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 ARCH_32BIT_OFF_T
 280         bool
 281         depends on !64BIT
 282         help
 283           All new 32-bit architectures should have 64-bit off_t type on
 284           userspace side which corresponds to the loff_t kernel type. This
 285           is the requirement for modern ABIs. Some existing architectures
 286           still support 32-bit off_t. This option is enabled for all such
 287           architectures explicitly.
 288
 289 config HAVE_REGS_AND_STACK_ACCESS_API
 290         bool
 291         help
 292           This symbol should be selected by an architecure if it supports
 293           the API needed to access registers and stack entries from pt_regs,
 294           declared in asm/ptrace.h
 295           For example the kprobes-based event tracer needs this API.
 296
 297 config HAVE_RSEQ
 298         bool
 299         depends on HAVE_REGS_AND_STACK_ACCESS_API
 300         help
 301           This symbol should be selected by an architecture if it
 302           supports an implementation of restartable sequences.
 303
 304 config HAVE_FUNCTION_ARG_ACCESS_API
 305         bool
 306         help
 307           This symbol should be selected by an architecure if it supports
 308           the API needed to access function arguments from pt_regs,
 309           declared in asm/ptrace.h
 310
 311 config HAVE_CLK
 312         bool
 313         help
 314           The <linux/clk.h> calls support software clock gating and
 315           thus are a key power management tool on many systems.
 316
 317 config HAVE_HW_BREAKPOINT
 318         bool
 319         depends on PERF_EVENTS
 320
 321 config HAVE_MIXED_BREAKPOINTS_REGS
 322         bool
 323         depends on HAVE_HW_BREAKPOINT
 324         help
 325           Depending on the arch implementation of hardware breakpoints,
 326           some of them have separate registers for data and instruction
 327           breakpoints addresses, others have mixed registers to store
 328           them but define the access type in a control register.
 329           Select this option if your arch implements breakpoints under the
 330           latter fashion.
 331
 332 config HAVE_USER_RETURN_NOTIFIER
 333         bool
 334
 335 config HAVE_PERF_EVENTS_NMI
 336         bool
 337         help
 338           System hardware can generate an NMI using the perf event
 339           subsystem.  Also has support for calculating CPU cycle events
 340           to determine how many clock cycles in a given period.
 341
 342 config HAVE_HARDLOCKUP_DETECTOR_PERF
 343         bool
 344         depends on HAVE_PERF_EVENTS_NMI
 345         help
 346           The arch chooses to use the generic perf-NMI-based hardlockup
 347           detector. Must define HAVE_PERF_EVENTS_NMI.
 348
 349 config HAVE_NMI_WATCHDOG
 350         depends on HAVE_NMI
 351         bool
 352         help
 353           The arch provides a low level NMI watchdog. It provides
 354           asm/nmi.h, and defines its own arch_touch_nmi_watchdog().
 355
 356 config HAVE_HARDLOCKUP_DETECTOR_ARCH
 357         bool
 358         select HAVE_NMI_WATCHDOG
 359         help
 360           The arch chooses to provide its own hardlockup detector, which is
 361           a superset of the HAVE_NMI_WATCHDOG. It also conforms to config
 362           interfaces and parameters provided by hardlockup detector subsystem.
 363
 364 config HAVE_PERF_REGS
 365         bool
 366         help
 367           Support selective register dumps for perf events. This includes
 368           bit-mapping of each registers and a unique architecture id.
 369
 370 config HAVE_PERF_USER_STACK_DUMP
 371         bool
 372         help
 373           Support user stack dumps for perf event samples. This needs
 374           access to the user stack pointer which is not unified across
 375           architectures.
 376
 377 config HAVE_ARCH_JUMP_LABEL
 378         bool
 379
 380 config HAVE_ARCH_JUMP_LABEL_RELATIVE
 381         bool
 382
 383 config HAVE_RCU_TABLE_FREE
 384         bool
 385
 386 config HAVE_RCU_TABLE_INVALIDATE
 387         bool
 388
 389 config ARCH_HAVE_NMI_SAFE_CMPXCHG
 390         bool
 391
 392 config HAVE_ALIGNED_STRUCT_PAGE
 393         bool
 394         help
 395           This makes sure that struct pages are double word aligned and that
 396           e.g. the SLUB allocator can perform double word atomic operations
 397           on a struct page for better performance. However selecting this
 398           might increase the size of a struct page by a word.
 399
 400 config HAVE_CMPXCHG_LOCAL
 401         bool
 402
 403 config HAVE_CMPXCHG_DOUBLE
 404         bool
 405
 406 config ARCH_WEAK_RELEASE_ACQUIRE
 407         bool
 408
 409 config ARCH_WANT_IPC_PARSE_VERSION
 410         bool
 411
 412 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 413         bool
 414
 415 config ARCH_WANT_OLD_COMPAT_IPC
 416         select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 417         bool
 418
 419 config HAVE_ARCH_SECCOMP_FILTER
 420         bool
 421         help
 422           An arch should select this symbol if it provides all of these things:
 423           - syscall_get_arch()
 424           - syscall_get_arguments()
 425           - syscall_rollback()
 426           - syscall_set_return_value()
 427           - SIGSYS siginfo_t support
 428           - secure_computing is called from a ptrace_event()-safe context
 429           - secure_computing return value is checked and a return value of -1
 430             results in the system call being skipped immediately.
 431           - seccomp syscall wired up
 432
 433 config SECCOMP_FILTER
 434         def_bool y
 435         depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
 436         help
 437           Enable tasks to build secure computing environments defined
 438           in terms of Berkeley Packet Filter programs which implement
 439           task-defined system call filtering polices.
 440
 441           See Documentation/userspace-api/seccomp_filter.rst for details.
 442
 443 config HAVE_ARCH_STACKLEAK
 444         bool
 445         help
 446           An architecture should select this if it has the code which
 447           fills the used part of the kernel stack with the STACKLEAK_POISON
 448           value before returning from system calls.
 449
 450 config HAVE_STACKPROTECTOR
 451         bool
 452         help
 453           An arch should select this symbol if:
 454           - it has implemented a stack canary (e.g. __stack_chk_guard)
 455
 456 config CC_HAS_STACKPROTECTOR_NONE
 457         def_bool $(cc-option,-fno-stack-protector)
 458
 459 config STACKPROTECTOR
 460         bool "Stack Protector buffer overflow detection"
 461         depends on HAVE_STACKPROTECTOR
 462         depends on $(cc-option,-fstack-protector)
 463         default y
 464         help
 465           This option turns on the "stack-protector" GCC feature. This
 466           feature puts, at the beginning of functions, a canary value on
 467           the stack just before the return address, and validates
 468           the value just before actually returning.  Stack based buffer
 469           overflows (that need to overwrite this return address) now also
 470           overwrite the canary, which gets detected and the attack is then
 471           neutralized via a kernel panic.
 472
 473           Functions will have the stack-protector canary logic added if they
 474           have an 8-byte or larger character array on the stack.
 475
 476           This feature requires gcc version 4.2 or above, or a distribution
 477           gcc with the feature backported ("-fstack-protector").
 478
 479           On an x86 "defconfig" build, this feature adds canary checks to
 480           about 3% of all kernel functions, which increases kernel code size
 481           by about 0.3%.
 482
 483 config STACKPROTECTOR_STRONG
 484         bool "Strong Stack Protector"
 485         depends on STACKPROTECTOR
 486         depends on $(cc-option,-fstack-protector-strong)
 487         default y
 488         help
 489           Functions will have the stack-protector canary logic added in any
 490           of the following conditions:
 491
 492           - local variable's address used as part of the right hand side of an
 493             assignment or function argument
 494           - local variable is an array (or union containing an array),
 495             regardless of array type or length
 496           - uses register local variables
 497
 498           This feature requires gcc version 4.9 or above, or a distribution
 499           gcc with the feature backported ("-fstack-protector-strong").
 500
 501           On an x86 "defconfig" build, this feature adds canary checks to
 502           about 20% of all kernel functions, which increases the kernel code
 503           size by about 2%.
 504
 505 config HAVE_ARCH_WITHIN_STACK_FRAMES
 506         bool
 507         help
 508           An architecture should select this if it can walk the kernel stack
 509           frames to determine if an object is part of either the arguments
 510           or local variables (i.e. that it excludes saved return addresses,
 511           and similar) by implementing an inline arch_within_stack_frames(),
 512           which is used by CONFIG_HARDENED_USERCOPY.
 513
 514 config HAVE_CONTEXT_TRACKING
 515         bool
 516         help
 517           Provide kernel/user boundaries probes necessary for subsystems
 518           that need it, such as userspace RCU extended quiescent state.
 519           Syscalls need to be wrapped inside user_exit()-user_enter() through
 520           the slow path using TIF_NOHZ flag. Exceptions handlers must be
 521           wrapped as well. Irqs are already protected inside
 522           rcu_irq_enter/rcu_irq_exit() but preemption or signal handling on
 523           irq exit still need to be protected.
