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net: filter: make BPF conversion more readable
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Introduce BPF helper macros to define instructions
(similar to old BPF_STMT/BPF_JUMP macros)

Use them while converting classic BPF to internal
and in BPF testsuite later.

Signed-off-by: Alexei Starovoitov <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
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@davem330
Alexei Starovoitov authored and davem330 committed May 12, 2014
1 parent 05ab2da commit 9739eef
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Showing 2 changed files with 101 additions and 92 deletions.
51 changes: 51 additions & 0 deletions include/linux/filter.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -79,6 +79,57 @@ enum {
/* BPF program can access up to 512 bytes of stack space. */
#define MAX_BPF_STACK 512

/* bpf_add|sub|...: a += x, bpf_mov: a = x */
#define BPF_ALU64_REG(op, a, x) \
((struct sock_filter_int) {BPF_ALU64|BPF_OP(op)|BPF_X, a, x, 0, 0})
#define BPF_ALU32_REG(op, a, x) \
((struct sock_filter_int) {BPF_ALU|BPF_OP(op)|BPF_X, a, x, 0, 0})

/* bpf_add|sub|...: a += imm, bpf_mov: a = imm */
#define BPF_ALU64_IMM(op, a, imm) \
((struct sock_filter_int) {BPF_ALU64|BPF_OP(op)|BPF_K, a, 0, 0, imm})
#define BPF_ALU32_IMM(op, a, imm) \
((struct sock_filter_int) {BPF_ALU|BPF_OP(op)|BPF_K, a, 0, 0, imm})

/* R0 = *(uint *) (skb->data + off) */
#define BPF_LD_ABS(size, off) \
((struct sock_filter_int) {BPF_LD|BPF_SIZE(size)|BPF_ABS, 0, 0, 0, off})

/* R0 = *(uint *) (skb->data + x + off) */
#define BPF_LD_IND(size, x, off) \
((struct sock_filter_int) {BPF_LD|BPF_SIZE(size)|BPF_IND, 0, x, 0, off})

/* a = *(uint *) (x + off) */
#define BPF_LDX_MEM(sz, a, x, off) \
((struct sock_filter_int) {BPF_LDX|BPF_SIZE(sz)|BPF_MEM, a, x, off, 0})

/* if (a 'op' x) goto pc+off */
#define BPF_JMP_REG(op, a, x, off) \
((struct sock_filter_int) {BPF_JMP|BPF_OP(op)|BPF_X, a, x, off, 0})

/* if (a 'op' imm) goto pc+off */
#define BPF_JMP_IMM(op, a, imm, off) \
((struct sock_filter_int) {BPF_JMP|BPF_OP(op)|BPF_K, a, 0, off, imm})

#define BPF_EXIT_INSN() \
((struct sock_filter_int) {BPF_JMP|BPF_EXIT, 0, 0, 0, 0})

static inline int size_to_bpf(int size)
{
switch (size) {
case 1:
return BPF_B;
case 2:
return BPF_H;
case 4:
return BPF_W;
case 8:
return BPF_DW;
default:
return -EINVAL;
}
}

/* Macro to invoke filter function. */
#define SK_RUN_FILTER(filter, ctx) (*filter->bpf_func)(ctx, filter->insnsi)

Expand Down
142 changes: 50 additions & 92 deletions net/core/filter.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -668,10 +668,9 @@ 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);

insn->code = BPF_LDX | BPF_MEM | BPF_H;
insn->a_reg = BPF_REG_A;
insn->x_reg = BPF_REG_CTX;
insn->off = offsetof(struct sk_buff, protocol);
/* A = *(u16 *) (ctx + offsetof(protocol)) */
*insn = BPF_LDX_MEM(BPF_H, BPF_REG_A, BPF_REG_CTX,
offsetof(struct sk_buff, protocol));
insn++;

/* A = ntohs(A) [emitting a nop or swap16] */
Expand All @@ -681,37 +680,27 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
break;

case SKF_AD_OFF + SKF_AD_PKTTYPE:
insn->code = BPF_LDX | BPF_MEM | BPF_B;
insn->a_reg = BPF_REG_A;
insn->x_reg = BPF_REG_CTX;
insn->off = pkt_type_offset();
*insn = BPF_LDX_MEM(BPF_B, BPF_REG_A, BPF_REG_CTX,
pkt_type_offset());
if (insn->off < 0)
return false;
insn++;

insn->code = BPF_ALU | BPF_AND | BPF_K;
insn->a_reg = BPF_REG_A;
insn->imm = PKT_TYPE_MAX;
*insn = BPF_ALU32_IMM(BPF_AND, BPF_REG_A, PKT_TYPE_MAX);
break;

