arch/Kconfig

   1 # SPDX-License-Identifier: GPL-2.0
   2 #
   3 # General architecture dependent options
   4 #
   5
   6 config CRASH_CORE
   7         bool
   8
   9 config KEXEC_CORE
  10         select CRASH_CORE
  11         bool
  12
  13 config HAVE_IMA_KEXEC
  14         bool
  15
  16 config OPROFILE
  17         tristate "OProfile system profiling"
  18         depends on PROFILING
  19         depends on HAVE_OPROFILE
  20         select RING_BUFFER
  21         select RING_BUFFER_ALLOW_SWAP
  22         help
  23           OProfile is a profiling system capable of profiling the
  24           whole system, include the kernel, kernel modules, libraries,
  25           and applications.
  26
  27           If unsure, say N.
  28
  29 config OPROFILE_EVENT_MULTIPLEX
  30         bool "OProfile multiplexing support (EXPERIMENTAL)"
  31         default n
  32         depends on OPROFILE && X86
  33         help
  34           The number of hardware counters is limited. The multiplexing
  35           feature enables OProfile to gather more events than counters
  36           are provided by the hardware. This is realized by switching
  37           between events at a user specified time interval.
  38
  39           If unsure, say N.
  40
  41 config HAVE_OPROFILE
  42         bool
  43
  44 config OPROFILE_NMI_TIMER
  45         def_bool y
  46         depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI && !PPC64
  47
  48 config KPROBES
  49         bool "Kprobes"
  50         depends on MODULES
  51         depends on HAVE_KPROBES
  52         select KALLSYMS
  53         help
  54           Kprobes allows you to trap at almost any kernel address and
  55           execute a callback function.  register_kprobe() establishes
  56           a probepoint and specifies the callback.  Kprobes is useful
  57           for kernel debugging, non-intrusive instrumentation and testing.
  58           If in doubt, say "N".
  59
  60 config JUMP_LABEL
  61        bool "Optimize very unlikely/likely branches"
  62        depends on HAVE_ARCH_JUMP_LABEL
  63        help
  64          This option enables a transparent branch optimization that
  65          makes certain almost-always-true or almost-always-false branch
  66          conditions even cheaper to execute within the kernel.
  67
  68          Certain performance-sensitive kernel code, such as trace points,
  69          scheduler functionality, networking code and KVM have such
  70          branches and include support for this optimization technique.
  71
  72          If it is detected that the compiler has support for "asm goto",
  73          the kernel will compile such branches with just a nop
  74          instruction. When the condition flag is toggled to true, the
  75          nop will be converted to a jump instruction to execute the
  76          conditional block of instructions.
  77
  78          This technique lowers overhead and stress on the branch prediction
  79          of the processor and generally makes the kernel faster. The update
  80          of the condition is slower, but those are always very rare.
  81
  82          ( On 32-bit x86, the necessary options added to the compiler
  83            flags may increase the size of the kernel slightly. )
  84
  85 config STATIC_KEYS_SELFTEST
  86         bool "Static key selftest"
  87         depends on JUMP_LABEL
  88         help
  89           Boot time self-test of the branch patching code.
  90
  91 config OPTPROBES
  92         def_bool y
  93         depends on KPROBES && HAVE_OPTPROBES
  94         select TASKS_RCU if PREEMPT
  95
  96 config KPROBES_ON_FTRACE
  97         def_bool y
  98         depends on KPROBES && HAVE_KPROBES_ON_FTRACE
  99         depends on DYNAMIC_FTRACE_WITH_REGS
 100         help
 101          If function tracer is enabled and the arch supports full
 102          passing of pt_regs to function tracing, then kprobes can
 103          optimize on top of function tracing.
 104
 105 config UPROBES
 106         def_bool n
 107         depends on ARCH_SUPPORTS_UPROBES
 108         help
 109           Uprobes is the user-space counterpart to kprobes: they
 110           enable instrumentation applications (such as 'perf probe')
 111           to establish unintrusive probes in user-space binaries and
 112           libraries, by executing handler functions when the probes
 113           are hit by user-space applications.
 114
 115           ( These probes come in the form of single-byte breakpoints,
 116             managed by the kernel and kept transparent to the probed
 117             application. )
 118
 119 config HAVE_64BIT_ALIGNED_ACCESS
 120         def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
 121         help
 122           Some architectures require 64 bit accesses to be 64 bit
 123           aligned, which also requires structs containing 64 bit values
 124           to be 64 bit aligned too. This includes some 32 bit
 125           architectures which can do 64 bit accesses, as well as 64 bit
 126           architectures without unaligned access.
