net: filter: cleanup A/X name usage

The macro 'A' used in internal BPF interpreter:
 #define A regs[insn->a_reg]
was easily confused with the name of classic BPF register 'A', since
'A' would mean two different things depending on context.

This patch is trying to clean up the naming and clarify its usage in the
following way:

- A and X are names of two classic BPF registers

- BPF_REG_A denotes internal BPF register R0 used to map classic register A
  in internal BPF programs generated from classic

- BPF_REG_X denotes internal BPF register R7 used to map classic register X
  in internal BPF programs generated from classic

- internal BPF instruction format:
struct sock_filter_int {
        __u8    code;           /* opcode */
        __u8    dst_reg:4;      /* dest register */
        __u8    src_reg:4;      /* source register */
        __s16   off;            /* signed offset */
        __s32   imm;            /* signed immediate constant */
};

- BPF_X/BPF_K is 1 bit used to encode source operand of instruction
In classic:
  BPF_X - means use register X as source operand
  BPF_K - means use 32-bit immediate as source operand
In internal:
  BPF_X - means use 'src_reg' register as source operand
  BPF_K - means use 32-bit immediate as source operand

Suggested-by: Chema Gonzalez <chema@google.com>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Chema Gonzalez <chema@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 99 insertions, 99 deletions

diff --git a/net/core/filter.c b/net/core/filter.c
index 6bd2e35..b3f2175 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -59,12 +59,12 @@
 #define BPF_R10	regs[BPF_REG_10]
 
 /* Named registers */
-#define A	regs[insn->a_reg]
-#define X	regs[insn->x_reg]
+#define DST	regs[insn->dst_reg]
+#define SRC	regs[insn->src_reg]
 #define FP	regs[BPF_REG_FP]
 #define ARG1	regs[BPF_REG_ARG1]
 #define CTX	regs[BPF_REG_CTX]
-#define K	insn->imm
+#define IMM	insn->imm
 
 /* No hurry in this branch
  *
@@ -264,7 +264,7 @@ static unsigned int __sk_run_filter(void *ctx, const struct sock_filter_int *ins
 	FP = (u64) (unsigned long) &stack[ARRAY_SIZE(stack)];
 	ARG1 = (u64) (unsigned long) ctx;
 
-	/* Register for user BPF programs need to be reset first. */
+	/* Registers used in classic BPF programs need to be reset first. */
 	regs[BPF_REG_A] = 0;
 	regs[BPF_REG_X] = 0;
 
@@ -274,16 +274,16 @@ select_insn:
 	/* ALU */
 #define ALU(OPCODE, OP)			\
 	ALU64_##OPCODE##_X:		\
-		A = A OP X;		\
+		DST = DST OP SRC;	\
 		CONT;			\
 	ALU_##OPCODE##_X:		\
-		A = (u32) A OP (u32) X;	\
+		DST = (u32) DST OP (u32) SRC;	\
 		CONT;			\
 	ALU64_##OPCODE##_K:		\
-		A = A OP K;		\
+		DST = DST OP IMM;		\
 		CONT;			\
 	ALU_##OPCODE##_K:		\
-		A = (u32) A OP (u32) K;	\
+		DST = (u32) DST OP (u32) IMM;	\
 		CONT;
 
