arch/Kconfig

   1 # SPDX-License-Identifier: GPL-2.0
   2 #
   3 # General architecture dependent options
   4 #
   5
   6 #
   7 # Note: arch/$(SRCARCH)/Kconfig needs to be included first so that it can
   8 # override the default values in this file.
   9 #
  10 source "arch/$(SRCARCH)/Kconfig"
  11
  12 menu "General architecture-dependent options"
  13
  14 config CRASH_CORE
  15         bool
  16
  17 config KEXEC_CORE
  18         select CRASH_CORE
  19         bool
  20
  21 config HAVE_IMA_KEXEC
  22         bool
  23
  24 config HOTPLUG_SMT
  25         bool
  26
  27 config OPROFILE
  28         tristate "OProfile system profiling"
  29         depends on PROFILING
  30         depends on HAVE_OPROFILE
  31         select RING_BUFFER
  32         select RING_BUFFER_ALLOW_SWAP
  33         help
  34           OProfile is a profiling system capable of profiling the
  35           whole system, include the kernel, kernel modules, libraries,
  36           and applications.
  37
  38           If unsure, say N.
  39
  40 config OPROFILE_EVENT_MULTIPLEX
  41         bool "OProfile multiplexing support (EXPERIMENTAL)"
  42         default n
  43         depends on OPROFILE && X86
  44         help
  45           The number of hardware counters is limited. The multiplexing
  46           feature enables OProfile to gather more events than counters
  47           are provided by the hardware. This is realized by switching
  48           between events at a user specified time interval.
  49
  50           If unsure, say N.
  51
  52 config HAVE_OPROFILE
  53         bool
  54
  55 config OPROFILE_NMI_TIMER
  56         def_bool y
  57         depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI && !PPC64
  58
  59 config KPROBES
  60         bool "Kprobes"
  61         depends on MODULES
  62         depends on HAVE_KPROBES
  63         select KALLSYMS
  64         help
  65           Kprobes allows you to trap at almost any kernel address and
  66           execute a callback function.  register_kprobe() establishes
  67           a probepoint and specifies the callback.  Kprobes is useful
  68           for kernel debugging, non-intrusive instrumentation and testing.
  69           If in doubt, say "N".
  70
  71 config JUMP_LABEL
  72        bool "Optimize very unlikely/likely branches"
  73        depends on HAVE_ARCH_JUMP_LABEL
  74        depends on CC_HAS_ASM_GOTO
  75        help
  76          This option enables a transparent branch optimization that
  77          makes certain almost-always-true or almost-always-false branch
  78          conditions even cheaper to execute within the kernel.
  79
  80          Certain performance-sensitive kernel code, such as trace points,
  81          scheduler functionality, networking code and KVM have such
  82          branches and include support for this optimization technique.
  83
  84          If it is detected that the compiler has support for "asm goto",
  85          the kernel will compile such branches with just a nop
  86          instruction. When the condition flag is toggled to true, the
  87          nop will be converted to a jump instruction to execute the
  88          conditional block of instructions.
  89
  90          This technique lowers overhead and stress on the branch prediction
  91          of the processor and generally makes the kernel faster. The update
  92          of the condition is slower, but those are always very rare.
  93
  94          ( On 32-bit x86, the necessary options added to the compiler
  95            flags may increase the size of the kernel slightly. )
  96
  97 config STATIC_KEYS_SELFTEST
  98         bool "Static key selftest"
  99         depends on JUMP_LABEL
 100         help
 101           Boot time self-test of the branch patching code.
 102
 103 config OPTPROBES
 104         def_bool y
 105         depends on KPROBES && HAVE_OPTPROBES
 106         select TASKS_RCU if PREEMPT
 107
 108 config KPROBES_ON_FTRACE
 109         def_bool y
 110         depends on KPROBES && HAVE_KPROBES_ON_FTRACE
 111         depends on DYNAMIC_FTRACE_WITH_REGS
 112         help
 113          If function tracer is enabled and the arch supports full
 114          passing of pt_regs to function tracing, then kprobes can
 115          optimize on top of function tracing.
