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Date: Fri, 5 Sep 2014 13:13:49 -0400 (EDT) From: Mikulas Patocka <mpatocka@...hat.com> To: Daniel Borkmann <dborkman@...hat.com> cc: Hannes Frederic Sowa <hannes@...hat.com>, Alexei Starovoitov <ast@...mgrid.com>, Pablo Neira Ayuso <pablo@...filter.org>, "David S. Miller" <davem@...emloft.net>, linux-kernel@...r.kernel.org, netdev@...r.kernel.org Subject: Re: [PATCH] bpf: fix a false positive kmemcheck warning 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 <mpatocka@...hat.com> > > > > > > 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. Mikulas -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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