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 HOTPLUG_SMT
  17         bool
  18
  19 config OPROFILE
  20         tristate "OProfile system profiling"
  21         depends on PROFILING
  22         depends on HAVE_OPROFILE
  23         select RING_BUFFER
  24         select RING_BUFFER_ALLOW_SWAP
  25         help
  26           OProfile is a profiling system capable of profiling the
  27           whole system, include the kernel, kernel modules, libraries,
  28           and applications.
  29
  30           If unsure, say N.
  31
  32 config OPROFILE_EVENT_MULTIPLEX
  33         bool "OProfile multiplexing support (EXPERIMENTAL)"
  34         default n
  35         depends on OPROFILE && X86
  36         help
  37           The number of hardware counters is limited. The multiplexing
  38           feature enables OProfile to gather more events than counters
  39           are provided by the hardware. This is realized by switching
  40           between events at a user specified time interval.
  41
  42           If unsure, say N.
  43
  44 config HAVE_OPROFILE
  45         bool
  46
  47 config OPROFILE_NMI_TIMER
  48         def_bool y
  49         depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI && !PPC64
  50
  51 config KPROBES
  52         bool "Kprobes"
  53         depends on MODULES
  54         depends on HAVE_KPROBES
  55         select KALLSYMS
  56         help
  57           Kprobes allows you to trap at almost any kernel address and
  58           execute a callback function.  register_kprobe() establishes
  59           a probepoint and specifies the callback.  Kprobes is useful
  60           for kernel debugging, non-intrusive instrumentation and testing.
  61           If in doubt, say "N".
  62
  63 config JUMP_LABEL
  64        bool "Optimize very unlikely/likely branches"
  65        depends on HAVE_ARCH_JUMP_LABEL
  66        help
  67          This option enables a transparent branch optimization that
  68          makes certain almost-always-true or almost-always-false branch
  69          conditions even cheaper to execute within the kernel.
  70
  71          Certain performance-sensitive kernel code, such as trace points,
  72          scheduler functionality, networking code and KVM have such
  73          branches and include support for this optimization technique.
  74
  75          If it is detected that the compiler has support for "asm goto",
  76          the kernel will compile such branches with just a nop
  77          instruction. When the condition flag is toggled to true, the
  78          nop will be converted to a jump instruction to execute the
  79          conditional block of instructions.
  80
  81          This technique lowers overhead and stress on the branch prediction
  82          of the processor and generally makes the kernel faster. The update
  83          of the condition is slower, but those are always very rare.
  84
  85          ( On 32-bit x86, the necessary options added to the compiler
  86            flags may increase the size of the kernel slightly. )
  87
  88 config STATIC_KEYS_SELFTEST
  89         bool "Static key selftest"
  90         depends on JUMP_LABEL
  91         help
  92           Boot time self-test of the branch patching code.
  93
  94 config OPTPROBES
  95         def_bool y
  96         depends on KPROBES && HAVE_OPTPROBES
  97         select TASKS_RCU if PREEMPT
  98
  99 config KPROBES_ON_FTRACE
 100         def_bool y
 101         depends on KPROBES && HAVE_KPROBES_ON_FTRACE
 102         depends on DYNAMIC_FTRACE_WITH_REGS
 103         help
 104          If function tracer is enabled and the arch supports full
 105          passing of pt_regs to function tracing, then kprobes can
 106          optimize on top of function tracing.
 107
 108 config UPROBES
 109         def_bool n
 110         depends on ARCH_SUPPORTS_UPROBES
 111         help
 112           Uprobes is the user-space counterpart to kprobes: they
 113           enable instrumentation applications (such as 'perf probe')
 114           to establish unintrusive probes in user-space binaries and
 115           libraries, by executing handler functions when the probes
 116           are hit by user-space applications.
 117
 118           ( These probes come in the form of single-byte breakpoints,
 119             managed by the kernel and kept transparent to the probed
 120             application. )
 121
 122 config HAVE_64BIT_ALIGNED_ACCESS
 123         def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
 124         help
 125           Some architectures require 64 bit accesses to be 64 bit
 126           aligned, which also requires structs containing 64 bit values
 127           to be 64 bit aligned too. This includes some 32 bit
 128           architectures which can do 64 bit accesses, as well as 64 bit
 129           architectures without unaligned access.
 130
 131           This symbol should be selected by an architecture if 64 bit
 132           accesses are required to be 64 bit aligned in this way even
 133           though it is not a 64 bit architecture.
