Re: [PATCH v1 1/4] media: rc: introduce BPF_PROG_IR_DECODER

[Y Song]

On Mon, May 14, 2018 at 2:10 PM, Sean Young <sean@xxxxxxxx> wrote:
> Add support for BPF_PROG_IR_DECODER. This type of BPF program can call
> rc_keydown() to reported decoded IR scancodes, or rc_repeat() to report
> that the last key should be repeated.
>
> Signed-off-by: Sean Young <sean@xxxxxxxx>
> ---
>  drivers/media/rc/Kconfig          |  8 +++
>  drivers/media/rc/Makefile         |  1 +
>  drivers/media/rc/ir-bpf-decoder.c | 93 +++++++++++++++++++++++++++++++
>  include/linux/bpf_types.h         |  3 +
>  include/uapi/linux/bpf.h          | 16 +++++-
>  5 files changed, 120 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/media/rc/ir-bpf-decoder.c
>
> diff --git a/drivers/media/rc/Kconfig b/drivers/media/rc/Kconfig
> index eb2c3b6eca7f..10ad6167d87c 100644
> --- a/drivers/media/rc/Kconfig
> +++ b/drivers/media/rc/Kconfig
> @@ -120,6 +120,14 @@ config IR_IMON_DECODER
>            remote control and you would like to use it with a raw IR
>            receiver, or if you wish to use an encoder to transmit this IR.
>
> +config IR_BPF_DECODER
> +       bool "Enable IR raw decoder using BPF"
> +       depends on BPF_SYSCALL
> +       depends on RC_CORE=y
> +       help
> +          Enable this option to make it possible to load custom IR
> +          decoders written in BPF.
> +
>  endif #RC_DECODERS
>
>  menuconfig RC_DEVICES
> diff --git a/drivers/media/rc/Makefile b/drivers/media/rc/Makefile
> index 2e1c87066f6c..12e1118430d0 100644
> --- a/drivers/media/rc/Makefile
> +++ b/drivers/media/rc/Makefile
> @@ -5,6 +5,7 @@ obj-y += keymaps/
>  obj-$(CONFIG_RC_CORE) += rc-core.o
>  rc-core-y := rc-main.o rc-ir-raw.o
>  rc-core-$(CONFIG_LIRC) += lirc_dev.o
> +rc-core-$(CONFIG_IR_BPF_DECODER) += ir-bpf-decoder.o
>  obj-$(CONFIG_IR_NEC_DECODER) += ir-nec-decoder.o
>  obj-$(CONFIG_IR_RC5_DECODER) += ir-rc5-decoder.o
>  obj-$(CONFIG_IR_RC6_DECODER) += ir-rc6-decoder.o
> diff --git a/drivers/media/rc/ir-bpf-decoder.c b/drivers/media/rc/ir-bpf-decoder.c
> new file mode 100644
> index 000000000000..aaa5e208b1a5
> --- /dev/null
> +++ b/drivers/media/rc/ir-bpf-decoder.c
> @@ -0,0 +1,93 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// ir-bpf-decoder.c - handles bpf decoders
> +//
> +// Copyright (C) 2018 Sean Young <sean@xxxxxxxx>
> +
> +#include <linux/bpf.h>
> +#include <linux/filter.h>
> +#include "rc-core-priv.h"
> +
> +/*
> + * BPF interface for raw IR decoder
> + */
> +const struct bpf_prog_ops ir_decoder_prog_ops = {
> +};
> +
> +BPF_CALL_1(bpf_rc_repeat, struct ir_raw_event*, event)
> +{
> +       struct ir_raw_event_ctrl *ctrl;
> +
> +       ctrl = container_of(event, struct ir_raw_event_ctrl, prev_ev);
> +
> +       rc_repeat(ctrl->dev);
> +       return 0;
> +}
> +
> +static const struct bpf_func_proto rc_repeat_proto = {
> +       .func      = bpf_rc_repeat,
> +       .gpl_only  = true, // rc_repeat is EXPORT_SYMBOL_GPL
> +       .ret_type  = RET_VOID,

I suggest using RET_INTEGER here since we do return an integer 0.
RET_INTEGER will also make it easy to extend if you want to return
a non-zero value for error code or other reasons.

> +       .arg1_type = ARG_PTR_TO_CTX,
> +};
> +
> +BPF_CALL_4(bpf_rc_keydown, struct ir_raw_event*, event, u32, protocol,
> +          u32, scancode, u32, toggle)
> +{
> +       struct ir_raw_event_ctrl *ctrl;
> +
> +       ctrl = container_of(event, struct ir_raw_event_ctrl, prev_ev);
> +       rc_keydown(ctrl->dev, protocol, scancode, toggle != 0);
> +       return 0;
> +}
> +
> +static const struct bpf_func_proto rc_keydown_proto = {
> +       .func      = bpf_rc_keydown,
> +       .gpl_only  = true, // rc_keydown is EXPORT_SYMBOL_GPL
> +       .ret_type  = RET_VOID,

ditto. RET_INTEGER is preferable.

