[RFC PATCH v2 04/26] bpf: extract jmp and default handler and introduce UBPF_BUILD flag

[He Kuang]

This patch is a preparation for compiling bpf vm into external
libraries. Parts of the instruction handlers are wrapped into macros
or functions so that userspace libraries can override them. There's no
functionality change without UBPF_BUILD flag.

Signed-off-by: He Kuang <hekuang@xxxxxxxxxx>
Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
---
 kernel/bpf/vm.c | 94 ++++++++++++++++++++++++++++++++++-----------------------
 1 file changed, 56 insertions(+), 38 deletions(-)

diff --git a/kernel/bpf/vm.c b/kernel/bpf/vm.c
index 45a2880..add5669 100644
--- a/kernel/bpf/vm.c
+++ b/kernel/bpf/vm.c
@@ -1,8 +1,6 @@
 #include <linux/types.h>
 #include <asm/byteorder.h>
-#include <asm/unaligned.h>
 #include <linux/byteorder/generic.h>
-#include <linux/ratelimit.h>
 #include <linux/compiler.h>
 #include <linux/export.h>
 #include <linux/filter.h>
@@ -11,6 +9,11 @@
 #include <linux/frame.h>
 #include <linux/bpf.h>
 
+#ifndef UBPF_BUILD
+#include <asm/unaligned.h>
+#include <linux/ratelimit.h>
+#endif
+
 /* Registers */
 #define BPF_R0	regs[BPF_REG_0]
 #define BPF_R1	regs[BPF_REG_1]
@@ -32,6 +35,49 @@
 #define CTX	regs[BPF_REG_CTX]
 #define IMM	insn->imm
 
+#ifndef UBPF_BUILD
+/* Function call scratches BPF_R1-BPF_R5 registers,
+ * preserves BPF_R6-BPF_R9, and stores return value
+ * into BPF_R0.
+ */
+#define bpf_vm_jmp_call_handler(regs, ctx, insn)			\
+	(BPF_R0 = (__bpf_call_base + insn->imm)(BPF_R1, BPF_R2, BPF_R3,	\
+						BPF_R4, BPF_R5))
+
+/* If we ever reach this, we have a bug somewhere. */
+#define bpf_vm_default_label_handler(ctx, insn)			\
+	WARN_RATELIMIT(1, "unknown opcode %02x\n", insn->code)
+
+static inline int bpf_vm_jmp_tail_call_handler(u64 *regs, u32 *p_tail_call_cnt,
+					       const struct bpf_insn **p_insn)
+{
+	struct bpf_map *map = (struct bpf_map *) (unsigned long) BPF_R2;
+	struct bpf_array *array = container_of(map, struct bpf_array, map);
+	struct bpf_prog *prog;
+	u64 index = BPF_R3;
+
+	if (unlikely(index >= array->map.max_entries))
+		return -1;
+
+	if (unlikely(*p_tail_call_cnt > MAX_TAIL_CALL_CNT))
+		return -1;
+
+	(*p_tail_call_cnt)++;
+
+	prog = READ_ONCE(array->ptrs[index]);
+	if (unlikely(!prog))
+		return -1;
+
+	/* ARG1 at this point is guaranteed to point to CTX from
+	 * the verifier side due to the fact that the tail call is
+	 * handeled like a helper, that is, bpf_tail_call_proto,
+	 * where arg1_type is ARG_PTR_TO_CTX.
+	 */
+	*p_insn = prog->insnsi;
+	return 0;
+}
+#endif /* UBPF_BUILD */
+
 unsigned int __bpf_prog_run(void *ctx, const struct bpf_insn *insn)
 {
 	u64 stack[MAX_BPF_STACK / sizeof(u64)];
@@ -270,42 +316,15 @@ select_insn:
 
 	/* CALL */
 	JMP_CALL:
-		/* Function call scratches BPF_R1-BPF_R5 registers,
-		 * preserves BPF_R6-BPF_R9, and stores return value
-		 * into BPF_R0.
-		 */
-		BPF_R0 = (__bpf_call_base + insn->imm)(BPF_R1, BPF_R2, BPF_R3,
-						       BPF_R4, BPF_R5);
+		bpf_vm_jmp_call_handler(regs, ctx, insn);
 		CONT;
 
-	JMP_TAIL_CALL: {
-		struct bpf_map *map = (struct bpf_map *) (unsigned long) BPF_R2;
-		struct bpf_array *array = container_of(map, struct bpf_array, map);
-		struct bpf_prog *prog;
-		u64 index = BPF_R3;
-
-		if (unlikely(index >= array->map.max_entries))
-			goto out;
-
-		if (unlikely(tail_call_cnt > MAX_TAIL_CALL_CNT))
-			goto out;
-
-		tail_call_cnt++;
-
-		prog = READ_ONCE(array->ptrs[index]);
-		if (unlikely(!prog))
-			goto out;
-
-		/* ARG1 at this point is guaranteed to point to CTX from
-		 * the verifier side due to the fact that the tail call is
-		 * handeled like a helper, that is, bpf_tail_call_proto,
-		 * where arg1_type is ARG_PTR_TO_CTX.
-		 */
-		insn = prog->insnsi;
-		goto select_insn;
-out:
-		CONT;
-	}
+	JMP_TAIL_CALL:
+		tmp = bpf_vm_jmp_tail_call_handler(regs, &tail_call_cnt, &insn);
+		if (tmp)
+			CONT;
+		else
+			goto select_insn;
 	/* JMP */
 	JMP_JA:
 		insn += insn->off;
@@ -485,8 +504,7 @@ load_byte:
 		goto load_byte;
 
 	default_label:
-		/* If we ever reach this, we have a bug somewhere. */
-		WARN_RATELIMIT(1, "unknown opcode %02x\n", insn->code);
+		bpf_vm_default_label_handler(ctx, insn);
 		return 0;
 }
 STACK_FRAME_NON_STANDARD(__bpf_prog_run); /* jump table */
-- 
1.8.5.2