[PATCH] filter: added BPF random opcode

[PATCH] filter: added BPF random opcode

[Chema Gonzalez]

This should allow random packet sampling.

Signed-off-by: Chema Gonzalez <chema@google.com>
---
 Documentation/networking/filter.txt |  1 +
 include/linux/filter.h              |  1 +
 include/uapi/linux/filter.h         |  3 ++-
 net/core/filter.c                   | 12 ++++++++++++
 tools/net/bpf_exp.l                 |  1 +
 tools/net/bpf_exp.y                 | 11 ++++++++++-
 tools/net/icmp_random.bpf           | 12 ++++++++++++
 7 files changed, 39 insertions(+), 2 deletions(-)
 create mode 100644 tools/net/icmp_random.bpf

diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt
index 81f940f..7192b46 100644
--- a/Documentation/networking/filter.txt
+++ b/Documentation/networking/filter.txt
@@ -281,6 +281,7 @@ Possible BPF extensions are shown in the following table:
   cpu                                   raw_smp_processor_id()
   vlan_tci                              vlan_tx_tag_get(skb)
   vlan_pr                               vlan_tx_tag_present(skb)
+  random                                prandom_u32()
 
 These extensions can also be prefixed with '#'.
 Examples for low-level BPF:
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 262dcbb..49c28aa 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -224,6 +224,7 @@ enum {
 	BPF_S_ANC_VLAN_TAG,
 	BPF_S_ANC_VLAN_TAG_PRESENT,
 	BPF_S_ANC_PAY_OFFSET,
+	BPF_S_ANC_RANDOM,
 };
 
 #endif /* __LINUX_FILTER_H__ */
diff --git a/include/uapi/linux/filter.h b/include/uapi/linux/filter.h
index 8eb9cca..253b4d4 100644
--- a/include/uapi/linux/filter.h
+++ b/include/uapi/linux/filter.h
@@ -130,7 +130,8 @@ struct sock_fprog {	/* Required for SO_ATTACH_FILTER. */
 #define SKF_AD_VLAN_TAG	44
 #define SKF_AD_VLAN_TAG_PRESENT 48
 #define SKF_AD_PAY_OFFSET	52
-#define SKF_AD_MAX	56
+#define SKF_AD_RANDOM	56
+#define SKF_AD_MAX	60
 #define SKF_NET_OFF   (-0x100000)
 #define SKF_LL_OFF    (-0x200000)
 
diff --git a/net/core/filter.c b/net/core/filter.c
index 765556b..b2a80a1 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -637,6 +637,12 @@ static u64 __get_raw_cpu_id(u64 ctx, u64 A, u64 X, u64 r4, u64 r5)
 	return raw_smp_processor_id();
 }
 
+/* note that this only generates 32-bit random numbers */
+static u64 __skb_get_random(u64 ctx, u64 A, u64 X, u64 r4, u64 r5)
+{
+	return (u64)prandom_u32();
+}
+
 /* Register mappings for user programs. */
 #define A_REG		0
 #define X_REG		7
@@ -773,6 +779,7 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
 	case SKF_AD_OFF + SKF_AD_NLATTR:
 	case SKF_AD_OFF + SKF_AD_NLATTR_NEST:
 	case SKF_AD_OFF + SKF_AD_CPU:
+	case SKF_AD_OFF + SKF_AD_RANDOM:
 		/* arg1 = ctx */
 		insn->code = BPF_ALU64 | BPF_MOV | BPF_X;
 		insn->a_reg = ARG1_REG;
@@ -806,6 +813,9 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
 		case SKF_AD_OFF + SKF_AD_CPU:
 			insn->imm = __get_raw_cpu_id - __bpf_call_base;
 			break;
+		case SKF_AD_OFF + SKF_AD_RANDOM:
+			insn->imm = __skb_get_random - __bpf_call_base;
+			break;
 		}
 		break;
 
@@ -1356,6 +1366,7 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
 			ANCILLARY(VLAN_TAG);
 			ANCILLARY(VLAN_TAG_PRESENT);
 			ANCILLARY(PAY_OFFSET);
+			ANCILLARY(RANDOM);
 			}
 
 			/* ancillary operation unknown or unsupported */
@@ -1741,6 +1752,7 @@ void sk_decode_filter(struct sock_filter *filt, struct sock_filter *to)
 		[BPF_S_ANC_VLAN_TAG]	= BPF_LD|BPF_B|BPF_ABS,
 		[BPF_S_ANC_VLAN_TAG_PRESENT] = BPF_LD|BPF_B|BPF_ABS,
 		[BPF_S_ANC_PAY_OFFSET]	= BPF_LD|BPF_B|BPF_ABS,
+		[BPF_S_ANC_RANDOM]	= BPF_LD|BPF_B|BPF_ABS,
 		[BPF_S_LD_W_LEN]	= BPF_LD|BPF_W|BPF_LEN,
 		[BPF_S_LD_W_IND]	= BPF_LD|BPF_W|BPF_IND,
 		[BPF_S_LD_H_IND]	= BPF_LD|BPF_H|BPF_IND,
diff --git a/tools/net/bpf_exp.l b/tools/net/bpf_exp.l
index bf7be77..804256f 100644
--- a/tools/net/bpf_exp.l
+++ b/tools/net/bpf_exp.l
@@ -92,6 +92,7 @@ extern void yyerror(const char *str);
 "#"?("cpu")	{ return K_CPU; }
 "#"?("vlan_tci") { return K_VLANT; }
 "#"?("vlan_pr")	{ return K_VLANP; }
+"#"?("random")	{ return K_RAND; }
 
 ":"		{ return ':'; }
 ","		{ return ','; }
diff --git a/tools/net/bpf_exp.y b/tools/net/bpf_exp.y
index d15efc9..e6306c5 100644
--- a/tools/net/bpf_exp.y
+++ b/tools/net/bpf_exp.y
@@ -56,7 +56,7 @@ static void bpf_set_jmp_label(char *label, enum jmp_type type);
 %token OP_LDXI
 
 %token K_PKT_LEN K_PROTO K_TYPE K_NLATTR K_NLATTR_NEST K_MARK K_QUEUE K_HATYPE
-%token K_RXHASH K_CPU K_IFIDX K_VLANT K_VLANP K_POFF
+%token K_RXHASH K_CPU K_IFIDX K_VLANT K_VLANP K_POFF K_RAND
 
 %token ':' ',' '[' ']' '(' ')' 'x' 'a' '+' 'M' '*' '&' '#' '%'
 
