linux/arch/Kconfig
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   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
  12menu "General architecture-dependent options"
  13
  14config CRASH_CORE
  15        bool
  16
  17config KEXEC_CORE
  18        select CRASH_CORE
  19        bool
  20
  21config KEXEC_ELF
  22        bool
  23
  24config HAVE_IMA_KEXEC
  25        bool
  26
  27config SET_FS
  28        bool
  29
  30config HOTPLUG_SMT
  31        bool
  32
  33config GENERIC_ENTRY
  34       bool
  35
  36config 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
  48config 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
  74config 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
  80config 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
  86config OPTPROBES
  87        def_bool y
  88        depends on KPROBES && HAVE_OPTPROBES
  89        select TASKS_RCU if PREEMPTION
  90
  91config 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
 100config 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
 114config 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
 130config 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
 149config 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
 168config KRETPROBES
 169        def_bool y
 170        depends on KPROBES && HAVE_KRETPROBES
 171
 172config 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
 179config HAVE_IOREMAP_PROT
 180        bool
 181
 182config HAVE_KPROBES
 183        bool
 184
 185config HAVE_KRETPROBES
 186        bool
 187
 188config HAVE_OPTPROBES
 189        bool
 190
 191config HAVE_KPROBES_ON_FTRACE
 192        bool
 193
 194config HAVE_FUNCTION_ERROR_INJECTION
 195        bool
 196
 197config 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#
 213config HAVE_ARCH_TRACEHOOK
 214        bool
 215
 216config HAVE_DMA_CONTIGUOUS
 217        bool
 218
 219config GENERIC_SMP_IDLE_THREAD
 220        bool
 221
 222config GENERIC_IDLE_POLL_SETUP
 223        bool
 224
 225config 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#
 235config ARCH_HAS_KEEPINITRD
 236        bool
 237
 238# Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
 239config ARCH_HAS_SET_MEMORY
 240        bool
 241
 242# Select if arch has all set_direct_map_invalid/default() functions
 243config 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#
 251config 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#
 258config ARCH_HAS_DMA_CLEAR_UNCACHED
 259        bool
 260
 261# Select if arch init_task must go in the __init_task_data section
 262config ARCH_TASK_STRUCT_ON_STACK
 263        bool
 264
 265# Select if arch has its private alloc_task_struct() function
 266config ARCH_TASK_STRUCT_ALLOCATOR
 267        bool
 268
 269config 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
 281config ARCH_THREAD_STACK_ALLOCATOR
 282        bool
 283
 284# Select if arch wants to size task_struct dynamically via arch_task_struct_size:
 285config ARCH_WANTS_DYNAMIC_TASK_STRUCT
 286        bool
 287
 288config ARCH_WANTS_NO_INSTR
 289        bool
 290        help
 291          An architecture should select this if the noinstr macro is being used on
 292          functions to denote that the toolchain should avoid instrumenting such
 293          functions and is required for correctness.
 294
 295config ARCH_32BIT_OFF_T
 296        bool
 297        depends on !64BIT
 298        help
 299          All new 32-bit architectures should have 64-bit off_t type on
 300          userspace side which corresponds to the loff_t kernel type. This
 301          is the requirement for modern ABIs. Some existing architectures
 302          still support 32-bit off_t. This option is enabled for all such
 303          architectures explicitly.
 304
 305# Selected by 64 bit architectures which have a 32 bit f_tinode in struct ustat
 306config ARCH_32BIT_USTAT_F_TINODE
 307        bool
 308
 309config HAVE_ASM_MODVERSIONS
 310        bool
 311        help
 312          This symbol should be selected by an architecture if it provides
 313          <asm/asm-prototypes.h> to support the module versioning for symbols
 314          exported from assembly code.
 315
 316config HAVE_REGS_AND_STACK_ACCESS_API
 317        bool
 318        help
 319          This symbol should be selected by an architecture if it supports
 320          the API needed to access registers and stack entries from pt_regs,
 321          declared in asm/ptrace.h
 322          For example the kprobes-based event tracer needs this API.
 323
 324config HAVE_RSEQ
 325        bool
 326        depends on HAVE_REGS_AND_STACK_ACCESS_API
 327        help
 328          This symbol should be selected by an architecture if it
 329          supports an implementation of restartable sequences.
 330
 331config HAVE_FUNCTION_ARG_ACCESS_API
 332        bool
 333        help
 334          This symbol should be selected by an architecture if it supports
 335          the API needed to access function arguments from pt_regs,
 336          declared in asm/ptrace.h
 337
 338config HAVE_HW_BREAKPOINT
 339        bool
 340        depends on PERF_EVENTS
 341
 342config HAVE_MIXED_BREAKPOINTS_REGS
 343        bool
 344        depends on HAVE_HW_BREAKPOINT
 345        help
 346          Depending on the arch implementation of hardware breakpoints,
 347          some of them have separate registers for data and instruction
 348          breakpoints addresses, others have mixed registers to store
 349          them but define the access type in a control register.
