From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752020AbeDZC1O (ORCPT ); Wed, 25 Apr 2018 22:27:14 -0400 Received: from mail-pg0-f66.google.com ([74.125.83.66]:33572 "EHLO mail-pg0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751274AbeDZC1M (ORCPT ); Wed, 25 Apr 2018 22:27:12 -0400 X-Google-Smtp-Source: AIpwx4+gmxQtgDeKVUG9f6dEaNb/ZM9jvdsR9cb3cOQBw23t45dCDA5BCBaf5MTYncyNC2teqS6oWQ== From: Leo Yan To: Alexei Starovoitov , Daniel Borkmann , "David S. Miller" , Jonathan Corbet , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Cc: Leo Yan Subject: [PATCH bpf-next] bpf, doc: Update bpf_jit_enable limitation for CONFIG_BPF_JIT_ALWAYS_ON Date: Thu, 26 Apr 2018 10:26:51 +0800 Message-Id: <1524709611-29437-1-git-send-email-leo.yan@linaro.org> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When CONFIG_BPF_JIT_ALWAYS_ON is enabled, kernel has limitation for bpf_jit_enable, so it has fixed value 1 and we cannot set it to 2 for JIT opcode dumping; this patch is to update the doc for it. Signed-off-by: Leo Yan --- Documentation/networking/filter.txt | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt index fd55c7d..feddab9 100644 --- a/Documentation/networking/filter.txt +++ b/Documentation/networking/filter.txt @@ -483,6 +483,12 @@ Example output from dmesg: [ 3389.935851] JIT code: 00000030: 00 e8 28 94 ff e0 83 f8 01 75 07 b8 ff ff 00 00 [ 3389.935852] JIT code: 00000040: eb 02 31 c0 c9 c3 +When CONFIG_BPF_JIT_ALWAYS_ON is enabled, bpf_jit_enable is set to 1 by default +and it returns failure if change to any other value from proc node; this is +for security consideration to avoid leaking info to unprivileged users. In this +case, we can't directly dump JIT opcode image from kernel log, alternatively we +need to use bpf tool for the dumping. + In the kernel source tree under tools/bpf/, there's bpf_jit_disasm for generating disassembly out of the kernel log's hexdump: -- 1.9.1