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 12config ARCH_CONFIGURES_CPU_MITIGATIONS 13 bool 14 15if !ARCH_CONFIGURES_CPU_MITIGATIONS 16config CPU_MITIGATIONS 17 def_bool y 18endif 19 20# 21# Selected by architectures that need custom DMA operations for e.g. legacy 22# IOMMUs not handled by dma-iommu. Drivers must never select this symbol. 23# 24config ARCH_HAS_DMA_OPS 25 depends on HAS_DMA 26 select DMA_OPS_HELPERS 27 bool 28 29menu "General architecture-dependent options" 30 31config ARCH_HAS_SUBPAGE_FAULTS 32 bool 33 help 34 Select if the architecture can check permissions at sub-page 35 granularity (e.g. arm64 MTE). The probe_user_*() functions 36 must be implemented. 37 38config HOTPLUG_SMT 39 bool 40 41config SMT_NUM_THREADS_DYNAMIC 42 bool 43 44# Selected by HOTPLUG_CORE_SYNC_DEAD or HOTPLUG_CORE_SYNC_FULL 45config HOTPLUG_CORE_SYNC 46 bool 47 48# Basic CPU dead synchronization selected by architecture 49config HOTPLUG_CORE_SYNC_DEAD 50 bool 51 select HOTPLUG_CORE_SYNC 52 53# Full CPU synchronization with alive state selected by architecture 54config HOTPLUG_CORE_SYNC_FULL 55 bool 56 select HOTPLUG_CORE_SYNC_DEAD if HOTPLUG_CPU 57 select HOTPLUG_CORE_SYNC 58 59config HOTPLUG_SPLIT_STARTUP 60 bool 61 select HOTPLUG_CORE_SYNC_FULL 62 63config HOTPLUG_PARALLEL 64 bool 65 select HOTPLUG_SPLIT_STARTUP 66 67config GENERIC_ENTRY 68 bool 69 70config KPROBES 71 bool "Kprobes" 72 depends on HAVE_KPROBES 73 select KALLSYMS 74 select EXECMEM 75 select NEED_TASKS_RCU 76 help 77 Kprobes allows you to trap at almost any kernel address and 78 execute a callback function. register_kprobe() establishes 79 a probepoint and specifies the callback. Kprobes is useful 80 for kernel debugging, non-intrusive instrumentation and testing. 81 If in doubt, say "N". 82 83config JUMP_LABEL 84 bool "Optimize very unlikely/likely branches" 85 depends on HAVE_ARCH_JUMP_LABEL 86 select OBJTOOL if HAVE_JUMP_LABEL_HACK 87 help 88 This option enables a transparent branch optimization that 89 makes certain almost-always-true or almost-always-false branch 90 conditions even cheaper to execute within the kernel. 91 92 Certain performance-sensitive kernel code, such as trace points, 93 scheduler functionality, networking code and KVM have such 94 branches and include support for this optimization technique. 95 96 If it is detected that the compiler has support for "asm goto", 97 the kernel will compile such branches with just a nop 98 instruction. When the condition flag is toggled to true, the 99 nop will be converted to a jump instruction to execute the 100 conditional block of instructions. 101 102 This technique lowers overhead and stress on the branch prediction 103 of the processor and generally makes the kernel faster. The update 104 of the condition is slower, but those are always very rare. 105 106 ( On 32-bit x86, the necessary options added to the compiler 107 flags may increase the size of the kernel slightly. ) 108 109config STATIC_KEYS_SELFTEST 110 bool "Static key selftest" 111 depends on JUMP_LABEL 112 help 113 Boot time self-test of the branch patching code. 114 115config STATIC_CALL_SELFTEST 116 bool "Static call selftest" 117 depends on HAVE_STATIC_CALL 118 help 119 Boot time self-test of the call patching code. 120 121config OPTPROBES 122 def_bool y 123 depends on KPROBES && HAVE_OPTPROBES 124 select NEED_TASKS_RCU 125 126config KPROBES_ON_FTRACE 127 def_bool y 128 depends on KPROBES && HAVE_KPROBES_ON_FTRACE 129 depends on DYNAMIC_FTRACE_WITH_REGS 130 help 131 If function tracer is enabled and the arch supports full 132 passing of pt_regs to function tracing, then kprobes can 133 optimize on top of function tracing. 134 135config UPROBES 136 def_bool n 137 depends on ARCH_SUPPORTS_UPROBES 138 select TASKS_TRACE_RCU 139 help 140 Uprobes is the user-space counterpart to kprobes: they 141 enable instrumentation applications (such as 'perf probe') 142 to establish unintrusive probes in user-space binaries and 143 libraries, by executing handler functions when the probes 144 are hit by user-space applications. 145 146 ( These probes come in the form of single-byte breakpoints, 147 managed by the kernel and kept transparent to the probed 148 application. ) 149 150config HAVE_64BIT_ALIGNED_ACCESS 151 def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS 152 help 153 Some architectures require 64 bit accesses to be 64 bit 154 aligned, which also requires structs containing 64 bit values 155 to be 64 bit aligned too. This includes some 32 bit 156 architectures which can do 64 bit accesses, as well as 64 bit 157 architectures without unaligned access. 158 159 This symbol should be selected by an architecture if 64 bit 160 accesses are required to be 64 bit aligned in this way even 161 though it is not a 64 bit architecture. 162 163 See Documentation/core-api/unaligned-memory-access.rst for 164 more information on the topic of unaligned memory accesses. 165 166config HAVE_EFFICIENT_UNALIGNED_ACCESS 167 bool 168 help 169 Some architectures are unable to perform unaligned accesses 170 without the use of get_unaligned/put_unaligned. Others are 171 unable to perform such accesses efficiently (e.g. trap on 172 unaligned access and require fixing it up in the exception 173 handler.) 174 175 This symbol should be selected by an architecture if it can 176 perform unaligned accesses efficiently to allow different 177 code paths to be selected for these cases. Some network 178 drivers, for example, could opt to not fix up alignment 179 problems with received packets if doing so would not help 180 much. 181 182 See Documentation/core-api/unaligned-memory-access.rst for more 183 information on the topic of unaligned memory accesses. 184 185config ARCH_USE_BUILTIN_BSWAP 186 bool 187 help 188 Modern versions of GCC (since 4.4) have builtin functions 189 for handling byte-swapping. Using these, instead of the old 190 inline assembler that the architecture code provides in the 191 __arch_bswapXX() macros, allows the compiler to see what's 192 happening and offers more opportunity for optimisation. In 193 particular, the compiler will be able to combine the byteswap 194 with a nearby load or store and use load-and-swap or 195 store-and-swap instructions if the architecture has them. It 196 should almost *never* result in code which is worse than the 197 hand-coded assembler in <asm/swab.h>. But just in case it 198 does, the use of the builtins is optional. 199 200 Any architecture with load-and-swap or store-and-swap 201 instructions should set this. And it shouldn't hurt to set it 202 on architectures that don't have such instructions. 