 524
 525 config HAVE_VIRT_CPU_ACCOUNTING
 526         bool
 527
 528 config ARCH_HAS_SCALED_CPUTIME
 529         bool
 530
 531 config HAVE_VIRT_CPU_ACCOUNTING_GEN
 532         bool
 533         default y if 64BIT
 534         help
 535           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 536           Before enabling this option, arch code must be audited
 537           to ensure there are no races in concurrent read/write of
 538           cputime_t. For example, reading/writing 64-bit cputime_t on
 539           some 32-bit arches may require multiple accesses, so proper
 540           locking is needed to protect against concurrent accesses.
 541
 542
 543 config HAVE_IRQ_TIME_ACCOUNTING
 544         bool
 545         help
 546           Archs need to ensure they use a high enough resolution clock to
 547           support irq time accounting and then call enable_sched_clock_irqtime().
 548
 549 config HAVE_MOVE_PMD
 550         bool
 551         help
 552           Archs that select this are able to move page tables at the PMD level.
 553
 554 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 555         bool
 556
 557 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 558         bool
 559
 560 config HAVE_ARCH_HUGE_VMAP
 561         bool
 562
 563 config HAVE_ARCH_SOFT_DIRTY
 564         bool
 565
 566 config HAVE_MOD_ARCH_SPECIFIC
 567         bool
 568         help
 569           The arch uses struct mod_arch_specific to store data.  Many arches
 570           just need a simple module loader without arch specific data - those
 571           should not enable this.
 572
 573 config MODULES_USE_ELF_RELA
 574         bool
 575         help
 576           Modules only use ELF RELA relocations.  Modules with ELF REL
 577           relocations will give an error.
 578
 579 config MODULES_USE_ELF_REL
 580         bool
 581         help
 582           Modules only use ELF REL relocations.  Modules with ELF RELA
 583           relocations will give an error.
 584
 585 config HAVE_IRQ_EXIT_ON_IRQ_STACK
 586         bool
 587         help
 588           Architecture doesn't only execute the irq handler on the irq stack
 589           but also irq_exit(). This way we can process softirqs on this irq
 590           stack instead of switching to a new one when we call __do_softirq()
 591           in the end of an hardirq.
 592           This spares a stack switch and improves cache usage on softirq
 593           processing.
 594
 595 config PGTABLE_LEVELS
 596         int
 597         default 2
 598
 599 config ARCH_HAS_ELF_RANDOMIZE
 600         bool
 601         help
 602           An architecture supports choosing randomized locations for
 603           stack, mmap, brk, and ET_DYN. Defined functions:
 604           - arch_mmap_rnd()
 605           - arch_randomize_brk()
 606
 607 config HAVE_ARCH_MMAP_RND_BITS
 608         bool
 609         help
 610           An arch should select this symbol if it supports setting a variable
 611           number of bits for use in establishing the base address for mmap
 612           allocations, has MMU enabled and provides values for both:
 613           - ARCH_MMAP_RND_BITS_MIN
 614           - ARCH_MMAP_RND_BITS_MAX
 615
 616 config HAVE_EXIT_THREAD
 617         bool
 618         help
 619           An architecture implements exit_thread.
 620
 621 config ARCH_MMAP_RND_BITS_MIN
 622         int
 623
 624 config ARCH_MMAP_RND_BITS_MAX
 625         int
 626
 627 config ARCH_MMAP_RND_BITS_DEFAULT
 628         int
 629
 630 config ARCH_MMAP_RND_BITS
 631         int "Number of bits to use for ASLR of mmap base address" if EXPERT
 632         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
 633         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
 634         default ARCH_MMAP_RND_BITS_MIN
 635         depends on HAVE_ARCH_MMAP_RND_BITS
 636         help
 637           This value can be used to select the number of bits to use to
 638           determine the random offset to the base address of vma regions
 639           resulting from mmap allocations. This value will be bounded
 640           by the architecture's minimum and maximum supported values.
