[PATCH v3 2/3] lsm: introduce security_lsm_config_*_policy hooks

[Tetsuo Handa]

On 2025/06/24 23:30, Maxime Bélair wrote:
> +config LSM_CONFIG_SELF_POLICY_MAX_BUFFER_SIZE
> +	int "Maximum buffer size for lsm_config_self_policy"
> +	range 16384 1073741824
> +	depends on SECURITY
> +	default 4194304
> +	help
> +	  The maximum size of the buffer argument of lsm_config_self_policy.
> +
> +	  The default value of 4194304 (4MiB) is reasonable and should be large
> +	  enough to fit policies in for most cases.
> +

Do we want to define LSM_CONFIG_{SELF,SYSTEM}_POLICY_MAX_BUFFER_SIZE as Kconfig?

If security_lsm_config_{self,system}_policy() are meant to be used by multiple
LSM modules, the upper limit each LSM module wants to impose would vary. Also,
1073741824 is larger than KMALLOC_MAX_SIZE; kmalloc()-based memory copying
functions will hit WARN_ON_ONCE_GFP() at __alloc_frozen_pages_noprof().

Since some of LSM modules might use vmalloc()-based memory copying functions from
security_lsm_config_{self,system}_policy(), the upper limit should be imposed by
individual LSM module which provides security_lsm_config_{self,system}_policy().