On 7/24/20 7:58 AM, Alexei Starovoitov wrote:
From: Alexei Starovoitov <ast@xxxxxxxxxx>
Add kernel module with user mode driver that populates bpffs with
BPF iterators.
$ mount bpffs /my/bpffs/ -t bpf
$ ls -la /my/bpffs/
total 4
drwxrwxrwt 2 root root 0 Jul 2 00:27 .
drwxr-xr-x 19 root root 4096 Jul 2 00:09 ..
-rw------- 1 root root 0 Jul 2 00:27 maps.debug
-rw------- 1 root root 0 Jul 2 00:27 progs.debug
The user mode driver will load BPF Type Formats, create BPF maps, populate BPF
maps, load two BPF programs, attach them to BPF iterators, and finally send two
bpf_link IDs back to the kernel.
The kernel will pin two bpf_links into newly mounted bpffs instance under
names "progs.debug" and "maps.debug". These two files become human readable.
$ cat /my/bpffs/progs.debug
id name pages attached
11 dump_bpf_map 1 bpf_iter_bpf_map
12 dump_bpf_prog 1 bpf_iter_bpf_prog
27 test_pkt_access 1
32 test_main 1 test_pkt_access test_pkt_access
33 test_subprog1 1 test_pkt_access_subprog1 test_pkt_access
34 test_subprog2 1 test_pkt_access_subprog2 test_pkt_access
35 test_subprog3 1 test_pkt_access_subprog3 test_pkt_access
36 new_get_skb_len 1 get_skb_len test_pkt_access
37 new_get_skb_ifi 1 get_skb_ifindex test_pkt_access
38 new_get_constan 1 get_constant test_pkt_access
The BPF program dump_bpf_prog() in iterators.bpf.c is printing this data about
all BPF programs currently loaded in the system. This information is unstable
and will change from kernel to kernel as ".debug" suffix conveys.
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
---
init/Kconfig | 2 +
kernel/bpf/Makefile | 1 +
kernel/bpf/inode.c | 132 +++++++++++++++++-
kernel/bpf/preload/Kconfig | 18 +++
kernel/bpf/preload/Makefile | 21 +++
kernel/bpf/preload/bpf_preload.h | 16 +++
kernel/bpf/preload/bpf_preload_kern.c | 83 +++++++++++
kernel/bpf/preload/bpf_preload_umd_blob.S | 7 +
.../preload/iterators/bpf_preload_common.h | 13 ++
kernel/bpf/preload/iterators/iterators.c | 94 +++++++++++++
10 files changed, 384 insertions(+), 3 deletions(-)
create mode 100644 kernel/bpf/preload/Kconfig
create mode 100644 kernel/bpf/preload/Makefile
create mode 100644 kernel/bpf/preload/bpf_preload.h
create mode 100644 kernel/bpf/preload/bpf_preload_kern.c
create mode 100644 kernel/bpf/preload/bpf_preload_umd_blob.S
create mode 100644 kernel/bpf/preload/iterators/bpf_preload_common.h
create mode 100644 kernel/bpf/preload/iterators/iterators.c
[...]
+struct bpf_preload_ops bpf_preload_ops = { .info.driver_name = "bpf_preload" };
+EXPORT_SYMBOL_GPL(bpf_preload_ops);
+
+#if !IS_BUILTIN(CONFIG_BPF_PRELOAD_UMD)
+static struct module *bpf_preload_mod;
+#endif
+
+static bool bpf_preload_mod_get(void)
+{
+ bool ret = true;
+
+#if IS_BUILTIN(CONFIG_BPF_PRELOAD_UMD)
+ return ret;
+#else
+ /* if bpf_preload.ko wasn't loaded earlier then load it now */
+ if (!bpf_preload_ops.do_preload) {
+ request_module("bpf_preload");
+ if (!bpf_preload_ops.do_preload) {
+ pr_err("bpf_preload module is missing.\n"
+ "bpffs will not have iterators.\n");
+ return false;
+ }
+ }
+ /* and grab the reference, so it doesn't disappear while the kernel
+ * is interacting with kernel module and its UMD
+ */
+ preempt_disable();
+ bpf_preload_mod = __module_address((long)bpf_preload_ops.do_preload);
+ if (!bpf_preload_mod || !try_module_get(bpf_preload_mod)) {
Set looks good overall, but this combination looks a bit odd. Meaning, we request the
module via request_module(), in its init fn, it will set bpf_preload_ops.do_preload
callback, and here we need to search kallsyms on __module_address(bpf_preload_ops.do_preload)
just to get the module struct in order to place a ref on it via try_module_get().