 134
 135           See Documentation/unaligned-memory-access.txt for more
 136           information on the topic of unaligned memory accesses.
 137
 138 config HAVE_EFFICIENT_UNALIGNED_ACCESS
 139         bool
 140         help
 141           Some architectures are unable to perform unaligned accesses
 142           without the use of get_unaligned/put_unaligned. Others are
 143           unable to perform such accesses efficiently (e.g. trap on
 144           unaligned access and require fixing it up in the exception
 145           handler.)
 146
 147           This symbol should be selected by an architecture if it can
 148           perform unaligned accesses efficiently to allow different
 149           code paths to be selected for these cases. Some network
 150           drivers, for example, could opt to not fix up alignment
 151           problems with received packets if doing so would not help
 152           much.
 153
 154           See Documentation/unaligned-memory-access.txt for more
 155           information on the topic of unaligned memory accesses.
 156
 157 config ARCH_USE_BUILTIN_BSWAP
 158        bool
 159        help
 160          Modern versions of GCC (since 4.4) have builtin functions
 161          for handling byte-swapping. Using these, instead of the old
 162          inline assembler that the architecture code provides in the
 163          __arch_bswapXX() macros, allows the compiler to see what's
 164          happening and offers more opportunity for optimisation. In
 165          particular, the compiler will be able to combine the byteswap
 166          with a nearby load or store and use load-and-swap or
 167          store-and-swap instructions if the architecture has them. It
 168          should almost *never* result in code which is worse than the
 169          hand-coded assembler in <asm/swab.h>.  But just in case it
 170          does, the use of the builtins is optional.
 171
 172          Any architecture with load-and-swap or store-and-swap
 173          instructions should set this. And it shouldn't hurt to set it
 174          on architectures that don't have such instructions.
 175
 176 config KRETPROBES
 177         def_bool y
 178         depends on KPROBES && HAVE_KRETPROBES
 179
 180 config USER_RETURN_NOTIFIER
 181         bool
 182         depends on HAVE_USER_RETURN_NOTIFIER
 183         help
 184           Provide a kernel-internal notification when a cpu is about to
 185           switch to user mode.
 186
 187 config HAVE_IOREMAP_PROT
 188         bool
 189
 190 config HAVE_KPROBES
 191         bool
 192
 193 config HAVE_KRETPROBES
 194         bool
 195
 196 config HAVE_OPTPROBES
 197         bool
 198
 199 config HAVE_KPROBES_ON_FTRACE
 200         bool
 201
 202 config HAVE_FUNCTION_ERROR_INJECTION
 203         bool
 204
 205 config HAVE_NMI
 206         bool
 207
 208 #
 209 # An arch should select this if it provides all these things:
 210 #
 211 #       task_pt_regs()          in asm/processor.h or asm/ptrace.h
 212 #       arch_has_single_step()  if there is hardware single-step support
 213 #       arch_has_block_step()   if there is hardware block-step support
 214 #       asm/syscall.h           supplying asm-generic/syscall.h interface
 215 #       linux/regset.h          user_regset interfaces
 216 #       CORE_DUMP_USE_REGSET    #define'd in linux/elf.h
 217 #       TIF_SYSCALL_TRACE       calls tracehook_report_syscall_{entry,exit}
 218 #       TIF_NOTIFY_RESUME       calls tracehook_notify_resume()
 219 #       signal delivery         calls tracehook_signal_handler()
 220 #
 221 config HAVE_ARCH_TRACEHOOK
 222         bool
 223
 224 config HAVE_DMA_CONTIGUOUS
 225         bool
 226
 227 config GENERIC_SMP_IDLE_THREAD
 228        bool
 229
 230 config GENERIC_IDLE_POLL_SETUP
 231        bool
 232
 233 config ARCH_HAS_FORTIFY_SOURCE
 234         bool
 235         help
 236           An architecture should select this when it can successfully
 237           build and run with CONFIG_FORTIFY_SOURCE.
 238
 239 # Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
 240 config ARCH_HAS_SET_MEMORY
 241         bool
 242
 243 # Select if arch init_task must go in the __init_task_data section
 244 config ARCH_TASK_STRUCT_ON_STACK
 245        bool
 246
 247 # Select if arch has its private alloc_task_struct() function
 248 config ARCH_TASK_STRUCT_ALLOCATOR
 249         bool
 250
 251 config HAVE_ARCH_THREAD_STRUCT_WHITELIST
 252         bool
 253         depends on !ARCH_TASK_STRUCT_ALLOCATOR
 254         help
 255           An architecture should select this to provide hardened usercopy
 256           knowledge about what region of the thread_struct should be
 257           whitelisted for copying to userspace. Normally this is only the
 258           FPU registers. Specifically, arch_thread_struct_whitelist()
 259           should be implemented. Without this, the entire thread_struct
 260           field in task_struct will be left whitelisted.
