[PATCH bpf] selftests/bpf: Fix "missing ENDBR" BUG for destructor kfunc

[Chen Hu <hu1.chen@xxxxxxxxx>]

With CONFIG_X86_KERNEL_IBT enabled, the test_verifier triggers the
following BUG:

  traps: Missing ENDBR: bpf_kfunc_call_test_release+0x0/0x30
  ------------[ cut here ]------------
  kernel BUG at arch/x86/kernel/traps.c:254!
  invalid opcode: 0000 [#1] PREEMPT SMP
  <TASK>
   asm_exc_control_protection+0x26/0x50
  RIP: 0010:bpf_kfunc_call_test_release+0x0/0x30
  Code: 00 48 c7 c7 18 f2 e1 b4 e8 0d ca 8c ff 48 c7 c0 00 f2 e1 b4 c3
	0f 1f 44 00 00 66 0f 1f 00 0f 1f 44 00 00 0f 0b 31 c0 c3 66 90
       <66> 0f 1f 00 0f 1f 44 00 00 48 85 ff 74 13 4c 8d 47 18 b8 ff ff ff
   bpf_map_free_kptrs+0x2e/0x70
   array_map_free+0x57/0x140
   process_one_work+0x194/0x3a0
   worker_thread+0x54/0x3a0
   ? rescuer_thread+0x390/0x390
   kthread+0xe9/0x110
   ? kthread_complete_and_exit+0x20/0x20

This is because there are no compile-time references to the destructor
kfuncs, bpf_kfunc_call_test_release() for example. So objtool marked
them sealable and ENDBR in the functions were sealed (converted to NOP)
by apply_ibt_endbr().

This fix creates dummy compile-time references to destructor kfuncs so
ENDBR stay there.

Signed-off-by: Chen Hu <hu1.chen@xxxxxxxxx>
Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
---
 include/linux/btf_ids.h | 7 +++++++
 net/bpf/test_run.c      | 2 ++
 2 files changed, 9 insertions(+)

diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
index 2aea877d644f..6c6b520ea58f 100644
--- a/include/linux/btf_ids.h
+++ b/include/linux/btf_ids.h
@@ -266,4 +266,11 @@ MAX_BTF_TRACING_TYPE,
 
 extern u32 btf_tracing_ids[];
 
+#if defined(CONFIG_X86_KERNEL_IBT) && !defined(__DISABLE_EXPORTS)
+#define BTF_IBT_NOSEAL(name)					\
+	asm(IBT_NOSEAL(#name));
+#else
+#define BTF_IBT_NOSEAL(name)
+#endif /* CONFIG_X86_KERNEL_IBT */
+
 #endif
diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 13d578ce2a09..465952e5de11 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -1653,6 +1653,8 @@ BTF_ID(struct, prog_test_ref_kfunc)
 BTF_ID(func, bpf_kfunc_call_test_release)
 BTF_ID(struct, prog_test_member)
 BTF_ID(func, bpf_kfunc_call_memb_release)
+BTF_IBT_NOSEAL(bpf_kfunc_call_test_release)
+BTF_IBT_NOSEAL(bpf_kfunc_call_memb_release)
 
 static int __init bpf_prog_test_run_init(void)
 {
-- 
2.34.1