203 204config KRETPROBES 205 def_bool y 206 depends on KPROBES && (HAVE_KRETPROBES || HAVE_RETHOOK) 207 208config KRETPROBE_ON_RETHOOK 209 def_bool y 210 depends on HAVE_RETHOOK 211 depends on KRETPROBES 212 select RETHOOK 213 214config USER_RETURN_NOTIFIER 215 bool 216 depends on HAVE_USER_RETURN_NOTIFIER 217 help 218 Provide a kernel-internal notification when a cpu is about to 219 switch to user mode. 220 221config HAVE_IOREMAP_PROT 222 bool 223 224config HAVE_KPROBES 225 bool 226 227config HAVE_KRETPROBES 228 bool 229 230config HAVE_OPTPROBES 231 bool 232 233config HAVE_KPROBES_ON_FTRACE 234 bool 235 236config ARCH_CORRECT_STACKTRACE_ON_KRETPROBE 237 bool 238 help 239 Since kretprobes modifies return address on the stack, the 240 stacktrace may see the kretprobe trampoline address instead 241 of correct one. If the architecture stacktrace code and 242 unwinder can adjust such entries, select this configuration. 243 244config HAVE_FUNCTION_ERROR_INJECTION 245 bool 246 247config HAVE_NMI 248 bool 249 250config HAVE_FUNCTION_DESCRIPTORS 251 bool 252 253config TRACE_IRQFLAGS_SUPPORT 254 bool 255 256config TRACE_IRQFLAGS_NMI_SUPPORT 257 bool 258 259# 260# An arch should select this if it provides all these things: 261# 262# task_pt_regs() in asm/processor.h or asm/ptrace.h 263# arch_has_single_step() if there is hardware single-step support 264# arch_has_block_step() if there is hardware block-step support 265# asm/syscall.h supplying asm-generic/syscall.h interface 266# linux/regset.h user_regset interfaces 267# CORE_DUMP_USE_REGSET #define'd in linux/elf.h 268# TIF_SYSCALL_TRACE calls ptrace_report_syscall_{entry,exit} 269# TIF_NOTIFY_RESUME calls resume_user_mode_work() 270# 271config HAVE_ARCH_TRACEHOOK 272 bool 273 274config HAVE_DMA_CONTIGUOUS 275 bool 276 277config GENERIC_SMP_IDLE_THREAD 278 bool 279 280config GENERIC_IDLE_POLL_SETUP 281 bool 282 283config ARCH_HAS_FORTIFY_SOURCE 284 bool 285 help 286 An architecture should select this when it can successfully 287 build and run with CONFIG_FORTIFY_SOURCE. 288 289# 290# Select if the arch provides a historic keepinit alias for the retain_initrd 291# command line option 292# 293config ARCH_HAS_KEEPINITRD 294 bool 295 296# Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h 297config ARCH_HAS_SET_MEMORY 298 bool 299 300# Select if arch has all set_direct_map_invalid/default() functions 301config ARCH_HAS_SET_DIRECT_MAP 302 bool 303 304# 305# Select if the architecture provides the arch_dma_set_uncached symbol to 306# either provide an uncached segment alias for a DMA allocation, or 307# to remap the page tables in place. 308# 309config ARCH_HAS_DMA_SET_UNCACHED 310 bool 311 312# 313# Select if the architectures provides the arch_dma_clear_uncached symbol 314# to undo an in-place page table remap for uncached access. 315# 316config ARCH_HAS_DMA_CLEAR_UNCACHED 317 bool 318 319config ARCH_HAS_CPU_FINALIZE_INIT 320 bool 321 322# The architecture has a per-task state that includes the mm's PASID 323config ARCH_HAS_CPU_PASID 324 bool 325 select IOMMU_MM_DATA 326 327config HAVE_ARCH_THREAD_STRUCT_WHITELIST 328 bool 329 help 330 An architecture should select this to provide hardened usercopy 331 knowledge about what region of the thread_struct should be 332 whitelisted for copying to userspace. Normally this is only the 333 FPU registers. Specifically, arch_thread_struct_whitelist() 334 should be implemented. Without this, the entire thread_struct 335 field in task_struct will be left whitelisted. 336 337# Select if arch wants to size task_struct dynamically via arch_task_struct_size: 338config ARCH_WANTS_DYNAMIC_TASK_STRUCT 339 bool 340 341config ARCH_WANTS_NO_INSTR 342 bool 343 help 344 An architecture should select this if the noinstr macro is being used on 345 functions to denote that the toolchain should avoid instrumenting such 346 functions and is required for correctness. 347 348config ARCH_32BIT_OFF_T 349 bool 350 depends on !64BIT 351 help 352 All new 32-bit architectures should have 64-bit off_t type on 353 userspace side which corresponds to the loff_t kernel type. This 354 is the requirement for modern ABIs. Some existing architectures 355 still support 32-bit off_t. This option is enabled for all such 356 architectures explicitly. 357 358# Selected by 64 bit architectures which have a 32 bit f_tinode in struct ustat 359config ARCH_32BIT_USTAT_F_TINODE 360 bool 361 362config HAVE_ASM_MODVERSIONS 363 bool 364 help 365 This symbol should be selected by an architecture if it provides 366 <asm/asm-prototypes.h> to support the module versioning for symbols 367 exported from assembly code. 368 369config HAVE_REGS_AND_STACK_ACCESS_API 370 bool 371 help 372 This symbol should be selected by an architecture if it supports 373 the API needed to access registers and stack entries from pt_regs, 374 declared in asm/ptrace.h 375 For example the kprobes-based event tracer needs this API. 376 377config HAVE_RSEQ 378 bool 379 depends on HAVE_REGS_AND_STACK_ACCESS_API 380 help 381 This symbol should be selected by an architecture if it 382 supports an implementation of restartable sequences. 383 384config HAVE_RUST 385 bool 386 help 387 This symbol should be selected by an architecture if it 388 supports Rust. 389 390config HAVE_FUNCTION_ARG_ACCESS_API 391 bool 392 help 393 This symbol should be selected by an architecture if it supports 394 the API needed to access function arguments from pt_regs, 395 declared in asm/ptrace.h 396 397config HAVE_HW_BREAKPOINT 398 bool 399 depends on PERF_EVENTS 400 401config HAVE_MIXED_BREAKPOINTS_REGS 402 bool 403 depends on HAVE_HW_BREAKPOINT 404 help 405 Depending on the arch implementation of hardware breakpoints, 406 some of them have separate registers for data and instruction 407 breakpoints addresses, others have mixed registers to store 408 them but define the access type in a control register. 409 Select this option if your arch implements breakpoints under the 410 latter fashion. 411 412config HAVE_USER_RETURN_NOTIFIER 413 bool 414 415config HAVE_PERF_EVENTS_NMI 416 bool 417 help 418 System hardware can generate an NMI using the perf event 419 subsystem. Also has support for calculating CPU cycle events 420 to determine how many clock cycles in a given period. 421 422config HAVE_HARDLOCKUP_DETECTOR_PERF 423 bool 424 depends on HAVE_PERF_EVENTS_NMI 425 help 426 The arch chooses to use the generic perf-NMI-based hardlockup 427 detector. Must define HAVE_PERF_EVENTS_NMI. 428 429config HAVE_HARDLOCKUP_DETECTOR_ARCH 430 bool 431 help 432 The arch provides its own hardlockup detector implementation instead 433 of the generic ones. 434 435 It uses the same command line parameters, and sysctl interface, 436 as the generic hardlockup detectors. 437 438config HAVE_PERF_REGS 439 bool 440 help 441 Support selective register dumps for perf events. This includes 442 bit-mapping of each registers and a unique architecture id. 443 444config HAVE_PERF_USER_STACK_DUMP 445 bool 446 help 447 Support user stack dumps for perf event samples. This needs 448 access to the user stack pointer which is not unified across 449 architectures. 