arch/Kconfig

   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 menu "General architecture-dependent options"
  13
  14 config CRASH_CORE
  15         bool
  16
  17 config KEXEC_CORE
  18         select CRASH_CORE
  19         bool
  20
  21 config KEXEC_ELF
  22         bool
  23
  24 config HAVE_IMA_KEXEC
  25         bool
  26
  27 config SET_FS
  28         bool
  29
  30 config HOTPLUG_SMT
  31         bool
  32
  33 config GENERIC_ENTRY
  34        bool
  35
  36 config KPROBES
  37         bool "Kprobes"
  38         depends on MODULES
  39         depends on HAVE_KPROBES
  40         select KALLSYMS
  41         help
  42           Kprobes allows you to trap at almost any kernel address and
  43           execute a callback function.  register_kprobe() establishes
  44           a probepoint and specifies the callback.  Kprobes is useful
  45           for kernel debugging, non-intrusive instrumentation and testing.
  46           If in doubt, say "N".
  47
  48 config JUMP_LABEL
  49         bool "Optimize very unlikely/likely branches"
  50         depends on HAVE_ARCH_JUMP_LABEL
  51         depends on CC_HAS_ASM_GOTO
  52         help
  53          This option enables a transparent branch optimization that
  54          makes certain almost-always-true or almost-always-false branch
  55          conditions even cheaper to execute within the kernel.
  56
  57          Certain performance-sensitive kernel code, such as trace points,
  58          scheduler functionality, networking code and KVM have such
  59          branches and include support for this optimization technique.
  60
  61          If it is detected that the compiler has support for "asm goto",
  62          the kernel will compile such branches with just a nop
  63          instruction. When the condition flag is toggled to true, the
  64          nop will be converted to a jump instruction to execute the
  65          conditional block of instructions.
  66
  67          This technique lowers overhead and stress on the branch prediction
  68          of the processor and generally makes the kernel faster. The update
  69          of the condition is slower, but those are always very rare.
  70
  71          ( On 32-bit x86, the necessary options added to the compiler
  72            flags may increase the size of the kernel slightly. )
  73
  74 config STATIC_KEYS_SELFTEST
  75         bool "Static key selftest"
  76         depends on JUMP_LABEL
  77         help
  78           Boot time self-test of the branch patching code.
  79
  80 config STATIC_CALL_SELFTEST
  81         bool "Static call selftest"
  82         depends on HAVE_STATIC_CALL
  83         help
  84           Boot time self-test of the call patching code.
  85
  86 config OPTPROBES
  87         def_bool y
  88         depends on KPROBES && HAVE_OPTPROBES
  89         select TASKS_RCU if PREEMPTION
  90
  91 config KPROBES_ON_FTRACE
  92         def_bool y
  93         depends on KPROBES && HAVE_KPROBES_ON_FTRACE
  94         depends on DYNAMIC_FTRACE_WITH_REGS
  95         help
  96          If function tracer is enabled and the arch supports full
  97          passing of pt_regs to function tracing, then kprobes can
  98          optimize on top of function tracing.
  99
 100 config UPROBES
 101         def_bool n
 102         depends on ARCH_SUPPORTS_UPROBES
 103         help
 104           Uprobes is the user-space counterpart to kprobes: they
 105           enable instrumentation applications (such as 'perf probe')
 106           to establish unintrusive probes in user-space binaries and
 107           libraries, by executing handler functions when the probes
 108           are hit by user-space applications.
 109
 110           ( These probes come in the form of single-byte breakpoints,
 111             managed by the kernel and kept transparent to the probed
 112             application. )
 113
 114 config HAVE_64BIT_ALIGNED_ACCESS
 115         def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
 116         help
 117           Some architectures require 64 bit accesses to be 64 bit
 118           aligned, which also requires structs containing 64 bit values
 119           to be 64 bit aligned too. This includes some 32 bit
 120           architectures which can do 64 bit accesses, as well as 64 bit
 121           architectures without unaligned access.
 122
 123           This symbol should be selected by an architecture if 64 bit
 124           accesses are required to be 64 bit aligned in this way even
 125           though it is not a 64 bit architecture.
 126
 127           See Documentation/core-api/unaligned-memory-access.rst for
 128           more information on the topic of unaligned memory accesses.
 129
 130 config HAVE_EFFICIENT_UNALIGNED_ACCESS
 131         bool
 132         help
 133           Some architectures are unable to perform unaligned accesses
 134           without the use of get_unaligned/put_unaligned. Others are
 135           unable to perform such accesses efficiently (e.g. trap on
 136           unaligned access and require fixing it up in the exception
 137           handler.)
 138
 139           This symbol should be selected by an architecture if it can
 140           perform unaligned accesses efficiently to allow different
 141           code paths to be selected for these cases. Some network
 142           drivers, for example, could opt to not fix up alignment
 143           problems with received packets if doing so would not help
 144           much.
 145
 146           See Documentation/core-api/unaligned-memory-access.rst for more
 147           information on the topic of unaligned memory accesses.
 148
 149 config ARCH_USE_BUILTIN_BSWAP
 150         bool
 151         help
 152          Modern versions of GCC (since 4.4) have builtin functions
 153          for handling byte-swapping. Using these, instead of the old
 154          inline assembler that the architecture code provides in the
 155          __arch_bswapXX() macros, allows the compiler to see what's
 156          happening and offers more opportunity for optimisation. In
 157          particular, the compiler will be able to combine the byteswap
 158          with a nearby load or store and use load-and-swap or
 159          store-and-swap instructions if the architecture has them. It
 160          should almost *never* result in code which is worse than the
 161          hand-coded assembler in <asm/swab.h>.  But just in case it
 162          does, the use of the builtins is optional.
 163
 164          Any architecture with load-and-swap or store-and-swap
 165          instructions should set this. And it shouldn't hurt to set it
 166          on architectures that don't have such instructions.
