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 #
 202 # An arch should select this if it provides all these things:
 203 #
 204 #       task_pt_regs()          in asm/processor.h or asm/ptrace.h
 205 #       arch_has_single_step()  if there is hardware single-step support
 206 #       arch_has_block_step()   if there is hardware block-step support
 207 #       asm/syscall.h           supplying asm-generic/syscall.h interface
 208 #       linux/regset.h          user_regset interfaces
 209 #       CORE_DUMP_USE_REGSET    #define'd in linux/elf.h
 210 #       TIF_SYSCALL_TRACE       calls tracehook_report_syscall_{entry,exit}
 211 #       TIF_NOTIFY_RESUME       calls tracehook_notify_resume()
 212 #       signal delivery         calls tracehook_signal_handler()
 213 #
 214 config HAVE_ARCH_TRACEHOOK
 215         bool
 216
 217 config HAVE_DMA_CONTIGUOUS
 218         bool
 219
 220 config GENERIC_SMP_IDLE_THREAD
 221        bool
 222
 223 config GENERIC_IDLE_POLL_SETUP
 224        bool
 225
 226 config ARCH_HAS_FORTIFY_SOURCE
 227         bool
 228         help
 229           An architecture should select this when it can successfully
 230           build and run with CONFIG_FORTIFY_SOURCE.
 231
 232 # Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
 233 config ARCH_HAS_SET_MEMORY
 234         bool
 235
 236 # Select if arch init_task initializer is different to init/init_task.c
 237 config ARCH_INIT_TASK
 238        bool
 239
 240 # Select if arch has its private alloc_task_struct() function
 241 config ARCH_TASK_STRUCT_ALLOCATOR
 242         bool
 243
 244 # Select if arch has its private alloc_thread_stack() function
 245 config ARCH_THREAD_STACK_ALLOCATOR
 246         bool
 247
 248 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
 249 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
 250         bool
 251
 252 config HAVE_REGS_AND_STACK_ACCESS_API
 253         bool
 254         help
 255           This symbol should be selected by an architecure if it supports
 256           the API needed to access registers and stack entries from pt_regs,
 257           declared in asm/ptrace.h
 258           For example the kprobes-based event tracer needs this API.
 259
 260 config HAVE_CLK
 261         bool
 262         help
 263           The <linux/clk.h> calls support software clock gating and
 264           thus are a key power management tool on many systems.
 265
 266 config HAVE_DMA_API_DEBUG
 267         bool
 268
 269 config HAVE_HW_BREAKPOINT
 270         bool
 271         depends on PERF_EVENTS
 272
 273 config HAVE_MIXED_BREAKPOINTS_REGS
 274         bool
 275         depends on HAVE_HW_BREAKPOINT
 276         help
 277           Depending on the arch implementation of hardware breakpoints,
 278           some of them have separate registers for data and instruction
 279           breakpoints addresses, others have mixed registers to store
 280           them but define the access type in a control register.
 281           Select this option if your arch implements breakpoints under the
 282           latter fashion.
 283
 284 config HAVE_USER_RETURN_NOTIFIER
 285         bool
 286
 287 config HAVE_PERF_EVENTS_NMI
 288         bool
 289         help
 290           System hardware can generate an NMI using the perf event
 291           subsystem.  Also has support for calculating CPU cycle events
 292           to determine how many clock cycles in a given period.
 293
 294 config HAVE_HARDLOCKUP_DETECTOR_PERF
 295         bool
 296         depends on HAVE_PERF_EVENTS_NMI
 297         help
 298           The arch chooses to use the generic perf-NMI-based hardlockup
 299           detector. Must define HAVE_PERF_EVENTS_NMI.
 300
 301 config HAVE_NMI_WATCHDOG
 302         depends on HAVE_NMI
 303         bool
 304         help
 305           The arch provides a low level NMI watchdog. It provides
 306           asm/nmi.h, and defines its own arch_touch_nmi_watchdog().
