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 HAVE_RCU_TABLE_INVALIDATE
 358         bool
 359
 360 config ARCH_HAVE_NMI_SAFE_CMPXCHG
 361         bool
 362
 363 config HAVE_ALIGNED_STRUCT_PAGE
 364         bool
 365         help
 366           This makes sure that struct pages are double word aligned and that
 367           e.g. the SLUB allocator can perform double word atomic operations
 368           on a struct page for better performance. However selecting this
 369           might increase the size of a struct page by a word.
 370
 371 config HAVE_CMPXCHG_LOCAL
 372         bool
 373
 374 config HAVE_CMPXCHG_DOUBLE
 375         bool
 376
 377 config ARCH_WEAK_RELEASE_ACQUIRE
 378         bool
 379
 380 config ARCH_WANT_IPC_PARSE_VERSION
 381         bool
 382
 383 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 384         bool
 385
 386 config ARCH_WANT_OLD_COMPAT_IPC
 387         select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 388         bool
 389
 390 config HAVE_ARCH_SECCOMP_FILTER
 391         bool
 392         help
 393           An arch should select this symbol if it provides all of these things:
 394           - syscall_get_arch()
 395           - syscall_get_arguments()
 396           - syscall_rollback()
 397           - syscall_set_return_value()
 398           - SIGSYS siginfo_t support
 399           - secure_computing is called from a ptrace_event()-safe context
 400           - secure_computing return value is checked and a return value of -1
 401             results in the system call being skipped immediately.
 402           - seccomp syscall wired up
 403
 404 config SECCOMP_FILTER
 405         def_bool y
 406         depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
 407         help
 408           Enable tasks to build secure computing environments defined
 409           in terms of Berkeley Packet Filter programs which implement
 410           task-defined system call filtering polices.
 411
 412           See Documentation/userspace-api/seccomp_filter.rst for details.
 413
 414 preferred-plugin-hostcc := $(if-success,[ $(gcc-version) -ge 40800 ],$(HOSTCXX),$(HOSTCC))
 415
 416 config PLUGIN_HOSTCC
 417         string
 418         default "$(shell,$(srctree)/scripts/gcc-plugin.sh "$(preferred-plugin-hostcc)" "$(HOSTCXX)" "$(CC)")"
 419         help
 420           Host compiler used to build GCC plugins.  This can be $(HOSTCXX),
 421           $(HOSTCC), or a null string if GCC plugin is unsupported.
 422
 423 config HAVE_GCC_PLUGINS
 424         bool
 425         help
 426           An arch should select this symbol if it supports building with
 427           GCC plugins.
 428
 429 menuconfig GCC_PLUGINS
 430         bool "GCC plugins"
 431         depends on HAVE_GCC_PLUGINS
 432         depends on PLUGIN_HOSTCC != ""
 433         help
 434           GCC plugins are loadable modules that provide extra features to the
 435           compiler. They are useful for runtime instrumentation and static analysis.
 436
 437           See Documentation/gcc-plugins.txt for details.
 438
 439 config GCC_PLUGIN_CYC_COMPLEXITY
 440         bool "Compute the cyclomatic complexity of a function" if EXPERT
 441         depends on GCC_PLUGINS
 442         depends on !COMPILE_TEST        # too noisy
 443         help
 444           The complexity M of a function's control flow graph is defined as:
 445            M = E - N + 2P
 446           where
 447
 448           E = the number of edges
 449           N = the number of nodes
 450           P = the number of connected components (exit nodes).
 451
 452           Enabling this plugin reports the complexity to stderr during the
 453           build. It mainly serves as a simple example of how to create a
 454           gcc plugin for the kernel.
 455
 456 config GCC_PLUGIN_SANCOV
 457         bool
 458         depends on GCC_PLUGINS
 459         help
 460           This plugin inserts a __sanitizer_cov_trace_pc() call at the start of
 461           basic blocks. It supports all gcc versions with plugin support (from
 462           gcc-4.5 on). It is based on the commit "Add fuzzing coverage support"
 463           by Dmitry Vyukov <dvyukov@google.com>.
