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bpf: Recognize btf_decl_tag("arg: Arena") as PTR_TO_ARENA.

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In global bpf functions recognize btf_decl_tag("arg:arena") as PTR_TO_ARENA.

Note, when the verifier sees:

__weak void foo(struct bar *p)

it recognizes 'p' as PTR_TO_MEM and 'struct bar' has to be a struct with scalars.
Hence the only way to use arena pointers in global functions is to tag them with "arg:arena".

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/bpf/20240308010812.89848-7-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2024-03-07 17:08:04 -08:00 committed by Andrii Nakryiko
parent 6082b6c328
commit 2edc3de6fb
3 changed files with 31 additions and 4 deletions
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1
include/linux/bpf.h
View file

@ -712,6 +712,7 @@ enum bpf_arg_type {
* on eBPF program stack
*/
ARG_PTR_TO_MEM, /* pointer to valid memory (stack, packet, map value) */
ARG_PTR_TO_ARENA,
ARG_CONST_SIZE, /* number of bytes accessed from memory */
ARG_CONST_SIZE_OR_ZERO, /* number of bytes accessed from memory or 0 */

19
kernel/bpf/btf.c
View file

@ -7111,10 +7111,11 @@ static int btf_get_ptr_to_btf_id(struct bpf_verifier_log *log, int arg_idx,
}
enum btf_arg_tag {
ARG_TAG_CTX = 0x1,
ARG_TAG_NONNULL = 0x2,
ARG_TAG_TRUSTED = 0x4,
ARG_TAG_NULLABLE = 0x8,
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),
};
/* Process BTF of a function to produce high-level expectation of function
@ -7226,6 +7227,8 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
tags |= ARG_TAG_NONNULL;
} else if (strcmp(tag, "nullable") == 0) {
tags |= ARG_TAG_NULLABLE;
} else if (strcmp(tag, "arena") == 0) {
tags |= ARG_TAG_ARENA;
} else {
bpf_log(log, "arg#%d has unsupported set of tags\n", i);
return -EOPNOTSUPP;
@ -7280,6 +7283,14 @@ 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_ARENA) {
if (tags & ~ARG_TAG_ARENA) {
bpf_log(log, "arg#%d arena cannot be combined with any other tags\n", i);
return -EINVAL;
}
sub->args[i].arg_type = ARG_PTR_TO_ARENA;
continue;
}
if (is_global) { /* generic user data pointer */
u32 mem_size;

15
kernel/bpf/verifier.c
View file

@ -9379,6 +9379,18 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
bpf_log(log, "arg#%d is expected to be non-NULL\n", i);
return -EINVAL;
}
} else if (base_type(arg->arg_type) == ARG_PTR_TO_ARENA) {
/*
* Can pass any value and the kernel won't crash, but
* only PTR_TO_ARENA or SCALAR make sense. Everything
* else is a bug in the bpf program. Point it out to
* the user at the verification time instead of
* run-time debug nightmare.
*/
if (reg->type != PTR_TO_ARENA && reg->type != SCALAR_VALUE) {
bpf_log(log, "R%d is not a pointer to arena or scalar.\n", regno);
return -EINVAL;
}
} else if (arg->arg_type == (ARG_PTR_TO_DYNPTR | MEM_RDONLY)) {
ret = process_dynptr_func(env, regno, -1, arg->arg_type, 0);
if (ret)
@ -20448,6 +20460,9 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog)
reg->btf = bpf_get_btf_vmlinux(); /* can't fail at this point */
reg->btf_id = arg->btf_id;
reg->id = ++env->id_gen;
} else if (base_type(arg->arg_type) == ARG_PTR_TO_ARENA) {
/* caller can pass either PTR_TO_ARENA or SCALAR */
mark_reg_unknown(env, regs, i);
} else {
WARN_ONCE(1, "BUG: unhandled arg#%d type %d\n",
i - BPF_REG_1, arg->arg_type);