 127
 128           This symbol should be selected by an architecture if 64 bit
 129           accesses are required to be 64 bit aligned in this way even
 130           though it is not a 64 bit architecture.
 131
 132           See Documentation/unaligned-memory-access.txt for more
 133           information on the topic of unaligned memory accesses.
 134
 135 config HAVE_EFFICIENT_UNALIGNED_ACCESS
 136         bool
 137         help
 138           Some architectures are unable to perform unaligned accesses
 139           without the use of get_unaligned/put_unaligned. Others are
 140           unable to perform such accesses efficiently (e.g. trap on
 141           unaligned access and require fixing it up in the exception
 142           handler.)
 143
 144           This symbol should be selected by an architecture if it can
 145           perform unaligned accesses efficiently to allow different
 146           code paths to be selected for these cases. Some network
 147           drivers, for example, could opt to not fix up alignment
 148           problems with received packets if doing so would not help
 149           much.
 150
 151           See Documentation/unaligned-memory-access.txt for more
 152           information on the topic of unaligned memory accesses.
 153
 154 config ARCH_USE_BUILTIN_BSWAP
 155        bool
 156        help
 157          Modern versions of GCC (since 4.4) have builtin functions
 158          for handling byte-swapping. Using these, instead of the old
 159          inline assembler that the architecture code provides in the
 160          __arch_bswapXX() macros, allows the compiler to see what's
 161          happening and offers more opportunity for optimisation. In
 162          particular, the compiler will be able to combine the byteswap
 163          with a nearby load or store and use load-and-swap or
 164          store-and-swap instructions if the architecture has them. It
 165          should almost *never* result in code which is worse than the
 166          hand-coded assembler in <asm/swab.h>.  But just in case it
 167          does, the use of the builtins is optional.
 168
 169          Any architecture with load-and-swap or store-and-swap
 170          instructions should set this. And it shouldn't hurt to set it
 171          on architectures that don't have such instructions.
 172
 173 config KRETPROBES
 174         def_bool y
 175         depends on KPROBES && HAVE_KRETPROBES
 176
 177 config USER_RETURN_NOTIFIER
 178         bool
 179         depends on HAVE_USER_RETURN_NOTIFIER
 180         help
 181           Provide a kernel-internal notification when a cpu is about to
 182           switch to user mode.
 183
 184 config HAVE_IOREMAP_PROT
 185         bool
 186
 187 config HAVE_KPROBES
 188         bool
 189
 190 config HAVE_KRETPROBES
 191         bool
 192
 193 config HAVE_OPTPROBES
 194         bool
 195
 196 config HAVE_KPROBES_ON_FTRACE
 197         bool
 198
 199 config HAVE_FUNCTION_ERROR_INJECTION
 200         bool
 201
 202 config HAVE_NMI
 203         bool
 204
 205 #
 206 # An arch should select this if it provides all these things:
 207 #
 208 #       task_pt_regs()          in asm/processor.h or asm/ptrace.h
 209 #       arch_has_single_step()  if there is hardware single-step support
 210 #       arch_has_block_step()   if there is hardware block-step support
 211 #       asm/syscall.h           supplying asm-generic/syscall.h interface
 212 #       linux/regset.h          user_regset interfaces
 213 #       CORE_DUMP_USE_REGSET    #define'd in linux/elf.h
 214 #       TIF_SYSCALL_TRACE       calls tracehook_report_syscall_{entry,exit}
 215 #       TIF_NOTIFY_RESUME       calls tracehook_notify_resume()
 216 #       signal delivery         calls tracehook_signal_handler()
 217 #
 218 config HAVE_ARCH_TRACEHOOK
 219         bool
 220
 221 config HAVE_DMA_CONTIGUOUS
 222         bool
 223
 224 config GENERIC_SMP_IDLE_THREAD
 225        bool
 226
 227 config GENERIC_IDLE_POLL_SETUP
 228        bool
 229
 230 config ARCH_HAS_FORTIFY_SOURCE
 231         bool
 232         help
 233           An architecture should select this when it can successfully
 234           build and run with CONFIG_FORTIFY_SOURCE.