 464
 465 config GCC_PLUGIN_LATENT_ENTROPY
 466         bool "Generate some entropy during boot and runtime"
 467         depends on GCC_PLUGINS
 468         help
 469           By saying Y here the kernel will instrument some kernel code to
 470           extract some entropy from both original and artificially created
 471           program state.  This will help especially embedded systems where
 472           there is little 'natural' source of entropy normally.  The cost
 473           is some slowdown of the boot process (about 0.5%) and fork and
 474           irq processing.
 475
 476           Note that entropy extracted this way is not cryptographically
 477           secure!
 478
 479           This plugin was ported from grsecurity/PaX. More information at:
 480            * https://grsecurity.net/
 481            * https://pax.grsecurity.net/
 482
 483 config GCC_PLUGIN_STRUCTLEAK
 484         bool "Force initialization of variables containing userspace addresses"
 485         depends on GCC_PLUGINS
 486         # Currently STRUCTLEAK inserts initialization out of live scope of
 487         # variables from KASAN point of view. This leads to KASAN false
 488         # positive reports. Prohibit this combination for now.
 489         depends on !KASAN_EXTRA
 490         help
 491           This plugin zero-initializes any structures containing a
 492           __user attribute. This can prevent some classes of information
 493           exposures.
 494
 495           This plugin was ported from grsecurity/PaX. More information at:
 496            * https://grsecurity.net/
 497            * https://pax.grsecurity.net/
 498
 499 config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
 500         bool "Force initialize all struct type variables passed by reference"
 501         depends on GCC_PLUGIN_STRUCTLEAK
 502         depends on !COMPILE_TEST
 503         help
 504           Zero initialize any struct type local variable that may be passed by
 505           reference without having been initialized.
 506
 507 config GCC_PLUGIN_STRUCTLEAK_VERBOSE
 508         bool "Report forcefully initialized variables"
 509         depends on GCC_PLUGIN_STRUCTLEAK
 510         depends on !COMPILE_TEST        # too noisy
 511         help
 512           This option will cause a warning to be printed each time the
 513           structleak plugin finds a variable it thinks needs to be
 514           initialized. Since not all existing initializers are detected
 515           by the plugin, this can produce false positive warnings.
 516
 517 config GCC_PLUGIN_RANDSTRUCT
 518         bool "Randomize layout of sensitive kernel structures"
 519         depends on GCC_PLUGINS
 520         select MODVERSIONS if MODULES
 521         help
 522           If you say Y here, the layouts of structures that are entirely
 523           function pointers (and have not been manually annotated with
 524           __no_randomize_layout), or structures that have been explicitly
 525           marked with __randomize_layout, will be randomized at compile-time.
 526           This can introduce the requirement of an additional information
 527           exposure vulnerability for exploits targeting these structure
 528           types.
 529
 530           Enabling this feature will introduce some performance impact,
 531           slightly increase memory usage, and prevent the use of forensic
 532           tools like Volatility against the system (unless the kernel
 533           source tree isn't cleaned after kernel installation).
 534
 535           The seed used for compilation is located at
 536           scripts/gcc-plgins/randomize_layout_seed.h.  It remains after
 537           a make clean to allow for external modules to be compiled with
 538           the existing seed and will be removed by a make mrproper or
 539           make distclean.
 540
 541           Note that the implementation requires gcc 4.7 or newer.
 542
 543           This plugin was ported from grsecurity/PaX. More information at:
 544            * https://grsecurity.net/
 545            * https://pax.grsecurity.net/
 546
 547 config GCC_PLUGIN_RANDSTRUCT_PERFORMANCE
 548         bool "Use cacheline-aware structure randomization"
 549         depends on GCC_PLUGIN_RANDSTRUCT
 550         depends on !COMPILE_TEST        # do not reduce test coverage
 551         help
 552           If you say Y here, the RANDSTRUCT randomization will make a
 553           best effort at restricting randomization to cacheline-sized
 554           groups of elements.  It will further not randomize bitfields
 555           in structures.  This reduces the performance hit of RANDSTRUCT
 556           at the cost of weakened randomization.