 307
 308 config HAVE_HARDLOCKUP_DETECTOR_ARCH
 309         bool
 310         select HAVE_NMI_WATCHDOG
 311         help
 312           The arch chooses to provide its own hardlockup detector, which is
 313           a superset of the HAVE_NMI_WATCHDOG. It also conforms to config
 314           interfaces and parameters provided by hardlockup detector subsystem.
 315
 316 config HAVE_PERF_REGS
 317         bool
 318         help
 319           Support selective register dumps for perf events. This includes
 320           bit-mapping of each registers and a unique architecture id.
 321
 322 config HAVE_PERF_USER_STACK_DUMP
 323         bool
 324         help
 325           Support user stack dumps for perf event samples. This needs
 326           access to the user stack pointer which is not unified across
 327           architectures.
 328
 329 config HAVE_ARCH_JUMP_LABEL
 330         bool
 331
 332 config HAVE_RCU_TABLE_FREE
 333         bool
 334
 335 config ARCH_HAVE_NMI_SAFE_CMPXCHG
 336         bool
 337
 338 config HAVE_ALIGNED_STRUCT_PAGE
 339         bool
 340         help
 341           This makes sure that struct pages are double word aligned and that
 342           e.g. the SLUB allocator can perform double word atomic operations
 343           on a struct page for better performance. However selecting this
 344           might increase the size of a struct page by a word.
 345
 346 config HAVE_CMPXCHG_LOCAL
 347         bool
 348
 349 config HAVE_CMPXCHG_DOUBLE
 350         bool
 351
 352 config ARCH_WEAK_RELEASE_ACQUIRE
 353         bool
 354
 355 config ARCH_WANT_IPC_PARSE_VERSION
 356         bool
 357
 358 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 359         bool
 360
 361 config ARCH_WANT_OLD_COMPAT_IPC
 362         select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 363         bool
 364
 365 config HAVE_ARCH_SECCOMP_FILTER
 366         bool
 367         help
 368           An arch should select this symbol if it provides all of these things:
 369           - syscall_get_arch()
 370           - syscall_get_arguments()
 371           - syscall_rollback()
 372           - syscall_set_return_value()
 373           - SIGSYS siginfo_t support
 374           - secure_computing is called from a ptrace_event()-safe context
 375           - secure_computing return value is checked and a return value of -1
 376             results in the system call being skipped immediately.
 377           - seccomp syscall wired up
 378
 379 config SECCOMP_FILTER
 380         def_bool y
 381         depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
 382         help
 383           Enable tasks to build secure computing environments defined
 384           in terms of Berkeley Packet Filter programs which implement
 385           task-defined system call filtering polices.
 386
 387           See Documentation/prctl/seccomp_filter.txt for details.
 388
 389 config HAVE_GCC_PLUGINS
 390         bool
 391         help
 392           An arch should select this symbol if it supports building with
 393           GCC plugins.
 394
 395 menuconfig GCC_PLUGINS
 396         bool "GCC plugins"
 397         depends on HAVE_GCC_PLUGINS
 398         depends on !COMPILE_TEST
 399         help
 400           GCC plugins are loadable modules that provide extra features to the
 401           compiler. They are useful for runtime instrumentation and static analysis.
 402
 403           See Documentation/gcc-plugins.txt for details.
 404
 405 config GCC_PLUGIN_CYC_COMPLEXITY
 406         bool "Compute the cyclomatic complexity of a function" if EXPERT
 407         depends on GCC_PLUGINS
 408         depends on !COMPILE_TEST
 409         help
 410           The complexity M of a function's control flow graph is defined as:
 411            M = E - N + 2P
 412           where
 413
 414           E = the number of edges
 415           N = the number of nodes
 416           P = the number of connected components (exit nodes).
 417
 418           Enabling this plugin reports the complexity to stderr during the
 419           build. It mainly serves as a simple example of how to create a
 420           gcc plugin for the kernel.
