# # General architecture dependent options # config KEXEC_CORE bool config HAVE_IMA_KEXEC bool config OPROFILE tristate "OProfile system profiling" depends on PROFILING depends on HAVE_OPROFILE select RING_BUFFER select RING_BUFFER_ALLOW_SWAP help OProfile is a profiling system capable of profiling the whole system, include the kernel, kernel modules, libraries, and applications. If unsure, say N. config OPROFILE_EVENT_MULTIPLEX bool "OProfile multiplexing support (EXPERIMENTAL)" default n depends on OPROFILE && X86 help The number of hardware counters is limited. The multiplexing feature enables OProfile to gather more events than counters are provided by the hardware. This is realized by switching between events at an user specified time interval. If unsure, say N. config HAVE_OPROFILE bool config OPROFILE_NMI_TIMER def_bool y depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI && !PPC64 config KPROBES bool "Kprobes" depends on MODULES depends on HAVE_KPROBES select KALLSYMS help Kprobes allows you to trap at almost any kernel address and execute a callback function. register_kprobe() establishes a probepoint and specifies the callback. Kprobes is useful for kernel debugging, non-intrusive instrumentation and testing. If in doubt, say "N". config JUMP_LABEL bool "Optimize very unlikely/likely branches" depends on HAVE_ARCH_JUMP_LABEL help This option enables a transparent branch optimization that makes certain almost-always-true or almost-always-false branch conditions even cheaper to execute within the kernel. Certain performance-sensitive kernel code, such as trace points, scheduler functionality, networking code and KVM have such branches and include support for this optimization technique. If it is detected that the compiler has support for "asm goto", the kernel will compile such branches with just a nop instruction. When the condition flag is toggled to true, the nop will be converted to a jump instruction to execute the conditional block of instructions. This technique lowers overhead and stress on the branch prediction of the processor and generally makes the kernel faster. The update of the condition is slower, but those are always very rare. ( On 32-bit x86, the necessary options added to the compiler flags may increase the size of the kernel slightly. ) config STATIC_KEYS_SELFTEST bool "Static key selftest" depends on JUMP_LABEL help Boot time self-test of the branch patching code. config OPTPROBES def_bool y depends on KPROBES && HAVE_OPTPROBES depends on !PREEMPT config KPROBES_ON_FTRACE def_bool y depends on KPROBES && HAVE_KPROBES_ON_FTRACE depends on DYNAMIC_FTRACE_WITH_REGS help If function tracer is enabled and the arch supports full passing of pt_regs to function tracing, then kprobes can optimize on top of function tracing. config UPROBES def_bool n depends on ARCH_SUPPORTS_UPROBES help Uprobes is the user-space counterpart to kprobes: they enable instrumentation applications (such as 'perf probe') to establish unintrusive probes in user-space binaries and libraries, by executing handler functions when the probes are hit by user-space applications. ( These probes come in the form of single-byte breakpoints, managed by the kernel and kept transparent to the probed application. ) config HAVE_64BIT_ALIGNED_ACCESS def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS help Some architectures require 64 bit accesses to be 64 bit aligned, which also requires structs containing 64 bit values to be 64 bit aligned too. This includes some 32 bit architectures which can do 64 bit accesses, as well as 64 bit architectures without unaligned access. This symbol should be selected by an architecture if 64 bit accesses are required to be 64 bit aligned in this way even though it is not a 64 bit architecture. See Documentation/unaligned-memory-access.txt for more information on the topic of unaligned memory accesses. config HAVE_EFFICIENT_UNALIGNED_ACCESS bool help Some architectures are unable to perform unaligned accesses without the use of get_unaligned/put_unaligned. Others are unable to perform such accesses efficiently (e.g. trap on unaligned access and require fixing it up in the exception handler.) This symbol should be selected by an architecture if it can perform unaligned accesses efficiently to allow different code paths to be selected for these cases. Some network drivers, for example, could opt to not fix up alignment problems with received packets if doing so would not help much. See Documentation/unaligned-memory-access.txt for more information on the topic of unaligned memory accesses. config ARCH_USE_BUILTIN_BSWAP bool help Modern