From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-177.mta1.migadu.com (out-177.mta1.migadu.com [95.215.58.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 584D8154456 for ; Thu, 15 Aug 2024 22:14:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.177 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723760063; cv=none; b=Y+KNvQygUbY6phVe1cvcl+NnYeZAi7WbtZztMO05xehkbOrtuheh7EaN/wAyTPE8zKvxgeduAtP4nE/BUytGWFQA3VWSiq8ha6dx3Hekjj7sPZxpgJUlyh87byyB58fjrL6THcaMB2ZejdiwU7zN/LMoPVhHPfID8KO6t9SMiYo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723760063; c=relaxed/simple; bh=62RcMdgSn3oo3tSBy6DL778qabCdkvItbw5J2IqLDV0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qorPUFM3r9ZIdMUvk086K8PhfAcRDezuGL9OmHmlxu/cNqtt/r46+ygZFbVvmqIiy7vxBkJIQmvoy9BFonS7XRo+0uVUl6miGTvghJZnnKoZWIe5h0P35vvnoSs8b9vEkBfeuJfQXQ6Gv7ihC32VLK56QOub8qJ8yWx3epxCMHI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=A+jeAP0R; arc=none smtp.client-ip=95.215.58.177 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="A+jeAP0R" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1723760058; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=MEGo0P6wJ3ynBWQNFoBSMJkQbbLm9oZkOQkRexkLPGE=; b=A+jeAP0R79ZtEAoMtchEr1pgPCAg5uyaURIJWXKTRzOezGs4y8zuWqzd6MVwLv9llwllU/ 7ymj/c5bMJUaqNyEk9MyJrtgxq0XkIY9Mh+Nz1Lk1tg7QRolFW5GKL/pWtyndj3oKkTG3T fst5eRyHnpzF4iqOGiwseVcbkb8O95k= Date: Thu, 15 Aug 2024 15:14:10 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [RFC PATCH bpf-next 1/6] bpf: Add gen_epilogue to bpf_verifier_ops To: Eduard Zingerman , bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Yonghong Song , Amery Hung , kernel-team@meta.com References: <20240813184943.3759630-1-martin.lau@linux.dev> <20240813184943.3759630-2-martin.lau@linux.dev> <19903da56fbfb99e4ad6fdea646aaff885e9fd4d.camel@gmail.com> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau In-Reply-To: <19903da56fbfb99e4ad6fdea646aaff885e9fd4d.camel@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 8/14/24 1:56 PM, Eduard Zingerman wrote: > On Tue, 2024-08-13 at 11:49 -0700, Martin KaFai Lau wrote: >> From: Martin KaFai Lau >> >> This patch adds a .gen_epilogue to the bpf_verifier_ops. It is similar >> to the existing .gen_prologue. Instead of allowing a subsystem >> to run code at the beginning of a bpf prog, it allows the subsystem >> to run code just before the bpf prog exit. >> >> One of the use case is to allow the upcoming bpf qdisc to ensure that >> the skb->dev is the same as the qdisc->dev_queue->dev. The bpf qdisc >> struct_ops implementation could either fix it up or drop the skb. >> Another use case could be in bpf_tcp_ca.c to enforce snd_cwnd >> has sane value (e.g. non zero). >> >> The epilogue can do the useful thing (like checking skb->dev) if it >> can access the bpf prog's ctx. Unlike prologue, r1 may not hold the >> ctx pointer. This patch saves the r1 in the stack if the .gen_epilogue >> has returned some instructions in the "epilogue_buf". >> >> The existing .gen_prologue is done in convert_ctx_accesses(). >> The new .gen_epilogue is done in the convert_ctx_accesses() also. >> When it sees the (BPF_JMP | BPF_EXIT) instruction, it will be patched >> with the earlier generated "epilogue_buf". The epilogue patching is >> only done for the main prog. >> >> Signed-off-by: Martin KaFai Lau >> --- > > Apart from the note below I don't see any obvious problems with this code. > > Reviewed-by: Eduard Zingerman > > [...] > >> --- a/kernel/bpf/verifier.c >> +++ b/kernel/bpf/verifier.c >> @@ -19610,15 +19610,37 @@ static int opt_subreg_zext_lo32_rnd_hi32(struct bpf_verifier_env *env, >> */ >> static int convert_ctx_accesses(struct bpf_verifier_env *env) >> { >> + struct bpf_subprog_info *subprogs = env->subprog_info; >> const struct bpf_verifier_ops *ops = env->ops; >> - int i, cnt, size, ctx_field_size, delta = 0; >> + int i, cnt, size, ctx_field_size, delta = 0, epilogue_cnt = 0; >> const int insn_cnt = env->prog->len; >> - struct bpf_insn insn_buf[16], *insn; >> + struct bpf_insn insn_buf[16], epilogue_buf[16], *insn; >> u32 target_size, size_default, off; >> struct bpf_prog *new_prog; >> enum bpf_access_type type; >> bool is_narrower_load; >> >> + if (ops->gen_epilogue) { >> + epilogue_cnt = ops->gen_epilogue(epilogue_buf, env->prog, >> + -(subprogs[0].stack_depth + 8)); >> + if (epilogue_cnt >= ARRAY_SIZE(epilogue_buf)) { >> + verbose(env, "bpf verifier is misconfigured\n"); >> + return -EINVAL; >> + } else if (epilogue_cnt) { >> + /* Save the ARG_PTR_TO_CTX for the epilogue to use */ >> + cnt = 0; >> + subprogs[0].stack_depth += 8; > > Note: two other places that allocate additional stack > (optimize_bpf_loop(), do_misc_fixups()) > also bump 'env->prog->aux->stack_depth'. Thanks for pointing it out. In this case, I will stay with calling .gen_epilogue in convert_ctx_accesses(). > >> + insn_buf[cnt++] = BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_1, >> + -subprogs[0].stack_depth); >> + insn_buf[cnt++] = env->prog->insnsi[0]; >> + new_prog = bpf_patch_insn_data(env, 0, insn_buf, cnt); >> + if (!new_prog) >> + return -ENOMEM; >> + env->prog = new_prog; >> + delta += cnt - 1; >> + } >> + } >> + > > [...] >