[PATCH bpf v2] selftests/bpf: Fix "missing ENDBR" BUG for destructor kfunc

[Chen Hu]

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.

Fixes: 05a945deefaa ("selftests/bpf: Add verifier tests for kptr")
Signed-off-by: Chen Hu <hu1.chen@xxxxxxxxx>
Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
---
v2:
- Use generic macro name and place the macro after function body as
- suggested by Jiri Olsa

v1: https://lore.kernel.org/all/20221121085113.611504-1-hu1.chen@xxxxxxxxx/

 include/linux/btf_ids.h | 7 +++++++
 net/bpf/test_run.c      | 4 ++++
 2 files changed, 11 insertions(+)

diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
index 2aea877d644f..db02691b506d 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 FUNC_IBT_NOSEAL(name)					\
+	asm(IBT_NOSEAL(#name));
+#else
+#define FUNC_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..07263b7cc12d 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -597,10 +597,14 @@ noinline void bpf_kfunc_call_test_release(struct prog_test_ref_kfunc *p)
 	refcount_dec(&p->cnt);
 }
 
+FUNC_IBT_NOSEAL(bpf_kfunc_call_test_release)
+
 noinline void bpf_kfunc_call_memb_release(struct prog_test_member *p)
 {
 }
 
+FUNC_IBT_NOSEAL(bpf_kfunc_call_memb_release)
+
 noinline void bpf_kfunc_call_memb1_release(struct prog_test_member1 *p)
 {
 	WARN_ON_ONCE(1);
-- 
2.34.1