134 lines
3.8 KiB
Nix
134 lines
3.8 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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assert (versionAtLeast version "4.9");
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''
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# Report BUG() conditions and kill the offending process.
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BUG y
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${optionalString (versionAtLeast version "4.10") ''
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BUG_ON_DATA_CORRUPTION y
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''}
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${optionalString (stdenv.hostPlatform.platform.kernelArch == "x86_64") ''
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DEFAULT_MMAP_MIN_ADDR 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 n
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X86_X32 n
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${optionalString (versionOlder version "4.17") ''
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MODIFY_LDT_SYSCALL? n
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''}
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VMAP_STACK y # Catch kernel stack overflows
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# Randomize position of kernel and memory.
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RANDOMIZE_BASE y
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RANDOMIZE_MEMORY y
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# Disable legacy virtual syscalls by default (modern glibc use vDSO instead).
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#
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# Note that the vanilla default is to *emulate* the legacy vsyscall mechanism,
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# which is supposed to be safer than the native variant (wrt. ret2libc), so
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# disabling it mainly helps reduce surface.
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LEGACY_VSYSCALL_NONE y
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''}
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# Safer page access permissions (wrt. code injection). Default on >=4.11.
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${optionalString (versionOlder version "4.11") ''
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DEBUG_RODATA y
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DEBUG_SET_MODULE_RONX y
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''}
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# Mark LSM hooks read-only after init. Conflicts with SECURITY_SELINUX_DISABLE
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# (disabling SELinux at runtime); hence, SELinux can only be disabled at boot
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# via the selinux=0 boot parameter.
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${optionalString (versionAtLeast version "4.12") ''
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SECURITY_SELINUX_DISABLE n
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''}
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${optionalString ((versionAtLeast version "4.12") && (versionOlder version "4.17")) ''
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SECURITY_WRITABLE_HOOKS n
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''}
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DEBUG_WX y # boot-time warning on RWX mappings
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# Stricter /dev/mem
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STRICT_DEVMEM? y
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IO_STRICT_DEVMEM? y
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# Perform additional validation of commonly targeted structures.
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DEBUG_CREDENTIALS y
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DEBUG_NOTIFIERS y
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DEBUG_LIST y
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DEBUG_PI_LIST y # doesn't BUG()
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DEBUG_SG y
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SCHED_STACK_END_CHECK y
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${optionalString (versionAtLeast version "4.13") ''
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REFCOUNT_FULL y
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''}
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# Perform usercopy bounds checking.
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HARDENED_USERCOPY y
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${optionalString (versionAtLeast version "4.16") ''
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HARDENED_USERCOPY_FALLBACK n
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''}
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# Randomize allocator freelists.
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SLAB_FREELIST_RANDOM y
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${optionalString (versionAtLeast version "4.14") ''
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SLAB_FREELIST_HARDENED y
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''}
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# Wipe higher-level memory allocations on free() with page_poison=1
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PAGE_POISONING y
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PAGE_POISONING_NO_SANITY y
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PAGE_POISONING_ZERO y
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# Reboot devices immediately if kernel experiences an Oops.
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PANIC_ON_OOPS y
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PANIC_TIMEOUT -1
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${optionalString (versionOlder version "4.18") ''
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GCC_PLUGINS y # Enable gcc plugin options
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# Gather additional entropy at boot time for systems that may not have appropriate entropy sources.
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GCC_PLUGIN_LATENT_ENTROPY y
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${optionalString (versionAtLeast version "4.11") ''
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GCC_PLUGIN_STRUCTLEAK y # A port of the PaX structleak plugin
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''}
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${optionalString (versionAtLeast version "4.14") ''
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GCC_PLUGIN_STRUCTLEAK_BYREF_ALL y # Also cover structs passed by address
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''}
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''}
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# Disable various dangerous settings
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ACPI_CUSTOM_METHOD n # Allows writing directly to physical memory
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PROC_KCORE n # Exposes kernel text image layout
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INET_DIAG n # 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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${optionalString (versionOlder version "4.18") ''
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CC_STACKPROTECTOR_REGULAR n
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CC_STACKPROTECTOR_STRONG y
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''}
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# Enable compile/run-time buffer overflow detection ala glibc's _FORTIFY_SOURCE
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${optionalString (versionAtLeast version "4.13") ''
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FORTIFY_SOURCE y
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''}
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''
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