 261
 262 # Select if arch has its private alloc_thread_stack() function
 263 config ARCH_THREAD_STACK_ALLOCATOR
 264         bool
 265
 266 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
 267 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
 268         bool
 269
 270 config HAVE_REGS_AND_STACK_ACCESS_API
 271         bool
 272         help
 273           This symbol should be selected by an architecure if it supports
 274           the API needed to access registers and stack entries from pt_regs,
 275           declared in asm/ptrace.h
 276           For example the kprobes-based event tracer needs this API.
 277
 278 config HAVE_RSEQ
 279         bool
 280         depends on HAVE_REGS_AND_STACK_ACCESS_API
 281         help
 282           This symbol should be selected by an architecture if it
 283           supports an implementation of restartable sequences.
 284
 285 config HAVE_CLK
 286         bool
 287         help
 288           The <linux/clk.h> calls support software clock gating and
 289           thus are a key power management tool on many systems.
 290
 291 config HAVE_HW_BREAKPOINT
 292         bool
 293         depends on PERF_EVENTS
 294
 295 config HAVE_MIXED_BREAKPOINTS_REGS
 296         bool
 297         depends on HAVE_HW_BREAKPOINT
 298         help
 299           Depending on the arch implementation of hardware breakpoints,
 300           some of them have separate registers for data and instruction
 301           breakpoints addresses, others have mixed registers to store
 302           them but define the access type in a control register.
 303           Select this option if your arch implements breakpoints under the
 304           latter fashion.
 305
 306 config HAVE_USER_RETURN_NOTIFIER
 307         bool
 308
 309 config HAVE_PERF_EVENTS_NMI
 310         bool
 311         help
 312           System hardware can generate an NMI using the perf event
 313           subsystem.  Also has support for calculating CPU cycle events
 314           to determine how many clock cycles in a given period.
 315
 316 config HAVE_HARDLOCKUP_DETECTOR_PERF
 317         bool
 318         depends on HAVE_PERF_EVENTS_NMI
 319         help
 320           The arch chooses to use the generic perf-NMI-based hardlockup
 321           detector. Must define HAVE_PERF_EVENTS_NMI.
 322
 323 config HAVE_NMI_WATCHDOG
 324         depends on HAVE_NMI
 325         bool
 326         help
 327           The arch provides a low level NMI watchdog. It provides
 328           asm/nmi.h, and defines its own arch_touch_nmi_watchdog().
 329
 330 config HAVE_HARDLOCKUP_DETECTOR_ARCH
 331         bool
 332         select HAVE_NMI_WATCHDOG
 333         help
 334           The arch chooses to provide its own hardlockup detector, which is
 335           a superset of the HAVE_NMI_WATCHDOG. It also conforms to config
 336           interfaces and parameters provided by hardlockup detector subsystem.
 337
 338 config HAVE_PERF_REGS
 339         bool
 340         help
 341           Support selective register dumps for perf events. This includes
 342           bit-mapping of each registers and a unique architecture id.
 343
 344 config HAVE_PERF_USER_STACK_DUMP
 345         bool
 346         help
 347           Support user stack dumps for perf event samples. This needs
 348           access to the user stack pointer which is not unified across
 349           architectures.
 350
 351 config HAVE_ARCH_JUMP_LABEL
 352         bool
 353
 354 config HAVE_RCU_TABLE_FREE
 355         bool
 356
 357 config ARCH_HAVE_NMI_SAFE_CMPXCHG
 358         bool
 359
 360 config HAVE_ALIGNED_STRUCT_PAGE
 361         bool
 362         help
 363           This makes sure that struct pages are double word aligned and that
 364           e.g. the SLUB allocator can perform double word atomic operations
 365           on a struct page for better performance. However selecting this
 366           might increase the size of a struct page by a word.
