Re: [PATCH bpf-next v1 1/6] HID: initial BPF implementation

Benjamin Tissoires
2022-02-28T17:54:12Z

On Sat, Feb 26, 2022 at 8:27 AM Song Liu <song@kernel.org> wrote:
>
> On Thu, Feb 24, 2022 at 3:09 AM Benjamin Tissoires
> <benjamin.tissoires@redhat.com> wrote:
> >
> > HID is a protocol that could benefit from using BPF too.
> >
> > This patch implements a net-like use of BPF capability for HID.
> > Any incoming report coming from the device gets injected into a series
> > of BPF programs that can modify it or even discard it by setting the
> > size in the context to 0.
> >
> > The kernel/bpf implementation is based on net-namespace.c, with only
> > the bpf_link part kept, there is no real points in keeping the
> > bpf_prog_{attach|detach} API.
> >
> > The implementation is split into 2 parts:
> > - the kernel/bpf part which isn't aware of the HID usage, but takes care
> > of handling the BPF links
> > - the drivers/hid/hid-bpf.c part which knows about HID
> >
> > Note that HID can be compiled in as a module, and so the functions that
> > kernel/bpf/hid.c needs to call in hid.ko are exported in struct hid_hooks.
> >
> > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
> > ---
> > drivers/hid/Makefile | 1 +
> > drivers/hid/hid-bpf.c | 176 ++++++++
> > drivers/hid/hid-core.c | 21 +-
> > include/linux/bpf-hid.h | 87 ++++
> > include/linux/bpf_types.h | 4 +
> > include/linux/hid.h | 16 +
> > include/uapi/linux/bpf.h | 7 +
> > include/uapi/linux/bpf_hid.h | 39 ++
> > kernel/bpf/Makefile | 3 +
> > kernel/bpf/hid.c | 437 +++++++++++++++++++
> > kernel/bpf/syscall.c | 8 +
> > samples/bpf/.gitignore | 1 +
> > samples/bpf/Makefile | 4 +
> > samples/bpf/hid_mouse_kern.c | 66 +++
> > samples/bpf/hid_mouse_user.c | 129 ++++++
> > tools/include/uapi/linux/bpf.h | 7 +
> > tools/lib/bpf/libbpf.c | 7 +
> > tools/lib/bpf/libbpf.h | 2 +
> > tools/lib/bpf/libbpf.map | 1 +
> > tools/testing/selftests/bpf/prog_tests/hid.c | 318 ++++++++++++++
> > tools/testing/selftests/bpf/progs/hid.c | 20 +
> > 21 files changed, 1351 insertions(+), 3 deletions(-)
> > create mode 100644 drivers/hid/hid-bpf.c
> > create mode 100644 include/linux/bpf-hid.h
> > create mode 100644 include/uapi/linux/bpf_hid.h
> > create mode 100644 kernel/bpf/hid.c
> > create mode 100644 samples/bpf/hid_mouse_kern.c
> > create mode 100644 samples/bpf/hid_mouse_user.c
> > create mode 100644 tools/testing/selftests/bpf/prog_tests/hid.c
> > create mode 100644 tools/testing/selftests/bpf/progs/hid.c
>
> Please split kernel changes, libbpf changes, selftests, and sample code into
> separate patches.

OK, done locally.

>
> >
> > diff --git a/drivers/hid/Makefile b/drivers/hid/Makefile
> > index 6d3e630e81af..08d2d7619937 100644
> > --- a/drivers/hid/Makefile
> > +++ b/drivers/hid/Makefile
> > @@ -4,6 +4,7 @@
> > #
> > hid-y := hid-core.o hid-input.o hid-quirks.o
> > hid-$(CONFIG_DEBUG_FS) += hid-debug.o
> > +hid-$(CONFIG_BPF) += hid-bpf.o
> >
> > obj-$(CONFIG_HID) += hid.o
> > obj-$(CONFIG_UHID) += uhid.o
> > diff --git a/drivers/hid/hid-bpf.c b/drivers/hid/hid-bpf.c
> > new file mode 100644
> > index 000000000000..6c8445820944
> > --- /dev/null
> > +++ b/drivers/hid/hid-bpf.c
> > @@ -0,0 +1,176 @@
> > +// SPDX-License-Identifier: GPL-2.0-or-later
> > +/*
> > + * BPF in HID support for Linux
> > + *
> > + * Copyright (c) 2021 Benjamin Tissoires
>
> Maybe 2022?

heh, maybe :)