@@ -164,6 +164,9 @@ ldb
 	| OP_LDB K_POFF {
 		bpf_set_curr_instr(BPF_LD | BPF_B | BPF_ABS, 0, 0,
 				   SKF_AD_OFF + SKF_AD_PAY_OFFSET); }
+	| OP_LDB K_RAND {
+		bpf_set_curr_instr(BPF_LD | BPF_B | BPF_ABS, 0, 0,
+				   SKF_AD_OFF + SKF_AD_RANDOM); }
 	;
 
 ldh
@@ -212,6 +215,9 @@ ldh
 	| OP_LDH K_POFF {
 		bpf_set_curr_instr(BPF_LD | BPF_H | BPF_ABS, 0, 0,
 				   SKF_AD_OFF + SKF_AD_PAY_OFFSET); }
+	| OP_LDH K_RAND {
+		bpf_set_curr_instr(BPF_LD | BPF_H | BPF_ABS, 0, 0,
+				   SKF_AD_OFF + SKF_AD_RANDOM); }
 	;
 
 ldi
@@ -265,6 +271,9 @@ ld
 	| OP_LD K_POFF {
 		bpf_set_curr_instr(BPF_LD | BPF_W | BPF_ABS, 0, 0,
 				   SKF_AD_OFF + SKF_AD_PAY_OFFSET); }
+	| OP_LD K_RAND {
+		bpf_set_curr_instr(BPF_LD | BPF_W | BPF_ABS, 0, 0,
+				   SKF_AD_OFF + SKF_AD_RANDOM); }
 	| OP_LD 'M' '[' number ']' {
 		bpf_set_curr_instr(BPF_LD | BPF_MEM, 0, 0, $4); }
 	| OP_LD '[' 'x' '+' number ']' {
diff --git a/tools/net/icmp_random.bpf b/tools/net/icmp_random.bpf
new file mode 100644
index 0000000..b9adcbf
--- /dev/null
+++ b/tools/net/icmp_random.bpf
@@ -0,0 +1,12 @@
+# icmp random packet sampling, 1 in 4
+ldh [12]
+jne #0x800, drop
+ldb [23]
+jneq #1, drop
+# get a random uint32 number
+ld random
+mod #4
+jneq #1, drop
+ret #-1
+drop: ret #0
+
-- 
1.9.1.423.g4596e3a

Re: [PATCH] filter: added BPF random opcode

[Daniel Borkmann]

Hi Chema,

[cc'ing Alexei as well]

note, net-next is still closed, so you might need to resend this later
on again when it opens up.

On 04/15/2014 01:02 AM, Chema Gonzalez wrote:
> This should allow random packet sampling.
>
> Signed-off-by: Chema Gonzalez <chema@google.com>
> ---
>   Documentation/networking/filter.txt |  1 +
>   include/linux/filter.h              |  1 +
>   include/uapi/linux/filter.h         |  3 ++-
>   net/core/filter.c                   | 12 ++++++++++++
>   tools/net/bpf_exp.l                 |  1 +
>   tools/net/bpf_exp.y                 | 11 ++++++++++-
>   tools/net/icmp_random.bpf           | 12 ++++++++++++
>   7 files changed, 39 insertions(+), 2 deletions(-)
>   create mode 100644 tools/net/icmp_random.bpf
>
> diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt
> index 81f940f..7192b46 100644
> --- a/Documentation/networking/filter.txt
> +++ b/Documentation/networking/filter.txt
> @@ -281,6 +281,7 @@ Possible BPF extensions are shown in the following table:
>     cpu                                   raw_smp_processor_id()
>     vlan_tci                              vlan_tx_tag_get(skb)
>     vlan_pr                               vlan_tx_tag_present(skb)
> +  random                                prandom_u32()
>
>   These extensions can also be prefixed with '#'.
>   Examples for low-level BPF:
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 262dcbb..49c28aa 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -224,6 +224,7 @@ enum {
>   	BPF_S_ANC_VLAN_TAG,
>   	BPF_S_ANC_VLAN_TAG_PRESENT,
>   	BPF_S_ANC_PAY_OFFSET,
> +	BPF_S_ANC_RANDOM,
>   };
>
>   #endif /* __LINUX_FILTER_H__ */
> diff --git a/include/uapi/linux/filter.h b/include/uapi/linux/filter.h
> index 8eb9cca..253b4d4 100644
> --- a/include/uapi/linux/filter.h
> +++ b/include/uapi/linux/filter.h
> @@ -130,7 +130,8 @@ struct sock_fprog {	/* Required for SO_ATTACH_FILTER. */
>   #define SKF_AD_VLAN_TAG	44
>   #define SKF_AD_VLAN_TAG_PRESENT 48
>   #define SKF_AD_PAY_OFFSET	52
> -#define SKF_AD_MAX	56
> +#define SKF_AD_RANDOM	56
> +#define SKF_AD_MAX	60
>   #define SKF_NET_OFF   (-0x100000)
>   #define SKF_LL_OFF    (-0x200000)
>
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 765556b..b2a80a1 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -637,6 +637,12 @@ static u64 __get_raw_cpu_id(u64 ctx, u64 A, u64 X, u64 r4, u64 r5)
>   	return raw_smp_processor_id();
>   }
>
> +/* note that this only generates 32-bit random numbers */
> +static u64 __skb_get_random(u64 ctx, u64 A, u64 X, u64 r4, u64 r5)
> +{
> +	return (u64)prandom_u32();
> +}
> +
>   /* Register mappings for user programs. */
>   #define A_REG		0
>   #define X_REG		7
> @@ -773,6 +779,7 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
>   	case SKF_AD_OFF + SKF_AD_NLATTR:
>   	case SKF_AD_OFF + SKF_AD_NLATTR_NEST:
>   	case SKF_AD_OFF + SKF_AD_CPU:
> +	case SKF_AD_OFF + SKF_AD_RANDOM:

I think instead of a function call, this sould rather be modelled
directly into the internal insn set and thus converted differently,
so we can spare us the call.

>   		/* arg1 = ctx */
>   		insn->code = BPF_ALU64 | BPF_MOV | BPF_X;
>   		insn->a_reg = ARG1_REG;
> @@ -806,6 +813,9 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
>   		case SKF_AD_OFF + SKF_AD_CPU:
>   			insn->imm = __get_raw_cpu_id - __bpf_call_base;
>   			break;
> +		case SKF_AD_OFF + SKF_AD_RANDOM:
> +			insn->imm = __skb_get_random - __bpf_call_base;
> +			break;
>   		}
>   		break;
>
> @@ -1356,6 +1366,7 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
>   			ANCILLARY(VLAN_TAG);
>   			ANCILLARY(VLAN_TAG_PRESENT);
>   			ANCILLARY(PAY_OFFSET);
> +			ANCILLARY(RANDOM);
>   			}
>
>   			/* ancillary operation unknown or unsupported */
> @@ -1741,6 +1752,7 @@ void sk_decode_filter(struct sock_filter *filt, struct sock_filter *to)
>   		[BPF_S_ANC_VLAN_TAG]	= BPF_LD|BPF_B|BPF_ABS,
>   		[BPF_S_ANC_VLAN_TAG_PRESENT] = BPF_LD|BPF_B|BPF_ABS,
>   		[BPF_S_ANC_PAY_OFFSET]	= BPF_LD|BPF_B|BPF_ABS,
> +		[BPF_S_ANC_RANDOM]	= BPF_LD|BPF_B|BPF_ABS,
>   		[BPF_S_LD_W_LEN]	= BPF_LD|BPF_W|BPF_LEN,
>   		[BPF_S_LD_W_IND]	= BPF_LD|BPF_W|BPF_IND,
>   		[BPF_S_LD_H_IND]	= BPF_LD|BPF_H|BPF_IND,
> diff --git a/tools/net/bpf_exp.l b/tools/net/bpf_exp.l
> index bf7be77..804256f 100644
> --- a/tools/net/bpf_exp.l
> +++ b/tools/net/bpf_exp.l
> @@ -92,6 +92,7 @@ extern void yyerror(const char *str);
>   "#"?("cpu")	{ return K_CPU; }
>   "#"?("vlan_tci") { return K_VLANT; }
>   "#"?("vlan_pr")	{ return K_VLANP; }
> +"#"?("random")	{ return K_RAND; }

Thanks for also updating bpf_asm ! :)

I think using just "rnd" is cleaner here.

>   ":"		{ return ':'; }
>   ","		{ return ','; }
> diff --git a/tools/net/bpf_exp.y b/tools/net/bpf_exp.y
> index d15efc9..e6306c5 100644
> --- a/tools/net/bpf_exp.y
> +++ b/tools/net/bpf_exp.y
> @@ -56,7 +56,7 @@ static void bpf_set_jmp_label(char *label, enum jmp_type type);
>   %token OP_LDXI
>
>   %token K_PKT_LEN K_PROTO K_TYPE K_NLATTR K_NLATTR_NEST K_MARK K_QUEUE K_HATYPE
> -%token K_RXHASH K_CPU K_IFIDX K_VLANT K_VLANP K_POFF
> +%token K_RXHASH K_CPU K_IFIDX K_VLANT K_VLANP K_POFF K_RAND
>
>   %token ':' ',' '[' ']' '(' ')' 'x' 'a' '+' 'M' '*' '&' '#' '%'
>
> @@ -164,6 +164,9 @@ ldb
>   	| OP_LDB K_POFF {
>   		bpf_set_curr_instr(BPF_LD | BPF_B | BPF_ABS, 0, 0,
>   				   SKF_AD_OFF + SKF_AD_PAY_OFFSET); }
> +	| OP_LDB K_RAND {
> +		bpf_set_curr_instr(BPF_LD | BPF_B | BPF_ABS, 0, 0,
> +				   SKF_AD_OFF + SKF_AD_RANDOM); }
>   	;
>
>   ldh
> @@ -212,6 +215,9 @@ ldh
>   	| OP_LDH K_POFF {
>   		bpf_set_curr_instr(BPF_LD | BPF_H | BPF_ABS, 0, 0,
>   				   SKF_AD_OFF + SKF_AD_PAY_OFFSET); }
> +	| OP_LDH K_RAND {
> +		bpf_set_curr_instr(BPF_LD | BPF_H | BPF_ABS, 0, 0,
> +				   SKF_AD_OFF + SKF_AD_RANDOM); }
>   	;
>
>   ldi
> @@ -265,6 +271,9 @@ ld
>   	| OP_LD K_POFF {
>   		bpf_set_curr_instr(BPF_LD | BPF_W | BPF_ABS, 0, 0,
>   				   SKF_AD_OFF + SKF_AD_PAY_OFFSET); }
> +	| OP_LD K_RAND {
> +		bpf_set_curr_instr(BPF_LD | BPF_W | BPF_ABS, 0, 0,
> +				   SKF_AD_OFF + SKF_AD_RANDOM); }
>   	| OP_LD 'M' '[' number ']' {
>   		bpf_set_curr_instr(BPF_LD | BPF_MEM, 0, 0, $4); }
>   	| OP_LD '[' 'x' '+' number ']' {
> diff --git a/tools/net/icmp_random.bpf b/tools/net/icmp_random.bpf
> new file mode 100644
> index 0000000..b9adcbf
> --- /dev/null
> +++ b/tools/net/icmp_random.bpf
> @@ -0,0 +1,12 @@
> +# icmp random packet sampling, 1 in 4
> +ldh [12]
> +jne #0x800, drop
> +ldb [23]
> +jneq #1, drop
> +# get a random uint32 number
> +ld random
> +mod #4
> +jneq #1, drop
> +ret #-1
> +drop: ret #0
> +
>

This example should rather go into Documentation/networking/filter.txt's
example section, rather than tools/net/ .

Re: [PATCH] filter: added BPF random opcode

[Eric Dumazet]

On Tue, 2014-04-15 at 09:24 +0200, Daniel Borkmann wrote:

> > @@ -773,6 +779,7 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
> >   	case SKF_AD_OFF + SKF_AD_NLATTR:
> >   	case SKF_AD_OFF + SKF_AD_NLATTR_NEST:
> >   	case SKF_AD_OFF + SKF_AD_CPU:
> > +	case SKF_AD_OFF + SKF_AD_RANDOM:
> 
> I think instead of a function call, this sould rather be modelled
> directly into the internal insn set and thus converted differently,
> so we can spare us the call.

Hmmm... this would need percpu storage, thus preempt disable/enable
calls, and prandom_u32_state() is about 40 instructions.

This is really not worth the pain.

