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 #
 249 # Select if the arch provides a historic keepinit alias for the retain_initrd
 250 # command line option
 251 #
 252 config ARCH_HAS_KEEPINITRD
 253         bool
 254
 255 # Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
 256 config ARCH_HAS_SET_MEMORY
 257         bool
 258
 259 # Select if arch has all set_direct_map_invalid/default() functions
 260 config ARCH_HAS_SET_DIRECT_MAP
 261         bool
 262
 263 #
 264 # Select if arch has an uncached kernel segment and provides the
 265 # uncached_kernel_address / cached_kernel_address symbols to use it
 266 #
 267 config ARCH_HAS_UNCACHED_SEGMENT
 268         select ARCH_HAS_DMA_PREP_COHERENT
 269         bool
 270
 271 # Select if arch init_task must go in the __init_task_data section
 272 config ARCH_TASK_STRUCT_ON_STACK
 273        bool
 274
 275 # Select if arch has its private alloc_task_struct() function
 276 config ARCH_TASK_STRUCT_ALLOCATOR
 277         bool
 278
 279 config HAVE_ARCH_THREAD_STRUCT_WHITELIST
 280         bool
 281         depends on !ARCH_TASK_STRUCT_ALLOCATOR
 282         help
 283           An architecture should select this to provide hardened usercopy
 284           knowledge about what region of the thread_struct should be
 285           whitelisted for copying to userspace. Normally this is only the
 286           FPU registers. Specifically, arch_thread_struct_whitelist()
 287           should be implemented. Without this, the entire thread_struct
 288           field in task_struct will be left whitelisted.
 289
 290 # Select if arch has its private alloc_thread_stack() function
 291 config ARCH_THREAD_STACK_ALLOCATOR
 292         bool
 293
 294 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
 295 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
 296         bool
 297
 298 config ARCH_32BIT_OFF_T
 299         bool
 300         depends on !64BIT
 301         help
 302           All new 32-bit architectures should have 64-bit off_t type on
 303           userspace side which corresponds to the loff_t kernel type. This
 304           is the requirement for modern ABIs. Some existing architectures
 305           still support 32-bit off_t. This option is enabled for all such
 306           architectures explicitly.
 307
 308 config HAVE_REGS_AND_STACK_ACCESS_API
 309         bool
 310         help
 311           This symbol should be selected by an architecure if it supports
 312           the API needed to access registers and stack entries from pt_regs,
 313           declared in asm/ptrace.h
 314           For example the kprobes-based event tracer needs this API.
 315
 316 config HAVE_RSEQ
 317         bool
 318         depends on HAVE_REGS_AND_STACK_ACCESS_API
 319         help
 320           This symbol should be selected by an architecture if it
 321           supports an implementation of restartable sequences.
 322
 323 config HAVE_FUNCTION_ARG_ACCESS_API
 324         bool
 325         help
 326           This symbol should be selected by an architecure if it supports
 327           the API needed to access function arguments from pt_regs,
 328           declared in asm/ptrace.h
 329
 330 config HAVE_CLK
 331         bool
 332         help
 333           The <linux/clk.h> calls support software clock gating and
 334           thus are a key power management tool on many systems.
 335
 336 config HAVE_HW_BREAKPOINT
 337         bool
 338         depends on PERF_EVENTS
 339
 340 config HAVE_MIXED_BREAKPOINTS_REGS
 341         bool
 342         depends on HAVE_HW_BREAKPOINT
 343         help
 344           Depending on the arch implementation of hardware breakpoints,
 345           some of them have separate registers for data and instruction
 346           breakpoints addresses, others have mixed registers to store
 347           them but define the access type in a control register.
 348           Select this option if your arch implements breakpoints under the
 349           latter fashion.
 350
 351 config HAVE_USER_RETURN_NOTIFIER
 352         bool
 353
 354 config HAVE_PERF_EVENTS_NMI
 355         bool
 356         help
 357           System hardware can generate an NMI using the perf event
 358           subsystem.  Also has support for calculating CPU cycle events
 359           to determine how many clock cycles in a given period.