 367
 368 config HAVE_CMPXCHG_LOCAL
 369         bool
 370
 371 config HAVE_CMPXCHG_DOUBLE
 372         bool
 373
 374 config ARCH_WEAK_RELEASE_ACQUIRE
 375         bool
 376
 377 config ARCH_WANT_IPC_PARSE_VERSION
 378         bool
 379
 380 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 381         bool
 382
 383 config ARCH_WANT_OLD_COMPAT_IPC
 384         select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 385         bool
 386
 387 config HAVE_ARCH_SECCOMP_FILTER
 388         bool
 389         help
 390           An arch should select this symbol if it provides all of these things:
 391           - syscall_get_arch()
 392           - syscall_get_arguments()
 393           - syscall_rollback()
 394           - syscall_set_return_value()
 395           - SIGSYS siginfo_t support
 396           - secure_computing is called from a ptrace_event()-safe context
 397           - secure_computing return value is checked and a return value of -1
 398             results in the system call being skipped immediately.
 399           - seccomp syscall wired up
 400
 401 config SECCOMP_FILTER
 402         def_bool y
 403         depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
 404         help
 405           Enable tasks to build secure computing environments defined
 406           in terms of Berkeley Packet Filter programs which implement
 407           task-defined system call filtering polices.
 408
 409           See Documentation/userspace-api/seccomp_filter.rst for details.
 410
 411 preferred-plugin-hostcc := $(if-success,[ $(gcc-version) -ge 40800 ],$(HOSTCXX),$(HOSTCC))
 412
 413 config PLUGIN_HOSTCC
 414         string
 415         default "$(shell,$(srctree)/scripts/gcc-plugin.sh "$(preferred-plugin-hostcc)" "$(HOSTCXX)" "$(CC)")"
 416         help
 417           Host compiler used to build GCC plugins.  This can be $(HOSTCXX),
 418           $(HOSTCC), or a null string if GCC plugin is unsupported.
 419
 420 config HAVE_GCC_PLUGINS
 421         bool
 422         help
 423           An arch should select this symbol if it supports building with
 424           GCC plugins.
 425
 426 menuconfig GCC_PLUGINS
 427         bool "GCC plugins"
 428         depends on HAVE_GCC_PLUGINS
 429         depends on PLUGIN_HOSTCC != ""
 430         help
 431           GCC plugins are loadable modules that provide extra features to the
 432           compiler. They are useful for runtime instrumentation and static analysis.
 433
 434           See Documentation/gcc-plugins.txt for details.
 435
 436 config GCC_PLUGIN_CYC_COMPLEXITY
 437         bool "Compute the cyclomatic complexity of a function" if EXPERT
 438         depends on GCC_PLUGINS
 439         depends on !COMPILE_TEST        # too noisy
 440         help
 441           The complexity M of a function's control flow graph is defined as:
 442            M = E - N + 2P
 443           where
 444
 445           E = the number of edges
 446           N = the number of nodes
 447           P = the number of connected components (exit nodes).
 448
 449           Enabling this plugin reports the complexity to stderr during the
 450           build. It mainly serves as a simple example of how to create a
 451           gcc plugin for the kernel.
 452
 453 config GCC_PLUGIN_SANCOV
 454         bool
 455         depends on GCC_PLUGINS
 456         help
 457           This plugin inserts a __sanitizer_cov_trace_pc() call at the start of
 458           basic blocks. It supports all gcc versions with plugin support (from
 459           gcc-4.5 on). It is based on the commit "Add fuzzing coverage support"
 460           by Dmitry Vyukov <dvyukov@google.com>.
 461
 462 config GCC_PLUGIN_LATENT_ENTROPY
 463         bool "Generate some entropy during boot and runtime"
 464         depends on GCC_PLUGINS
 465         help
 466           By saying Y here the kernel will instrument some kernel code to
 467           extract some entropy from both original and artificially created
 468           program state.  This will help especially embedded systems where
 469           there is little 'natural' source of entropy normally.  The cost
 470           is some slowdown of the boot process (about 0.5%) and fork and
 471           irq processing.
 472
 473           Note that entropy extracted this way is not cryptographically
 474           secure!
 475
 476           This plugin was ported from grsecurity/PaX. More information at:
 477            * https://grsecurity.net/
 478            * https://pax.grsecurity.net/
 479
 480 config GCC_PLUGIN_STRUCTLEAK
 481         bool "Force initialization of variables containing userspace addresses"
 482         depends on GCC_PLUGINS
 483         # Currently STRUCTLEAK inserts initialization out of live scope of
 484         # variables from KASAN point of view. This leads to KASAN false
 485         # positive reports. Prohibit this combination for now.
 486         depends on !KASAN_EXTRA
 487         help
 488           This plugin zero-initializes any structures containing a
 489           __user attribute. This can prevent some classes of information
 490           exposures.
