From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3C0D2C433FE for ; Fri, 15 Apr 2022 03:39:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349092AbiDODmP (ORCPT ); Thu, 14 Apr 2022 23:42:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41818 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241106AbiDODmN (ORCPT ); Thu, 14 Apr 2022 23:42:13 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CC3FA1C108; Thu, 14 Apr 2022 20:39:42 -0700 (PDT) Received: from kwepemi500013.china.huawei.com (unknown [172.30.72.57]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4KfhqK2y9ZzgYgr; Fri, 15 Apr 2022 11:37:49 +0800 (CST) Received: from [10.67.111.192] (10.67.111.192) by kwepemi500013.china.huawei.com (7.221.188.120) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Fri, 15 Apr 2022 11:39:38 +0800 Message-ID: Date: Fri, 15 Apr 2022 11:39:38 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH bpf-next v2 4/6] bpf, arm64: Impelment bpf_arch_text_poke() for arm64 Content-Language: en-US To: Hou Tao , , , , , CC: Catalin Marinas , Will Deacon , Steven Rostedt , Ingo Molnar , Daniel Borkmann , Alexei Starovoitov , Zi Shen Lim , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , "David S . Miller" , Hideaki YOSHIFUJI , David Ahern , Thomas Gleixner , Borislav Petkov , Dave Hansen , , , Shuah Khan , Mark Rutland , Ard Biesheuvel , Pasha Tatashin , Peter Collingbourne , Daniel Kiss , Sudeep Holla , Steven Price , Marc Zyngier , Mark Brown , Kumar Kartikeya Dwivedi , Delyan Kratunov References: <20220414162220.1985095-1-xukuohai@huawei.com> <20220414162220.1985095-5-xukuohai@huawei.com> From: Xu Kuohai In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.67.111.192] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To kwepemi500013.china.huawei.com (7.221.188.120) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 4/15/2022 10:34 AM, Hou Tao wrote: > Hi, > > On 4/15/2022 12:22 AM, Xu Kuohai wrote: >> Impelment bpf_arch_text_poke() for arm64, so bpf trampoline code can use >> it to replace nop with jump, or replace jump with nop. >> >> Signed-off-by: Xu Kuohai >> Acked-by: Song Liu >> --- >> arch/arm64/net/bpf_jit_comp.c | 52 +++++++++++++++++++++++++++++++++++ >> 1 file changed, 52 insertions(+) >> >> diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c >> index 8ab4035dea27..1a1c3ea75ee2 100644 >> --- a/arch/arm64/net/bpf_jit_comp.c >> +++ b/arch/arm64/net/bpf_jit_comp.c >> @@ -9,6 +9,7 @@ >> >> #include >> #include >> +#include >> #include >> #include >> #include >> @@ -18,6 +19,7 @@ >> #include >> #include >> #include >> +#include >> #include >> >> #include "bpf_jit.h" >> @@ -1529,3 +1531,53 @@ void bpf_jit_free_exec(void *addr) >> { >> return vfree(addr); >> } >> + >> +static int gen_branch_or_nop(enum aarch64_insn_branch_type type, void *ip, >> + void *addr, u32 *insn) >> +{ >> + if (!addr) >> + *insn = aarch64_insn_gen_nop(); >> + else >> + *insn = aarch64_insn_gen_branch_imm((unsigned long)ip, >> + (unsigned long)addr, >> + type); >> + >> + return *insn != AARCH64_BREAK_FAULT ? 0 : -EFAULT; >> +} >> + >> +int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type, >> + void *old_addr, void *new_addr) >> +{ >> + int ret; >> + u32 old_insn; >> + u32 new_insn; >> + u32 replaced; >> + enum aarch64_insn_branch_type branch_type; >> + > In bpf_arch_text_poke() of x86, it disables the poking of kernel module, can you > explain why it is OK to do so in arm64 ? Because there is no test cases for > fentry on linux kernel module, could you please add some tests for it ? Oops, I forget to check this condition. It's not safe to patch a ko without ko unloading disabled. For arm64, the fentry is only patched by ftrace since the nop instruciton to be instrumented is not the first instruction, so bpf_text_poke() fails when comparing the old instruction (pointed to by the "old_addr") with the nop. Since the nop in fentry is reserved by ftrace, I dont think it's reasonable to patch the nop by another interface not provided by ftrace. Besides, for long jumps outside the range of 128MB, a single branch instruction is not sufficient, perhaps we could use ftrace trampoline or some other method to support long jumps. >> + if (poke_type == BPF_MOD_CALL) >> + branch_type = AARCH64_INSN_BRANCH_LINK; >> + else >> + branch_type = AARCH64_INSN_BRANCH_NOLINK; >> + >> + if (gen_branch_or_nop(branch_type, ip, old_addr, &old_insn) < 0) >> + return -EFAULT; >> + >> + if (gen_branch_or_nop(branch_type, ip, new_addr, &new_insn) < 0) >> + return -EFAULT; >> + >> + mutex_lock(&text_mutex); >> + if (aarch64_insn_read(ip, &replaced)) { >> + ret = -EFAULT; >> + goto out; >> + } >> + >> + if (replaced != old_insn) { >> + ret = -EFAULT; >> + goto out; >> + } >> + >> + ret = aarch64_insn_patch_text_nosync((void *)ip, new_insn); >> +out: >> + mutex_unlock(&text_mutex); >> + return ret; >> +} > > .