linux-kernel - Re: [PATCH bpf-next v3] bpf: arm64: Fix panic due to missing BTI at indirect jump targets

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Message-ID: <0c441710-5250-4706-ba81-b6b4b1277313@huaweicloud.com>
Date: Wed, 31 Dec 2025 10:05:27 +0800
From: Xu Kuohai <xukuohai@...weicloud.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>,
 Yonghong Song <yonghong.song@...ux.dev>, Puranjay Mohan
 <puranjay@...nel.org>, Anton Protopopov <a.s.protopopov@...il.com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH bpf-next v3] bpf: arm64: Fix panic due to missing BTI at
 indirect jump targets

On 12/31/2025 2:20 AM, Alexei Starovoitov wrote:
> On Fri, Dec 26, 2025 at 11:49 PM Xu Kuohai <xukuohai@...weicloud.com> wrote:
>>
>> From: Xu Kuohai <xukuohai@...wei.com>
>>
>> When BTI is enabled, the indirect jump selftest triggers BTI exception:
>>
>> Internal error: Oops - BTI: 0000000036000003 [#1]  SMP
>> ...
>> Call trace:
>>   bpf_prog_2e5f1c71c13ac3e0_big_jump_table+0x54/0xf8 (P)
>>   bpf_prog_run_pin_on_cpu+0x140/0x464
>>   bpf_prog_test_run_syscall+0x274/0x3ac
>>   bpf_prog_test_run+0x224/0x2b0
>>   __sys_bpf+0x4cc/0x5c8
>>   __arm64_sys_bpf+0x7c/0x94
>>   invoke_syscall+0x78/0x20c
>>   el0_svc_common+0x11c/0x1c0
>>   do_el0_svc+0x48/0x58
>>   el0_svc+0x54/0x19c
>>   el0t_64_sync_handler+0x84/0x12c
>>   el0t_64_sync+0x198/0x19c
>>
>> This happens because no BTI instruction is generated by the JIT for
>> indirect jump targets.
>>
>> Fix it by emitting BTI instruction for every possible indirect jump
>> targets when BTI is enabled. The targets are identified by traversing
>> all instruction arrays of jump table type used by the BPF program,
>> since indirect jump targets can only be read from instruction arrays
>> of jump table type.
> 
> earlier you said:
> 
>> As Anton noted, even though jump tables are currently the only type
>> of instruction array, users may still create insn_arrays that are not
>> used as jump tables. In such cases, there is no need to emit BTIs.
> 
> yes, but it's not worth it to make this micro optimization in JIT.
> If it's in insn_array just emit BTI unconditionally.
> No need to do this filtering.
>

Hmm, that is what the v1 version does. Please take a look. If it’s okay,
I’ll resend a rebased version.

v1: https://lore.kernel.org/bpf/20251127140318.3944249-1-xukuohai@huaweicloud.com/

> pw-bot: cr