 235
 236 # Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
 237 config ARCH_HAS_SET_MEMORY
 238         bool
 239
 240 # Select if arch init_task must go in the __init_task_data section
 241 config ARCH_TASK_STRUCT_ON_STACK
 242        bool
 243
 244 # Select if arch has its private alloc_task_struct() function
 245 config ARCH_TASK_STRUCT_ALLOCATOR
 246         bool
 247
 248 config HAVE_ARCH_THREAD_STRUCT_WHITELIST
 249         bool
 250         depends on !ARCH_TASK_STRUCT_ALLOCATOR
 251         help
 252           An architecture should select this to provide hardened usercopy
 253           knowledge about what region of the thread_struct should be
 254           whitelisted for copying to userspace. Normally this is only the
 255           FPU registers. Specifically, arch_thread_struct_whitelist()
 256           should be implemented. Without this, the entire thread_struct
 257           field in task_struct will be left whitelisted.
 258
 259 # Select if arch has its private alloc_thread_stack() function
 260 config ARCH_THREAD_STACK_ALLOCATOR
 261         bool
 262
 263 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
 264 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
 265         bool
 266
 267 config HAVE_REGS_AND_STACK_ACCESS_API
 268         bool
 269         help
 270           This symbol should be selected by an architecure if it supports
 271           the API needed to access registers and stack entries from pt_regs,
 272           declared in asm/ptrace.h
 273           For example the kprobes-based event tracer needs this API.
 274
 275 config HAVE_RSEQ
 276         bool
 277         depends on HAVE_REGS_AND_STACK_ACCESS_API
 278         help
 279           This symbol should be selected by an architecture if it
 280           supports an implementation of restartable sequences.
 281
 282 config HAVE_CLK
 283         bool
 284         help
 285           The <linux/clk.h> calls support software clock gating and
 286           thus are a key power management tool on many systems.
 287
 288 config HAVE_HW_BREAKPOINT
 289         bool
 290         depends on PERF_EVENTS
 291
 292 config HAVE_MIXED_BREAKPOINTS_REGS
 293         bool
 294         depends on HAVE_HW_BREAKPOINT
 295         help
 296           Depending on the arch implementation of hardware breakpoints,
 297           some of them have separate registers for data and instruction
 298           breakpoints addresses, others have mixed registers to store
 299           them but define the access type in a control register.
 300           Select this option if your arch implements breakpoints under the
 301           latter fashion.
 302
 303 config HAVE_USER_RETURN_NOTIFIER
 304         bool
 305
 306 config HAVE_PERF_EVENTS_NMI
 307         bool
 308         help
 309           System hardware can generate an NMI using the perf event
 310           subsystem.  Also has support for calculating CPU cycle events
 311           to determine how many clock cycles in a given period.
 312
 313 config HAVE_HARDLOCKUP_DETECTOR_PERF
 314         bool
 315         depends on HAVE_PERF_EVENTS_NMI
 316         help
 317           The arch chooses to use the generic perf-NMI-based hardlockup
 318           detector. Must define HAVE_PERF_EVENTS_NMI.
 319
 320 config HAVE_NMI_WATCHDOG
 321         depends on HAVE_NMI
 322         bool
 323         help
 324           The arch provides a low level NMI watchdog. It provides
 325           asm/nmi.h, and defines its own arch_touch_nmi_watchdog().
 326
 327 config HAVE_HARDLOCKUP_DETECTOR_ARCH
 328         bool
 329         select HAVE_NMI_WATCHDOG
 330         help
 331           The arch chooses to provide its own hardlockup detector, which is
 332           a superset of the HAVE_NMI_WATCHDOG. It also conforms to config
 333           interfaces and parameters provided by hardlockup detector subsystem.
 334
 335 config HAVE_PERF_REGS
 336         bool
 337         help
 338           Support selective register dumps for perf events. This includes
 339           bit-mapping of each registers and a unique architecture id.
 340
 341 config HAVE_PERF_USER_STACK_DUMP
 342         bool
 343         help
 344           Support user stack dumps for perf event samples. This needs
 345           access to the user stack pointer which is not unified across
 346           architectures.
 347
 348 config HAVE_ARCH_JUMP_LABEL
 349         bool
 350
 351 config HAVE_RCU_TABLE_FREE
 352         bool
 353
 354 config ARCH_HAVE_NMI_SAFE_CMPXCHG
 355         bool
 356
 357 config HAVE_ALIGNED_STRUCT_PAGE
 358         bool
 359         help
 360           This makes sure that struct pages are double word aligned and that
 361           e.g. the SLUB allocator can perform double word atomic operations
 362           on a struct page for better performance. However selecting this
 363           might increase the size of a struct page by a word.
