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0bf1bafb17
linux/arch/Kconfig
Linus Torvalds 09c0796adf Tracing updates for 5.11 
The major update to this release is that there's a new arch config option called:
 CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS. Currently, only x86_64 enables it.
 All the ftrace callbacks now take a struct ftrace_regs instead of a struct
 pt_regs. If the architecture has HAVE_DYNAMIC_FTRACE_WITH_ARGS enabled, then
 the ftrace_regs will have enough information to read the arguments of the
 function being traced, as well as access to the stack pointer. This way, if
 a user (like live kernel patching) only cares about the arguments, then it
 can avoid using the heavier weight "regs" callback, that puts in enough
 information in the struct ftrace_regs to simulate a breakpoint exception
 (needed for kprobes).
 
 New config option that audits the timestamps of the ftrace ring buffer at
 most every event recorded.  The "check_buffer()" calls will conflict with
 mainline, because I purposely added the check without including the fix that
 it caught, which is in mainline. Running a kernel built from the commit of
 the added check will trigger it.
 
 Ftrace recursion protection has been cleaned up to move the protection to
 the callback itself (this saves on an extra function call for those
 callbacks).
 
 Perf now handles its own RCU protection and does not depend on ftrace to do
 it for it (saving on that extra function call).
 
 New debug option to add "recursed_functions" file to tracefs that lists all
 the places that triggered the recursion protection of the function tracer.
 This will show where things need to be fixed as recursion slows down the
 function tracer.
 
 The eval enum mapping updates done at boot up are now offloaded to a work
 queue, as it caused a noticeable pause on slow embedded boards.
 
 Various clean ups and last minute fixes.
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Merge tag 'trace-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing updates from Steven Rostedt:
 "The major update to this release is that there's a new arch config
  option called CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS.

  Currently, only x86_64 enables it. All the ftrace callbacks now take a
  struct ftrace_regs instead of a struct pt_regs. If the architecture
  has HAVE_DYNAMIC_FTRACE_WITH_ARGS enabled, then the ftrace_regs will
  have enough information to read the arguments of the function being
  traced, as well as access to the stack pointer.

  This way, if a user (like live kernel patching) only cares about the
  arguments, then it can avoid using the heavier weight "regs" callback,
  that puts in enough information in the struct ftrace_regs to simulate
  a breakpoint exception (needed for kprobes).

  A new config option that audits the timestamps of the ftrace ring
  buffer at most every event recorded.

  Ftrace recursion protection has been cleaned up to move the protection
  to the callback itself (this saves on an extra function call for those
  callbacks).

  Perf now handles its own RCU protection and does not depend on ftrace
  to do it for it (saving on that extra function call).

  New debug option to add "recursed_functions" file to tracefs that
  lists all the places that triggered the recursion protection of the
  function tracer. This will show where things need to be fixed as
  recursion slows down the function tracer.

  The eval enum mapping updates done at boot up are now offloaded to a
  work queue, as it caused a noticeable pause on slow embedded boards.

  Various clean ups and last minute fixes"

* tag 'trace-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: (33 commits)
  tracing: Offload eval map updates to a work queue
  Revert: "ring-buffer: Remove HAVE_64BIT_ALIGNED_ACCESS"
  ring-buffer: Add rb_check_bpage in __rb_allocate_pages
  ring-buffer: Fix two typos in comments
  tracing: Drop unneeded assignment in ring_buffer_resize()
  tracing: Disable ftrace selftests when any tracer is running
  seq_buf: Avoid type mismatch for seq_buf_init
  ring-buffer: Fix a typo in function description
  ring-buffer: Remove obsolete rb_event_is_commit()
  ring-buffer: Add test to validate the time stamp deltas
  ftrace/documentation: Fix RST C code blocks
  tracing: Clean up after filter logic rewriting
  tracing: Remove the useless value assignment in test_create_synth_event()
  livepatch: Use the default ftrace_ops instead of REGS when ARGS is available
  ftrace/x86: Allow for arguments to be passed in to ftrace_regs by default
  ftrace: Have the callbacks receive a struct ftrace_regs instead of pt_regs
  MAINTAINERS: assign ./fs/tracefs to TRACING
  tracing: Fix some typos in comments
  ftrace: Remove unused varible 'ret'
  ring-buffer: Add recording of ring buffer recursion into recursed_functions
  ...
2020-12-17 13:22:17 -08:00