 491
 492           This plugin was ported from grsecurity/PaX. More information at:
 493            * https://grsecurity.net/
 494            * https://pax.grsecurity.net/
 495
 496 config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
 497         bool "Force initialize all struct type variables passed by reference"
 498         depends on GCC_PLUGIN_STRUCTLEAK
 499         depends on !COMPILE_TEST
 500         help
 501           Zero initialize any struct type local variable that may be passed by
 502           reference without having been initialized.
 503
 504 config GCC_PLUGIN_STRUCTLEAK_VERBOSE
 505         bool "Report forcefully initialized variables"
 506         depends on GCC_PLUGIN_STRUCTLEAK
 507         depends on !COMPILE_TEST        # too noisy
 508         help
 509           This option will cause a warning to be printed each time the
 510           structleak plugin finds a variable it thinks needs to be
 511           initialized. Since not all existing initializers are detected
 512           by the plugin, this can produce false positive warnings.
 513
 514 config GCC_PLUGIN_RANDSTRUCT
 515         bool "Randomize layout of sensitive kernel structures"
 516         depends on GCC_PLUGINS
 517         select MODVERSIONS if MODULES
 518         help
 519           If you say Y here, the layouts of structures that are entirely
 520           function pointers (and have not been manually annotated with
 521           __no_randomize_layout), or structures that have been explicitly
 522           marked with __randomize_layout, will be randomized at compile-time.
 523           This can introduce the requirement of an additional information
 524           exposure vulnerability for exploits targeting these structure
 525           types.
 526
 527           Enabling this feature will introduce some performance impact,
 528           slightly increase memory usage, and prevent the use of forensic
 529           tools like Volatility against the system (unless the kernel
 530           source tree isn't cleaned after kernel installation).
 531
 532           The seed used for compilation is located at
 533           scripts/gcc-plgins/randomize_layout_seed.h.  It remains after
 534           a make clean to allow for external modules to be compiled with
 535           the existing seed and will be removed by a make mrproper or
 536           make distclean.
 537
 538           Note that the implementation requires gcc 4.7 or newer.
 539
 540           This plugin was ported from grsecurity/PaX. More information at:
 541            * https://grsecurity.net/
 542            * https://pax.grsecurity.net/
 543
 544 config GCC_PLUGIN_RANDSTRUCT_PERFORMANCE
 545         bool "Use cacheline-aware structure randomization"
 546         depends on GCC_PLUGIN_RANDSTRUCT
 547         depends on !COMPILE_TEST        # do not reduce test coverage
 548         help
 549           If you say Y here, the RANDSTRUCT randomization will make a
 550           best effort at restricting randomization to cacheline-sized
 551           groups of elements.  It will further not randomize bitfields
 552           in structures.  This reduces the performance hit of RANDSTRUCT
 553           at the cost of weakened randomization.
 554
 555 config HAVE_STACKPROTECTOR
 556         bool
 557         help
 558           An arch should select this symbol if:
 559           - it has implemented a stack canary (e.g. __stack_chk_guard)
 560
 561 config CC_HAS_STACKPROTECTOR_NONE
 562         def_bool $(cc-option,-fno-stack-protector)
 563
 564 config STACKPROTECTOR
 565         bool "Stack Protector buffer overflow detection"
 566         depends on HAVE_STACKPROTECTOR
 567         depends on $(cc-option,-fstack-protector)
 568         default y
 569         help
 570           This option turns on the "stack-protector" GCC feature. This
 571           feature puts, at the beginning of functions, a canary value on
 572           the stack just before the return address, and validates
 573           the value just before actually returning.  Stack based buffer
 574           overflows (that need to overwrite this return address) now also
 575           overwrite the canary, which gets detected and the attack is then
 576           neutralized via a kernel panic.
 577
 578           Functions will have the stack-protector canary logic added if they
 579           have an 8-byte or larger character array on the stack.
 580
 581           This feature requires gcc version 4.2 or above, or a distribution
 582           gcc with the feature backported ("-fstack-protector").
 583
 584           On an x86 "defconfig" build, this feature adds canary checks to
 585           about 3% of all kernel functions, which increases kernel code size
 586           by about 0.3%.
 587
 588 config STACKPROTECTOR_STRONG
 589         bool "Strong Stack Protector"
 590         depends on STACKPROTECTOR
 591         depends on $(cc-option,-fstack-protector-strong)
 592         default y
 593         help
 594           Functions will have the stack-protector canary logic added in any
 595           of the following conditions:
 596
 597           - local variable's address used as part of the right hand side of an
 598             assignment or function argument
 599           - local variable is an array (or union containing an array),
 600             regardless of array type or length
 601           - uses register local variables
 602
 603           This feature requires gcc version 4.9 or above, or a distribution
 604           gcc with the feature backported ("-fstack-protector-strong").