 167
 168 config KRETPROBES
 169         def_bool y
 170         depends on KPROBES && HAVE_KRETPROBES
 171
 172 config USER_RETURN_NOTIFIER
 173         bool
 174         depends on HAVE_USER_RETURN_NOTIFIER
 175         help
 176           Provide a kernel-internal notification when a cpu is about to
 177           switch to user mode.
 178
 179 config HAVE_IOREMAP_PROT
 180         bool
 181
 182 config HAVE_KPROBES
 183         bool
 184
 185 config HAVE_KRETPROBES
 186         bool
 187
 188 config HAVE_OPTPROBES
 189         bool
 190
 191 config HAVE_KPROBES_ON_FTRACE
 192         bool
 193
 194 config HAVE_FUNCTION_ERROR_INJECTION
 195         bool
 196
 197 config HAVE_NMI
 198         bool
 199
 200 #
 201 # An arch should select this if it provides all these things:
 202 #
 203 #       task_pt_regs()          in asm/processor.h or asm/ptrace.h
 204 #       arch_has_single_step()  if there is hardware single-step support
 205 #       arch_has_block_step()   if there is hardware block-step support
 206 #       asm/syscall.h           supplying asm-generic/syscall.h interface
 207 #       linux/regset.h          user_regset interfaces
 208 #       CORE_DUMP_USE_REGSET    #define'd in linux/elf.h
 209 #       TIF_SYSCALL_TRACE       calls tracehook_report_syscall_{entry,exit}
 210 #       TIF_NOTIFY_RESUME       calls tracehook_notify_resume()
 211 #       signal delivery         calls tracehook_signal_handler()
 212 #
 213 config HAVE_ARCH_TRACEHOOK
 214         bool
 215
 216 config HAVE_DMA_CONTIGUOUS
 217         bool
 218
 219 config GENERIC_SMP_IDLE_THREAD
 220         bool
 221
 222 config GENERIC_IDLE_POLL_SETUP
 223         bool
 224
 225 config ARCH_HAS_FORTIFY_SOURCE
 226         bool
 227         help
 228           An architecture should select this when it can successfully
 229           build and run with CONFIG_FORTIFY_SOURCE.
 230
 231 #
 232 # Select if the arch provides a historic keepinit alias for the retain_initrd
 233 # command line option
 234 #
 235 config ARCH_HAS_KEEPINITRD
 236         bool
 237
 238 # Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
 239 config ARCH_HAS_SET_MEMORY
 240         bool
 241
 242 # Select if arch has all set_direct_map_invalid/default() functions
 243 config ARCH_HAS_SET_DIRECT_MAP
 244         bool
 245
 246 #
 247 # Select if the architecture provides the arch_dma_set_uncached symbol to
 248 # either provide an uncached segment alias for a DMA allocation, or
 249 # to remap the page tables in place.
 250 #
 251 config ARCH_HAS_DMA_SET_UNCACHED
 252         bool
 253
 254 #
 255 # Select if the architectures provides the arch_dma_clear_uncached symbol
 256 # to undo an in-place page table remap for uncached access.
 257 #
 258 config ARCH_HAS_DMA_CLEAR_UNCACHED
 259         bool
 260
 261 # Select if arch init_task must go in the __init_task_data section
 262 config ARCH_TASK_STRUCT_ON_STACK
 263         bool
 264
 265 # Select if arch has its private alloc_task_struct() function
 266 config ARCH_TASK_STRUCT_ALLOCATOR
 267         bool
 268
 269 config HAVE_ARCH_THREAD_STRUCT_WHITELIST
 270         bool
 271         depends on !ARCH_TASK_STRUCT_ALLOCATOR
 272         help
 273           An architecture should select this to provide hardened usercopy
 274           knowledge about what region of the thread_struct should be
 275           whitelisted for copying to userspace. Normally this is only the
 276           FPU registers. Specifically, arch_thread_struct_whitelist()
 277           should be implemented. Without this, the entire thread_struct
 278           field in task_struct will be left whitelisted.
 279
 280 # Select if arch has its private alloc_thread_stack() function
 281 config ARCH_THREAD_STACK_ALLOCATOR
 282         bool
 283
 284 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
 285 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
 286         bool
 287
 288 config ARCH_32BIT_OFF_T
 289         bool
 290         depends on !64BIT
 291         help
 292           All new 32-bit architectures should have 64-bit off_t type on
 293           userspace side which corresponds to the loff_t kernel type. This
 294           is the requirement for modern ABIs. Some existing architectures
 295           still support 32-bit off_t. This option is enabled for all such
 296           architectures explicitly.
 297
 298 # Selected by 64 bit architectures which have a 32 bit f_tinode in struct ustat
 299 config ARCH_32BIT_USTAT_F_TINODE
 300         bool
 301
 302 config HAVE_ASM_MODVERSIONS
 303         bool
 304         help
 305           This symbol should be selected by an architecture if it provides
 306           <asm/asm-prototypes.h> to support the module versioning for symbols
 307           exported from assembly code.
 308
 309 config HAVE_REGS_AND_STACK_ACCESS_API
 310         bool
 311         help
 312           This symbol should be selected by an architecture if it supports
 313           the API needed to access registers and stack entries from pt_regs,
 314           declared in asm/ptrace.h
 315           For example the kprobes-based event tracer needs this API.
 316
 317 config HAVE_RSEQ
 318         bool
 319         depends on HAVE_REGS_AND_STACK_ACCESS_API
 320         help
 321           This symbol should be selected by an architecture if it
 322           supports an implementation of restartable sequences.
 323
 324 config HAVE_FUNCTION_ARG_ACCESS_API
 325         bool
 326         help
 327           This symbol should be selected by an architecture if it supports
 328           the API needed to access function arguments from pt_regs,
 329           declared in asm/ptrace.h
 330
 331 config HAVE_HW_BREAKPOINT
 332         bool
 333         depends on PERF_EVENTS
 334
 335 config HAVE_MIXED_BREAKPOINTS_REGS
 336         bool
 337         depends on HAVE_HW_BREAKPOINT
 338         help
 339           Depending on the arch implementation of hardware breakpoints,
 340           some of them have separate registers for data and instruction
 341           breakpoints addresses, others have mixed registers to store
 342           them but define the access type in a control register.