 557
 558 config HAVE_STACKPROTECTOR
 559         bool
 560         help
 561           An arch should select this symbol if:
 562           - it has implemented a stack canary (e.g. __stack_chk_guard)
 563
 564 config CC_HAS_STACKPROTECTOR_NONE
 565         def_bool $(cc-option,-fno-stack-protector)
 566
 567 config STACKPROTECTOR
 568         bool "Stack Protector buffer overflow detection"
 569         depends on HAVE_STACKPROTECTOR
 570         depends on $(cc-option,-fstack-protector)
 571         default y
 572         help
 573           This option turns on the "stack-protector" GCC feature. This
 574           feature puts, at the beginning of functions, a canary value on
 575           the stack just before the return address, and validates
 576           the value just before actually returning.  Stack based buffer
 577           overflows (that need to overwrite this return address) now also
 578           overwrite the canary, which gets detected and the attack is then
 579           neutralized via a kernel panic.
 580
 581           Functions will have the stack-protector canary logic added if they
 582           have an 8-byte or larger character array on the stack.
 583
 584           This feature requires gcc version 4.2 or above, or a distribution
 585           gcc with the feature backported ("-fstack-protector").
 586
 587           On an x86 "defconfig" build, this feature adds canary checks to
 588           about 3% of all kernel functions, which increases kernel code size
 589           by about 0.3%.
 590
 591 config STACKPROTECTOR_STRONG
 592         bool "Strong Stack Protector"
 593         depends on STACKPROTECTOR
 594         depends on $(cc-option,-fstack-protector-strong)
 595         default y
 596         help
 597           Functions will have the stack-protector canary logic added in any
 598           of the following conditions:
 599
 600           - local variable's address used as part of the right hand side of an
 601             assignment or function argument
 602           - local variable is an array (or union containing an array),
 603             regardless of array type or length
 604           - uses register local variables
 605
 606           This feature requires gcc version 4.9 or above, or a distribution
 607           gcc with the feature backported ("-fstack-protector-strong").
 608
 609           On an x86 "defconfig" build, this feature adds canary checks to
 610           about 20% of all kernel functions, which increases the kernel code
 611           size by about 2%.
 612
 613 config HAVE_ARCH_WITHIN_STACK_FRAMES
 614         bool
 615         help
 616           An architecture should select this if it can walk the kernel stack
 617           frames to determine if an object is part of either the arguments
 618           or local variables (i.e. that it excludes saved return addresses,
 619           and similar) by implementing an inline arch_within_stack_frames(),
 620           which is used by CONFIG_HARDENED_USERCOPY.
 621
 622 config HAVE_CONTEXT_TRACKING
 623         bool
 624         help
 625           Provide kernel/user boundaries probes necessary for subsystems
 626           that need it, such as userspace RCU extended quiescent state.
 627           Syscalls need to be wrapped inside user_exit()-user_enter() through
 628           the slow path using TIF_NOHZ flag. Exceptions handlers must be
 629           wrapped as well. Irqs are already protected inside
 630           rcu_irq_enter/rcu_irq_exit() but preemption or signal handling on
 631           irq exit still need to be protected.
 632
 633 config HAVE_VIRT_CPU_ACCOUNTING
 634         bool
 635
 636 config ARCH_HAS_SCALED_CPUTIME
 637         bool
 638
 639 config HAVE_VIRT_CPU_ACCOUNTING_GEN
 640         bool
 641         default y if 64BIT
 642         help
 643           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 644           Before enabling this option, arch code must be audited
 645           to ensure there are no races in concurrent read/write of
 646           cputime_t. For example, reading/writing 64-bit cputime_t on
 647           some 32-bit arches may require multiple accesses, so proper
 648           locking is needed to protect against concurrent accesses.
