[PATCH bpf-next 1/2] lsm: add bpf_security_locked_down() kfunc
From: Justin Suess <hidden>
Date: 2026-08-15 11:20:48
Also in:
bpf, lkml
Subsystem:
security subsystem, the rest · Maintainers:
Paul Moore, James Morris, "Serge E. Hallyn", Linus Torvalds
Add a new kfunc bpf_security_locked_down, which calls security_locked_down and returns the result. Create a new file security/lsm_kfuncs.c for LSM framework kfuncs. Reject reasons outside (LOCKDOWN_NONE, LOCKDOWN_CONFIDENTIALITY_MAX) with -EINVAL before dispatching the hook. Limit the kfunc to BPF_PROG_TYPE_LSM and BPF_PROG_TYPE_SYSCALL programs, and refuse it to programs attached to the locked_down hook itself, which would recurse into the dispatch. Signed-off-by: Justin Suess <redacted> --- security/Makefile | 1 + security/lsm_kfuncs.c | 84 +++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 85 insertions(+) create mode 100644 security/lsm_kfuncs.c
diff --git a/security/Makefile b/security/Makefile
index 4601230ba442..dee8ff218548 100644
--- a/security/Makefile
+++ b/security/Makefile@@ -12,6 +12,7 @@ obj-$(CONFIG_MMU) += min_addr.o # Object file lists obj-$(CONFIG_SECURITY) += security.o lsm_notifier.o lsm_init.o +obj-$(CONFIG_BPF_SYSCALL) += lsm_kfuncs.o obj-$(CONFIG_SECURITYFS) += inode.o obj-$(CONFIG_SECURITY_SELINUX) += selinux/ obj-$(CONFIG_SECURITY_SMACK) += smack/
diff --git a/security/lsm_kfuncs.c b/security/lsm_kfuncs.c
new file mode 100644
index 000000000000..a324e7d978ca
--- /dev/null
+++ b/security/lsm_kfuncs.c@@ -0,0 +1,84 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * kfuncs exposing LSM interfaces to BPF programs. + * + * Copyright (C) 2026 Justin Suess + */ +#include <linux/bpf.h> +#include <linux/btf.h> +#include <linux/btf_ids.h> +#include <linux/init.h> +#include <linux/security.h> + +__bpf_kfunc_start_defs(); + +/** + * bpf_security_locked_down - Call the security_locked_down() LSM hook + * @what: lockdown reason to query + * + * Return: 0 if @what is not locked down, -EPERM if it is, or -EINVAL if + * @what is outside (LOCKDOWN_NONE, LOCKDOWN_CONFIDENTIALITY_MAX). + */ +__bpf_kfunc int bpf_security_locked_down(enum lockdown_reason what) +{ + if (what <= LOCKDOWN_NONE || what >= LOCKDOWN_CONFIDENTIALITY_MAX) + return -EINVAL; + return security_locked_down(what); +} + +__bpf_kfunc_end_defs(); + +BTF_KFUNCS_START(lsm_kfunc_ids) +BTF_ID_FLAGS(func, bpf_security_locked_down) +BTF_KFUNCS_END(lsm_kfunc_ids) + +#ifdef CONFIG_BPF_LSM +BTF_ID_LIST_SINGLE(lsm_locked_down_hook_id, func, bpf_lsm_locked_down) +#endif + +static int lsm_kfunc_filter(const struct bpf_prog *prog, u32 kfunc_id) +{ + /* Filters run for every kfunc resolved through the hook. */ + if (!btf_id_set8_contains(&lsm_kfunc_ids, kfunc_id)) + return 0; + + /* + * Raw prog->type: keep out the rest of the shared tracing kfunc + * set (incl. perf/NMI) and extension programs. + */ + switch (prog->type) { + case BPF_PROG_TYPE_SYSCALL: + return 0; +#ifdef CONFIG_BPF_LSM + case BPF_PROG_TYPE_LSM: + /* + * A locked_down program calling this kfunc would recurse. + * Match on attach_btf_id: attach_func_name is not yet set + * when the filter runs from check_cfg. + */ + if (prog->aux->attach_btf_id == lsm_locked_down_hook_id[0]) + return -EACCES; + return 0; +#endif + default: + return -EACCES; + } +} + +static const struct btf_kfunc_id_set lsm_kfunc_set = { + .owner = THIS_MODULE, + .set = &lsm_kfunc_ids, + .filter = lsm_kfunc_filter, +}; + +static int __init lsm_kfuncs_init(void) +{ + int err; + + err = register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &lsm_kfunc_set); + err = err ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &lsm_kfunc_set); + if (err) + pr_warn("lsm_kfuncs: kfunc registration failed: %d\n", err); + return err; +} +late_initcall(lsm_kfuncs_init);
--
2.54.0