 116
 117 config UPROBES
 118         def_bool n
 119         depends on ARCH_SUPPORTS_UPROBES
 120         help
 121           Uprobes is the user-space counterpart to kprobes: they
 122           enable instrumentation applications (such as 'perf probe')
 123           to establish unintrusive probes in user-space binaries and
 124           libraries, by executing handler functions when the probes
 125           are hit by user-space applications.
 126
 127           ( These probes come in the form of single-byte breakpoints,
 128             managed by the kernel and kept transparent to the probed
 129             application. )
 130
 131 config HAVE_64BIT_ALIGNED_ACCESS
 132         def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
 133         help
 134           Some architectures require 64 bit accesses to be 64 bit
 135           aligned, which also requires structs containing 64 bit values
 136           to be 64 bit aligned too. This includes some 32 bit
 137           architectures which can do 64 bit accesses, as well as 64 bit
 138           architectures without unaligned access.
 139
 140           This symbol should be selected by an architecture if 64 bit
 141           accesses are required to be 64 bit aligned in this way even
 142           though it is not a 64 bit architecture.
 143
 144           See Documentation/unaligned-memory-access.txt for more
 145           information on the topic of unaligned memory accesses.
 146
 147 config HAVE_EFFICIENT_UNALIGNED_ACCESS
 148         bool
 149         help
 150           Some architectures are unable to perform unaligned accesses
 151           without the use of get_unaligned/put_unaligned. Others are
 152           unable to perform such accesses efficiently (e.g. trap on
 153           unaligned access and require fixing it up in the exception
 154           handler.)
 155
 156           This symbol should be selected by an architecture if it can
 157           perform unaligned accesses efficiently to allow different
 158           code paths to be selected for these cases. Some network
 159           drivers, for example, could opt to not fix up alignment
 160           problems with received packets if doing so would not help
 161           much.
 162
 163           See Documentation/unaligned-memory-access.txt for more
 164           information on the topic of unaligned memory accesses.
 165
 166 config ARCH_USE_BUILTIN_BSWAP
 167        bool
 168        help
 169          Modern versions of GCC (since 4.4) have builtin functions
 170          for handling byte-swapping. Using these, instead of the old
 171          inline assembler that the architecture code provides in the
 172          __arch_bswapXX() macros, allows the compiler to see what's
 173          happening and offers more opportunity for optimisation. In
 174          particular, the compiler will be able to combine the byteswap
 175          with a nearby load or store and use load-and-swap or
 176          store-and-swap instructions if the architecture has them. It
 177          should almost *never* result in code which is worse than the
 178          hand-coded assembler in <asm/swab.h>.  But just in case it
 179          does, the use of the builtins is optional.
 180
 181          Any architecture with load-and-swap or store-and-swap
 182          instructions should set this. And it shouldn't hurt to set it
 183          on architectures that don't have such instructions.
 184
 185 config KRETPROBES
 186         def_bool y
 187         depends on KPROBES && HAVE_KRETPROBES
 188
 189 config USER_RETURN_NOTIFIER
 190         bool
 191         depends on HAVE_USER_RETURN_NOTIFIER
 192         help
 193           Provide a kernel-internal notification when a cpu is about to
 194           switch to user mode.