case SKF_AD_OFF + SKF_AD_IFINDEX:
case SKF_AD_OFF + SKF_AD_HATYPE:
if (FIELD_SIZEOF(struct sk_buff, dev) == 8)
insn->code = BPF_LDX | BPF_MEM | BPF_DW;
else
insn->code = BPF_LDX | BPF_MEM | BPF_W;
insn->a_reg = BPF_REG_TMP;
insn->x_reg = BPF_REG_CTX;
insn->off = offsetof(struct sk_buff, dev);
*insn = BPF_LDX_MEM(size_to_bpf(FIELD_SIZEOF(struct sk_buff, dev)),
BPF_REG_TMP, BPF_REG_CTX,
offsetof(struct sk_buff, dev));
insn++;

insn->code = BPF_JMP | BPF_JNE | BPF_K;
insn->a_reg = BPF_REG_TMP;
insn->imm = 0;
insn->off = 1;
/* if (tmp != 0) goto pc+1 */
*insn = BPF_JMP_IMM(BPF_JNE, BPF_REG_TMP, 0, 1);
insn++;

insn->code = BPF_JMP | BPF_EXIT;
*insn = BPF_EXIT_INSN();
insn++;

BUILD_BUG_ON(FIELD_SIZEOF(struct net_device, ifindex) != 4);
Expand All @@ -732,55 +721,45 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
case SKF_AD_OFF + SKF_AD_MARK:
BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4);

insn->code = BPF_LDX | BPF_MEM | BPF_W;
insn->a_reg = BPF_REG_A;
insn->x_reg = BPF_REG_CTX;
insn->off = offsetof(struct sk_buff, mark);
*insn = BPF_LDX_MEM(BPF_W, BPF_REG_A, BPF_REG_CTX,
offsetof(struct sk_buff, mark));
break;

case SKF_AD_OFF + SKF_AD_RXHASH:
BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, hash) != 4);

insn->code = BPF_LDX | BPF_MEM | BPF_W;
insn->a_reg = BPF_REG_A;
insn->x_reg = BPF_REG_CTX;
insn->off = offsetof(struct sk_buff, hash);
*insn = BPF_LDX_MEM(BPF_W, BPF_REG_A, BPF_REG_CTX,
offsetof(struct sk_buff, hash));
break;

case SKF_AD_OFF + SKF_AD_QUEUE:
BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, queue_mapping) != 2);

insn->code = BPF_LDX | BPF_MEM | BPF_H;
insn->a_reg = BPF_REG_A;
insn->x_reg = BPF_REG_CTX;
insn->off = offsetof(struct sk_buff, queue_mapping);
*insn = BPF_LDX_MEM(BPF_H, BPF_REG_A, BPF_REG_CTX,
offsetof(struct sk_buff, queue_mapping));
break;

case SKF_AD_OFF + SKF_AD_VLAN_TAG:
case SKF_AD_OFF + SKF_AD_VLAN_TAG_PRESENT:
BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, vlan_tci) != 2);

insn->code = BPF_LDX | BPF_MEM | BPF_H;
insn->a_reg = BPF_REG_A;
insn->x_reg = BPF_REG_CTX;
insn->off = offsetof(struct sk_buff, 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));
insn++;

BUILD_BUG_ON(VLAN_TAG_PRESENT != 0x1000);

if (fp->k == SKF_AD_OFF + SKF_AD_VLAN_TAG) {
insn->code = BPF_ALU | BPF_AND | BPF_K;
insn->a_reg = BPF_REG_A;
insn->imm = ~VLAN_TAG_PRESENT;
*insn = BPF_ALU32_IMM(BPF_AND, BPF_REG_A,
~VLAN_TAG_PRESENT);
} else {
insn->code = BPF_ALU | BPF_RSH | BPF_K;
insn->a_reg = BPF_REG_A;
insn->imm = 12;
/* A >>= 12 */
*insn = BPF_ALU32_IMM(BPF_RSH, BPF_REG_A, 12);
insn++;

insn->code = BPF_ALU | BPF_AND | BPF_K;
insn->a_reg = BPF_REG_A;
insn->imm = 1;
/* A &= 1 */
*insn = BPF_ALU32_IMM(BPF_AND, BPF_REG_A, 1);
}
break;

Expand All @@ -790,21 +769,15 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
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 = BPF_REG_ARG1;
insn->x_reg = BPF_REG_CTX;
*insn = BPF_ALU64_REG(BPF_MOV, BPF_REG_ARG1, BPF_REG_CTX);
insn++;

/* arg2 = A */
insn->code = BPF_ALU64 | BPF_MOV | BPF_X;
insn->a_reg = BPF_REG_ARG2;
insn->x_reg = BPF_REG_A;
*insn = BPF_ALU64_REG(BPF_MOV, BPF_REG_ARG2, BPF_REG_A);
insn++;

/* arg3 = X */
insn->code = BPF_ALU64 | BPF_MOV | BPF_X;
insn->a_reg = BPF_REG_ARG3;
insn->x_reg = BPF_REG_X;
*insn = BPF_ALU64_REG(BPF_MOV, BPF_REG_ARG3, BPF_REG_X);
insn++;

