From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
Yonghong Song <yhs@fb.com>, Martin KaFai Lau <kafai@fb.com>,
David Miller <davem@redhat.com>,
John Fastabend <john.fastabend@gmail.com>,
Jesper Dangaard Brouer <hawk@kernel.org>,
Wenbo Zhang <ethercflow@gmail.com>,
KP Singh <kpsingh@chromium.org>, Andrii Nakryiko <andriin@fb.com>,
Brendan Gregg <bgregg@netflix.com>,
Florent Revest <revest@chromium.org>,
Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH 4/9] bpf: Allow nested BTF object to be refferenced by BTF object + offset
Date: Thu, 14 May 2020 15:32:29 -0700 [thread overview]
Message-ID: <CAEf4BzZXyCjjaofaOROTKCRr5fqHkdZkBHZmfiqqQiKTyOYv1Q@mail.gmail.com> (raw)
In-Reply-To: <20200506132946.2164578-5-jolsa@kernel.org>
On Wed, May 6, 2020 at 6:31 AM Jiri Olsa <jolsa@kernel.org> wrote:
>
> Adding btf_struct_address function that takes 2 BTF objects
> and offset as arguments and checks wether object A is nested
> in object B on given offset.
>
> This function is be used when checking the helper function
> PTR_TO_BTF_ID arguments. If the argument has an offset value,
> the btf_struct_address will check if the final address is
> the expected BTF ID.
>
> This way we can access nested BTF objects under PTR_TO_BTF_ID
> pointer type and pass them to helpers, while they still point
> to valid kernel BTF objects.
>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> include/linux/bpf.h | 3 ++
> kernel/bpf/btf.c | 69 +++++++++++++++++++++++++++++++++++++++++++
> kernel/bpf/verifier.c | 32 +++++++++++++-------
> 3 files changed, 94 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 1262ec460ab3..bc589cdd8c34 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1213,6 +1213,9 @@ int btf_struct_access(struct bpf_verifier_log *log,
> const struct btf_type *t, int off, int size,
> enum bpf_access_type atype,
> u32 *next_btf_id);
> +int btf_struct_address(struct bpf_verifier_log *log,
> + const struct btf_type *t,
> + u32 off, u32 exp_id);
> int btf_resolve_helper_id(struct bpf_verifier_log *log,
> const struct bpf_func_proto *fn, int);
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index a2cfba89a8e1..07f22469acab 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -4004,6 +4004,75 @@ int btf_struct_access(struct bpf_verifier_log *log,
> return -EINVAL;
> }
>
> +int btf_struct_address(struct bpf_verifier_log *log,
> + const struct btf_type *t,
> + u32 off, u32 exp_id)
The logic in this function is quite tricky and overlaps heavily with
btf_struct_access. You are already missing flexible array support that
Yonghong added recently. Let's see if it's possible to extract all
this "find field in a struct by offset" logic into reusable function?
> +{
> + u32 i, moff, mtrue_end, msize = 0;
> + const struct btf_member *member;
> + const struct btf_type *mtype;
> + const char *tname, *mname;
> +
> +again:
> + tname = __btf_name_by_offset(btf_vmlinux, t->name_off);
> + if (!btf_type_is_struct(t)) {
> + bpf_log(log, "Type '%s' is not a struct\n", tname);
> + return -EINVAL;
> + }
> +
> + if (off > t->size) {
>=, actually?
> + bpf_log(log, "address beyond struct %s at off %u size %u\n",
> + tname, off, t->size);
> + return -EACCES;
> + }
> +
[...]
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 70ad009577f8..b988df5ada20 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -3665,6 +3665,7 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
> {
> struct bpf_reg_state *regs = cur_regs(env), *reg = ®s[regno];
> enum bpf_reg_type expected_type, type = reg->type;
> + const struct btf_type *btf_type;
> int err = 0;
>
> if (arg_type == ARG_DONTCARE)
> @@ -3743,17 +3744,28 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
> expected_type = PTR_TO_BTF_ID;
> if (type != expected_type)
> goto err_type;
> - if (reg->btf_id != meta->btf_id) {
> - verbose(env, "Helper has type %s got %s in R%d\n",
> - kernel_type_name(meta->btf_id),
> - kernel_type_name(reg->btf_id), regno);
> + if (reg->off) {
well, off==0 can still point to (arbitrarily) nested structs that are
first member of outer struct... So I guess it would be better to
search for inner struct if btf_id is unexpected regardless of off
value?
