bpf: Implement get_current_task_btf and RET_PTR_TO_BTF_ID

The currently available bpf_get_current_task returns an unsigned integer
which can be used along with BPF_CORE_READ to read data from
the task_struct but still cannot be used as an input argument to a
helper that accepts an ARG_PTR_TO_BTF_ID of type task_struct.

In order to implement this helper a new return type, RET_PTR_TO_BTF_ID,
is added. This is similar to RET_PTR_TO_BTF_ID_OR_NULL but does not
require checking the nullness of returned pointer.

Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20201106103747.2780972-6-kpsingh@chromium.org

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 2fffd30e13acfc4d1dc8afa8cdc12d0e434b17f4..73d5381a5d5c4e8b70a2848c4b97f43c25fa4fc7 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -310,6 +310,7 @@ enum bpf_return_type {
        RET_PTR_TO_BTF_ID_OR_NULL,      /* returns a pointer to a btf_id or NULL */
        RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL, /* returns a pointer to a valid memory or a btf_id or NULL */
        RET_PTR_TO_MEM_OR_BTF_ID,       /* returns a pointer to a valid memory or a btf_id */
+       RET_PTR_TO_BTF_ID,              /* returns a pointer to a btf_id */
 };
 
 /* eBPF function prototype used by verifier to allow BPF_CALLs from eBPF programs

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index f4037b2161a67b69c606c8bd9b7fbde8d7a7520f..9879d6793e9045675420be644c13554916a45c5c 100644 (file)
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3779,6 +3779,14 @@ union bpf_attr {
  *             0 on success.
  *
  *             **-ENOENT** if the bpf_local_storage cannot be found.
+ *
+ * struct task_struct *bpf_get_current_task_btf(void)
+ *     Description
+ *             Return a BTF pointer to the "current" task.
+ *             This pointer can also be used in helpers that accept an
+ *             *ARG_PTR_TO_BTF_ID* of type *task_struct*.
+ *     Return
+ *             Pointer to the current task.
  */
 #define __BPF_FUNC_MAPPER(FN)          \
        FN(unspec),                     \
@@ -3939,6 +3947,7 @@ union bpf_attr {
        FN(redirect_peer),              \
        FN(task_storage_get),           \
        FN(task_storage_delete),        \
+       FN(get_current_task_btf),       \
        /* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 00960f6a83ecfbb152ac350b124d8b51d2a1fc05..10da26e55130ab6ae83d281668c0580c04430de0 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5186,11 +5186,14 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
                                PTR_TO_BTF_ID : PTR_TO_BTF_ID_OR_NULL;
                        regs[BPF_REG_0].btf_id = meta.ret_btf_id;
                }
-       } else if (fn->ret_type == RET_PTR_TO_BTF_ID_OR_NULL) {
+       } else if (fn->ret_type == RET_PTR_TO_BTF_ID_OR_NULL ||
+                  fn->ret_type == RET_PTR_TO_BTF_ID) {
                int ret_btf_id;
 
                mark_reg_known_zero(env, regs, BPF_REG_0);
-               regs[BPF_REG_0].type = PTR_TO_BTF_ID_OR_NULL;
+               regs[BPF_REG_0].type = fn->ret_type == RET_PTR_TO_BTF_ID ?
+                                                    PTR_TO_BTF_ID :
+                                                    PTR_TO_BTF_ID_OR_NULL;
                ret_btf_id = *fn->ret_btf_id;
                if (ret_btf_id == 0) {
                        verbose(env, "invalid return type %d of func %s#%d\n",

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 4517c8b66518fdc500b5874be4653b0be98f7f4e..e4515b0f62a8d3324bfeaa9a86d9a5865560dee7 100644 (file)
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1022,6 +1022,20 @@ const struct bpf_func_proto bpf_get_current_task_proto = {
        .ret_type       = RET_INTEGER,
 };
 
+BPF_CALL_0(bpf_get_current_task_btf)
+{
+       return (unsigned long) current;
+}
+
+BTF_ID_LIST_SINGLE(bpf_get_current_btf_ids, struct, task_struct)
+
+static const struct bpf_func_proto bpf_get_current_task_btf_proto = {
+       .func           = bpf_get_current_task_btf,
+       .gpl_only       = true,
+       .ret_type       = RET_PTR_TO_BTF_ID,
+       .ret_btf_id     = &bpf_get_current_btf_ids[0],
+};
+
 BPF_CALL_2(bpf_current_task_under_cgroup, struct bpf_map *, map, u32, idx)
 {
        struct bpf_array *array = container_of(map, struct bpf_array, map);
@@ -1265,6 +1279,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
                return &bpf_get_current_pid_tgid_proto;
        case BPF_FUNC_get_current_task:
                return &bpf_get_current_task_proto;
+       case BPF_FUNC_get_current_task_btf:
+               return &bpf_get_current_task_btf_proto;
        case BPF_FUNC_get_current_uid_gid:
                return &bpf_get_current_uid_gid_proto;
        case BPF_FUNC_get_current_comm:

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index f4037b2161a67b69c606c8bd9b7fbde8d7a7520f..9879d6793e9045675420be644c13554916a45c5c 100644 (file)
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3779,6 +3779,14 @@ union bpf_attr {
  *             0 on success.
  *
  *             **-ENOENT** if the bpf_local_storage cannot be found.
+ *
+ * struct task_struct *bpf_get_current_task_btf(void)
+ *     Description
+ *             Return a BTF pointer to the "current" task.
+ *             This pointer can also be used in helpers that accept an
+ *             *ARG_PTR_TO_BTF_ID* of type *task_struct*.
+ *     Return
+ *             Pointer to the current task.
  */
 #define __BPF_FUNC_MAPPER(FN)          \
        FN(unspec),                     \
@@ -3939,6 +3947,7 @@ union bpf_attr {
        FN(redirect_peer),              \
        FN(task_storage_get),           \
        FN(task_storage_delete),        \
+       FN(get_current_task_btf),       \
        /* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper