[PATCH v11 2/5] security: Count the LSMs enabled at compile time

[Casey Schaufler]

On 5/9/2024 1:14 PM, KP Singh wrote:
> These macros are a clever trick to determine a count of the number of
> LSMs that are enabled in the config to ascertain the maximum number of
> static calls that need to be configured per LSM hook.
>
> Without this one would need to generate static calls for the total
> number of LSMs in the kernel (even if they are not compiled) times the
> number of LSM hooks which ends up being quite wasteful.
>
> Suggested-by: Kui-Feng Lee <sinquersw at gmail.com>
> Suggested-by: Andrii Nakryiko <andrii at kernel.org>
> Acked-by: Song Liu <song at kernel.org>
> Acked-by: Andrii Nakryiko <andrii at kernel.org>
> Reviewed-by: Kees Cook <keescook at chromium.org>
> Signed-off-by: KP Singh <kpsingh at kernel.org>

Reviewed-by: Casey Schaufler <casey at schaufler-ca.com>

> ---
>  include/linux/args.h      |   6 +-
>  include/linux/lsm_count.h | 128 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 131 insertions(+), 3 deletions(-)
>  create mode 100644 include/linux/lsm_count.h
>
> diff --git a/include/linux/args.h b/include/linux/args.h
> index 8ff60a54eb7d..2e8e65d975c7 100644
> --- a/include/linux/args.h
> +++ b/include/linux/args.h
> @@ -17,9 +17,9 @@
>   * that as _n.
>   */
>  
> -/* This counts to 12. Any more, it will return 13th argument. */
> -#define __COUNT_ARGS(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _n, X...) _n
> -#define COUNT_ARGS(X...) __COUNT_ARGS(, ##X, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
> +/* This counts to 15. Any more, it will return 16th argument. */
> +#define __COUNT_ARGS(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _n, X...) _n
> +#define COUNT_ARGS(X...) __COUNT_ARGS(, ##X, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
>  
>  /* Concatenate two parameters, but allow them to be expanded beforehand. */
>  #define __CONCAT(a, b) a ## b
> diff --git a/include/linux/lsm_count.h b/include/linux/lsm_count.h
> new file mode 100644
> index 000000000000..73c7cc81349b
> --- /dev/null
> +++ b/include/linux/lsm_count.h
> @@ -0,0 +1,128 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + * Copyright (C) 2023 Google LLC.
> + */
> +
> +#ifndef __LINUX_LSM_COUNT_H
> +#define __LINUX_LSM_COUNT_H
> +
> +#include <linux/args.h>
> +
> +#ifdef CONFIG_SECURITY
> +
> +/*
> + * Macros to count the number of LSMs enabled in the kernel at compile time.
> + */
> +
> +/*
> + * Capabilities is enabled when CONFIG_SECURITY is enabled.
> + */
> +#if IS_ENABLED(CONFIG_SECURITY)
> +#define CAPABILITIES_ENABLED 1,
> +#else
> +#define CAPABILITIES_ENABLED
> +#endif
> +
> +#if IS_ENABLED(CONFIG_SECURITY_SELINUX)
> +#define SELINUX_ENABLED 1,
> +#else
> +#define SELINUX_ENABLED
> +#endif
> +
> +#if IS_ENABLED(CONFIG_SECURITY_SMACK)
> +#define SMACK_ENABLED 1,
> +#else
> +#define SMACK_ENABLED
> +#endif
> +
> +#if IS_ENABLED(CONFIG_SECURITY_APPARMOR)
> +#define APPARMOR_ENABLED 1,
> +#else
> +#define APPARMOR_ENABLED
> +#endif
> +
> +#if IS_ENABLED(CONFIG_SECURITY_TOMOYO)
> +#define TOMOYO_ENABLED 1,
> +#else
> +#define TOMOYO_ENABLED
> +#endif
> +
> +#if IS_ENABLED(CONFIG_SECURITY_YAMA)
> +#define YAMA_ENABLED 1,
> +#else
> +#define YAMA_ENABLED
> +#endif
> +
> +#if IS_ENABLED(CONFIG_SECURITY_LOADPIN)
> +#define LOADPIN_ENABLED 1,
> +#else
> +#define LOADPIN_ENABLED
> +#endif
> +
> +#if IS_ENABLED(CONFIG_SECURITY_LOCKDOWN_LSM)
> +#define LOCKDOWN_ENABLED 1,
> +#else
> +#define LOCKDOWN_ENABLED
> +#endif
> +
> +#if IS_ENABLED(CONFIG_SECURITY_SAFESETID)
> +#define SAFESETID_ENABLED 1,
> +#else
> +#define SAFESETID_ENABLED
> +#endif
> +
> +#if IS_ENABLED(CONFIG_BPF_LSM)
> +#define BPF_LSM_ENABLED 1,
> +#else
> +#define BPF_LSM_ENABLED
> +#endif
> +
> +#if IS_ENABLED(CONFIG_SECURITY_LANDLOCK)
> +#define LANDLOCK_ENABLED 1,
> +#else
> +#define LANDLOCK_ENABLED
> +#endif
> +
> +#if IS_ENABLED(CONFIG_IMA)
> +#define IMA_ENABLED 1,
> +#else
> +#define IMA_ENABLED
> +#endif
> +
> +#if IS_ENABLED(CONFIG_EVM)
> +#define EVM_ENABLED 1,
> +#else
> +#define EVM_ENABLED
> +#endif
> +
> +/*
> + *  There is a trailing comma that we need to be accounted for. This is done by
> + *  using a skipped argument in __COUNT_LSMS
> + */
> +#define __COUNT_LSMS(skipped_arg, args...) COUNT_ARGS(args...)
> +#define COUNT_LSMS(args...) __COUNT_LSMS(args)
> +
> +#define MAX_LSM_COUNT			\
> +	COUNT_LSMS(			\
> +		CAPABILITIES_ENABLED	\
> +		SELINUX_ENABLED		\
> +		SMACK_ENABLED		\
> +		APPARMOR_ENABLED	\
> +		TOMOYO_ENABLED		\
> +		YAMA_ENABLED		\
> +		LOADPIN_ENABLED		\
> +		LOCKDOWN_ENABLED	\
> +		SAFESETID_ENABLED	\
> +		BPF_LSM_ENABLED		\
> +		LANDLOCK_ENABLED	\
> +		IMA_ENABLED		\
> +		EVM_ENABLED)
> +
> +#else
> +
> +#define MAX_LSM_COUNT 0
> +
> +#endif /* CONFIG_SECURITY */
> +
> +#endif  /* __LINUX_LSM_COUNT_H */