Re: [PATCH] filter: added BPF random opcode

[Daniel Borkmann]

On 04/15/2014 04:41 PM, Eric Dumazet wrote:
> On Tue, 2014-04-15 at 09:24 +0200, Daniel Borkmann wrote:
>
>>> @@ -773,6 +779,7 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
>>>    	case SKF_AD_OFF + SKF_AD_NLATTR:
>>>    	case SKF_AD_OFF + SKF_AD_NLATTR_NEST:
>>>    	case SKF_AD_OFF + SKF_AD_CPU:
>>> +	case SKF_AD_OFF + SKF_AD_RANDOM:
>>
>> I think instead of a function call, this sould rather be modelled
>> directly into the internal insn set and thus converted differently,
>> so we can spare us the call.
>
> Hmmm... this would need percpu storage, thus preempt disable/enable
> calls, and prandom_u32_state() is about 40 instructions.
>
> This is really not worth the pain.

Absolutely, that was not what I meant actually. Calling to
prandom_u32_state() is fine, no need to have another prng just
for that. I was just wondering if it makes sense to model that
directly as an instruction into a jump-table target that calls
prandom_u32() from there instead 'indirectly'. Need to think
about this a bit more ...

Re: [PATCH] filter: added BPF random opcode

[Chema Gonzalez]

On Tue, Apr 15, 2014 at 8:04 AM, Daniel Borkmann <dborkman@redhat.com> wrote:
> On 04/15/2014 04:41 PM, Eric Dumazet wrote:
>>
>> On Tue, 2014-04-15 at 09:24 +0200, Daniel Borkmann wrote:
>>
>>>> @@ -773,6 +779,7 @@ static bool convert_bpf_extensions(struct
>>>> sock_filter *fp,
>>>>         case SKF_AD_OFF + SKF_AD_NLATTR:
>>>>         case SKF_AD_OFF + SKF_AD_NLATTR_NEST:
>>>>         case SKF_AD_OFF + SKF_AD_CPU:
>>>> +       case SKF_AD_OFF + SKF_AD_RANDOM:
>>>
>>>
>>> I think instead of a function call, this sould rather be modelled
>>> directly into the internal insn set and thus converted differently,
>>> so we can spare us the call.
>>
>>
>> Hmmm... this would need percpu storage, thus preempt disable/enable
>> calls, and prandom_u32_state() is about 40 instructions.
>>
>> This is really not worth the pain.
>
>
> Absolutely, that was not what I meant actually. Calling to
> prandom_u32_state() is fine, no need to have another prng just
> for that. I was just wondering if it makes sense to model that
> directly as an instruction into a jump-table target that calls
> prandom_u32() from there instead 'indirectly'. Need to think
> about this a bit more ...
I thought about that. In fact, the original patch (written for
FreeBSD) worked by extending the ISA with a new load mode that did "A
= random();". After seeing your eBPF work, I got convinced that we
want to get a generic ISA when possible, where random is typically not
an insn. Also, the bpf_call approach makes it much easier to integrate
with the different JITs.

-Chema

Re: [PATCH] filter: added BPF random opcode

[Chema Gonzalez]

On Tue, Apr 15, 2014 at 12:24 AM, Daniel Borkmann <dborkman@redhat.com> wrote:
> Hi Chema,
>
> [cc'ing Alexei as well]
>
> note, net-next is still closed, so you might need to resend this later
> on again when it opens up.
I will. Thanks!

> On 04/15/2014 01:02 AM, Chema Gonzalez wrote:
>> diff --git a/tools/net/bpf_exp.l b/tools/net/bpf_exp.l
>> index bf7be77..804256f 100644
>> --- a/tools/net/bpf_exp.l
>> +++ b/tools/net/bpf_exp.l
>> @@ -92,6 +92,7 @@ extern void yyerror(const char *str);
>>   "#"?("cpu")   { return K_CPU; }
>>   "#"?("vlan_tci") { return K_VLANT; }
>>   "#"?("vlan_pr")       { return K_VLANP; }
>> +"#"?("random") { return K_RAND; }
>
>
> Thanks for also updating bpf_asm ! :)
bpf_asm was key in ensuring this worked. In fact, we should modify the
Makefile so that it relies on the local filter.h before the
/usr/include/ one (my Ubuntu Precise /usr/include/linux/filter.h does
not define BPF_MOD, BPF_XOR, SKF_AD_VLAN_TAG, SKF_AD_VLAN_TAG_PRESENT,
or SKF_AD_PAY_OFFSET).

> I think using just "rnd" is cleaner here.
I think using always random (in fact I may s/K_RAND/K_RANDOM/g) allows
easier grepping.

>> diff --git a/tools/net/icmp_random.bpf b/tools/net/icmp_random.bpf
>> new file mode 100644
>> index 0000000..b9adcbf
>> --- /dev/null
>> +++ b/tools/net/icmp_random.bpf
>> @@ -0,0 +1,12 @@
>> +# icmp random packet sampling, 1 in 4
>> +ldh [12]
>> +jne #0x800, drop
>> +ldb [23]
>> +jneq #1, drop
>> +# get a random uint32 number
>> +ld random
>> +mod #4
>> +jneq #1, drop
>> +ret #-1
>> +drop: ret #0
>> +
>>
>
> This example should rather go into Documentation/networking/filter.txt's
> example section, rather than tools/net/ .
I'll add it there.

Now, I'd like to add a new directory for BPF programs (tools/net/bpf/
?). It allows playing with bpf_asm.

-Chema

Re: [PATCH] filter: added BPF random opcode

[Daniel Borkmann]

On 04/15/2014 06:30 PM, Chema Gonzalez wrote:
> On Tue, Apr 15, 2014 at 12:24 AM, Daniel Borkmann <dborkman@redhat.com> wrote:
>> Hi Chema,
>>
>> [cc'ing Alexei as well]
>>
>> note, net-next is still closed, so you might need to resend this later
>> on again when it opens up.
> I will. Thanks!

Great, thanks.

>> On 04/15/2014 01:02 AM, Chema Gonzalez wrote:
>>> diff --git a/tools/net/bpf_exp.l b/tools/net/bpf_exp.l
>>> index bf7be77..804256f 100644
>>> --- a/tools/net/bpf_exp.l
>>> +++ b/tools/net/bpf_exp.l
>>> @@ -92,6 +92,7 @@ extern void yyerror(const char *str);
>>>    "#"?("cpu")   { return K_CPU; }
>>>    "#"?("vlan_tci") { return K_VLANT; }
>>>    "#"?("vlan_pr")       { return K_VLANP; }
>>> +"#"?("random") { return K_RAND; }
>>
>>
>> Thanks for also updating bpf_asm ! :)
> bpf_asm was key in ensuring this worked. In fact, we should modify the
> Makefile so that it relies on the local filter.h before the
> /usr/include/ one (my Ubuntu Precise /usr/include/linux/filter.h does
> not define BPF_MOD, BPF_XOR, SKF_AD_VLAN_TAG, SKF_AD_VLAN_TAG_PRESENT,
> or SKF_AD_PAY_OFFSET).