 360
 361 config HAVE_HARDLOCKUP_DETECTOR_PERF
 362         bool
 363         depends on HAVE_PERF_EVENTS_NMI
 364         help
 365           The arch chooses to use the generic perf-NMI-based hardlockup
 366           detector. Must define HAVE_PERF_EVENTS_NMI.
 367
 368 config HAVE_NMI_WATCHDOG
 369         depends on HAVE_NMI
 370         bool
 371         help
 372           The arch provides a low level NMI watchdog. It provides
 373           asm/nmi.h, and defines its own arch_touch_nmi_watchdog().
 374
 375 config HAVE_HARDLOCKUP_DETECTOR_ARCH
 376         bool
 377         select HAVE_NMI_WATCHDOG
 378         help
 379           The arch chooses to provide its own hardlockup detector, which is
 380           a superset of the HAVE_NMI_WATCHDOG. It also conforms to config
 381           interfaces and parameters provided by hardlockup detector subsystem.
 382
 383 config HAVE_PERF_REGS
 384         bool
 385         help
 386           Support selective register dumps for perf events. This includes
 387           bit-mapping of each registers and a unique architecture id.
 388
 389 config HAVE_PERF_USER_STACK_DUMP
 390         bool
 391         help
 392           Support user stack dumps for perf event samples. This needs
 393           access to the user stack pointer which is not unified across
 394           architectures.
 395
 396 config HAVE_ARCH_JUMP_LABEL
 397         bool
 398
 399 config HAVE_ARCH_JUMP_LABEL_RELATIVE
 400         bool
 401
 402 config HAVE_RCU_TABLE_FREE
 403         bool
 404
 405 config HAVE_RCU_TABLE_NO_INVALIDATE
 406         bool
 407
 408 config HAVE_MMU_GATHER_PAGE_SIZE
 409         bool
 410
 411 config HAVE_MMU_GATHER_NO_GATHER
 412         bool
 413
 414 config ARCH_HAVE_NMI_SAFE_CMPXCHG
 415         bool
 416
 417 config HAVE_ALIGNED_STRUCT_PAGE
 418         bool
 419         help
 420           This makes sure that struct pages are double word aligned and that
 421           e.g. the SLUB allocator can perform double word atomic operations
 422           on a struct page for better performance. However selecting this
 423           might increase the size of a struct page by a word.
 424
 425 config HAVE_CMPXCHG_LOCAL
 426         bool
 427
 428 config HAVE_CMPXCHG_DOUBLE
 429         bool
 430
 431 config ARCH_WEAK_RELEASE_ACQUIRE
 432         bool
 433
 434 config ARCH_WANT_IPC_PARSE_VERSION
 435         bool
 436
 437 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 438         bool
 439
 440 config ARCH_WANT_OLD_COMPAT_IPC
 441         select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 442         bool
 443
 444 config HAVE_ARCH_SECCOMP_FILTER
 445         bool
 446         help
 447           An arch should select this symbol if it provides all of these things:
 448           - syscall_get_arch()
 449           - syscall_get_arguments()
 450           - syscall_rollback()
 451           - syscall_set_return_value()
 452           - SIGSYS siginfo_t support
 453           - secure_computing is called from a ptrace_event()-safe context
 454           - secure_computing return value is checked and a return value of -1
 455             results in the system call being skipped immediately.
 456           - seccomp syscall wired up
 457
 458 config SECCOMP_FILTER
 459         def_bool y
 460         depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
 461         help
 462           Enable tasks to build secure computing environments defined
 463           in terms of Berkeley Packet Filter programs which implement
 464           task-defined system call filtering polices.
 465
 466           See Documentation/userspace-api/seccomp_filter.rst for details.
 467
 468 config HAVE_ARCH_STACKLEAK
 469         bool
 470         help
 471           An architecture should select this if it has the code which
 472           fills the used part of the kernel stack with the STACKLEAK_POISON
 473           value before returning from system calls.