 605
 606           On an x86 "defconfig" build, this feature adds canary checks to
 607           about 20% of all kernel functions, which increases the kernel code
 608           size by about 2%.
 609
 610 config HAVE_ARCH_WITHIN_STACK_FRAMES
 611         bool
 612         help
 613           An architecture should select this if it can walk the kernel stack
 614           frames to determine if an object is part of either the arguments
 615           or local variables (i.e. that it excludes saved return addresses,
 616           and similar) by implementing an inline arch_within_stack_frames(),
 617           which is used by CONFIG_HARDENED_USERCOPY.
 618
 619 config HAVE_CONTEXT_TRACKING
 620         bool
 621         help
 622           Provide kernel/user boundaries probes necessary for subsystems
 623           that need it, such as userspace RCU extended quiescent state.
 624           Syscalls need to be wrapped inside user_exit()-user_enter() through
 625           the slow path using TIF_NOHZ flag. Exceptions handlers must be
 626           wrapped as well. Irqs are already protected inside
 627           rcu_irq_enter/rcu_irq_exit() but preemption or signal handling on
 628           irq exit still need to be protected.
 629
 630 config HAVE_VIRT_CPU_ACCOUNTING
 631         bool
 632
 633 config ARCH_HAS_SCALED_CPUTIME
 634         bool
 635
 636 config HAVE_VIRT_CPU_ACCOUNTING_GEN
 637         bool
 638         default y if 64BIT
 639         help
 640           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 641           Before enabling this option, arch code must be audited
 642           to ensure there are no races in concurrent read/write of
 643           cputime_t. For example, reading/writing 64-bit cputime_t on
 644           some 32-bit arches may require multiple accesses, so proper
 645           locking is needed to protect against concurrent accesses.
 646
 647
 648 config HAVE_IRQ_TIME_ACCOUNTING
 649         bool
 650         help
 651           Archs need to ensure they use a high enough resolution clock to
 652           support irq time accounting and then call enable_sched_clock_irqtime().
 653
 654 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 655         bool
 656
 657 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 658         bool
 659
 660 config HAVE_ARCH_HUGE_VMAP
 661         bool
 662
 663 config HAVE_ARCH_SOFT_DIRTY
 664         bool
 665
 666 config HAVE_MOD_ARCH_SPECIFIC
 667         bool
 668         help
 669           The arch uses struct mod_arch_specific to store data.  Many arches
 670           just need a simple module loader without arch specific data - those
 671           should not enable this.
 672
 673 config MODULES_USE_ELF_RELA
 674         bool
 675         help
 676           Modules only use ELF RELA relocations.  Modules with ELF REL
 677           relocations will give an error.
 678
 679 config MODULES_USE_ELF_REL
 680         bool
 681         help
 682           Modules only use ELF REL relocations.  Modules with ELF RELA
 683           relocations will give an error.
 684
 685 config HAVE_IRQ_EXIT_ON_IRQ_STACK
 686         bool
 687         help
 688           Architecture doesn't only execute the irq handler on the irq stack
 689           but also irq_exit(). This way we can process softirqs on this irq
 690           stack instead of switching to a new one when we call __do_softirq()
 691           in the end of an hardirq.
 692           This spares a stack switch and improves cache usage on softirq
 693           processing.
 694
 695 config PGTABLE_LEVELS
 696         int
 697         default 2
 698
 699 config ARCH_HAS_ELF_RANDOMIZE
 700         bool
 701         help
 702           An architecture supports choosing randomized locations for
 703           stack, mmap, brk, and ET_DYN. Defined functions:
 704           - arch_mmap_rnd()
 705           - arch_randomize_brk()
 706
 707 config HAVE_ARCH_MMAP_RND_BITS
 708         bool
 709         help
 710           An arch should select this symbol if it supports setting a variable
 711           number of bits for use in establishing the base address for mmap
 712           allocations, has MMU enabled and provides values for both:
 713           - ARCH_MMAP_RND_BITS_MIN
 714           - ARCH_MMAP_RND_BITS_MAX
 715
 716 config HAVE_EXIT_THREAD
 717         bool
 718         help
 719           An architecture implements exit_thread.
 720
 721 config ARCH_MMAP_RND_BITS_MIN
 722         int
 723
 724 config ARCH_MMAP_RND_BITS_MAX
 725         int
 726
 727 config ARCH_MMAP_RND_BITS_DEFAULT
 728         int
 729
 730 config ARCH_MMAP_RND_BITS
 731         int "Number of bits to use for ASLR of mmap base address" if EXPERT
 732         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
 733         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
 734         default ARCH_MMAP_RND_BITS_MIN
 735         depends on HAVE_ARCH_MMAP_RND_BITS
 736         help
 737           This value can be used to select the number of bits to use to
 738           determine the random offset to the base address of vma regions
 739           resulting from mmap allocations. This value will be bounded
 740           by the architecture's minimum and maximum supported values.