> +       .arg1_type = ARG_PTR_TO_CTX,
> +       .arg2_type = ARG_ANYTHING,
> +       .arg3_type = ARG_ANYTHING,
> +       .arg4_type = ARG_ANYTHING,
> +};
> +
> +static const struct bpf_func_proto *ir_decoder_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> +{
> +       switch (func_id) {
> +       case BPF_FUNC_rc_repeat:
> +               return &rc_repeat_proto;
> +       case BPF_FUNC_rc_keydown:
> +               return &rc_keydown_proto;
> +       case BPF_FUNC_map_lookup_elem:
> +               return &bpf_map_lookup_elem_proto;
> +       case BPF_FUNC_map_update_elem:
> +               return &bpf_map_update_elem_proto;
> +       case BPF_FUNC_map_delete_elem:
> +               return &bpf_map_delete_elem_proto;
> +       case BPF_FUNC_ktime_get_ns:
> +               return &bpf_ktime_get_ns_proto;
> +       case BPF_FUNC_tail_call:
> +               return &bpf_tail_call_proto;
> +       case BPF_FUNC_get_prandom_u32:
> +               return &bpf_get_prandom_u32_proto;
> +       default:
> +               return NULL;
> +       }
> +}
> +
> +static bool ir_decoder_is_valid_access(int off, int size,
> +                                      enum bpf_access_type type,
> +                                      const struct bpf_prog *prog,
> +                                      struct bpf_insn_access_aux *info)
> +{
> +       if (type == BPF_WRITE)
> +               return false;
> +       if (off < 0 || off + size > sizeof(struct ir_raw_event))
> +               return false;

You probably need more than just checking the boundary.
>From patch #3, the structure is:
 struct ir_raw_event {
        union {
                __u32           duration;
                __u32           carrier;
        };
        __u8                    duty_cycle;

        unsigned                pulse:1;
        unsigned                reset:1;
        unsigned                timeout:1;
       unsigned                carrier_report:1;
};

You would like the memory access to be aligned,
so accessing duration/carrier with 4-byte alignment, and
pulse/reset/timeout/carrier_report 4-byte alignment as well.

You could only allow __u32 access to duration/carrier.
But if you want bpf program to access duration/carrier with
code like (__u16)(ctx->duration), then the compiler may
translate the load to a 2-byte load. You may need to handle
endianness here. You can check net/core/filter.c function
bpf_skb_is_valid_access for some examples.

> +
> +       return true;
> +}
> +
> +const struct bpf_verifier_ops ir_decoder_verifier_ops = {
> +       .get_func_proto  = ir_decoder_func_proto,
> +       .is_valid_access = ir_decoder_is_valid_access
> +};
> diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
> index 2b28fcf6f6ae..ee5355715ee0 100644
> --- a/include/linux/bpf_types.h
> +++ b/include/linux/bpf_types.h
> @@ -25,6 +25,9 @@ BPF_PROG_TYPE(BPF_PROG_TYPE_RAW_TRACEPOINT, raw_tracepoint)
>  #ifdef CONFIG_CGROUP_BPF
>  BPF_PROG_TYPE(BPF_PROG_TYPE_CGROUP_DEVICE, cg_dev)
>  #endif
> +#ifdef CONFIG_IR_BPF_DECODER
> +BPF_PROG_TYPE(BPF_PROG_TYPE_RAWIR_DECODER, ir_decoder)
> +#endif
>
>  BPF_MAP_TYPE(BPF_MAP_TYPE_ARRAY, array_map_ops)
>  BPF_MAP_TYPE(BPF_MAP_TYPE_PERCPU_ARRAY, percpu_array_map_ops)
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index c5ec89732a8d..6ad053e831c0 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -137,6 +137,7 @@ enum bpf_prog_type {
>         BPF_PROG_TYPE_SK_MSG,
>         BPF_PROG_TYPE_RAW_TRACEPOINT,
>         BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
> +       BPF_PROG_TYPE_RAWIR_DECODER,
>  };
>
>  enum bpf_attach_type {
> @@ -755,6 +756,17 @@ union bpf_attr {
>   *     @addr: pointer to struct sockaddr to bind socket to
>   *     @addr_len: length of sockaddr structure
>   *     Return: 0 on success or negative error code
> + *
> + * int bpf_rc_keydown(ctx, protocol, scancode, toggle)
> + *     Report decoded scancode with toggle value
> + *     @ctx: pointer to ctx
> + *     @protocol: decoded protocol
> + *     @scancode: decoded scancode
> + *     @toggle: set to 1 if button was toggled, else 0
> + *
> + * int bpf_rc_repeat(ctx)
> + *     Repeat the last decoded scancode
> + *     @ctx: pointer to ctx

The comment format has changed dramatically for
documentation reason. Could you rebase your change
on top of bpf-next tree? You will need to rewrite the above
helper description so tools can generate proper documentation
for them.

>   */
>  #define __BPF_FUNC_MAPPER(FN)          \
>         FN(unspec),                     \
> @@ -821,7 +833,9 @@ union bpf_attr {
>         FN(msg_apply_bytes),            \
>         FN(msg_cork_bytes),             \
>         FN(msg_pull_data),              \
> -       FN(bind),
> +       FN(bind),                       \
> +       FN(rc_repeat),                  \
> +       FN(rc_keydown),
>
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>   * function eBPF program intends to call
> --
> 2.17.0
>