Create a system call lsm_self_attr() to provide the security
module maintained attributes of the current process. Historically
these attributes have been exposed to user space via entries in
procfs under /proc/self/attr.

Attributes are provided as a collection of lsm_ctx structures
which are placed into a user supplied buffer. Each structure
identifys the security module providing the attribute, which
of the possible attributes is provided, the size of the
attribute, and finally the attribute value. The format of the
attribute value is defined by the security module, but will
always be \0 terminated. The ctx_len value will be larger than
strlen(ctx).

        ------------------------------
        | unsigned int id            |
        ------------------------------
        | unsigned int flags         |
        ------------------------------
        | __kernel_size_t ctx_len    |
        ------------------------------
        | unsigned char ctx[ctx_len] |
        ------------------------------
        | unsigned int id            |
        ------------------------------
        | unsigned int flags         |
        ------------------------------
        | __kernel_size_t ctx_len    |
        ------------------------------
        | unsigned char ctx[ctx_len] |
        ------------------------------

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
---
 include/linux/syscalls.h |   2 +
 include/uapi/linux/lsm.h |  21 ++++++
 kernel/sys_ni.c          |   3 +
 security/Makefile        |   1 +
 security/lsm_syscalls.c  | 156 +++++++++++++++++++++++++++++++++++++++
 5 files changed, 183 insertions(+)
 create mode 100644 security/lsm_syscalls.c

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index a34b0f9a9972..2d9033e9e5a0 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h

@@ -71,6 +71,7 @@ struct clone_args;
 struct open_how;
 struct mount_attr;
 struct landlock_ruleset_attr;
+struct lsm_cxt;
 enum landlock_rule_type;
 
 #include <linux/types.h>

@@ -1056,6 +1057,7 @@ asmlinkage long sys_memfd_secret(unsigned int flags);
 asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
 					    unsigned long home_node,
 					    unsigned long flags);
+asmlinkage long sys_lsm_self_attr(struct lsm_ctx *ctx, size_t *size, int flags);
 
 /*
  * Architecture-specific system calls

diff --git a/include/uapi/linux/lsm.h b/include/uapi/linux/lsm.h
index 61e13b1b9ece..1d27fb5b7746 100644
--- a/include/uapi/linux/lsm.h
+++ b/include/uapi/linux/lsm.h

@@ -9,6 +9,27 @@
 #ifndef _UAPI_LINUX_LSM_H
 #define _UAPI_LINUX_LSM_H
 
+#include <linux/types.h>
+#include <linux/unistd.h>
+
+/**
+ * struct lsm_ctx - LSM context
+ * @id: the LSM id number, see LSM_ID_XXX
+ * @flags: context specifier and LSM specific flags
+ * @ctx_len: the size of @ctx
+ * @ctx: the LSM context, a nul terminated string
+ *
+ * @ctx in a nul terminated string.
+ *	(strlen(@ctx) < @ctx_len) is always true.
+ *	(strlen(@ctx) == @ctx_len + 1) is not guaranteed.
+ */
+struct lsm_ctx {
+	unsigned int		id;
+	unsigned int		flags;
+	__kernel_size_t		ctx_len;
+	unsigned char		ctx[];