 421
 422 config GCC_PLUGIN_SANCOV
 423         bool
 424         depends on GCC_PLUGINS
 425         help
 426           This plugin inserts a __sanitizer_cov_trace_pc() call at the start of
 427           basic blocks. It supports all gcc versions with plugin support (from
 428           gcc-4.5 on). It is based on the commit "Add fuzzing coverage support"
 429           by Dmitry Vyukov <dvyukov@google.com>.
 430
 431 config GCC_PLUGIN_LATENT_ENTROPY
 432         bool "Generate some entropy during boot and runtime"
 433         depends on GCC_PLUGINS
 434         help
 435           By saying Y here the kernel will instrument some kernel code to
 436           extract some entropy from both original and artificially created
 437           program state.  This will help especially embedded systems where
 438           there is little 'natural' source of entropy normally.  The cost
 439           is some slowdown of the boot process (about 0.5%) and fork and
 440           irq processing.
 441
 442           Note that entropy extracted this way is not cryptographically
 443           secure!
 444
 445           This plugin was ported from grsecurity/PaX. More information at:
 446            * https://grsecurity.net/
 447            * https://pax.grsecurity.net/
 448
 449 config GCC_PLUGIN_STRUCTLEAK
 450         bool "Force initialization of variables containing userspace addresses"
 451         depends on GCC_PLUGINS
 452         help
 453           This plugin zero-initializes any structures containing a
 454           __user attribute. This can prevent some classes of information
 455           exposures.
 456
 457           This plugin was ported from grsecurity/PaX. More information at:
 458            * https://grsecurity.net/
 459            * https://pax.grsecurity.net/
 460
 461 config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
 462         bool "Force initialize all struct type variables passed by reference"
 463         depends on GCC_PLUGIN_STRUCTLEAK
 464         help
 465           Zero initialize any struct type local variable that may be passed by
 466           reference without having been initialized.
 467
 468 config GCC_PLUGIN_STRUCTLEAK_VERBOSE
 469         bool "Report forcefully initialized variables"
 470         depends on GCC_PLUGIN_STRUCTLEAK
 471         depends on !COMPILE_TEST
 472         help
 473           This option will cause a warning to be printed each time the
 474           structleak plugin finds a variable it thinks needs to be
 475           initialized. Since not all existing initializers are detected
 476           by the plugin, this can produce false positive warnings.
 477
 478 config GCC_PLUGIN_RANDSTRUCT
 479         bool "Randomize layout of sensitive kernel structures"
 480         depends on GCC_PLUGINS
 481         select MODVERSIONS if MODULES
 482         help
 483           If you say Y here, the layouts of structures that are entirely
 484           function pointers (and have not been manually annotated with
 485           __no_randomize_layout), or structures that have been explicitly
 486           marked with __randomize_layout, will be randomized at compile-time.
 487           This can introduce the requirement of an additional information
 488           exposure vulnerability for exploits targeting these structure
 489           types.
 490
 491           Enabling this feature will introduce some performance impact,
 492           slightly increase memory usage, and prevent the use of forensic
 493           tools like Volatility against the system (unless the kernel
 494           source tree isn't cleaned after kernel installation).
 495
 496           The seed used for compilation is located at
 497           scripts/gcc-plgins/randomize_layout_seed.h.  It remains after
 498           a make clean to allow for external modules to be compiled with
 499           the existing seed and will be removed by a make mrproper or
 500           make distclean.
 501
 502           Note that the implementation requires gcc 4.7 or newer.
 503
 504           This plugin was ported from grsecurity/PaX. More information at:
 505            * https://grsecurity.net/
 506            * https://pax.grsecurity.net/
 507
 508 config GCC_PLUGIN_RANDSTRUCT_PERFORMANCE
 509         bool "Use cacheline-aware structure randomization"
 510         depends on GCC_PLUGIN_RANDSTRUCT
 511         depends on !COMPILE_TEST
 512         help
 513           If you say Y here, the RANDSTRUCT randomization will make a
 514           best effort at restricting randomization to cacheline-sized
 515           groups of elements.  It will further not randomize bitfields
 516           in structures.  This reduces the performance hit of RANDSTRUCT
 517           at the cost of weakened randomization.