Good point, feel free to send a patch. :)

>> I think using just "rnd" is cleaner here.
> I think using always random (in fact I may s/K_RAND/K_RANDOM/g) allows
> easier grepping.

I know it's just nitpicking, but I'd be happier if that would
either be rnd or rand in bpf_asm.

>>> diff --git a/tools/net/icmp_random.bpf b/tools/net/icmp_random.bpf
>>> new file mode 100644
>>> index 0000000..b9adcbf
>>> --- /dev/null
>>> +++ b/tools/net/icmp_random.bpf
>>> @@ -0,0 +1,12 @@
>>> +# icmp random packet sampling, 1 in 4
>>> +ldh [12]
>>> +jne #0x800, drop
>>> +ldb [23]
>>> +jneq #1, drop
>>> +# get a random uint32 number
>>> +ld random
>>> +mod #4
>>> +jneq #1, drop
>>> +ret #-1
>>> +drop: ret #0
>>> +
>>>
>>
>> This example should rather go into Documentation/networking/filter.txt's
>> example section, rather than tools/net/ .
> I'll add it there.

Ok, thanks.

> Now, I'd like to add a new directory for BPF programs (tools/net/bpf/
> ?). It allows playing with bpf_asm.

For 'playing', I'd rather be happy to add that to the documentation file
in Documentation/networking/filter.txt where we have other examples, or
alternatively, if there is really no other way around, a new folder inside
of Documentation/networking/ .

Re: [PATCH] filter: added BPF random opcode

[Chema Gonzalez]

On Tue, Apr 15, 2014 at 9:44 AM, Daniel Borkmann <dborkman@redhat.com> wrote:
>>> I think using just "rnd" is cleaner here.
>>
>> I think using always random (in fact I may s/K_RAND/K_RANDOM/g) allows
>> easier grepping.
>
>
> I know it's just nitpicking, but I'd be happier if that would
> either be rnd or rand in bpf_asm.
"rand" it is.

>>> This example should rather go into Documentation/networking/filter.txt's
>>> example section, rather than tools/net/ .
>>
>> I'll add it there.
>
>
> Ok, thanks.
Done.

> For 'playing', I'd rather be happy to add that to the documentation file
> in Documentation/networking/filter.txt where we have other examples, or
> alternatively, if there is really no other way around, a new folder inside
> of Documentation/networking/ .
I think it would be better close to the tools/net/bpf* tools. Anyway,
I removed it for now.

-Chema

Re: [PATCH] filter: added BPF random opcode

[Alexei Starovoitov]

On Wed, Apr 16, 2014 at 6:38 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> On Tue, 2014-04-15 at 23:24 -0700, Alexei Starovoitov wrote:
>
>> In particular I don't find the reason of moving random
>> packet sampling into kernel to be that great.
>> pcap cannot receive them quickly enough anyway,
>> so there are drops already.
>> Just randomly pick packets that reached the user space.
>> Why add this to the kernel? I don't see how it can improve accuracy.
>
> It has nothing to do with speed or accuracy.
>
> Being able to intercept 0.001 % of the packets (and not 0.001 % of the
> flows...) can be useful to network operators.
>
> _Then_ if its super super super fast, thats better, of course.
>
> Suggesting to intercept all packets, then filtering 99.999 % of them in
> user space is not going to work. Its going to be super super super slow.

correct.
I was suggesting user space approach, because example does:
+  ld rand
+  mod #4
+  jneq #1, drop

If 4 is replaced with rate of packets per second and which can be
roughly estimated before creating the filter, then this example would
make sense.
On a loaded server the rate will be in tens of millions, but when it idles
this fixed rand()%1000000==1 won't be sending anything to
userspace for hours.

I suspect adding 'ld rand' just 'felt' useful and no real
filters were created with it.
For true packet sampling 'ld getnstime' would be needed too.
As I said I like the approach, I just want to see a real use case for it.

Re: [PATCH] filter: added BPF random opcode

[Eric Dumazet]

On Tue, 2014-04-15 at 23:24 -0700, Alexei Starovoitov wrote:

> In particular I don't find the reason of moving random
> packet sampling into kernel to be that great.
> pcap cannot receive them quickly enough anyway,
> so there are drops already.
> Just randomly pick packets that reached the user space.
> Why add this to the kernel? I don't see how it can improve accuracy.

It has nothing to do with speed or accuracy.

Being able to intercept 0.001 % of the packets (and not 0.001 % of the
flows...) can be useful to network operators.

_Then_ if its super super super fast, thats better, of course.

Suggesting to intercept all packets, then filtering 99.999 % of them in
user space is not going to work. Its going to be super super super slow.

Re: [PATCH] filter: added BPF random opcode

[Chema Gonzalez]

On Tue, Apr 15, 2014 at 11:24 PM, Alexei Starovoitov <ast@plumgrid.com> wrote:
> On Tue, Apr 15, 2014 at 11:16 AM, Chema Gonzalez <chema@google.com> wrote:
>> This should allow random packet sampling.
>
> I think commit log should have more than one line,
> especially for the new feature that affects uapi
I will beef it up in the next version (this time I'll wait for the
net-next window to open).

> In particular I don't find the reason of moving random
> packet sampling into kernel to be that great.
> pcap cannot receive them quickly enough anyway,
> so there are drops already.
> Just randomly pick packets that reached the user space.
> Why add this to the kernel? I don't see how it can improve accuracy.
The main use I see for this is random packet sampling. If you're
getting packet drops in pcap, you definitely want the kernel to do the
sampling. Sampling the packets that survived all the way through
userspace instead of the packets that arrived to the nic is biased.

The new message will be:

"""
filter: added BPF random opcode

Added a new ancillary load (bpf call in eBPF parlance) that produces
a 32-bit random number. We are implementing it as an ancillary load
(instead of an ISA opcode) because (a) it is simpler, (b) allows easy
JITing, and (c) seems more in line with generic ISAs that do not have
"get a random number" as a instruction, but as an OS call.

The main use for this ancillary load is to perform random packet sampling.
"""

> At the same time I think the extension technic itself is nice and clean :)
> The call approach is definitely how we envisioned it to be used.
> Right now we have only x86-64 jit that is waiting for net-next to be opened,
> but this extension will be automatically jit-ed due to 'call approach'. Nice.
>
> When you post patch revision please add vN tag.
I will.