 649
 650
 651 config HAVE_IRQ_TIME_ACCOUNTING
 652         bool
 653         help
 654           Archs need to ensure they use a high enough resolution clock to
 655           support irq time accounting and then call enable_sched_clock_irqtime().
 656
 657 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 658         bool
 659
 660 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 661         bool
 662
 663 config HAVE_ARCH_HUGE_VMAP
 664         bool
 665
 666 config HAVE_ARCH_SOFT_DIRTY
 667         bool
 668
 669 config HAVE_MOD_ARCH_SPECIFIC
 670         bool
 671         help
 672           The arch uses struct mod_arch_specific to store data.  Many arches
 673           just need a simple module loader without arch specific data - those
 674           should not enable this.
 675
 676 config MODULES_USE_ELF_RELA
 677         bool
 678         help
 679           Modules only use ELF RELA relocations.  Modules with ELF REL
 680           relocations will give an error.
 681
 682 config MODULES_USE_ELF_REL
 683         bool
 684         help
 685           Modules only use ELF REL relocations.  Modules with ELF RELA
 686           relocations will give an error.
 687
 688 config HAVE_IRQ_EXIT_ON_IRQ_STACK
 689         bool
 690         help
 691           Architecture doesn't only execute the irq handler on the irq stack
 692           but also irq_exit(). This way we can process softirqs on this irq
 693           stack instead of switching to a new one when we call __do_softirq()
 694           in the end of an hardirq.
 695           This spares a stack switch and improves cache usage on softirq
 696           processing.
 697
 698 config PGTABLE_LEVELS
 699         int
 700         default 2
 701
 702 config ARCH_HAS_ELF_RANDOMIZE
 703         bool
 704         help
 705           An architecture supports choosing randomized locations for
 706           stack, mmap, brk, and ET_DYN. Defined functions:
 707           - arch_mmap_rnd()
 708           - arch_randomize_brk()
 709
 710 config HAVE_ARCH_MMAP_RND_BITS
 711         bool
 712         help
 713           An arch should select this symbol if it supports setting a variable
 714           number of bits for use in establishing the base address for mmap
 715           allocations, has MMU enabled and provides values for both:
 716           - ARCH_MMAP_RND_BITS_MIN
 717           - ARCH_MMAP_RND_BITS_MAX
 718
 719 config HAVE_EXIT_THREAD
 720         bool
 721         help
 722           An architecture implements exit_thread.
 723
 724 config ARCH_MMAP_RND_BITS_MIN
 725         int
 726
 727 config ARCH_MMAP_RND_BITS_MAX
 728         int
 729
 730 config ARCH_MMAP_RND_BITS_DEFAULT
 731         int
 732
 733 config ARCH_MMAP_RND_BITS
 734         int "Number of bits to use for ASLR of mmap base address" if EXPERT
 735         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
 736         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
 737         default ARCH_MMAP_RND_BITS_MIN
 738         depends on HAVE_ARCH_MMAP_RND_BITS
 739         help
 740           This value can be used to select the number of bits to use to
 741           determine the random offset to the base address of vma regions
 742           resulting from mmap allocations. This value will be bounded
 743           by the architecture's minimum and maximum supported values.
 744
 745           This value can be changed after boot using the
 746           /proc/sys/vm/mmap_rnd_bits tunable
 747
 748 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
 749         bool
 750         help
 751           An arch should select this symbol if it supports running applications
 752           in compatibility mode, supports setting a variable number of bits for
 753           use in establishing the base address for mmap allocations, has MMU
 754           enabled and provides values for both:
 755           - ARCH_MMAP_RND_COMPAT_BITS_MIN
 756           - ARCH_MMAP_RND_COMPAT_BITS_MAX
 757
 758 config ARCH_MMAP_RND_COMPAT_BITS_MIN
 759         int
 760
 761 config ARCH_MMAP_RND_COMPAT_BITS_MAX
 762         int
 763
 764 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 765         int
 766
 767 config ARCH_MMAP_RND_COMPAT_BITS
 768         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
 769         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
 770         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 771         default ARCH_MMAP_RND_COMPAT_BITS_MIN
 772         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
 773         help
 774           This value can be used to select the number of bits to use to
 775           determine the random offset to the base address of vma regions
 776           resulting from mmap allocations for compatible applications This
 777           value will be bounded by the architecture's minimum and maximum
 778           supported values.
