arch/Kconfig

   1 #
   2 # General architecture dependent options
   3 #
   4
   5 config CRASH_CORE
   6         bool
   7
   8 config KEXEC_CORE
   9         select CRASH_CORE
  10         bool
  11
  12 config HAVE_IMA_KEXEC
  13         bool
  14
  15 config OPROFILE
  16         tristate "OProfile system profiling"
  17         depends on PROFILING
  18         depends on HAVE_OPROFILE
  19         select RING_BUFFER
  20         select RING_BUFFER_ALLOW_SWAP
  21         help
  22           OProfile is a profiling system capable of profiling the
  23           whole system, include the kernel, kernel modules, libraries,
  24           and applications.
  25
  26           If unsure, say N.
  27
  28 config OPROFILE_EVENT_MULTIPLEX
  29         bool "OProfile multiplexing support (EXPERIMENTAL)"
  30         default n
  31         depends on OPROFILE && X86
  32         help
  33           The number of hardware counters is limited. The multiplexing
  34           feature enables OProfile to gather more events than counters
  35           are provided by the hardware. This is realized by switching
  36           between events at a user specified time interval.
  37
  38           If unsure, say N.
  39
  40 config HAVE_OPROFILE
  41         bool
  42
  43 config OPROFILE_NMI_TIMER
  44         def_bool y
  45         depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI && !PPC64
  46
  47 config KPROBES
  48         bool "Kprobes"
  49         depends on MODULES
  50         depends on HAVE_KPROBES
  51         select KALLSYMS
  52         help
  53           Kprobes allows you to trap at almost any kernel address and
  54           execute a callback function.  register_kprobe() establishes
  55           a probepoint and specifies the callback.  Kprobes is useful
  56           for kernel debugging, non-intrusive instrumentation and testing.
  57           If in doubt, say "N".
  58
  59 config JUMP_LABEL
  60        bool "Optimize very unlikely/likely branches"
  61        depends on HAVE_ARCH_JUMP_LABEL
  62        help
  63          This option enables a transparent branch optimization that
  64          makes certain almost-always-true or almost-always-false branch
  65          conditions even cheaper to execute within the kernel.
  66
  67          Certain performance-sensitive kernel code, such as trace points,
  68          scheduler functionality, networking code and KVM have such
  69          branches and include support for this optimization technique.
  70
  71          If it is detected that the compiler has support for "asm goto",
  72          the kernel will compile such branches with just a nop
  73          instruction. When the condition flag is toggled to true, the
  74          nop will be converted to a jump instruction to execute the
  75          conditional block of instructions.
  76
  77          This technique lowers overhead and stress on the branch prediction
  78          of the processor and generally makes the kernel faster. The update
  79          of the condition is slower, but those are always very rare.
  80
  81          ( On 32-bit x86, the necessary options added to the compiler
  82            flags may increase the size of the kernel slightly. )
  83
  84 config STATIC_KEYS_SELFTEST
  85         bool "Static key selftest"
  86         depends on JUMP_LABEL
  87         help
  88           Boot time self-test of the branch patching code.
  89
  90 config OPTPROBES
  91         def_bool y
  92         depends on KPROBES && HAVE_OPTPROBES
  93         depends on !PREEMPT
  94
  95 config KPROBES_ON_FTRACE
  96         def_bool y
  97         depends on KPROBES && HAVE_KPROBES_ON_FTRACE
  98         depends on DYNAMIC_FTRACE_WITH_REGS
  99         help
 100          If function tracer is enabled and the arch supports full
 101          passing of pt_regs to function tracing, then kprobes can
 102          optimize on top of function tracing.
 103
 104 config UPROBES
 105         def_bool n
 106         depends on ARCH_SUPPORTS_UPROBES
 107         help
 108           Uprobes is the user-space counterpart to kprobes: they
 109           enable instrumentation applications (such as 'perf probe')
 110           to establish unintrusive probes in user-space binaries and
 111           libraries, by executing handler functions when the probes
 112           are hit by user-space applications.