 343           Select this option if your arch implements breakpoints under the
 344           latter fashion.
 345
 346 config HAVE_USER_RETURN_NOTIFIER
 347         bool
 348
 349 config HAVE_PERF_EVENTS_NMI
 350         bool
 351         help
 352           System hardware can generate an NMI using the perf event
 353           subsystem.  Also has support for calculating CPU cycle events
 354           to determine how many clock cycles in a given period.
 355
 356 config HAVE_HARDLOCKUP_DETECTOR_PERF
 357         bool
 358         depends on HAVE_PERF_EVENTS_NMI
 359         help
 360           The arch chooses to use the generic perf-NMI-based hardlockup
 361           detector. Must define HAVE_PERF_EVENTS_NMI.
 362
 363 config HAVE_NMI_WATCHDOG
 364         depends on HAVE_NMI
 365         bool
 366         help
 367           The arch provides a low level NMI watchdog. It provides
 368           asm/nmi.h, and defines its own arch_touch_nmi_watchdog().
 369
 370 config HAVE_HARDLOCKUP_DETECTOR_ARCH
 371         bool
 372         select HAVE_NMI_WATCHDOG
 373         help
 374           The arch chooses to provide its own hardlockup detector, which is
 375           a superset of the HAVE_NMI_WATCHDOG. It also conforms to config
 376           interfaces and parameters provided by hardlockup detector subsystem.
 377
 378 config HAVE_PERF_REGS
 379         bool
 380         help
 381           Support selective register dumps for perf events. This includes
 382           bit-mapping of each registers and a unique architecture id.
 383
 384 config HAVE_PERF_USER_STACK_DUMP
 385         bool
 386         help
 387           Support user stack dumps for perf event samples. This needs
 388           access to the user stack pointer which is not unified across
 389           architectures.
 390
 391 config HAVE_ARCH_JUMP_LABEL
 392         bool
 393
 394 config HAVE_ARCH_JUMP_LABEL_RELATIVE
 395         bool
 396
 397 config MMU_GATHER_TABLE_FREE
 398         bool
 399
 400 config MMU_GATHER_RCU_TABLE_FREE
 401         bool
 402         select MMU_GATHER_TABLE_FREE
 403
 404 config MMU_GATHER_PAGE_SIZE
 405         bool
 406
 407 config MMU_GATHER_NO_RANGE
 408         bool
 409
 410 config MMU_GATHER_NO_GATHER
 411         bool
 412         depends on MMU_GATHER_TABLE_FREE
 413
 414 config ARCH_WANT_IRQS_OFF_ACTIVATE_MM
 415         bool
 416         help
 417           Temporary select until all architectures can be converted to have
 418           irqs disabled over activate_mm. Architectures that do IPI based TLB
 419           shootdowns should enable this.
 420
 421 config ARCH_HAVE_NMI_SAFE_CMPXCHG
 422         bool
 423
 424 config HAVE_ALIGNED_STRUCT_PAGE
 425         bool
 426         help
 427           This makes sure that struct pages are double word aligned and that
 428           e.g. the SLUB allocator can perform double word atomic operations
 429           on a struct page for better performance. However selecting this
 430           might increase the size of a struct page by a word.
 431
 432 config HAVE_CMPXCHG_LOCAL
 433         bool
 434
 435 config HAVE_CMPXCHG_DOUBLE
 436         bool
 437
 438 config ARCH_WEAK_RELEASE_ACQUIRE
 439         bool
 440
 441 config ARCH_WANT_IPC_PARSE_VERSION
 442         bool
 443
 444 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 445         bool
 446
 447 config ARCH_WANT_OLD_COMPAT_IPC
 448         select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 449         bool
 450
 451 config HAVE_ARCH_SECCOMP
 452         bool
 453         help
 454           An arch should select this symbol to support seccomp mode 1 (the fixed
 455           syscall policy), and must provide an overrides for __NR_seccomp_sigreturn,
 456           and compat syscalls if the asm-generic/seccomp.h defaults need adjustment:
 457           - __NR_seccomp_read_32
 458           - __NR_seccomp_write_32
 459           - __NR_seccomp_exit_32
 460           - __NR_seccomp_sigreturn_32
 461
 462 config HAVE_ARCH_SECCOMP_FILTER
 463         bool
 464         select HAVE_ARCH_SECCOMP
 465         help
 466           An arch should select this symbol if it provides all of these things:
 467           - all the requirements for HAVE_ARCH_SECCOMP
 468           - syscall_get_arch()
 469           - syscall_get_arguments()
 470           - syscall_rollback()
 471           - syscall_set_return_value()
 472           - SIGSYS siginfo_t support
 473           - secure_computing is called from a ptrace_event()-safe context
 474           - secure_computing return value is checked and a return value of -1
 475             results in the system call being skipped immediately.
 476           - seccomp syscall wired up
 477           - if !HAVE_SPARSE_SYSCALL_NR, have SECCOMP_ARCH_NATIVE,
 478             SECCOMP_ARCH_NATIVE_NR, SECCOMP_ARCH_NATIVE_NAME defined. If
 479             COMPAT is supported, have the SECCOMP_ARCH_COMPAT* defines too.
 480
 481 config SECCOMP
 482         prompt "Enable seccomp to safely execute untrusted bytecode"
 483         def_bool y
 484         depends on HAVE_ARCH_SECCOMP
 485         help
 486           This kernel feature is useful for number crunching applications
 487           that may need to handle untrusted bytecode during their
 488           execution. By using pipes or other transports made available
 489           to the process as file descriptors supporting the read/write
 490           syscalls, it's possible to isolate those applications in their
 491           own address space using seccomp. Once seccomp is enabled via
 492           prctl(PR_SET_SECCOMP) or the seccomp() syscall, it cannot be
 493           disabled and the task is only allowed to execute a few safe
 494           syscalls defined by each seccomp mode.