 350          Select this option if your arch implements breakpoints under the
 351          latter fashion.
 352
 353config HAVE_USER_RETURN_NOTIFIER
 354        bool
 355
 356config HAVE_PERF_EVENTS_NMI
 357        bool
 358        help
 359          System hardware can generate an NMI using the perf event
 360          subsystem.  Also has support for calculating CPU cycle events
 361          to determine how many clock cycles in a given period.
 362
 363config HAVE_HARDLOCKUP_DETECTOR_PERF
 364        bool
 365        depends on HAVE_PERF_EVENTS_NMI
 366        help
 367          The arch chooses to use the generic perf-NMI-based hardlockup
 368          detector. Must define HAVE_PERF_EVENTS_NMI.
 369
 370config HAVE_NMI_WATCHDOG
 371        depends on HAVE_NMI
 372        bool
 373        help
 374          The arch provides a low level NMI watchdog. It provides
 375          asm/nmi.h, and defines its own arch_touch_nmi_watchdog().
 376
 377config HAVE_HARDLOCKUP_DETECTOR_ARCH
 378        bool
 379        select HAVE_NMI_WATCHDOG
 380        help
 381          The arch chooses to provide its own hardlockup detector, which is
 382          a superset of the HAVE_NMI_WATCHDOG. It also conforms to config
 383          interfaces and parameters provided by hardlockup detector subsystem.
 384
 385config HAVE_PERF_REGS
 386        bool
 387        help
 388          Support selective register dumps for perf events. This includes
 389          bit-mapping of each registers and a unique architecture id.
 390
 391config HAVE_PERF_USER_STACK_DUMP
 392        bool
 393        help
 394          Support user stack dumps for perf event samples. This needs
 395          access to the user stack pointer which is not unified across
 396          architectures.
 397
 398config HAVE_ARCH_JUMP_LABEL
 399        bool
 400
 401config HAVE_ARCH_JUMP_LABEL_RELATIVE
 402        bool
 403
 404config MMU_GATHER_TABLE_FREE
 405        bool
 406
 407config MMU_GATHER_RCU_TABLE_FREE
 408        bool
 409        select MMU_GATHER_TABLE_FREE
 410
 411config MMU_GATHER_PAGE_SIZE
 412        bool
 413
 414config MMU_GATHER_NO_RANGE
 415        bool
 416
 417config MMU_GATHER_NO_GATHER
 418        bool
 419        depends on MMU_GATHER_TABLE_FREE
 420
 421config ARCH_WANT_IRQS_OFF_ACTIVATE_MM
 422        bool
 423        help
 424          Temporary select until all architectures can be converted to have
 425          irqs disabled over activate_mm. Architectures that do IPI based TLB
 426          shootdowns should enable this.
 427
 428config ARCH_HAVE_NMI_SAFE_CMPXCHG
 429        bool
 430
 431config HAVE_ALIGNED_STRUCT_PAGE
 432        bool
 433        help
 434          This makes sure that struct pages are double word aligned and that
 435          e.g. the SLUB allocator can perform double word atomic operations
 436          on a struct page for better performance. However selecting this
 437          might increase the size of a struct page by a word.
 438
 439config HAVE_CMPXCHG_LOCAL
 440        bool
 441
 442config HAVE_CMPXCHG_DOUBLE
 443        bool
 444
 445config ARCH_WEAK_RELEASE_ACQUIRE
 446        bool
 447
 448config ARCH_WANT_IPC_PARSE_VERSION
 449        bool
 450
 451config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 452        bool
 453
 454config ARCH_WANT_OLD_COMPAT_IPC
 455        select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 456        bool
 457
 458config HAVE_ARCH_SECCOMP
 459        bool
 460        help
 461          An arch should select this symbol to support seccomp mode 1 (the fixed
 462          syscall policy), and must provide an overrides for __NR_seccomp_sigreturn,
 463          and compat syscalls if the asm-generic/seccomp.h defaults need adjustment:
 464          - __NR_seccomp_read_32
 465          - __NR_seccomp_write_32
 466          - __NR_seccomp_exit_32
 467          - __NR_seccomp_sigreturn_32
 468
 469config HAVE_ARCH_SECCOMP_FILTER
 470        bool
 471        select HAVE_ARCH_SECCOMP
 472        help
 473          An arch should select this symbol if it provides all of these things:
 474          - all the requirements for HAVE_ARCH_SECCOMP
 475          - syscall_get_arch()
 476          - syscall_get_arguments()
 477          - syscall_rollback()
 478          - syscall_set_return_value()
 479          - SIGSYS siginfo_t support
 480          - secure_computing is called from a ptrace_event()-safe context
 481          - secure_computing return value is checked and a return value of -1
 482            results in the system call being skipped immediately.
