On Fri, Sep 5, 2014 at 9:01 AM, Mikulas Patocka <[email protected]> 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.
It will conflict with pending Hannes's patch.
Once it's in, I can rebase and actually make it unconditional.
These bit savings probably not worth it, since bpf_prog is
dominated by program anyway.
JITs would need to be updated as well, since they're now do
->jited = 1;
I can fix this all up.
Do you mind sharing the kmemcheck warning you see?
> 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
why diff says 2.6 ? Kinda odd.
> @@ -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);
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