 518
 519 config HAVE_CC_STACKPROTECTOR
 520         bool
 521         help
 522           An arch should select this symbol if:
 523           - its compiler supports the -fstack-protector option
 524           - it has implemented a stack canary (e.g. __stack_chk_guard)
 525
 526 config CC_STACKPROTECTOR
 527         def_bool n
 528         help
 529           Set when a stack-protector mode is enabled, so that the build
 530           can enable kernel-side support for the GCC feature.
 531
 532 choice
 533         prompt "Stack Protector buffer overflow detection"
 534         depends on HAVE_CC_STACKPROTECTOR
 535         default CC_STACKPROTECTOR_NONE
 536         help
 537           This option turns on the "stack-protector" GCC feature. This
 538           feature puts, at the beginning of functions, a canary value on
 539           the stack just before the return address, and validates
 540           the value just before actually returning.  Stack based buffer
 541           overflows (that need to overwrite this return address) now also
 542           overwrite the canary, which gets detected and the attack is then
 543           neutralized via a kernel panic.
 544
 545 config CC_STACKPROTECTOR_NONE
 546         bool "None"
 547         help
 548           Disable "stack-protector" GCC feature.
 549
 550 config CC_STACKPROTECTOR_REGULAR
 551         bool "Regular"
 552         select CC_STACKPROTECTOR
 553         help
 554           Functions will have the stack-protector canary logic added if they
 555           have an 8-byte or larger character array on the stack.
 556
 557           This feature requires gcc version 4.2 or above, or a distribution
 558           gcc with the feature backported ("-fstack-protector").
 559
 560           On an x86 "defconfig" build, this feature adds canary checks to
 561           about 3% of all kernel functions, which increases kernel code size
 562           by about 0.3%.
 563
 564 config CC_STACKPROTECTOR_STRONG
 565         bool "Strong"
 566         select CC_STACKPROTECTOR
 567         help
 568           Functions will have the stack-protector canary logic added in any
 569           of the following conditions:
 570
 571           - local variable's address used as part of the right hand side of an
 572             assignment or function argument
 573           - local variable is an array (or union containing an array),
 574             regardless of array type or length
 575           - uses register local variables
 576
 577           This feature requires gcc version 4.9 or above, or a distribution
 578           gcc with the feature backported ("-fstack-protector-strong").
 579
 580           On an x86 "defconfig" build, this feature adds canary checks to
 581           about 20% of all kernel functions, which increases the kernel code
 582           size by about 2%.
 583
 584 endchoice
 585
 586 config THIN_ARCHIVES
 587         def_bool y
 588         help
 589           Select this if the architecture wants to use thin archives
 590           instead of ld -r to create the built-in.o files.
 591
 592 config LD_DEAD_CODE_DATA_ELIMINATION
 593         bool
 594         help
 595           Select this if the architecture wants to do dead code and
 596           data elimination with the linker by compiling with
 597           -ffunction-sections -fdata-sections and linking with
 598           --gc-sections.
 599
 600           This requires that the arch annotates or otherwise protects
 601           its external entry points from being discarded. Linker scripts
 602           must also merge .text.*, .data.*, and .bss.* correctly into
 603           output sections. Care must be taken not to pull in unrelated
 604           sections (e.g., '.text.init'). Typically '.' in section names
 605           is used to distinguish them from label names / C identifiers.
 606
 607 config HAVE_ARCH_WITHIN_STACK_FRAMES
 608         bool
 609         help
 610           An architecture should select this if it can walk the kernel stack
 611           frames to determine if an object is part of either the arguments
 612           or local variables (i.e. that it excludes saved return addresses,
 613           and similar) by implementing an inline arch_within_stack_frames(),
 614           which is used by CONFIG_HARDENED_USERCOPY.
 615
 616 config HAVE_CONTEXT_TRACKING
 617         bool
 618         help
 619           Provide kernel/user boundaries probes necessary for subsystems
 620           that need it, such as userspace RCU extended quiescent state.
