help 1449 An arch should select this symbol if it can support kernel stack 1450 offset randomization with calls to add_random_kstack_offset() 1451 during syscall entry and choose_random_kstack_offset() during 1452 syscall exit. Careful removal of -fstack-protector-strong and 1453 -fstack-protector should also be applied to the entry code and 1454 closely examined, as the artificial stack bump looks like an array 1455 to the compiler, so it will attempt to add canary checks regardless 1456 of the static branch state. 1457 1458config RANDOMIZE_KSTACK_OFFSET 1459 bool "Support for randomizing kernel stack offset on syscall entry" if EXPERT 1460 default y 1461 depends on HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET 1462 depends on INIT_STACK_NONE || !CC_IS_CLANG || CLANG_VERSION >= 140000 1463 help 1464 The kernel stack offset can be randomized (after pt_regs) by 1465 roughly 5 bits of entropy, frustrating memory corruption 1466 attacks that depend on stack address determinism or 1467 cross-syscall address exposures. 1468 1469 The feature is controlled via the "randomize_kstack_offset=on/off" 1470 kernel boot param, and if turned off has zero overhead due to its use 1471 of static branches (see JUMP_LABEL). 1472 1473 If unsure, say Y. 1474 1475config RANDOMIZE_KSTACK_OFFSET_DEFAULT 1476 bool "Default state of kernel stack offset randomization" 1477 depends on RANDOMIZE_KSTACK_OFFSET 1478 help 1479 Kernel stack offset randomization is controlled by kernel boot param 1480 "randomize_kstack_offset=on/off", and this config chooses the default 1481 boot state. 1482 1483config ARCH_OPTIONAL_KERNEL_RWX 1484 def_bool n 1485 1486config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT 1487 def_bool n 1488 1489config ARCH_HAS_STRICT_KERNEL_RWX 1490 def_bool n 1491 1492config STRICT_KERNEL_RWX 1493 bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX 1494 depends on ARCH_HAS_STRICT_KERNEL_RWX 1495 default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT 1496 help 1497 If this is set, kernel text and rodata memory will be made read-only, 1498 and non-text memory will be made non-executable. This provides 1499 protection against certain security exploits (e.g. executing the heap 1500 or modifying text) 1501 1502 These features are considered standard security practice these days. 1503 You should say Y here in almost all cases. 1504 1505config ARCH_HAS_STRICT_MODULE_RWX 1506 def_bool n 1507 1508config STRICT_MODULE_RWX 1509 bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX 1510 depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES 1511 default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT 1512 help 1513 If this is set, module text and rodata memory will be made read-only, 1514 and non-text memory will be made non-executable. This provides 1515 protection against certain security exploits (e.g. writing to text) 1516 1517# select if the architecture provides an asm/dma-direct.h header 1518config ARCH_HAS_PHYS_TO_DMA 1519 bool 1520 1521config HAVE_ARCH_COMPILER_H 1522 bool 1523 help 1524 An architecture can select this if it provides an 1525 asm/compiler.h header that should be included after 1526 linux/compiler-*.h in order to override macro definitions that those 1527 headers generally provide. 1528 1529config HAVE_ARCH_PREL32_RELOCATIONS 1530 bool 1531 help 1532 May be selected by an architecture if it supports place-relative 1533 32-bit relocations, both in the toolchain and in the module loader, 1534 in which case relative references can be used in special sections 1535 for PCI fixup, initcalls etc which are only half the size on 64 bit 1536 architectures, and don't require runtime relocation on relocatable 1537 kernels. 1538 1539config ARCH_USE_MEMREMAP_PROT 1540 bool 1541 1542config LOCK_EVENT_COUNTS 1543 bool "Locking event counts collection" 1544 depends on DEBUG_FS 1545 help 1546 Enable light-weight counting of various locking related events 1547 in the system with minimal performance impact. This reduces 1548 the chance of application behavior change because of timing 1549 differences. The counts are reported via debugfs. 1550 1551# Select if the architecture has support for applying RELR relocations. 1552config ARCH_HAS_RELR 1553 bool 1554 1555config RELR 1556 bool "Use RELR relocation packing" 1557 depends on ARCH_HAS_RELR && TOOLS_SUPPORT_RELR 1558 default y 1559 help 1560 Store the kernel's dynamic relocations in the RELR relocation packing 1561 format. Requires a compatible linker (LLD supports this feature), as 1562 well as compatible NM and OBJCOPY utilities (llvm-nm and llvm-objcopy 1563 are compatible). 1564 1565config ARCH_HAS_MEM_ENCRYPT 1566 bool 1567 1568config ARCH_HAS_CC_PLATFORM 1569 bool 1570 1571config HAVE_SPARSE_SYSCALL_NR 1572 bool 1573 help 1574 An architecture should select this if its syscall numbering is sparse 1575 to save space. For example, MIPS architecture has a syscall array with 1576 entries at 4000, 5000 and 6000 locations. This option turns on syscall 1577 related optimizations for a given architecture. 