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