 483          - seccomp syscall wired up
 484          - if !HAVE_SPARSE_SYSCALL_NR, have SECCOMP_ARCH_NATIVE,
 485            SECCOMP_ARCH_NATIVE_NR, SECCOMP_ARCH_NATIVE_NAME defined. If
 486            COMPAT is supported, have the SECCOMP_ARCH_COMPAT* defines too.
 487
 488config SECCOMP
 489        prompt "Enable seccomp to safely execute untrusted bytecode"
 490        def_bool y
 491        depends on HAVE_ARCH_SECCOMP
 492        help
 493          This kernel feature is useful for number crunching applications
 494          that may need to handle untrusted bytecode during their
 495          execution. By using pipes or other transports made available
 496          to the process as file descriptors supporting the read/write
 497          syscalls, it's possible to isolate those applications in their
 498          own address space using seccomp. Once seccomp is enabled via
 499          prctl(PR_SET_SECCOMP) or the seccomp() syscall, it cannot be
 500          disabled and the task is only allowed to execute a few safe
 501          syscalls defined by each seccomp mode.
 502
 503          If unsure, say Y.
 504
 505config SECCOMP_FILTER
 506        def_bool y
 507        depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
 508        help
 509          Enable tasks to build secure computing environments defined
 510          in terms of Berkeley Packet Filter programs which implement
 511          task-defined system call filtering polices.
 512
 513          See Documentation/userspace-api/seccomp_filter.rst for details.
 514
 515config SECCOMP_CACHE_DEBUG
 516        bool "Show seccomp filter cache status in /proc/pid/seccomp_cache"
 517        depends on SECCOMP_FILTER && !HAVE_SPARSE_SYSCALL_NR
 518        depends on PROC_FS
 519        help
 520          This enables the /proc/pid/seccomp_cache interface to monitor
 521          seccomp cache data. The file format is subject to change. Reading
 522          the file requires CAP_SYS_ADMIN.
 523
 524          This option is for debugging only. Enabling presents the risk that
 525          an adversary may be able to infer the seccomp filter logic.
 526
 527          If unsure, say N.
 528
 529config HAVE_ARCH_STACKLEAK
 530        bool
 531        help
 532          An architecture should select this if it has the code which
 533          fills the used part of the kernel stack with the STACKLEAK_POISON
 534          value before returning from system calls.
 535
 536config HAVE_STACKPROTECTOR
 537        bool
 538        help
 539          An arch should select this symbol if:
 540          - it has implemented a stack canary (e.g. __stack_chk_guard)
 541
 542config STACKPROTECTOR
 543        bool "Stack Protector buffer overflow detection"
 544        depends on HAVE_STACKPROTECTOR
 545        depends on $(cc-option,-fstack-protector)
 546        default y
 547        help
 548          This option turns on the "stack-protector" GCC feature. This
 549          feature puts, at the beginning of functions, a canary value on
 550          the stack just before the return address, and validates
 551          the value just before actually returning.  Stack based buffer
 552          overflows (that need to overwrite this return address) now also
 553          overwrite the canary, which gets detected and the attack is then
 554          neutralized via a kernel panic.
 555
 556          Functions will have the stack-protector canary logic added if they
 557          have an 8-byte or larger character array on the stack.
 558
 559          This feature requires gcc version 4.2 or above, or a distribution
 560          gcc with the feature backported ("-fstack-protector").
 561
 562          On an x86 "defconfig" build, this feature adds canary checks to
 563          about 3% of all kernel functions, which increases kernel code size
 564          by about 0.3%.
 565
 566config STACKPROTECTOR_STRONG
 567        bool "Strong Stack Protector"
 568        depends on STACKPROTECTOR
 569        depends on $(cc-option,-fstack-protector-strong)
 570        default y
 571        help
 572          Functions will have the stack-protector canary logic added in any
 573          of the following conditions:
 574
 575          - local variable's address used as part of the right hand side of an
 576            assignment or function argument
 577          - local variable is an array (or union containing an array),
 578            regardless of array type or length
 579          - uses register local variables
 580
 581          This feature requires gcc version 4.9 or above, or a distribution
 582          gcc with the feature backported ("-fstack-protector-strong").
 583
 584          On an x86 "defconfig" build, this feature adds canary checks to
 585          about 20% of all kernel functions, which increases the kernel code
 586          size by about 2%.
 587
 588config ARCH_SUPPORTS_SHADOW_CALL_STACK
 589        bool
 590        help
 591          An architecture should select this if it supports Clang's Shadow
 592          Call Stack and implements runtime support for shadow stack
 593          switching.
 594
 595config SHADOW_CALL_STACK
 596        bool "Clang Shadow Call Stack"
 597        depends on CC_IS_CLANG && ARCH_SUPPORTS_SHADOW_CALL_STACK
 598        depends on DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
 599        help
 600          This option enables Clang's Shadow Call Stack, which uses a
 601          shadow stack to protect function return addresses from being
 602          overwritten by an attacker. More information can be found in
 603          Clang's documentation:
 604
 605            https://clang.llvm.org/docs/ShadowCallStack.html
 606
 607          Note that security guarantees in the kernel differ from the
 608          ones documented for user space. The kernel must store addresses
 609          of shadow stacks in memory, which means an attacker capable of
 610          reading and writing arbitrary memory may be able to locate them
 611          and hijack control flow by modifying the stacks.