Why can't the bpf_preload module simply do:
static const struct bpf_preload_umd_ops umd_ops = {
.preload = do_preload,
.finish = do_finish,
.owner = THIS_MODULE,
};
And then in load_umd():
static int __init load_umd(void)
{
int err;
err = umd_load_blob(&bpf_preload_ops.info, &bpf_preload_umd_start,
&bpf_preload_umd_end - &bpf_preload_umd_start);
if (!err)
bpf_preload_umd_ops = &umd_ops;
return err;
}
Then later in bpf_preload_mod_get() you just do ...
try_module_get(bpf_preload_umd_ops->owner)
... and can avoid this whole detour with symbol address search which looks odd and
unneeded for this case.
Thanks,
Daniel
+ bpf_preload_mod = NULL;
+ pr_err("bpf_preload module get failed.\n");
+ ret = false;
+ }
+ preempt_enable();
+ return ret;
+#endif
+}
+
+static void bpf_preload_mod_put(void)
+{
+#if !IS_BUILTIN(CONFIG_BPF_PRELOAD_UMD)
+ if (bpf_preload_mod) {
+ /* now user can "rmmod bpf_preload" if necessary */
+ module_put(bpf_preload_mod);
+ bpf_preload_mod = NULL;
+ }
+#endif
+}
+
+static int populate_bpffs(struct dentry *parent)
+{
+ struct bpf_preload_info objs[BPF_PRELOAD_LINKS] = {};
+ struct bpf_link *links[BPF_PRELOAD_LINKS] = {};
+ int err = 0, i;
+
+ /* grab the mutex to make sure the kernel interactions with bpf_preload
+ * UMD are serialized
+ */
+ mutex_lock(&bpf_preload_ops.lock);
+
+ /* if bpf_preload.ko wasn't built into vmlinux then load it */
+ if (!bpf_preload_mod_get())
+ goto out;
+
+ if (!bpf_preload_ops.info.tgid) {
+ /* do_preload will start UMD that will load BPF iterator programs */
+ err = bpf_preload_ops.do_preload(objs);
+ if (err)
+ goto out_put;
+ for (i = 0; i < BPF_PRELOAD_LINKS; i++) {
+ links[i] = bpf_link_by_id(objs[i].link_id);
+ if (IS_ERR(links[i])) {
+ err = PTR_ERR(links[i]);
+ goto out_put;
+ }
+ }
+ for (i = 0; i < BPF_PRELOAD_LINKS; i++) {
+ err = bpf_iter_link_pin_kernel(parent,
+ objs[i].link_name, links[i]);
+ if (err)
+ goto out_put;
+ /* do not unlink successfully pinned links even
+ * if later link fails to pin
+ */
+ links[i] = NULL;
+ }
+ /* do_finish() will tell UMD process to exit */
+ err = bpf_preload_ops.do_finish();
+ if (err)
+ goto out_put;
+ }
+out_put:
+ bpf_preload_mod_put();
+out:
+ mutex_unlock(&bpf_preload_ops.lock);
+ for (i = 0; i < BPF_PRELOAD_LINKS && err; i++)
+ if (!IS_ERR_OR_NULL(links[i]))
+ bpf_link_put(links[i]);
[...]
