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 <mpato...@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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