 612
 613config LTO
 614        bool
 615        help
 616          Selected if the kernel will be built using the compiler's LTO feature.
 617
 618config LTO_CLANG
 619        bool
 620        select LTO
 621        help
 622          Selected if the kernel will be built using Clang's LTO feature.
 623
 624config ARCH_SUPPORTS_LTO_CLANG
 625        bool
 626        help
 627          An architecture should select this option if it supports:
 628          - compiling with Clang,
 629          - compiling inline assembly with Clang's integrated assembler,
 630          - and linking with LLD.
 631
 632config ARCH_SUPPORTS_LTO_CLANG_THIN
 633        bool
 634        help
 635          An architecture should select this option if it can support Clang's
 636          ThinLTO mode.
 637
 638config HAS_LTO_CLANG
 639        def_bool y
 640        # Clang >= 11: https://github.com/ClangBuiltLinux/linux/issues/510
 641        depends on CC_IS_CLANG && CLANG_VERSION >= 110000 && LD_IS_LLD && AS_IS_LLVM
 642        depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
 643        depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
 644        depends on ARCH_SUPPORTS_LTO_CLANG
 645        depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT
 646        depends on !KASAN || KASAN_HW_TAGS
 647        depends on !GCOV_KERNEL
 648        help
 649          The compiler and Kconfig options support building with Clang's
 650          LTO.
 651
 652choice
 653        prompt "Link Time Optimization (LTO)"
 654        default LTO_NONE
 655        help
 656          This option enables Link Time Optimization (LTO), which allows the
 657          compiler to optimize binaries globally.
 658
 659          If unsure, select LTO_NONE. Note that LTO is very resource-intensive
 660          so it's disabled by default.
 661
 662config LTO_NONE
 663        bool "None"
 664        help
 665          Build the kernel normally, without Link Time Optimization (LTO).
 666
 667config LTO_CLANG_FULL
 668        bool "Clang Full LTO (EXPERIMENTAL)"
 669        depends on HAS_LTO_CLANG
 670        depends on !COMPILE_TEST
 671        select LTO_CLANG
 672        help
 673          This option enables Clang's full Link Time Optimization (LTO), which
 674          allows the compiler to optimize the kernel globally. If you enable
 675          this option, the compiler generates LLVM bitcode instead of ELF
 676          object files, and the actual compilation from bitcode happens at
 677          the LTO link step, which may take several minutes depending on the
 678          kernel configuration. More information can be found from LLVM's
 679          documentation:
 680
 681            https://llvm.org/docs/LinkTimeOptimization.html
 682
 683          During link time, this option can use a large amount of RAM, and
 684          may take much longer than the ThinLTO option.
 685
 686config LTO_CLANG_THIN
 687        bool "Clang ThinLTO (EXPERIMENTAL)"
 688        depends on HAS_LTO_CLANG && ARCH_SUPPORTS_LTO_CLANG_THIN
 689        select LTO_CLANG
 690        help
 691          This option enables Clang's ThinLTO, which allows for parallel
 692          optimization and faster incremental compiles compared to the
 693          CONFIG_LTO_CLANG_FULL option. More information can be found
 694          from Clang's documentation:
 695
 696            https://clang.llvm.org/docs/ThinLTO.html
 697
 698          If unsure, say Y.
 699endchoice
 700
 701config ARCH_SUPPORTS_CFI_CLANG
 702        bool
 703        help
 704          An architecture should select this option if it can support Clang's
 705          Control-Flow Integrity (CFI) checking.
 706
 707config CFI_CLANG
 708        bool "Use Clang's Control Flow Integrity (CFI)"
 709        depends on LTO_CLANG && ARCH_SUPPORTS_CFI_CLANG
 710        # Clang >= 12:
 711        # - https://bugs.llvm.org/show_bug.cgi?id=46258
 712        # - https://bugs.llvm.org/show_bug.cgi?id=47479
 713        depends on CLANG_VERSION >= 120000
 714        select KALLSYMS
 715        help
 716          This option enables Clang’s forward-edge Control Flow Integrity
 717          (CFI) checking, where the compiler injects a runtime check to each
 718          indirect function call to ensure the target is a valid function with
 719          the correct static type. This restricts possible call targets and
 720          makes it more difficult for an attacker to exploit bugs that allow
 721          the modification of stored function pointers. More information can be
 722          found from Clang's documentation:
 723
 724            https://clang.llvm.org/docs/ControlFlowIntegrity.html
 725
 726config CFI_CLANG_SHADOW
 727        bool "Use CFI shadow to speed up cross-module checks"
 728        default y
 729        depends on CFI_CLANG && MODULES
 730        help
 731          If you select this option, the kernel builds a fast look-up table of
 732          CFI check functions in loaded modules to reduce performance overhead.
 733
 734          If unsure, say Y.
 735
 736config CFI_PERMISSIVE
 737        bool "Use CFI in permissive mode"
 738        depends on CFI_CLANG
 739        help
 740          When selected, Control Flow Integrity (CFI) violations result in a
 741          warning instead of a kernel panic. This option should only be used
 742          for finding indirect call type mismatches during development.