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# SPDX-License-Identifier: GPL-2.0
#
# General architecture dependent options
#
#
# Note: arch/$(SRCARCH)/Kconfig needs to be included first so that it can
# override the default values in this file.
#
source "arch/$(SRCARCH)/Kconfig"
menu "General architecture-dependent options"
config CRASH_CORE
bool
config KEXEC_CORE
select CRASH_CORE
bool
config KEXEC_ELF
bool
config HAVE_IMA_KEXEC
bool
config SET_FS
bool
config HOTPLUG_SMT
bool
config GENERIC_ENTRY
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 a 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
depends on CC_HAS_ASM_GOTO
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 STATIC_CALL_SELFTEST
bool "Static call selftest"
depends on HAVE_STATIC_CALL
help
Boot time self-test of the call patching code.
config OPTPROBES
def_bool y
depends on KPROBES && HAVE_OPTPROBES
select TASKS_RCU if PREEMPTION
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/core-api/unaligned-memory-access.rst 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 <asm/swab.h>. 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_FUNCTION_ERROR_INJECTION
bool
config 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
config ARCH_HAS_FORTIFY_SOURCE
bool
help
An architecture should select this when it can successfully
build and run with CONFIG_FORTIFY_SOURCE.
#
# Select if the arch provides a historic keepinit alias for the retain_initrd
# command line option
#
config ARCH_HAS_KEEPINITRD
bool
# Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
config ARCH_HAS_SET_MEMORY
bool
# Select if arch has all set_direct_map_invalid/default() functions
config ARCH_HAS_SET_DIRECT_MAP
bool
#
# Select if the architecture provides the arch_dma_set_uncached symbol to
# either provide an uncached segment alias for a DMA allocation, or
# to remap the page tables in place.
#
config ARCH_HAS_DMA_SET_UNCACHED
bool
#
# Select if the architectures provides the arch_dma_clear_uncached symbol
# to undo an in-place page table remap for uncached access.
#
config ARCH_HAS_DMA_CLEAR_UNCACHED
bool
# Select if arch init_task must go in the __init_task_data section
config ARCH_TASK_STRUCT_ON_STACK
bool
# Select if arch has its private alloc_task_struct() function
config ARCH_TASK_STRUCT_ALLOCATOR
bool
config HAVE_ARCH_THREAD_STRUCT_WHITELIST
bool
depends on !ARCH_TASK_STRUCT_ALLOCATOR
help
An architecture should select this to provide hardened usercopy
knowledge about what region of the thread_struct should be
whitelisted for copying to userspace. Normally this is only the
FPU registers. Specifically, arch_thread_struct_whitelist()
should be implemented. Without this, the entire thread_struct
field in task_struct will be left whitelisted.
# 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 ARCH_32BIT_OFF_T
bool
depends on !64BIT
help
All new 32-bit architectures should have 64-bit off_t type on
userspace side which corresponds to the loff_t kernel type. This
is the requirement for modern ABIs. Some existing architectures
still support 32-bit off_t. This option is enabled for all such
architectures explicitly.
config HAVE_ASM_MODVERSIONS
bool
help
This symbol should be selected by an architecture if it provides
<asm/asm-prototypes.h> to support the module versioning for symbols
exported from assembly code.
config HAVE_REGS_AND_STACK_ACCESS_API
bool
help
This symbol should be selected by an architecture 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_RSEQ
bool
depends on HAVE_REGS_AND_STACK_ACCESS_API
help
This symbol should be selected by an architecture if it
supports an implementation of restartable sequences.
config HAVE_FUNCTION_ARG_ACCESS_API
bool
help
This symbol should be selected by an architecture if it supports
the API needed to access function arguments from pt_regs,
declared in asm/ptrace.h
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_HARDLOCKUP_DETECTOR_PERF
bool
depends on HAVE_PERF_EVENTS_NMI
help
The arch chooses to use the generic perf-NMI-based hardlockup
detector. Must define HAVE_PERF_EVENTS_NMI.
config HAVE_NMI_WATCHDOG
depends on HAVE_NMI
bool
help
The arch provides a low level NMI watchdog. It provides
asm/nmi.h, and defines its own arch_touch_nmi_watchdog().
config HAVE_HARDLOCKUP_DETECTOR_ARCH
bool
select HAVE_NMI_WATCHDOG
help
The arch chooses to provide its own hardlockup detector, which is
a superset of the HAVE_NMI_WATCHDOG. It also conforms to config
interfaces and parameters provided by hardlockup detector subsystem.
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_ARCH_JUMP_LABEL_RELATIVE
bool
config MMU_GATHER_TABLE_FREE
bool
config MMU_GATHER_RCU_TABLE_FREE
bool
select MMU_GATHER_TABLE_FREE
config MMU_GATHER_PAGE_SIZE
bool
config MMU_GATHER_NO_RANGE
bool
config MMU_GATHER_NO_GATHER
bool
depends on MMU_GATHER_TABLE_FREE
config ARCH_WANT_IRQS_OFF_ACTIVATE_MM
bool
help
Temporary select until all architectures can be converted to have
irqs disabled over activate_mm. Architectures that do IPI based TLB
shootdowns should enable this.
