From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Borkmann Subject: Re: [PATCH] bpf: fix a false positive kmemcheck warning Date: Fri, 05 Sep 2014 19:17:38 +0200 Message-ID: <5409F032.50101@redhat.com> References: <5409E2C8.2080200@redhat.com> <1409936457.5306.2.camel@localhost> <5409EE70.9020304@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Hannes Frederic Sowa , Alexei Starovoitov , Pablo Neira Ayuso , "David S. Miller" , linux-kernel@vger.kernel.org, netdev@vger.kernel.org To: Mikulas Patocka Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 09/05/2014 07:13 PM, Mikulas Patocka wrote: > On Fri, 5 Sep 2014, Daniel Borkmann wrote: >> On 09/05/2014 07:00 PM, Hannes Frederic Sowa wrote: >>> On Fr, 2014-09-05 at 18:20 +0200, Daniel Borkmann wrote: >>>> Hi Mikulas, >>>> >>>> On 09/05/2014 06:01 PM, Mikulas Patocka wrote: >>>>> This patch fixes false positive kmemcheck warning in bpf. >>>>> >>>>> When we try to write the variable len, the compiler generates a code >>>>> that >>>>> reads the 32-bit word, modifies the bits belonging to "len" and writes >>>>> the >>>>> 32-bit word back. The reading of the word results in kmemcheck warning >>>>> due >>>>> to reading uninitialized memory. This patch fixes it by avoiding using >>>>> bit >>>>> fields when kmemcheck is enabled. >>>>> >>>>> Signed-off-by: Mikulas Patocka >>>> >>>> You need to submit this patch to netdev (Cc'ed). >>>> >>>>> --- >>>>> include/linux/filter.h | 5 +++++ >>>>> 1 file changed, 5 insertions(+) >>>>> >>>>> Index: linux-2.6/include/linux/filter.h >>>>> =================================================================== >>>>> --- linux-2.6.orig/include/linux/filter.h 2014-09-04 23:04:26.000000000 >>>>> +0200 >>>>> +++ linux-2.6/include/linux/filter.h 2014-09-04 23:43:05.000000000 >>>>> +0200 >>>>> @@ -325,8 +325,13 @@ struct sock; >>>>> struct seccomp_data; >>>>> >>>>> struct bpf_prog { >>>>> +#ifdef CONFIG_KMEMCHECK >>>>> + bool jited; >>>>> + u32 len; >>>>> +#else >>>>> u32 jited:1, /* Is our filter >>>>> JIT'ed? */ >>>>> len:31; /* Number of filter >>>>> blocks */ >>>>> +#endif >>>>> struct sock_fprog_kern *orig_prog; /* Original BPF >>>>> program */ >>>>> unsigned int (*bpf_func)(const struct sk_buff *skb, >>>>> const struct bpf_insn >>>>> *filter); >>>> >>>> I don't really like this if-def. If you really want to fix it, can't >>>> you just use : >>>> >>>> kmemcheck_bitfield_begin(bpf_anc_data) >>>> ... >>>> kmemcheck_bitfield_end(bpf_anc_data) >>> >>> you also need to annotate the bitfield after allocation: >>> struct bpf_prog *prog = kalloc(...); >>> kmemcheck_annotate_bitfield(prog, bpf_anc_data); >> >> Yes, sure, sorry if that was not clear from my side, that was what I >> intended to say with kmemcheck /infrastructure/. :) > > So, change it to use these markings. I'm not an expert in this area, so I > don't know all the places where this structure could be allocated. If you > know them all, mark it in this way. Ok, fine by me. I have some pending items, so I'll put it on top of them.