 743
 744          If unsure, say N.
 745
 746config HAVE_ARCH_WITHIN_STACK_FRAMES
 747        bool
 748        help
 749          An architecture should select this if it can walk the kernel stack
 750          frames to determine if an object is part of either the arguments
 751          or local variables (i.e. that it excludes saved return addresses,
 752          and similar) by implementing an inline arch_within_stack_frames(),
 753          which is used by CONFIG_HARDENED_USERCOPY.
 754
 755config HAVE_CONTEXT_TRACKING
 756        bool
 757        help
 758          Provide kernel/user boundaries probes necessary for subsystems
 759          that need it, such as userspace RCU extended quiescent state.
 760          Syscalls need to be wrapped inside user_exit()-user_enter(), either
 761          optimized behind static key or through the slow path using TIF_NOHZ
 762          flag. Exceptions handlers must be wrapped as well. Irqs are already
 763          protected inside rcu_irq_enter/rcu_irq_exit() but preemption or signal
 764          handling on irq exit still need to be protected.
 765
 766config HAVE_CONTEXT_TRACKING_OFFSTACK
 767        bool
 768        help
 769          Architecture neither relies on exception_enter()/exception_exit()
 770          nor on schedule_user(). Also preempt_schedule_notrace() and
 771          preempt_schedule_irq() can't be called in a preemptible section
 772          while context tracking is CONTEXT_USER. This feature reflects a sane
 773          entry implementation where the following requirements are met on
 774          critical entry code, ie: before user_exit() or after user_enter():
 775
 776          - Critical entry code isn't preemptible (or better yet:
 777            not interruptible).
 778          - No use of RCU read side critical sections, unless rcu_nmi_enter()
 779            got called.
 780          - No use of instrumentation, unless instrumentation_begin() got
 781            called.
 782
 783config HAVE_TIF_NOHZ
 784        bool
 785        help
 786          Arch relies on TIF_NOHZ and syscall slow path to implement context
 787          tracking calls to user_enter()/user_exit().
 788
 789config HAVE_VIRT_CPU_ACCOUNTING
 790        bool
 791
 792config HAVE_VIRT_CPU_ACCOUNTING_IDLE
 793        bool
 794        help
 795          Architecture has its own way to account idle CPU time and therefore
 796          doesn't implement vtime_account_idle().
 797
 798config ARCH_HAS_SCALED_CPUTIME
 799        bool
 800
 801config HAVE_VIRT_CPU_ACCOUNTING_GEN
 802        bool
 803        default y if 64BIT
 804        help
 805          With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 806          Before enabling this option, arch code must be audited
 807          to ensure there are no races in concurrent read/write of
 808          cputime_t. For example, reading/writing 64-bit cputime_t on
 809          some 32-bit arches may require multiple accesses, so proper
 810          locking is needed to protect against concurrent accesses.
 811
 812config HAVE_IRQ_TIME_ACCOUNTING
 813        bool
 814        help
 815          Archs need to ensure they use a high enough resolution clock to
 816          support irq time accounting and then call enable_sched_clock_irqtime().
 817
 818config HAVE_MOVE_PUD
 819        bool
 820        help
 821          Architectures that select this are able to move page tables at the
 822          PUD level. If there are only 3 page table levels, the move effectively
 823          happens at the PGD level.
 824
 825config HAVE_MOVE_PMD
 826        bool
 827        help
 828          Archs that select this are able to move page tables at the PMD level.
 829
 830config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 831        bool
 832
 833config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 834        bool
 835
 836config HAVE_ARCH_HUGE_VMAP
 837        bool
 838
 839#
 840#  Archs that select this would be capable of PMD-sized vmaps (i.e.,
 841#  arch_vmap_pmd_supported() returns true), and they must make no assumptions
 842#  that vmalloc memory is mapped with PAGE_SIZE ptes. The VM_NO_HUGE_VMAP flag
 843#  can be used to prohibit arch-specific allocations from using hugepages to
 844#  help with this (e.g., modules may require it).
 845#
 846config HAVE_ARCH_HUGE_VMALLOC
 847        depends on HAVE_ARCH_HUGE_VMAP
 848        bool
 849
 850config ARCH_WANT_HUGE_PMD_SHARE
 851        bool
 852
 853config HAVE_ARCH_SOFT_DIRTY
 854        bool
 855
 856config HAVE_MOD_ARCH_SPECIFIC
 857        bool
 858        help
 859          The arch uses struct mod_arch_specific to store data.  Many arches
 860          just need a simple module loader without arch specific data - those
 861          should not enable this.
 862
 863config MODULES_USE_ELF_RELA
 864        bool
 865        help
 866          Modules only use ELF RELA relocations.  Modules with ELF REL
 867          relocations will give an error.