 779
 780           This value can be changed after boot using the
 781           /proc/sys/vm/mmap_rnd_compat_bits tunable
 782
 783 config HAVE_ARCH_COMPAT_MMAP_BASES
 784         bool
 785         help
 786           This allows 64bit applications to invoke 32-bit mmap() syscall
 787           and vice-versa 32-bit applications to call 64-bit mmap().
 788           Required for applications doing different bitness syscalls.
 789
 790 config HAVE_COPY_THREAD_TLS
 791         bool
 792         help
 793           Architecture provides copy_thread_tls to accept tls argument via
 794           normal C parameter passing, rather than extracting the syscall
 795           argument from pt_regs.
 796
 797 config HAVE_STACK_VALIDATION
 798         bool
 799         help
 800           Architecture supports the 'objtool check' host tool command, which
 801           performs compile-time stack metadata validation.
 802
 803 config HAVE_RELIABLE_STACKTRACE
 804         bool
 805         help
 806           Architecture has a save_stack_trace_tsk_reliable() function which
 807           only returns a stack trace if it can guarantee the trace is reliable.
 808
 809 config HAVE_ARCH_HASH
 810         bool
 811         default n
 812         help
 813           If this is set, the architecture provides an <asm/hash.h>
 814           file which provides platform-specific implementations of some
 815           functions in <linux/hash.h> or fs/namei.c.
 816
 817 config ISA_BUS_API
 818         def_bool ISA
 819
 820 #
 821 # ABI hall of shame
 822 #
 823 config CLONE_BACKWARDS
 824         bool
 825         help
 826           Architecture has tls passed as the 4th argument of clone(2),
 827           not the 5th one.
 828
 829 config CLONE_BACKWARDS2
 830         bool
 831         help
 832           Architecture has the first two arguments of clone(2) swapped.
 833
 834 config CLONE_BACKWARDS3
 835         bool
 836         help
 837           Architecture has tls passed as the 3rd argument of clone(2),
 838           not the 5th one.
 839
 840 config ODD_RT_SIGACTION
 841         bool
 842         help
 843           Architecture has unusual rt_sigaction(2) arguments
 844
 845 config OLD_SIGSUSPEND
 846         bool
 847         help
 848           Architecture has old sigsuspend(2) syscall, of one-argument variety
 849
 850 config OLD_SIGSUSPEND3
 851         bool
 852         help
 853           Even weirder antique ABI - three-argument sigsuspend(2)
 854
 855 config OLD_SIGACTION
 856         bool
 857         help
 858           Architecture has old sigaction(2) syscall.  Nope, not the same
 859           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
 860           but fairly different variant of sigaction(2), thanks to OSF/1
 861           compatibility...
 862
 863 config COMPAT_OLD_SIGACTION
 864         bool
 865
 866 config 64BIT_TIME
 867         def_bool ARCH_HAS_64BIT_TIME
 868         help
 869           This should be selected by all architectures that need to support
 870           new system calls with a 64-bit time_t. This is relevant on all 32-bit
 871           architectures, and 64-bit architectures as part of compat syscall
 872           handling.
 873
 874 config COMPAT_32BIT_TIME
 875         def_bool (!64BIT && 64BIT_TIME) || COMPAT
 876         help
 877           This enables 32 bit time_t support in addition to 64 bit time_t support.
 878           This is relevant on all 32-bit architectures, and 64-bit architectures
 879           as part of compat syscall handling.
