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