On 03/11/2022 15:57, Benjamin Tissoires wrote:
Declare an entry point that can use fmod_ret BPF programs, and
also an API to access and change the incoming data.
A simpler implementation would consist in just calling
hid_bpf_device_event() for any incoming event and let users deal
with the fact that they will be called for any event of any device.
The goal of HID-BPF is to partially replace drivers, so this situation
can be problematic because we might have programs which will step on
each other toes.
For that, we add a new API hid_bpf_attach_prog() that can be called
from a syscall and we manually deal with a jump table in hid-bpf.
Whenever we add a program to the jump table (in other words, when we
attach a program to a HID device), we keep the number of time we added
this program in the jump table so we can release it whenever there are
no other users.
HID devices have an RCU protected list of available programs in the
jump table, and those programs are called one after the other thanks
to bpf_tail_call().
To achieve the detection of users losing their fds on the programs we
attached, we add 2 tracing facilities on bpf_prog_release() (for when
a fd is closed) and bpf_free_inode() (for when a pinned program gets
unpinned).
Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx>
...
+static int __init hid_bpf_init(void)
+{
+ int err;
+
+ /* Note: if we exit with an error any time here, we would entirely break HID, which
+ * is probably not something we want. So we log an error and return success.
+ *
+ * This is not a big deal: the syscall allowing to attach a BPF program to a HID device
+ * will not be available, so nobody will be able to use the functionality.
+ */
+
+ err = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &hid_bpf_kfunc_set);
+ if (err) {
+ pr_warn("error while setting HID BPF tracing kfuncs: %d", err);
+ return 0;
+ }
+
+ err = hid_bpf_preload_skel();
+ if (err) {
+ pr_warn("error while preloading HID BPF dispatcher: %d", err);
+ return 0;
+ }
+
+ /* register syscalls after we are sure we can load our preloaded bpf program */
+ err = register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &hid_bpf_syscall_kfunc_set);
+ if (err) {
+ pr_warn("error while setting HID BPF syscall kfuncs: %d", err);
+ return 0;
+ }
+
+ return 0;
+}
We have a kernel test that checks for new warning and error messages on
boot and with this change I am now seeing the following error message on
our Tegra platforms ...
WARNING KERN hid_bpf: error while preloading HID BPF dispatcher: -13
I have a quick look at the code, but I can't say I am familiar with
this. So I wanted to ask if a way to fix this or avoid this? I see the
code returns 0, so one option would be to make this an informational or
debug print.
Thanks
Jon
--
nvpublic
