bpf: Introduce BPF support for kernel module function calls

This change adds support on the kernel side to allow for BPF programs to
call kernel module functions. Userspace will prepare an array of module
BTF fds that is passed in during BPF_PROG_LOAD using fd_array parameter.
In the kernel, the module BTFs are placed in the auxilliary struct for
bpf_prog, and loaded as needed.

The verifier then uses insn->off to index into the fd_array. insn->off
0 is reserved for vmlinux BTF (for backwards compat), so userspace must
use an fd_array index > 0 for module kfunc support. kfunc_btf_tab is
sorted based on offset in an array, and each offset corresponds to one
descriptor, with a max limit up to 256 such module BTFs.

We also change existing kfunc_tab to distinguish each element based on
imm, off pair as each such call will now be distinct.

Another change is to check_kfunc_call callback, which now include a
struct module * pointer, this is to be used in later patch such that the
kfunc_id and module pointer are matched for dynamically registered BTF
sets from loadable modules, so that same kfunc_id in two modules doesn't
lead to check_kfunc_call succeeding. For the duration of the
check_kfunc_call, the reference to struct module exists, as it returns
the pointer stored in kfunc_btf_tab.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211002011757.311265-2-memxor@gmail.com

2 files changed, 2 insertions, 2 deletions

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 072f0c16c779..b1f6f5237de6 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -241,7 +241,7 @@ BTF_ID(func, bpf_kfunc_call_test2)
 BTF_ID(func, bpf_kfunc_call_test3)
 BTF_SET_END(test_sk_kfunc_ids)
 
-bool bpf_prog_test_check_kfunc_call(u32 kfunc_id)
+bool bpf_prog_test_check_kfunc_call(u32 kfunc_id, struct module *owner)
 {
 	return btf_id_set_contains(&test_sk_kfunc_ids, kfunc_id);
 }
diff --git a/net/ipv4/bpf_tcp_ca.c b/net/ipv4/bpf_tcp_ca.c
index 0dcee9df1326..b3afd3361f34 100644
--- a/net/ipv4/bpf_tcp_ca.c
+++ b/net/ipv4/bpf_tcp_ca.c
@@ -255,7 +255,7 @@ BTF_ID(func, bbr_set_state)
 #endif	/* CONFIG_X86 */
 BTF_SET_END(bpf_tcp_ca_kfunc_ids)
 
-static bool bpf_tcp_ca_check_kfunc_call(u32 kfunc_btf_id)
+static bool bpf_tcp_ca_check_kfunc_call(u32 kfunc_btf_id, struct module *owner)
 {
 	return btf_id_set_contains(&bpf_tcp_ca_kfunc_ids, kfunc_btf_id);
 }