Merge branch 'Support kernel module ksym variables'

Andrii Nakryiko says:

====================

Add support for using kernel module global variables (__ksym externs in BPF
program). BPF verifier will now support ldimm64 with src_reg=BPF_PSEUDO_BTF_ID
and non-zero insn[1].imm field, specifying module BTF's FD. In such case,
module BTF object, similarly to BPF maps referenced from ldimm64 with
src_reg=BPF_PSEUDO_MAP_FD, will be recorded in bpf_progran's auxiliary data
and refcnt will be increased for both BTF object itself and its kernel module.
This makes sure kernel module won't be unloaded from under active attached BPF
program. These refcounts will be dropped when BPF program is unloaded.

New selftest validates all this is working as intended. bpf_testmod.ko is
extended with per-CPU variable. Selftests expects the latest pahole changes
(soon to be released as v1.20) to generate per-CPU variable BTF info for
kernel module.

v2->v3:
  - added comments, addressed feedack (Yonghong, Hao);
v1->v2:
  - fixed few compiler warnings, posted as separate pre-patches;
rfc->v1:
  - use sys_membarrier(MEMBARRIER_CMD_GLOBAL) (Alexei).

Cc: Hao Luo <haoluo@google.com>
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 32 insertions, 18 deletions

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 6ae748f6ea11..2abbc3800568 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -395,7 +395,8 @@ struct extern_desc {
 			unsigned long long addr;
 
 			/* target btf_id of the corresponding kernel var. */
-			int vmlinux_btf_id;
+			int kernel_btf_obj_fd;
+			int kernel_btf_id;
 
 			/* local btf_id of the ksym extern's type. */
 			__u32 type_id;
@@ -6162,7 +6163,8 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog)
 			} else /* EXT_KSYM */ {
 				if (ext->ksym.type_id) { /* typed ksyms */
 					insn[0].src_reg = BPF_PSEUDO_BTF_ID;
-					insn[0].imm = ext->ksym.vmlinux_btf_id;
+					insn[0].imm = ext->ksym.kernel_btf_id;
+					insn[1].imm = ext->ksym.kernel_btf_obj_fd;
 				} else { /* typeless ksyms */
 					insn[0].imm = (__u32)ext->ksym.addr;
 					insn[1].imm = ext->ksym.addr >> 32;
@@ -7319,7 +7321,8 @@ out:
 static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj)
 {
 	struct extern_desc *ext;
-	int i, id;
+	struct btf *btf;
+	int i, j, id, btf_fd, err;
 
 	for (i = 0; i < obj->nr_extern; i++) {
 		const struct btf_type *targ_var, *targ_type;
@@ -7331,10 +7334,25 @@ static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj)
 		if (ext->type != EXT_KSYM || !ext->ksym.type_id)
 			continue;
 
-		id = btf__find_by_name_kind(obj->btf_vmlinux, ext->name,
-					    BTF_KIND_VAR);
+		btf = obj->btf_vmlinux;
+		btf_fd = 0;
+		id = btf__find_by_name_kind(btf, ext->name, BTF_KIND_VAR);
+		if (id == -ENOENT) {
+			err = load_module_btfs(obj);
+			if (err)
+				return err;
+
+			for (j = 0; j < obj->btf_module_cnt; j++) {
+				btf = obj->btf_modules[j].btf;
+				/* we assume module BTF FD is always >0 */
+				btf_fd = obj->btf_modules[j].fd;
+				id = btf__find_by_name_kind(btf, ext->name, BTF_KIND_VAR);
+				if (id != -ENOENT)
+					break;
+			}
+		}
 		if (id <= 0) {
-			pr_warn("extern (ksym) '%s': failed to find BTF ID in vmlinux BTF.\n",
+			pr_warn("extern (ksym) '%s': failed to find BTF ID in kernel BTF(s).\n",
 				ext->name);
 			return -ESRCH;
 		}
@@ -7343,24 +7361,19 @@ static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj)
 		local_type_id = ext->ksym.type_id;
 
 		/* find target type_id */
-		targ_var = btf__type_by_id(obj->btf_vmlinux, id);
-		targ_var_name = btf__name_by_offset(obj->btf_vmlinux,
-						    targ_var->name_off);
-		targ_type = skip_mods_and_typedefs(obj->btf_vmlinux,
-						   targ_var->type,
-						   &targ_type_id);
+		targ_var = btf__type_by_id(btf, id);
+		targ_var_name = btf__name_by_offset(btf, targ_var->name_off);
+		targ_type = skip_mods_and_typedefs(btf, targ_var->type, &targ_type_id);
 
 		ret = bpf_core_types_are_compat(obj->btf, local_type_id,
-						obj->btf_vmlinux, targ_type_id);
+						btf, targ_type_id);
 		if (ret <= 0) {
 			const struct btf_type *local_type;
 			const char *targ_name, *local_name;
 
 			local_type = btf__type_by_id(obj->btf, local_type_id);
-			local_name = btf__name_by_offset(obj->btf,
-							 local_type->name_off);
-			targ_name = btf__name_by_offset(obj->btf_vmlinux,
-							targ_type->name_off);
+			local_name = btf__name_by_offset(obj->btf, local_type->name_off);
+			targ_name = btf__name_by_offset(btf, targ_type->name_off);
 
 			pr_warn("extern (ksym) '%s': incompatible types, expected [%d] %s %s, but kernel has [%d] %s %s\n",
 				ext->name, local_type_id,
@@ -7370,7 +7383,8 @@ static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj)
 		}
 
 		ext->is_set = true;
-		ext->ksym.vmlinux_btf_id = id;
+		ext->ksym.kernel_btf_obj_fd = btf_fd;
+		ext->ksym.kernel_btf_id = id;
 		pr_debug("extern (ksym) '%s': resolved to [%d] %s %s\n",
 			 ext->name, id, btf_kind_str(targ_var), targ_var_name);
 	}