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_WEAK_RELEASE_ACQUIRE
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
bool
help
An arch should select this symbol to support seccomp mode 1 (the fixed
syscall policy), and must provide an overrides for __NR_seccomp_sigreturn,
and compat syscalls if the asm-generic/seccomp.h defaults need adjustment:
- __NR_seccomp_read_32
- __NR_seccomp_write_32
- __NR_seccomp_exit_32
- __NR_seccomp_sigreturn_32
config HAVE_ARCH_SECCOMP_FILTER
bool
select HAVE_ARCH_SECCOMP
help
An arch should select this symbol if it provides all of these things:
- all the requirements for HAVE_ARCH_SECCOMP
- 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
- if !HAVE_SPARSE_SYSCALL_NR, have SECCOMP_ARCH_NATIVE,
SECCOMP_ARCH_NATIVE_NR, SECCOMP_ARCH_NATIVE_NAME defined. If
COMPAT is supported, have the SECCOMP_ARCH_COMPAT* defines too.
config SECCOMP
prompt "Enable seccomp to safely execute untrusted bytecode"
def_bool y
depends on HAVE_ARCH_SECCOMP
help
This kernel feature is useful for number crunching applications
that may need to handle untrusted bytecode during their
execution. By using pipes or other transports made available
to the process as file descriptors supporting the read/write
syscalls, it's possible to isolate those applications in their
own address space using seccomp. Once seccomp is enabled via
prctl(PR_SET_SECCOMP) or the seccomp() syscall, it cannot be
disabled and the task is only allowed to execute a few safe
syscalls defined by each seccomp mode.
If unsure, say Y.
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/userspace-api/seccomp_filter.rst for details.
config SECCOMP_CACHE_DEBUG
bool "Show seccomp filter cache status in /proc/pid/seccomp_cache"
depends on SECCOMP_FILTER && !HAVE_SPARSE_SYSCALL_NR
depends on PROC_FS
help
This enables the /proc/pid/seccomp_cache interface to monitor
seccomp cache data. The file format is subject to change. Reading
the file requires CAP_SYS_ADMIN.
This option is for debugging only. Enabling presents the risk that
an adversary may be able to infer the seccomp filter logic.
If unsure, say N.
config HAVE_ARCH_STACKLEAK
bool
help
An architecture should select this if it has the code which
fills the used part of the kernel stack with the STACKLEAK_POISON
value before returning from system calls.
config HAVE_STACKPROTECTOR
bool
help
An arch should select this symbol if:
- it has implemented a stack canary (e.g. __stack_chk_guard)
config STACKPROTECTOR
bool "Stack Protector buffer overflow detection"
depends on HAVE_STACKPROTECTOR
depends on $(cc-option,-fstack-protector)
default y
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.
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 STACKPROTECTOR_STRONG
bool "Strong Stack Protector"
depends on STACKPROTECTOR
depends on $(cc-option,-fstack-protector-strong)
default y
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%.
config ARCH_SUPPORTS_SHADOW_CALL_STACK
bool
help
An architecture should select this if it supports Clang's Shadow
Call Stack and implements runtime support for shadow stack
switching.
config SHADOW_CALL_STACK
bool "Clang Shadow Call Stack"
depends on CC_IS_CLANG && ARCH_SUPPORTS_SHADOW_CALL_STACK
depends on DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
help
This option enables Clang's Shadow Call Stack, which uses a
shadow stack to protect function return addresses from being
overwritten by an attacker. More information can be found in
Clang's documentation:
https://clang.llvm.org/docs/ShadowCallStack.html
Note that security guarantees in the kernel differ from the
ones documented for user space. The kernel must store addresses
of shadow stacks in memory, which means an attacker capable of
reading and writing arbitrary memory may be able to locate them
and hijack control flow by modifying the stacks.
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(), either
optimized behind static key or 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_CONTEXT_TRACKING_OFFSTACK
bool
help
Architecture neither relies on exception_enter()/exception_exit()
nor on schedule_user(). Also preempt_schedule_notrace() and
preempt_schedule_irq() can't be called in a preemptible section
while context tracking is CONTEXT_USER. This feature reflects a sane
entry implementation where the following requirements are met on
critical entry code, ie: before user_exit() or after user_enter():
- Critical entry code isn't preemptible (or better yet:
not interruptible).
- No use of RCU read side critical sections, unless rcu_nmi_enter()
got called.
- No use of instrumentation, unless instrumentation_begin() got
called.
config HAVE_TIF_NOHZ
bool
help
Arch relies on TIF_NOHZ and syscall slow path to implement context
tracking calls to user_enter()/user_exit().
config HAVE_VIRT_CPU_ACCOUNTING
bool
config HAVE_VIRT_CPU_ACCOUNTING_IDLE
bool
help
Architecture has its own way to account idle CPU time and therefore
doesn't implement vtime_account_idle().
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_MOVE_PUD
