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Message-ID: <d6555f27-95bf-5474-3006-6f8d399ab556@intel.com> Date: Fri, 25 Nov 2022 21:44:29 +0800 From: "Chen, Hu1" <hu1.chen@...el.com> To: Peter Zijlstra <peterz@...radead.org>, Jiri Olsa <olsajiri@...il.com> CC: <jpoimboe@...nel.org>, <memxor@...il.com>, <bpf@...r.kernel.org>, "Pengfei Xu" <pengfei.xu@...el.com>, Alexei Starovoitov <ast@...nel.org>, "Daniel Borkmann" <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, "Martin KaFai Lau" <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>, "Chen, Hu1" <hu1.chen@...el.com> Subject: Re: [PATCH bpf v2] selftests/bpf: Fix "missing ENDBR" BUG for destructor kfunc 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 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.
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