 364
 365 config HAVE_CMPXCHG_LOCAL
 366         bool
 367
 368 config HAVE_CMPXCHG_DOUBLE
 369         bool
 370
 371 config ARCH_WEAK_RELEASE_ACQUIRE
 372         bool
 373
 374 config ARCH_WANT_IPC_PARSE_VERSION
 375         bool
 376
 377 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 378         bool
 379
 380 config ARCH_WANT_OLD_COMPAT_IPC
 381         select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 382         bool
 383
 384 config HAVE_ARCH_SECCOMP_FILTER
 385         bool
 386         help
 387           An arch should select this symbol if it provides all of these things:
 388           - syscall_get_arch()
 389           - syscall_get_arguments()
 390           - syscall_rollback()
 391           - syscall_set_return_value()
 392           - SIGSYS siginfo_t support
 393           - secure_computing is called from a ptrace_event()-safe context
 394           - secure_computing return value is checked and a return value of -1
 395             results in the system call being skipped immediately.
 396           - seccomp syscall wired up
 397
 398 config SECCOMP_FILTER
 399         def_bool y
 400         depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
 401         help
 402           Enable tasks to build secure computing environments defined
 403           in terms of Berkeley Packet Filter programs which implement
 404           task-defined system call filtering polices.
 405
 406           See Documentation/userspace-api/seccomp_filter.rst for details.
 407
 408 preferred-plugin-hostcc := $(if-success,[ $(gcc-version) -ge 40800 ],$(HOSTCXX),$(HOSTCC))
 409
 410 config PLUGIN_HOSTCC
 411         string
 412         default "$(shell,$(srctree)/scripts/gcc-plugin.sh "$(preferred-plugin-hostcc)" "$(HOSTCXX)" "$(CC)")"
 413         help
 414           Host compiler used to build GCC plugins.  This can be $(HOSTCXX),
 415           $(HOSTCC), or a null string if GCC plugin is unsupported.
 416
 417 config HAVE_GCC_PLUGINS
 418         bool
 419         help
 420           An arch should select this symbol if it supports building with
 421           GCC plugins.
 422
 423 menuconfig GCC_PLUGINS
 424         bool "GCC plugins"
 425         depends on HAVE_GCC_PLUGINS
 426         depends on PLUGIN_HOSTCC != ""
 427         help
 428           GCC plugins are loadable modules that provide extra features to the
 429           compiler. They are useful for runtime instrumentation and static analysis.
 430
 431           See Documentation/gcc-plugins.txt for details.
 432
 433 config GCC_PLUGIN_CYC_COMPLEXITY
 434         bool "Compute the cyclomatic complexity of a function" if EXPERT
 435         depends on GCC_PLUGINS
 436         depends on !COMPILE_TEST        # too noisy
 437         help
 438           The complexity M of a function's control flow graph is defined as:
 439            M = E - N + 2P
 440           where
 441
 442           E = the number of edges
 443           N = the number of nodes
 444           P = the number of connected components (exit nodes).
 445
 446           Enabling this plugin reports the complexity to stderr during the
 447           build. It mainly serves as a simple example of how to create a
 448           gcc plugin for the kernel.
 449
 450 config GCC_PLUGIN_SANCOV
 451         bool
 452         depends on GCC_PLUGINS
 453         help
 454           This plugin inserts a __sanitizer_cov_trace_pc() call at the start of
 455           basic blocks. It supports all gcc versions with plugin support (from
 456           gcc-4.5 on). It is based on the commit "Add fuzzing coverage support"
 457           by Dmitry Vyukov <dvyukov@google.com>.
 458
 459 config GCC_PLUGIN_LATENT_ENTROPY
 460         bool "Generate some entropy during boot and runtime"
 461         depends on GCC_PLUGINS
 462         help
 463           By saying Y here the kernel will instrument some kernel code to
 464           extract some entropy from both original and artificially created
 465           program state.  This will help especially embedded systems where
 466           there is little 'natural' source of entropy normally.  The cost
 467           is some slowdown of the boot process (about 0.5%) and fork and
 468           irq processing.
 469
 470           Note that entropy extracted this way is not cryptographically
 471           secure!
 472
 473           This plugin was ported from grsecurity/PaX. More information at:
 474            * https://grsecurity.net/
 475            * https://pax.grsecurity.net/
 476
 477 config GCC_PLUGIN_STRUCTLEAK
 478         bool "Force initialization of variables containing userspace addresses"
 479         depends on GCC_PLUGINS
 480         # Currently STRUCTLEAK inserts initialization out of live scope of
 481         # variables from KASAN point of view. This leads to KASAN false
 482         # positive reports. Prohibit this combination for now.
 483         depends on !KASAN_EXTRA
 484         help
 485           This plugin zero-initializes any structures containing a
 486           __user attribute. This can prevent some classes of information
 487           exposures.
