On Fri, Nov 25, 2022 at 09:44:29PM +0800, Chen, Hu1 wrote: > On 11/22/2022 10:14 PM, Peter Zijlstra wrote: > > On Tue, Nov 22, 2022 at 02:48:07PM +0100, Jiri Olsa wrote: > >> On Mon, Nov 21, 2022 at 11:32:43PM -0800, Chen Hu wrote: > >>> 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(). > > > > If there is no compile time reference to it, what stops an LTO linker > > from throwing it out in the first place? > > > > Ah, my stupid. > > The only references to this function from kernel space are: > $ grep -r bpf_kfunc_call_test_release > net/bpf/test_run.c:noinline void bpf_kfunc_call_test_release(struct prog_test_ref_kfunc *p) > net/bpf/test_run.c:BTF_ID_FLAGS(func, bpf_kfunc_call_test_release, KF_RELEASE) > net/bpf/test_run.c:BTF_ID(func, bpf_kfunc_call_test_release) > > Macro BTF_ID_... puts the function names to .BTF_ids section. It looks > like: > __BTF_ID__func__bpf_kfunc_call_test_release__692 bpf_kfunc_call_test_release test function called bpf program as kfunc (check tools/testing/selftests/bpf/progs/*.c) it's placed in BTF ID lists so verifier can validate its ID when called from bpf program.. it has no other caller from kernel side jirka > > When running, it uses kallsyms_lookup_name() to find the function > address via names in .BTF_ids section. > > > Hi jirka, > Please kindly correct me if my understanding of BTF_ids is wrong.