 495
 496           If unsure, say Y.
 497
 498 config SECCOMP_FILTER
 499         def_bool y
 500         depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
 501         help
 502           Enable tasks to build secure computing environments defined
 503           in terms of Berkeley Packet Filter programs which implement
 504           task-defined system call filtering polices.
 505
 506           See Documentation/userspace-api/seccomp_filter.rst for details.
 507
 508 config SECCOMP_CACHE_DEBUG
 509         bool "Show seccomp filter cache status in /proc/pid/seccomp_cache"
 510         depends on SECCOMP_FILTER && !HAVE_SPARSE_SYSCALL_NR
 511         depends on PROC_FS
 512         help
 513           This enables the /proc/pid/seccomp_cache interface to monitor
 514           seccomp cache data. The file format is subject to change. Reading
 515           the file requires CAP_SYS_ADMIN.
 516
 517           This option is for debugging only. Enabling presents the risk that
 518           an adversary may be able to infer the seccomp filter logic.
 519
 520           If unsure, say N.
 521
 522 config HAVE_ARCH_STACKLEAK
 523         bool
 524         help
 525           An architecture should select this if it has the code which
 526           fills the used part of the kernel stack with the STACKLEAK_POISON
 527           value before returning from system calls.
 528
 529 config HAVE_STACKPROTECTOR
 530         bool
 531         help
 532           An arch should select this symbol if:
 533           - it has implemented a stack canary (e.g. __stack_chk_guard)
 534
 535 config STACKPROTECTOR
 536         bool "Stack Protector buffer overflow detection"
 537         depends on HAVE_STACKPROTECTOR
 538         depends on $(cc-option,-fstack-protector)
 539         default y
 540         help
 541           This option turns on the "stack-protector" GCC feature. This
 542           feature puts, at the beginning of functions, a canary value on
 543           the stack just before the return address, and validates
 544           the value just before actually returning.  Stack based buffer
 545           overflows (that need to overwrite this return address) now also
 546           overwrite the canary, which gets detected and the attack is then
 547           neutralized via a kernel panic.
 548
 549           Functions will have the stack-protector canary logic added if they
 550           have an 8-byte or larger character array on the stack.
 551
 552           This feature requires gcc version 4.2 or above, or a distribution
 553           gcc with the feature backported ("-fstack-protector").
 554
 555           On an x86 "defconfig" build, this feature adds canary checks to
 556           about 3% of all kernel functions, which increases kernel code size
 557           by about 0.3%.
 558
 559 config STACKPROTECTOR_STRONG
 560         bool "Strong Stack Protector"
 561         depends on STACKPROTECTOR
 562         depends on $(cc-option,-fstack-protector-strong)
 563         default y
 564         help
 565           Functions will have the stack-protector canary logic added in any
 566           of the following conditions:
 567
 568           - local variable's address used as part of the right hand side of an
 569             assignment or function argument
 570           - local variable is an array (or union containing an array),
 571             regardless of array type or length
 572           - uses register local variables
 573
 574           This feature requires gcc version 4.9 or above, or a distribution
 575           gcc with the feature backported ("-fstack-protector-strong").
 576
 577           On an x86 "defconfig" build, this feature adds canary checks to
 578           about 20% of all kernel functions, which increases the kernel code
 579           size by about 2%.
 580
 581 config ARCH_SUPPORTS_SHADOW_CALL_STACK
 582         bool
 583         help
 584           An architecture should select this if it supports Clang's Shadow
 585           Call Stack and implements runtime support for shadow stack
 586           switching.
 587
 588 config SHADOW_CALL_STACK
 589         bool "Clang Shadow Call Stack"
 590         depends on CC_IS_CLANG && ARCH_SUPPORTS_SHADOW_CALL_STACK
 591         depends on DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
 592         help
 593           This option enables Clang's Shadow Call Stack, which uses a
 594           shadow stack to protect function return addresses from being
 595           overwritten by an attacker. More information can be found in
 596           Clang's documentation:
 597
 598             https://clang.llvm.org/docs/ShadowCallStack.html
 599
 600           Note that security guarantees in the kernel differ from the
 601           ones documented for user space. The kernel must store addresses
 602           of shadow stacks in memory, which means an attacker capable of
 603           reading and writing arbitrary memory may be able to locate them
 604           and hijack control flow by modifying the stacks.
 605
 606 config LTO
 607         bool
 608         help
 609           Selected if the kernel will be built using the compiler's LTO feature.
 610
 611 config LTO_CLANG
 612         bool
 613         select LTO
 614         help
 615           Selected if the kernel will be built using Clang's LTO feature.
 616
 617 config ARCH_SUPPORTS_LTO_CLANG
 618         bool
 619         help
 620           An architecture should select this option if it supports:
 621           - compiling with Clang,
 622           - compiling inline assembly with Clang's integrated assembler,
 623           - and linking with LLD.
 624
 625 config ARCH_SUPPORTS_LTO_CLANG_THIN
 626         bool
 627         help
 628           An architecture should select this option if it can support Clang's
 629           ThinLTO mode.
 630
 631 config HAS_LTO_CLANG
 632         def_bool y
 633         # Clang >= 11: https://github.com/ClangBuiltLinux/linux/issues/510
 634         depends on CC_IS_CLANG && CLANG_VERSION >= 110000 && LD_IS_LLD && AS_IS_LLVM
 635         depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
 636         depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
 637         depends on ARCH_SUPPORTS_LTO_CLANG
 638         depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT
 639         depends on !KASAN || KASAN_HW_TAGS
 640         depends on !GCOV_KERNEL
 641         help
 642           The compiler and Kconfig options support building with Clang's
 643           LTO.
 644
 645 choice
 646         prompt "Link Time Optimization (LTO)"
 647         default LTO_NONE
 648         help
 649           This option enables Link Time Optimization (LTO), which allows the
 650           compiler to optimize binaries globally.
