[PATCH v2 net-next] net: filter: export pkt_type_offset() helper

[Denis Kirjanov <kda@linux-powerpc.org>]

Currently we have 2 pkt_type_offset functions doing
the same thing and spread across the architecture files.
Let's use the generic helper routine.

Signed-off-by: Denis Kirjanov <kda@linux-powerpc.org>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Daniel Borkmann <dborkman@redhat.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>

V2: Initialize the pkt_type_offset through the pure_initcall()
---
 arch/mips/net/bpf_jit.c      | 27 ++-------------------------
 arch/s390/net/bpf_jit_comp.c | 31 -------------------------------
 include/linux/filter.h       |  2 ++
 net/core/filter.c            | 16 +++++++++++++---
 4 files changed, 17 insertions(+), 59 deletions(-)

diff --git a/arch/mips/net/bpf_jit.c b/arch/mips/net/bpf_jit.c
index 05a5661..bb9b53f 100644
--- a/arch/mips/net/bpf_jit.c
+++ b/arch/mips/net/bpf_jit.c
@@ -765,27 +765,6 @@ static u64 jit_get_skb_w(struct sk_buff *skb, unsigned offset)
 	return (u64)err << 32 | ntohl(ret);
 }
 
-#ifdef __BIG_ENDIAN_BITFIELD
-#define PKT_TYPE_MAX	(7 << 5)
-#else
-#define PKT_TYPE_MAX	7
-#endif
-static int pkt_type_offset(void)
-{
-	struct sk_buff skb_probe = {
-		.pkt_type = ~0,
-	};
-	u8 *ct = (u8 *)&skb_probe;
-	unsigned int off;
-
-	for (off = 0; off < sizeof(struct sk_buff); off++) {
-		if (ct[off] == PKT_TYPE_MAX)
-			return off;
-	}
-	pr_err_once("Please fix pkt_type_offset(), as pkt_type couldn't be found\n");
-	return -1;
-}
-
 static int build_body(struct jit_ctx *ctx)
 {
 	void *load_func[] = {jit_get_skb_b, jit_get_skb_h, jit_get_skb_w};
@@ -1332,11 +1311,9 @@ jmp_cmp:
 		case BPF_ANC | SKF_AD_PKTTYPE:
 			ctx->flags |= SEEN_SKB;
 
-			off = pkt_type_offset();
-
-			if (off < 0)
+			if (pkt_type_offset < 0)
 				return -1;
-			emit_load_byte(r_tmp, r_skb, off, ctx);
+			emit_load_byte(r_tmp, r_skb, pkt_type_offset, ctx);
 			/* Keep only the last 3 bits */
 			emit_andi(r_A, r_tmp, PKT_TYPE_MAX, ctx);
 #ifdef __BIG_ENDIAN_BITFIELD
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 61e45b7..caa0cab 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -223,37 +223,6 @@ static void bpf_jit_epilogue(struct bpf_jit *jit)
 	EMIT2(0x07fe);
 }
 
-/* Helper to find the offset of pkt_type in sk_buff
- * Make sure its still a 3bit field starting at the MSBs within a byte.
- */
-#define PKT_TYPE_MAX 0xe0
-static int pkt_type_offset;
-
-static int __init bpf_pkt_type_offset_init(void)
-{
-	struct sk_buff skb_probe = {
-		.pkt_type = ~0,
-	};
-	char *ct = (char *)&skb_probe;
-	int off;
-
-	pkt_type_offset = -1;
-	for (off = 0; off < sizeof(struct sk_buff); off++) {
-		if (!ct[off])
-			continue;
-		if (ct[off] == PKT_TYPE_MAX)
-			pkt_type_offset = off;
-		else {
-			/* Found non matching bit pattern, fix needed. */
-			WARN_ON_ONCE(1);
-			pkt_type_offset = -1;
-			return -1;
-		}
-	}
-	return 0;
-}
-device_initcall(bpf_pkt_type_offset_init);
-
 /*
  * make sure we dont leak kernel information to user
  */
diff --git a/include/linux/filter.h b/include/linux/filter.h
index a5227ab..6814b54 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -424,6 +424,8 @@ static inline void *bpf_load_pointer(const struct sk_buff *skb, int k,
 	return bpf_internal_load_pointer_neg_helper(skb, k, size);
 }
 
+extern __read_mostly int pkt_type_offset;
+
 #ifdef CONFIG_BPF_JIT
 #include <stdarg.h>
 #include <linux/linkage.h>
diff --git a/net/core/filter.c b/net/core/filter.c
index d814b8a..edd17f1 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -96,21 +96,29 @@ EXPORT_SYMBOL(sk_filter);
 #else
 #define PKT_TYPE_MAX	7
 #endif
-static unsigned int pkt_type_offset(void)
+
+__read_mostly int pkt_type_offset;
+
+static int __init init_pkt_type_offset(void)
 {
 	struct sk_buff skb_probe = { .pkt_type = ~0, };
 	u8 *ct = (u8 *) &skb_probe;
 	unsigned int off;
 
+	pkt_type_offset = -1;
 	for (off = 0; off < sizeof(struct sk_buff); off++) {
-		if (ct[off] == PKT_TYPE_MAX)
+		if (ct[off] == PKT_TYPE_MAX) {
+			pkt_type_offset = off;
 			return off;
+		}
 	}
 
 	pr_err_once("Please fix %s, as pkt_type couldn't be found!\n", __func__);
 	return -1;
 }
 
+pure_initcall(init_pkt_type_offset);
+
 static u64 __skb_get_pay_offset(u64 ctx, u64 a, u64 x, u64 r4, u64 r5)
 {
 	return __skb_get_poff((struct sk_buff *)(unsigned long) ctx);
@@ -190,8 +198,10 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
 		break;
 
 	case SKF_AD_OFF + SKF_AD_PKTTYPE:
+		if (pkt_type_offset < 0)
+			return false;
 		*insn = BPF_LDX_MEM(BPF_B, BPF_REG_A, BPF_REG_CTX,
-				    pkt_type_offset());
+				    pkt_type_offset);
 		if (insn->off < 0)
 			return false;
 		insn++;
-- 
2.0.0