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