>
> [...]
>
> > +static int hid_bpf_run_progs(struct hid_device *hdev, enum bpf_hid_attach_type type,
> > + struct hid_bpf_ctx *ctx, u8 *data, int size)
> > +{
> > + enum hid_bpf_event event = HID_BPF_UNDEF;
> > +
> > + if (type < 0 || !ctx)
> > + return -EINVAL;
> > +
> > + switch (type) {
> > + case BPF_HID_ATTACH_DEVICE_EVENT:
> > + event = HID_BPF_DEVICE_EVENT;
> > + if (size > sizeof(ctx->u.device.data))
> > + return -E2BIG;
> > + break;
> > + default:
> > + return -EINVAL;
> > + }
> > +
> > + if (!hdev->bpf.run_array[type])
> > + return 0;
> > +
> > + memset(ctx, 0, sizeof(*ctx));
> > + ctx->hdev = hdev;
> > + ctx->type = event;
> > +
> > + if (size && data) {
> > + switch (event) {
> > + case HID_BPF_DEVICE_EVENT:
> > + memcpy(ctx->u.device.data, data, size);
> > + ctx->u.device.size = size;
> > + break;
> > + default:
> > + /* do nothing */
> > + }
> > + }
> > +
> > + BPF_PROG_RUN_ARRAY(hdev->bpf.run_array[type], ctx, bpf_prog_run);
>
> I guess we need "return BPF_PROG_RUN_ARRAY(...)"?

ack

>
> > +
> > + return 0;
> > +}
> > +
> > +u8 *hid_bpf_raw_event(struct hid_device *hdev, u8 *data, int *size)
> > +{
> > + int ret;
> > +
> > + if (bpf_hid_link_empty(&hdev->bpf, BPF_HID_ATTACH_DEVICE_EVENT))
> > + return data;
> > +
> > + ret = hid_bpf_run_progs(hdev, BPF_HID_ATTACH_DEVICE_EVENT,
> > + hdev->bpf.ctx, data, *size);
> > + if (ret)
> > + return data;
>
> shall we return ERR_PTR(ret)?

I initially wanted to have a bpf_program returning something other
than 0 being a signal to silently ignore the report.
But the API will be more consistent if we simply return an error in
the same way we do for bpf.ctx->u.device.size just below.

IOW, will change in v2

>
> > +
> > + if (!hdev->bpf.ctx->u.device.size)
> > + return ERR_PTR(-EINVAL);
> > +
> > + *size = hdev->bpf.ctx->u.device.size;
> > +
> > + return hdev->bpf.ctx->u.device.data;
> > +}
>
> [...]
>
> > diff --git a/include/uapi/linux/bpf_hid.h b/include/uapi/linux/bpf_hid.h
> > new file mode 100644
> > index 000000000000..243ac45a253f
> > --- /dev/null
> > +++ b/include/uapi/linux/bpf_hid.h
> > @@ -0,0 +1,39 @@
> > +/* SPDX-License-Identifier: GPL-2.0-or-later WITH Linux-syscall-note */
> > +
> > +/*
> > + * HID BPF public headers
> > + *
> > + * Copyright (c) 2021 Benjamin Tissoires
> > + */
> > +
> > +#ifndef _UAPI__LINUX_BPF_HID_H__
> > +#define _UAPI__LINUX_BPF_HID_H__
> > +
> > +#include <linux/types.h>
> > +
> > +#define HID_BPF_MAX_BUFFER_SIZE 16384 /* 16kb */
> > +
> > +struct hid_device;
> > +
> > +enum hid_bpf_event {
> > + HID_BPF_UNDEF = 0,
> > + HID_BPF_DEVICE_EVENT,
> > +};
> > +
> > +/* type is HID_BPF_DEVICE_EVENT */
> > +struct hid_bpf_ctx_device_event {
> > + __u8 data[HID_BPF_MAX_BUFFER_SIZE];
>
> 16kB sounds pretty big to me, do we usually need that much?

That's painful but it seems so: see commit 6a0eaf5123e0 ("HID:
Increase HID maximum report size to 16KB").

I wanted to have a static definition of the buffer, but maybe I could
terminate the struct with `_u8 data[]` and dynamically (re-)alloc the
buffer depending on the context.

If the verifier doesn't reject that (why would it? given that it
should rely on hid_is_valid_access()), I'll implement this in v2.