 621           Syscalls need to be wrapped inside user_exit()-user_enter() through
 622           the slow path using TIF_NOHZ flag. Exceptions handlers must be
 623           wrapped as well. Irqs are already protected inside
 624           rcu_irq_enter/rcu_irq_exit() but preemption or signal handling on
 625           irq exit still need to be protected.
 626
 627 config HAVE_VIRT_CPU_ACCOUNTING
 628         bool
 629
 630 config ARCH_HAS_SCALED_CPUTIME
 631         bool
 632
 633 config HAVE_VIRT_CPU_ACCOUNTING_GEN
 634         bool
 635         default y if 64BIT
 636         help
 637           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 638           Before enabling this option, arch code must be audited
 639           to ensure there are no races in concurrent read/write of
 640           cputime_t. For example, reading/writing 64-bit cputime_t on
 641           some 32-bit arches may require multiple accesses, so proper
 642           locking is needed to protect against concurrent accesses.
 643
 644
 645 config HAVE_IRQ_TIME_ACCOUNTING
 646         bool
 647         help
 648           Archs need to ensure they use a high enough resolution clock to
 649           support irq time accounting and then call enable_sched_clock_irqtime().
 650
 651 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 652         bool
 653
 654 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 655         bool
 656
 657 config HAVE_ARCH_HUGE_VMAP
 658         bool
 659
 660 config HAVE_ARCH_SOFT_DIRTY
 661         bool
 662
 663 config HAVE_MOD_ARCH_SPECIFIC
 664         bool
 665         help
 666           The arch uses struct mod_arch_specific to store data.  Many arches
 667           just need a simple module loader without arch specific data - those
 668           should not enable this.
 669
 670 config MODULES_USE_ELF_RELA
 671         bool
 672         help
 673           Modules only use ELF RELA relocations.  Modules with ELF REL
 674           relocations will give an error.
 675
 676 config MODULES_USE_ELF_REL
 677         bool
 678         help
 679           Modules only use ELF REL relocations.  Modules with ELF RELA
 680           relocations will give an error.
 681
 682 config HAVE_UNDERSCORE_SYMBOL_PREFIX
 683         bool
 684         help
 685           Some architectures generate an _ in front of C symbols; things like
 686           module loading and assembly files need to know about this.
 687
 688 config HAVE_IRQ_EXIT_ON_IRQ_STACK
 689         bool
 690         help
 691           Architecture doesn't only execute the irq handler on the irq stack
 692           but also irq_exit(). This way we can process softirqs on this irq
 693           stack instead of switching to a new one when we call __do_softirq()
 694           in the end of an hardirq.
 695           This spares a stack switch and improves cache usage on softirq
 696           processing.
 697
 698 config PGTABLE_LEVELS
 699         int
 700         default 2
 701
 702 config ARCH_HAS_ELF_RANDOMIZE
 703         bool
 704         help
 705           An architecture supports choosing randomized locations for
 706           stack, mmap, brk, and ET_DYN. Defined functions:
 707           - arch_mmap_rnd()
 708           - arch_randomize_brk()
 709
 710 config HAVE_ARCH_MMAP_RND_BITS
 711         bool
 712         help
 713           An arch should select this symbol if it supports setting a variable
 714           number of bits for use in establishing the base address for mmap
 715           allocations, has MMU enabled and provides values for both:
 716           - ARCH_MMAP_RND_BITS_MIN
 717           - ARCH_MMAP_RND_BITS_MAX
 718
 719 config HAVE_EXIT_THREAD
 720         bool
 721         help
 722           An architecture implements exit_thread.
 723
 724 config ARCH_MMAP_RND_BITS_MIN
 725         int
 726
 727 config ARCH_MMAP_RND_BITS_MAX
 728         int
 729
 730 config ARCH_MMAP_RND_BITS_DEFAULT
 731         int
 732
 733 config ARCH_MMAP_RND_BITS
 734         int "Number of bits to use for ASLR of mmap base address" if EXPERT
 735         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
 736         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
 737         default ARCH_MMAP_RND_BITS_MIN
 738         depends on HAVE_ARCH_MMAP_RND_BITS
 739         help
 740           This value can be used to select the number of bits to use to
 741           determine the random offset to the base address of vma regions
 742           resulting from mmap allocations. This value will be bounded
 743           by the architecture's minimum and maximum supported values.
