bpf: check changes_pkt_data property for extension programs

When processing calls to global sub-programs, verifier decides whether
to invalidate all packet pointers in current state depending on the
changes_pkt_data property of the global sub-program.

Because of this, an extension program replacing a global sub-program
must be compatible with changes_pkt_data property of the sub-program
being replaced.

This commit:
- adds changes_pkt_data flag to struct bpf_prog_aux:
  - this flag is set in check_cfg() for main sub-program;
  - in jit_subprogs() for other sub-programs;
- modifies bpf_check_attach_btf_id() to check changes_pkt_data flag;
- moves call to check_attach_btf_id() after the call to check_cfg(),
  because it needs changes_pkt_data flag to be set:

    bpf_check:
      ...                             ...
    - check_attach_btf_id             resolve_pseudo_ldimm64
      resolve_pseudo_ldimm64   -->    bpf_prog_is_offloaded
      bpf_prog_is_offloaded           check_cfg
      check_cfg                     + check_attach_btf_id
      ...                             ...

The following fields are set by check_attach_btf_id():
- env->ops
- prog->aux->attach_btf_trace
- prog->aux->attach_func_name
- prog->aux->attach_func_proto
- prog->aux->dst_trampoline
- prog->aux->mod
- prog->aux->saved_dst_attach_type
- prog->aux->saved_dst_prog_type
- prog->expected_attach_type

Neither of these fields are used by resolve_pseudo_ldimm64() or
bpf_prog_offload_verifier_prep() (for netronome and netdevsim
drivers), so the reordering is safe.

Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20241210041100.1898468-6-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index eaee2a819f4c150a34a7b1075584711609682e4c..fe392d07497302740a6c1c9f4cc30f2471cfd0ed 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1527,6 +1527,7 @@ struct bpf_prog_aux {
        bool is_extended; /* true if extended by freplace program */
        bool jits_use_priv_stack;
        bool priv_stack_requested;
+       bool changes_pkt_data;
        u64 prog_array_member_cnt; /* counts how many times as member of prog_array */
        struct mutex ext_mutex; /* mutex for is_extended and prog_array_member_cnt */
        struct bpf_arena *arena;

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 6a29b68cebd6f3d30efac7c98b63ed6de23585cc..c2e5d0e6e3d014c50a577ee58969b07061f6c910 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -16872,6 +16872,7 @@ walk_cfg:
                }
        }
        ret = 0; /* cfg looks good */
+       env->prog->aux->changes_pkt_data = env->subprog_info[0].changes_pkt_data;
 
 err_free:
        kvfree(insn_state);
@@ -20361,6 +20362,7 @@ static int jit_subprogs(struct bpf_verifier_env *env)
                func[i]->aux->num_exentries = num_exentries;
                func[i]->aux->tail_call_reachable = env->subprog_info[i].tail_call_reachable;
                func[i]->aux->exception_cb = env->subprog_info[i].is_exception_cb;
+               func[i]->aux->changes_pkt_data = env->subprog_info[i].changes_pkt_data;
                if (!i)
                        func[i]->aux->exception_boundary = env->seen_exception;
                func[i] = bpf_int_jit_compile(func[i]);
@@ -22225,6 +22227,12 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
                                        "Extension programs should be JITed\n");
                                return -EINVAL;
                        }
+                       if (prog->aux->changes_pkt_data &&
+                           !aux->func[subprog]->aux->changes_pkt_data) {
+                               bpf_log(log,
+                                       "Extension program changes packet data, while original does not\n");
+                               return -EINVAL;
+                       }
                }
                if (!tgt_prog->jited) {
                        bpf_log(log, "Can attach to only JITed progs\n");
@@ -22690,10 +22698,6 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3
        if (ret < 0)
                goto skip_full_check;
 
-       ret = check_attach_btf_id(env);
-       if (ret)
-               goto skip_full_check;
-
        ret = resolve_pseudo_ldimm64(env);
        if (ret < 0)
                goto skip_full_check;
@@ -22708,6 +22712,10 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3
        if (ret < 0)
                goto skip_full_check;
 
+       ret = check_attach_btf_id(env);
+       if (ret)
+               goto skip_full_check;
+
        ret = mark_fastcall_patterns(env);
        if (ret < 0)
                goto skip_full_check;