 488
 489           This plugin was ported from grsecurity/PaX. More information at:
 490            * https://grsecurity.net/
 491            * https://pax.grsecurity.net/
 492
 493 config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
 494         bool "Force initialize all struct type variables passed by reference"
 495         depends on GCC_PLUGIN_STRUCTLEAK
 496         depends on !COMPILE_TEST
 497         help
 498           Zero initialize any struct type local variable that may be passed by
 499           reference without having been initialized.
 500
 501 config GCC_PLUGIN_STRUCTLEAK_VERBOSE
 502         bool "Report forcefully initialized variables"
 503         depends on GCC_PLUGIN_STRUCTLEAK
 504         depends on !COMPILE_TEST        # too noisy
 505         help
 506           This option will cause a warning to be printed each time the
 507           structleak plugin finds a variable it thinks needs to be
 508           initialized. Since not all existing initializers are detected
 509           by the plugin, this can produce false positive warnings.
 510
 511 config GCC_PLUGIN_RANDSTRUCT
 512         bool "Randomize layout of sensitive kernel structures"
 513         depends on GCC_PLUGINS
 514         select MODVERSIONS if MODULES
 515         help
 516           If you say Y here, the layouts of structures that are entirely
 517           function pointers (and have not been manually annotated with
 518           __no_randomize_layout), or structures that have been explicitly
 519           marked with __randomize_layout, will be randomized at compile-time.
 520           This can introduce the requirement of an additional information
 521           exposure vulnerability for exploits targeting these structure
 522           types.
 523
 524           Enabling this feature will introduce some performance impact,
 525           slightly increase memory usage, and prevent the use of forensic
 526           tools like Volatility against the system (unless the kernel
 527           source tree isn't cleaned after kernel installation).
 528
 529           The seed used for compilation is located at
 530           scripts/gcc-plgins/randomize_layout_seed.h.  It remains after
 531           a make clean to allow for external modules to be compiled with
 532           the existing seed and will be removed by a make mrproper or
 533           make distclean.
 534
 535           Note that the implementation requires gcc 4.7 or newer.
 536
 537           This plugin was ported from grsecurity/PaX. More information at:
 538            * https://grsecurity.net/
 539            * https://pax.grsecurity.net/
 540
 541 config GCC_PLUGIN_RANDSTRUCT_PERFORMANCE
 542         bool "Use cacheline-aware structure randomization"
 543         depends on GCC_PLUGIN_RANDSTRUCT
 544         depends on !COMPILE_TEST        # do not reduce test coverage
 545         help
 546           If you say Y here, the RANDSTRUCT randomization will make a
 547           best effort at restricting randomization to cacheline-sized
 548           groups of elements.  It will further not randomize bitfields
 549           in structures.  This reduces the performance hit of RANDSTRUCT
 550           at the cost of weakened randomization.
 551
 552 config HAVE_STACKPROTECTOR
 553         bool
 554         help
 555           An arch should select this symbol if:
 556           - it has implemented a stack canary (e.g. __stack_chk_guard)
 557
 558 config CC_HAS_STACKPROTECTOR_NONE
 559         def_bool $(cc-option,-fno-stack-protector)
 560
 561 config STACKPROTECTOR
 562         bool "Stack Protector buffer overflow detection"
 563         depends on HAVE_STACKPROTECTOR
 564         depends on $(cc-option,-fstack-protector)
 565         default y
 566         help
 567           This option turns on the "stack-protector" GCC feature. This
 568           feature puts, at the beginning of functions, a canary value on
 569           the stack just before the return address, and validates
 570           the value just before actually returning.  Stack based buffer
 571           overflows (that need to overwrite this return address) now also
 572           overwrite the canary, which gets detected and the attack is then
 573           neutralized via a kernel panic.
 574
 575           Functions will have the stack-protector canary logic added if they
 576           have an 8-byte or larger character array on the stack.
 577
 578           This feature requires gcc version 4.2 or above, or a distribution
 579           gcc with the feature backported ("-fstack-protector").
 580
 581           On an x86 "defconfig" build, this feature adds canary checks to
 582           about 3% of all kernel functions, which increases kernel code size
 583           by about 0.3%.
 584
 585 config STACKPROTECTOR_STRONG
 586         bool "Strong Stack Protector"
 587         depends on STACKPROTECTOR
 588         depends on $(cc-option,-fstack-protector-strong)
 589         default y
 590         help
 591           Functions will have the stack-protector canary logic added in any
 592           of the following conditions:
 593
 594           - local variable's address used as part of the right hand side of an
 595             assignment or function argument
 596           - local variable is an array (or union containing an array),
 597             regardless of array type or length
 598           - uses register local variables
 599
 600           This feature requires gcc version 4.9 or above, or a distribution
 601           gcc with the feature backported ("-fstack-protector-strong").
 602
 603           On an x86 "defconfig" build, this feature adds canary checks to
 604           about 20% of all kernel functions, which increases the kernel code
 605           size by about 2%.
 606
 607 config HAVE_ARCH_WITHIN_STACK_FRAMES
 608         bool
 609         help
 610           An architecture should select this if it can walk the kernel stack
 611           frames to determine if an object is part of either the arguments
 612           or local variables (i.e. that it excludes saved return addresses,
 613           and similar) by implementing an inline arch_within_stack_frames(),
 614           which is used by CONFIG_HARDENED_USERCOPY.
 615
 616 config HAVE_CONTEXT_TRACKING
 617         bool
 618         help
 619           Provide kernel/user boundaries probes necessary for subsystems
 620           that need it, such as userspace RCU extended quiescent state.
 621           Syscalls need to be wrapped inside user_exit()-user_enter() through
 622           the slow path using TIF_NOHZ flag. Exceptions handlers must be
 623           wrapped as well. Irqs are already protected inside
 624           rcu_irq_enter/rcu_irq_exit() but preemption or signal handling on
 625           irq exit still need to be protected.
 626
 627 config HAVE_VIRT_CPU_ACCOUNTING
 628         bool
 629
 630 config ARCH_HAS_SCALED_CPUTIME
 631         bool
 632
 633 config HAVE_VIRT_CPU_ACCOUNTING_GEN
 634         bool
 635         default y if 64BIT
 636         help
 637           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 638           Before enabling this option, arch code must be audited
 639           to ensure there are no races in concurrent read/write of
 640           cputime_t. For example, reading/writing 64-bit cputime_t on
 641           some 32-bit arches may require multiple accesses, so proper
 642           locking is needed to protect against concurrent accesses.
 643
 644
 645 config HAVE_IRQ_TIME_ACCOUNTING
 646         bool
 647         help
 648           Archs need to ensure they use a high enough resolution clock to
 649           support irq time accounting and then call enable_sched_clock_irqtime().
 650
 651 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 652         bool
 653
 654 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 655         bool
 656
 657 config HAVE_ARCH_HUGE_VMAP
 658         bool
 659
 660 config HAVE_ARCH_SOFT_DIRTY
 661         bool
 662
 663 config HAVE_MOD_ARCH_SPECIFIC
 664         bool
 665         help
 666           The arch uses struct mod_arch_specific to store data.  Many arches
 667           just need a simple module loader without arch specific data - those
 668           should not enable this.
 669
 670 config MODULES_USE_ELF_RELA
 671         bool
 672         help
 673           Modules only use ELF RELA relocations.  Modules with ELF REL
 674           relocations will give an error.
 675
 676 config MODULES_USE_ELF_REL
 677         bool
 678         help
 679           Modules only use ELF REL relocations.  Modules with ELF RELA
 680           relocations will give an error.
 681
 682 config HAVE_IRQ_EXIT_ON_IRQ_STACK
 683         bool
 684         help
 685           Architecture doesn't only execute the irq handler on the irq stack
 686           but also irq_exit(). This way we can process softirqs on this irq
 687           stack instead of switching to a new one when we call __do_softirq()
 688           in the end of an hardirq.
 689           This spares a stack switch and improves cache usage on softirq
 690           processing.
 691
 692 config PGTABLE_LEVELS
 693         int
 694         default 2
 695
 696 config ARCH_HAS_ELF_RANDOMIZE
 697         bool
 698         help
 699           An architecture supports choosing randomized locations for
 700           stack, mmap, brk, and ET_DYN. Defined functions:
 701           - arch_mmap_rnd()
 702           - arch_randomize_brk()
 703
 704 config HAVE_ARCH_MMAP_RND_BITS
 705         bool
 706         help
 707           An arch should select this symbol if it supports setting a variable
 708           number of bits for use in establishing the base address for mmap
 709           allocations, has MMU enabled and provides values for both:
 710           - ARCH_MMAP_RND_BITS_MIN
 711           - ARCH_MMAP_RND_BITS_MAX
 712
 713 config HAVE_EXIT_THREAD
 714         bool
 715         help
 716           An architecture implements exit_thread.
 717
 718 config ARCH_MMAP_RND_BITS_MIN
 719         int
 720
 721 config ARCH_MMAP_RND_BITS_MAX
 722         int
 723
 724 config ARCH_MMAP_RND_BITS_DEFAULT
 725         int
 726
 727 config ARCH_MMAP_RND_BITS
 728         int "Number of bits to use for ASLR of mmap base address" if EXPERT
 729         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
 730         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
 731         default ARCH_MMAP_RND_BITS_MIN
 732         depends on HAVE_ARCH_MMAP_RND_BITS
 733         help
 734           This value can be used to select the number of bits to use to
 735           determine the random offset to the base address of vma regions
 736           resulting from mmap allocations. This value will be bounded
 737           by the architecture's minimum and maximum supported values.
 738
 739           This value can be changed after boot using the
 740           /proc/sys/vm/mmap_rnd_bits tunable
 741
 742 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
 743         bool
 744         help
 745           An arch should select this symbol if it supports running applications
 746           in compatibility mode, supports setting a variable number of bits for
 747           use in establishing the base address for mmap allocations, has MMU
 748           enabled and provides values for both:
 749           - ARCH_MMAP_RND_COMPAT_BITS_MIN
 750           - ARCH_MMAP_RND_COMPAT_BITS_MAX
 751
 752 config ARCH_MMAP_RND_COMPAT_BITS_MIN
 753         int
 754
 755 config ARCH_MMAP_RND_COMPAT_BITS_MAX
 756         int
 757
 758 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 759         int
 760
 761 config ARCH_MMAP_RND_COMPAT_BITS
 762         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
 763         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
 764         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 765         default ARCH_MMAP_RND_COMPAT_BITS_MIN
 766         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
 767         help
 768           This value can be used to select the number of bits to use to
 769           determine the random offset to the base address of vma regions
 770           resulting from mmap allocations for compatible applications This
 771           value will be bounded by the architecture's minimum and maximum
 772           supported values.
 773
 774           This value can be changed after boot using the
 775           /proc/sys/vm/mmap_rnd_compat_bits tunable
 776
 777 config HAVE_ARCH_COMPAT_MMAP_BASES
 778         bool
 779         help
 780           This allows 64bit applications to invoke 32-bit mmap() syscall
 781           and vice-versa 32-bit applications to call 64-bit mmap().
 782           Required for applications doing different bitness syscalls.
 783
 784 config HAVE_COPY_THREAD_TLS
 785         bool
 786         help
 787           Architecture provides copy_thread_tls to accept tls argument via
 788           normal C parameter passing, rather than extracting the syscall
 789           argument from pt_regs.
 790
 791 config HAVE_STACK_VALIDATION
 792         bool
 793         help
 794           Architecture supports the 'objtool check' host tool command, which
 795           performs compile-time stack metadata validation.
 796
 797 config HAVE_RELIABLE_STACKTRACE
 798         bool
 799         help
 800           Architecture has a save_stack_trace_tsk_reliable() function which
 801           only returns a stack trace if it can guarantee the trace is reliable.
 802
 803 config HAVE_ARCH_HASH
 804         bool
 805         default n
 806         help
 807           If this is set, the architecture provides an <asm/hash.h>
 808           file which provides platform-specific implementations of some
 809           functions in <linux/hash.h> or fs/namei.c.
 810
 811 config ISA_BUS_API
 812         def_bool ISA
 813
 814 #
 815 # ABI hall of shame
 816 #
 817 config CLONE_BACKWARDS
 818         bool
 819         help
 820           Architecture has tls passed as the 4th argument of clone(2),
 821           not the 5th one.
 822
 823 config CLONE_BACKWARDS2
 824         bool
 825         help
 826           Architecture has the first two arguments of clone(2) swapped.
 827
 828 config CLONE_BACKWARDS3
 829         bool
 830         help
 831           Architecture has tls passed as the 3rd argument of clone(2),
 832           not the 5th one.
 833
 834 config ODD_RT_SIGACTION
 835         bool
 836         help
 837           Architecture has unusual rt_sigaction(2) arguments
 838
 839 config OLD_SIGSUSPEND
 840         bool
 841         help
 842           Architecture has old sigsuspend(2) syscall, of one-argument variety
 843
 844 config OLD_SIGSUSPEND3
 845         bool
 846         help
 847           Even weirder antique ABI - three-argument sigsuspend(2)
 848
 849 config OLD_SIGACTION
 850         bool
 851         help
 852           Architecture has old sigaction(2) syscall.  Nope, not the same
 853           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
 854           but fairly different variant of sigaction(2), thanks to OSF/1
 855           compatibility...
 856
 857 config COMPAT_OLD_SIGACTION
 858         bool
 859
 860 config 64BIT_TIME
 861         def_bool ARCH_HAS_64BIT_TIME
 862         help
 863           This should be selected by all architectures that need to support
 864           new system calls with a 64-bit time_t. This is relevant on all 32-bit
 865           architectures, and 64-bit architectures as part of compat syscall
 866           handling.
 867
 868 config COMPAT_32BIT_TIME
 869         def_bool (!64BIT && 64BIT_TIME) || COMPAT
 870         help
 871           This enables 32 bit time_t support in addition to 64 bit time_t support.
 872           This is relevant on all 32-bit architectures, and 64-bit architectures
 873           as part of compat syscall handling.
 874
 875 config ARCH_NO_COHERENT_DMA_MMAP
 876         bool
 877
 878 config CPU_NO_EFFICIENT_FFS
 879         def_bool n
 880
 881 config HAVE_ARCH_VMAP_STACK
 882         def_bool n
 883         help
 884           An arch should select this symbol if it can support kernel stacks
 885           in vmalloc space.  This means:
 886
 887           - vmalloc space must be large enough to hold many kernel stacks.
 888             This may rule out many 32-bit architectures.
 889
 890           - Stacks in vmalloc space need to work reliably.  For example, if
 891             vmap page tables are created on demand, either this mechanism
 892             needs to work while the stack points to a virtual address with
 893             unpopulated page tables or arch code (switch_to() and switch_mm(),
 894             most likely) needs to ensure that the stack's page table entries
 895             are populated before running on a possibly unpopulated stack.
 896
 897           - If the stack overflows into a guard page, something reasonable
 898             should happen.  The definition of "reasonable" is flexible, but
 899             instantly rebooting without logging anything would be unfriendly.
 900
 901 config VMAP_STACK
 902         default y
 903         bool "Use a virtually-mapped stack"
 904         depends on HAVE_ARCH_VMAP_STACK && !KASAN
 905         ---help---
 906           Enable this if you want the use virtually-mapped kernel stacks
 907           with guard pages.  This causes kernel stack overflows to be
 908           caught immediately rather than causing difficult-to-diagnose
 909           corruption.
 910
 911           This is presently incompatible with KASAN because KASAN expects
 912           the stack to map directly to the KASAN shadow map using a formula
 913           that is incorrect if the stack is in vmalloc space.
 914
 915 config ARCH_OPTIONAL_KERNEL_RWX
 916         def_bool n
 917
 918 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 919         def_bool n
 920
 921 config ARCH_HAS_STRICT_KERNEL_RWX
 922         def_bool n
 923
 924 config STRICT_KERNEL_RWX
 925         bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
 926         depends on ARCH_HAS_STRICT_KERNEL_RWX
 927         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 928         help
 929           If this is set, kernel text and rodata memory will be made read-only,
 930           and non-text memory will be made non-executable. This provides
 931           protection against certain security exploits (e.g. executing the heap
 932           or modifying text)
 933
 934           These features are considered standard security practice these days.
 935           You should say Y here in almost all cases.
 936
 937 config ARCH_HAS_STRICT_MODULE_RWX
 938         def_bool n
 939
 940 config STRICT_MODULE_RWX
 941         bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
 942         depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
 943         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 944         help
 945           If this is set, module text and rodata memory will be made read-only,
 946           and non-text memory will be made non-executable. This provides
 947           protection against certain security exploits (e.g. writing to text)
 948
 949 # select if the architecture provides an asm/dma-direct.h header
 950 config ARCH_HAS_PHYS_TO_DMA
 951         bool
 952
 953 config ARCH_HAS_REFCOUNT
 954         bool
 955         help
 956           An architecture selects this when it has implemented refcount_t
 957           using open coded assembly primitives that provide an optimized
 958           refcount_t implementation, possibly at the expense of some full
 959           refcount state checks of CONFIG_REFCOUNT_FULL=y.
 960
 961           The refcount overflow check behavior, however, must be retained.
 962           Catching overflows is the primary security concern for protecting
 963           against bugs in reference counts.
 964
 965 config REFCOUNT_FULL
 966         bool "Perform full reference count validation at the expense of speed"
 967         help
 968           Enabling this switches the refcounting infrastructure from a fast
 969           unchecked atomic_t implementation to a fully state checked
 970           implementation, which can be (slightly) slower but provides protections
 971           against various use-after-free conditions that can be used in
 972           security flaw exploits.
 973
 974 source "kernel/gcov/Kconfig"