bpf: Introduce BPF_PROG_TYPE_LSM

Introduce types and configs for bpf programs that can be attached to
LSM hooks. The programs can be enabled by the config option
CONFIG_BPF_LSM.

Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Brendan Jackman <jackmanb@google.com>
Reviewed-by: Florent Revest <revest@google.com>
Reviewed-by: Thomas Garnier <thgarnie@google.com>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: James Morris <jamorris@linux.microsoft.com>
Link: https://lore.kernel.org/bpf/20200329004356.27286-2-kpsingh@chromium.org

MAINTAINERS

@@ -3147,6 +3147,7 @@ R:	Martin KaFai Lau <kafai@fb.com>
 R:	Song Liu <songliubraving@fb.com>
 R:	Yonghong Song <yhs@fb.com>
 R:	Andrii Nakryiko <andriin@fb.com>
+R:	KP Singh <kpsingh@chromium.org>
 L:	netdev@vger.kernel.org
 L:	bpf@vger.kernel.org
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git

include/linux/bpf.h

@@ -1515,6 +1515,9 @@ extern const struct bpf_func_proto bpf_tcp_sock_proto;
 extern const struct bpf_func_proto bpf_jiffies64_proto;
 extern const struct bpf_func_proto bpf_get_ns_current_pid_tgid_proto;
 
+const struct bpf_func_proto *bpf_tracing_func_proto(
+	enum bpf_func_id func_id, const struct bpf_prog *prog);
+
 /* Shared helpers among cBPF and eBPF. */
 void bpf_user_rnd_init_once(void);
 u64 bpf_user_rnd_u32(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);

include/linux/bpf_types.h

@@ -70,6 +70,10 @@ BPF_PROG_TYPE(BPF_PROG_TYPE_STRUCT_OPS, bpf_struct_ops,
 	      void *, void *)
 BPF_PROG_TYPE(BPF_PROG_TYPE_EXT, bpf_extension,
 	      void *, void *)
+#ifdef CONFIG_BPF_LSM
+BPF_PROG_TYPE(BPF_PROG_TYPE_LSM, lsm,
+	       void *, void *)
+#endif /* CONFIG_BPF_LSM */
 #endif
 
 BPF_MAP_TYPE(BPF_MAP_TYPE_ARRAY, array_map_ops)

include/uapi/linux/bpf.h

@@ -181,6 +181,7 @@ enum bpf_prog_type {
 	BPF_PROG_TYPE_TRACING,
 	BPF_PROG_TYPE_STRUCT_OPS,
 	BPF_PROG_TYPE_EXT,
+	BPF_PROG_TYPE_LSM,
 };
 
 enum bpf_attach_type {
@@ -211,6 +212,7 @@ enum bpf_attach_type {
 	BPF_TRACE_FENTRY,
 	BPF_TRACE_FEXIT,
 	BPF_MODIFY_RETURN,
+	BPF_LSM_MAC,
 	__MAX_BPF_ATTACH_TYPE
 };
 

init/Kconfig

@@ -1616,6 +1616,18 @@ config KALLSYMS_BASE_RELATIVE
 # end of the "standard kernel features (expert users)" menu
 
 # syscall, maps, verifier
+
+config BPF_LSM
+	bool "LSM Instrumentation with BPF"
+	depends on BPF_SYSCALL
+	depends on SECURITY
+	depends on BPF_JIT
+	help
+	  Enables instrumentation of the security hooks with eBPF programs for
+	  implementing dynamic MAC and Audit Policies.
+
+	  If you are unsure how to answer this question, answer N.
+
 config BPF_SYSCALL
 	bool "Enable bpf() system call"
 	select BPF

kernel/bpf/Makefile

@@ -29,4 +29,5 @@ obj-$(CONFIG_DEBUG_INFO_BTF) += sysfs_btf.o
 endif
 ifeq ($(CONFIG_BPF_JIT),y)
 obj-$(CONFIG_BPF_SYSCALL) += bpf_struct_ops.o
+obj-${CONFIG_BPF_LSM} += bpf_lsm.o
 endif

kernel/bpf/bpf_lsm.c

@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (C) 2020 Google LLC.
+ */
+
+#include <linux/filter.h>
+#include <linux/bpf.h>
+#include <linux/btf.h>
+
+const struct bpf_prog_ops lsm_prog_ops = {
+};
+
+const struct bpf_verifier_ops lsm_verifier_ops = {
+	.get_func_proto = bpf_tracing_func_proto,
+	.is_valid_access = btf_ctx_access,
+};

kernel/trace/bpf_trace.c

@@ -779,8 +779,8 @@ static const struct bpf_func_proto bpf_send_signal_thread_proto = {
 	.arg1_type	= ARG_ANYTHING,
 };
 
-static const struct bpf_func_proto *
+const struct bpf_func_proto *
-tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
+bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
 	switch (func_id) {
 	case BPF_FUNC_map_lookup_elem:
@@ -865,7 +865,7 @@ kprobe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_override_return_proto;
 #endif
 	default:
-		return tracing_func_proto(func_id, prog);
+		return bpf_tracing_func_proto(func_id, prog);
 	}
 }
 
@@ -975,7 +975,7 @@ tp_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 	case BPF_FUNC_get_stack:
 		return &bpf_get_stack_proto_tp;
 	default:
-		return tracing_func_proto(func_id, prog);
+		return bpf_tracing_func_proto(func_id, prog);
 	}
 }
 
@@ -1082,7 +1082,7 @@ pe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 	case BPF_FUNC_read_branch_records:
 		return &bpf_read_branch_records_proto;
 	default:
-		return tracing_func_proto(func_id, prog);
+		return bpf_tracing_func_proto(func_id, prog);
 	}
 }
 
@@ -1210,7 +1210,7 @@ raw_tp_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 	case BPF_FUNC_get_stack:
 		return &bpf_get_stack_proto_raw_tp;
 	default:
-		return tracing_func_proto(func_id, prog);
+		return bpf_tracing_func_proto(func_id, prog);
 	}
 }
 

tools/include/uapi/linux/bpf.h

@@ -181,6 +181,7 @@ enum bpf_prog_type {
 	BPF_PROG_TYPE_TRACING,
 	BPF_PROG_TYPE_STRUCT_OPS,
 	BPF_PROG_TYPE_EXT,
+	BPF_PROG_TYPE_LSM,
 };
 
 enum bpf_attach_type {
@@ -211,6 +212,7 @@ enum bpf_attach_type {
 	BPF_TRACE_FENTRY,
 	BPF_TRACE_FEXIT,
 	BPF_MODIFY_RETURN,
+	BPF_LSM_MAC,
 	__MAX_BPF_ATTACH_TYPE
 };
 

tools/lib/bpf/libbpf_probes.c

@@ -108,6 +108,7 @@ probe_load(enum bpf_prog_type prog_type, const struct bpf_insn *insns,
 	case BPF_PROG_TYPE_TRACING:
 	case BPF_PROG_TYPE_STRUCT_OPS:
 	case BPF_PROG_TYPE_EXT:
+	case BPF_PROG_TYPE_LSM:
 	default:
 		break;
 	}