 744
 745           This value can be changed after boot using the
 746           /proc/sys/vm/mmap_rnd_bits tunable
 747
 748 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
 749         bool
 750         help
 751           An arch should select this symbol if it supports running applications
 752           in compatibility mode, supports setting a variable number of bits for
 753           use in establishing the base address for mmap allocations, has MMU
 754           enabled and provides values for both:
 755           - ARCH_MMAP_RND_COMPAT_BITS_MIN
 756           - ARCH_MMAP_RND_COMPAT_BITS_MAX
 757
 758 config ARCH_MMAP_RND_COMPAT_BITS_MIN
 759         int
 760
 761 config ARCH_MMAP_RND_COMPAT_BITS_MAX
 762         int
 763
 764 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 765         int
 766
 767 config ARCH_MMAP_RND_COMPAT_BITS
 768         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
 769         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
 770         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 771         default ARCH_MMAP_RND_COMPAT_BITS_MIN
 772         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
 773         help
 774           This value can be used to select the number of bits to use to
 775           determine the random offset to the base address of vma regions
 776           resulting from mmap allocations for compatible applications This
 777           value will be bounded by the architecture's minimum and maximum
 778           supported values.
 779
 780           This value can be changed after boot using the
 781           /proc/sys/vm/mmap_rnd_compat_bits tunable
 782
 783 config HAVE_ARCH_COMPAT_MMAP_BASES
 784         bool
 785         help
 786           This allows 64bit applications to invoke 32-bit mmap() syscall
 787           and vice-versa 32-bit applications to call 64-bit mmap().
 788           Required for applications doing different bitness syscalls.
 789
 790 config HAVE_COPY_THREAD_TLS
 791         bool
 792         help
 793           Architecture provides copy_thread_tls to accept tls argument via
 794           normal C parameter passing, rather than extracting the syscall
 795           argument from pt_regs.
 796
 797 config HAVE_STACK_VALIDATION
 798         bool
 799         help
 800           Architecture supports the 'objtool check' host tool command, which
 801           performs compile-time stack metadata validation.
 802
 803 config HAVE_RELIABLE_STACKTRACE
 804         bool
 805         help
 806           Architecture has a save_stack_trace_tsk_reliable() function which
 807           only returns a stack trace if it can guarantee the trace is reliable.
 808
 809 config HAVE_ARCH_HASH
 810         bool
 811         default n
 812         help
 813           If this is set, the architecture provides an <asm/hash.h>
 814           file which provides platform-specific implementations of some
 815           functions in <linux/hash.h> or fs/namei.c.
 816
 817 config ISA_BUS_API
 818         def_bool ISA
 819
 820 #
 821 # ABI hall of shame
 822 #
 823 config CLONE_BACKWARDS
 824         bool
 825         help
 826           Architecture has tls passed as the 4th argument of clone(2),
 827           not the 5th one.
 828
 829 config CLONE_BACKWARDS2
 830         bool
 831         help
 832           Architecture has the first two arguments of clone(2) swapped.
 833
 834 config CLONE_BACKWARDS3
 835         bool
 836         help
 837           Architecture has tls passed as the 3rd argument of clone(2),
 838           not the 5th one.
 839
 840 config ODD_RT_SIGACTION
 841         bool
 842         help
 843           Architecture has unusual rt_sigaction(2) arguments
 844
 845 config OLD_SIGSUSPEND
 846         bool
 847         help
 848           Architecture has old sigsuspend(2) syscall, of one-argument variety
 849
 850 config OLD_SIGSUSPEND3
 851         bool
 852         help
 853           Even weirder antique ABI - three-argument sigsuspend(2)
 854
 855 config OLD_SIGACTION
 856         bool
 857         help
 858           Architecture has old sigaction(2) syscall.  Nope, not the same
 859           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
 860           but fairly different variant of sigaction(2), thanks to OSF/1
 861           compatibility...