 741
 742           This value can be changed after boot using the
 743           /proc/sys/vm/mmap_rnd_bits tunable
 744
 745 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
 746         bool
 747         help
 748           An arch should select this symbol if it supports running applications
 749           in compatibility mode, supports setting a variable number of bits for
 750           use in establishing the base address for mmap allocations, has MMU
 751           enabled and provides values for both:
 752           - ARCH_MMAP_RND_COMPAT_BITS_MIN
 753           - ARCH_MMAP_RND_COMPAT_BITS_MAX
 754
 755 config ARCH_MMAP_RND_COMPAT_BITS_MIN
 756         int
 757
 758 config ARCH_MMAP_RND_COMPAT_BITS_MAX
 759         int
 760
 761 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 762         int
 763
 764 config ARCH_MMAP_RND_COMPAT_BITS
 765         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
 766         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
 767         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 768         default ARCH_MMAP_RND_COMPAT_BITS_MIN
 769         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
 770         help
 771           This value can be used to select the number of bits to use to
 772           determine the random offset to the base address of vma regions
 773           resulting from mmap allocations for compatible applications This
 774           value will be bounded by the architecture's minimum and maximum
 775           supported values.
 776
 777           This value can be changed after boot using the
 778           /proc/sys/vm/mmap_rnd_compat_bits tunable
 779
 780 config HAVE_ARCH_COMPAT_MMAP_BASES
 781         bool
 782         help
 783           This allows 64bit applications to invoke 32-bit mmap() syscall
 784           and vice-versa 32-bit applications to call 64-bit mmap().
 785           Required for applications doing different bitness syscalls.
 786
 787 config HAVE_COPY_THREAD_TLS
 788         bool
 789         help
 790           Architecture provides copy_thread_tls to accept tls argument via
 791           normal C parameter passing, rather than extracting the syscall
 792           argument from pt_regs.
 793
 794 config HAVE_STACK_VALIDATION
 795         bool
 796         help
 797           Architecture supports the 'objtool check' host tool command, which
 798           performs compile-time stack metadata validation.
 799
 800 config HAVE_RELIABLE_STACKTRACE
 801         bool
 802         help
 803           Architecture has a save_stack_trace_tsk_reliable() function which
 804           only returns a stack trace if it can guarantee the trace is reliable.
 805
 806 config HAVE_ARCH_HASH
 807         bool
 808         default n
 809         help
 810           If this is set, the architecture provides an <asm/hash.h>
 811           file which provides platform-specific implementations of some
 812           functions in <linux/hash.h> or fs/namei.c.
 813
 814 config ISA_BUS_API
 815         def_bool ISA
 816
 817 #
 818 # ABI hall of shame
 819 #
 820 config CLONE_BACKWARDS
 821         bool
 822         help
 823           Architecture has tls passed as the 4th argument of clone(2),
 824           not the 5th one.
 825
 826 config CLONE_BACKWARDS2
 827         bool
 828         help
 829           Architecture has the first two arguments of clone(2) swapped.
 830
 831 config CLONE_BACKWARDS3
 832         bool
 833         help
 834           Architecture has tls passed as the 3rd argument of clone(2),
 835           not the 5th one.
 836
 837 config ODD_RT_SIGACTION
 838         bool
 839         help
 840           Architecture has unusual rt_sigaction(2) arguments
 841
 842 config OLD_SIGSUSPEND
 843         bool
 844         help
 845           Architecture has old sigsuspend(2) syscall, of one-argument variety
 846
 847 config OLD_SIGSUSPEND3
 848         bool
 849         help
 850           Even weirder antique ABI - three-argument sigsuspend(2)
 851
 852 config OLD_SIGACTION
 853         bool
 854         help
 855           Architecture has old sigaction(2) syscall.  Nope, not the same
 856           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
 857           but fairly different variant of sigaction(2), thanks to OSF/1
 858           compatibility...