450 451config HAVE_ARCH_JUMP_LABEL 452 bool 453 454config HAVE_ARCH_JUMP_LABEL_RELATIVE 455 bool 456 457config MMU_GATHER_TABLE_FREE 458 bool 459 460config MMU_GATHER_RCU_TABLE_FREE 461 bool 462 select MMU_GATHER_TABLE_FREE 463 464config MMU_GATHER_PAGE_SIZE 465 bool 466 467config MMU_GATHER_NO_RANGE 468 bool 469 select MMU_GATHER_MERGE_VMAS 470 471config MMU_GATHER_NO_FLUSH_CACHE 472 bool 473 474config MMU_GATHER_MERGE_VMAS 475 bool 476 477config MMU_GATHER_NO_GATHER 478 bool 479 depends on MMU_GATHER_TABLE_FREE 480 481config ARCH_WANT_IRQS_OFF_ACTIVATE_MM 482 bool 483 help 484 Temporary select until all architectures can be converted to have 485 irqs disabled over activate_mm. Architectures that do IPI based TLB 486 shootdowns should enable this. 487 488# Use normal mm refcounting for MMU_LAZY_TLB kernel thread references. 489# MMU_LAZY_TLB_REFCOUNT=n can improve the scalability of context switching 490# to/from kernel threads when the same mm is running on a lot of CPUs (a large 491# multi-threaded application), by reducing contention on the mm refcount. 492# 493# This can be disabled if the architecture ensures no CPUs are using an mm as a 494# "lazy tlb" beyond its final refcount (i.e., by the time __mmdrop frees the mm 495# or its kernel page tables). This could be arranged by arch_exit_mmap(), or 496# final exit(2) TLB flush, for example. 497# 498# To implement this, an arch *must*: 499# Ensure the _lazy_tlb variants of mmgrab/mmdrop are used when manipulating 500# the lazy tlb reference of a kthread's ->active_mm (non-arch code has been 501# converted already). 502config MMU_LAZY_TLB_REFCOUNT 503 def_bool y 504 depends on !MMU_LAZY_TLB_SHOOTDOWN 505 506# This option allows MMU_LAZY_TLB_REFCOUNT=n. It ensures no CPUs are using an 507# mm as a lazy tlb beyond its last reference count, by shooting down these 508# users before the mm is deallocated. __mmdrop() first IPIs all CPUs that may 509# be using the mm as a lazy tlb, so that they may switch themselves to using 510# init_mm for their active mm. mm_cpumask(mm) is used to determine which CPUs 511# may be using mm as a lazy tlb mm. 512# 513# To implement this, an arch *must*: 514# - At the time of the final mmdrop of the mm, ensure mm_cpumask(mm) contains 515# at least all possible CPUs in which the mm is lazy. 516# - It must meet the requirements for MMU_LAZY_TLB_REFCOUNT=n (see above). 517config MMU_LAZY_TLB_SHOOTDOWN 518 bool 519 520config ARCH_HAVE_NMI_SAFE_CMPXCHG 521 bool 522 523config ARCH_HAVE_EXTRA_ELF_NOTES 524 bool 525 help 526 An architecture should select this in order to enable adding an 527 arch-specific ELF note section to core files. It must provide two 528 functions: elf_coredump_extra_notes_size() and 529 elf_coredump_extra_notes_write() which are invoked by the ELF core 530 dumper. 531 532config ARCH_HAS_NMI_SAFE_THIS_CPU_OPS 533 bool 534 535config HAVE_ALIGNED_STRUCT_PAGE 536 bool 537 help 538 This makes sure that struct pages are double word aligned and that 539 e.g. the SLUB allocator can perform double word atomic operations 540 on a struct page for better performance. However selecting this 541 might increase the size of a struct page by a word. 542 543config HAVE_CMPXCHG_LOCAL 544 bool 545 546config HAVE_CMPXCHG_DOUBLE 547 bool 548 549config ARCH_WEAK_RELEASE_ACQUIRE 550 bool 551 552config ARCH_WANT_IPC_PARSE_VERSION 553 bool 554 555config ARCH_WANT_COMPAT_IPC_PARSE_VERSION 556 bool 557 558config ARCH_WANT_OLD_COMPAT_IPC 559 select ARCH_WANT_COMPAT_IPC_PARSE_VERSION 560 bool 561 562config HAVE_ARCH_SECCOMP 563 bool 564 help 565 An arch should select this symbol to support seccomp mode 1 (the fixed 566 syscall policy), and must provide an overrides for __NR_seccomp_sigreturn, 567 and compat syscalls if the asm-generic/seccomp.h defaults need adjustment: 568 - __NR_seccomp_read_32 569 - __NR_seccomp_write_32 570 - __NR_seccomp_exit_32 571 - __NR_seccomp_sigreturn_32 572 573config HAVE_ARCH_SECCOMP_FILTER 574 bool 575 select HAVE_ARCH_SECCOMP 576 help 577 An arch should select this symbol if it provides all of these things: 578 - all the requirements for HAVE_ARCH_SECCOMP 579 - syscall_get_arch() 580 - syscall_get_arguments() 581 - syscall_rollback() 582 - syscall_set_return_value() 583 - SIGSYS siginfo_t support 584 - secure_computing is called from a ptrace_event()-safe context 585 - secure_computing return value is checked and a return value of -1 586 results in the system call being skipped immediately. 587 - seccomp syscall wired up 588 - if !HAVE_SPARSE_SYSCALL_NR, have SECCOMP_ARCH_NATIVE, 589 SECCOMP_ARCH_NATIVE_NR, SECCOMP_ARCH_NATIVE_NAME defined. If 590 COMPAT is supported, have the SECCOMP_ARCH_COMPAT* defines too. 591 592config SECCOMP 593 prompt "Enable seccomp to safely execute untrusted bytecode" 594 def_bool y 595 depends on HAVE_ARCH_SECCOMP 596 help 597 This kernel feature is useful for number crunching applications 598 that may need to handle untrusted bytecode during their 599 execution. By using pipes or other transports made available 600 to the process as file descriptors supporting the read/write 601 syscalls, it's possible to isolate those applications in their 602 own address space using seccomp. Once seccomp is enabled via 603 prctl(PR_SET_SECCOMP) or the seccomp() syscall, it cannot be 604 disabled and the task is only allowed to execute a few safe 605 syscalls defined by each seccomp mode. 606 607 If unsure, say Y. 608 609config SECCOMP_FILTER 610 def_bool y 611 depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET 612 help 613 Enable tasks to build secure computing environments defined 614 in terms of Berkeley Packet Filter programs which implement 615 task-defined system call filtering polices. 616 617 See Documentation/userspace-api/seccomp_filter.rst for details. 618 619config SECCOMP_CACHE_DEBUG 620 bool "Show seccomp filter cache status in /proc/pid/seccomp_cache" 621 depends on SECCOMP_FILTER && !HAVE_SPARSE_SYSCALL_NR 622 depends on PROC_FS 623 help 624 This enables the /proc/pid/seccomp_cache interface to monitor 625 seccomp cache data. The file format is subject to change. Reading 626 the file requires CAP_SYS_ADMIN. 627 628 This option is for debugging only. Enabling presents the risk that 629 an adversary may be able to infer the seccomp filter logic. 630 631 If unsure, say N. 632 633config HAVE_ARCH_STACKLEAK 634 bool 635 help 636 An architecture should select this if it has the code which 637 fills the used part of the kernel stack with the STACKLEAK_POISON 638 value before returning from system calls. 639 640config HAVE_STACKPROTECTOR 641 bool 642 help 643 An arch should select this symbol if: 644 - it has implemented a stack canary (e.g. __stack_chk_guard) 645 646config STACKPROTECTOR 647 bool "Stack Protector buffer overflow detection" 648 depends on HAVE_STACKPROTECTOR 649 depends on $(cc-option,-fstack-protector) 650 default y 651 help 652 This option turns on the "stack-protector" GCC feature. This 653 feature puts, at the beginning of functions, a canary value on 654 the stack just before the return address, and validates 655 the value just before actually returning. Stack based buffer 656 overflows (that need to overwrite this return address) now also 657 overwrite the canary, which gets detected and the attack is then 658 neutralized via a kernel panic. 659 660 Functions will have the stack-protector canary logic added if they 661 have an 8-byte or larger character array on the stack. 