 113
 114           ( These probes come in the form of single-byte breakpoints,
 115             managed by the kernel and kept transparent to the probed
 116             application. )
 117
 118 config HAVE_64BIT_ALIGNED_ACCESS
 119         def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
 120         help
 121           Some architectures require 64 bit accesses to be 64 bit
 122           aligned, which also requires structs containing 64 bit values
 123           to be 64 bit aligned too. This includes some 32 bit
 124           architectures which can do 64 bit accesses, as well as 64 bit
 125           architectures without unaligned access.
 126
 127           This symbol should be selected by an architecture if 64 bit
 128           accesses are required to be 64 bit aligned in this way even
 129           though it is not a 64 bit architecture.
 130
 131           See Documentation/unaligned-memory-access.txt for more
 132           information on the topic of unaligned memory accesses.
 133
 134 config HAVE_EFFICIENT_UNALIGNED_ACCESS
 135         bool
 136         help
 137           Some architectures are unable to perform unaligned accesses
 138           without the use of get_unaligned/put_unaligned. Others are
 139           unable to perform such accesses efficiently (e.g. trap on
 140           unaligned access and require fixing it up in the exception
 141           handler.)
 142
 143           This symbol should be selected by an architecture if it can
 144           perform unaligned accesses efficiently to allow different
 145           code paths to be selected for these cases. Some network
 146           drivers, for example, could opt to not fix up alignment
 147           problems with received packets if doing so would not help
 148           much.
 149
 150           See Documentation/unaligned-memory-access.txt for more
 151           information on the topic of unaligned memory accesses.
 152
 153 config ARCH_USE_BUILTIN_BSWAP
 154        bool
 155        help
 156          Modern versions of GCC (since 4.4) have builtin functions
 157          for handling byte-swapping. Using these, instead of the old
 158          inline assembler that the architecture code provides in the
 159          __arch_bswapXX() macros, allows the compiler to see what's
 160          happening and offers more opportunity for optimisation. In
 161          particular, the compiler will be able to combine the byteswap
 162          with a nearby load or store and use load-and-swap or
 163          store-and-swap instructions if the architecture has them. It
 164          should almost *never* result in code which is worse than the
 165          hand-coded assembler in <asm/swab.h>.  But just in case it
 166          does, the use of the builtins is optional.
 167
 168          Any architecture with load-and-swap or store-and-swap
 169          instructions should set this. And it shouldn't hurt to set it
 170          on architectures that don't have such instructions.
 171
 172 config KRETPROBES
 173         def_bool y
 174         depends on KPROBES && HAVE_KRETPROBES
 175
 176 config USER_RETURN_NOTIFIER
 177         bool
 178         depends on HAVE_USER_RETURN_NOTIFIER
 179         help
 180           Provide a kernel-internal notification when a cpu is about to
 181           switch to user mode.
 182
 183 config HAVE_IOREMAP_PROT
 184         bool
 185
 186 config HAVE_KPROBES
 187         bool
 188
 189 config HAVE_KRETPROBES
 190         bool
 191
 192 config HAVE_OPTPROBES
 193         bool
 194
 195 config HAVE_KPROBES_ON_FTRACE
 196         bool
 197
 198 config HAVE_NMI
 199         bool
 200
 201 config HAVE_NMI_WATCHDOG
 202         depends on HAVE_NMI
 203         bool
 204 #
 205 # An arch should select this if it provides all these things:
 206 #
 207 #       task_pt_regs()          in asm/processor.h or asm/ptrace.h
 208 #       arch_has_single_step()  if there is hardware single-step support
 209 #       arch_has_block_step()   if there is hardware block-step support
 210 #       asm/syscall.h           supplying asm-generic/syscall.h interface
 211 #       linux/regset.h          user_regset interfaces
 212 #       CORE_DUMP_USE_REGSET    #define'd in linux/elf.h
 213 #       TIF_SYSCALL_TRACE       calls tracehook_report_syscall_{entry,exit}
 214 #       TIF_NOTIFY_RESUME       calls tracehook_notify_resume()
 215 #       signal delivery         calls tracehook_signal_handler()