 641
 642           This value can be changed after boot using the
 643           /proc/sys/vm/mmap_rnd_bits tunable
 644
 645 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
 646         bool
 647         help
 648           An arch should select this symbol if it supports running applications
 649           in compatibility mode, supports setting a variable number of bits for
 650           use in establishing the base address for mmap allocations, has MMU
 651           enabled and provides values for both:
 652           - ARCH_MMAP_RND_COMPAT_BITS_MIN
 653           - ARCH_MMAP_RND_COMPAT_BITS_MAX
 654
 655 config ARCH_MMAP_RND_COMPAT_BITS_MIN
 656         int
 657
 658 config ARCH_MMAP_RND_COMPAT_BITS_MAX
 659         int
 660
 661 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 662         int
 663
 664 config ARCH_MMAP_RND_COMPAT_BITS
 665         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
 666         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
 667         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 668         default ARCH_MMAP_RND_COMPAT_BITS_MIN
 669         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
 670         help
 671           This value can be used to select the number of bits to use to
 672           determine the random offset to the base address of vma regions
 673           resulting from mmap allocations for compatible applications This
 674           value will be bounded by the architecture's minimum and maximum
 675           supported values.
 676
 677           This value can be changed after boot using the
 678           /proc/sys/vm/mmap_rnd_compat_bits tunable
 679
 680 config HAVE_ARCH_COMPAT_MMAP_BASES
 681         bool
 682         help
 683           This allows 64bit applications to invoke 32-bit mmap() syscall
 684           and vice-versa 32-bit applications to call 64-bit mmap().
 685           Required for applications doing different bitness syscalls.
 686
 687 config HAVE_COPY_THREAD_TLS
 688         bool
 689         help
 690           Architecture provides copy_thread_tls to accept tls argument via
 691           normal C parameter passing, rather than extracting the syscall
 692           argument from pt_regs.
 693
 694 config HAVE_STACK_VALIDATION
 695         bool
 696         help
 697           Architecture supports the 'objtool check' host tool command, which
 698           performs compile-time stack metadata validation.
 699
 700 config HAVE_RELIABLE_STACKTRACE
 701         bool
 702         help
 703           Architecture has a save_stack_trace_tsk_reliable() function which
 704           only returns a stack trace if it can guarantee the trace is reliable.
 705
 706 config HAVE_ARCH_HASH
 707         bool
 708         default n
 709         help
 710           If this is set, the architecture provides an <asm/hash.h>
 711           file which provides platform-specific implementations of some
 712           functions in <linux/hash.h> or fs/namei.c.
 713
 714 config HAVE_ARCH_NVRAM_OPS
 715         bool
 716
 717 config ISA_BUS_API
 718         def_bool ISA
 719
 720 #
 721 # ABI hall of shame
 722 #
 723 config CLONE_BACKWARDS
 724         bool
 725         help
 726           Architecture has tls passed as the 4th argument of clone(2),
 727           not the 5th one.
 728
 729 config CLONE_BACKWARDS2
 730         bool
 731         help
 732           Architecture has the first two arguments of clone(2) swapped.
 733
 734 config CLONE_BACKWARDS3
 735         bool
 736         help
 737           Architecture has tls passed as the 3rd argument of clone(2),
 738           not the 5th one.
 739
 740 config ODD_RT_SIGACTION
 741         bool
 742         help
 743           Architecture has unusual rt_sigaction(2) arguments
 744
 745 config OLD_SIGSUSPEND
 746         bool
 747         help
 748           Architecture has old sigsuspend(2) syscall, of one-argument variety
 749
 750 config OLD_SIGSUSPEND3
 751         bool
 752         help
 753           Even weirder antique ABI - three-argument sigsuspend(2)
 754
 755 config OLD_SIGACTION
 756         bool
 757         help
 758           Architecture has old sigaction(2) syscall.  Nope, not the same
 759           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
 760           but fairly different variant of sigaction(2), thanks to OSF/1
 761           compatibility...
 762
 763 config COMPAT_OLD_SIGACTION
 764         bool
 765
 766 config 64BIT_TIME
 767         def_bool ARCH_HAS_64BIT_TIME
 768         help
 769           This should be selected by all architectures that need to support
 770           new system calls with a 64-bit time_t. This is relevant on all 32-bit
 771           architectures, and 64-bit architectures as part of compat syscall
 772           handling.
 773
 774 config COMPAT_32BIT_TIME
 775         def_bool !64BIT || COMPAT
 776         help
 777           This enables 32 bit time_t support in addition to 64 bit time_t support.
 778           This is relevant on all 32-bit architectures, and 64-bit architectures
 779           as part of compat syscall handling.