1578 1579config ARCH_HAS_VDSO_TIME_DATA 1580 bool 1581 1582config HAVE_STATIC_CALL 1583 bool 1584 1585config HAVE_STATIC_CALL_INLINE 1586 bool 1587 depends on HAVE_STATIC_CALL 1588 select OBJTOOL 1589 1590config HAVE_PREEMPT_DYNAMIC 1591 bool 1592 1593config HAVE_PREEMPT_DYNAMIC_CALL 1594 bool 1595 depends on HAVE_STATIC_CALL 1596 select HAVE_PREEMPT_DYNAMIC 1597 help 1598 An architecture should select this if it can handle the preemption 1599 model being selected at boot time using static calls. 1600 1601 Where an architecture selects HAVE_STATIC_CALL_INLINE, any call to a 1602 preemption function will be patched directly. 1603 1604 Where an architecture does not select HAVE_STATIC_CALL_INLINE, any 1605 call to a preemption function will go through a trampoline, and the 1606 trampoline will be patched. 1607 1608 It is strongly advised to support inline static call to avoid any 1609 overhead. 1610 1611config HAVE_PREEMPT_DYNAMIC_KEY 1612 bool 1613 depends on HAVE_ARCH_JUMP_LABEL 1614 select HAVE_PREEMPT_DYNAMIC 1615 help 1616 An architecture should select this if it can handle the preemption 1617 model being selected at boot time using static keys. 1618 1619 Each preemption function will be given an early return based on a 1620 static key. This should have slightly lower overhead than non-inline 1621 static calls, as this effectively inlines each trampoline into the 1622 start of its callee. This may avoid redundant work, and may 1623 integrate better with CFI schemes. 1624 1625 This will have greater overhead than using inline static calls as 1626 the call to the preemption function cannot be entirely elided. 1627 1628config ARCH_WANT_LD_ORPHAN_WARN 1629 bool 1630 help 1631 An arch should select this symbol once all linker sections are explicitly 1632 included, size-asserted, or discarded in the linker scripts. This is 1633 important because we never want expected sections to be placed heuristically 1634 by the linker, since the locations of such sections can change between linker 1635 versions. 1636 1637config HAVE_ARCH_PFN_VALID 1638 bool 1639 1640config ARCH_SUPPORTS_DEBUG_PAGEALLOC 1641 bool 1642 1643config ARCH_SUPPORTS_PAGE_TABLE_CHECK 1644 bool 1645 1646config ARCH_SPLIT_ARG64 1647 bool 1648 help 1649 If a 32-bit architecture requires 64-bit arguments to be split into 1650 pairs of 32-bit arguments, select this option. 1651 1652config ARCH_HAS_ELFCORE_COMPAT 1653 bool 1654 1655config ARCH_HAS_PARANOID_L1D_FLUSH 1656 bool 1657 1658config ARCH_HAVE_TRACE_MMIO_ACCESS 1659 bool 1660 1661config DYNAMIC_SIGFRAME 1662 bool 1663 1664# Select, if arch has a named attribute group bound to NUMA device nodes. 1665config HAVE_ARCH_NODE_DEV_GROUP 1666 bool 1667 1668config ARCH_HAS_HW_PTE_YOUNG 1669 bool 1670 help 1671 Architectures that select this option are capable of setting the 1672 accessed bit in PTE entries when using them as part of linear address 1673 translations. Architectures that require runtime check should select 1674 this option and override arch_has_hw_pte_young(). 1675 1676config ARCH_HAS_NONLEAF_PMD_YOUNG 1677 bool 1678 help 1679 Architectures that select this option are capable of setting the 1680 accessed bit in non-leaf PMD entries when using them as part of linear 1681 address translations. Page table walkers that clear the accessed bit 1682 may use this capability to reduce their search space. 1683 1684config ARCH_HAS_KERNEL_FPU_SUPPORT 1685 bool 1686 help 1687 Architectures that select this option can run floating-point code in 1688 the kernel, as described in Documentation/core-api/floating-point.rst. 1689 1690source "kernel/gcov/Kconfig" 1691 1692source "scripts/gcc-plugins/Kconfig" 1693 1694config FUNCTION_ALIGNMENT_4B 1695 bool 1696 1697config FUNCTION_ALIGNMENT_8B 1698 bool 1699 1700config FUNCTION_ALIGNMENT_16B 1701 bool 1702 1703config FUNCTION_ALIGNMENT_32B 1704 bool 1705 1706config FUNCTION_ALIGNMENT_64B 1707 bool 1708 1709config FUNCTION_ALIGNMENT 1710 int 1711 default 64 if FUNCTION_ALIGNMENT_64B 1712 default 32 if FUNCTION_ALIGNMENT_32B 1713 default 16 if FUNCTION_ALIGNMENT_16B 1714 default 8 if FUNCTION_ALIGNMENT_8B 1715 default 4 if FUNCTION_ALIGNMENT_4B 1716 default 0 1717 1718config CC_HAS_MIN_FUNCTION_ALIGNMENT 1719 # Detect availability of the GCC option -fmin-function-alignment which 1720 # guarantees minimal alignment for all functions, unlike 1721 # -falign-functions which the compiler ignores for cold functions. 1722 def_bool $(cc-option, -fmin-function-alignment=8) 1723 1724config CC_HAS_SANE_FUNCTION_ALIGNMENT 1725 # Set if the guaranteed alignment with -fmin-function-alignment is 1726 # available or extra care is required in the kernel. Clang provides 1727 # strict alignment always, even with -falign-functions. 1728 def_bool CC_HAS_MIN_FUNCTION_ALIGNMENT || CC_IS_CLANG 1729 1730config ARCH_NEED_CMPXCHG_1_EMU 1731 bool 1732 1733config ARCH_WANTS_PRE_LINK_VMLINUX 1734 bool 1735 help 1736 An architecture can select this if it provides arch/<arch>/tools/Makefile 1737 with .arch.vmlinux.o target to be linked into vmlinux. 1738 1739endmenu 1740