bpf: lsm: Implement attach, detach and execution

JITed BPF programs are dynamically attached to the LSM hooks
using BPF trampolines. The trampoline prologue generates code to handle
conversion of the signature of the hook to the appropriate BPF context.

The allocated trampoline programs are attached to the nop functions
initialized as LSM hooks.

BPF_PROG_TYPE_LSM programs must have a GPL compatible license and
and need CAP_SYS_ADMIN (required for loading eBPF programs).

Upon attachment:

* A BPF fexit trampoline is used for LSM hooks with a void return type.
* A BPF fmod_ret trampoline is used for LSM hooks which return an
  int. The attached programs can override the return value of the
  bpf LSM hook to indicate a MAC Policy decision.

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>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: James Morris <jamorris@linux.microsoft.com>
Link: https://lore.kernel.org/bpf/20200329004356.27286-5-kpsingh@chromium.org

1 files changed, 15 insertions, 4 deletions

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 46ba86c540e2..047b2e876399 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -20,6 +20,7 @@
 #include <linux/perf_event.h>
 #include <linux/ctype.h>
 #include <linux/error-injection.h>
+#include <linux/bpf_lsm.h>
 
 #include "disasm.h"
 
@@ -6492,8 +6493,9 @@ static int check_return_code(struct bpf_verifier_env *env)
 	struct tnum range = tnum_range(0, 1);
 	int err;
 
-	/* The struct_ops func-ptr's return type could be "void" */
-	if (env->prog->type == BPF_PROG_TYPE_STRUCT_OPS &&
+	/* LSM and struct_ops func-ptr's return type could be "void" */
+	if ((env->prog->type == BPF_PROG_TYPE_STRUCT_OPS ||
+	     env->prog->type == BPF_PROG_TYPE_LSM) &&
 	    !prog->aux->attach_func_proto->type)
 		return 0;
 
@@ -9923,7 +9925,9 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 	if (prog->type == BPF_PROG_TYPE_STRUCT_OPS)
 		return check_struct_ops_btf_id(env);
 
-	if (prog->type != BPF_PROG_TYPE_TRACING && !prog_extension)
+	if (prog->type != BPF_PROG_TYPE_TRACING &&
+	    prog->type != BPF_PROG_TYPE_LSM &&
+	    !prog_extension)
 		return 0;
 
 	if (!btf_id) {
@@ -10054,8 +10058,16 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 			return -EINVAL;
 		/* fallthrough */
 	case BPF_MODIFY_RETURN:
+	case BPF_LSM_MAC:
 	case BPF_TRACE_FENTRY:
 	case BPF_TRACE_FEXIT:
+		prog->aux->attach_func_name = tname;
+		if (prog->type == BPF_PROG_TYPE_LSM) {
+			ret = bpf_lsm_verify_prog(&env->log, prog);
+			if (ret < 0)
+				return ret;
+		}
+
 		if (!btf_type_is_func(t)) {
 			verbose(env, "attach_btf_id %u is not a function\n",
 				btf_id);
@@ -10070,7 +10082,6 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 		tr = bpf_trampoline_lookup(key);
 		if (!tr)
 			return -ENOMEM;
-		prog->aux->attach_func_name = tname;
 		/* t is either vmlinux type or another program's type */
 		prog->aux->attach_func_proto = t;
 		mutex_lock(&tr->mutex);