 216 #
 217 config HAVE_ARCH_TRACEHOOK
 218         bool
 219
 220 config HAVE_DMA_CONTIGUOUS
 221         bool
 222
 223 config GENERIC_SMP_IDLE_THREAD
 224        bool
 225
 226 config GENERIC_IDLE_POLL_SETUP
 227        bool
 228
 229 # Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
 230 config ARCH_HAS_SET_MEMORY
 231         bool
 232
 233 # Select if arch init_task initializer is different to init/init_task.c
 234 config ARCH_INIT_TASK
 235        bool
 236
 237 # Select if arch has its private alloc_task_struct() function
 238 config ARCH_TASK_STRUCT_ALLOCATOR
 239         bool
 240
 241 # Select if arch has its private alloc_thread_stack() function
 242 config ARCH_THREAD_STACK_ALLOCATOR
 243         bool
 244
 245 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
 246 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
 247         bool
 248
 249 config HAVE_REGS_AND_STACK_ACCESS_API
 250         bool
 251         help
 252           This symbol should be selected by an architecure if it supports
 253           the API needed to access registers and stack entries from pt_regs,
 254           declared in asm/ptrace.h
 255           For example the kprobes-based event tracer needs this API.
 256
 257 config HAVE_CLK
 258         bool
 259         help
 260           The <linux/clk.h> calls support software clock gating and
 261           thus are a key power management tool on many systems.
 262
 263 config HAVE_DMA_API_DEBUG
 264         bool
 265
 266 config HAVE_HW_BREAKPOINT
 267         bool
 268         depends on PERF_EVENTS
 269
 270 config HAVE_MIXED_BREAKPOINTS_REGS
 271         bool
 272         depends on HAVE_HW_BREAKPOINT
 273         help
 274           Depending on the arch implementation of hardware breakpoints,
 275           some of them have separate registers for data and instruction
 276           breakpoints addresses, others have mixed registers to store
 277           them but define the access type in a control register.
 278           Select this option if your arch implements breakpoints under the
 279           latter fashion.
 280
 281 config HAVE_USER_RETURN_NOTIFIER
 282         bool
 283
 284 config HAVE_PERF_EVENTS_NMI
 285         bool
 286         help
 287           System hardware can generate an NMI using the perf event
 288           subsystem.  Also has support for calculating CPU cycle events
 289           to determine how many clock cycles in a given period.
 290
 291 config HAVE_PERF_REGS
 292         bool
 293         help
 294           Support selective register dumps for perf events. This includes
 295           bit-mapping of each registers and a unique architecture id.
 296
 297 config HAVE_PERF_USER_STACK_DUMP
 298         bool
 299         help
 300           Support user stack dumps for perf event samples. This needs
 301           access to the user stack pointer which is not unified across
 302           architectures.
 303
 304 config HAVE_ARCH_JUMP_LABEL
 305         bool
 306
 307 config HAVE_RCU_TABLE_FREE
 308         bool
 309
 310 config ARCH_HAVE_NMI_SAFE_CMPXCHG
 311         bool
 312
 313 config HAVE_ALIGNED_STRUCT_PAGE
 314         bool
 315         help
 316           This makes sure that struct pages are double word aligned and that
 317           e.g. the SLUB allocator can perform double word atomic operations
 318           on a struct page for better performance. However selecting this
 319           might increase the size of a struct page by a word.
 320
 321 config HAVE_CMPXCHG_LOCAL
 322         bool
 323
 324 config HAVE_CMPXCHG_DOUBLE
 325         bool
 326
 327 config ARCH_WEAK_RELEASE_ACQUIRE
 328         bool
 329
 330 config ARCH_WANT_IPC_PARSE_VERSION
 331         bool
 332
 333 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 334         bool
 335
 336 config ARCH_WANT_OLD_COMPAT_IPC
 337         select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 338         bool
 339
 340 config HAVE_ARCH_SECCOMP_FILTER
 341         bool
 342         help
 343           An arch should select this symbol if it provides all of these things:
 344           - syscall_get_arch()
 345           - syscall_get_arguments()
 346           - syscall_rollback()
 347           - syscall_set_return_value()
 348           - SIGSYS siginfo_t support
 349           - secure_computing is called from a ptrace_event()-safe context
 350           - secure_computing return value is checked and a return value of -1
 351             results in the system call being skipped immediately.