> + btf_type = btf_type_by_id(btf_vmlinux, reg->btf_id);
> + if (btf_struct_address(&env->log, btf_type, reg->off, meta->btf_id)) {
> + verbose(env, "Helper has type %s got %s in R%d, off %d\n",
> + kernel_type_name(meta->btf_id),
> + kernel_type_name(reg->btf_id), regno, reg->off);
>
> - return -EACCES;
> - }
> - if (!tnum_is_const(reg->var_off) || reg->var_off.value || reg->off) {
> - verbose(env, "R%d is a pointer to in-kernel struct with non-zero offset\n",
> - regno);
> - return -EACCES;
> + return -EACCES;
> + }
> + } else {
> + if (reg->btf_id != meta->btf_id) {
> + verbose(env, "Helper has type %s got %s in R%d\n",
> + kernel_type_name(meta->btf_id),
> + kernel_type_name(reg->btf_id), regno);
> +
> + return -EACCES;
> + }
> + if (!tnum_is_const(reg->var_off) || reg->var_off.value) {
> + verbose(env, "R%d is a pointer to in-kernel struct with non-zero offset\n",
> + regno);
> + return -EACCES;
> + }
> }
> } else if (arg_type == ARG_PTR_TO_SPIN_LOCK) {
> if (meta->func_id == BPF_FUNC_spin_lock) {
> --
> 2.25.4
>
next prev parent reply other threads:[~2020-05-14 22:32 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-06 13:29 [RFCv2 0/9] bpf: Add d_path helper Jiri Olsa
2020-05-06 13:29 ` [PATCH 1/9] " Jiri Olsa
2020-05-14 22:06 ` Andrii Nakryiko
2020-05-15 14:59 ` Jiri Olsa
2020-05-06 13:29 ` [PATCH 2/9] bpf: Add d_path whitelist Jiri Olsa
2020-05-06 13:29 ` [PATCH 3/9] bpf: Add bpfwl tool to construct bpf whitelists Jiri Olsa
2020-05-14 22:20 ` Andrii Nakryiko
2020-05-15 14:58 ` Jiri Olsa
2020-05-06 13:29 ` [PATCH 4/9] bpf: Allow nested BTF object to be refferenced by BTF object + offset Jiri Olsa
2020-05-14 22:32 ` Andrii Nakryiko [this message]
2020-05-06 13:29 ` [PATCH 5/9] bpf: Add support to check on BTF id whitelist for d_path helper Jiri Olsa
2020-05-06 13:29 ` [PATCH 6/9] bpf: Compile bpfwl tool at kernel compilation start Jiri Olsa
2020-05-14 22:38 ` Andrii Nakryiko
2020-05-15 14:57 ` Jiri Olsa
2020-05-06 13:29 ` [PATCH 7/9] bpf: Compile the BTF id whitelist data in vmlinux Jiri Olsa
2020-05-13 18:29 ` Alexei Starovoitov
2020-05-14 8:05 ` Jiri Olsa
2020-05-14 22:46 ` Andrii Nakryiko
2020-05-15 14:57 ` Jiri Olsa
2020-05-28 17:23 ` Jiri Olsa
2020-05-29 20:48 ` Andrii Nakryiko
2020-05-31 15:10 ` Jiri Olsa
2020-06-01 19:06 ` Andrii Nakryiko
2020-06-02 8:16 ` Jiri Olsa
2020-05-06 13:29 ` [PATCH 8/9] selftests/bpf: Add test for d_path helper Jiri Olsa
2020-05-14 22:48 ` Andrii Nakryiko
2020-05-15 14:57 ` Jiri Olsa
2020-05-06 13:29 ` [PATCH 9/9] selftests/bpf: Add verifier " Jiri Olsa
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