 651
 652           If unsure, select LTO_NONE. Note that LTO is very resource-intensive
 653           so it's disabled by default.
 654
 655 config LTO_NONE
 656         bool "None"
 657         help
 658           Build the kernel normally, without Link Time Optimization (LTO).
 659
 660 config LTO_CLANG_FULL
 661         bool "Clang Full LTO (EXPERIMENTAL)"
 662         depends on HAS_LTO_CLANG
 663         depends on !COMPILE_TEST
 664         select LTO_CLANG
 665         help
 666           This option enables Clang's full Link Time Optimization (LTO), which
 667           allows the compiler to optimize the kernel globally. If you enable
 668           this option, the compiler generates LLVM bitcode instead of ELF
 669           object files, and the actual compilation from bitcode happens at
 670           the LTO link step, which may take several minutes depending on the
 671           kernel configuration. More information can be found from LLVM's
 672           documentation:
 673
 674             https://llvm.org/docs/LinkTimeOptimization.html
 675
 676           During link time, this option can use a large amount of RAM, and
 677           may take much longer than the ThinLTO option.
 678
 679 config LTO_CLANG_THIN
 680         bool "Clang ThinLTO (EXPERIMENTAL)"
 681         depends on HAS_LTO_CLANG && ARCH_SUPPORTS_LTO_CLANG_THIN
 682         select LTO_CLANG
 683         help
 684           This option enables Clang's ThinLTO, which allows for parallel
 685           optimization and faster incremental compiles compared to the
 686           CONFIG_LTO_CLANG_FULL option. More information can be found
 687           from Clang's documentation:
 688
 689             https://clang.llvm.org/docs/ThinLTO.html
 690
 691           If unsure, say Y.
 692 endchoice
 693
 694 config ARCH_SUPPORTS_CFI_CLANG
 695         bool
 696         help
 697           An architecture should select this option if it can support Clang's
 698           Control-Flow Integrity (CFI) checking.
 699
 700 config CFI_CLANG
 701         bool "Use Clang's Control Flow Integrity (CFI)"
 702         depends on LTO_CLANG && ARCH_SUPPORTS_CFI_CLANG
 703         # Clang >= 12:
 704         # - https://bugs.llvm.org/show_bug.cgi?id=46258
 705         # - https://bugs.llvm.org/show_bug.cgi?id=47479
 706         depends on CLANG_VERSION >= 120000
 707         select KALLSYMS
 708         help
 709           This option enables Clang’s forward-edge Control Flow Integrity
 710           (CFI) checking, where the compiler injects a runtime check to each
 711           indirect function call to ensure the target is a valid function with
 712           the correct static type. This restricts possible call targets and
 713           makes it more difficult for an attacker to exploit bugs that allow
 714           the modification of stored function pointers. More information can be
 715           found from Clang's documentation:
 716
 717             https://clang.llvm.org/docs/ControlFlowIntegrity.html
 718
 719 config CFI_CLANG_SHADOW
 720         bool "Use CFI shadow to speed up cross-module checks"
 721         default y
 722         depends on CFI_CLANG && MODULES
 723         help
 724           If you select this option, the kernel builds a fast look-up table of
 725           CFI check functions in loaded modules to reduce performance overhead.
 726
 727           If unsure, say Y.
 728
 729 config CFI_PERMISSIVE
 730         bool "Use CFI in permissive mode"
 731         depends on CFI_CLANG
 732         help
 733           When selected, Control Flow Integrity (CFI) violations result in a
 734           warning instead of a kernel panic. This option should only be used
 735           for finding indirect call type mismatches during development.
 736
 737           If unsure, say N.
 738
 739 config HAVE_ARCH_WITHIN_STACK_FRAMES
 740         bool
 741         help
 742           An architecture should select this if it can walk the kernel stack
 743           frames to determine if an object is part of either the arguments
 744           or local variables (i.e. that it excludes saved return addresses,
 745           and similar) by implementing an inline arch_within_stack_frames(),
 746           which is used by CONFIG_HARDENED_USERCOPY.
 747
 748 config HAVE_CONTEXT_TRACKING
 749         bool
 750         help
 751           Provide kernel/user boundaries probes necessary for subsystems
 752           that need it, such as userspace RCU extended quiescent state.
 753           Syscalls need to be wrapped inside user_exit()-user_enter(), either
 754           optimized behind static key or through the slow path using TIF_NOHZ
 755           flag. Exceptions handlers must be wrapped as well. Irqs are already
 756           protected inside rcu_irq_enter/rcu_irq_exit() but preemption or signal
 757           handling on irq exit still need to be protected.
 758
 759 config HAVE_CONTEXT_TRACKING_OFFSTACK
 760         bool
 761         help
 762           Architecture neither relies on exception_enter()/exception_exit()
 763           nor on schedule_user(). Also preempt_schedule_notrace() and
 764           preempt_schedule_irq() can't be called in a preemptible section
 765           while context tracking is CONTEXT_USER. This feature reflects a sane
 766           entry implementation where the following requirements are met on
 767           critical entry code, ie: before user_exit() or after user_enter():
 768
 769           - Critical entry code isn't preemptible (or better yet:
 770             not interruptible).
 771           - No use of RCU read side critical sections, unless rcu_nmi_enter()
 772             got called.
 773           - No use of instrumentation, unless instrumentation_begin() got
 774             called.
 775
 776 config HAVE_TIF_NOHZ
 777         bool
 778         help
 779           Arch relies on TIF_NOHZ and syscall slow path to implement context
 780           tracking calls to user_enter()/user_exit().
