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87bc514620
The purpose of this LSM is to allow processes to drop to a less privileged user id without having to grant them full CAP_SETUID (or use file caps). The LSM allows configuring a whitelist policy of permitted from:to uid transitions. The policy is enforced upon calls to setuid(2) and related syscalls. Policies are configured through securityfs by writing to - safesetid/add_whitelist_policy ; and - safesetid/flush_whitelist_policies A process attempting a transition not permitted by current policy is killed (to avoid accidentally running with higher privileges than intended). A uid that has a configured policy is prevented from obtaining auxiliary setuid privileges (e.g., setting up user namespaces). See also: https://www.kernel.org/doc/html/latest/admin-guide/LSM/SafeSetID.html
124 lines
4.6 KiB
Nix
124 lines
4.6 KiB
Nix
# Based on recommendations from:
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# http://kernsec.org/wiki/index.php/Kernel_Self_Protection_Project#Recommended_settings
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# https://wiki.gentoo.org/wiki/Hardened/Hardened_Kernel_Project
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#
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# Dangerous features that can be permanently (for the boot session) disabled at
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# boot via sysctl or kernel cmdline are left enabled here, for improved
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# flexibility.
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#
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# See also <nixos/modules/profiles/hardened.nix>
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{ stdenv, version }:
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with stdenv.lib;
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with import ../../../../lib/kernel.nix { inherit (stdenv) lib; inherit version; };
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assert (versionAtLeast version "4.9");
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optionalAttrs (stdenv.hostPlatform.platform.kernelArch == "x86_64") {
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DEFAULT_MMAP_MIN_ADDR = freeform "65536"; # Prevent allocation of first 64K of memory
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# Reduce attack surface by disabling various emulations
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IA32_EMULATION = no;
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X86_X32 = no;
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# Note: this config depends on EXPERT y and so will not take effect, hence
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# it is left "optional" for now.
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MODIFY_LDT_SYSCALL = option no;
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VMAP_STACK = yes; # Catch kernel stack overflows
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# Randomize position of kernel and memory.
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RANDOMIZE_BASE = yes;
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RANDOMIZE_MEMORY = yes;
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# Disable legacy virtual syscalls by default (modern glibc use vDSO instead).
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#
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# Note that the vanilla default is to *emulate* the legacy vsyscall mechanism,
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# which is supposed to be safer than the native variant (wrt. ret2libc), so
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# disabling it mainly helps reduce surface.
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LEGACY_VSYSCALL_NONE = yes;
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} // {
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# Report BUG() conditions and kill the offending process.
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BUG = yes;
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BUG_ON_DATA_CORRUPTION = whenAtLeast "4.10" yes;
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# Safer page access permissions (wrt. code injection). Default on >=4.11.
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DEBUG_RODATA = whenOlder "4.11" yes;
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DEBUG_SET_MODULE_RONX = whenOlder "4.11" yes;
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# Mark LSM hooks read-only after init. SECURITY_WRITABLE_HOOKS n
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# conflicts with SECURITY_SELINUX_DISABLE y; disabling the latter
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# implicitly marks LSM hooks read-only after init.
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#
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# SELinux can only be disabled at boot via selinux=0
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#
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# We set SECURITY_WRITABLE_HOOKS n primarily for documentation purposes; the
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# config builder fails to detect that it has indeed been unset.
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SECURITY_SELINUX_DISABLE = whenAtLeast "4.12" no;
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SECURITY_WRITABLE_HOOKS = whenAtLeast "4.12" (option no);
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DEBUG_WX = yes; # boot-time warning on RWX mappings
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STRICT_KERNEL_RWX = whenAtLeast "4.11" yes;
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# Stricter /dev/mem
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STRICT_DEVMEM = option yes;
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IO_STRICT_DEVMEM = option yes;
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# Perform additional validation of commonly targeted structures.
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DEBUG_CREDENTIALS = yes;
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DEBUG_NOTIFIERS = yes;
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DEBUG_LIST = yes;
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DEBUG_PI_LIST = yes; # doesn't BUG()
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DEBUG_SG = yes;
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SCHED_STACK_END_CHECK = yes;
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REFCOUNT_FULL = whenAtLeast "4.13" yes;
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# Perform usercopy bounds checking.
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HARDENED_USERCOPY = yes;
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HARDENED_USERCOPY_FALLBACK = whenAtLeast "4.16" no; # for full whitelist enforcement
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# Randomize allocator freelists.
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SLAB_FREELIST_RANDOM = yes;
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SLAB_FREELIST_HARDENED = whenAtLeast "4.14" yes;
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# Allow enabling slub/slab free poisoning with slub_debug=P
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SLUB_DEBUG = yes;
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# Wipe higher-level memory allocations on free() with page_poison=1
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PAGE_POISONING = yes;
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PAGE_POISONING_NO_SANITY = yes;
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PAGE_POISONING_ZERO = yes;
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# Enable the SafeSetId LSM
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SECURITY_SAFESETID = whenAtLeast "5.1" yes;
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# Reboot devices immediately if kernel experiences an Oops.
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PANIC_ON_OOPS = yes;
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PANIC_TIMEOUT = freeform "-1";
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GCC_PLUGINS = yes; # Enable gcc plugin options
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# Gather additional entropy at boot time for systems that may = no;ot have appropriate entropy sources.
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GCC_PLUGIN_LATENT_ENTROPY = yes;
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GCC_PLUGIN_STRUCTLEAK = whenAtLeast "4.11" yes; # A port of the PaX structleak plugin
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GCC_PLUGIN_STRUCTLEAK_BYREF_ALL = whenAtLeast "4.14" yes; # Also cover structs passed by address
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GCC_PLUGIN_STACKLEAK = whenAtLeast "4.20" yes; # A port of the PaX stackleak plugin
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GCC_PLUGIN_RANDSTRUCT = whenAtLeast "4.13" yes; # A port of the PaX randstruct plugin
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GCC_PLUGIN_RANDSTRUCT_PERFORMANCE = whenAtLeast "4.13" yes;
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# Disable various dangerous settings
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ACPI_CUSTOM_METHOD = no; # Allows writing directly to physical memory
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PROC_KCORE = no; # Exposes kernel text image layout
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INET_DIAG = no; # Has been used for heap based attacks in the past
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# Use -fstack-protector-strong (gcc 4.9+) for best stack canary coverage.
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CC_STACKPROTECTOR_REGULAR = whenOlder "4.18" no;
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CC_STACKPROTECTOR_STRONG = whenOlder "4.18" yes;
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# Enable compile/run-time buffer overflow detection ala glibc's _FORTIFY_SOURCE
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FORTIFY_SOURCE = whenAtLeast "4.13" yes;
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}
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