 195
 196 config HAVE_IOREMAP_PROT
 197         bool
 198
 199 config HAVE_KPROBES
 200         bool
 201
 202 config HAVE_KRETPROBES
 203         bool
 204
 205 config HAVE_OPTPROBES
 206         bool
 207
 208 config HAVE_KPROBES_ON_FTRACE
 209         bool
 210
 211 config HAVE_FUNCTION_ERROR_INJECTION
 212         bool
 213
 214 config HAVE_NMI
 215         bool
 216
 217 #
 218 # An arch should select this if it provides all these things:
 219 #
 220 #       task_pt_regs()          in asm/processor.h or asm/ptrace.h
 221 #       arch_has_single_step()  if there is hardware single-step support
 222 #       arch_has_block_step()   if there is hardware block-step support
 223 #       asm/syscall.h           supplying asm-generic/syscall.h interface
 224 #       linux/regset.h          user_regset interfaces
 225 #       CORE_DUMP_USE_REGSET    #define'd in linux/elf.h
 226 #       TIF_SYSCALL_TRACE       calls tracehook_report_syscall_{entry,exit}
 227 #       TIF_NOTIFY_RESUME       calls tracehook_notify_resume()
 228 #       signal delivery         calls tracehook_signal_handler()
 229 #
 230 config HAVE_ARCH_TRACEHOOK
 231         bool
 232
 233 config HAVE_DMA_CONTIGUOUS
 234         bool
 235
 236 config GENERIC_SMP_IDLE_THREAD
 237        bool
 238
 239 config GENERIC_IDLE_POLL_SETUP
 240        bool
 241
 242 config ARCH_HAS_FORTIFY_SOURCE
 243         bool
 244         help
 245           An architecture should select this when it can successfully
 246           build and run with CONFIG_FORTIFY_SOURCE.
 247
 248 # Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
 249 config ARCH_HAS_SET_MEMORY
 250         bool
 251
 252 # Select if arch init_task must go in the __init_task_data section
 253 config ARCH_TASK_STRUCT_ON_STACK
 254        bool
 255
 256 # Select if arch has its private alloc_task_struct() function
 257 config ARCH_TASK_STRUCT_ALLOCATOR
 258         bool
 259
 260 config HAVE_ARCH_THREAD_STRUCT_WHITELIST
 261         bool
 262         depends on !ARCH_TASK_STRUCT_ALLOCATOR
 263         help
 264           An architecture should select this to provide hardened usercopy
 265           knowledge about what region of the thread_struct should be
 266           whitelisted for copying to userspace. Normally this is only the
 267           FPU registers. Specifically, arch_thread_struct_whitelist()
 268           should be implemented. Without this, the entire thread_struct
 269           field in task_struct will be left whitelisted.
 270
 271 # Select if arch has its private alloc_thread_stack() function
 272 config ARCH_THREAD_STACK_ALLOCATOR
 273         bool
 274
 275 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
 276 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
 277         bool
 278
 279 config HAVE_REGS_AND_STACK_ACCESS_API
 280         bool
 281         help
 282           This symbol should be selected by an architecure if it supports
 283           the API needed to access registers and stack entries from pt_regs,
 284           declared in asm/ptrace.h
 285           For example the kprobes-based event tracer needs this API.
 286
 287 config HAVE_RSEQ
 288         bool
 289         depends on HAVE_REGS_AND_STACK_ACCESS_API
 290         help
 291           This symbol should be selected by an architecture if it
 292           supports an implementation of restartable sequences.
 293
 294 config HAVE_FUNCTION_ARG_ACCESS_API
 295         bool
 296         help
 297           This symbol should be selected by an architecure if it supports
 298           the API needed to access function arguments from pt_regs,
 299           declared in asm/ptrace.h
 300
 301 config HAVE_CLK
 302         bool
 303         help
 304           The <linux/clk.h> calls support software clock gating and
 305           thus are a key power management tool on many systems.
 306
 307 config HAVE_HW_BREAKPOINT
 308         bool
 309         depends on PERF_EVENTS
 310
 311 config HAVE_MIXED_BREAKPOINTS_REGS
 312         bool
 313         depends on HAVE_HW_BREAKPOINT
 314         help
 315           Depending on the arch implementation of hardware breakpoints,
 316           some of them have separate registers for data and instruction
 317           breakpoints addresses, others have mixed registers to store
 318           them but define the access type in a control register.
 319           Select this option if your arch implements breakpoints under the
 320           latter fashion.
 321
 322 config HAVE_USER_RETURN_NOTIFIER
 323         bool
 324
 325 config HAVE_PERF_EVENTS_NMI
 326         bool
 327         help
 328           System hardware can generate an NMI using the perf event
 329           subsystem.  Also has support for calculating CPU cycle events
 330           to determine how many clock cycles in a given period.