 352           - seccomp syscall wired up
 353
 354 config SECCOMP_FILTER
 355         def_bool y
 356         depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
 357         help
 358           Enable tasks to build secure computing environments defined
 359           in terms of Berkeley Packet Filter programs which implement
 360           task-defined system call filtering polices.
 361
 362           See Documentation/prctl/seccomp_filter.txt for details.
 363
 364 config HAVE_GCC_PLUGINS
 365         bool
 366         help
 367           An arch should select this symbol if it supports building with
 368           GCC plugins.
 369
 370 menuconfig GCC_PLUGINS
 371         bool "GCC plugins"
 372         depends on HAVE_GCC_PLUGINS
 373         depends on !COMPILE_TEST
 374         help
 375           GCC plugins are loadable modules that provide extra features to the
 376           compiler. They are useful for runtime instrumentation and static analysis.
 377
 378           See Documentation/gcc-plugins.txt for details.
 379
 380 config GCC_PLUGIN_CYC_COMPLEXITY
 381         bool "Compute the cyclomatic complexity of a function" if EXPERT
 382         depends on GCC_PLUGINS
 383         depends on !COMPILE_TEST
 384         help
 385           The complexity M of a function's control flow graph is defined as:
 386            M = E - N + 2P
 387           where
 388
 389           E = the number of edges
 390           N = the number of nodes
 391           P = the number of connected components (exit nodes).
 392
 393           Enabling this plugin reports the complexity to stderr during the
 394           build. It mainly serves as a simple example of how to create a
 395           gcc plugin for the kernel.
 396
 397 config GCC_PLUGIN_SANCOV
 398         bool
 399         depends on GCC_PLUGINS
 400         help
 401           This plugin inserts a __sanitizer_cov_trace_pc() call at the start of
 402           basic blocks. It supports all gcc versions with plugin support (from
 403           gcc-4.5 on). It is based on the commit "Add fuzzing coverage support"
 404           by Dmitry Vyukov <dvyukov@google.com>.
 405
 406 config GCC_PLUGIN_LATENT_ENTROPY
 407         bool "Generate some entropy during boot and runtime"
 408         depends on GCC_PLUGINS
 409         help
 410           By saying Y here the kernel will instrument some kernel code to
 411           extract some entropy from both original and artificially created
 412           program state.  This will help especially embedded systems where
 413           there is little 'natural' source of entropy normally.  The cost
 414           is some slowdown of the boot process (about 0.5%) and fork and
 415           irq processing.
 416
 417           Note that entropy extracted this way is not cryptographically
 418           secure!
 419
 420           This plugin was ported from grsecurity/PaX. More information at:
 421            * https://grsecurity.net/
 422            * https://pax.grsecurity.net/
 423
 424 config GCC_PLUGIN_STRUCTLEAK
 425         bool "Force initialization of variables containing userspace addresses"
 426         depends on GCC_PLUGINS
 427         help
 428           This plugin zero-initializes any structures containing a
 429           __user attribute. This can prevent some classes of information
 430           exposures.
 431
 432           This plugin was ported from grsecurity/PaX. More information at:
 433            * https://grsecurity.net/
 434            * https://pax.grsecurity.net/
 435
 436 config GCC_PLUGIN_STRUCTLEAK_VERBOSE
 437         bool "Report forcefully initialized variables"
 438         depends on GCC_PLUGIN_STRUCTLEAK
 439         depends on !COMPILE_TEST
 440         help
 441           This option will cause a warning to be printed each time the
 442           structleak plugin finds a variable it thinks needs to be
 443           initialized. Since not all existing initializers are detected
 444           by the plugin, this can produce false positive warnings.
 445
 446 config GCC_PLUGIN_RANDSTRUCT
 447         bool "Randomize layout of sensitive kernel structures"
 448         depends on GCC_PLUGINS
 449         select MODVERSIONS if MODULES
 450         help
 451           If you say Y here, the layouts of structures explicitly
 452           marked by __randomize_layout will be randomized at
 453           compile-time.  This can introduce the requirement of an
 454           additional information exposure vulnerability for exploits
 455           targeting these structure types.
 456
 457           Enabling this feature will introduce some performance impact,
 458           slightly increase memory usage, and prevent the use of forensic
 459           tools like Volatility against the system (unless the kernel
 460           source tree isn't cleaned after kernel installation).