>> +/* note that this only generates 32-bit random numbers */
>> +static u64 __skb_get_random(u64 ctx, u64 A, u64 X, u64 r4, u64 r5)
>
> function name is misleading. It has nothing to do with 'skb'. Please
> drop that prefix.
I renamed the function "__get_random_u32".

>> +{
>> +       return (u64)prandom_u32();
>
> we have 64-bit registers now, so would be nice to generalize it to 64-bit random
> since 8/16/32 can be made with bpf_and operation.
> but I don't see how to cleanly do it yet, so I guess the current form is fine.
>
> I like the approach, but would be nice to hear better justification
> for extending uapi.

-Chema

Re: [PATCH] filter: added BPF random opcode

[Daniel Borkmann]

On 04/16/2014 08:24 AM, Alexei Starovoitov wrote:
...
> At the same time I think the extension technic itself is nice and clean :)
> The call approach is definitely how we envisioned it to be used.
> Right now we have only x86-64 jit that is waiting for net-next to be opened,
> but this extension will be automatically jit-ed due to 'call approach'. Nice.

Ok, in terms of JIT it's definitely better that way, agreed.

Re: [PATCH] filter: added BPF random opcode

[Alexei Starovoitov]

On Tue, Apr 15, 2014 at 11:16 AM, Chema Gonzalez <chema@google.com> wrote:
> This should allow random packet sampling.

I think commit log should have more than one line,
especially for the new feature that affects uapi

In particular I don't find the reason of moving random
packet sampling into kernel to be that great.
pcap cannot receive them quickly enough anyway,
so there are drops already.
Just randomly pick packets that reached the user space.
Why add this to the kernel? I don't see how it can improve accuracy.

At the same time I think the extension technic itself is nice and clean :)
The call approach is definitely how we envisioned it to be used.
Right now we have only x86-64 jit that is waiting for net-next to be opened,
but this extension will be automatically jit-ed due to 'call approach'. Nice.

When you post patch revision please add vN tag.

Minor nits below:

> Signed-off-by: Chema Gonzalez <chema@google.com>
> ---
>  Documentation/networking/filter.txt | 13 +++++++++++++
>  include/linux/filter.h              |  1 +
>  include/uapi/linux/filter.h         |  3 ++-
>  net/core/filter.c                   | 12 ++++++++++++
>  tools/net/bpf_exp.l                 |  1 +
>  tools/net/bpf_exp.y                 | 11 ++++++++++-
>  6 files changed, 39 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt
> index 81f940f..82e1cb0 100644
> --- a/Documentation/networking/filter.txt
> +++ b/Documentation/networking/filter.txt
> @@ -281,6 +281,7 @@ Possible BPF extensions are shown in the following table:
>    cpu                                   raw_smp_processor_id()
>    vlan_tci                              vlan_tx_tag_get(skb)
>    vlan_pr                               vlan_tx_tag_present(skb)
> +  rand                                  prandom_u32()
>
>  These extensions can also be prefixed with '#'.
>  Examples for low-level BPF:
> @@ -308,6 +309,18 @@ Examples for low-level BPF:
>    ret #-1
>    drop: ret #0
>
> +** icmp random packet sampling, 1 in 4
> +  ldh [12]
> +  jne #0x800, drop
> +  ldb [23]
> +  jneq #1, drop
> +  # get a random uint32 number
> +  ld rand
> +  mod #4
> +  jneq #1, drop
> +  ret #-1
> +  drop: ret #0
> +
>  ** SECCOMP filter example:
>
>    ld [4]                  /* offsetof(struct seccomp_data, arch) */
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 262dcbb..49c28aa 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -224,6 +224,7 @@ enum {
>         BPF_S_ANC_VLAN_TAG,
>         BPF_S_ANC_VLAN_TAG_PRESENT,
>         BPF_S_ANC_PAY_OFFSET,
> +       BPF_S_ANC_RANDOM,
>  };
>
>  #endif /* __LINUX_FILTER_H__ */
> diff --git a/include/uapi/linux/filter.h b/include/uapi/linux/filter.h
> index 8eb9cca..253b4d4 100644
> --- a/include/uapi/linux/filter.h
> +++ b/include/uapi/linux/filter.h
> @@ -130,7 +130,8 @@ struct sock_fprog { /* Required for SO_ATTACH_FILTER. */
>  #define SKF_AD_VLAN_TAG        44
>  #define SKF_AD_VLAN_TAG_PRESENT 48
>  #define SKF_AD_PAY_OFFSET      52
> -#define SKF_AD_MAX     56
> +#define SKF_AD_RANDOM  56
> +#define SKF_AD_MAX     60
>  #define SKF_NET_OFF   (-0x100000)
>  #define SKF_LL_OFF    (-0x200000)
>
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 765556b..b2a80a1 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -637,6 +637,12 @@ static u64 __get_raw_cpu_id(u64 ctx, u64 A, u64 X, u64 r4, u64 r5)
>         return raw_smp_processor_id();
>  }
>
> +/* note that this only generates 32-bit random numbers */
> +static u64 __skb_get_random(u64 ctx, u64 A, u64 X, u64 r4, u64 r5)

function name is misleading. It has nothing to do with 'skb'. Please
drop that prefix.

> +{
> +       return (u64)prandom_u32();

we have 64-bit registers now, so would be nice to generalize it to 64-bit random
since 8/16/32 can be made with bpf_and operation.
but I don't see how to cleanly do it yet, so I guess the current form is fine.

I like the approach, but would be nice to hear better justification
for extending uapi.

Thanks!