 781
 782 config HAVE_VIRT_CPU_ACCOUNTING
 783         bool
 784
 785 config HAVE_VIRT_CPU_ACCOUNTING_IDLE
 786         bool
 787         help
 788           Architecture has its own way to account idle CPU time and therefore
 789           doesn't implement vtime_account_idle().
 790
 791 config ARCH_HAS_SCALED_CPUTIME
 792         bool
 793
 794 config HAVE_VIRT_CPU_ACCOUNTING_GEN
 795         bool
 796         default y if 64BIT
 797         help
 798           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 799           Before enabling this option, arch code must be audited
 800           to ensure there are no races in concurrent read/write of
 801           cputime_t. For example, reading/writing 64-bit cputime_t on
 802           some 32-bit arches may require multiple accesses, so proper
 803           locking is needed to protect against concurrent accesses.
 804
 805 config HAVE_IRQ_TIME_ACCOUNTING
 806         bool
 807         help
 808           Archs need to ensure they use a high enough resolution clock to
 809           support irq time accounting and then call enable_sched_clock_irqtime().
 810
 811 config HAVE_MOVE_PUD
 812         bool
 813         help
 814           Architectures that select this are able to move page tables at the
 815           PUD level. If there are only 3 page table levels, the move effectively
 816           happens at the PGD level.
 817
 818 config HAVE_MOVE_PMD
 819         bool
 820         help
 821           Archs that select this are able to move page tables at the PMD level.
 822
 823 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 824         bool
 825
 826 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 827         bool
 828
 829 config HAVE_ARCH_HUGE_VMAP
 830         bool
 831
 832 #
 833 #  Archs that select this would be capable of PMD-sized vmaps (i.e.,
 834 #  arch_vmap_pmd_supported() returns true), and they must make no assumptions
 835 #  that vmalloc memory is mapped with PAGE_SIZE ptes. The VM_NO_HUGE_VMAP flag
 836 #  can be used to prohibit arch-specific allocations from using hugepages to
 837 #  help with this (e.g., modules may require it).
 838 #
 839 config HAVE_ARCH_HUGE_VMALLOC
 840         depends on HAVE_ARCH_HUGE_VMAP
 841         bool
 842
 843 config ARCH_WANT_HUGE_PMD_SHARE
 844         bool
 845
 846 config HAVE_ARCH_SOFT_DIRTY
 847         bool
 848
 849 config HAVE_MOD_ARCH_SPECIFIC
 850         bool
 851         help
 852           The arch uses struct mod_arch_specific to store data.  Many arches
 853           just need a simple module loader without arch specific data - those
 854           should not enable this.
 855
 856 config MODULES_USE_ELF_RELA
 857         bool
 858         help
 859           Modules only use ELF RELA relocations.  Modules with ELF REL
 860           relocations will give an error.
 861
 862 config MODULES_USE_ELF_REL
 863         bool
 864         help
 865           Modules only use ELF REL relocations.  Modules with ELF RELA
 866           relocations will give an error.
 867
 868 config HAVE_IRQ_EXIT_ON_IRQ_STACK
 869         bool
 870         help
 871           Architecture doesn't only execute the irq handler on the irq stack
 872           but also irq_exit(). This way we can process softirqs on this irq
 873           stack instead of switching to a new one when we call __do_softirq()
 874           in the end of an hardirq.
 875           This spares a stack switch and improves cache usage on softirq
 876           processing.
 877
 878 config HAVE_SOFTIRQ_ON_OWN_STACK
 879         bool
 880         help
 881           Architecture provides a function to run __do_softirq() on a
 882           seperate stack.
 883
 884 config PGTABLE_LEVELS
 885         int
 886         default 2
 887
 888 config ARCH_HAS_ELF_RANDOMIZE
 889         bool
 890         help
 891           An architecture supports choosing randomized locations for
 892           stack, mmap, brk, and ET_DYN. Defined functions:
 893           - arch_mmap_rnd()
 894           - arch_randomize_brk()
 895
 896 config HAVE_ARCH_MMAP_RND_BITS
 897         bool
 898         help
 899           An arch should select this symbol if it supports setting a variable
 900           number of bits for use in establishing the base address for mmap
 901           allocations, has MMU enabled and provides values for both:
 902           - ARCH_MMAP_RND_BITS_MIN
 903           - ARCH_MMAP_RND_BITS_MAX
 904
 905 config HAVE_EXIT_THREAD
 906         bool
 907         help
 908           An architecture implements exit_thread.
 909
 910 config ARCH_MMAP_RND_BITS_MIN
 911         int
 912
 913 config ARCH_MMAP_RND_BITS_MAX
 914         int
 915
 916 config ARCH_MMAP_RND_BITS_DEFAULT
 917         int
 918
 919 config ARCH_MMAP_RND_BITS
 920         int "Number of bits to use for ASLR of mmap base address" if EXPERT
 921         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
 922         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
 923         default ARCH_MMAP_RND_BITS_MIN
 924         depends on HAVE_ARCH_MMAP_RND_BITS
 925         help
 926           This value can be used to select the number of bits to use to
 927           determine the random offset to the base address of vma regions
 928           resulting from mmap allocations. This value will be bounded
 929           by the architecture's minimum and maximum supported values.
 930
 931           This value can be changed after boot using the
 932           /proc/sys/vm/mmap_rnd_bits tunable
 933
 934 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
 935         bool
 936         help
 937           An arch should select this symbol if it supports running applications
 938           in compatibility mode, supports setting a variable number of bits for
 939           use in establishing the base address for mmap allocations, has MMU
 940           enabled and provides values for both:
 941           - ARCH_MMAP_RND_COMPAT_BITS_MIN
 942           - ARCH_MMAP_RND_COMPAT_BITS_MAX
 943
 944 config ARCH_MMAP_RND_COMPAT_BITS_MIN
 945         int
 946
 947 config ARCH_MMAP_RND_COMPAT_BITS_MAX
 948         int
 949
 950 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 951         int
 952
 953 config ARCH_MMAP_RND_COMPAT_BITS
 954         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
 955         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
 956         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 957         default ARCH_MMAP_RND_COMPAT_BITS_MIN
 958         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
 959         help
 960           This value can be used to select the number of bits to use to
 961           determine the random offset to the base address of vma regions
 962           resulting from mmap allocations for compatible applications This
 963           value will be bounded by the architecture's minimum and maximum
 964           supported values.