>
> > + unsigned long size;
> > +};
> > +
> > +struct hid_bpf_ctx {
> > + enum hid_bpf_event type;
> > + struct hid_device *hdev;
> > +
> > + union {
> > + struct hid_bpf_ctx_device_event device;
> > + } u;
> > +};
> > +
> > +#endif /* _UAPI__LINUX_BPF_HID_H__ */
> [...]
>
> > diff --git a/kernel/bpf/hid.c b/kernel/bpf/hid.c
> > new file mode 100644
> > index 000000000000..d3cb952bfc26
> > --- /dev/null
> > +++ b/kernel/bpf/hid.c
>
> [...]
>
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index 9c7a72b65eee..230ca6964a7e 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -3,6 +3,7 @@
> > */
> > #include <linux/bpf.h>
> > #include <linux/bpf-cgroup.h>
> > +#include <linux/bpf-hid.h>
> > #include <linux/bpf_trace.h>
> > #include <linux/bpf_lirc.h>
> > #include <linux/bpf_verifier.h>
> > @@ -2174,6 +2175,7 @@ static bool is_net_admin_prog_type(enum bpf_prog_type prog_type)
> > case BPF_PROG_TYPE_CGROUP_SYSCTL:
> > case BPF_PROG_TYPE_SOCK_OPS:
> > case BPF_PROG_TYPE_EXT: /* extends any prog */
> > + case BPF_PROG_TYPE_HID:
>
> Is this net_admin type?

Not really :)
I initially copied over from the LIRC2 code, which is something quite
similar in terms of abuse of BPF.

Maybe I should add an extra patch before introducing
is_sys_admin_prog_type() and move over LIRC2 there before adding HID.

>
> > return true;
> > case BPF_PROG_TYPE_CGROUP_SKB:
> > /* always unpriv */
> > @@ -3188,6 +3190,8 @@ attach_type_to_prog_type(enum bpf_attach_type attach_type)
> > return BPF_PROG_TYPE_SK_LOOKUP;
> > case BPF_XDP:
> > return BPF_PROG_TYPE_XDP;
> > + case BPF_HID_DEVICE_EVENT:
> > + return BPF_PROG_TYPE_HID;
> > default:
> > return BPF_PROG_TYPE_UNSPEC;
> > }
> > @@ -3331,6 +3335,8 @@ static int bpf_prog_query(const union bpf_attr *attr,
> > case BPF_SK_MSG_VERDICT:
> > case BPF_SK_SKB_VERDICT:
> > return sock_map_bpf_prog_query(attr, uattr);
> > + case BPF_HID_DEVICE_EVENT:
> > + return bpf_hid_prog_query(attr, uattr);
> > default:
> > return -EINVAL;
> > }
> > @@ -4325,6 +4331,8 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
> > ret = bpf_perf_link_attach(attr, prog);
> > break;
> > #endif
> > + case BPF_PROG_TYPE_HID:
> > + return bpf_hid_link_create(attr, prog);
> > default:
> > ret = -EINVAL;
> > }
>
> [...]
>
> > diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> > index afe3d0d7f5f2..5978b92cacd3 100644
> > --- a/tools/include/uapi/linux/bpf.h
> > +++ b/tools/include/uapi/linux/bpf.h
> > @@ -952,6 +952,7 @@ enum bpf_prog_type {
> > BPF_PROG_TYPE_LSM,
> > BPF_PROG_TYPE_SK_LOOKUP,
> > BPF_PROG_TYPE_SYSCALL, /* a program that can execute syscalls */
> > + BPF_PROG_TYPE_HID,
> > };
> >
> > enum bpf_attach_type {
> > @@ -997,6 +998,7 @@ enum bpf_attach_type {
> > BPF_SK_REUSEPORT_SELECT,
> > BPF_SK_REUSEPORT_SELECT_OR_MIGRATE,
> > BPF_PERF_EVENT,
> > + BPF_HID_DEVICE_EVENT,
> > __MAX_BPF_ATTACH_TYPE
> > };
> >
> > @@ -1011,6 +1013,7 @@ enum bpf_link_type {
> > BPF_LINK_TYPE_NETNS = 5,
> > BPF_LINK_TYPE_XDP = 6,
> > BPF_LINK_TYPE_PERF_EVENT = 7,
> > + BPF_LINK_TYPE_HID = 8,
> >
> > MAX_BPF_LINK_TYPE,
> > };
> > @@ -5870,6 +5873,10 @@ struct bpf_link_info {
> > struct {
> > __u32 ifindex;
> > } xdp;
> > + struct {
> > + __s32 hidraw_ino;
> > + __u32 attach_type;
> > + } hid;
> > };
> > } __attribute__((aligned(8)));
> >
>

And thanks for the initial review :)

Cheers,
Benjamin