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Mon, 21 Mar 2022 09:20:35 -0700 (PDT) X-Google-Smtp-Source: ABdhPJzjF27dG7tlIwqHRmGo/L1Pqa+cqzwxC/hE5t254t/WUOFy/f2ich/A4jW9Ku25eWsmp14ZXqbMpd+Hu20Rbjo= X-Received: by 2002:a05:6a00:2182:b0:4fa:6d20:d95d with SMTP id h2-20020a056a00218200b004fa6d20d95dmr18135864pfi.83.1647879635332; Mon, 21 Mar 2022 09:20:35 -0700 (PDT) MIME-Version: 1.0 References: <20220318161528.1531164-1-benjamin.tissoires@redhat.com> <20220318161528.1531164-7-benjamin.tissoires@redhat.com> In-Reply-To: From: Benjamin Tissoires Date: Mon, 21 Mar 2022 17:20:24 +0100 Message-ID: Subject: Re: [PATCH bpf-next v3 06/17] HID: allow to change the report descriptor from an eBPF program To: Song Liu Cc: Greg KH , Jiri Kosina , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Shuah Khan , Dave Marchevsky , Joe Stringer , Jonathan Corbet , Tero Kristo , open list , "open list:HID CORE LAYER" , Networking , bpf , linux-kselftest@vger.kernel.org, Linux Doc Mailing List Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 18, 2022 at 10:10 PM Song Liu wrote: > > On Fri, Mar 18, 2022 at 9:17 AM Benjamin Tissoires > wrote: > > > > Make use of BPF_HID_ATTACH_RDESC_FIXUP so we can trigger an rdesc fixup > > in the bpf world. > > > > Whenever the program gets attached/detached, the device is reconnected > > meaning that userspace will see it disappearing and reappearing with > > the new report descriptor. > > > > Signed-off-by: Benjamin Tissoires > > > > --- > > > > changes in v3: > > - ensure the ctx.size is properly bounded by allocated size > > - s/link_attached/post_link_attach/ > > - removed the switch statement with only one case > > > > changes in v2: > > - split the series by bpf/libbpf/hid/selftests and samples > > --- > > drivers/hid/hid-bpf.c | 62 ++++++++++++++++++++++++++++++++++++++++++ > > drivers/hid/hid-core.c | 3 +- > > include/linux/hid.h | 6 ++++ > > 3 files changed, 70 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/hid/hid-bpf.c b/drivers/hid/hid-bpf.c > > index 5060ebcb9979..45c87ff47324 100644 > > --- a/drivers/hid/hid-bpf.c > > +++ b/drivers/hid/hid-bpf.c > > @@ -50,6 +50,14 @@ static struct hid_device *hid_bpf_fd_to_hdev(int fd) > > return hdev; > > } > > > > +static int hid_reconnect(struct hid_device *hdev) > > +{ > > + if (!test_and_set_bit(ffs(HID_STAT_REPROBED), &hdev->status)) > > + return device_reprobe(&hdev->dev); > > + > > + return 0; > > +} > > + > > static int hid_bpf_pre_link_attach(struct hid_device *hdev, enum bpf_hid_attach_type type) > > { > > int err = 0; > > @@ -92,6 +100,12 @@ static int hid_bpf_pre_link_attach(struct hid_device *hdev, enum bpf_hid_attach_ > > return err; > > } > > > > +static void hid_bpf_post_link_attach(struct hid_device *hdev, enum bpf_hid_attach_type type) > > +{ > > + if (type == BPF_HID_ATTACH_RDESC_FIXUP) > > + hid_reconnect(hdev); > > +} > > + > > static void hid_bpf_array_detach(struct hid_device *hdev, enum bpf_hid_attach_type type) > > { > > switch (type) { > > @@ -99,6 +113,9 @@ static void hid_bpf_array_detach(struct hid_device *hdev, enum bpf_hid_attach_ty > > kfree(hdev->bpf.device_data); > > hdev->bpf.device_data = NULL; > > break; > > + case BPF_HID_ATTACH_RDESC_FIXUP: > > + hid_reconnect(hdev); > > + break; > > default: > > /* do nothing */ > > break; > > @@ -116,6 +133,9 @@ static int hid_bpf_run_progs(struct hid_device *hdev, struct hid_bpf_ctx_kern *c > > case HID_BPF_DEVICE_EVENT: > > type = BPF_HID_ATTACH_DEVICE_EVENT; > > break; > > + case HID_BPF_RDESC_FIXUP: > > + type = BPF_HID_ATTACH_RDESC_FIXUP; > > + break; > > default: > > return -EINVAL; > > } > > @@ -155,11 +175,53 @@ u8 *hid_bpf_raw_event(struct hid_device *hdev, u8 *data, int *size) > > return ctx.data; > > } > > > > +u8 *hid_bpf_report_fixup(struct hid_device *hdev, u8 *rdesc, unsigned int *size) > > +{ > > + int ret; > > + struct hid_bpf_ctx_kern ctx = { > > + .type = HID_BPF_RDESC_FIXUP, > > + .hdev = hdev, > > + .size = *size, > > + }; > > + > > + if (bpf_hid_link_empty(&hdev->bpf, BPF_HID_ATTACH_RDESC_FIXUP)) > > Do we need to lock bpf_hid_mutex before calling bpf_hid_link_empty()? > (or maybe we > already did?) The mutex is not locked before this call, indeed. However, bpf_hid_link_empty() is an inlined function that just calls in the end list_empty(). Given that all the list heads are created just once for the entire life of the HID device, I *think* this is thread safe and does not require mutex locking. (I might be wrong) So when first plugging in the device, if there is a fighting process that attempts to add a program, if the program managed to insert itself before we enter this code, then the list won't be empty and we will execute BPF_PROG_RUN_ARRAY(), and if not, well, we ignore it and wait for reconnect(). But now I am starting to wonder if I need to also protect BPF_PROG_RUN_ARRAY() under bpf_hid_mutex... Cheers, Benjamin > > > > + goto ignore_bpf; > > + > > + ctx.data = kmemdup(rdesc, HID_MAX_DESCRIPTOR_SIZE, GFP_KERNEL); > > + if (!ctx.data) > > + goto ignore_bpf; > > + > > + ctx.allocated_size = HID_MAX_DESCRIPTOR_SIZE; > > + > > + ret = hid_bpf_run_progs(hdev, &ctx); > > + if (ret) > > + goto ignore_bpf; > > + > > + if (ctx.size > ctx.allocated_size) > > + goto ignore_bpf; > > + > > + *size = ctx.size; > > + > > + if (*size) { > > + rdesc = krealloc(ctx.data, *size, GFP_KERNEL); > > + } else { > > + rdesc = NULL; > > + kfree(ctx.data); > > + } > > + > > + return rdesc; > > + > > + ignore_bpf: > > + kfree(ctx.data); > > + return kmemdup(rdesc, *size, GFP_KERNEL); > > +} > > + > > int __init hid_bpf_module_init(void) > > { > > struct bpf_hid_hooks hooks = { > > .hdev_from_fd = hid_bpf_fd_to_hdev, > > .pre_link_attach = hid_bpf_pre_link_attach, > > + .post_link_attach = hid_bpf_post_link_attach, > > .array_detach = hid_bpf_array_detach, > > }; > > > > diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c > > index 937fab7eb9c6..3182c39db006 100644 > > --- a/drivers/hid/hid-core.c > > +++ b/drivers/hid/hid-core.c > > @@ -1213,7 +1213,8 @@ int hid_open_report(struct hid_device *device) > > return -ENODEV; > > size = device->dev_rsize; > > > > - buf = kmemdup(start, size, GFP_KERNEL); > > + /* hid_bpf_report_fixup() ensures we work on a copy of rdesc */ > > + buf = hid_bpf_report_fixup(device, start, &size); > > if (buf == NULL) > > return -ENOMEM; > > > > diff --git a/include/linux/hid.h b/include/linux/hid.h > > index 8fd79011f461..66d949d10b78 100644 > > --- a/include/linux/hid.h > > +++ b/include/linux/hid.h > > @@ -1213,10 +1213,16 @@ do { \ > > > > #ifdef CONFIG_BPF > > u8 *hid_bpf_raw_event(struct hid_device *hdev, u8 *rd, int *size); > > +u8 *hid_bpf_report_fixup(struct hid_device *hdev, u8 *rdesc, unsigned int *size); > > int hid_bpf_module_init(void); > > void hid_bpf_module_exit(void); > > #else > > static inline u8 *hid_bpf_raw_event(struct hid_device *hdev, u8 *rd, int *size) { return rd; } > > +static inline u8 *hid_bpf_report_fixup(struct hid_device *hdev, u8 *rdesc, > > + unsigned int *size) > > +{ > > + return kmemdup(rdesc, *size, GFP_KERNEL); > > +} > > static inline int hid_bpf_module_init(void) { return 0; } > > static inline void hid_bpf_module_exit(void) {} > > #endif > > -- > > 2.35.1 > > >