From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751694AbbKGFzg (ORCPT ); Sat, 7 Nov 2015 00:55:36 -0500 Received: from mail-ig0-f177.google.com ([209.85.213.177]:35501 "EHLO mail-ig0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751021AbbKGFze (ORCPT ); Sat, 7 Nov 2015 00:55:34 -0500 Message-ID: <563D9252.6040402@linaro.org> Date: Fri, 06 Nov 2015 21:55:30 -0800 From: "Shi, Yang" User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: ast@kernel.org, daniel@iogearbox.net, catalin.marinas@arm.com, will.deacon@arm.com CC: zlim.lnx@gmail.com, xi.wang@gmail.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linaro-kernel@lists.linaro.org Subject: Re: [PATCH] arm64: bpf: fix JIT stack setup References: <1446874494-14500-1-git-send-email-yang.shi@linaro.org> In-Reply-To: <1446874494-14500-1-git-send-email-yang.shi@linaro.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Please ignore this one, forgot to cc to linux-arm-kernel list. Sorry for the inconvenience. Yang On 11/6/2015 9:34 PM, Yang Shi wrote: > ARM64 JIT used FP (x29) as eBPF fp register, but FP is subjected to > change during function call so it may cause the BPF prog stack base address > change too. Whenever, it pointed to the bottom of BPF prog stack instead of > the top. > > So, when copying data via bpf_probe_read, it will be copied to (SP - offset), > then it may overwrite the saved FP/LR. > > Use x25 to replace FP as BPF stack base register (fp). Since x25 is callee > saved register, so it will keep intact during function call. > It is initialized in BPF prog prologue when BPF prog is started to run > everytime. When BPF prog exits, it could be just tossed. > > Other than this the BPf prog stack base need to be setup before function > call stack. > > So, the BPF stack layout looks like: > > high > original A64_SP => 0:+-----+ BPF prologue > | | FP/LR and callee saved registers > BPF fp register => +64:+-----+ > | | > | ... | BPF prog stack > | | > | | > current A64_SP => +-----+ > | | > | ... | Function call stack > | | > +-----+ > low > > Signed-off-by: Yang Shi > CC: Zi Shen Lim > CC: Xi Wang > --- > arch/arm64/net/bpf_jit_comp.c | 38 +++++++++++++++++++++++++++++++------- > 1 file changed, 31 insertions(+), 7 deletions(-) > > diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c > index a44e529..6809647 100644 > --- a/arch/arm64/net/bpf_jit_comp.c > +++ b/arch/arm64/net/bpf_jit_comp.c > @@ -50,7 +50,7 @@ static const int bpf2a64[] = { > [BPF_REG_8] = A64_R(21), > [BPF_REG_9] = A64_R(22), > /* read-only frame pointer to access stack */ > - [BPF_REG_FP] = A64_FP, > + [BPF_REG_FP] = A64_R(25), > /* temporary register for internal BPF JIT */ > [TMP_REG_1] = A64_R(23), > [TMP_REG_2] = A64_R(24), > @@ -155,18 +155,42 @@ static void build_prologue(struct jit_ctx *ctx) > stack_size += 4; /* extra for skb_copy_bits buffer */ > stack_size = STACK_ALIGN(stack_size); > > + /* > + * BPF prog stack layout > + * > + * high > + * original A64_SP => 0:+-----+ BPF prologue > + * | | FP/LR and callee saved registers > + * BPF fp register => +64:+-----+ > + * | | > + * | ... | BPF prog stack > + * | | > + * | | > + * current A64_SP => +-----+ > + * | | > + * | ... | Function call stack > + * | | > + * +-----+ > + * low > + * > + */ > + > + /* Save FP and LR registers to stay align with ARM64 AAPCS */ > + emit(A64_PUSH(A64_FP, A64_LR, A64_SP), ctx); > + > /* Save callee-saved register */ > emit(A64_PUSH(r6, r7, A64_SP), ctx); > emit(A64_PUSH(r8, r9, A64_SP), ctx); > if (ctx->tmp_used) > emit(A64_PUSH(tmp1, tmp2, A64_SP), ctx); > > - /* Set up BPF stack */ > - emit(A64_SUB_I(1, A64_SP, A64_SP, stack_size), ctx); > - > - /* Set up frame pointer */ > + /* Set up BPF prog stack base register (x25) */ > emit(A64_MOV(1, fp, A64_SP), ctx); > > + /* Set up function call stack */ > + emit(A64_SUB_I(1, A64_SP, A64_SP, stack_size), ctx); > + emit(A64_MOV(1, A64_FP, A64_SP), ctx); > + > /* Clear registers A and X */ > emit_a64_mov_i64(ra, 0, ctx); > emit_a64_mov_i64(rx, 0, ctx); > @@ -196,8 +220,8 @@ static void build_epilogue(struct jit_ctx *ctx) > emit(A64_POP(r8, r9, A64_SP), ctx); > emit(A64_POP(r6, r7, A64_SP), ctx); > > - /* Restore frame pointer */ > - emit(A64_MOV(1, fp, A64_SP), ctx); > + /* Restore FP/LR registers */ > + emit(A64_POP(A64_FP, A64_LR, A64_SP), ctx); > > /* Set return value */ > emit(A64_MOV(1, A64_R(0), r0), ctx); >