 331
 332 config HAVE_HARDLOCKUP_DETECTOR_PERF
 333         bool
 334         depends on HAVE_PERF_EVENTS_NMI
 335         help
 336           The arch chooses to use the generic perf-NMI-based hardlockup
 337           detector. Must define HAVE_PERF_EVENTS_NMI.
 338
 339 config HAVE_NMI_WATCHDOG
 340         depends on HAVE_NMI
 341         bool
 342         help
 343           The arch provides a low level NMI watchdog. It provides
 344           asm/nmi.h, and defines its own arch_touch_nmi_watchdog().
 345
 346 config HAVE_HARDLOCKUP_DETECTOR_ARCH
 347         bool
 348         select HAVE_NMI_WATCHDOG
 349         help
 350           The arch chooses to provide its own hardlockup detector, which is
 351           a superset of the HAVE_NMI_WATCHDOG. It also conforms to config
 352           interfaces and parameters provided by hardlockup detector subsystem.
 353
 354 config HAVE_PERF_REGS
 355         bool
 356         help
 357           Support selective register dumps for perf events. This includes
 358           bit-mapping of each registers and a unique architecture id.
 359
 360 config HAVE_PERF_USER_STACK_DUMP
 361         bool
 362         help
 363           Support user stack dumps for perf event samples. This needs
 364           access to the user stack pointer which is not unified across
 365           architectures.
 366
 367 config HAVE_ARCH_JUMP_LABEL
 368         bool
 369
 370 config HAVE_ARCH_JUMP_LABEL_RELATIVE
 371         bool
 372
 373 config HAVE_RCU_TABLE_FREE
 374         bool
 375
 376 config HAVE_RCU_TABLE_INVALIDATE
 377         bool
 378
 379 config ARCH_HAVE_NMI_SAFE_CMPXCHG
 380         bool
 381
 382 config HAVE_ALIGNED_STRUCT_PAGE
 383         bool
 384         help
 385           This makes sure that struct pages are double word aligned and that
 386           e.g. the SLUB allocator can perform double word atomic operations
 387           on a struct page for better performance. However selecting this
 388           might increase the size of a struct page by a word.
 389
 390 config HAVE_CMPXCHG_LOCAL
 391         bool
 392
 393 config HAVE_CMPXCHG_DOUBLE
 394         bool
 395
 396 config ARCH_WEAK_RELEASE_ACQUIRE
 397         bool
 398
 399 config ARCH_WANT_IPC_PARSE_VERSION
 400         bool
 401
 402 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 403         bool
 404
 405 config ARCH_WANT_OLD_COMPAT_IPC
 406         select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 407         bool
 408
 409 config HAVE_ARCH_SECCOMP_FILTER
 410         bool
 411         help
 412           An arch should select this symbol if it provides all of these things:
 413           - syscall_get_arch()
 414           - syscall_get_arguments()
 415           - syscall_rollback()
 416           - syscall_set_return_value()
 417           - SIGSYS siginfo_t support
 418           - secure_computing is called from a ptrace_event()-safe context
 419           - secure_computing return value is checked and a return value of -1
 420             results in the system call being skipped immediately.
 421           - seccomp syscall wired up
 422
 423 config SECCOMP_FILTER
 424         def_bool y
 425         depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
 426         help
 427           Enable tasks to build secure computing environments defined
 428           in terms of Berkeley Packet Filter programs which implement
 429           task-defined system call filtering polices.
 430
 431           See Documentation/userspace-api/seccomp_filter.rst for details.
 432
 433 config HAVE_ARCH_STACKLEAK
 434         bool
 435         help
 436           An architecture should select this if it has the code which
 437           fills the used part of the kernel stack with the STACKLEAK_POISON
 438           value before returning from system calls.