 	ALU(ADD,  +)
@@ -296,92 +296,92 @@ select_insn:
 	ALU(MUL,  *)
 #undef ALU
 	ALU_NEG:
-		A = (u32) -A;
+		DST = (u32) -DST;
 		CONT;
 	ALU64_NEG:
-		A = -A;
+		DST = -DST;
 		CONT;
 	ALU_MOV_X:
-		A = (u32) X;
+		DST = (u32) SRC;
 		CONT;
 	ALU_MOV_K:
-		A = (u32) K;
+		DST = (u32) IMM;
 		CONT;
 	ALU64_MOV_X:
-		A = X;
+		DST = SRC;
 		CONT;
 	ALU64_MOV_K:
-		A = K;
+		DST = IMM;
 		CONT;
 	ALU64_ARSH_X:
-		(*(s64 *) &A) >>= X;
+		(*(s64 *) &DST) >>= SRC;
 		CONT;
 	ALU64_ARSH_K:
-		(*(s64 *) &A) >>= K;
+		(*(s64 *) &DST) >>= IMM;
 		CONT;
 	ALU64_MOD_X:
-		if (unlikely(X == 0))
+		if (unlikely(SRC == 0))
 			return 0;
-		tmp = A;
-		A = do_div(tmp, X);
+		tmp = DST;
+		DST = do_div(tmp, SRC);
 		CONT;
 	ALU_MOD_X:
-		if (unlikely(X == 0))
+		if (unlikely(SRC == 0))
 			return 0;
-		tmp = (u32) A;
-		A = do_div(tmp, (u32) X);
+		tmp = (u32) DST;
+		DST = do_div(tmp, (u32) SRC);
 		CONT;
 	ALU64_MOD_K:
-		tmp = A;
-		A = do_div(tmp, K);
+		tmp = DST;
+		DST = do_div(tmp, IMM);
 		CONT;
 	ALU_MOD_K:
-		tmp = (u32) A;
-		A = do_div(tmp, (u32) K);
+		tmp = (u32) DST;
+		DST = do_div(tmp, (u32) IMM);
 		CONT;
 	ALU64_DIV_X:
-		if (unlikely(X == 0))
+		if (unlikely(SRC == 0))
 			return 0;
-		do_div(A, X);
+		do_div(DST, SRC);
 		CONT;
 	ALU_DIV_X:
-		if (unlikely(X == 0))
+		if (unlikely(SRC == 0))
 			return 0;
-		tmp = (u32) A;
-		do_div(tmp, (u32) X);
-		A = (u32) tmp;
+		tmp = (u32) DST;
+		do_div(tmp, (u32) SRC);
+		DST = (u32) tmp;
 		CONT;
 	ALU64_DIV_K:
-		do_div(A, K);
+		do_div(DST, IMM);
 		CONT;
 	ALU_DIV_K:
-		tmp = (u32) A;
-		do_div(tmp, (u32) K);
-		A = (u32) tmp;
+		tmp = (u32) DST;
+		do_div(tmp, (u32) IMM);
+		DST = (u32) tmp;
 		CONT;
 	ALU_END_TO_BE:
-		switch (K) {
+		switch (IMM) {
 		case 16:
-			A = (__force u16) cpu_to_be16(A);
+			DST = (__force u16) cpu_to_be16(DST);
 			break;
 		case 32:
-			A = (__force u32) cpu_to_be32(A);
+			DST = (__force u32) cpu_to_be32(DST);
 			break;
 		case 64:
-			A = (__force u64) cpu_to_be64(A);
+			DST = (__force u64) cpu_to_be64(DST);
 			break;
 		}
 		CONT;
 	ALU_END_TO_LE:
-		switch (K) {
+		switch (IMM) {
 		case 16:
-			A = (__force u16) cpu_to_le16(A);
+			DST = (__force u16) cpu_to_le16(DST);
 			break;
 		case 32:
-			A = (__force u32) cpu_to_le32(A);
+			DST = (__force u32) cpu_to_le32(DST);
 			break;
 		case 64:
-			A = (__force u64) cpu_to_le64(A);
+			DST = (__force u64) cpu_to_le64(DST);
 			break;
 		}
 		CONT;
@@ -401,85 +401,85 @@ select_insn:
 		insn += insn->off;
 		CONT;
 	JMP_JEQ_X:
-		if (A == X) {
+		if (DST == SRC) {
 			insn += insn->off;
 			CONT_JMP;
 		}
 		CONT;
 	JMP_JEQ_K:
-		if (A == K) {
+		if (DST == IMM) {
 			insn += insn->off;
 			CONT_JMP;
 		}
 		CONT;
 	JMP_JNE_X:
-		if (A != X) {
+		if (DST != SRC) {
 			insn += insn->off;
 			CONT_JMP;
 		}
 		CONT;
 	JMP_JNE_K:
-		if (A != K) {
+		if (DST != IMM) {
 			insn += insn->off;
 			CONT_JMP;
 		}
 		CONT;
 	JMP_JGT_X:
-		if (A > X) {
+		if (DST > SRC) {
 			insn += insn->off;
 			CONT_JMP;
 		}
 		CONT;
 	JMP_JGT_K:
-		if (A > K) {
+		if (DST > IMM) {
 			insn += insn->off;
 			CONT_JMP;
 		}
 		CONT;
 	JMP_JGE_X:
-		if (A >= X) {
+		if (DST >= SRC) {
 			insn += insn->off;
 			CONT_JMP;
 		}
 		CONT;
 	JMP_JGE_K:
-		if (A >= K) {
+		if (DST >= IMM) {
 			insn += insn->off;
 			CONT_JMP;
 		}
 		CONT;
 	JMP_JSGT_X:
-		if (((s64) A) > ((s64) X)) {
+		if (((s64) DST) > ((s64) SRC)) {
 			insn += insn->off;
 			CONT_JMP;
 		}
 		CONT;
 	JMP_JSGT_K:
-		if (((s64) A) > ((s64) K)) {
+		if (((s64) DST) > ((s64) IMM)) {
 			insn += insn->off;
 			CONT_JMP;
 		}
 		CONT;
 	JMP_JSGE_X:
-		if (((s64) A) >= ((s64) X)) {
+		if (((s64) DST) >= ((s64) SRC)) {
 			insn += insn->off;
 			CONT_JMP;
 		}
 		CONT;
 	JMP_JSGE_K:
-		if (((s64) A) >= ((s64) K)) {
+		if (((s64) DST) >= ((s64) IMM)) {
 			insn += insn->off;
 			CONT_JMP;
 		}
 		CONT;
 	JMP_JSET_X:
-		if (A & X) {
+		if (DST & SRC) {
 			insn += insn->off;
 			CONT_JMP;
 		}
 		CONT;
 	JMP_JSET_K:
-		if (A & K) {
+		if (DST & IMM) {
 			insn += insn->off;
 			CONT_JMP;
 		}
@@ -488,15 +488,15 @@ select_insn:
 		return BPF_R0;
 