> +}
> +
>  /* Register mappings for user programs. */
>  #define A_REG          0
>  #define X_REG          7
> @@ -773,6 +779,7 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
>         case SKF_AD_OFF + SKF_AD_NLATTR:
>         case SKF_AD_OFF + SKF_AD_NLATTR_NEST:
>         case SKF_AD_OFF + SKF_AD_CPU:
> +       case SKF_AD_OFF + SKF_AD_RANDOM:
>                 /* arg1 = ctx */
>                 insn->code = BPF_ALU64 | BPF_MOV | BPF_X;
>                 insn->a_reg = ARG1_REG;
> @@ -806,6 +813,9 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
>                 case SKF_AD_OFF + SKF_AD_CPU:
>                         insn->imm = __get_raw_cpu_id - __bpf_call_base;
>                         break;
> +               case SKF_AD_OFF + SKF_AD_RANDOM:
> +                       insn->imm = __skb_get_random - __bpf_call_base;
> +                       break;
>                 }
>                 break;
>
> @@ -1356,6 +1366,7 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
>                         ANCILLARY(VLAN_TAG);
>                         ANCILLARY(VLAN_TAG_PRESENT);
>                         ANCILLARY(PAY_OFFSET);
> +                       ANCILLARY(RANDOM);
>                         }
>
>                         /* ancillary operation unknown or unsupported */
> @@ -1741,6 +1752,7 @@ void sk_decode_filter(struct sock_filter *filt, struct sock_filter *to)
>                 [BPF_S_ANC_VLAN_TAG]    = BPF_LD|BPF_B|BPF_ABS,
>                 [BPF_S_ANC_VLAN_TAG_PRESENT] = BPF_LD|BPF_B|BPF_ABS,
>                 [BPF_S_ANC_PAY_OFFSET]  = BPF_LD|BPF_B|BPF_ABS,
> +               [BPF_S_ANC_RANDOM]      = BPF_LD|BPF_B|BPF_ABS,
>                 [BPF_S_LD_W_LEN]        = BPF_LD|BPF_W|BPF_LEN,
>                 [BPF_S_LD_W_IND]        = BPF_LD|BPF_W|BPF_IND,
>                 [BPF_S_LD_H_IND]        = BPF_LD|BPF_H|BPF_IND,
> diff --git a/tools/net/bpf_exp.l b/tools/net/bpf_exp.l
> index bf7be77..833a966 100644
> --- a/tools/net/bpf_exp.l
> +++ b/tools/net/bpf_exp.l
> @@ -92,6 +92,7 @@ extern void yyerror(const char *str);
>  "#"?("cpu")    { return K_CPU; }
>  "#"?("vlan_tci") { return K_VLANT; }
>  "#"?("vlan_pr")        { return K_VLANP; }
> +"#"?("rand")   { return K_RAND; }
>
>  ":"            { return ':'; }
>  ","            { return ','; }
> diff --git a/tools/net/bpf_exp.y b/tools/net/bpf_exp.y
> index d15efc9..e6306c5 100644
> --- a/tools/net/bpf_exp.y
> +++ b/tools/net/bpf_exp.y
> @@ -56,7 +56,7 @@ static void bpf_set_jmp_label(char *label, enum jmp_type type);
>  %token OP_LDXI
>
>  %token K_PKT_LEN K_PROTO K_TYPE K_NLATTR K_NLATTR_NEST K_MARK K_QUEUE K_HATYPE
> -%token K_RXHASH K_CPU K_IFIDX K_VLANT K_VLANP K_POFF
> +%token K_RXHASH K_CPU K_IFIDX K_VLANT K_VLANP K_POFF K_RAND
>
>  %token ':' ',' '[' ']' '(' ')' 'x' 'a' '+' 'M' '*' '&' '#' '%'
>
> @@ -164,6 +164,9 @@ ldb
>         | OP_LDB K_POFF {
>                 bpf_set_curr_instr(BPF_LD | BPF_B | BPF_ABS, 0, 0,
>                                    SKF_AD_OFF + SKF_AD_PAY_OFFSET); }
> +       | OP_LDB K_RAND {
> +               bpf_set_curr_instr(BPF_LD | BPF_B | BPF_ABS, 0, 0,
> +                                  SKF_AD_OFF + SKF_AD_RANDOM); }
>         ;
>
>  ldh
> @@ -212,6 +215,9 @@ ldh
>         | OP_LDH K_POFF {
>                 bpf_set_curr_instr(BPF_LD | BPF_H | BPF_ABS, 0, 0,
>                                    SKF_AD_OFF + SKF_AD_PAY_OFFSET); }
> +       | OP_LDH K_RAND {
> +               bpf_set_curr_instr(BPF_LD | BPF_H | BPF_ABS, 0, 0,
> +                                  SKF_AD_OFF + SKF_AD_RANDOM); }
>         ;
>
>  ldi
> @@ -265,6 +271,9 @@ ld
>         | OP_LD K_POFF {
>                 bpf_set_curr_instr(BPF_LD | BPF_W | BPF_ABS, 0, 0,
>                                    SKF_AD_OFF + SKF_AD_PAY_OFFSET); }
> +       | OP_LD K_RAND {
> +               bpf_set_curr_instr(BPF_LD | BPF_W | BPF_ABS, 0, 0,
> +                                  SKF_AD_OFF + SKF_AD_RANDOM); }
>         | OP_LD 'M' '[' number ']' {
>                 bpf_set_curr_instr(BPF_LD | BPF_MEM, 0, 0, $4); }
>         | OP_LD '[' 'x' '+' number ']' {
> --
> 1.9.1.423.g4596e3a
>

[PATCH] filter: added BPF random opcode

[Chema Gonzalez]

This should allow random packet sampling.

Signed-off-by: Chema Gonzalez <chema@google.com>
---
 Documentation/networking/filter.txt | 13 +++++++++++++
 include/linux/filter.h              |  1 +
 include/uapi/linux/filter.h         |  3 ++-
 net/core/filter.c                   | 12 ++++++++++++
 tools/net/bpf_exp.l                 |  1 +
 tools/net/bpf_exp.y                 | 11 ++++++++++-
 6 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt
index 81f940f..82e1cb0 100644
--- a/Documentation/networking/filter.txt
+++ b/Documentation/networking/filter.txt
@@ -281,6 +281,7 @@ Possible BPF extensions are shown in the following table:
   cpu                                   raw_smp_processor_id()
   vlan_tci                              vlan_tx_tag_get(skb)
   vlan_pr                               vlan_tx_tag_present(skb)
+  rand                                  prandom_u32()
 
 These extensions can also be prefixed with '#'.
 Examples for low-level BPF:
@@ -308,6 +309,18 @@ Examples for low-level BPF:
   ret #-1
   drop: ret #0
 
+** icmp random packet sampling, 1 in 4
+  ldh [12]
+  jne #0x800, drop
+  ldb [23]
+  jneq #1, drop
+  # get a random uint32 number
+  ld rand
+  mod #4
+  jneq #1, drop
+  ret #-1
+  drop: ret #0
+
 ** SECCOMP filter example:
 
   ld [4]                  /* offsetof(struct seccomp_data, arch) */
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 262dcbb..49c28aa 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -224,6 +224,7 @@ enum {
 	BPF_S_ANC_VLAN_TAG,
 	BPF_S_ANC_VLAN_TAG_PRESENT,
 	BPF_S_ANC_PAY_OFFSET,
+	BPF_S_ANC_RANDOM,
 };
 
