Tweak the checks for android

> Android configs require various things that are currently disallowed in this
> tool. We can use CONFIG_ANDROID to detect Android configs and generate reports with fewer positives that cannot/should not be changed.

Based on a13xp0p0v#91

kernel_hardening_checker/checks.py

@@ -34,6 +34,7 @@ def add_kconfig_checks(l: List[ChecklistObjType], arch: str) -> None:
     modules_not_set = KconfigCheck('cut_attack_surface', 'kspp', 'MODULES', 'is not set') # radical, but may be useful in some cases
     devmem_not_set = KconfigCheck('cut_attack_surface', 'kspp', 'DEVMEM', 'is not set') # refers to LOCKDOWN
     bpf_syscall_not_set = KconfigCheck('cut_attack_surface', 'lockdown', 'BPF_SYSCALL', 'is not set') # refers to LOCKDOWN
+    is_android = KconfigCheck('-', '-', 'ANDROID', 'y')
 
     # 'self_protection', 'defconfig'
     l += [KconfigCheck('self_protection', 'defconfig', 'BUG', 'y')]
@@ -317,7 +318,7 @@ def add_kconfig_checks(l: List[ChecklistObjType], arch: str) -> None:
     l += [KconfigCheck('cut_attack_surface', 'kspp', 'X86_MSR', 'is not set')] # refers to LOCKDOWN
     l += [KconfigCheck('cut_attack_surface', 'kspp', 'LEGACY_TIOCSTI', 'is not set')]
     l += [KconfigCheck('cut_attack_surface', 'kspp', 'MODULE_FORCE_LOAD', 'is not set')]
-    l += [modules_not_set]
+    l += [OR(modules_not_set, is_android)] # Android requires kernel modules: https://source.android.com/docs/core/architecture/kernel/loadable-kernel-modules
     l += [devmem_not_set]
     l += [OR(KconfigCheck('cut_attack_surface', 'kspp', 'IO_STRICT_DEVMEM', 'y'),
              devmem_not_set)] # refers to LOCKDOWN
@@ -399,13 +400,14 @@ def add_kconfig_checks(l: List[ChecklistObjType], arch: str) -> None:
     l += [KconfigCheck('cut_attack_surface', 'clipos', 'AIO', 'is not set')]
 #   l += [KconfigCheck('cut_attack_surface', 'clipos', 'IKCONFIG', 'is not set')] # no, IKCONFIG is needed for this check :)
     l += [OR(KconfigCheck('cut_attack_surface', 'clipos', 'MAGIC_SYSRQ', 'is not set'),
+             is_android, # See https://android.googlesource.com/kernel/configs/#allowed
              KconfigCheck('cut_attack_surface', 'a13xp0p0v', 'MAGIC_SYSRQ_DEFAULT_ENABLE', '0x0'))]
 
     # 'cut_attack_surface', 'lockdown'
     l += [KconfigCheck('cut_attack_surface', 'lockdown', 'EFI_TEST', 'is not set')] # refers to LOCKDOWN
     l += [KconfigCheck('cut_attack_surface', 'lockdown', 'MMIOTRACE_TEST', 'is not set')] # refers to LOCKDOWN
     l += [KconfigCheck('cut_attack_surface', 'lockdown', 'KPROBES', 'is not set')] # refers to LOCKDOWN
-    l += [bpf_syscall_not_set] # refers to LOCKDOWN
+    l += [OR(bpf_syscall_not_set, is_android)] # refers to LOCKDOWN, Android requires BPF: https://source.android.com/docs/core/architecture/kernel/bpf
 
     # 'cut_attack_surface', 'a13xp0p0v'
     l += [KconfigCheck('cut_attack_surface', 'a13xp0p0v', 'MMIOTRACE', 'is not set')] # refers to LOCKDOWN (permissive)
@@ -420,6 +422,7 @@ def add_kconfig_checks(l: List[ChecklistObjType], arch: str) -> None:
     l += [KconfigCheck('cut_attack_surface', 'a13xp0p0v', 'XFS_SUPPORT_V4', 'is not set')]
     l += [KconfigCheck('cut_attack_surface', 'a13xp0p0v', 'BLK_DEV_WRITE_MOUNTED', 'is not set')]
     l += [OR(KconfigCheck('cut_attack_surface', 'a13xp0p0v', 'TRIM_UNUSED_KSYMS', 'y'),
+             is_android, # Android frequently uses out-of-tree modules: https://source.android.com/docs/core/architecture/kernel/vendor-module-guidelines
              modules_not_set)]
     l += [OR(KconfigCheck('cut_attack_surface', 'a13xp0p0v', 'MAGIC_SYSRQ_SERIAL', 'is not set'),
              KconfigCheck('cut_attack_surface', 'a13xp0p0v', 'MAGIC_SYSRQ_DEFAULT_ENABLE', '0x0'))]