 	/* STX and ST and LDX*/
-#define LDST(SIZEOP, SIZE)					\
-	STX_MEM_##SIZEOP:					\
-		*(SIZE *)(unsigned long) (A + insn->off) = X;	\
-		CONT;						\
-	ST_MEM_##SIZEOP:					\
-		*(SIZE *)(unsigned long) (A + insn->off) = K;	\
-		CONT;						\
-	LDX_MEM_##SIZEOP:					\
-		A = *(SIZE *)(unsigned long) (X + insn->off);	\
+#define LDST(SIZEOP, SIZE)						\
+	STX_MEM_##SIZEOP:						\
+		*(SIZE *)(unsigned long) (DST + insn->off) = SRC;	\
+		CONT;							\
+	ST_MEM_##SIZEOP:						\
+		*(SIZE *)(unsigned long) (DST + insn->off) = IMM;	\
+		CONT;							\
+	LDX_MEM_##SIZEOP:						\
+		DST = *(SIZE *)(unsigned long) (SRC + insn->off);	\
 		CONT;
 
 	LDST(B,   u8)
@@ -504,16 +504,16 @@ select_insn:
 	LDST(W,  u32)
 	LDST(DW, u64)
 #undef LDST
-	STX_XADD_W: /* lock xadd *(u32 *)(A + insn->off) += X */
-		atomic_add((u32) X, (atomic_t *)(unsigned long)
-			   (A + insn->off));
+	STX_XADD_W: /* lock xadd *(u32 *)(dst_reg + off16) += src_reg */
+		atomic_add((u32) SRC, (atomic_t *)(unsigned long)
+			   (DST + insn->off));
 		CONT;
-	STX_XADD_DW: /* lock xadd *(u64 *)(A + insn->off) += X */
-		atomic64_add((u64) X, (atomic64_t *)(unsigned long)
-			     (A + insn->off));
+	STX_XADD_DW: /* lock xadd *(u64 *)(dst_reg + off16) += src_reg */
+		atomic64_add((u64) SRC, (atomic64_t *)(unsigned long)
+			     (DST + insn->off));
 		CONT;
-	LD_ABS_W: /* BPF_R0 = ntohl(*(u32 *) (skb->data + K)) */
-		off = K;
+	LD_ABS_W: /* BPF_R0 = ntohl(*(u32 *) (skb->data + imm32)) */
+		off = IMM;
 load_word:
 		/* BPF_LD + BPD_ABS and BPF_LD + BPF_IND insns are
 		 * only appearing in the programs where ctx ==
@@ -527,51 +527,51 @@ load_word:
 		 * BPF_R6-BPF_R9, and store return value into BPF_R0.
 		 *
 		 * Implicit input:
-		 *   ctx
+		 *   ctx == skb == BPF_R6 == CTX
 		 *
 		 * Explicit input:
-		 *   X == any register
-		 *   K == 32-bit immediate
+		 *   SRC == any register
+		 *   IMM == 32-bit immediate
 		 *
 		 * Output:
 		 *   BPF_R0 - 8/16/32-bit skb data converted to cpu endianness
 		 */
 
-		ptr = load_pointer((struct sk_buff *) ctx, off, 4, &tmp);
+		ptr = load_pointer((struct sk_buff *) CTX, off, 4, &tmp);
 		if (likely(ptr != NULL)) {
 			BPF_R0 = get_unaligned_be32(ptr);
 			CONT;
 		}
 
 		return 0;
-	LD_ABS_H: /* BPF_R0 = ntohs(*(u16 *) (skb->data + K)) */
-		off = K;
+	LD_ABS_H: /* BPF_R0 = ntohs(*(u16 *) (skb->data + imm32)) */
+		off = IMM;
 load_half:
-		ptr = load_pointer((struct sk_buff *) ctx, off, 2, &tmp);
+		ptr = load_pointer((struct sk_buff *) CTX, off, 2, &tmp);
 		if (likely(ptr != NULL)) {
 			BPF_R0 = get_unaligned_be16(ptr);
 			CONT;
 		}
 