/* Emit call(ctx, arg2=A, arg3=X) */
Expand All @@ -829,9 +802,8 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
break;

case SKF_AD_OFF + SKF_AD_ALU_XOR_X:
insn->code = BPF_ALU | BPF_XOR | BPF_X;
insn->a_reg = BPF_REG_A;
insn->x_reg = BPF_REG_X;
/* A ^= X */
*insn = BPF_ALU32_REG(BPF_XOR, BPF_REG_A, BPF_REG_X);
break;

default:
Expand Down Expand Up @@ -897,9 +869,7 @@ int sk_convert_filter(struct sock_filter *prog, int len,
fp = prog;

if (new_insn) {
new_insn->code = BPF_ALU64 | BPF_MOV | BPF_X;
new_insn->a_reg = BPF_REG_CTX;
new_insn->x_reg = BPF_REG_ARG1;
*new_insn = BPF_ALU64_REG(BPF_MOV, BPF_REG_CTX, BPF_REG_ARG1);
}
new_insn++;

Expand Down Expand Up @@ -1027,34 +997,28 @@ int sk_convert_filter(struct sock_filter *prog, int len,

/* ldxb 4 * ([14] & 0xf) is remaped into 6 insns. */
case BPF_LDX | BPF_MSH | BPF_B:
insn->code = BPF_ALU64 | BPF_MOV | BPF_X;
insn->a_reg = BPF_REG_TMP;
insn->x_reg = BPF_REG_A;
/* tmp = A */
*insn = BPF_ALU64_REG(BPF_MOV, BPF_REG_TMP, BPF_REG_A);
insn++;

insn->code = BPF_LD | BPF_ABS | BPF_B;
insn->a_reg = BPF_REG_A;
insn->imm = fp->k;
/* A = R0 = *(u8 *) (skb->data + K) */
*insn = BPF_LD_ABS(BPF_B, fp->k);
insn++;

insn->code = BPF_ALU | BPF_AND | BPF_K;
insn->a_reg = BPF_REG_A;
insn->imm = 0xf;
/* A &= 0xf */
*insn = BPF_ALU32_IMM(BPF_AND, BPF_REG_A, 0xf);
insn++;

insn->code = BPF_ALU | BPF_LSH | BPF_K;
insn->a_reg = BPF_REG_A;
insn->imm = 2;
/* A <<= 2 */
*insn = BPF_ALU32_IMM(BPF_LSH, BPF_REG_A, 2);
insn++;

insn->code = BPF_ALU64 | BPF_MOV | BPF_X;
insn->a_reg = BPF_REG_X;
insn->x_reg = BPF_REG_A;
/* X = A */
*insn = BPF_ALU64_REG(BPF_MOV, BPF_REG_X, BPF_REG_A);
insn++;

insn->code = BPF_ALU64 | BPF_MOV | BPF_X;
insn->a_reg = BPF_REG_A;
insn->x_reg = BPF_REG_TMP;
/* A = tmp */
*insn = BPF_ALU64_REG(BPF_MOV, BPF_REG_A, BPF_REG_TMP);
break;

/* RET_K, RET_A are remaped into 2 insns. */
Expand All @@ -1068,7 +1032,7 @@ int sk_convert_filter(struct sock_filter *prog, int len,
insn->imm = fp->k;
insn++;

insn->code = BPF_JMP | BPF_EXIT;
*insn = BPF_EXIT_INSN();
break;

/* Store to stack. */
Expand Down Expand Up @@ -1102,16 +1066,12 @@ int sk_convert_filter(struct sock_filter *prog, int len,

/* X = A */
case BPF_MISC | BPF_TAX:
insn->code = BPF_ALU64 | BPF_MOV | BPF_X;
insn->a_reg = BPF_REG_X;
insn->x_reg = BPF_REG_A;
*insn = BPF_ALU64_REG(BPF_MOV, BPF_REG_X, BPF_REG_A);
break;

/* A = X */
case BPF_MISC | BPF_TXA:
insn->code = BPF_ALU64 | BPF_MOV | BPF_X;
insn->a_reg = BPF_REG_A;
insn->x_reg = BPF_REG_X;
*insn = BPF_ALU64_REG(BPF_MOV, BPF_REG_A, BPF_REG_X);
break;

/* A = skb->len or X = skb->len */
Expand All @@ -1126,10 +1086,8 @@ int sk_convert_filter(struct sock_filter *prog, int len,

/* access seccomp_data fields */
case BPF_LDX | BPF_ABS | BPF_W:
insn->code = BPF_LDX | BPF_MEM | BPF_W;
insn->a_reg = BPF_REG_A;
insn->x_reg = BPF_REG_CTX;
insn->off = fp->k;
/* A = *(u32 *) (ctx + K) */
*insn = BPF_LDX_MEM(BPF_W, BPF_REG_A, BPF_REG_CTX, fp->k);
break;

default:
Expand Down

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