Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752411AbdHHIq7 (ORCPT ); Tue, 8 Aug 2017 04:46:59 -0400 Received: from www62.your-server.de ([213.133.104.62]:53880 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752348AbdHHIq4 (ORCPT ); Tue, 8 Aug 2017 04:46:56 -0400 Message-ID: <59897A7C.10009@iogearbox.net> Date: Tue, 08 Aug 2017 10:46:52 +0200 From: Daniel Borkmann User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: James Hogan , Alexei Starovoitov CC: linux-kernel@vger.kernel.org, Steven Rostedt , Ingo Molnar , netdev@vger.kernel.org Subject: Re: [RFC PATCH 2/2] bpf: Initialise mod[] in bpf_trace_printk References: <20170807222514.24292-1-james.hogan@imgtec.com> <20170807222514.24292-3-james.hogan@imgtec.com> In-Reply-To: <20170807222514.24292-3-james.hogan@imgtec.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1600 Lines: 42 On 08/08/2017 12:25 AM, James Hogan wrote: > In bpf_trace_printk(), the elements in mod[] are left uninitialised, but > they are then incremented to track the width of the formats. Zero > initialise the array just in case the memory contains non-zero values on > entry. > > Fixes: 9c959c863f82 ("tracing: Allow BPF programs to call bpf_trace_printk()") > Signed-off-by: James Hogan > Cc: Alexei Starovoitov > Cc: Daniel Borkmann > Cc: Steven Rostedt > Cc: Ingo Molnar > Cc: netdev@vger.kernel.org > --- > When I checked (on MIPS32), the elements tended to have the value zero > anyway (does BPF zero the stack or something clever?), so this is a > purely theoretical fix. > --- > kernel/trace/bpf_trace.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index 32dcbe1b48f2..86a52857d941 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -129,7 +129,7 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1, > u64, arg2, u64, arg3) > { > bool str_seen = false; > - int mod[3] = {}; > + int mod[3] = { 0, 0, 0 }; I'm probably missing something, but is the behavior of gcc wrt above initializers different on mips (it zeroes just fine on x86 at least)? If yes, we'd probably need a cocci script to also check rest of the kernel given this is used in a number of places. Hm, could you elaborate? > int fmt_cnt = 0; > u64 unsafe_addr; > char buf[64]; >