versions of GCC (since 4.4) have builtin functions for handling byte-swapping. Using these, instead of the old inline assembler that the architecture code provides in the __arch_bswapXX() macros, allows the compiler to see what's happening and offers more opportunity for optimisation. In particular, the compiler will be able to combine the byteswap with a nearby load or store and use load-and-swap or store-and-swap instructions if the architecture has them. It should almost *never* result in code which is worse than the hand-coded assembler in . But just in case it does, the use of the builtins is optional. Any architecture with load-and-swap or store-and-swap instructions should set this. And it shouldn't hurt to set it on architectures that don't have such instructions. config KRETPROBES def_bool y depends on KPROBES && HAVE_KRETPROBES config USER_RETURN_NOTIFIER bool depends on HAVE_USER_RETURN_NOTIFIER help Provide a kernel-internal notification when a cpu is about to switch to user mode. config HAVE_IOREMAP_PROT bool config HAVE_KPROBES bool config HAVE_KRETPROBES bool config HAVE_OPTPROBES bool config HAVE_KPROBES_ON_FTRACE bool config HAVE_NMI bool config HAVE_NMI_WATCHDOG depends on HAVE_NMI bool # # An arch should select this if it provides all these things: # # task_pt_regs() in asm/processor.h or asm/ptrace.h # arch_has_single_step() if there is hardware single-step support # arch_has_block_step() if there is hardware block-step support # asm/syscall.h supplying asm-generic/syscall.h interface # linux/regset.h user_regset interfaces # CORE_DUMP_USE_REGSET #define'd in linux/elf.h # TIF_SYSCALL_TRACE calls tracehook_report_syscall_{entry,exit} # TIF_NOTIFY_RESUME calls tracehook_notify_resume() # signal delivery calls tracehook_signal_handler() # config HAVE_ARCH_TRACEHOOK bool config HAVE_DMA_CONTIGUOUS bool config GENERIC_SMP_IDLE_THREAD bool config GENERIC_IDLE_POLL_SETUP bool # Select if arch init_task initializer is different to init/init_task.c config ARCH_INIT_TASK bool # Select if arch has its private alloc_task_struct() function config ARCH_TASK_STRUCT_ALLOCATOR bool # Select if arch has its private alloc_thread_stack() function config ARCH_THREAD_STACK_ALLOCATOR bool # Select if arch wants to size task_struct dynamically via arch_task_struct_size: config ARCH_WANTS_DYNAMIC_TASK_STRUCT bool config HAVE_REGS_AND_STACK_ACCESS_API bool help This symbol should be selected by an architecure if it supports the API needed to access registers and stack entries from pt_regs, declared in asm/ptrace.h For example the kprobes-based event tracer needs this API. config HAVE_CLK bool help The calls support software clock gating and thus are a key power management tool on many systems. config HAVE_DMA_API_DEBUG bool config HAVE_HW_BREAKPOINT bool depends on PERF_EVENTS config HAVE_MIXED_BREAKPOINTS_REGS bool depends on HAVE_HW_BREAKPOINT help Depending on the arch implementation of hardware breakpoints, some of them have separate registers for data and instruction breakpoints addresses, others have mixed registers to store them but define the access type in a control register. Select this option if your arch implements breakpoints under the latter fashion. config HAVE_USER_RETURN_NOTIFIER bool config HAVE_PERF_EVENTS_NMI bool help System hardware can generate an NMI using the perf event subsystem. Also has support for calculating CPU cycle events to determine how many clock cycles in a given period. config HAVE_PERF_REGS bool help Support selective register dumps for perf events. This includes bit-mapping of each registers and a unique architecture id. config HAVE_PERF_USER_STACK_DUMP bool help Support user stack dumps for perf event samples. This needs access to the user stack pointer which is not unified across architectures. config HAVE_ARCH_JUMP_LABEL bool config HAVE_RCU_TABLE_FREE bool config ARCH_HAVE_NMI_SAFE_CMPXCHG bool config HAVE_ALIGNED_STRUCT_PAGE bool help This makes sure that struct pages are double word aligned and that e.g. the SLUB allocator can perform double word atomic operations on a struct page for better performance. However selecting this might increase the size of a struct page by a word. config HAVE_CMPXCHG_LOCAL bool config HAVE_CMPXCHG_DOUBLE bool config ARCH_WANT_IPC_PARSE_VERSION bool config ARCH_WANT_COMPAT_IPC_PARSE_VERSION bool config ARCH_WANT_OLD_COMPAT_IPC select ARCH_WANT_COMPAT_IPC_PARSE_VERSION bool config HAVE_ARCH_SECCOMP_FILTER bool help An arch should select this symbol if it provides all of these things: - syscall_get_arch() - syscall_get_arguments() - syscall_rollback() - syscall_set_return_value() - SIGSYS