662 663 This feature requires gcc version 4.2 or above, or a distribution 664 gcc with the feature backported ("-fstack-protector"). 665 666 On an x86 "defconfig" build, this feature adds canary checks to 667 about 3% of all kernel functions, which increases kernel code size 668 by about 0.3%. 669 670config STACKPROTECTOR_STRONG 671 bool "Strong Stack Protector" 672 depends on STACKPROTECTOR 673 depends on $(cc-option,-fstack-protector-strong) 674 default y 675 help 676 Functions will have the stack-protector canary logic added in any 677 of the following conditions: 678 679 - local variable's address used as part of the right hand side of an 680 assignment or function argument 681 - local variable is an array (or union containing an array), 682 regardless of array type or length 683 - uses register local variables 684 685 This feature requires gcc version 4.9 or above, or a distribution 686 gcc with the feature backported ("-fstack-protector-strong"). 687 688 On an x86 "defconfig" build, this feature adds canary checks to 689 about 20% of all kernel functions, which increases the kernel code 690 size by about 2%. 691 692config ARCH_SUPPORTS_SHADOW_CALL_STACK 693 bool 694 help 695 An architecture should select this if it supports the compiler's 696 Shadow Call Stack and implements runtime support for shadow stack 697 switching. 698 699config SHADOW_CALL_STACK 700 bool "Shadow Call Stack" 701 depends on ARCH_SUPPORTS_SHADOW_CALL_STACK 702 depends on DYNAMIC_FTRACE_WITH_ARGS || DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER 703 depends on MMU 704 help 705 This option enables the compiler's Shadow Call Stack, which 706 uses a shadow stack to protect function return addresses from 707 being overwritten by an attacker. More information can be found 708 in the compiler's documentation: 709 710 - Clang: https://clang.llvm.org/docs/ShadowCallStack.html 711 - GCC: https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html#Instrumentation-Options 712 713 Note that security guarantees in the kernel differ from the 714 ones documented for user space. The kernel must store addresses 715 of shadow stacks in memory, which means an attacker capable of 716 reading and writing arbitrary memory may be able to locate them 717 and hijack control flow by modifying the stacks. 718 719config DYNAMIC_SCS 720 bool 721 help 722 Set by the arch code if it relies on code patching to insert the 723 shadow call stack push and pop instructions rather than on the 724 compiler. 725 726config LTO 727 bool 728 help 729 Selected if the kernel will be built using the compiler's LTO feature. 730 731config LTO_CLANG 732 bool 733 select LTO 734 help 735 Selected if the kernel will be built using Clang's LTO feature. 736 737config ARCH_SUPPORTS_LTO_CLANG 738 bool 739 help 740 An architecture should select this option if it supports: 741 - compiling with Clang, 742 - compiling inline assembly with Clang's integrated assembler, 743 - and linking with LLD. 744 745config ARCH_SUPPORTS_LTO_CLANG_THIN 746 bool 747 help 748 An architecture should select this option if it can support Clang's 749 ThinLTO mode. 750 751config HAS_LTO_CLANG 752 def_bool y 753 depends on CC_IS_CLANG && LD_IS_LLD && AS_IS_LLVM 754 depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm) 755 depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm) 756 depends on ARCH_SUPPORTS_LTO_CLANG 757 depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT 758 # https://github.com/ClangBuiltLinux/linux/issues/1721 759 depends on (!KASAN || KASAN_HW_TAGS || CLANG_VERSION >= 170000) || !DEBUG_INFO 760 depends on (!KCOV || CLANG_VERSION >= 170000) || !DEBUG_INFO 761 depends on !GCOV_KERNEL 762 help 763 The compiler and Kconfig options support building with Clang's 764 LTO. 765 766choice 767 prompt "Link Time Optimization (LTO)" 768 default LTO_NONE 769 help 770 This option enables Link Time Optimization (LTO), which allows the 771 compiler to optimize binaries globally. 772 773 If unsure, select LTO_NONE. Note that LTO is very resource-intensive 774 so it's disabled by default. 775 776config LTO_NONE 777 bool "None" 778 help 779 Build the kernel normally, without Link Time Optimization (LTO). 780 781config LTO_CLANG_FULL 782 bool "Clang Full LTO (EXPERIMENTAL)" 783 depends on HAS_LTO_CLANG 784 depends on !COMPILE_TEST 785 select LTO_CLANG 786 help 787 This option enables Clang's full Link Time Optimization (LTO), which 788 allows the compiler to optimize the kernel globally. If you enable 789 this option, the compiler generates LLVM bitcode instead of ELF 790 object files, and the actual compilation from bitcode happens at 791 the LTO link step, which may take several minutes depending on the 792 kernel configuration. More information can be found from LLVM's 793 documentation: 794 795 https://llvm.org/docs/LinkTimeOptimization.html 796 797 During link time, this option can use a large amount of RAM, and 798 may take much longer than the ThinLTO option. 799 800config LTO_CLANG_THIN 801 bool "Clang ThinLTO (EXPERIMENTAL)" 802 depends on HAS_LTO_CLANG && ARCH_SUPPORTS_LTO_CLANG_THIN 803 select LTO_CLANG 804 help 805 This option enables Clang's ThinLTO, which allows for parallel 806 optimization and faster incremental compiles compared to the 807 CONFIG_LTO_CLANG_FULL option. More information can be found 808 from Clang's documentation: 809 810 https://clang.llvm.org/docs/ThinLTO.html 811 812 If unsure, say Y. 813endchoice 814 815config ARCH_SUPPORTS_CFI_CLANG 816 bool 817 help 818 An architecture should select this option if it can support Clang's 819 Control-Flow Integrity (CFI) checking. 820 821config ARCH_USES_CFI_TRAPS 822 bool 823 824config CFI_CLANG 825 bool "Use Clang's Control Flow Integrity (CFI)" 826 depends on ARCH_SUPPORTS_CFI_CLANG 827 depends on $(cc-option,-fsanitize=kcfi) 828 help 829 This option enables Clang's forward-edge Control Flow Integrity 830 (CFI) checking, where the compiler injects a runtime check to each 831 indirect function call to ensure the target is a valid function with 832 the correct static type. This restricts possible call targets and 833 makes it more difficult for an attacker to exploit bugs that allow 834 the modification of stored function pointers. More information can be 835 found from Clang's documentation: 836 837 https://clang.llvm.org/docs/ControlFlowIntegrity.html 838 839config CFI_ICALL_NORMALIZE_INTEGERS 840 bool "Normalize CFI tags for integers" 841 depends on CFI_CLANG 842 depends on HAVE_CFI_ICALL_NORMALIZE_INTEGERS_CLANG 843 help 844 This option normalizes the CFI tags for integer types so that all 845 integer types of the same size and signedness receive the same CFI 846 tag. 847 848 The option is separate from CONFIG_RUST because it affects the ABI. 849 When working with build systems that care about the ABI, it is 850 convenient to be able to turn on this flag first, before Rust is 851 turned on. 852 853 This option is necessary for using CFI with Rust. If unsure, say N. 854 855config HAVE_CFI_ICALL_NORMALIZE_INTEGERS_CLANG 856 def_bool y 857 depends on $(cc-option,-fsanitize=kcfi -fsanitize-cfi-icall-experimental-normalize-integers) 858 # With GCOV/KASAN we need this fix: https://github.com/llvm/llvm-project/pull/104826 859 depends on CLANG_VERSION >= 190103 || (!GCOV_KERNEL && !KASAN_GENERIC && !KASAN_SW_TAGS) 860 861config HAVE_CFI_ICALL_NORMALIZE_INTEGERS_RUSTC 862 def_bool y 863 depends on HAVE_CFI_ICALL_NORMALIZE_INTEGERS_CLANG 864 depends on RUSTC_VERSION >= 107900 865 # With GCOV/KASAN we need this fix: https://github.com/rust-lang/rust/pull/129373 866 depends on (RUSTC_LLVM_VERSION >= 190103 && RUSTC_VERSION >= 108200) || \ 867 (!GCOV_KERNEL && !KASAN_GENERIC && !KASAN_SW_TAGS) 868 869config CFI_PERMISSIVE 870 bool "Use CFI in permissive mode" 871 depends on CFI_CLANG 872 help 873 When selected, Control Flow Integrity (CFI) violations result in a 874 warning instead of a kernel panic. This option should only be used 875 for finding indirect call type mismatches during development. 