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bpf: attribute __arg_untrusted for global function parameters 

Add support for PTR_TO_BTF_ID | PTR_UNTRUSTED global function
parameters. Anything is allowed to pass to such parameters, as these
are read-only and probe read instructions would protect against
invalid memory access.

Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20250704230354.1323244-5-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
pull/1309/head
Eduard Zingerman 2025-07-04 16:03:50 -07:00 committed by Alexei Starovoitov
parent f1f5d6f25d
commit 182f7df704
2 changed files with 39 additions and 5 deletions
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38
kernel/bpf/btf.c
View File

@ -7646,11 +7646,12 @@ cand_cache_unlock:
}
enum btf_arg_tag {
ARG_TAG_CTX = BIT_ULL(0),
ARG_TAG_NONNULL = BIT_ULL(1),
ARG_TAG_TRUSTED = BIT_ULL(2),
ARG_TAG_NULLABLE = BIT_ULL(3),
ARG_TAG_ARENA = BIT_ULL(4),
ARG_TAG_CTX = BIT_ULL(0),
ARG_TAG_NONNULL = BIT_ULL(1),
ARG_TAG_TRUSTED = BIT_ULL(2),
ARG_TAG_UNTRUSTED = BIT_ULL(3),
ARG_TAG_NULLABLE = BIT_ULL(4),
ARG_TAG_ARENA = BIT_ULL(5),
};
/* Process BTF of a function to produce high-level expectation of function
@ -7758,6 +7759,8 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
tags |= ARG_TAG_CTX;
} else if (strcmp(tag, "trusted") == 0) {
tags |= ARG_TAG_TRUSTED;
} else if (strcmp(tag, "untrusted") == 0) {
tags |= ARG_TAG_UNTRUSTED;
} else if (strcmp(tag, "nonnull") == 0) {
tags |= ARG_TAG_NONNULL;
} else if (strcmp(tag, "nullable") == 0) {
@ -7818,6 +7821,31 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
sub->args[i].btf_id = kern_type_id;
continue;
}
if (tags & ARG_TAG_UNTRUSTED) {
struct btf *vmlinux_btf;
int kern_type_id;
if (tags & ~ARG_TAG_UNTRUSTED) {
bpf_log(log, "arg#%d untrusted cannot be combined with any other tags\n", i);
return -EINVAL;
}
kern_type_id = btf_get_ptr_to_btf_id(log, i, btf, t);
if (kern_type_id < 0)
return kern_type_id;
vmlinux_btf = bpf_get_btf_vmlinux();
ref_t = btf_type_by_id(vmlinux_btf, kern_type_id);
if (!btf_type_is_struct(ref_t)) {
tname = __btf_name_by_offset(vmlinux_btf, t->name_off);
bpf_log(log, "arg#%d has type %s '%s', but only struct types are allowed\n",
i, btf_type_str(ref_t), tname);
return -EINVAL;
}
sub->args[i].arg_type = ARG_PTR_TO_BTF_ID | PTR_UNTRUSTED;
sub->args[i].btf_id = kern_type_id;
continue;
}
if (tags & ARG_TAG_ARENA) {
if (tags & ~ARG_TAG_ARENA) {
bpf_log(log, "arg#%d arena cannot be combined with any other tags\n", i);

6
kernel/bpf/verifier.c
View File

@ -10437,6 +10437,12 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
bpf_log(log, "R%d is not a scalar\n", regno);
return -EINVAL;
}
} else if (arg->arg_type & PTR_UNTRUSTED) {
/*
* Anything is allowed for untrusted arguments, as these are
* read-only and probe read instructions would protect against
* invalid memory access.
*/
} else if (arg->arg_type == ARG_PTR_TO_CTX) {
ret = check_func_arg_reg_off(env, reg, regno, ARG_DONTCARE);
if (ret < 0)