bool
help
Architectures that select this are able to move page tables at the
PUD level. If there are only 3 page table levels, the move effectively
happens at the PGD level.
config HAVE_MOVE_PMD
bool
help
Archs that select this are able to move page tables at the PMD level.
config HAVE_ARCH_TRANSPARENT_HUGEPAGE
bool
config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
bool
config HAVE_ARCH_HUGE_VMAP
bool
config ARCH_WANT_HUGE_PMD_SHARE
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_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_ARCH_COMPAT_MMAP_BASES
bool
help
This allows 64bit applications to invoke 32-bit mmap() syscall
and vice-versa 32-bit applications to call 64-bit mmap().
Required for applications doing different bitness syscalls.
# This allows to use a set of generic functions to determine mmap base
# address by giving priority to top-down scheme only if the process
# is not in legacy mode (compat task, unlimited stack size or
# sysctl_legacy_va_layout).
# Architecture that selects this option can provide its own version of:
# - STACK_RND_MASK
config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
bool
depends on MMU
select ARCH_HAS_ELF_RANDOMIZE
config HAVE_STACK_VALIDATION
bool
help
Architecture supports the 'objtool check' host tool command, which
performs compile-time stack metadata validation.
config HAVE_RELIABLE_STACKTRACE
bool
help
Architecture has either save_stack_trace_tsk_reliable() or
arch_stack_walk_reliable() function which only returns a stack trace
if it can guarantee the trace is reliable.
config HAVE_ARCH_HASH
bool
default n
help
If this is set, the architecture provides an <asm/hash.h>
file which provides platform-specific implementations of some
functions in <linux/hash.h> or fs/namei.c.
config HAVE_ARCH_NVRAM_OPS
bool
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 COMPAT_32BIT_TIME
bool "Provide system calls for 32-bit time_t"
default !64BIT || COMPAT
help
This enables 32 bit time_t support in addition to 64 bit time_t support.
This is relevant on all 32-bit architectures, and 64-bit architectures
as part of compat syscall handling.
config ARCH_NO_PREEMPT
bool
config ARCH_SUPPORTS_RT
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
depends on !KASAN || KASAN_VMALLOC
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.
To use this with KASAN, the architecture must support backing
virtual mappings with real shadow memory, and KASAN_VMALLOC must
be enabled.
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)
# select if the architecture provides an asm/dma-direct.h header
config ARCH_HAS_PHYS_TO_DMA
bool
config HAVE_ARCH_COMPILER_H
bool
help
An architecture can select this if it provides an
asm/compiler.h header that should be included after
linux/compiler-*.h in order to override macro definitions that those
headers generally provide.
config HAVE_ARCH_PREL32_RELOCATIONS
bool
help
May be selected by an architecture if it supports place-relative
32-bit relocations, both in the toolchain and in the module loader,
in which case relative references can be used in special sections
for PCI fixup, initcalls etc which are only half the size on 64 bit
architectures, and don't require runtime relocation on relocatable
kernels.
config ARCH_USE_MEMREMAP_PROT
bool
config LOCK_EVENT_COUNTS
bool "Locking event counts collection"
depends on DEBUG_FS
help
Enable light-weight counting of various locking related events
in the system with minimal performance impact. This reduces
the chance of application behavior change because of timing
differences. The counts are reported via debugfs.
# Select if the architecture has support for applying RELR relocations.
config ARCH_HAS_RELR
bool
config RELR
bool "Use RELR relocation packing"
depends on ARCH_HAS_RELR && TOOLS_SUPPORT_RELR
default y
help
Store the kernel's dynamic relocations in the RELR relocation packing
format. Requires a compatible linker (LLD supports this feature), as
well as compatible NM and OBJCOPY utilities (llvm-nm and llvm-objcopy
are compatible).
config ARCH_HAS_MEM_ENCRYPT
bool
config HAVE_SPARSE_SYSCALL_NR
bool
help
An architecture should select this if its syscall numbering is sparse
to save space. For example, MIPS architecture has a syscall array with
entries at 4000, 5000 and 6000 locations. This option turns on syscall
related optimizations for a given architecture.
config ARCH_HAS_VDSO_DATA
bool
config HAVE_STATIC_CALL
bool
config HAVE_STATIC_CALL_INLINE
bool
depends on HAVE_STATIC_CALL
config ARCH_WANT_LD_ORPHAN_WARN
bool
help
An arch should select this symbol once all linker sections are explicitly
included, size-asserted, or discarded in the linker scripts. This is
important because we never want expected sections to be placed heuristically
by the linker, since the locations of such sections can change between linker
versions.
config HAVE_ARCH_PFN_VALID
bool
config ARCH_SUPPORTS_DEBUG_PAGEALLOC
bool
source "kernel/gcov/Kconfig"
source "scripts/gcc-plugins/Kconfig"
endmenu
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