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SubjectRe: [PATCH v1 1/4] media: rc: introduce BPF_PROG_IR_DECODER
On Mon, May 14, 2018 at 2:10 PM, Sean Young <sean@mess.org> 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@mess.org>
> ---
> 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@mess.org>
> +
> +#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
>

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