 474
 475 config HAVE_STACKPROTECTOR
 476         bool
 477         help
 478           An arch should select this symbol if:
 479           - it has implemented a stack canary (e.g. __stack_chk_guard)
 480
 481 config CC_HAS_STACKPROTECTOR_NONE
 482         def_bool $(cc-option,-fno-stack-protector)
 483
 484 config STACKPROTECTOR
 485         bool "Stack Protector buffer overflow detection"
 486         depends on HAVE_STACKPROTECTOR
 487         depends on $(cc-option,-fstack-protector)
 488         default y
 489         help
 490           This option turns on the "stack-protector" GCC feature. This
 491           feature puts, at the beginning of functions, a canary value on
 492           the stack just before the return address, and validates
 493           the value just before actually returning.  Stack based buffer
 494           overflows (that need to overwrite this return address) now also
 495           overwrite the canary, which gets detected and the attack is then
 496           neutralized via a kernel panic.
 497
 498           Functions will have the stack-protector canary logic added if they
 499           have an 8-byte or larger character array on the stack.
 500
 501           This feature requires gcc version 4.2 or above, or a distribution
 502           gcc with the feature backported ("-fstack-protector").
 503
 504           On an x86 "defconfig" build, this feature adds canary checks to
 505           about 3% of all kernel functions, which increases kernel code size
 506           by about 0.3%.
 507
 508 config STACKPROTECTOR_STRONG
 509         bool "Strong Stack Protector"
 510         depends on STACKPROTECTOR
 511         depends on $(cc-option,-fstack-protector-strong)
 512         default y
 513         help
 514           Functions will have the stack-protector canary logic added in any
 515           of the following conditions:
 516
 517           - local variable's address used as part of the right hand side of an
 518             assignment or function argument
 519           - local variable is an array (or union containing an array),
 520             regardless of array type or length
 521           - uses register local variables
 522
 523           This feature requires gcc version 4.9 or above, or a distribution
 524           gcc with the feature backported ("-fstack-protector-strong").
 525
 526           On an x86 "defconfig" build, this feature adds canary checks to
 527           about 20% of all kernel functions, which increases the kernel code
 528           size by about 2%.
 529
 530 config HAVE_ARCH_WITHIN_STACK_FRAMES
 531         bool
 532         help
 533           An architecture should select this if it can walk the kernel stack
 534           frames to determine if an object is part of either the arguments
 535           or local variables (i.e. that it excludes saved return addresses,
 536           and similar) by implementing an inline arch_within_stack_frames(),
 537           which is used by CONFIG_HARDENED_USERCOPY.
 538
 539 config HAVE_CONTEXT_TRACKING
 540         bool
 541         help
 542           Provide kernel/user boundaries probes necessary for subsystems
 543           that need it, such as userspace RCU extended quiescent state.
 544           Syscalls need to be wrapped inside user_exit()-user_enter() through
 545           the slow path using TIF_NOHZ flag. Exceptions handlers must be
 546           wrapped as well. Irqs are already protected inside
 547           rcu_irq_enter/rcu_irq_exit() but preemption or signal handling on
 548           irq exit still need to be protected.
 549
 550 config HAVE_VIRT_CPU_ACCOUNTING
 551         bool
 552
 553 config ARCH_HAS_SCALED_CPUTIME
 554         bool
 555
 556 config HAVE_VIRT_CPU_ACCOUNTING_GEN
 557         bool
 558         default y if 64BIT
 559         help
 560           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 561           Before enabling this option, arch code must be audited
 562           to ensure there are no races in concurrent read/write of
 563           cputime_t. For example, reading/writing 64-bit cputime_t on
 564           some 32-bit arches may require multiple accesses, so proper
 565           locking is needed to protect against concurrent accesses.
 566
 567
 568 config HAVE_IRQ_TIME_ACCOUNTING
 569         bool
 570         help
 571           Archs need to ensure they use a high enough resolution clock to
 572           support irq time accounting and then call enable_sched_clock_irqtime().
 573
 574 config HAVE_MOVE_PMD
 575         bool
 576         help
 577           Archs that select this are able to move page tables at the PMD level.
 578
 579 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 580         bool
 581
 582 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 583         bool
 584
 585 config HAVE_ARCH_HUGE_VMAP
 586         bool
 587
 588 config HAVE_ARCH_SOFT_DIRTY
 589         bool
 590
 591 config HAVE_MOD_ARCH_SPECIFIC
 592         bool
 593         help
 594           The arch uses struct mod_arch_specific to store data.  Many arches
 595           just need a simple module loader without arch specific data - those
 596           should not enable this.