 868
 869config MODULES_USE_ELF_REL
 870        bool
 871        help
 872          Modules only use ELF REL relocations.  Modules with ELF RELA
 873          relocations will give an error.
 874
 875config HAVE_IRQ_EXIT_ON_IRQ_STACK
 876        bool
 877        help
 878          Architecture doesn't only execute the irq handler on the irq stack
 879          but also irq_exit(). This way we can process softirqs on this irq
 880          stack instead of switching to a new one when we call __do_softirq()
 881          in the end of an hardirq.
 882          This spares a stack switch and improves cache usage on softirq
 883          processing.
 884
 885config HAVE_SOFTIRQ_ON_OWN_STACK
 886        bool
 887        help
 888          Architecture provides a function to run __do_softirq() on a
 889          seperate stack.
 890
 891config PGTABLE_LEVELS
 892        int
 893        default 2
 894
 895config ARCH_HAS_ELF_RANDOMIZE
 896        bool
 897        help
 898          An architecture supports choosing randomized locations for
 899          stack, mmap, brk, and ET_DYN. Defined functions:
 900          - arch_mmap_rnd()
 901          - arch_randomize_brk()
 902
 903config HAVE_ARCH_MMAP_RND_BITS
 904        bool
 905        help
 906          An arch should select this symbol if it supports setting a variable
 907          number of bits for use in establishing the base address for mmap
 908          allocations, has MMU enabled and provides values for both:
 909          - ARCH_MMAP_RND_BITS_MIN
 910          - ARCH_MMAP_RND_BITS_MAX
 911
 912config HAVE_EXIT_THREAD
 913        bool
 914        help
 915          An architecture implements exit_thread.
 916
 917config ARCH_MMAP_RND_BITS_MIN
 918        int
 919
 920config ARCH_MMAP_RND_BITS_MAX
 921        int
 922
 923config ARCH_MMAP_RND_BITS_DEFAULT
 924        int
 925
 926config ARCH_MMAP_RND_BITS
 927        int "Number of bits to use for ASLR of mmap base address" if EXPERT
 928        range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
 929        default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
 930        default ARCH_MMAP_RND_BITS_MIN
 931        depends on HAVE_ARCH_MMAP_RND_BITS
 932        help
 933          This value can be used to select the number of bits to use to
 934          determine the random offset to the base address of vma regions
 935          resulting from mmap allocations. This value will be bounded
 936          by the architecture's minimum and maximum supported values.
 937
 938          This value can be changed after boot using the
 939          /proc/sys/vm/mmap_rnd_bits tunable
 940
 941config HAVE_ARCH_MMAP_RND_COMPAT_BITS
 942        bool
 943        help
 944          An arch should select this symbol if it supports running applications
 945          in compatibility mode, supports setting a variable number of bits for
 946          use in establishing the base address for mmap allocations, has MMU
 947          enabled and provides values for both:
 948          - ARCH_MMAP_RND_COMPAT_BITS_MIN
 949          - ARCH_MMAP_RND_COMPAT_BITS_MAX
 950
 951config ARCH_MMAP_RND_COMPAT_BITS_MIN
 952        int
 953
 954config ARCH_MMAP_RND_COMPAT_BITS_MAX
 955        int
 956
 957config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 958        int
 959
 960config ARCH_MMAP_RND_COMPAT_BITS
 961        int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
 962        range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
 963        default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 964        default ARCH_MMAP_RND_COMPAT_BITS_MIN
 965        depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
 966        help
 967          This value can be used to select the number of bits to use to
 968          determine the random offset to the base address of vma regions
 969          resulting from mmap allocations for compatible applications This
 970          value will be bounded by the architecture's minimum and maximum
 971          supported values.
 972
 973          This value can be changed after boot using the
 974          /proc/sys/vm/mmap_rnd_compat_bits tunable
 975
 976config HAVE_ARCH_COMPAT_MMAP_BASES
 977        bool
 978        help
 979          This allows 64bit applications to invoke 32-bit mmap() syscall
 980          and vice-versa 32-bit applications to call 64-bit mmap().
 981          Required for applications doing different bitness syscalls.
 982
 983# This allows to use a set of generic functions to determine mmap base
 984# address by giving priority to top-down scheme only if the process
 985# is not in legacy mode (compat task, unlimited stack size or
 986# sysctl_legacy_va_layout).
 987# Architecture that selects this option can provide its own version of:
 988# - STACK_RND_MASK
 989config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
 990        bool
 991        depends on MMU
 992        select ARCH_HAS_ELF_RANDOMIZE
 993
 994config HAVE_STACK_VALIDATION
 995        bool
 996        help
 997          Architecture supports the 'objtool check' host tool command, which
 998          performs compile-time stack metadata validation.
 999
1000config HAVE_RELIABLE_STACKTRACE
1001        bool
1002        help
1003          Architecture has either save_stack_trace_tsk_reliable() or
1004          arch_stack_walk_reliable() function which only returns a stack trace
1005          if it can guarantee the trace is reliable.
