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 X-Spam-Level: X-Spam-Status: No, score=-11.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0E580C43461 for ; Tue, 15 Sep 2020 13:11:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B97E320829 for ; Tue, 15 Sep 2020 13:11:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600175515; bh=u/HTMK9SYBgCqASpK328ZsVw4zxDrK6hSpUMfxoRGKw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=IUrgkK1IRYWsq5gDJV8kbJQEXo5rXbOmZkf5y3OJmsO222vrfzu35ugRL5+0ro1VN XxxoSzP+tGz5617LlPnh9QeooQbgqOJlBqd0gygtFIGyW+YBlLB8Cf08i3bUK8RgXZ Lzv6q2vhoJxXwmp7DAQV8J6xQ1t4/ZwmuJJyNyWU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726571AbgIONLs (ORCPT ); Tue, 15 Sep 2020 09:11:48 -0400 Received: from mail.kernel.org ([198.145.29.99]:36762 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726498AbgIONLO (ORCPT ); Tue, 15 Sep 2020 09:11:14 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EC0A520872; Tue, 15 Sep 2020 13:11:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600175470; bh=u/HTMK9SYBgCqASpK328ZsVw4zxDrK6hSpUMfxoRGKw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=zV2bRb447YudntQTxCq5cx2hsf+YfN2kbD2p5EqaMRL+St1Y33ZWmsv2Ze0mdR7Sf Se+09pdD9vpCL9V9m6Xn0izS8bxbmU8jedSPALDVzeQZQqREX3WSQ/AbA/pxSHDgRG QQbW/1YpEn7age6n20mMP155ep19TpDqgMmAPNtM= Date: Tue, 15 Sep 2020 14:11:03 +0100 From: Will Deacon To: Ilias Apalodimas Cc: bpf@vger.kernel.org, ardb@kernel.org, naresh.kamboju@linaro.org, Jiri Olsa , Jean-Philippe Brucker , Yauheni Kaliuta , Daniel Borkmann , Alexei Starovoitov , Zi Shen Lim , Catalin Marinas , Martin KaFai Lau , Song Liu , Yonghong Song , Andrii Nakryiko , John Fastabend , KP Singh , "David S. Miller" , Jakub Kicinski , Jesper Dangaard Brouer , netdev@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] arm64: bpf: Fix branch offset in JIT Message-ID: <20200915131102.GA26439@willie-the-truck> References: <20200914160355.19179-1-ilias.apalodimas@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200914160355.19179-1-ilias.apalodimas@linaro.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Hi Ilias, On Mon, Sep 14, 2020 at 07:03:55PM +0300, Ilias Apalodimas wrote: > Running the eBPF test_verifier leads to random errors looking like this: > > [ 6525.735488] Unexpected kernel BRK exception at EL1 > [ 6525.735502] Internal error: ptrace BRK handler: f2000100 [#1] SMP Does this happen because we poison the BPF memory with BRK instructions? Maybe we should look at using a special immediate so we can detect this, rather than end up in the ptrace handler. > diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c > index f8912e45be7a..0974effff58c 100644 > --- a/arch/arm64/net/bpf_jit_comp.c > +++ b/arch/arm64/net/bpf_jit_comp.c > @@ -143,9 +143,13 @@ static inline void emit_addr_mov_i64(const int reg, const u64 val, > } > } > > -static inline int bpf2a64_offset(int bpf_to, int bpf_from, > +static inline int bpf2a64_offset(int bpf_insn, int off, > const struct jit_ctx *ctx) > { > + /* arm64 offset is relative to the branch instruction */ > + int bpf_from = bpf_insn + 1; > + /* BPF JMP offset is relative to the next instruction */ > + int bpf_to = bpf_insn + off + 1; > int to = ctx->offset[bpf_to]; > /* -1 to account for the Branch instruction */ > int from = ctx->offset[bpf_from] - 1; I think this is a bit confusing with all the variables. How about just doing: /* BPF JMP offset is relative to the next BPF instruction */ bpf_insn++; /* * Whereas arm64 branch instructions encode the offset from the * branch itself, so we must subtract 1 from the instruction offset. */ return ctx->offset[bpf_insn + off] - ctx->offset[bpf_insn] - 1; > @@ -642,7 +646,7 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, > > /* JUMP off */ > case BPF_JMP | BPF_JA: > - jmp_offset = bpf2a64_offset(i + off, i, ctx); > + jmp_offset = bpf2a64_offset(i, off, ctx); > check_imm26(jmp_offset); > emit(A64_B(jmp_offset), ctx); > break; > @@ -669,7 +673,7 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, > case BPF_JMP32 | BPF_JSLE | BPF_X: > emit(A64_CMP(is64, dst, src), ctx); > emit_cond_jmp: > - jmp_offset = bpf2a64_offset(i + off, i, ctx); > + jmp_offset = bpf2a64_offset(i, off, ctx); > check_imm19(jmp_offset); > switch (BPF_OP(code)) { > case BPF_JEQ: > @@ -912,18 +916,26 @@ static int build_body(struct jit_ctx *ctx, bool extra_pass) > const struct bpf_insn *insn = &prog->insnsi[i]; > int ret; > > + /* > + * offset[0] offset of the end of prologue, start of the > + * first insn. > + * offset[x] - offset of the end of x insn. So does offset[1] point at the last arm64 instruction for the first BPF instruction, or does it point to the first arm64 instruction for the second BPF instruction? > + */ > + if (ctx->image == NULL) > + ctx->offset[i] = ctx->idx; > + > ret = build_insn(insn, ctx, extra_pass); > if (ret > 0) { > i++; > if (ctx->image == NULL) > - ctx->offset[i] = ctx->idx; > + ctx->offset[i] = ctx->offset[i - 1]; Does it matter that we set the offset for both halves of a 16-byte BPF instruction? I think that's a change in behaviour here. > continue; > } > - if (ctx->image == NULL) > - ctx->offset[i] = ctx->idx; > if (ret) > return ret; > } > + if (ctx->image == NULL) > + ctx->offset[i] = ctx->idx; I think it would be cleared to set ctx->offset[0] before the for loop (with a comment about what it is) and then change the for loop to iterate from 1 all the way to prog->len. Will