Messages in this thread | | | Subject | Re: [PATCH] bpf: fix a false positive kmemcheck warning | From | Hannes Frederic Sowa <> | Date | Fri, 05 Sep 2014 19:00:57 +0200 |
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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@redhat.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);
Bye, Hannes
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