Commit 8f2b44cd authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
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bpf: add arg:nullable tag to be combined with trusted pointers 



Add ability to mark arg:trusted arguments with optional arg:nullable
tag to mark it as PTR_TO_BTF_ID_OR_NULL variant, which will allow
callers to pass NULL, and subsequently will force global subprog's code
to do NULL check. This allows to have "optional" PTR_TO_BTF_ID values
passed into global subprogs.

For now arg:nullable cannot be combined with anything else.

Acked-by: default avatarEduard Zingerman <eddyz87@gmail.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240130000648.2144827-3-andrii@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent e2b3c4ff

kernel/bpf/btf.c

+10 −0
Original line number Diff line number Diff line
@@ -7056,6 +7056,7 @@ enum btf_arg_tag { 
	ARG_TAG_CTX = 0x1,

	ARG_TAG_NONNULL = 0x2,

	ARG_TAG_TRUSTED = 0x4,

	ARG_TAG_NULLABLE = 0x8,

};



/* Process BTF of a function to produce high-level expectation of function
@@ -7161,6 +7162,8 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog) 
				tags |= ARG_TAG_TRUSTED;

			} else if (strcmp(tag, "nonnull") == 0) {

				tags |= ARG_TAG_NONNULL;

			} else if (strcmp(tag, "nullable") == 0) {

				tags |= ARG_TAG_NULLABLE;

			} else {

				bpf_log(log, "arg#%d has unsupported set of tags\n", i);

				return -EOPNOTSUPP;
@@ -7210,12 +7213,19 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog) 
				return kern_type_id;



			sub->args[i].arg_type = ARG_PTR_TO_BTF_ID | PTR_TRUSTED;

			if (tags & ARG_TAG_NULLABLE)

				sub->args[i].arg_type |= PTR_MAYBE_NULL;

			sub->args[i].btf_id = kern_type_id;

			continue;

		}

		if (is_global) { /* generic user data pointer */

			u32 mem_size;



			if (tags & ARG_TAG_NULLABLE) {

				bpf_log(log, "arg#%d has invalid combination of tags\n", i);

				return -EINVAL;

			}



			t = btf_type_skip_modifiers(btf, t->type, NULL);

			ref_t = btf_resolve_size(btf, t, &mem_size);

			if (IS_ERR(ref_t)) {