 461
 462           The seed used for compilation is located at
 463           scripts/gcc-plgins/randomize_layout_seed.h.  It remains after
 464           a make clean to allow for external modules to be compiled with
 465           the existing seed and will be removed by a make mrproper or
 466           make distclean.
 467
 468           Note that the implementation requires gcc 4.7 or newer.
 469
 470           This plugin was ported from grsecurity/PaX. More information at:
 471            * https://grsecurity.net/
 472            * https://pax.grsecurity.net/
 473
 474 config GCC_PLUGIN_RANDSTRUCT_PERFORMANCE
 475         bool "Use cacheline-aware structure randomization"
 476         depends on GCC_PLUGIN_RANDSTRUCT
 477         depends on !COMPILE_TEST
 478         help
 479           If you say Y here, the RANDSTRUCT randomization will make a
 480           best effort at restricting randomization to cacheline-sized
 481           groups of elements.  It will further not randomize bitfields
 482           in structures.  This reduces the performance hit of RANDSTRUCT
 483           at the cost of weakened randomization.
 484
 485 config HAVE_CC_STACKPROTECTOR
 486         bool
 487         help
 488           An arch should select this symbol if:
 489           - its compiler supports the -fstack-protector option
 490           - it has implemented a stack canary (e.g. __stack_chk_guard)
 491
 492 config CC_STACKPROTECTOR
 493         def_bool n
 494         help
 495           Set when a stack-protector mode is enabled, so that the build
 496           can enable kernel-side support for the GCC feature.
 497
 498 choice
 499         prompt "Stack Protector buffer overflow detection"
 500         depends on HAVE_CC_STACKPROTECTOR
 501         default CC_STACKPROTECTOR_NONE
 502         help
 503           This option turns on the "stack-protector" GCC feature. This
 504           feature puts, at the beginning of functions, a canary value on
 505           the stack just before the return address, and validates
 506           the value just before actually returning.  Stack based buffer
 507           overflows (that need to overwrite this return address) now also
 508           overwrite the canary, which gets detected and the attack is then
 509           neutralized via a kernel panic.
 510
 511 config CC_STACKPROTECTOR_NONE
 512         bool "None"
 513         help
 514           Disable "stack-protector" GCC feature.
 515
 516 config CC_STACKPROTECTOR_REGULAR
 517         bool "Regular"
 518         select CC_STACKPROTECTOR
 519         help
 520           Functions will have the stack-protector canary logic added if they
 521           have an 8-byte or larger character array on the stack.
 522
 523           This feature requires gcc version 4.2 or above, or a distribution
 524           gcc with the feature backported ("-fstack-protector").
 525
 526           On an x86 "defconfig" build, this feature adds canary checks to
 527           about 3% of all kernel functions, which increases kernel code size
 528           by about 0.3%.
 529
 530 config CC_STACKPROTECTOR_STRONG
 531         bool "Strong"
 532         select CC_STACKPROTECTOR
 533         help
 534           Functions will have the stack-protector canary logic added in any
 535           of the following conditions:
 536
 537           - local variable's address used as part of the right hand side of an
 538             assignment or function argument
 539           - local variable is an array (or union containing an array),
 540             regardless of array type or length
 541           - uses register local variables
 542
 543           This feature requires gcc version 4.9 or above, or a distribution
 544           gcc with the feature backported ("-fstack-protector-strong").
 545
 546           On an x86 "defconfig" build, this feature adds canary checks to
 547           about 20% of all kernel functions, which increases the kernel code
 548           size by about 2%.
 549
 550 endchoice
 551
 552 config THIN_ARCHIVES
 553         def_bool y
 554         help
 555           Select this if the architecture wants to use thin archives
 556           instead of ld -r to create the built-in.o files.
 557
 558 config LD_DEAD_CODE_DATA_ELIMINATION
 559         bool
 560         help
 561           Select this if the architecture wants to do dead code and
 562           data elimination with the linker by compiling with
 563           -ffunction-sections -fdata-sections and linking with
 564           --gc-sections.
