[bpf-next,1/3] bpf: verifier: Store null elision decision in insn_aux_data

Commit Message

Daniel Xu Jan. 21, 2025, 4:35 a.m. UTC

Save the null elision decision from verification so that it can be
reused later during bpf_map_lookup_elem inlining. There's a generated
jump that can be omitted if the null was elided.

Signed-off-by: Daniel Xu <[e-mail]>
---
 include/linux/bpf_verifier.h | 4 ++++
 kernel/bpf/verifier.c        | 4 +++-
 2 files changed, 7 insertions(+), 1 deletion(-)

Comments

Alexei Starovoitov Jan. 23, 2025, 12:23 a.m. UTC | #1

On Mon, Jan 20, 2025 at 8:35 PM Daniel Xu <[e-mail]> wrote:
>
> Save the null elision decision from verification so that it can be
> reused later during bpf_map_lookup_elem inlining. There's a generated
> jump that can be omitted if the null was elided.
>
> Signed-off-by: Daniel Xu <[e-mail]>
> ---
>  include/linux/bpf_verifier.h | 4 ++++
>  kernel/bpf/verifier.c        | 4 +++-
>  2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> index 32c23f2a3086..1bcd6d66e546 100644
> --- a/include/linux/bpf_verifier.h
> +++ b/include/linux/bpf_verifier.h
> @@ -515,6 +515,10 @@ struct bpf_map_ptr_state {
>         struct bpf_map *map_ptr;
>         bool poison;
>         bool unpriv;
> +       /* true if instruction is a bpf_map_lookup_elem() with statically
> +        * known in-bounds key.
> +        */
> +       bool inbounds;
>  };
>
>  /* Possible states for alu_state member. */
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 74525392714e..e83145c2260d 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -11265,8 +11265,10 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
>                 if (func_id == BPF_FUNC_map_lookup_elem &&
>                     can_elide_value_nullness(meta.map_ptr->map_type) &&
>                     meta.const_map_key >= 0 &&
> -                   meta.const_map_key < meta.map_ptr->max_entries)
> +                   meta.const_map_key < meta.map_ptr->max_entries) {
>                         ret_flag &= ~PTR_MAYBE_NULL;
> +                       env->insn_aux_data[insn_idx].map_ptr_state.inbounds = true;
> +               }

I don't think it handles the case where the same call insn
is used with const key and non-const/out-of-range.
insn_aux_data will be sticky and incorrect.

pw-bot: cr

Patch

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 32c23f2a3086..1bcd6d66e546 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -515,6 +515,10 @@  struct bpf_map_ptr_state {
 	struct bpf_map *map_ptr;
 	bool poison;
 	bool unpriv;
+	/* true if instruction is a bpf_map_lookup_elem() with statically
+	 * known in-bounds key.
+	 */
+	bool inbounds;
 };
 
 /* Possible states for alu_state member. */
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 74525392714e..e83145c2260d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -11265,8 +11265,10 @@  static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
 		if (func_id == BPF_FUNC_map_lookup_elem &&
 		    can_elide_value_nullness(meta.map_ptr->map_type) &&
 		    meta.const_map_key >= 0 &&
-		    meta.const_map_key < meta.map_ptr->max_entries)
+		    meta.const_map_key < meta.map_ptr->max_entries) {
 			ret_flag &= ~PTR_MAYBE_NULL;
+			env->insn_aux_data[insn_idx].map_ptr_state.inbounds = true;
+		}
 
 		regs[BPF_REG_0].map_ptr = meta.map_ptr;
 		regs[BPF_REG_0].map_uid = meta.map_uid;