 439
 440 config HAVE_STACKPROTECTOR
 441         bool
 442         help
 443           An arch should select this symbol if:
 444           - it has implemented a stack canary (e.g. __stack_chk_guard)
 445
 446 config CC_HAS_STACKPROTECTOR_NONE
 447         def_bool $(cc-option,-fno-stack-protector)
 448
 449 config STACKPROTECTOR
 450         bool "Stack Protector buffer overflow detection"
 451         depends on HAVE_STACKPROTECTOR
 452         depends on $(cc-option,-fstack-protector)
 453         default y
 454         help
 455           This option turns on the "stack-protector" GCC feature. This
 456           feature puts, at the beginning of functions, a canary value on
 457           the stack just before the return address, and validates
 458           the value just before actually returning.  Stack based buffer
 459           overflows (that need to overwrite this return address) now also
 460           overwrite the canary, which gets detected and the attack is then
 461           neutralized via a kernel panic.
 462
 463           Functions will have the stack-protector canary logic added if they
 464           have an 8-byte or larger character array on the stack.
 465
 466           This feature requires gcc version 4.2 or above, or a distribution
 467           gcc with the feature backported ("-fstack-protector").
 468
 469           On an x86 "defconfig" build, this feature adds canary checks to
 470           about 3% of all kernel functions, which increases kernel code size
 471           by about 0.3%.
 472
 473 config STACKPROTECTOR_STRONG
 474         bool "Strong Stack Protector"
 475         depends on STACKPROTECTOR
 476         depends on $(cc-option,-fstack-protector-strong)
 477         default y
 478         help
 479           Functions will have the stack-protector canary logic added in any
 480           of the following conditions:
 481
 482           - local variable's address used as part of the right hand side of an
 483             assignment or function argument
 484           - local variable is an array (or union containing an array),
 485             regardless of array type or length
 486           - uses register local variables
 487
 488           This feature requires gcc version 4.9 or above, or a distribution
 489           gcc with the feature backported ("-fstack-protector-strong").
 490
 491           On an x86 "defconfig" build, this feature adds canary checks to
 492           about 20% of all kernel functions, which increases the kernel code
 493           size by about 2%.
 494
 495 config HAVE_ARCH_WITHIN_STACK_FRAMES
 496         bool
 497         help
 498           An architecture should select this if it can walk the kernel stack
 499           frames to determine if an object is part of either the arguments
 500           or local variables (i.e. that it excludes saved return addresses,
 501           and similar) by implementing an inline arch_within_stack_frames(),
 502           which is used by CONFIG_HARDENED_USERCOPY.
 503
 504 config HAVE_CONTEXT_TRACKING
 505         bool
 506         help
 507           Provide kernel/user boundaries probes necessary for subsystems
 508           that need it, such as userspace RCU extended quiescent state.
 509           Syscalls need to be wrapped inside user_exit()-user_enter() through
 510           the slow path using TIF_NOHZ flag. Exceptions handlers must be
 511           wrapped as well. Irqs are already protected inside
 512           rcu_irq_enter/rcu_irq_exit() but preemption or signal handling on
 513           irq exit still need to be protected.
 514
 515 config HAVE_VIRT_CPU_ACCOUNTING
 516         bool
 517
 518 config ARCH_HAS_SCALED_CPUTIME
 519         bool
 520
 521 config HAVE_VIRT_CPU_ACCOUNTING_GEN
 522         bool
 523         default y if 64BIT
 524         help
 525           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 526           Before enabling this option, arch code must be audited
 527           to ensure there are no races in concurrent read/write of
 528           cputime_t. For example, reading/writing 64-bit cputime_t on
 529           some 32-bit arches may require multiple accesses, so proper
 530           locking is needed to protect against concurrent accesses.
 531
 532
 533 config HAVE_IRQ_TIME_ACCOUNTING
 534         bool
 535         help
 536           Archs need to ensure they use a high enough resolution clock to
 537           support irq time accounting and then call enable_sched_clock_irqtime().
 538
 539 config HAVE_MOVE_PMD
 540         bool
 541         help
 542           Archs that select this are able to move page tables at the PMD level.
 543
 544 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 545         bool
 546
 547 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 548         bool
 549
 550 config HAVE_ARCH_HUGE_VMAP
 551         bool
 552
 553 config HAVE_ARCH_SOFT_DIRTY
 554         bool
 555
 556 config HAVE_MOD_ARCH_SPECIFIC
 557         bool
 558         help
 559           The arch uses struct mod_arch_specific to store data.  Many arches
 560           just need a simple module loader without arch specific data - those
 561           should not enable this.
 562
 563 config MODULES_USE_ELF_RELA
 564         bool
 565         help
 566           Modules only use ELF RELA relocations.  Modules with ELF REL
 567           relocations will give an error.
 568
 569 config MODULES_USE_ELF_REL
 570         bool
 571         help
 572           Modules only use ELF REL relocations.  Modules with ELF RELA
 573           relocations will give an error.
 574
 575 config HAVE_IRQ_EXIT_ON_IRQ_STACK
 576         bool
 577         help
 578           Architecture doesn't only execute the irq handler on the irq stack
 579           but also irq_exit(). This way we can process softirqs on this irq
 580           stack instead of switching to a new one when we call __do_softirq()
 581           in the end of an hardirq.
 582           This spares a stack switch and improves cache usage on softirq
 583           processing.
 584
 585 config PGTABLE_LEVELS
 586         int
 587         default 2
 588
 589 config ARCH_HAS_ELF_RANDOMIZE
 590         bool
 591         help
 592           An architecture supports choosing randomized locations for
 593           stack, mmap, brk, and ET_DYN. Defined functions:
 594           - arch_mmap_rnd()
 595           - arch_randomize_brk()
 596
 597 config HAVE_ARCH_MMAP_RND_BITS
 598         bool
 599         help
 600           An arch should select this symbol if it supports setting a variable
 601           number of bits for use in establishing the base address for mmap
 602           allocations, has MMU enabled and provides values for both:
 603           - ARCH_MMAP_RND_BITS_MIN
 604           - ARCH_MMAP_RND_BITS_MAX
 605
 606 config HAVE_EXIT_THREAD
 607         bool
 608         help
 609           An architecture implements exit_thread.
 610
 611 config ARCH_MMAP_RND_BITS_MIN
 612         int
 613
 614 config ARCH_MMAP_RND_BITS_MAX
 615         int
 616
 617 config ARCH_MMAP_RND_BITS_DEFAULT
 618         int
 619
 620 config ARCH_MMAP_RND_BITS
 621         int "Number of bits to use for ASLR of mmap base address" if EXPERT
 622         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
 623         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
 624         default ARCH_MMAP_RND_BITS_MIN
 625         depends on HAVE_ARCH_MMAP_RND_BITS
 626         help
 627           This value can be used to select the number of bits to use to
 628           determine the random offset to the base address of vma regions
 629           resulting from mmap allocations. This value will be bounded
 630           by the architecture's minimum and maximum supported values.
 631
 632           This value can be changed after boot using the
 633           /proc/sys/vm/mmap_rnd_bits tunable
 634
 635 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
 636         bool
 637         help
 638           An arch should select this symbol if it supports running applications
 639           in compatibility mode, supports setting a variable number of bits for
 640           use in establishing the base address for mmap allocations, has MMU
 641           enabled and provides values for both:
 642           - ARCH_MMAP_RND_COMPAT_BITS_MIN
 643           - ARCH_MMAP_RND_COMPAT_BITS_MAX
 644
 645 config ARCH_MMAP_RND_COMPAT_BITS_MIN
 646         int
 647
 648 config ARCH_MMAP_RND_COMPAT_BITS_MAX
 649         int
 650
 651 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 652         int
 653
 654 config ARCH_MMAP_RND_COMPAT_BITS
 655         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
 656         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
 657         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 658         default ARCH_MMAP_RND_COMPAT_BITS_MIN
 659         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
 660         help
 661           This value can be used to select the number of bits to use to
 662           determine the random offset to the base address of vma regions
 663           resulting from mmap allocations for compatible applications This
 664           value will be bounded by the architecture's minimum and maximum
 665           supported values.