876 877 If unsure, say N. 878 879config HAVE_ARCH_WITHIN_STACK_FRAMES 880 bool 881 help 882 An architecture should select this if it can walk the kernel stack 883 frames to determine if an object is part of either the arguments 884 or local variables (i.e. that it excludes saved return addresses, 885 and similar) by implementing an inline arch_within_stack_frames(), 886 which is used by CONFIG_HARDENED_USERCOPY. 887 888config HAVE_CONTEXT_TRACKING_USER 889 bool 890 help 891 Provide kernel/user boundaries probes necessary for subsystems 892 that need it, such as userspace RCU extended quiescent state. 893 Syscalls need to be wrapped inside user_exit()-user_enter(), either 894 optimized behind static key or through the slow path using TIF_NOHZ 895 flag. Exceptions handlers must be wrapped as well. Irqs are already 896 protected inside ct_irq_enter/ct_irq_exit() but preemption or signal 897 handling on irq exit still need to be protected. 898 899config HAVE_CONTEXT_TRACKING_USER_OFFSTACK 900 bool 901 help 902 Architecture neither relies on exception_enter()/exception_exit() 903 nor on schedule_user(). Also preempt_schedule_notrace() and 904 preempt_schedule_irq() can't be called in a preemptible section 905 while context tracking is CT_STATE_USER. This feature reflects a sane 906 entry implementation where the following requirements are met on 907 critical entry code, ie: before user_exit() or after user_enter(): 908 909 - Critical entry code isn't preemptible (or better yet: 910 not interruptible). 911 - No use of RCU read side critical sections, unless ct_nmi_enter() 912 got called. 913 - No use of instrumentation, unless instrumentation_begin() got 914 called. 915 916config HAVE_TIF_NOHZ 917 bool 918 help 919 Arch relies on TIF_NOHZ and syscall slow path to implement context 920 tracking calls to user_enter()/user_exit(). 921 922config HAVE_VIRT_CPU_ACCOUNTING 923 bool 924 925config HAVE_VIRT_CPU_ACCOUNTING_IDLE 926 bool 927 help 928 Architecture has its own way to account idle CPU time and therefore 929 doesn't implement vtime_account_idle(). 930 931config ARCH_HAS_SCALED_CPUTIME 932 bool 933 934config HAVE_VIRT_CPU_ACCOUNTING_GEN 935 bool 936 default y if 64BIT 937 help 938 With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit. 939 Before enabling this option, arch code must be audited 940 to ensure there are no races in concurrent read/write of 941 cputime_t. For example, reading/writing 64-bit cputime_t on 942 some 32-bit arches may require multiple accesses, so proper 943 locking is needed to protect against concurrent accesses. 944 945config HAVE_IRQ_TIME_ACCOUNTING 946 bool 947 help 948 Archs need to ensure they use a high enough resolution clock to 949 support irq time accounting and then call enable_sched_clock_irqtime(). 950 951config HAVE_MOVE_PUD 952 bool 953 help 954 Architectures that select this are able to move page tables at the 955 PUD level. If there are only 3 page table levels, the move effectively 956 happens at the PGD level. 957 958config HAVE_MOVE_PMD 959 bool 960 help 961 Archs that select this are able to move page tables at the PMD level. 962 963config HAVE_ARCH_TRANSPARENT_HUGEPAGE 964 bool 965 966config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD 967 bool 968 969config HAVE_ARCH_HUGE_VMAP 970 bool 971 972# 973# Archs that select this would be capable of PMD-sized vmaps (i.e., 974# arch_vmap_pmd_supported() returns true). The VM_ALLOW_HUGE_VMAP flag 975# must be used to enable allocations to use hugepages. 976# 977config HAVE_ARCH_HUGE_VMALLOC 978 depends on HAVE_ARCH_HUGE_VMAP 979 bool 980 981config ARCH_WANT_HUGE_PMD_SHARE 982 bool 983 984# Archs that want to use pmd_mkwrite on kernel memory need it defined even 985# if there are no userspace memory management features that use it 986config ARCH_WANT_KERNEL_PMD_MKWRITE 987 bool 988 989config ARCH_WANT_PMD_MKWRITE 990 def_bool TRANSPARENT_HUGEPAGE || ARCH_WANT_KERNEL_PMD_MKWRITE 991 992config HAVE_ARCH_SOFT_DIRTY 993 bool 994 995config HAVE_MOD_ARCH_SPECIFIC 996 bool 997 help 998 The arch uses struct mod_arch_specific to store data. Many arches 999 just need a simple module loader without arch specific data - those 1000 should not enable this. 1001 1002config MODULES_USE_ELF_RELA 1003 bool 1004 help 1005 Modules only use ELF RELA relocations. Modules with ELF REL 1006 relocations will give an error. 1007 1008config MODULES_USE_ELF_REL 1009 bool 1010 help 1011 Modules only use ELF REL relocations. Modules with ELF RELA 1012 relocations will give an error. 1013 1014config ARCH_WANTS_MODULES_DATA_IN_VMALLOC 1015 bool 1016 help 1017 For architectures like powerpc/32 which have constraints on module 1018 allocation and need to allocate module data outside of module area. 1019 1020config ARCH_WANTS_EXECMEM_LATE 1021 bool 1022 help 1023 For architectures that do not allocate executable memory early on 1024 boot, but rather require its initialization late when there is 1025 enough entropy for module space randomization, for instance 1026 arm64. 1027 1028config ARCH_HAS_EXECMEM_ROX 1029 bool 1030 depends on MMU && !HIGHMEM 1031 help 1032 For architectures that support allocations of executable memory 1033 with read-only execute permissions. Architecture must implement 1034 execmem_fill_trapping_insns() callback to enable this. 1035 1036config HAVE_IRQ_EXIT_ON_IRQ_STACK 1037 bool 1038 help 1039 Architecture doesn't only execute the irq handler on the irq stack 1040 but also irq_exit(). This way we can process softirqs on this irq 1041 stack instead of switching to a new one when we call __do_softirq() 1042 in the end of an hardirq. 1043 This spares a stack switch and improves cache usage on softirq 1044 processing. 1045 1046config HAVE_SOFTIRQ_ON_OWN_STACK 1047 bool 1048 help 1049 Architecture provides a function to run __do_softirq() on a 1050 separate stack. 1051 1052config SOFTIRQ_ON_OWN_STACK 1053 def_bool HAVE_SOFTIRQ_ON_OWN_STACK && !PREEMPT_RT 1054 1055config ALTERNATE_USER_ADDRESS_SPACE 1056 bool 1057 help 1058 Architectures set this when the CPU uses separate address 1059 spaces for kernel and user space pointers. In this case, the 1060 access_ok() check on a __user pointer is skipped. 