 565
 566           This requires that the arch annotates or otherwise protects
 567           its external entry points from being discarded. Linker scripts
 568           must also merge .text.*, .data.*, and .bss.* correctly into
 569           output sections. Care must be taken not to pull in unrelated
 570           sections (e.g., '.text.init'). Typically '.' in section names
 571           is used to distinguish them from label names / C identifiers.
 572
 573 config HAVE_ARCH_WITHIN_STACK_FRAMES
 574         bool
 575         help
 576           An architecture should select this if it can walk the kernel stack
 577           frames to determine if an object is part of either the arguments
 578           or local variables (i.e. that it excludes saved return addresses,
 579           and similar) by implementing an inline arch_within_stack_frames(),
 580           which is used by CONFIG_HARDENED_USERCOPY.
 581
 582 config HAVE_CONTEXT_TRACKING
 583         bool
 584         help
 585           Provide kernel/user boundaries probes necessary for subsystems
 586           that need it, such as userspace RCU extended quiescent state.
 587           Syscalls need to be wrapped inside user_exit()-user_enter() through
 588           the slow path using TIF_NOHZ flag. Exceptions handlers must be
 589           wrapped as well. Irqs are already protected inside
 590           rcu_irq_enter/rcu_irq_exit() but preemption or signal handling on
 591           irq exit still need to be protected.
 592
 593 config HAVE_VIRT_CPU_ACCOUNTING
 594         bool
 595
 596 config ARCH_HAS_SCALED_CPUTIME
 597         bool
 598
 599 config HAVE_VIRT_CPU_ACCOUNTING_GEN
 600         bool
 601         default y if 64BIT
 602         help
 603           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 604           Before enabling this option, arch code must be audited
 605           to ensure there are no races in concurrent read/write of
 606           cputime_t. For example, reading/writing 64-bit cputime_t on
 607           some 32-bit arches may require multiple accesses, so proper
 608           locking is needed to protect against concurrent accesses.
 609
 610
 611 config HAVE_IRQ_TIME_ACCOUNTING
 612         bool
 613         help
 614           Archs need to ensure they use a high enough resolution clock to
 615           support irq time accounting and then call enable_sched_clock_irqtime().
 616
 617 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 618         bool
 619
 620 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 621         bool
 622
 623 config HAVE_ARCH_HUGE_VMAP
 624         bool
 625
 626 config HAVE_ARCH_SOFT_DIRTY
 627         bool
 628
 629 config HAVE_MOD_ARCH_SPECIFIC
 630         bool
 631         help
 632           The arch uses struct mod_arch_specific to store data.  Many arches
 633           just need a simple module loader without arch specific data - those
 634           should not enable this.
 635
 636 config MODULES_USE_ELF_RELA
 637         bool
 638         help
 639           Modules only use ELF RELA relocations.  Modules with ELF REL
 640           relocations will give an error.
 641
 642 config MODULES_USE_ELF_REL
 643         bool
 644         help
 645           Modules only use ELF REL relocations.  Modules with ELF RELA
 646           relocations will give an error.
 647
 648 config HAVE_UNDERSCORE_SYMBOL_PREFIX
 649         bool
 650         help
 651           Some architectures generate an _ in front of C symbols; things like
 652           module loading and assembly files need to know about this.
 653
 654 config HAVE_IRQ_EXIT_ON_IRQ_STACK
 655         bool
 656         help
 657           Architecture doesn't only execute the irq handler on the irq stack
 658           but also irq_exit(). This way we can process softirqs on this irq
 659           stack instead of switching to a new one when we call __do_softirq()
 660           in the end of an hardirq.
 661           This spares a stack switch and improves cache usage on softirq
 662           processing.
 663
 664 config PGTABLE_LEVELS
 665         int
 666         default 2
 667
 668 config ARCH_HAS_ELF_RANDOMIZE
 669         bool
 670         help
 671           An architecture supports choosing randomized locations for
 672           stack, mmap, brk, and ET_DYN. Defined functions:
 673           - arch_mmap_rnd()
 674           - arch_randomize_brk()
 675
 676 config HAVE_ARCH_MMAP_RND_BITS
 677         bool
 678         help
 679           An arch should select this symbol if it supports setting a variable
 680           number of bits for use in establishing the base address for mmap
 681           allocations, has MMU enabled and provides values for both:
 682           - ARCH_MMAP_RND_BITS_MIN
 683           - ARCH_MMAP_RND_BITS_MAX
 684
 685 config HAVE_EXIT_THREAD
 686         bool
 687         help
 688           An architecture implements exit_thread.
 689
 690 config ARCH_MMAP_RND_BITS_MIN
 691         int
 692
 693 config ARCH_MMAP_RND_BITS_MAX
 694         int
 695
 696 config ARCH_MMAP_RND_BITS_DEFAULT
 697         int
 698
 699 config ARCH_MMAP_RND_BITS
 700         int "Number of bits to use for ASLR of mmap base address" if EXPERT
 701         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
 702         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
 703         default ARCH_MMAP_RND_BITS_MIN
 704         depends on HAVE_ARCH_MMAP_RND_BITS
 705         help
 706           This value can be used to select the number of bits to use to
 707           determine the random offset to the base address of vma regions
 708           resulting from mmap allocations. This value will be bounded
 709           by the architecture's minimum and maximum supported values.
 710
 711           This value can be changed after boot using the
 712           /proc/sys/vm/mmap_rnd_bits tunable
 713
 714 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
 715         bool
 716         help
 717           An arch should select this symbol if it supports running applications
 718           in compatibility mode, supports setting a variable number of bits for
 719           use in establishing the base address for mmap allocations, has MMU
 720           enabled and provides values for both:
 721           - ARCH_MMAP_RND_COMPAT_BITS_MIN
 722           - ARCH_MMAP_RND_COMPAT_BITS_MAX
 723
 724 config ARCH_MMAP_RND_COMPAT_BITS_MIN
 725         int
 726
 727 config ARCH_MMAP_RND_COMPAT_BITS_MAX
 728         int
 729
 730 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 731         int
 732
 733 config ARCH_MMAP_RND_COMPAT_BITS
 734         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
 735         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
 736         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 737         default ARCH_MMAP_RND_COMPAT_BITS_MIN
 738         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
 739         help
 740           This value can be used to select the number of bits to use to
 741           determine the random offset to the base address of vma regions
 742           resulting from mmap allocations for compatible applications This
 743           value will be bounded by the architecture's minimum and maximum
 744           supported values.
 745
 746           This value can be changed after boot using the
 747           /proc/sys/vm/mmap_rnd_compat_bits tunable
 748
 749 config HAVE_ARCH_COMPAT_MMAP_BASES
 750         bool
 751         help
 752           This allows 64bit applications to invoke 32-bit mmap() syscall
 753           and vice-versa 32-bit applications to call 64-bit mmap().
 754           Required for applications doing different bitness syscalls.
 755
 756 config HAVE_COPY_THREAD_TLS
 757         bool
 758         help
 759           Architecture provides copy_thread_tls to accept tls argument via
 760           normal C parameter passing, rather than extracting the syscall
 761           argument from pt_regs.
 762
 763 config HAVE_STACK_VALIDATION
 764         bool
 765         help
 766           Architecture supports the 'objtool check' host tool command, which
 767           performs compile-time stack metadata validation.
 768
 769 config HAVE_RELIABLE_STACKTRACE
 770         bool
 771         help
 772           Architecture has a save_stack_trace_tsk_reliable() function which
 773           only returns a stack trace if it can guarantee the trace is reliable.
 774
 775 config HAVE_ARCH_HASH
 776         bool
 777         default n
 778         help
 779           If this is set, the architecture provides an <asm/hash.h>
 780           file which provides platform-specific implementations of some
 781           functions in <linux/hash.h> or fs/namei.c.
 782
 783 config ISA_BUS_API
 784         def_bool ISA
 785
 786 #
 787 # ABI hall of shame
 788 #
 789 config CLONE_BACKWARDS
 790         bool
 791         help
 792           Architecture has tls passed as the 4th argument of clone(2),
 793           not the 5th one.
 794
 795 config CLONE_BACKWARDS2
 796         bool
 797         help
 798           Architecture has the first two arguments of clone(2) swapped.
 799
 800 config CLONE_BACKWARDS3
 801         bool
 802         help
 803           Architecture has tls passed as the 3rd argument of clone(2),
 804           not the 5th one.
