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, 39 insertions, 18 deletions

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index b2584b25748c..a616b63f23b4 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -25,6 +25,7 @@
 #include <linux/nospec.h>
 #include <linux/audit.h>
 #include <uapi/linux/btf.h>
+#include <linux/bpf_lsm.h>
 
 #define IS_FD_ARRAY(map) ((map)->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY || \
 			  (map)->map_type == BPF_MAP_TYPE_CGROUP_ARRAY || \
@@ -1935,6 +1936,7 @@ bpf_prog_load_check_attach(enum bpf_prog_type prog_type,
 
 		switch (prog_type) {
 		case BPF_PROG_TYPE_TRACING:
+		case BPF_PROG_TYPE_LSM:
 		case BPF_PROG_TYPE_STRUCT_OPS:
 		case BPF_PROG_TYPE_EXT:
 			break;
@@ -2366,10 +2368,28 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog)
 	struct file *link_file;
 	int link_fd, err;
 
-	if (prog->expected_attach_type != BPF_TRACE_FENTRY &&
-	    prog->expected_attach_type != BPF_TRACE_FEXIT &&
-	    prog->expected_attach_type != BPF_MODIFY_RETURN &&
-	    prog->type != BPF_PROG_TYPE_EXT) {
+	switch (prog->type) {
+	case BPF_PROG_TYPE_TRACING:
+		if (prog->expected_attach_type != BPF_TRACE_FENTRY &&
+		    prog->expected_attach_type != BPF_TRACE_FEXIT &&
+		    prog->expected_attach_type != BPF_MODIFY_RETURN) {
+			err = -EINVAL;
+			goto out_put_prog;
+		}
+		break;
+	case BPF_PROG_TYPE_EXT:
+		if (prog->expected_attach_type != 0) {
+			err = -EINVAL;
+			goto out_put_prog;
+		}
+		break;
+	case BPF_PROG_TYPE_LSM:
+		if (prog->expected_attach_type != BPF_LSM_MAC) {
+			err = -EINVAL;
+			goto out_put_prog;
+		}
+		break;
+	default:
 		err = -EINVAL;
 		goto out_put_prog;
 	}
@@ -2448,16 +2468,10 @@ static int bpf_raw_tracepoint_open(const union bpf_attr *attr)
 	if (IS_ERR(prog))
 		return PTR_ERR(prog);
 
-	if (prog->type != BPF_PROG_TYPE_RAW_TRACEPOINT &&
-	    prog->type != BPF_PROG_TYPE_TRACING &&
-	    prog->type != BPF_PROG_TYPE_EXT &&
-	    prog->type != BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE) {
-		err = -EINVAL;
-		goto out_put_prog;
-	}
-
-	if (prog->type == BPF_PROG_TYPE_TRACING ||
-	    prog->type == BPF_PROG_TYPE_EXT) {
+	switch (prog->type) {
+	case BPF_PROG_TYPE_TRACING:
+	case BPF_PROG_TYPE_EXT:
+	case BPF_PROG_TYPE_LSM:
 		if (attr->raw_tracepoint.name) {
 			/* The attach point for this category of programs
 			 * should be specified via btf_id during program load.
@@ -2465,11 +2479,14 @@ static int bpf_raw_tracepoint_open(const union bpf_attr *attr)
 			err = -EINVAL;
 			goto out_put_prog;
 		}
-		if (prog->expected_attach_type == BPF_TRACE_RAW_TP)
+		if (prog->type == BPF_PROG_TYPE_TRACING &&
+		    prog->expected_attach_type == BPF_TRACE_RAW_TP) {
 			tp_name = prog->aux->attach_func_name;
-		else
-			return bpf_tracing_prog_attach(prog);
-	} else {
+			break;
+		}
+		return bpf_tracing_prog_attach(prog);
+	case BPF_PROG_TYPE_RAW_TRACEPOINT:
+	case BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE:
 		if (strncpy_from_user(buf,
 				      u64_to_user_ptr(attr->raw_tracepoint.name),
 				      sizeof(buf) - 1) < 0) {
@@ -2478,6 +2495,10 @@ static int bpf_raw_tracepoint_open(const union bpf_attr *attr)
 		}
 		buf[sizeof(buf) - 1] = 0;
 		tp_name = buf;
+		break;
+	default:
+		err = -EINVAL;
+		goto out_put_prog;
 	}
 
 	btp = bpf_get_raw_tracepoint(tp_name);