 597
 598 config MODULES_USE_ELF_RELA
 599         bool
 600         help
 601           Modules only use ELF RELA relocations.  Modules with ELF REL
 602           relocations will give an error.
 603
 604 config MODULES_USE_ELF_REL
 605         bool
 606         help
 607           Modules only use ELF REL relocations.  Modules with ELF RELA
 608           relocations will give an error.
 609
 610 config HAVE_IRQ_EXIT_ON_IRQ_STACK
 611         bool
 612         help
 613           Architecture doesn't only execute the irq handler on the irq stack
 614           but also irq_exit(). This way we can process softirqs on this irq
 615           stack instead of switching to a new one when we call __do_softirq()
 616           in the end of an hardirq.
 617           This spares a stack switch and improves cache usage on softirq
 618           processing.
 619
 620 config PGTABLE_LEVELS
 621         int
 622         default 2
 623
 624 config ARCH_HAS_ELF_RANDOMIZE
 625         bool
 626         help
 627           An architecture supports choosing randomized locations for
 628           stack, mmap, brk, and ET_DYN. Defined functions:
 629           - arch_mmap_rnd()
 630           - arch_randomize_brk()
 631
 632 config HAVE_ARCH_MMAP_RND_BITS
 633         bool
 634         help
 635           An arch should select this symbol if it supports setting a variable
 636           number of bits for use in establishing the base address for mmap
 637           allocations, has MMU enabled and provides values for both:
 638           - ARCH_MMAP_RND_BITS_MIN
 639           - ARCH_MMAP_RND_BITS_MAX
 640
 641 config HAVE_EXIT_THREAD
 642         bool
 643         help
 644           An architecture implements exit_thread.
 645
 646 config ARCH_MMAP_RND_BITS_MIN
 647         int
 648
 649 config ARCH_MMAP_RND_BITS_MAX
 650         int
 651
 652 config ARCH_MMAP_RND_BITS_DEFAULT
 653         int
 654
 655 config ARCH_MMAP_RND_BITS
 656         int "Number of bits to use for ASLR of mmap base address" if EXPERT
 657         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
 658         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
 659         default ARCH_MMAP_RND_BITS_MIN
 660         depends on HAVE_ARCH_MMAP_RND_BITS
 661         help
 662           This value can be used to select the number of bits to use to
 663           determine the random offset to the base address of vma regions
 664           resulting from mmap allocations. This value will be bounded
 665           by the architecture's minimum and maximum supported values.
 666
 667           This value can be changed after boot using the
 668           /proc/sys/vm/mmap_rnd_bits tunable
 669
 670 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
 671         bool
 672         help
 673           An arch should select this symbol if it supports running applications
 674           in compatibility mode, supports setting a variable number of bits for
 675           use in establishing the base address for mmap allocations, has MMU
 676           enabled and provides values for both:
 677           - ARCH_MMAP_RND_COMPAT_BITS_MIN
 678           - ARCH_MMAP_RND_COMPAT_BITS_MAX
 679
 680 config ARCH_MMAP_RND_COMPAT_BITS_MIN
 681         int
 682
 683 config ARCH_MMAP_RND_COMPAT_BITS_MAX
 684         int
 685
 686 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 687         int
 688
 689 config ARCH_MMAP_RND_COMPAT_BITS
 690         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
 691         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
 692         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 693         default ARCH_MMAP_RND_COMPAT_BITS_MIN
 694         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
 695         help
 696           This value can be used to select the number of bits to use to
 697           determine the random offset to the base address of vma regions
 698           resulting from mmap allocations for compatible applications This
 699           value will be bounded by the architecture's minimum and maximum
 700           supported values.
 701
 702           This value can be changed after boot using the
 703           /proc/sys/vm/mmap_rnd_compat_bits tunable
 704
 705 config HAVE_ARCH_COMPAT_MMAP_BASES
 706         bool
 707         help
 708           This allows 64bit applications to invoke 32-bit mmap() syscall
 709           and vice-versa 32-bit applications to call 64-bit mmap().