 805
 806 config ODD_RT_SIGACTION
 807         bool
 808         help
 809           Architecture has unusual rt_sigaction(2) arguments
 810
 811 config OLD_SIGSUSPEND
 812         bool
 813         help
 814           Architecture has old sigsuspend(2) syscall, of one-argument variety
 815
 816 config OLD_SIGSUSPEND3
 817         bool
 818         help
 819           Even weirder antique ABI - three-argument sigsuspend(2)
 820
 821 config OLD_SIGACTION
 822         bool
 823         help
 824           Architecture has old sigaction(2) syscall.  Nope, not the same
 825           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
 826           but fairly different variant of sigaction(2), thanks to OSF/1
 827           compatibility...
 828
 829 config COMPAT_OLD_SIGACTION
 830         bool
 831
 832 config ARCH_NO_COHERENT_DMA_MMAP
 833         bool
 834
 835 config CPU_NO_EFFICIENT_FFS
 836         def_bool n
 837
 838 config HAVE_ARCH_VMAP_STACK
 839         def_bool n
 840         help
 841           An arch should select this symbol if it can support kernel stacks
 842           in vmalloc space.  This means:
 843
 844           - vmalloc space must be large enough to hold many kernel stacks.
 845             This may rule out many 32-bit architectures.
 846
 847           - Stacks in vmalloc space need to work reliably.  For example, if
 848             vmap page tables are created on demand, either this mechanism
 849             needs to work while the stack points to a virtual address with
 850             unpopulated page tables or arch code (switch_to() and switch_mm(),
 851             most likely) needs to ensure that the stack's page table entries
 852             are populated before running on a possibly unpopulated stack.
 853
 854           - If the stack overflows into a guard page, something reasonable
 855             should happen.  The definition of "reasonable" is flexible, but
 856             instantly rebooting without logging anything would be unfriendly.
 857
 858 config VMAP_STACK
 859         default y
 860         bool "Use a virtually-mapped stack"
 861         depends on HAVE_ARCH_VMAP_STACK && !KASAN
 862         ---help---
 863           Enable this if you want the use virtually-mapped kernel stacks
 864           with guard pages.  This causes kernel stack overflows to be
 865           caught immediately rather than causing difficult-to-diagnose
 866           corruption.
 867
 868           This is presently incompatible with KASAN because KASAN expects
 869           the stack to map directly to the KASAN shadow map using a formula
 870           that is incorrect if the stack is in vmalloc space.
 871
 872 config ARCH_OPTIONAL_KERNEL_RWX
 873         def_bool n
 874
 875 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 876         def_bool n
 877
 878 config ARCH_HAS_STRICT_KERNEL_RWX
 879         def_bool n
 880
 881 config STRICT_KERNEL_RWX
 882         bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
 883         depends on ARCH_HAS_STRICT_KERNEL_RWX
 884         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 885         help
 886           If this is set, kernel text and rodata memory will be made read-only,
 887           and non-text memory will be made non-executable. This provides
 888           protection against certain security exploits (e.g. executing the heap
 889           or modifying text)
 890
 891           These features are considered standard security practice these days.
 892           You should say Y here in almost all cases.
 893
 894 config ARCH_HAS_STRICT_MODULE_RWX
 895         def_bool n
 896
 897 config STRICT_MODULE_RWX
 898         bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
 899         depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
 900         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 901         help
 902           If this is set, module text and rodata memory will be made read-only,
 903           and non-text memory will be made non-executable. This provides
 904           protection against certain security exploits (e.g. writing to text)
 905
 906 config ARCH_WANT_RELAX_ORDER
 907         bool
 908
 909 config REFCOUNT_FULL
 910         bool "Perform full reference count validation at the expense of speed"
 911         help
 912           Enabling this switches the refcounting infrastructure from a fast
 913           unchecked atomic_t implementation to a fully state checked
 914           implementation, which can be (slightly) slower but provides protections
 915           against various use-after-free conditions that can be used in
 916           security flaw exploits.
 917
 918 source "kernel/gcov/Kconfig"