1061 1062config PGTABLE_LEVELS 1063 int 1064 default 2 1065 1066config ARCH_HAS_ELF_RANDOMIZE 1067 bool 1068 help 1069 An architecture supports choosing randomized locations for 1070 stack, mmap, brk, and ET_DYN. Defined functions: 1071 - arch_mmap_rnd() 1072 - arch_randomize_brk() 1073 1074config HAVE_ARCH_MMAP_RND_BITS 1075 bool 1076 help 1077 An arch should select this symbol if it supports setting a variable 1078 number of bits for use in establishing the base address for mmap 1079 allocations, has MMU enabled and provides values for both: 1080 - ARCH_MMAP_RND_BITS_MIN 1081 - ARCH_MMAP_RND_BITS_MAX 1082 1083config HAVE_EXIT_THREAD 1084 bool 1085 help 1086 An architecture implements exit_thread. 1087 1088config ARCH_MMAP_RND_BITS_MIN 1089 int 1090 1091config ARCH_MMAP_RND_BITS_MAX 1092 int 1093 1094config ARCH_MMAP_RND_BITS_DEFAULT 1095 int 1096 1097config ARCH_MMAP_RND_BITS 1098 int "Number of bits to use for ASLR of mmap base address" if EXPERT 1099 range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX 1100 default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT 1101 default ARCH_MMAP_RND_BITS_MIN 1102 depends on HAVE_ARCH_MMAP_RND_BITS 1103 help 1104 This value can be used to select the number of bits to use to 1105 determine the random offset to the base address of vma regions 1106 resulting from mmap allocations. This value will be bounded 1107 by the architecture's minimum and maximum supported values. 1108 1109 This value can be changed after boot using the 1110 /proc/sys/vm/mmap_rnd_bits tunable 1111 1112config HAVE_ARCH_MMAP_RND_COMPAT_BITS 1113 bool 1114 help 1115 An arch should select this symbol if it supports running applications 1116 in compatibility mode, supports setting a variable number of bits for 1117 use in establishing the base address for mmap allocations, has MMU 1118 enabled and provides values for both: 1119 - ARCH_MMAP_RND_COMPAT_BITS_MIN 1120 - ARCH_MMAP_RND_COMPAT_BITS_MAX 1121 1122config ARCH_MMAP_RND_COMPAT_BITS_MIN 1123 int 1124 1125config ARCH_MMAP_RND_COMPAT_BITS_MAX 1126 int 1127 1128config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT 1129 int 1130 1131config ARCH_MMAP_RND_COMPAT_BITS 1132 int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT 1133 range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX 1134 default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT 1135 default ARCH_MMAP_RND_COMPAT_BITS_MIN 1136 depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS 1137 help 1138 This value can be used to select the number of bits to use to 1139 determine the random offset to the base address of vma regions 1140 resulting from mmap allocations for compatible applications This 1141 value will be bounded by the architecture's minimum and maximum 1142 supported values. 1143 1144 This value can be changed after boot using the 1145 /proc/sys/vm/mmap_rnd_compat_bits tunable 1146 1147config HAVE_ARCH_COMPAT_MMAP_BASES 1148 bool 1149 help 1150 This allows 64bit applications to invoke 32-bit mmap() syscall 1151 and vice-versa 32-bit applications to call 64-bit mmap(). 1152 Required for applications doing different bitness syscalls. 1153 1154config HAVE_PAGE_SIZE_4KB 1155 bool 1156 1157config HAVE_PAGE_SIZE_8KB 1158 bool 1159 1160config HAVE_PAGE_SIZE_16KB 1161 bool 1162 1163config HAVE_PAGE_SIZE_32KB 1164 bool 1165 1166config HAVE_PAGE_SIZE_64KB 1167 bool 1168 1169config HAVE_PAGE_SIZE_256KB 1170 bool 1171 1172choice 1173 prompt "MMU page size" 1174 1175config PAGE_SIZE_4KB 1176 bool "4KiB pages" 1177 depends on HAVE_PAGE_SIZE_4KB 1178 help 1179 This option select the standard 4KiB Linux page size and the only 1180 available option on many architectures. Using 4KiB page size will 1181 minimize memory consumption and is therefore recommended for low 1182 memory systems. 1183 Some software that is written for x86 systems makes incorrect 1184 assumptions about the page size and only runs on 4KiB pages. 1185 1186config PAGE_SIZE_8KB 1187 bool "8KiB pages" 1188 depends on HAVE_PAGE_SIZE_8KB 1189 help 1190 This option is the only supported page size on a few older 1191 processors, and can be slightly faster than 4KiB pages. 1192 1193config PAGE_SIZE_16KB 1194 bool "16KiB pages" 1195 depends on HAVE_PAGE_SIZE_16KB 1196 help 1197 This option is usually a good compromise between memory 1198 consumption and performance for typical desktop and server 1199 workloads, often saving a level of page table lookups compared 1200 to 4KB pages as well as reducing TLB pressure and overhead of 1201 per-page operations in the kernel at the expense of a larger 1202 page cache. 1203 1204config PAGE_SIZE_32KB 1205 bool "32KiB pages" 1206 depends on HAVE_PAGE_SIZE_32KB 1207 help 1208 Using 32KiB page size will result in slightly higher performance 1209 kernel at the price of higher memory consumption compared to 1210 16KiB pages. This option is available only on cnMIPS cores. 1211 Note that you will need a suitable Linux distribution to 1212 support this. 1213 1214config PAGE_SIZE_64KB 1215 bool "64KiB pages" 1216 depends on HAVE_PAGE_SIZE_64KB 1217 help 1218 Using 64KiB page size will result in slightly higher performance 1219 kernel at the price of much higher memory consumption compared to 1220 4KiB or 16KiB pages. 1221 This is not suitable for general-purpose workloads but the 1222 better performance may be worth the cost for certain types of 1223 supercomputing or database applications that work mostly with 1224 large in-memory data rather than small files. 1225 1226config PAGE_SIZE_256KB 1227 bool "256KiB pages" 1228 depends on HAVE_PAGE_SIZE_256KB 1229 help 1230 256KiB pages have little practical value due to their extreme 1231 memory usage. The kernel will only be able to run applications 1232 that have been compiled with '-zmax-page-size' set to 256KiB 1233 (the default is 64KiB or 4KiB on most architectures). 1234 1235endchoice 1236 1237config PAGE_SIZE_LESS_THAN_64KB 1238 def_bool y 1239 depends on !PAGE_SIZE_64KB 1240 depends on PAGE_SIZE_LESS_THAN_256KB 1241 1242config PAGE_SIZE_LESS_THAN_256KB 1243 def_bool y 1244 depends on !PAGE_SIZE_256KB 1245 1246config PAGE_SHIFT 1247 int 1248 default 12 if PAGE_SIZE_4KB 1249 default 13 if PAGE_SIZE_8KB 1250 default 14 if PAGE_SIZE_16KB 1251 default 15 if PAGE_SIZE_32KB 1252 default 16 if PAGE_SIZE_64KB 1253 default 18 if PAGE_SIZE_256KB 1254 1255# This allows to use a set of generic functions to determine mmap base 1256# address by giving priority to top-down scheme only if the process 1257# is not in legacy mode (compat task, unlimited stack size or 1258# sysctl_legacy_va_layout). 1259# Architecture that selects this option can provide its own version of: 1260# - STACK_RND_MASK 1261config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT 1262 bool 1263 depends on MMU 1264 select ARCH_HAS_ELF_RANDOMIZE 1265 1266config HAVE_OBJTOOL 1267 bool 1268 1269config HAVE_JUMP_LABEL_HACK 1270 bool 1271 1272config HAVE_NOINSTR_HACK 1273 bool 1274 1275config HAVE_NOINSTR_VALIDATION 1276 bool 1277 1278config HAVE_UACCESS_VALIDATION 1279 bool 1280 select OBJTOOL 1281 1282config HAVE_STACK_VALIDATION 1283 bool 1284 help 1285 Architecture supports objtool compile-time frame pointer rule 1286 validation. 