Re: [PATCH net-next] filter: add MOD operation

[George Bakos <gbakos () alpinista org>]

Here's a patch to libpcap-1.3 to test against. I still need to
include changes to man pages.

g

On Sat, 08 Sep 2012 10:03:35 +0200
Eric Dumazet <eric.dumazet () gmail com> wrote:

> From: Eric Dumazet <edumazet () google com>
>
> On Fri, 2012-09-07 at 20:03 -0700, Andi Kleen wrote:
> > On Fri, Sep 07, 2012 at 07:49:10AM +0000, George Bakos wrote:
> > > Gents,
> > > Any fundamental reason why the following (, etc.) shouldn't be
> > > included in net/core/filter.c?
> > >
> > >                 case BPF_S_ALU_MOD_X:
> > >                         if (X == 0)
> > >                                 return 0;
> > >                         A %= X;
> > >                         continue;
> >
> > Copying netdev.
> >
> > In principle no reason against it, but you may need to update
> > the various BPF JITs too that Linux now has too.
>
> Hi Andi, thanks for the forward
>
> In recent commit ffe06c17afbb was added ALU_XOR_X,
> so we could add ALU_MOD_X as well.
>
> ALU_MOD_K is a bit more complex as we cant use an ancillary, and must
> instead use a new BPF_OP code :
>
> /* alu/jmp fields */
> #define BPF_OP(code)    ((code) & 0xf0)
> #define         BPF_ADD         0x00
> #define         BPF_SUB         0x10
> #define         BPF_MUL         0x20
> #define         BPF_DIV         0x30
> #define         BPF_OR          0x40
> #define         BPF_AND         0x50
> #define         BPF_LSH         0x60
> #define         BPF_RSH         0x70
> #define         BPF_NEG         0x80
>
> So I guess we could use
>
> #define         BPF_MOD         0x90
>
> About the various arches JIT, there is no hurry :
> We can update them later.
>
> At JIT 'compile' time, if we find a not yet handled instruction, we fall
> back to the net/core/filter.c interpreter.
>
> If the following patch is accepted, I'll do the x86 part as a followup.
>
> Thanks !
>
> [PATCH net-next] filter: add MOD operation
>
> Add a new ALU opcode, to compute a modulus.
>
> Commit ffe06c17afbbb used an ancillary to implement XOR_X,
> but here we reserve one of the available ALU opcode to implement both
> MOD_X and MOD_K
>
> Signed-off-by: Eric Dumazet <edumazet () google com>
> Suggested-by: George Bakos <gbakos () alpinista org>
> Cc: Jay Schulist <jschlst () samba org>
> Cc: Jiri Pirko <jpirko () redhat com>
> Cc: Andi Kleen <ak () linux intel com>
> ---
>  include/linux/filter.h |    4 ++++
>  net/core/filter.c      |   15 +++++++++++++++
>  2 files changed, 19 insertions(+)
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 82b0135..3cf5fd5 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -74,6 +74,8 @@ struct sock_fprog { /* Required for SO_ATTACH_FILTER. */
>  #define         BPF_LSH         0x60
>  #define         BPF_RSH         0x70
>  #define         BPF_NEG         0x80
> +#define              BPF_MOD         0x90
> +
>  #define         BPF_JA          0x00
>  #define         BPF_JEQ         0x10
>  #define         BPF_JGT         0x20
> @@ -196,6 +198,8 @@ enum {
>       BPF_S_ALU_MUL_K,
>       BPF_S_ALU_MUL_X,
>       BPF_S_ALU_DIV_X,
> +     BPF_S_ALU_MOD_K,
> +     BPF_S_ALU_MOD_X,
>       BPF_S_ALU_AND_K,
>       BPF_S_ALU_AND_X,
>       BPF_S_ALU_OR_K,
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 907efd2..fbe3a8d 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -167,6 +167,14 @@ unsigned int sk_run_filter(const struct sk_buff *skb,
>               case BPF_S_ALU_DIV_K:
>                       A = reciprocal_divide(A, K);
>                       continue;
> +             case BPF_S_ALU_MOD_X:
> +                     if (X == 0)
> +                             return 0;
> +                     A %= X;
> +                     continue;
> +             case BPF_S_ALU_MOD_K:
> +                     A %= K;
> +                     continue;
>               case BPF_S_ALU_AND_X:
>                       A &= X;
>                       continue;
> @@ -469,6 +477,8 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
>               [BPF_ALU|BPF_MUL|BPF_K]  = BPF_S_ALU_MUL_K,
>               [BPF_ALU|BPF_MUL|BPF_X]  = BPF_S_ALU_MUL_X,
>               [BPF_ALU|BPF_DIV|BPF_X]  = BPF_S_ALU_DIV_X,
> +             [BPF_ALU|BPF_MOD|BPF_K]  = BPF_S_ALU_MOD_K,
> +             [BPF_ALU|BPF_MOD|BPF_X]  = BPF_S_ALU_MOD_X,
>               [BPF_ALU|BPF_AND|BPF_K]  = BPF_S_ALU_AND_K,
>               [BPF_ALU|BPF_AND|BPF_X]  = BPF_S_ALU_AND_X,
>               [BPF_ALU|BPF_OR|BPF_K]   = BPF_S_ALU_OR_K,
> @@ -531,6 +541,11 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
>                               return -EINVAL;
>                       ftest->k = reciprocal_value(ftest->k);
>                       break;
> +             case BPF_S_ALU_MOD_K:
> +                     /* check for division by zero */
> +                     if (ftest->k == 0)
> +                             return -EINVAL;
> +                     break;
>               case BPF_S_LD_MEM:
>               case BPF_S_LDX_MEM:
>               case BPF_S_ST:


--

Attachment: libpcap-1.3.0-with-modulus.patch
Description:

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