siginfo_t support - secure_computing is called from a ptrace_event()-safe context - secure_computing return value is checked and a return value of -1 results in the system call being skipped immediately. - seccomp syscall wired up config SECCOMP_FILTER def_bool y depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET help Enable tasks to build secure computing environments defined in terms of Berkeley Packet Filter programs which implement task-defined system call filtering polices. See Documentation/prctl/seccomp_filter.txt for details. config HAVE_GCC_PLUGINS bool help An arch should select this symbol if it supports building with GCC plugins. menuconfig GCC_PLUGINS bool "GCC plugins" depends on HAVE_GCC_PLUGINS depends on !COMPILE_TEST help GCC plugins are loadable modules that provide extra features to the compiler. They are useful for runtime instrumentation and static analysis. See Documentation/gcc-plugins.txt for details. config GCC_PLUGIN_CYC_COMPLEXITY bool "Compute the cyclomatic complexity of a function" if EXPERT depends on GCC_PLUGINS depends on !COMPILE_TEST help The complexity M of a function's control flow graph is defined as: M = E - N + 2P where E = the number of edges N = the number of nodes P = the number of connected components (exit nodes). Enabling this plugin reports the complexity to stderr during the build. It mainly serves as a simple example of how to create a gcc plugin for the kernel. config GCC_PLUGIN_SANCOV bool depends on GCC_PLUGINS help This plugin inserts a __sanitizer_cov_trace_pc() call at the start of basic blocks. It supports all gcc versions with plugin support (from gcc-4.5 on). It is based on the commit "Add fuzzing coverage support" by Dmitry Vyukov . config GCC_PLUGIN_LATENT_ENTROPY bool "Generate some entropy during boot and runtime" depends on GCC_PLUGINS help By saying Y here the kernel will instrument some kernel code to extract some entropy from both original and artificially created program state. This will help especially embedded systems where there is little 'natural' source of entropy normally. The cost is some slowdown of the boot process (about 0.5%) and fork and irq processing. Note that entropy extracted this way is not cryptographically secure! This plugin was ported from grsecurity/PaX. More information at: * https://grsecurity.net/ * https://pax.grsecurity.net/ config HAVE_CC_STACKPROTECTOR bool help An arch should select this symbol if: - its compiler supports the -fstack-protector option - it has implemented a stack canary (e.g. __stack_chk_guard) config CC_STACKPROTECTOR def_bool n help Set when a stack-protector mode is enabled, so that the build can enable kernel-side support for the GCC feature. choice prompt "Stack Protector buffer overflow detection" depends on HAVE_CC_STACKPROTECTOR default CC_STACKPROTECTOR_NONE help This option turns on the "stack-protector" GCC feature. This feature puts, at the beginning of functions, a canary value on the stack just before the return address, and validates the value just before actually returning. Stack based buffer overflows (that need to overwrite this return address) now also overwrite the canary, which gets detected and the attack is then neutralized via a kernel panic. config CC_STACKPROTECTOR_NONE bool "None" help Disable "stack-protector" GCC feature. config CC_STACKPROTECTOR_REGULAR bool "Regular" select CC_STACKPROTECTOR help Functions will have the stack-protector canary logic added if they have an 8-byte or larger character array on the stack. This feature requires gcc version 4.2 or above, or a distribution gcc with the feature backported ("-fstack-protector"). On an x86 "defconfig" build, this feature adds canary checks to about 3% of all kernel functions, which increases kernel code size by about 0.3%. config CC_STACKPROTECTOR_STRONG bool "Strong" select CC_STACKPROTECTOR help Functions will have the stack-protector canary logic added in any of the following conditions: - local variable's address used as part of the right hand side of an assignment or function argument - local variable is an array (or union containing an array), regardless of array type or length - uses register local variables This feature requires gcc version 4.9 or above, or a distribution gcc with the feature backported ("-fstack-protector-strong"). On an x86 "defconfig" build, this feature adds canary checks to about 20% of all kernel functions, which increases the kernel code size by about 2%. endchoice config THIN_ARCHIVES bool help Select this if the architecture wants to use thin archives instead of ld -r to create the built-in.o files. config LD_DEAD_CODE_DATA_ELIMINATION bool help Select this if the architecture wants to do dead code and data elimination with the linker by compiling with -ffunction-sections -fdata-sections and linking with --gc-sections. This requires that the arch annotates or otherwise protects its external entry points from being discarded. Linker scripts must also merge .text.*, .data.*, and .bss.* correctly into output sections. Care must be taken not to pull in unrelated sections (e.g., '.text.init'). Typically '.' in section names is used to distinguish them from label names / C identifiers. config HAVE_ARCH_WITHIN_STACK_FRAMES bool help An architecture should select this if it can walk the kernel stack frames to determine if an object is part of either the arguments or local variables (i.e. that it excludes saved return addresses, and similar) by implementing an inline arch_within_stack_frames(), which is used by CONFIG_HARDENED_USERCOPY. config HAVE_CONTEXT_TRACKING bool help Provide kernel/user boundaries probes necessary for subsystems that need it, such as userspace RCU extended quiescent state. Syscalls need to be wrapped inside user_exit()-user_enter() through the slow path using TIF_NOHZ flag. Exceptions handlers must be wrapped as well. Irqs are already protected inside rcu_irq_enter/rcu_irq_exit() but preemption or signal handling on irq exit still need to be protected. config HAVE_VIRT_CPU_ACCOUNTING bool config ARCH_HAS_SCALED_CPUTIME bool config HAVE_VIRT_CPU_ACCOUNTING_GEN bool default y if 64BIT help With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit. Before enabling this option, arch code must be audited to ensure there are no races in concurrent read/write of cputime_t. For example, reading/writing 64-bit cputime_t on some 32-bit arches may require multiple accesses, so proper locking is needed to protect against concurrent accesses. config HAVE_IRQ_TIME_ACCOUNTING bool help Archs need to ensure they use a high enough resolution clock to support irq time accounting and then call enable_sched_clock_irqtime(). config HAVE_ARCH_TRANSPARENT_HUGEPAGE bool config HAVE_ARCH_HUGE_VMAP bool config HAVE_ARCH_SOFT_DIRTY bool config HAVE_MOD_ARCH_SPECIFIC bool help The arch uses struct mod_arch_specific to store data. Many arches just need a simple module loader without arch specific data - those should not enable this. config MODULES_USE_ELF_RELA bool help Modules only use ELF RELA relocations. Modules with ELF REL relocations will give an error. config MODULES_USE_ELF_REL bool help Modules only use ELF REL relocations. Modules with ELF RELA relocations will give an error. config HAVE_UNDERSCORE_SYMBOL_PREFIX bool help Some architectures generate an _ in front of C symbols; things like module loading and assembly files need to know about this. config HAVE_IRQ_EXIT_ON_IRQ_STACK bool help Architecture doesn't only execute the irq handler on the irq stack but also irq_exit(). This way we can process softirqs on this irq stack instead of switching to a new one when we call __do_softirq() in the end of an hardirq. This spares a stack switch and improves cache usage on softirq processing. config PGTABLE_LEVELS int default 2 config ARCH_HAS_ELF_RANDOMIZE bool help An architecture supports choosing randomized locations for stack, mmap, brk, and ET_DYN. Defined functions: - arch_mmap_rnd() - arch_randomize_brk() config HAVE_ARCH_MMAP_RND_BITS bool help An arch should select this symbol if it supports setting a variable number of bits for use in establishing the base address for mmap allocations, has MMU enabled and provides values for both: - ARCH_MMAP_RND_BITS_MIN - ARCH_MMAP_RND_BITS_MAX config HAVE_EXIT_THREAD bool help An architecture implements exit_thread. config ARCH_MMAP_RND_BITS_MIN int config ARCH_MMAP_RND_BITS_MAX int config ARCH_MMAP_RND_BITS_DEFAULT int config ARCH_MMAP_RND_BITS int "Number of bits to use for ASLR of mmap base address" if EXPERT range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT default ARCH_MMAP_RND_BITS_MIN depends on HAVE_ARCH_MMAP_RND_BITS help This value can be used to select the number of bits to use to determine the random offset to the base address of vma regions resulting from mmap allocations. This value will be bounded by the architecture's minimum and maximum supported values. This value can be changed after boot using the /proc/sys/vm/mmap_rnd_bits tunable config HAVE_ARCH_MMAP_RND_COMPAT_BITS bool help An arch should select this symbol if it supports running applications in compatibility mode, supports setting a variable number of bits for use in establishing the base address for mmap allocations, has MMU enabled and provides values