1287 1288config HAVE_RELIABLE_STACKTRACE 1289 bool 1290 help 1291 Architecture has either save_stack_trace_tsk_reliable() or 1292 arch_stack_walk_reliable() function which only returns a stack trace 1293 if it can guarantee the trace is reliable. 1294 1295config HAVE_ARCH_HASH 1296 bool 1297 default n 1298 help 1299 If this is set, the architecture provides an <asm/hash.h> 1300 file which provides platform-specific implementations of some 1301 functions in <linux/hash.h> or fs/namei.c. 1302 1303config HAVE_ARCH_NVRAM_OPS 1304 bool 1305 1306config ISA_BUS_API 1307 def_bool ISA 1308 1309# 1310# ABI hall of shame 1311# 1312config CLONE_BACKWARDS 1313 bool 1314 help 1315 Architecture has tls passed as the 4th argument of clone(2), 1316 not the 5th one. 1317 1318config CLONE_BACKWARDS2 1319 bool 1320 help 1321 Architecture has the first two arguments of clone(2) swapped. 1322 1323config CLONE_BACKWARDS3 1324 bool 1325 help 1326 Architecture has tls passed as the 3rd argument of clone(2), 1327 not the 5th one. 1328 1329config ODD_RT_SIGACTION 1330 bool 1331 help 1332 Architecture has unusual rt_sigaction(2) arguments 1333 1334config OLD_SIGSUSPEND 1335 bool 1336 help 1337 Architecture has old sigsuspend(2) syscall, of one-argument variety 1338 1339config OLD_SIGSUSPEND3 1340 bool 1341 help 1342 Even weirder antique ABI - three-argument sigsuspend(2) 1343 1344config OLD_SIGACTION 1345 bool 1346 help 1347 Architecture has old sigaction(2) syscall. Nope, not the same 1348 as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2), 1349 but fairly different variant of sigaction(2), thanks to OSF/1 1350 compatibility... 1351 1352config COMPAT_OLD_SIGACTION 1353 bool 1354 1355config COMPAT_32BIT_TIME 1356 bool "Provide system calls for 32-bit time_t" 1357 default !64BIT || COMPAT 1358 help 1359 This enables 32 bit time_t support in addition to 64 bit time_t support. 1360 This is relevant on all 32-bit architectures, and 64-bit architectures 1361 as part of compat syscall handling. 1362 1363config ARCH_NO_PREEMPT 1364 bool 1365 1366config ARCH_SUPPORTS_RT 1367 bool 1368 1369config CPU_NO_EFFICIENT_FFS 1370 def_bool n 1371 1372config HAVE_ARCH_VMAP_STACK 1373 def_bool n 1374 help 1375 An arch should select this symbol if it can support kernel stacks 1376 in vmalloc space. This means: 1377 1378 - vmalloc space must be large enough to hold many kernel stacks. 1379 This may rule out many 32-bit architectures. 1380 1381 - Stacks in vmalloc space need to work reliably. For example, if 1382 vmap page tables are created on demand, either this mechanism 1383 needs to work while the stack points to a virtual address with 1384 unpopulated page tables or arch code (switch_to() and switch_mm(), 1385 most likely) needs to ensure that the stack's page table entries 1386 are populated before running on a possibly unpopulated stack. 1387 1388 - If the stack overflows into a guard page, something reasonable 1389 should happen. The definition of "reasonable" is flexible, but 1390 instantly rebooting without logging anything would be unfriendly. 1391 1392config VMAP_STACK 1393 default y 1394 bool "Use a virtually-mapped stack" 1395 depends on HAVE_ARCH_VMAP_STACK 1396 depends on !KASAN || KASAN_HW_TAGS || KASAN_VMALLOC 1397 help 1398 Enable this if you want the use virtually-mapped kernel stacks 1399 with guard pages. This causes kernel stack overflows to be 1400 caught immediately rather than causing difficult-to-diagnose 1401 corruption. 1402 1403 To use this with software KASAN modes, the architecture must support 1404 backing virtual mappings with real shadow memory, and KASAN_VMALLOC 1405 must be enabled. 1406 1407config HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET 1408 def_bool n 1409 help 1410 An arch should select this symbol if it can support kernel stack 1411 offset randomization with calls to add_random_kstack_offset() 1412 during syscall entry and choose_random_kstack_offset() during 1413 syscall exit. Careful removal of -fstack-protector-strong and 1414 -fstack-protector should also be applied to the entry code and 1415 closely examined, as the artificial stack bump looks like an array 1416 to the compiler, so it will attempt to add canary checks regardless 1417 of the static branch state. 1418 1419config RANDOMIZE_KSTACK_OFFSET 1420 bool "Support for randomizing kernel stack offset on syscall entry" if EXPERT 1421 default y 1422 depends on HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET 1423 depends on INIT_STACK_NONE || !CC_IS_CLANG || CLANG_VERSION >= 140000 1424 help 1425 The kernel stack offset can be randomized (after pt_regs) by 1426 roughly 5 bits of entropy, frustrating memory corruption 1427 attacks that depend on stack address determinism or 1428 cross-syscall address exposures. 1429 1430 The feature is controlled via the "randomize_kstack_offset=on/off" 1431 kernel boot param, and if turned off has zero overhead due to its use 1432 of static branches (see JUMP_LABEL). 1433 1434 If unsure, say Y. 1435 1436config RANDOMIZE_KSTACK_OFFSET_DEFAULT 1437 bool "Default state of kernel stack offset randomization" 1438 depends on RANDOMIZE_KSTACK_OFFSET 1439 help 1440 Kernel stack offset randomization is controlled by kernel boot param 1441 "randomize_kstack_offset=on/off", and this config chooses the default 1442 boot state. 1443 1444config ARCH_OPTIONAL_KERNEL_RWX 1445 def_bool n 1446 1447config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT 1448 def_bool n 1449 1450config ARCH_HAS_STRICT_KERNEL_RWX 1451 def_bool n 1452 1453config STRICT_KERNEL_RWX 1454 bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX 1455 depends on ARCH_HAS_STRICT_KERNEL_RWX 1456 default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT 1457 help 1458 If this is set, kernel text and rodata memory will be made read-only, 1459 and non-text memory will be made non-executable. This provides 1460 protection against certain security exploits (e.g. executing the heap 1461 or modifying text) 1462 1463 These features are considered standard security practice these days. 1464 You should say Y here in almost all cases. 1465 1466config ARCH_HAS_STRICT_MODULE_RWX 1467 def_bool n 1468 1469config STRICT_MODULE_RWX 1470 bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX 1471 depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES 1472 default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT 1473 help 1474 If this is set, module text and rodata memory will be made read-only, 1475 and non-text memory will be made non-executable. This provides 1476 protection against certain security exploits (e.g. writing to text) 1477 1478# select if the architecture provides an asm/dma-direct.h header 1479config ARCH_HAS_PHYS_TO_DMA 1480 bool 1481 1482config HAVE_ARCH_COMPILER_H 1483 bool 1484 help 1485 An architecture can select this if it provides an 1486 asm/compiler.h header that should be included after 1487 linux/compiler-*.h in order to override macro definitions that those 1488 headers generally provide. 