1006
1007config HAVE_ARCH_HASH
1008        bool
1009        default n
1010        help
1011          If this is set, the architecture provides an <asm/hash.h>
1012          file which provides platform-specific implementations of some
1013          functions in <linux/hash.h> or fs/namei.c.
1014
1015config HAVE_ARCH_NVRAM_OPS
1016        bool
1017
1018config ISA_BUS_API
1019        def_bool ISA
1020
1021#
1022# ABI hall of shame
1023#
1024config CLONE_BACKWARDS
1025        bool
1026        help
1027          Architecture has tls passed as the 4th argument of clone(2),
1028          not the 5th one.
1029
1030config CLONE_BACKWARDS2
1031        bool
1032        help
1033          Architecture has the first two arguments of clone(2) swapped.
1034
1035config CLONE_BACKWARDS3
1036        bool
1037        help
1038          Architecture has tls passed as the 3rd argument of clone(2),
1039          not the 5th one.
1040
1041config ODD_RT_SIGACTION
1042        bool
1043        help
1044          Architecture has unusual rt_sigaction(2) arguments
1045
1046config OLD_SIGSUSPEND
1047        bool
1048        help
1049          Architecture has old sigsuspend(2) syscall, of one-argument variety
1050
1051config OLD_SIGSUSPEND3
1052        bool
1053        help
1054          Even weirder antique ABI - three-argument sigsuspend(2)
1055
1056config OLD_SIGACTION
1057        bool
1058        help
1059          Architecture has old sigaction(2) syscall.  Nope, not the same
1060          as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
1061          but fairly different variant of sigaction(2), thanks to OSF/1
1062          compatibility...
1063
1064config COMPAT_OLD_SIGACTION
1065        bool
1066
1067config COMPAT_32BIT_TIME
1068        bool "Provide system calls for 32-bit time_t"
1069        default !64BIT || COMPAT
1070        help
1071          This enables 32 bit time_t support in addition to 64 bit time_t support.
1072          This is relevant on all 32-bit architectures, and 64-bit architectures
1073          as part of compat syscall handling.
1074
1075config ARCH_NO_PREEMPT
1076        bool
1077
1078config ARCH_EPHEMERAL_INODES
1079        def_bool n
1080        help
1081          An arch should select this symbol if it doesn't keep track of inode
1082          instances on its own, but instead relies on something else (e.g. the
1083          host kernel for an UML kernel).
1084
1085config ARCH_SUPPORTS_RT
1086        bool
1087
1088config CPU_NO_EFFICIENT_FFS
1089        def_bool n
1090
1091config HAVE_ARCH_VMAP_STACK
1092        def_bool n
1093        help
1094          An arch should select this symbol if it can support kernel stacks
1095          in vmalloc space.  This means:
1096
1097          - vmalloc space must be large enough to hold many kernel stacks.
1098            This may rule out many 32-bit architectures.
1099
1100          - Stacks in vmalloc space need to work reliably.  For example, if
1101            vmap page tables are created on demand, either this mechanism
1102            needs to work while the stack points to a virtual address with
1103            unpopulated page tables or arch code (switch_to() and switch_mm(),
1104            most likely) needs to ensure that the stack's page table entries
1105            are populated before running on a possibly unpopulated stack.
1106
1107          - If the stack overflows into a guard page, something reasonable
1108            should happen.  The definition of "reasonable" is flexible, but
1109            instantly rebooting without logging anything would be unfriendly.
1110
1111config VMAP_STACK
1112        default y
1113        bool "Use a virtually-mapped stack"
1114        depends on HAVE_ARCH_VMAP_STACK
1115        depends on !KASAN || KASAN_HW_TAGS || KASAN_VMALLOC
1116        help
1117          Enable this if you want the use virtually-mapped kernel stacks
1118          with guard pages.  This causes kernel stack overflows to be
1119          caught immediately rather than causing difficult-to-diagnose
1120          corruption.
1121
1122          To use this with software KASAN modes, the architecture must support
1123          backing virtual mappings with real shadow memory, and KASAN_VMALLOC
1124          must be enabled.
1125
1126config HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
1127        def_bool n
1128        help
1129          An arch should select this symbol if it can support kernel stack
1130          offset randomization with calls to add_random_kstack_offset()
1131          during syscall entry and choose_random_kstack_offset() during
1132          syscall exit. Careful removal of -fstack-protector-strong and
1133          -fstack-protector should also be applied to the entry code and
1134          closely examined, as the artificial stack bump looks like an array
1135          to the compiler, so it will attempt to add canary checks regardless
1136          of the static branch state.
1137
1138config RANDOMIZE_KSTACK_OFFSET_DEFAULT
1139        bool "Randomize kernel stack offset on syscall entry"
1140        depends on HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
1141        help
1142          The kernel stack offset can be randomized (after pt_regs) by
1143          roughly 5 bits of entropy, frustrating memory corruption
1144          attacks that depend on stack address determinism or
1145          cross-syscall address exposures. This feature is controlled
1146          by kernel boot param "randomize_kstack_offset=on/off", and this
1147          config chooses the default boot state.