 710           Required for applications doing different bitness syscalls.
 711
 712 config HAVE_COPY_THREAD_TLS
 713         bool
 714         help
 715           Architecture provides copy_thread_tls to accept tls argument via
 716           normal C parameter passing, rather than extracting the syscall
 717           argument from pt_regs.
 718
 719 config HAVE_STACK_VALIDATION
 720         bool
 721         help
 722           Architecture supports the 'objtool check' host tool command, which
 723           performs compile-time stack metadata validation.
 724
 725 config HAVE_RELIABLE_STACKTRACE
 726         bool
 727         help
 728           Architecture has a save_stack_trace_tsk_reliable() function which
 729           only returns a stack trace if it can guarantee the trace is reliable.
 730
 731 config HAVE_ARCH_HASH
 732         bool
 733         default n
 734         help
 735           If this is set, the architecture provides an <asm/hash.h>
 736           file which provides platform-specific implementations of some
 737           functions in <linux/hash.h> or fs/namei.c.
 738
 739 config HAVE_ARCH_NVRAM_OPS
 740         bool
 741
 742 config ISA_BUS_API
 743         def_bool ISA
 744
 745 #
 746 # ABI hall of shame
 747 #
 748 config CLONE_BACKWARDS
 749         bool
 750         help
 751           Architecture has tls passed as the 4th argument of clone(2),
 752           not the 5th one.
 753
 754 config CLONE_BACKWARDS2
 755         bool
 756         help
 757           Architecture has the first two arguments of clone(2) swapped.
 758
 759 config CLONE_BACKWARDS3
 760         bool
 761         help
 762           Architecture has tls passed as the 3rd argument of clone(2),
 763           not the 5th one.
 764
 765 config ODD_RT_SIGACTION
 766         bool
 767         help
 768           Architecture has unusual rt_sigaction(2) arguments
 769
 770 config OLD_SIGSUSPEND
 771         bool
 772         help
 773           Architecture has old sigsuspend(2) syscall, of one-argument variety
 774
 775 config OLD_SIGSUSPEND3
 776         bool
 777         help
 778           Even weirder antique ABI - three-argument sigsuspend(2)
 779
 780 config OLD_SIGACTION
 781         bool
 782         help
 783           Architecture has old sigaction(2) syscall.  Nope, not the same
 784           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
 785           but fairly different variant of sigaction(2), thanks to OSF/1
 786           compatibility...
 787
 788 config COMPAT_OLD_SIGACTION
 789         bool
 790
 791 config 64BIT_TIME
 792         def_bool y
 793         help
 794           This should be selected by all architectures that need to support
 795           new system calls with a 64-bit time_t. This is relevant on all 32-bit
 796           architectures, and 64-bit architectures as part of compat syscall
 797           handling.
 798
 799 config COMPAT_32BIT_TIME
 800         def_bool !64BIT || COMPAT
 801         help
 802           This enables 32 bit time_t support in addition to 64 bit time_t support.
 803           This is relevant on all 32-bit architectures, and 64-bit architectures
 804           as part of compat syscall handling.
 805
 806 config ARCH_NO_COHERENT_DMA_MMAP
 807         bool
 808
 809 config ARCH_NO_PREEMPT
 810         bool
 811
 812 config CPU_NO_EFFICIENT_FFS
 813         def_bool n
 814
 815 config HAVE_ARCH_VMAP_STACK
 816         def_bool n
 817         help
 818           An arch should select this symbol if it can support kernel stacks
 819           in vmalloc space.  This means:
 820
 821           - vmalloc space must be large enough to hold many kernel stacks.
 822             This may rule out many 32-bit architectures.
 823
 824           - Stacks in vmalloc space need to work reliably.  For example, if
 825             vmap page tables are created on demand, either this mechanism
 826             needs to work while the stack points to a virtual address with
 827             unpopulated page tables or arch code (switch_to() and switch_mm(),
 828             most likely) needs to ensure that the stack's page table entries
 829             are populated before running on a possibly unpopulated stack.