 880
 881 config ARCH_NO_COHERENT_DMA_MMAP
 882         bool
 883
 884 config CPU_NO_EFFICIENT_FFS
 885         def_bool n
 886
 887 config HAVE_ARCH_VMAP_STACK
 888         def_bool n
 889         help
 890           An arch should select this symbol if it can support kernel stacks
 891           in vmalloc space.  This means:
 892
 893           - vmalloc space must be large enough to hold many kernel stacks.
 894             This may rule out many 32-bit architectures.
 895
 896           - Stacks in vmalloc space need to work reliably.  For example, if
 897             vmap page tables are created on demand, either this mechanism
 898             needs to work while the stack points to a virtual address with
 899             unpopulated page tables or arch code (switch_to() and switch_mm(),
 900             most likely) needs to ensure that the stack's page table entries
 901             are populated before running on a possibly unpopulated stack.
 902
 903           - If the stack overflows into a guard page, something reasonable
 904             should happen.  The definition of "reasonable" is flexible, but
 905             instantly rebooting without logging anything would be unfriendly.
 906
 907 config VMAP_STACK
 908         default y
 909         bool "Use a virtually-mapped stack"
 910         depends on HAVE_ARCH_VMAP_STACK && !KASAN
 911         ---help---
 912           Enable this if you want the use virtually-mapped kernel stacks
 913           with guard pages.  This causes kernel stack overflows to be
 914           caught immediately rather than causing difficult-to-diagnose
 915           corruption.
 916
 917           This is presently incompatible with KASAN because KASAN expects
 918           the stack to map directly to the KASAN shadow map using a formula
 919           that is incorrect if the stack is in vmalloc space.
 920
 921 config ARCH_OPTIONAL_KERNEL_RWX
 922         def_bool n
 923
 924 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 925         def_bool n
 926
 927 config ARCH_HAS_STRICT_KERNEL_RWX
 928         def_bool n
 929
 930 config STRICT_KERNEL_RWX
 931         bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
 932         depends on ARCH_HAS_STRICT_KERNEL_RWX
 933         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 934         help
 935           If this is set, kernel text and rodata memory will be made read-only,
 936           and non-text memory will be made non-executable. This provides
 937           protection against certain security exploits (e.g. executing the heap
 938           or modifying text)
 939
 940           These features are considered standard security practice these days.
 941           You should say Y here in almost all cases.
 942
 943 config ARCH_HAS_STRICT_MODULE_RWX
 944         def_bool n
 945
 946 config STRICT_MODULE_RWX
 947         bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
 948         depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
 949         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 950         help
 951           If this is set, module text and rodata memory will be made read-only,
 952           and non-text memory will be made non-executable. This provides
 953           protection against certain security exploits (e.g. writing to text)
 954
 955 # select if the architecture provides an asm/dma-direct.h header
 956 config ARCH_HAS_PHYS_TO_DMA
 957         bool
 958
 959 config ARCH_HAS_REFCOUNT
 960         bool
 961         help
 962           An architecture selects this when it has implemented refcount_t
 963           using open coded assembly primitives that provide an optimized
 964           refcount_t implementation, possibly at the expense of some full
 965           refcount state checks of CONFIG_REFCOUNT_FULL=y.
 966
 967           The refcount overflow check behavior, however, must be retained.
 968           Catching overflows is the primary security concern for protecting
 969           against bugs in reference counts.
 970
 971 config REFCOUNT_FULL
 972         bool "Perform full reference count validation at the expense of speed"
 973         help
 974           Enabling this switches the refcounting infrastructure from a fast
 975           unchecked atomic_t implementation to a fully state checked
 976           implementation, which can be (slightly) slower but provides protections
 977           against various use-after-free conditions that can be used in
 978           security flaw exploits.
 979
 980 config HAVE_ARCH_COMPILER_H
 981         bool
 982         help
 983           An architecture can select this if it provides an
 984           asm/compiler.h header that should be included after
 985           linux/compiler-*.h in order to override macro definitions that those
 986           headers generally provide.
 987
 988 source "kernel/gcov/Kconfig"