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