 830
 831           - If the stack overflows into a guard page, something reasonable
 832             should happen.  The definition of "reasonable" is flexible, but
 833             instantly rebooting without logging anything would be unfriendly.
 834
 835 config VMAP_STACK
 836         default y
 837         bool "Use a virtually-mapped stack"
 838         depends on HAVE_ARCH_VMAP_STACK && !KASAN
 839         ---help---
 840           Enable this if you want the use virtually-mapped kernel stacks
 841           with guard pages.  This causes kernel stack overflows to be
 842           caught immediately rather than causing difficult-to-diagnose
 843           corruption.
 844
 845           This is presently incompatible with KASAN because KASAN expects
 846           the stack to map directly to the KASAN shadow map using a formula
 847           that is incorrect if the stack is in vmalloc space.
 848
 849 config ARCH_OPTIONAL_KERNEL_RWX
 850         def_bool n
 851
 852 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 853         def_bool n
 854
 855 config ARCH_HAS_STRICT_KERNEL_RWX
 856         def_bool n
 857
 858 config STRICT_KERNEL_RWX
 859         bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
 860         depends on ARCH_HAS_STRICT_KERNEL_RWX
 861         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 862         help
 863           If this is set, kernel text and rodata memory will be made read-only,
 864           and non-text memory will be made non-executable. This provides
 865           protection against certain security exploits (e.g. executing the heap
 866           or modifying text)
 867
 868           These features are considered standard security practice these days.
 869           You should say Y here in almost all cases.
 870
 871 config ARCH_HAS_STRICT_MODULE_RWX
 872         def_bool n
 873
 874 config STRICT_MODULE_RWX
 875         bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
 876         depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
 877         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 878         help
 879           If this is set, module text and rodata memory will be made read-only,
 880           and non-text memory will be made non-executable. This provides
 881           protection against certain security exploits (e.g. writing to text)
 882
 883 # select if the architecture provides an asm/dma-direct.h header
 884 config ARCH_HAS_PHYS_TO_DMA
 885         bool
 886
 887 config ARCH_HAS_REFCOUNT
 888         bool
 889         help
 890           An architecture selects this when it has implemented refcount_t
 891           using open coded assembly primitives that provide an optimized
 892           refcount_t implementation, possibly at the expense of some full
 893           refcount state checks of CONFIG_REFCOUNT_FULL=y.
 894
 895           The refcount overflow check behavior, however, must be retained.
 896           Catching overflows is the primary security concern for protecting
 897           against bugs in reference counts.
 898
 899 config REFCOUNT_FULL
 900         bool "Perform full reference count validation at the expense of speed"
 901         help
 902           Enabling this switches the refcounting infrastructure from a fast
 903           unchecked atomic_t implementation to a fully state checked
 904           implementation, which can be (slightly) slower but provides protections
 905           against various use-after-free conditions that can be used in
 906           security flaw exploits.
 907
 908 config HAVE_ARCH_COMPILER_H
 909         bool
 910         help
 911           An architecture can select this if it provides an
 912           asm/compiler.h header that should be included after
 913           linux/compiler-*.h in order to override macro definitions that those
 914           headers generally provide.
 915
 916 config HAVE_ARCH_PREL32_RELOCATIONS
 917         bool
 918         help
 919           May be selected by an architecture if it supports place-relative
 920           32-bit relocations, both in the toolchain and in the module loader,
 921           in which case relative references can be used in special sections
 922           for PCI fixup, initcalls etc which are only half the size on 64 bit
 923           architectures, and don't require runtime relocation on relocatable
 924           kernels.
 925
 926 config ARCH_USE_MEMREMAP_PROT
 927         bool
 928
 929 config LOCK_EVENT_COUNTS
 930         bool "Locking event counts collection"
 931         depends on DEBUG_FS
 932         ---help---
 933           Enable light-weight counting of various locking related events
 934           in the system with minimal performance impact. This reduces
 935           the chance of application behavior change because of timing
 936           differences. The counts are reported via debugfs.
 937
 938 source "kernel/gcov/Kconfig"
 939
 940 source "scripts/gcc-plugins/Kconfig"
 941
 942 endmenu