Received-SPF: pass (google.com: domain of linux-kernel+bounces-208762-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Precedence: bulk
MIME-Version: 1.0
References: <20240608-hid_bpf_struct_ops-v3-0-6ac6ade58329@kernel.org> <20240608-hid_bpf_struct_ops-v3-15-6ac6ade58329@kernel.org>
In-Reply-To: <20240608-hid_bpf_struct_ops-v3-15-6ac6ade58329@kernel.org>
From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date: Mon, 10 Jun 2024 11:39:35 -0700
Message-ID: <CAADnVQLCyEZMyThCH6QNopBbWbNcpR+h2AaLhT0apEO7pOWrRQ@mail.gmail.com>
Subject: Re: [PATCH HID v3 15/16] HID: bpf: rework hid_bpf_ops_btf_struct_access
To: Benjamin Tissoires <bentiss@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>, Jiri Kosina <jikos@kernel.org>, Jonathan Corbet <corbet@lwn.net>, 
	Alexei Starovoitov <ast@kernel.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>, 
	bpf <bpf@vger.kernel.org>, 
	"open list:HID CORE LAYER" <linux-input@vger.kernel.org>, 
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Sat, Jun 8, 2024 at 2:01=E2=80=AFAM Benjamin Tissoires <bentiss@kernel.o=
rg> wrote:
>
> The idea is to provide a list of stucts and their editable fields.
>
> Currently no functional changes are introduced here, we will add some
> more writeable fields in the next patch.
>
> Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
>
> ---
>
> changes in v3:
> - rewrote WRITE_RANGE macro to not deal with offset from the caller side
>
> new in v2
> ---
>  drivers/hid/bpf/hid_bpf_struct_ops.c | 91 +++++++++++++++++++++++++++---=
------
>  1 file changed, 69 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/hid/bpf/hid_bpf_struct_ops.c b/drivers/hid/bpf/hid_b=
pf_struct_ops.c
> index 056d05d96962..b14eccb121e0 100644
> --- a/drivers/hid/bpf/hid_bpf_struct_ops.c
> +++ b/drivers/hid/bpf/hid_bpf_struct_ops.c
> @@ -16,6 +16,7 @@
>  #include <linux/hid_bpf.h>
>  #include <linux/init.h>
>  #include <linux/module.h>
> +#include <linux/stddef.h>
>  #include <linux/workqueue.h>
>  #include "hid_bpf_dispatch.h"
>
> @@ -52,40 +53,86 @@ static int hid_bpf_ops_check_member(const struct btf_=
type *t,
>         return 0;
>  }
>
> +struct hid_bpf_offset_write_range {
> +       const char *struct_name;
> +       u32 struct_length;
> +       u32 start;
> +       u32 end;
> +};
> +
>  static int hid_bpf_ops_btf_struct_access(struct bpf_verifier_log *log,
>                                            const struct bpf_reg_state *re=
g,
>                                            int off, int size)
>  {
> -       const struct btf_type *state;
> -       const struct btf_type *t;
> -       s32 type_id;
> +#define WRITE_RANGE(_name, _field, _is_string)                          =
       \
> +       {                                                                =
       \
> +               .struct_name =3D #_name,                                 =
         \
> +               .struct_length =3D sizeof(struct _name),                 =
         \
> +               .start =3D offsetof(struct _name, _field),               =
         \
> +               .end =3D offsetofend(struct _name, _field) - !!(_is_strin=
g),

so it works because char name[128]; had last byte as zero
before prog writes into it (in addition to potentially having
earlier 0 bytes), so the string is guaranteed
to be null-terminated regardless of what prog writes into it.
Right?

Overall:
Acked-by: Alexei Starovoitov <ast@kernel.org>