 862
 863 config COMPAT_OLD_SIGACTION
 864         bool
 865
 866 config ARCH_NO_COHERENT_DMA_MMAP
 867         bool
 868
 869 config CPU_NO_EFFICIENT_FFS
 870         def_bool n
 871
 872 config HAVE_ARCH_VMAP_STACK
 873         def_bool n
 874         help
 875           An arch should select this symbol if it can support kernel stacks
 876           in vmalloc space.  This means:
 877
 878           - vmalloc space must be large enough to hold many kernel stacks.
 879             This may rule out many 32-bit architectures.
 880
 881           - Stacks in vmalloc space need to work reliably.  For example, if
 882             vmap page tables are created on demand, either this mechanism
 883             needs to work while the stack points to a virtual address with
 884             unpopulated page tables or arch code (switch_to() and switch_mm(),
 885             most likely) needs to ensure that the stack's page table entries
 886             are populated before running on a possibly unpopulated stack.
 887
 888           - If the stack overflows into a guard page, something reasonable
 889             should happen.  The definition of "reasonable" is flexible, but
 890             instantly rebooting without logging anything would be unfriendly.
 891
 892 config VMAP_STACK
 893         default y
 894         bool "Use a virtually-mapped stack"
 895         depends on HAVE_ARCH_VMAP_STACK && !KASAN
 896         ---help---
 897           Enable this if you want the use virtually-mapped kernel stacks
 898           with guard pages.  This causes kernel stack overflows to be
 899           caught immediately rather than causing difficult-to-diagnose
 900           corruption.
 901
 902           This is presently incompatible with KASAN because KASAN expects
 903           the stack to map directly to the KASAN shadow map using a formula
 904           that is incorrect if the stack is in vmalloc space.
 905
 906 config ARCH_OPTIONAL_KERNEL_RWX
 907         def_bool n
 908
 909 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 910         def_bool n
 911
 912 config ARCH_HAS_STRICT_KERNEL_RWX
 913         def_bool n
 914
 915 config STRICT_KERNEL_RWX
 916         bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
 917         depends on ARCH_HAS_STRICT_KERNEL_RWX
 918         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 919         help
 920           If this is set, kernel text and rodata memory will be made read-only,
 921           and non-text memory will be made non-executable. This provides
 922           protection against certain security exploits (e.g. executing the heap
 923           or modifying text)
 924
 925           These features are considered standard security practice these days.
 926           You should say Y here in almost all cases.
 927
 928 config ARCH_HAS_STRICT_MODULE_RWX
 929         def_bool n
 930
 931 config STRICT_MODULE_RWX
 932         bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
 933         depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
 934         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 935         help
 936           If this is set, module text and rodata memory will be made read-only,
 937           and non-text memory will be made non-executable. This provides
 938           protection against certain security exploits (e.g. writing to text)
 939
 940 config ARCH_HAS_REFCOUNT
 941         bool
 942         help
 943           An architecture selects this when it has implemented refcount_t
 944           using open coded assembly primitives that provide an optimized
 945           refcount_t implementation, possibly at the expense of some full
 946           refcount state checks of CONFIG_REFCOUNT_FULL=y.
 947
 948           The refcount overflow check behavior, however, must be retained.
 949           Catching overflows is the primary security concern for protecting
 950           against bugs in reference counts.
 951
 952 config REFCOUNT_FULL
 953         bool "Perform full reference count validation at the expense of speed"
 954         help
 955           Enabling this switches the refcounting infrastructure from a fast
 956           unchecked atomic_t implementation to a fully state checked
 957           implementation, which can be (slightly) slower but provides protections
 958           against various use-after-free conditions that can be used in
 959           security flaw exploits.
 960
 961 source "kernel/gcov/Kconfig"