[RFC bpf-next 3/8] bpf: migrate jit blinding to list patching infra

[Jiong Wang <jiong.wang@netronome.com>]

List linerization function will figure out the new jump destination of
patched/blinded jumps. No need of destination adjustment inside
bpf_jit_blind_insn any more.

Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
---
 kernel/bpf/core.c | 76 ++++++++++++++++++++++++++-----------------------------
 1 file changed, 36 insertions(+), 40 deletions(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index e60703e..c3a5f84 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1162,7 +1162,6 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from,
 {
 	struct bpf_insn *to = to_buff;
 	u32 imm_rnd = get_random_int();
-	s16 off;
 
 	BUILD_BUG_ON(BPF_REG_AX  + 1 != MAX_BPF_JIT_REG);
 	BUILD_BUG_ON(MAX_BPF_REG + 1 != MAX_BPF_JIT_REG);
@@ -1234,13 +1233,10 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from,
 	case BPF_JMP | BPF_JSGE | BPF_K:
 	case BPF_JMP | BPF_JSLE | BPF_K:
 	case BPF_JMP | BPF_JSET | BPF_K:
-		/* Accommodate for extra offset in case of a backjump. */
-		off = from->off;
-		if (off < 0)
-			off -= 2;
 		*to++ = BPF_ALU64_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm);
 		*to++ = BPF_ALU64_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
-		*to++ = BPF_JMP_REG(from->code, from->dst_reg, BPF_REG_AX, off);
+		*to++ = BPF_JMP_REG(from->code, from->dst_reg, BPF_REG_AX,
+				    from->off);
 		break;
 
 	case BPF_JMP32 | BPF_JEQ  | BPF_K:
@@ -1254,14 +1250,10 @@ static int bpf_jit_blind_insn(const struct bpf_insn *from,
 	case BPF_JMP32 | BPF_JSGE | BPF_K:
 	case BPF_JMP32 | BPF_JSLE | BPF_K:
 	case BPF_JMP32 | BPF_JSET | BPF_K:
-		/* Accommodate for extra offset in case of a backjump. */
-		off = from->off;
-		if (off < 0)
-			off -= 2;
 		*to++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_AX, imm_rnd ^ from->imm);
 		*to++ = BPF_ALU32_IMM(BPF_XOR, BPF_REG_AX, imm_rnd);
 		*to++ = BPF_JMP32_REG(from->code, from->dst_reg, BPF_REG_AX,
-				      off);
+				      from->off);
 		break;
 
 	case BPF_LD | BPF_IMM | BPF_DW:
@@ -1332,10 +1324,9 @@ void bpf_jit_prog_release_other(struct bpf_prog *fp, struct bpf_prog *fp_other)
 struct bpf_prog *bpf_jit_blind_constants(struct bpf_prog *prog)
 {
 	struct bpf_insn insn_buff[16], aux[2];
-	struct bpf_prog *clone, *tmp;
-	int insn_delta, insn_cnt;
-	struct bpf_insn *insn;
-	int i, rewritten;
+	struct bpf_list_insn *list, *elem;
+	struct bpf_prog *clone, *ret_prog;
+	int rewritten;
 
 	if (!bpf_jit_blinding_enabled(prog) || prog->blinded)
 		return prog;
@@ -1344,43 +1335,48 @@ struct bpf_prog *bpf_jit_blind_constants(struct bpf_prog *prog)
 	if (!clone)
 		return ERR_PTR(-ENOMEM);
 
-	insn_cnt = clone->len;
-	insn = clone->insnsi;
+	list = bpf_create_list_insn(clone);
+	if (IS_ERR(list))
+		return (struct bpf_prog *)list;
+
+	/* kill uninitialized warning on some gcc versions. */
+	memset(&aux, 0, sizeof(aux));
+
+	for (elem = list; elem; elem = elem->next) {
+		struct bpf_list_insn *next = elem->next;
+		struct bpf_insn insn = elem->insn;
 
-	for (i = 0; i < insn_cnt; i++, insn++) {
 		/* We temporarily need to hold the original ld64 insn
 		 * so that we can still access the first part in the
 		 * second blinding run.
 		 */
-		if (insn[0].code == (BPF_LD | BPF_IMM | BPF_DW) &&
-		    insn[1].code == 0)
-			memcpy(aux, insn, sizeof(aux));
+		if (insn.code == (BPF_LD | BPF_IMM | BPF_DW)) {
+			struct bpf_insn next_insn = next->insn;
 
-		rewritten = bpf_jit_blind_insn(insn, aux, insn_buff);
+			if (next_insn.code == 0) {
+				aux[0] = insn;
+				aux[1] = next_insn;
+			}
+		}
+
+		rewritten = bpf_jit_blind_insn(&insn, aux, insn_buff);
 		if (!rewritten)
 			continue;
 
-		tmp = bpf_patch_insn_single(clone, i, insn_buff, rewritten);
-		if (IS_ERR(tmp)) {
-			/* Patching may have repointed aux->prog during
-			 * realloc from the original one, so we need to
-			 * fix it up here on error.
-			 */
-			bpf_jit_prog_release_other(prog, clone);
-			return tmp;
+		elem = bpf_patch_list_insn(elem, insn_buff, rewritten);
+		if (IS_ERR(elem)) {
+			ret_prog = (struct bpf_prog *)elem;
+			goto free_list_ret;
 		}
-
-		clone = tmp;
-		insn_delta = rewritten - 1;
-
-		/* Walk new program and skip insns we just inserted. */
-		insn = clone->insnsi + i + insn_delta;
-		insn_cnt += insn_delta;
-		i        += insn_delta;
 	}
 
-	clone->blinded = 1;
-	return clone;
+	clone = bpf_linearize_list_insn(clone, list);
+	if (!IS_ERR(clone))
+		clone->blinded = 1;
+	ret_prog = clone;
+free_list_ret:
+	bpf_destroy_list_insn(list);
+	return ret_prog;
 }
 #endif /* CONFIG_BPF_JIT */
 
-- 
2.7.4