 #endif /* __LINUX_FILTER_H__ */
diff --git a/include/uapi/linux/filter.h b/include/uapi/linux/filter.h
index 8eb9cca..253b4d4 100644
--- a/include/uapi/linux/filter.h
+++ b/include/uapi/linux/filter.h
@@ -130,7 +130,8 @@ struct sock_fprog {	/* Required for SO_ATTACH_FILTER. */
 #define SKF_AD_VLAN_TAG	44
 #define SKF_AD_VLAN_TAG_PRESENT 48
 #define SKF_AD_PAY_OFFSET	52
-#define SKF_AD_MAX	56
+#define SKF_AD_RANDOM	56
+#define SKF_AD_MAX	60
 #define SKF_NET_OFF   (-0x100000)
 #define SKF_LL_OFF    (-0x200000)
 
diff --git a/net/core/filter.c b/net/core/filter.c
index 765556b..b2a80a1 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -637,6 +637,12 @@ static u64 __get_raw_cpu_id(u64 ctx, u64 A, u64 X, u64 r4, u64 r5)
 	return raw_smp_processor_id();
 }
 
+/* note that this only generates 32-bit random numbers */
+static u64 __skb_get_random(u64 ctx, u64 A, u64 X, u64 r4, u64 r5)
+{
+	return (u64)prandom_u32();
+}
+
 /* Register mappings for user programs. */
 #define A_REG		0
 #define X_REG		7
@@ -773,6 +779,7 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
 	case SKF_AD_OFF + SKF_AD_NLATTR:
 	case SKF_AD_OFF + SKF_AD_NLATTR_NEST:
 	case SKF_AD_OFF + SKF_AD_CPU:
+	case SKF_AD_OFF + SKF_AD_RANDOM:
 		/* arg1 = ctx */
 		insn->code = BPF_ALU64 | BPF_MOV | BPF_X;
 		insn->a_reg = ARG1_REG;
@@ -806,6 +813,9 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
 		case SKF_AD_OFF + SKF_AD_CPU:
 			insn->imm = __get_raw_cpu_id - __bpf_call_base;
 			break;
+		case SKF_AD_OFF + SKF_AD_RANDOM:
+			insn->imm = __skb_get_random - __bpf_call_base;
+			break;
 		}
 		break;
 
@@ -1356,6 +1366,7 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
 			ANCILLARY(VLAN_TAG);
 			ANCILLARY(VLAN_TAG_PRESENT);
 			ANCILLARY(PAY_OFFSET);
+			ANCILLARY(RANDOM);
 			}
 
 			/* ancillary operation unknown or unsupported */
@@ -1741,6 +1752,7 @@ void sk_decode_filter(struct sock_filter *filt, struct sock_filter *to)
 		[BPF_S_ANC_VLAN_TAG]	= BPF_LD|BPF_B|BPF_ABS,
 		[BPF_S_ANC_VLAN_TAG_PRESENT] = BPF_LD|BPF_B|BPF_ABS,
 		[BPF_S_ANC_PAY_OFFSET]	= BPF_LD|BPF_B|BPF_ABS,
+		[BPF_S_ANC_RANDOM]	= BPF_LD|BPF_B|BPF_ABS,
 		[BPF_S_LD_W_LEN]	= BPF_LD|BPF_W|BPF_LEN,
 		[BPF_S_LD_W_IND]	= BPF_LD|BPF_W|BPF_IND,
 		[BPF_S_LD_H_IND]	= BPF_LD|BPF_H|BPF_IND,
diff --git a/tools/net/bpf_exp.l b/tools/net/bpf_exp.l
index bf7be77..833a966 100644
--- a/tools/net/bpf_exp.l
+++ b/tools/net/bpf_exp.l
@@ -92,6 +92,7 @@ extern void yyerror(const char *str);
 "#"?("cpu")	{ return K_CPU; }
 "#"?("vlan_tci") { return K_VLANT; }
 "#"?("vlan_pr")	{ return K_VLANP; }
+"#"?("rand")	{ return K_RAND; }
 
 ":"		{ return ':'; }
 ","		{ return ','; }
diff --git a/tools/net/bpf_exp.y b/tools/net/bpf_exp.y
index d15efc9..e6306c5 100644
--- a/tools/net/bpf_exp.y
+++ b/tools/net/bpf_exp.y
@@ -56,7 +56,7 @@ static void bpf_set_jmp_label(char *label, enum jmp_type type);
 %token OP_LDXI
 
 %token K_PKT_LEN K_PROTO K_TYPE K_NLATTR K_NLATTR_NEST K_MARK K_QUEUE K_HATYPE
-%token K_RXHASH K_CPU K_IFIDX K_VLANT K_VLANP K_POFF
+%token K_RXHASH K_CPU K_IFIDX K_VLANT K_VLANP K_POFF K_RAND
 
 %token ':' ',' '[' ']' '(' ')' 'x' 'a' '+' 'M' '*' '&' '#' '%'
 
@@ -164,6 +164,9 @@ ldb
 	| OP_LDB K_POFF {
 		bpf_set_curr_instr(BPF_LD | BPF_B | BPF_ABS, 0, 0,
 				   SKF_AD_OFF + SKF_AD_PAY_OFFSET); }
+	| OP_LDB K_RAND {
+		bpf_set_curr_instr(BPF_LD | BPF_B | BPF_ABS, 0, 0,
+				   SKF_AD_OFF + SKF_AD_RANDOM); }
 	;
 
 ldh
@@ -212,6 +215,9 @@ ldh
 	| OP_LDH K_POFF {
 		bpf_set_curr_instr(BPF_LD | BPF_H | BPF_ABS, 0, 0,
 				   SKF_AD_OFF + SKF_AD_PAY_OFFSET); }
+	| OP_LDH K_RAND {
+		bpf_set_curr_instr(BPF_LD | BPF_H | BPF_ABS, 0, 0,
+				   SKF_AD_OFF + SKF_AD_RANDOM); }
 	;
 
 ldi
@@ -265,6 +271,9 @@ ld
 	| OP_LD K_POFF {
 		bpf_set_curr_instr(BPF_LD | BPF_W | BPF_ABS, 0, 0,
 				   SKF_AD_OFF + SKF_AD_PAY_OFFSET); }
+	| OP_LD K_RAND {
+		bpf_set_curr_instr(BPF_LD | BPF_W | BPF_ABS, 0, 0,
+				   SKF_AD_OFF + SKF_AD_RANDOM); }
 	| OP_LD 'M' '[' number ']' {
 		bpf_set_curr_instr(BPF_LD | BPF_MEM, 0, 0, $4); }
 	| OP_LD '[' 'x' '+' number ']' {
-- 
1.9.1.423.g4596e3a