 666
 667           This value can be changed after boot using the
 668           /proc/sys/vm/mmap_rnd_compat_bits tunable
 669
 670 config HAVE_ARCH_COMPAT_MMAP_BASES
 671         bool
 672         help
 673           This allows 64bit applications to invoke 32-bit mmap() syscall
 674           and vice-versa 32-bit applications to call 64-bit mmap().
 675           Required for applications doing different bitness syscalls.
 676
 677 config HAVE_COPY_THREAD_TLS
 678         bool
 679         help
 680           Architecture provides copy_thread_tls to accept tls argument via
 681           normal C parameter passing, rather than extracting the syscall
 682           argument from pt_regs.
 683
 684 config HAVE_STACK_VALIDATION
 685         bool
 686         help
 687           Architecture supports the 'objtool check' host tool command, which
 688           performs compile-time stack metadata validation.
 689
 690 config HAVE_RELIABLE_STACKTRACE
 691         bool
 692         help
 693           Architecture has a save_stack_trace_tsk_reliable() function which
 694           only returns a stack trace if it can guarantee the trace is reliable.
 695
 696 config HAVE_ARCH_HASH
 697         bool
 698         default n
 699         help
 700           If this is set, the architecture provides an <asm/hash.h>
 701           file which provides platform-specific implementations of some
 702           functions in <linux/hash.h> or fs/namei.c.
 703
 704 config ISA_BUS_API
 705         def_bool ISA
 706
 707 #
 708 # ABI hall of shame
 709 #
 710 config CLONE_BACKWARDS
 711         bool
 712         help
 713           Architecture has tls passed as the 4th argument of clone(2),
 714           not the 5th one.
 715
 716 config CLONE_BACKWARDS2
 717         bool
 718         help
 719           Architecture has the first two arguments of clone(2) swapped.
 720
 721 config CLONE_BACKWARDS3
 722         bool
 723         help
 724           Architecture has tls passed as the 3rd argument of clone(2),
 725           not the 5th one.
 726
 727 config ODD_RT_SIGACTION
 728         bool
 729         help
 730           Architecture has unusual rt_sigaction(2) arguments
 731
 732 config OLD_SIGSUSPEND
 733         bool
 734         help
 735           Architecture has old sigsuspend(2) syscall, of one-argument variety
 736
 737 config OLD_SIGSUSPEND3
 738         bool
 739         help
 740           Even weirder antique ABI - three-argument sigsuspend(2)
 741
 742 config OLD_SIGACTION
 743         bool
 744         help
 745           Architecture has old sigaction(2) syscall.  Nope, not the same
 746           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
 747           but fairly different variant of sigaction(2), thanks to OSF/1
 748           compatibility...
 749
 750 config COMPAT_OLD_SIGACTION
 751         bool
 752
 753 config 64BIT_TIME
 754         def_bool ARCH_HAS_64BIT_TIME
 755         help
 756           This should be selected by all architectures that need to support
 757           new system calls with a 64-bit time_t. This is relevant on all 32-bit
 758           architectures, and 64-bit architectures as part of compat syscall
 759           handling.
 760
 761 config COMPAT_32BIT_TIME
 762         def_bool (!64BIT && 64BIT_TIME) || COMPAT
 763         help
 764           This enables 32 bit time_t support in addition to 64 bit time_t support.
 765           This is relevant on all 32-bit architectures, and 64-bit architectures
 766           as part of compat syscall handling.
 767
 768 config ARCH_NO_COHERENT_DMA_MMAP
 769         bool
 770
 771 config ARCH_NO_PREEMPT
 772         bool
 773
 774 config CPU_NO_EFFICIENT_FFS
 775         def_bool n
 776
 777 config HAVE_ARCH_VMAP_STACK
 778         def_bool n
 779         help
 780           An arch should select this symbol if it can support kernel stacks
 781           in vmalloc space.  This means:
 782
 783           - vmalloc space must be large enough to hold many kernel stacks.