 965
 966           This value can be changed after boot using the
 967           /proc/sys/vm/mmap_rnd_compat_bits tunable
 968
 969 config HAVE_ARCH_COMPAT_MMAP_BASES
 970         bool
 971         help
 972           This allows 64bit applications to invoke 32-bit mmap() syscall
 973           and vice-versa 32-bit applications to call 64-bit mmap().
 974           Required for applications doing different bitness syscalls.
 975
 976 # This allows to use a set of generic functions to determine mmap base
 977 # address by giving priority to top-down scheme only if the process
 978 # is not in legacy mode (compat task, unlimited stack size or
 979 # sysctl_legacy_va_layout).
 980 # Architecture that selects this option can provide its own version of:
 981 # - STACK_RND_MASK
 982 config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
 983         bool
 984         depends on MMU
 985         select ARCH_HAS_ELF_RANDOMIZE
 986
 987 config HAVE_STACK_VALIDATION
 988         bool
 989         help
 990           Architecture supports the 'objtool check' host tool command, which
 991           performs compile-time stack metadata validation.
 992
 993 config HAVE_RELIABLE_STACKTRACE
 994         bool
 995         help
 996           Architecture has either save_stack_trace_tsk_reliable() or
 997           arch_stack_walk_reliable() function which only returns a stack trace
 998           if it can guarantee the trace is reliable.
 999
1000 config HAVE_ARCH_HASH
1001         bool
1002         default n
1003         help
1004           If this is set, the architecture provides an <asm/hash.h>
1005           file which provides platform-specific implementations of some
1006           functions in <linux/hash.h> or fs/namei.c.
1007
1008 config HAVE_ARCH_NVRAM_OPS
1009         bool
1010
1011 config ISA_BUS_API
1012         def_bool ISA
1013
1014 #
1015 # ABI hall of shame
1016 #
1017 config CLONE_BACKWARDS
1018         bool
1019         help
1020           Architecture has tls passed as the 4th argument of clone(2),
1021           not the 5th one.
1022
1023 config CLONE_BACKWARDS2
1024         bool
1025         help
1026           Architecture has the first two arguments of clone(2) swapped.
1027
1028 config CLONE_BACKWARDS3
1029         bool
1030         help
1031           Architecture has tls passed as the 3rd argument of clone(2),
1032           not the 5th one.
1033
1034 config ODD_RT_SIGACTION
1035         bool
1036         help
1037           Architecture has unusual rt_sigaction(2) arguments
1038
1039 config OLD_SIGSUSPEND
1040         bool
1041         help
1042           Architecture has old sigsuspend(2) syscall, of one-argument variety
1043
1044 config OLD_SIGSUSPEND3
1045         bool
1046         help
1047           Even weirder antique ABI - three-argument sigsuspend(2)
1048
1049 config OLD_SIGACTION
1050         bool
1051         help
1052           Architecture has old sigaction(2) syscall.  Nope, not the same
1053           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
1054           but fairly different variant of sigaction(2), thanks to OSF/1
1055           compatibility...
1056
1057 config COMPAT_OLD_SIGACTION
1058         bool
1059
1060 config COMPAT_32BIT_TIME
1061         bool "Provide system calls for 32-bit time_t"
1062         default !64BIT || COMPAT
1063         help
1064           This enables 32 bit time_t support in addition to 64 bit time_t support.
1065           This is relevant on all 32-bit architectures, and 64-bit architectures
1066           as part of compat syscall handling.
1067
1068 config ARCH_NO_PREEMPT
1069         bool
1070
1071 config ARCH_EPHEMERAL_INODES
1072         def_bool n
1073         help
1074           An arch should select this symbol if it doesn't keep track of inode
1075           instances on its own, but instead relies on something else (e.g. the
1076           host kernel for an UML kernel).
1077
1078 config ARCH_SUPPORTS_RT
1079         bool
1080
1081 config CPU_NO_EFFICIENT_FFS
1082         def_bool n
1083
1084 config HAVE_ARCH_VMAP_STACK
1085         def_bool n
1086         help
1087           An arch should select this symbol if it can support kernel stacks
1088           in vmalloc space.  This means:
1089
1090           - vmalloc space must be large enough to hold many kernel stacks.
1091             This may rule out many 32-bit architectures.
1092
1093           - Stacks in vmalloc space need to work reliably.  For example, if
1094             vmap page tables are created on demand, either this mechanism
1095             needs to work while the stack points to a virtual address with
1096             unpopulated page tables or arch code (switch_to() and switch_mm(),
1097             most likely) needs to ensure that the stack's page table entries
1098             are populated before running on a possibly unpopulated stack.
1099
1100           - If the stack overflows into a guard page, something reasonable
1101             should happen.  The definition of "reasonable" is flexible, but
1102             instantly rebooting without logging anything would be unfriendly.
1103
1104 config VMAP_STACK
1105         default y
1106         bool "Use a virtually-mapped stack"
1107         depends on HAVE_ARCH_VMAP_STACK
1108         depends on !KASAN || KASAN_HW_TAGS || KASAN_VMALLOC
1109         help
1110           Enable this if you want the use virtually-mapped kernel stacks
1111           with guard pages.  This causes kernel stack overflows to be
1112           caught immediately rather than causing difficult-to-diagnose
1113           corruption.
1114
1115           To use this with software KASAN modes, the architecture must support
1116           backing virtual mappings with real shadow memory, and KASAN_VMALLOC
1117           must be enabled.
