$ git tag --contains a04a1198088a1378d0389c250cc684f649bcc91e | head -1
v6.10
$ 
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commit a04a1198088a1378d0389c250cc684f649bcc91e
Author: Casey Schaufler <casey@schaufler-ca.com>
Date:   Tue Sep 12 13:56:49 2023 -0700

    LSM: syscalls for current process attributes
    
    Create a system call lsm_get_self_attr() to provide the security
    module maintained attributes of the current process.
    Create a system call lsm_set_self_attr() to set a security
    module maintained attribute of the current process.
    Historically these attributes have been exposed to user space via
    entries in procfs under /proc/self/attr.
    
    The attribute value is provided in a lsm_ctx structure. The structure
    identifies the size of the attribute, and the attribute value. The format
    of the attribute value is defined by the security module. A flags field
    is included for LSM specific information. It is currently unused and must
    be 0. The total size of the data, including the lsm_ctx structure and any
    padding, is maintained as well.
    
    struct lsm_ctx {
            __u64 id;
            __u64 flags;
            __u64 len;
            __u64 ctx_len;
            __u8 ctx[];
    };
    
    Two new LSM hooks are used to interface with the LSMs.
    security_getselfattr() collects the lsm_ctx values from the
    LSMs that support the hook, accounting for space requirements.
    security_setselfattr() identifies which LSM the attribute is
    intended for and passes it along.

[ ... stuff deleted ... ]

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/**
 * sys_lsm_set_self_attr - Set current task's security module attribute
 * @attr: which attribute to set
 * @ctx: the LSM contexts
 * @size: size of @ctx
 * @flags: reserved for future use
 *
 * Sets the calling task's LSM context. On success this function
 * returns 0. If the attribute specified cannot be set a negative
 * value indicating the reason for the error is returned.
 */
SYSCALL_DEFINE4(lsm_set_self_attr, unsigned int, attr, struct lsm_ctx __user *,
                ctx, u32, size, u32, flags)
{
        return security_setselfattr(attr, ctx, size, flags);
}

/**
 * sys_lsm_get_self_attr - Return current task's security module attributes
 * @attr: which attribute to return
 * @ctx: the user-space destination for the information, or NULL
 * @size: pointer to the size of space available to receive the data
 * @flags: special handling options. LSM_FLAG_SINGLE indicates that only
 * attributes associated with the LSM identified in the passed @ctx be
 * reported.
 *
 * Returns the calling task's LSM contexts. On success this
 * function returns the number of @ctx array elements. This value
 * may be zero if there are no LSM contexts assigned. If @size is
 * insufficient to contain the return data -E2BIG is returned and
 * @size is set to the minimum required size. In all other cases
 * a negative value indicating the error is returned.
 */
SYSCALL_DEFINE4(lsm_get_self_attr, unsigned int, attr, struct lsm_ctx __user *,
                ctx, u32 __user *, size, u32, flags)
{
        return security_getselfattr(attr, ctx, size, flags);
}