 784             This may rule out many 32-bit architectures.
 785
 786           - Stacks in vmalloc space need to work reliably.  For example, if
 787             vmap page tables are created on demand, either this mechanism
 788             needs to work while the stack points to a virtual address with
 789             unpopulated page tables or arch code (switch_to() and switch_mm(),
 790             most likely) needs to ensure that the stack's page table entries
 791             are populated before running on a possibly unpopulated stack.
 792
 793           - If the stack overflows into a guard page, something reasonable
 794             should happen.  The definition of "reasonable" is flexible, but
 795             instantly rebooting without logging anything would be unfriendly.
 796
 797 config VMAP_STACK
 798         default y
 799         bool "Use a virtually-mapped stack"
 800         depends on HAVE_ARCH_VMAP_STACK && !KASAN
 801         ---help---
 802           Enable this if you want the use virtually-mapped kernel stacks
 803           with guard pages.  This causes kernel stack overflows to be
 804           caught immediately rather than causing difficult-to-diagnose
 805           corruption.
 806
 807           This is presently incompatible with KASAN because KASAN expects
 808           the stack to map directly to the KASAN shadow map using a formula
 809           that is incorrect if the stack is in vmalloc space.
 810
 811 config ARCH_OPTIONAL_KERNEL_RWX
 812         def_bool n
 813
 814 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 815         def_bool n
 816
 817 config ARCH_HAS_STRICT_KERNEL_RWX
 818         def_bool n
 819
 820 config STRICT_KERNEL_RWX
 821         bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
 822         depends on ARCH_HAS_STRICT_KERNEL_RWX
 823         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 824         help
 825           If this is set, kernel text and rodata memory will be made read-only,
 826           and non-text memory will be made non-executable. This provides
 827           protection against certain security exploits (e.g. executing the heap
 828           or modifying text)
 829
 830           These features are considered standard security practice these days.
 831           You should say Y here in almost all cases.
 832
 833 config ARCH_HAS_STRICT_MODULE_RWX
 834         def_bool n
 835
 836 config STRICT_MODULE_RWX
 837         bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
 838         depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
 839         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 840         help
 841           If this is set, module text and rodata memory will be made read-only,
 842           and non-text memory will be made non-executable. This provides
 843           protection against certain security exploits (e.g. writing to text)
 844
 845 # select if the architecture provides an asm/dma-direct.h header
 846 config ARCH_HAS_PHYS_TO_DMA
 847         bool
 848
 849 config ARCH_HAS_REFCOUNT
 850         bool
 851         help
 852           An architecture selects this when it has implemented refcount_t
 853           using open coded assembly primitives that provide an optimized
 854           refcount_t implementation, possibly at the expense of some full
 855           refcount state checks of CONFIG_REFCOUNT_FULL=y.
 856
 857           The refcount overflow check behavior, however, must be retained.
 858           Catching overflows is the primary security concern for protecting
 859           against bugs in reference counts.
 860
 861 config REFCOUNT_FULL
 862         bool "Perform full reference count validation at the expense of speed"
 863         help
 864           Enabling this switches the refcounting infrastructure from a fast
 865           unchecked atomic_t implementation to a fully state checked
 866           implementation, which can be (slightly) slower but provides protections
 867           against various use-after-free conditions that can be used in
 868           security flaw exploits.
 869
 870 config HAVE_ARCH_COMPILER_H
 871         bool
 872         help
 873           An architecture can select this if it provides an
 874           asm/compiler.h header that should be included after
 875           linux/compiler-*.h in order to override macro definitions that those
 876           headers generally provide.
 877
 878 config HAVE_ARCH_PREL32_RELOCATIONS
 879         bool
 880         help
 881           May be selected by an architecture if it supports place-relative
 882           32-bit relocations, both in the toolchain and in the module loader,
 883           in which case relative references can be used in special sections
 884           for PCI fixup, initcalls etc which are only half the size on 64 bit
 885           architectures, and don't require runtime relocation on relocatable
 886           kernels.
 887
 888 source "kernel/gcov/Kconfig"
 889
 890 source "scripts/gcc-plugins/Kconfig"
 891
 892 endmenu