1118
1119 config HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
1120         def_bool n
1121         help
1122           An arch should select this symbol if it can support kernel stack
1123           offset randomization with calls to add_random_kstack_offset()
1124           during syscall entry and choose_random_kstack_offset() during
1125           syscall exit. Careful removal of -fstack-protector-strong and
1126           -fstack-protector should also be applied to the entry code and
1127           closely examined, as the artificial stack bump looks like an array
1128           to the compiler, so it will attempt to add canary checks regardless
1129           of the static branch state.
1130
1131 config RANDOMIZE_KSTACK_OFFSET_DEFAULT
1132         bool "Randomize kernel stack offset on syscall entry"
1133         depends on HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
1134         help
1135           The kernel stack offset can be randomized (after pt_regs) by
1136           roughly 5 bits of entropy, frustrating memory corruption
1137           attacks that depend on stack address determinism or
1138           cross-syscall address exposures. This feature is controlled
1139           by kernel boot param "randomize_kstack_offset=on/off", and this
1140           config chooses the default boot state.
1141
1142 config ARCH_OPTIONAL_KERNEL_RWX
1143         def_bool n
1144
1145 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1146         def_bool n
1147
1148 config ARCH_HAS_STRICT_KERNEL_RWX
1149         def_bool n
1150
1151 config STRICT_KERNEL_RWX
1152         bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
1153         depends on ARCH_HAS_STRICT_KERNEL_RWX
1154         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1155         help
1156           If this is set, kernel text and rodata memory will be made read-only,
1157           and non-text memory will be made non-executable. This provides
1158           protection against certain security exploits (e.g. executing the heap
1159           or modifying text)
1160
1161           These features are considered standard security practice these days.
1162           You should say Y here in almost all cases.
1163
1164 config ARCH_HAS_STRICT_MODULE_RWX
1165         def_bool n
1166
1167 config STRICT_MODULE_RWX
1168         bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
1169         depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
1170         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1171         help
1172           If this is set, module text and rodata memory will be made read-only,
1173           and non-text memory will be made non-executable. This provides
1174           protection against certain security exploits (e.g. writing to text)
1175
1176 # select if the architecture provides an asm/dma-direct.h header
1177 config ARCH_HAS_PHYS_TO_DMA
1178         bool
1179
1180 config HAVE_ARCH_COMPILER_H
1181         bool
1182         help
1183           An architecture can select this if it provides an
1184           asm/compiler.h header that should be included after
1185           linux/compiler-*.h in order to override macro definitions that those
1186           headers generally provide.
1187
1188 config HAVE_ARCH_PREL32_RELOCATIONS
1189         bool
1190         help
1191           May be selected by an architecture if it supports place-relative
1192           32-bit relocations, both in the toolchain and in the module loader,
1193           in which case relative references can be used in special sections
1194           for PCI fixup, initcalls etc which are only half the size on 64 bit
1195           architectures, and don't require runtime relocation on relocatable
1196           kernels.
1197
1198 config ARCH_USE_MEMREMAP_PROT
1199         bool
1200
1201 config LOCK_EVENT_COUNTS
1202         bool "Locking event counts collection"
1203         depends on DEBUG_FS
1204         help
1205           Enable light-weight counting of various locking related events
1206           in the system with minimal performance impact. This reduces
1207           the chance of application behavior change because of timing
1208           differences. The counts are reported via debugfs.
1209
1210 # Select if the architecture has support for applying RELR relocations.
1211 config ARCH_HAS_RELR
1212         bool
1213
1214 config RELR
1215         bool "Use RELR relocation packing"
1216         depends on ARCH_HAS_RELR && TOOLS_SUPPORT_RELR
1217         default y
1218         help
1219           Store the kernel's dynamic relocations in the RELR relocation packing
1220           format. Requires a compatible linker (LLD supports this feature), as
1221           well as compatible NM and OBJCOPY utilities (llvm-nm and llvm-objcopy
1222           are compatible).
1223
1224 config ARCH_HAS_MEM_ENCRYPT
1225         bool
1226
1227 config HAVE_SPARSE_SYSCALL_NR
1228        bool
1229        help
1230           An architecture should select this if its syscall numbering is sparse
1231           to save space. For example, MIPS architecture has a syscall array with
1232           entries at 4000, 5000 and 6000 locations. This option turns on syscall
1233           related optimizations for a given architecture.
1234
1235 config ARCH_HAS_VDSO_DATA
1236         bool
1237
1238 config HAVE_STATIC_CALL
1239         bool
1240
1241 config HAVE_STATIC_CALL_INLINE
1242         bool
1243         depends on HAVE_STATIC_CALL
1244
1245 config HAVE_PREEMPT_DYNAMIC
1246         bool
1247         depends on HAVE_STATIC_CALL
1248         depends on GENERIC_ENTRY
1249         help
1250            Select this if the architecture support boot time preempt setting
1251            on top of static calls. It is strongly advised to support inline
1252            static call to avoid any overhead.
1253
1254 config ARCH_WANT_LD_ORPHAN_WARN
1255         bool
1256         help
1257           An arch should select this symbol once all linker sections are explicitly
1258           included, size-asserted, or discarded in the linker scripts. This is
1259           important because we never want expected sections to be placed heuristically
1260           by the linker, since the locations of such sections can change between linker
1261           versions.
1262
1263 config HAVE_ARCH_PFN_VALID
1264         bool
1265
1266 config ARCH_SUPPORTS_DEBUG_PAGEALLOC
1267         bool
1268
1269 config ARCH_SPLIT_ARG64
1270         bool
1271         help
1272            If a 32-bit architecture requires 64-bit arguments to be split into
1273            pairs of 32-bit arguments, select this option.
1274
1275 config ARCH_HAS_ELFCORE_COMPAT
1276         bool
1277
1278 source "kernel/gcov/Kconfig"
1279
1280 source "scripts/gcc-plugins/Kconfig"
1281
1282 endmenu