 859
 860 config COMPAT_OLD_SIGACTION
 861         bool
 862
 863 config 64BIT_TIME
 864         def_bool ARCH_HAS_64BIT_TIME
 865         help
 866           This should be selected by all architectures that need to support
 867           new system calls with a 64-bit time_t. This is relevant on all 32-bit
 868           architectures, and 64-bit architectures as part of compat syscall
 869           handling.
 870
 871 config COMPAT_32BIT_TIME
 872         def_bool (!64BIT && 64BIT_TIME) || COMPAT
 873         help
 874           This enables 32 bit time_t support in addition to 64 bit time_t support.
 875           This is relevant on all 32-bit architectures, and 64-bit architectures
 876           as part of compat syscall handling.
 877
 878 config ARCH_NO_COHERENT_DMA_MMAP
 879         bool
 880
 881 config CPU_NO_EFFICIENT_FFS
 882         def_bool n
 883
 884 config HAVE_ARCH_VMAP_STACK
 885         def_bool n
 886         help
 887           An arch should select this symbol if it can support kernel stacks
 888           in vmalloc space.  This means:
 889
 890           - vmalloc space must be large enough to hold many kernel stacks.
 891             This may rule out many 32-bit architectures.
 892
 893           - Stacks in vmalloc space need to work reliably.  For example, if
 894             vmap page tables are created on demand, either this mechanism
 895             needs to work while the stack points to a virtual address with
 896             unpopulated page tables or arch code (switch_to() and switch_mm(),
 897             most likely) needs to ensure that the stack's page table entries
 898             are populated before running on a possibly unpopulated stack.
 899
 900           - If the stack overflows into a guard page, something reasonable
 901             should happen.  The definition of "reasonable" is flexible, but
 902             instantly rebooting without logging anything would be unfriendly.
 903
 904 config VMAP_STACK
 905         default y
 906         bool "Use a virtually-mapped stack"
 907         depends on HAVE_ARCH_VMAP_STACK && !KASAN
 908         ---help---
 909           Enable this if you want the use virtually-mapped kernel stacks
 910           with guard pages.  This causes kernel stack overflows to be
 911           caught immediately rather than causing difficult-to-diagnose
 912           corruption.
 913
 914           This is presently incompatible with KASAN because KASAN expects
 915           the stack to map directly to the KASAN shadow map using a formula
 916           that is incorrect if the stack is in vmalloc space.
 917
 918 config ARCH_OPTIONAL_KERNEL_RWX
 919         def_bool n
 920
 921 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 922         def_bool n
 923
 924 config ARCH_HAS_STRICT_KERNEL_RWX
 925         def_bool n
 926
 927 config STRICT_KERNEL_RWX
 928         bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
 929         depends on ARCH_HAS_STRICT_KERNEL_RWX
 930         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 931         help
 932           If this is set, kernel text and rodata memory will be made read-only,
 933           and non-text memory will be made non-executable. This provides
 934           protection against certain security exploits (e.g. executing the heap
 935           or modifying text)
 936
 937           These features are considered standard security practice these days.
 938           You should say Y here in almost all cases.
 939
 940 config ARCH_HAS_STRICT_MODULE_RWX
 941         def_bool n
 942
 943 config STRICT_MODULE_RWX
 944         bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
 945         depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
 946         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 947         help
 948           If this is set, module text and rodata memory will be made read-only,
 949           and non-text memory will be made non-executable. This provides
 950           protection against certain security exploits (e.g. writing to text)
 951
 952 # select if the architecture provides an asm/dma-direct.h header
 953 config ARCH_HAS_PHYS_TO_DMA
 954         bool
 955
 956 config ARCH_HAS_REFCOUNT
 957         bool
 958         help
 959           An architecture selects this when it has implemented refcount_t
 960           using open coded assembly primitives that provide an optimized
 961           refcount_t implementation, possibly at the expense of some full
 962           refcount state checks of CONFIG_REFCOUNT_FULL=y.
 963
 964           The refcount overflow check behavior, however, must be retained.
 965           Catching overflows is the primary security concern for protecting
 966           against bugs in reference counts.
 967
 968 config REFCOUNT_FULL
 969         bool "Perform full reference count validation at the expense of speed"
 970         help
 971           Enabling this switches the refcounting infrastructure from a fast
 972           unchecked atomic_t implementation to a fully state checked
 973           implementation, which can be (slightly) slower but provides protections
 974           against various use-after-free conditions that can be used in
 975           security flaw exploits.
 976
 977 source "kernel/gcov/Kconfig"