 		return 0;
-	LD_ABS_B: /* BPF_R0 = *(u8 *) (ctx + K) */
-		off = K;
+	LD_ABS_B: /* BPF_R0 = *(u8 *) (skb->data + imm32) */
+		off = IMM;
 load_byte:
-		ptr = load_pointer((struct sk_buff *) ctx, off, 1, &tmp);
+		ptr = load_pointer((struct sk_buff *) CTX, off, 1, &tmp);
 		if (likely(ptr != NULL)) {
 			BPF_R0 = *(u8 *)ptr;
 			CONT;
 		}
 
 		return 0;
-	LD_IND_W: /* BPF_R0 = ntohl(*(u32 *) (skb->data + X + K)) */
-		off = K + X;
+	LD_IND_W: /* BPF_R0 = ntohl(*(u32 *) (skb->data + src_reg + imm32)) */
+		off = IMM + SRC;
 		goto load_word;
-	LD_IND_H: /* BPF_R0 = ntohs(*(u16 *) (skb->data + X + K)) */
-		off = K + X;
+	LD_IND_H: /* BPF_R0 = ntohs(*(u16 *) (skb->data + src_reg + imm32)) */
+		off = IMM + SRC;
 		goto load_half;
-	LD_IND_B: /* BPF_R0 = *(u8 *) (skb->data + X + K) */
-		off = K + X;
+	LD_IND_B: /* BPF_R0 = *(u8 *) (skb->data + src_reg + imm32) */
+		off = IMM + SRC;
 		goto load_byte;
 
 	default_label:
@@ -675,7 +675,7 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
 	case SKF_AD_OFF + SKF_AD_PROTOCOL:
 		BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, protocol) != 2);
 
-		/* A = *(u16 *) (ctx + offsetof(protocol)) */
+		/* A = *(u16 *) (CTX + offsetof(protocol)) */
 		*insn++ = BPF_LDX_MEM(BPF_H, BPF_REG_A, BPF_REG_CTX,
 				      offsetof(struct sk_buff, protocol));
 		/* A = ntohs(A) [emitting a nop or swap16] */
@@ -741,7 +741,7 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
 		BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, vlan_tci) != 2);
 		BUILD_BUG_ON(VLAN_TAG_PRESENT != 0x1000);
 
-		/* A = *(u16 *) (ctx + offsetof(vlan_tci)) */
+		/* A = *(u16 *) (CTX + offsetof(vlan_tci)) */
 		*insn++ = BPF_LDX_MEM(BPF_H, BPF_REG_A, BPF_REG_CTX,
 				      offsetof(struct sk_buff, vlan_tci));
 		if (fp->k == SKF_AD_OFF + SKF_AD_VLAN_TAG) {
@@ -760,13 +760,13 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
 	case SKF_AD_OFF + SKF_AD_NLATTR_NEST:
 	case SKF_AD_OFF + SKF_AD_CPU:
 	case SKF_AD_OFF + SKF_AD_RANDOM:
-		/* arg1 = ctx */
+		/* arg1 = CTX */
 		*insn++ = BPF_MOV64_REG(BPF_REG_ARG1, BPF_REG_CTX);
 		/* arg2 = A */
 		*insn++ = BPF_MOV64_REG(BPF_REG_ARG2, BPF_REG_A);
 		/* arg3 = X */
 		*insn++ = BPF_MOV64_REG(BPF_REG_ARG3, BPF_REG_X);
-		/* Emit call(ctx, arg2=A, arg3=X) */
+		/* Emit call(arg1=CTX, arg2=A, arg3=X) */
 		switch (fp->k) {
 		case SKF_AD_OFF + SKF_AD_PAY_OFFSET:
 			*insn = BPF_EMIT_CALL(__skb_get_pay_offset);
@@ -941,12 +941,12 @@ do_pass:
 				 */
 				*insn++ = BPF_MOV32_IMM(BPF_REG_TMP, fp->k);
 
-				insn->a_reg = BPF_REG_A;
-				insn->x_reg = BPF_REG_TMP;
+				insn->dst_reg = BPF_REG_A;
+				insn->src_reg = BPF_REG_TMP;
 				bpf_src = BPF_X;
 			} else {
-				insn->a_reg = BPF_REG_A;
-				insn->x_reg = BPF_REG_X;
+				insn->dst_reg = BPF_REG_A;
+				insn->src_reg = BPF_REG_X;
 				insn->imm = fp->k;
 				bpf_src = BPF_SRC(fp->code);
 			}