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linux/security/Kconfig
Daniel Micay 6974f0c455 include/linux/string.h: add the option of fortified string.h functions 
This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time.  Unlike glibc,
it covers buffer reads in addition to writes.

GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation.  They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks.  Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.

This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code.  There will likely be issues caught in
regular use at runtime too.

Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:

* Some of the fortified string functions (strncpy, strcat), don't yet
  place a limit on reads from the source based on __builtin_object_size of
  the source buffer.

* Extending coverage to more string functions like strlcat.

* It should be possible to optionally use __builtin_object_size(x, 1) for
  some functions (C strings) to detect intra-object overflows (like
  glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
  approach to avoid likely compatibility issues.

* The compile-time checks should be made available via a separate config
  option which can be enabled by default (or always enabled) once enough
  time has passed to get the issues it catches fixed.

Kees said:
 "This is great to have. While it was out-of-tree code, it would have
  blocked at least CVE-2016-3858 from being exploitable (improper size
  argument to strlcpy()). I've sent a number of fixes for
  out-of-bounds-reads that this detected upstream already"

[arnd@arndb.de: x86: fix fortified memcpy]
  Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
  Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-07-12 16:26:03 -07:00

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#
# Security configuration
#
menu "Security options"
source security/keys/Kconfig
config SECURITY_DMESG_RESTRICT
bool "Restrict unprivileged access to the kernel syslog"
default n
help
This enforces restrictions on unprivileged users reading the kernel
syslog via dmesg(8).
If this option is not selected, no restrictions will be enforced
unless the dmesg_restrict sysctl is explicitly set to (1).
If you are unsure how to answer this question, answer N.
config SECURITY
bool "Enable different security models"
depends on SYSFS
depends on MULTIUSER
help
This allows you to choose different security modules to be
configured into your kernel.
If this option is not selected, the default Linux security
model will be used.
If you are unsure how to answer this question, answer N.
config SECURITY_WRITABLE_HOOKS
depends on SECURITY
bool
default n
config SECURITYFS
bool "Enable the securityfs filesystem"
help
This will build the securityfs filesystem. It is currently used by
the TPM bios character driver and IMA, an integrity provider. It is
not used by SELinux or SMACK.
If you are unsure how to answer this question, answer N.
config SECURITY_NETWORK
bool "Socket and Networking Security Hooks"
depends on SECURITY
help
This enables the socket and networking security hooks.
If enabled, a security module can use these hooks to
implement socket and networking access controls.
If you are unsure how to answer this question, answer N.
config SECURITY_INFINIBAND
bool "Infiniband Security Hooks"
depends on SECURITY && INFINIBAND
help
This enables the Infiniband security hooks.
If enabled, a security module can use these hooks to
implement Infiniband access controls.
If you are unsure how to answer this question, answer N.
config SECURITY_NETWORK_XFRM
bool "XFRM (IPSec) Networking Security Hooks"
depends on XFRM && SECURITY_NETWORK
help
This enables the XFRM (IPSec) networking security hooks.
If enabled, a security module can use these hooks to
implement per-packet access controls based on labels
derived from IPSec policy. Non-IPSec communications are
designated as unlabelled, and only sockets authorized
to communicate unlabelled data can send without using
IPSec.
If you are unsure how to answer this question, answer N.
config SECURITY_PATH
bool "Security hooks for pathname based access control"
depends on SECURITY
help
This enables the security hooks for pathname based access control.
If enabled, a security module can use these hooks to
implement pathname based access controls.
If you are unsure how to answer this question, answer N.
config INTEL_TXT
bool "Enable Intel(R) Trusted Execution Technology (Intel(R) TXT)"
depends on HAVE_INTEL_TXT
help
This option enables support for booting the kernel with the
Trusted Boot (tboot) module. This will utilize
Intel(R) Trusted Execution Technology to perform a measured launch
of the kernel. If the system does not support Intel(R) TXT, this
will have no effect.
Intel TXT will provide higher assurance of system configuration and
initial state as well as data reset protection. This is used to
create a robust initial kernel measurement and verification, which
helps to ensure that kernel security mechanisms are functioning
correctly. This level of protection requires a root of trust outside
of the kernel itself.
Intel TXT also helps solve real end user concerns about having
confidence that their hardware is running the VMM or kernel that