1489 1490config HAVE_ARCH_PREL32_RELOCATIONS 1491 bool 1492 help 1493 May be selected by an architecture if it supports place-relative 1494 32-bit relocations, both in the toolchain and in the module loader, 1495 in which case relative references can be used in special sections 1496 for PCI fixup, initcalls etc which are only half the size on 64 bit 1497 architectures, and don't require runtime relocation on relocatable 1498 kernels. 1499 1500config ARCH_USE_MEMREMAP_PROT 1501 bool 1502 1503config LOCK_EVENT_COUNTS 1504 bool "Locking event counts collection" 1505 depends on DEBUG_FS 1506 help 1507 Enable light-weight counting of various locking related events 1508 in the system with minimal performance impact. This reduces 1509 the chance of application behavior change because of timing 1510 differences. The counts are reported via debugfs. 1511 1512# Select if the architecture has support for applying RELR relocations. 1513config ARCH_HAS_RELR 1514 bool 1515 1516config RELR 1517 bool "Use RELR relocation packing" 1518 depends on ARCH_HAS_RELR && TOOLS_SUPPORT_RELR 1519 default y 1520 help 1521 Store the kernel's dynamic relocations in the RELR relocation packing 1522 format. Requires a compatible linker (LLD supports this feature), as 1523 well as compatible NM and OBJCOPY utilities (llvm-nm and llvm-objcopy 1524 are compatible). 1525 1526config ARCH_HAS_MEM_ENCRYPT 1527 bool 1528 1529config ARCH_HAS_CC_PLATFORM 1530 bool 1531 1532config HAVE_SPARSE_SYSCALL_NR 1533 bool 1534 help 1535 An architecture should select this if its syscall numbering is sparse 1536 to save space. For example, MIPS architecture has a syscall array with 1537 entries at 4000, 5000 and 6000 locations. This option turns on syscall 1538 related optimizations for a given architecture. 1539 1540config ARCH_HAS_VDSO_TIME_DATA 1541 bool 1542 1543config HAVE_STATIC_CALL 1544 bool 1545 1546config HAVE_STATIC_CALL_INLINE 1547 bool 1548 depends on HAVE_STATIC_CALL 1549 select OBJTOOL 1550 1551config HAVE_PREEMPT_DYNAMIC 1552 bool 1553 1554config HAVE_PREEMPT_DYNAMIC_CALL 1555 bool 1556 depends on HAVE_STATIC_CALL 1557 select HAVE_PREEMPT_DYNAMIC 1558 help 1559 An architecture should select this if it can handle the preemption 1560 model being selected at boot time using static calls. 1561 1562 Where an architecture selects HAVE_STATIC_CALL_INLINE, any call to a 1563 preemption function will be patched directly. 1564 1565 Where an architecture does not select HAVE_STATIC_CALL_INLINE, any 1566 call to a preemption function will go through a trampoline, and the 1567 trampoline will be patched. 1568 1569 It is strongly advised to support inline static call to avoid any 1570 overhead. 1571 1572config HAVE_PREEMPT_DYNAMIC_KEY 1573 bool 1574 depends on HAVE_ARCH_JUMP_LABEL 1575 select HAVE_PREEMPT_DYNAMIC 1576 help 1577 An architecture should select this if it can handle the preemption 1578 model being selected at boot time using static keys. 1579 1580 Each preemption function will be given an early return based on a 1581 static key. This should have slightly lower overhead than non-inline 1582 static calls, as this effectively inlines each trampoline into the 1583 start of its callee. This may avoid redundant work, and may 1584 integrate better with CFI schemes. 1585 1586 This will have greater overhead than using inline static calls as 1587 the call to the preemption function cannot be entirely elided. 1588 1589config ARCH_WANT_LD_ORPHAN_WARN 1590 bool 1591 help 1592 An arch should select this symbol once all linker sections are explicitly 1593 included, size-asserted, or discarded in the linker scripts. This is 1594 important because we never want expected sections to be placed heuristically 1595 by the linker, since the locations of such sections can change between linker 1596 versions. 1597 1598config HAVE_ARCH_PFN_VALID 1599 bool 1600 1601config ARCH_SUPPORTS_DEBUG_PAGEALLOC 1602 bool 1603 1604config ARCH_SUPPORTS_PAGE_TABLE_CHECK 1605 bool 1606 1607config ARCH_SPLIT_ARG64 1608 bool 1609 help 1610 If a 32-bit architecture requires 64-bit arguments to be split into 1611 pairs of 32-bit arguments, select this option. 1612 1613config ARCH_HAS_ELFCORE_COMPAT 1614 bool 1615 1616config ARCH_HAS_PARANOID_L1D_FLUSH 1617 bool 1618 1619config ARCH_HAVE_TRACE_MMIO_ACCESS 1620 bool 1621 1622config DYNAMIC_SIGFRAME 1623 bool 1624 1625# Select, if arch has a named attribute group bound to NUMA device nodes. 1626config HAVE_ARCH_NODE_DEV_GROUP 1627 bool 1628 1629config ARCH_HAS_HW_PTE_YOUNG 1630 bool 1631 help 1632 Architectures that select this option are capable of setting the 1633 accessed bit in PTE entries when using them as part of linear address 1634 translations. Architectures that require runtime check should select 1635 this option and override arch_has_hw_pte_young(). 1636 1637config ARCH_HAS_NONLEAF_PMD_YOUNG 1638 bool 1639 help 1640 Architectures that select this option are capable of setting the 1641 accessed bit in non-leaf PMD entries when using them as part of linear 1642 address translations. Page table walkers that clear the accessed bit 1643 may use this capability to reduce their search space. 1644 1645config ARCH_HAS_KERNEL_FPU_SUPPORT 1646 bool 1647 help 1648 Architectures that select this option can run floating-point code in 1649 the kernel, as described in Documentation/core-api/floating-point.rst. 1650 1651source "kernel/gcov/Kconfig" 1652 1653source "scripts/gcc-plugins/Kconfig" 1654 1655config FUNCTION_ALIGNMENT_4B 1656 bool 1657 1658config FUNCTION_ALIGNMENT_8B 1659 bool 1660 1661config FUNCTION_ALIGNMENT_16B 1662 bool 1663 1664config FUNCTION_ALIGNMENT_32B 1665 bool 1666 1667config FUNCTION_ALIGNMENT_64B 1668 bool 1669 1670config FUNCTION_ALIGNMENT 1671 int 1672 default 64 if FUNCTION_ALIGNMENT_64B 1673 default 32 if FUNCTION_ALIGNMENT_32B 1674 default 16 if FUNCTION_ALIGNMENT_16B 1675 default 8 if FUNCTION_ALIGNMENT_8B 1676 default 4 if FUNCTION_ALIGNMENT_4B 1677 default 0 1678 1679config CC_HAS_MIN_FUNCTION_ALIGNMENT 1680 # Detect availability of the GCC option -fmin-function-alignment which 1681 # guarantees minimal alignment for all functions, unlike 1682 # -falign-functions which the compiler ignores for cold functions. 1683 def_bool $(cc-option, -fmin-function-alignment=8) 1684 1685config CC_HAS_SANE_FUNCTION_ALIGNMENT 1686 # Set if the guaranteed alignment with -fmin-function-alignment is 1687 # available or extra care is required in the kernel. Clang provides 1688 # strict alignment always, even with -falign-functions. 1689 def_bool CC_HAS_MIN_FUNCTION_ALIGNMENT || CC_IS_CLANG 1690 1691config ARCH_NEED_CMPXCHG_1_EMU 1692 bool 1693 1694config ARCH_WANTS_PRE_LINK_VMLINUX 1695 bool 1696 help 1697 An architecture can select this if it provides arch/<arch>/tools/Makefile 1698 with .arch.vmlinux.o target to be linked into vmlinux. 1699 1700endmenu 1701