for both: - ARCH_MMAP_RND_COMPAT_BITS_MIN - ARCH_MMAP_RND_COMPAT_BITS_MAX config ARCH_MMAP_RND_COMPAT_BITS_MIN int config ARCH_MMAP_RND_COMPAT_BITS_MAX int config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT int config ARCH_MMAP_RND_COMPAT_BITS int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT default ARCH_MMAP_RND_COMPAT_BITS_MIN depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS help This value can be used to select the number of bits to use to determine the random offset to the base address of vma regions resulting from mmap allocations for compatible applications This value will be bounded by the architecture's minimum and maximum supported values. This value can be changed after boot using the /proc/sys/vm/mmap_rnd_compat_bits tunable config HAVE_COPY_THREAD_TLS bool help Architecture provides copy_thread_tls to accept tls argument via normal C parameter passing, rather than extracting the syscall argument from pt_regs. config HAVE_STACK_VALIDATION bool help Architecture supports the 'objtool check' host tool command, which performs compile-time stack metadata validation. config HAVE_ARCH_HASH bool default n help If this is set, the architecture provides an file which provides platform-specific implementations of some functions in or fs/namei.c. config ISA_BUS_API def_bool ISA # # ABI hall of shame # config CLONE_BACKWARDS bool help Architecture has tls passed as the 4th argument of clone(2), not the 5th one. config CLONE_BACKWARDS2 bool help Architecture has the first two arguments of clone(2) swapped. config CLONE_BACKWARDS3 bool help Architecture has tls passed as the 3rd argument of clone(2), not the 5th one. config ODD_RT_SIGACTION bool help Architecture has unusual rt_sigaction(2) arguments config OLD_SIGSUSPEND bool help Architecture has old sigsuspend(2) syscall, of one-argument variety config OLD_SIGSUSPEND3 bool help Even weirder antique ABI - three-argument sigsuspend(2) config OLD_SIGACTION bool help Architecture has old sigaction(2) syscall. Nope, not the same as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2), but fairly different variant of sigaction(2), thanks to OSF/1 compatibility... config COMPAT_OLD_SIGACTION bool config ARCH_NO_COHERENT_DMA_MMAP bool config CPU_NO_EFFICIENT_FFS def_bool n config HAVE_ARCH_VMAP_STACK def_bool n help An arch should select this symbol if it can support kernel stacks in vmalloc space. This means: - vmalloc space must be large enough to hold many kernel stacks. This may rule out many 32-bit architectures. - Stacks in vmalloc space need to work reliably. For example, if vmap page tables are created on demand, either this mechanism needs to work while the stack points to a virtual address with unpopulated page tables or arch code (switch_to() and switch_mm(), most likely) needs to ensure that the stack's page table entries are populated before running on a possibly unpopulated stack. - If the stack overflows into a guard page, something reasonable should happen. The definition of "reasonable" is flexible, but instantly rebooting without logging anything would be unfriendly. config VMAP_STACK default y bool "Use a virtually-mapped stack" depends on HAVE_ARCH_VMAP_STACK && !KASAN ---help--- Enable this if you want the use virtually-mapped kernel stacks with guard pages. This causes kernel stack overflows to be caught immediately rather than causing difficult-to-diagnose corruption. This is presently incompatible with KASAN because KASAN expects the stack to map directly to the KASAN shadow map using a formula that is incorrect if the stack is in vmalloc space. config ARCH_OPTIONAL_KERNEL_RWX def_bool n config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT def_bool n config ARCH_HAS_STRICT_KERNEL_RWX def_bool n config STRICT_KERNEL_RWX bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX depends on ARCH_HAS_STRICT_KERNEL_RWX default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT help If this is set, kernel text and rodata memory will be made read-only, and non-text memory will be made non-executable. This provides protection against certain security exploits (e.g. executing the heap or modifying text) These features are considered standard security practice these days. You should say Y here in almost all cases. config ARCH_HAS_STRICT_MODULE_RWX def_bool n config STRICT_MODULE_RWX bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT help If this is set, module text and rodata memory will be made read-only, and non-text memory will be made non-executable. This provides protection against certain security exploits (e.g. writing to text) source "kernel/gcov/Kconfig"