it was configured with, especially since they may be responsible for
providing such assurances to VMs and services running on it.
See <http://www.intel.com/technology/security/> for more information
about Intel(R) TXT.
See <http://tboot.sourceforge.net> for more information about tboot.
See Documentation/intel_txt.txt for a description of how to enable
Intel TXT support in a kernel boot.
If you are unsure as to whether this is required, answer N.
config LSM_MMAP_MIN_ADDR
int "Low address space for LSM to protect from user allocation"
depends on SECURITY && SECURITY_SELINUX
default 32768 if ARM || (ARM64 && COMPAT)
default 65536
help
This is the portion of low virtual memory which should be protected
from userspace allocation. Keeping a user from writing to low pages
can help reduce the impact of kernel NULL pointer bugs.
For most ia64, ppc64 and x86 users with lots of address space
a value of 65536 is reasonable and should cause no problems.
On arm and other archs it should not be higher than 32768.
Programs which use vm86 functionality or have some need to map
this low address space will need the permission specific to the
systems running LSM.
config HAVE_HARDENED_USERCOPY_ALLOCATOR
bool
help
The heap allocator implements __check_heap_object() for
validating memory ranges against heap object sizes in
support of CONFIG_HARDENED_USERCOPY.
config HARDENED_USERCOPY
bool "Harden memory copies between kernel and userspace"
depends on HAVE_HARDENED_USERCOPY_ALLOCATOR
select BUG
help
This option checks for obviously wrong memory regions when
copying memory to/from the kernel (via copy_to_user() and
copy_from_user() functions) by rejecting memory ranges that
are larger than the specified heap object, span multiple
separately allocated pages, are not on the process stack,
or are part of the kernel text. This kills entire classes
of heap overflow exploits and similar kernel memory exposures.
config HARDENED_USERCOPY_PAGESPAN
bool "Refuse to copy allocations that span multiple pages"
depends on HARDENED_USERCOPY
depends on EXPERT
help
When a multi-page allocation is done without __GFP_COMP,
hardened usercopy will reject attempts to copy it. There are,
however, several cases of this in the kernel that have not all
been removed. This config is intended to be used only while
trying to find such users.
config FORTIFY_SOURCE
bool "Harden common str/mem functions against buffer overflows"
depends on ARCH_HAS_FORTIFY_SOURCE
help
Detect overflows of buffers in common string and memory functions
where the compiler can determine and validate the buffer sizes.
config STATIC_USERMODEHELPER
bool "Force all usermode helper calls through a single binary"
help
By default, the kernel can call many different userspace
binary programs through the "usermode helper" kernel
interface. Some of these binaries are statically defined
either in the kernel code itself, or as a kernel configuration
option. However, some of these are dynamically created at
runtime, or can be modified after the kernel has started up.
To provide an additional layer of security, route all of these
calls through a single executable that can not have its name
changed.
Note, it is up to this single binary to then call the relevant
"real" usermode helper binary, based on the first argument
passed to it. If desired, this program can filter and pick
and choose what real programs are called.
If you wish for all usermode helper programs are to be
disabled, choose this option and then set
STATIC_USERMODEHELPER_PATH to an empty string.
config STATIC_USERMODEHELPER_PATH
string "Path to the static usermode helper binary"
depends on STATIC_USERMODEHELPER
default "/sbin/usermode-helper"
help
The binary called by the kernel when any usermode helper
program is wish to be run. The "real" application's name will
be in the first argument passed to this program on the command
line.
If you wish for all usermode helper programs to be disabled,
specify an empty string here (i.e. "").
source security/selinux/Kconfig
source security/smack/Kconfig
source security/tomoyo/Kconfig
source security/apparmor/Kconfig
source security/loadpin/Kconfig
source security/yama/Kconfig
source security/integrity/Kconfig
choice
prompt "Default security module"
default DEFAULT_SECURITY_SELINUX if SECURITY_SELINUX
default DEFAULT_SECURITY_SMACK if SECURITY_SMACK
default DEFAULT_SECURITY_TOMOYO if SECURITY_TOMOYO
default DEFAULT_SECURITY_APPARMOR if SECURITY_APPARMOR
default DEFAULT_SECURITY_DAC
help
Select the security module that will be used by default if the
kernel parameter security= is not specified.
config DEFAULT_SECURITY_SELINUX
bool "SELinux" if SECURITY_SELINUX=y
config DEFAULT_SECURITY_SMACK
bool "Simplified Mandatory Access Control" if SECURITY_SMACK=y
config DEFAULT_SECURITY_TOMOYO
bool "TOMOYO" if SECURITY_TOMOYO=y
config DEFAULT_SECURITY_APPARMOR
bool "AppArmor" if SECURITY_APPARMOR=y
config DEFAULT_SECURITY_DAC
bool "Unix Discretionary Access Controls"
endchoice
config DEFAULT_SECURITY
string
default "selinux" if DEFAULT_SECURITY_SELINUX
default "smack" if DEFAULT_SECURITY_SMACK
default "tomoyo" if DEFAULT_SECURITY_TOMOYO
default "apparmor" if DEFAULT_SECURITY_APPARMOR
default "" if DEFAULT_SECURITY_DAC
endmenu
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