 780
 781 config ARCH_NO_COHERENT_DMA_MMAP
 782         bool
 783
 784 config ARCH_NO_PREEMPT
 785         bool
 786
 787 config CPU_NO_EFFICIENT_FFS
 788         def_bool n
 789
 790 config HAVE_ARCH_VMAP_STACK
 791         def_bool n
 792         help
 793           An arch should select this symbol if it can support kernel stacks
 794           in vmalloc space.  This means:
 795
 796           - vmalloc space must be large enough to hold many kernel stacks.
 797             This may rule out many 32-bit architectures.
 798
 799           - Stacks in vmalloc space need to work reliably.  For example, if
 800             vmap page tables are created on demand, either this mechanism
 801             needs to work while the stack points to a virtual address with
 802             unpopulated page tables or arch code (switch_to() and switch_mm(),
 803             most likely) needs to ensure that the stack's page table entries
 804             are populated before running on a possibly unpopulated stack.
 805
 806           - If the stack overflows into a guard page, something reasonable
 807             should happen.  The definition of "reasonable" is flexible, but
 808             instantly rebooting without logging anything would be unfriendly.
 809
 810 config VMAP_STACK
 811         default y
 812         bool "Use a virtually-mapped stack"
 813         depends on HAVE_ARCH_VMAP_STACK && !KASAN
 814         ---help---
 815           Enable this if you want the use virtually-mapped kernel stacks
 816           with guard pages.  This causes kernel stack overflows to be
 817           caught immediately rather than causing difficult-to-diagnose
 818           corruption.
 819
 820           This is presently incompatible with KASAN because KASAN expects
 821           the stack to map directly to the KASAN shadow map using a formula
 822           that is incorrect if the stack is in vmalloc space.
 823
 824 config ARCH_OPTIONAL_KERNEL_RWX
 825         def_bool n
 826
 827 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 828         def_bool n
 829
 830 config ARCH_HAS_STRICT_KERNEL_RWX
 831         def_bool n
 832
 833 config STRICT_KERNEL_RWX
 834         bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
 835         depends on ARCH_HAS_STRICT_KERNEL_RWX
 836         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 837         help
 838           If this is set, kernel text and rodata memory will be made read-only,
 839           and non-text memory will be made non-executable. This provides
 840           protection against certain security exploits (e.g. executing the heap
 841           or modifying text)
 842
 843           These features are considered standard security practice these days.
 844           You should say Y here in almost all cases.
 845
 846 config ARCH_HAS_STRICT_MODULE_RWX
 847         def_bool n
 848
 849 config STRICT_MODULE_RWX
 850         bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
 851         depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
 852         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 853         help
 854           If this is set, module text and rodata memory will be made read-only,
 855           and non-text memory will be made non-executable. This provides
 856           protection against certain security exploits (e.g. writing to text)
 857
 858 # select if the architecture provides an asm/dma-direct.h header
 859 config ARCH_HAS_PHYS_TO_DMA
 860         bool
 861
 862 config ARCH_HAS_REFCOUNT
 863         bool
 864         help
 865           An architecture selects this when it has implemented refcount_t
 866           using open coded assembly primitives that provide an optimized
 867           refcount_t implementation, possibly at the expense of some full
 868           refcount state checks of CONFIG_REFCOUNT_FULL=y.
 869
 870           The refcount overflow check behavior, however, must be retained.
 871           Catching overflows is the primary security concern for protecting
 872           against bugs in reference counts.
 873
 874 config REFCOUNT_FULL
 875         bool "Perform full reference count validation at the expense of speed"
 876         help
 877           Enabling this switches the refcounting infrastructure from a fast
 878           unchecked atomic_t implementation to a fully state checked
 879           implementation, which can be (slightly) slower but provides protections
 880           against various use-after-free conditions that can be used in
 881           security flaw exploits.
 882
 883 config HAVE_ARCH_COMPILER_H
 884         bool
 885         help
 886           An architecture can select this if it provides an
 887           asm/compiler.h header that should be included after
 888           linux/compiler-*.h in order to override macro definitions that those
 889           headers generally provide.
 890
 891 config HAVE_ARCH_PREL32_RELOCATIONS
 892         bool
 893         help
 894           May be selected by an architecture if it supports place-relative
 895           32-bit relocations, both in the toolchain and in the module loader,
 896           in which case relative references can be used in special sections
 897           for PCI fixup, initcalls etc which are only half the size on 64 bit
 898           architectures, and don't require runtime relocation on relocatable
 899           kernels.
 900
 901 config ARCH_USE_MEMREMAP_PROT
 902         bool
 903
 904 source "kernel/gcov/Kconfig"
 905
 906 source "scripts/gcc-plugins/Kconfig"
 907
 908 endmenu