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Date: Fri, 05 Sep 2014 18:20:24 +0200 From: Daniel Borkmann <dborkman@...hat.com> To: Mikulas Patocka <mpatocka@...hat.com> CC: 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 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) et al infrastructure as container (in case in future we will add some more bit flags, since len doesn't really need all 31 bit universe)? Note, there are currently some patches pending in patchwork that also fill the u32 hole thus the extra bool would introduce a new hole after that. Therefore, I think above would be better. Thanks, Daniel -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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