1148
1149config ARCH_OPTIONAL_KERNEL_RWX
1150        def_bool n
1151
1152config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1153        def_bool n
1154
1155config ARCH_HAS_STRICT_KERNEL_RWX
1156        def_bool n
1157
1158config STRICT_KERNEL_RWX
1159        bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
1160        depends on ARCH_HAS_STRICT_KERNEL_RWX
1161        default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1162        help
1163          If this is set, kernel text and rodata memory will be made read-only,
1164          and non-text memory will be made non-executable. This provides
1165          protection against certain security exploits (e.g. executing the heap
1166          or modifying text)
1167
1168          These features are considered standard security practice these days.
1169          You should say Y here in almost all cases.
1170
1171config ARCH_HAS_STRICT_MODULE_RWX
1172        def_bool n
1173
1174config STRICT_MODULE_RWX
1175        bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
1176        depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
1177        default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1178        help
1179          If this is set, module text and rodata memory will be made read-only,
1180          and non-text memory will be made non-executable. This provides
1181          protection against certain security exploits (e.g. writing to text)
1182
1183# select if the architecture provides an asm/dma-direct.h header
1184config ARCH_HAS_PHYS_TO_DMA
1185        bool
1186
1187config HAVE_ARCH_COMPILER_H
1188        bool
1189        help
1190          An architecture can select this if it provides an
1191          asm/compiler.h header that should be included after
1192          linux/compiler-*.h in order to override macro definitions that those
1193          headers generally provide.
1194
1195config HAVE_ARCH_PREL32_RELOCATIONS
1196        bool
1197        help
1198          May be selected by an architecture if it supports place-relative
1199          32-bit relocations, both in the toolchain and in the module loader,
1200          in which case relative references can be used in special sections
1201          for PCI fixup, initcalls etc which are only half the size on 64 bit
1202          architectures, and don't require runtime relocation on relocatable
1203          kernels.
1204
1205config ARCH_USE_MEMREMAP_PROT
1206        bool
1207
1208config LOCK_EVENT_COUNTS
1209        bool "Locking event counts collection"
1210        depends on DEBUG_FS
1211        help
1212          Enable light-weight counting of various locking related events
1213          in the system with minimal performance impact. This reduces
1214          the chance of application behavior change because of timing
1215          differences. The counts are reported via debugfs.
1216
1217# Select if the architecture has support for applying RELR relocations.
1218config ARCH_HAS_RELR
1219        bool
1220
1221config RELR
1222        bool "Use RELR relocation packing"
1223        depends on ARCH_HAS_RELR && TOOLS_SUPPORT_RELR
1224        default y
1225        help
1226          Store the kernel's dynamic relocations in the RELR relocation packing
1227          format. Requires a compatible linker (LLD supports this feature), as
1228          well as compatible NM and OBJCOPY utilities (llvm-nm and llvm-objcopy
1229          are compatible).
1230
1231config ARCH_HAS_MEM_ENCRYPT
1232        bool
1233
1234config HAVE_SPARSE_SYSCALL_NR
1235       bool
1236       help
1237          An architecture should select this if its syscall numbering is sparse
1238          to save space. For example, MIPS architecture has a syscall array with
1239          entries at 4000, 5000 and 6000 locations. This option turns on syscall
1240          related optimizations for a given architecture.
1241
1242config ARCH_HAS_VDSO_DATA
1243        bool
1244
1245config HAVE_STATIC_CALL
1246        bool
1247
1248config HAVE_STATIC_CALL_INLINE
1249        bool
1250        depends on HAVE_STATIC_CALL
1251
1252config HAVE_PREEMPT_DYNAMIC
1253        bool
1254        depends on HAVE_STATIC_CALL
1255        depends on GENERIC_ENTRY
1256        help
1257           Select this if the architecture support boot time preempt setting
1258           on top of static calls. It is strongly advised to support inline
1259           static call to avoid any overhead.
1260
1261config ARCH_WANT_LD_ORPHAN_WARN
1262        bool
1263        help
1264          An arch should select this symbol once all linker sections are explicitly
1265          included, size-asserted, or discarded in the linker scripts. This is
1266          important because we never want expected sections to be placed heuristically
1267          by the linker, since the locations of such sections can change between linker
1268          versions.
1269
1270config HAVE_ARCH_PFN_VALID
1271        bool
1272
1273config ARCH_SUPPORTS_DEBUG_PAGEALLOC
1274        bool
1275
1276config ARCH_SPLIT_ARG64
1277        bool
1278        help
1279           If a 32-bit architecture requires 64-bit arguments to be split into
1280           pairs of 32-bit arguments, select this option.
1281
1282config ARCH_HAS_ELFCORE_COMPAT
1283        bool
1284
1285source "kernel/gcov/Kconfig"
1286
1287source "scripts/gcc-plugins/Kconfig"
1288
1289endmenu
1290