[PATCH v5 bpf-next 13/23] bpf: move is_branch_taken() down

Andrii Nakryiko
2023-10-27T18:16:45Z

Move is_branch_taken() slightly down. In subsequent patched we'll need
both flip_opcode() and is_pkt_ptr_branch_taken() for is_branch_taken(),
but instead of sprinkling forward declarations around, it makes more
sense to move is_branch_taken() lower below is_pkt_ptr_branch_taken(),
and also keep it closer to very tightly related reg_set_min_max(), as
they are two critical parts of the same SCALAR range tracking logic.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
kernel/bpf/verifier.c | 84 +++++++++++++++++++++----------------------
1 file changed, 42 insertions(+), 42 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index fd328c579f10..25b5234ebda3 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -14339,48 +14339,6 @@ static int is_branch64_taken(struct bpf_reg_state *reg1, struct bpf_reg_state *r
return -1;
}

-/* compute branch direction of the expression "if (<reg1> opcode <reg2>) goto target;"
- * and return:
- * 1 - branch will be taken and "goto target" will be executed
- * 0 - branch will not be taken and fall-through to next insn
- * -1 - unknown. Example: "if (reg1 < 5)" is unknown when register value
- * range [0,10]
- */
-static int is_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_state *reg2,
- u8 opcode, bool is_jmp32)
-{
- struct tnum reg2_tnum = is_jmp32 ? tnum_subreg(reg2->var_off) : reg2->var_off;
- u64 val;
-
- if (!tnum_is_const(reg2_tnum))
- return -1;
- val = reg2_tnum.value;
-
- if (__is_pointer_value(false, reg1)) {
- if (!reg_not_null(reg1))
- return -1;
-
- /* If pointer is valid tests against zero will fail so we can
- * use this to direct branch taken.
- */
- if (val != 0)
- return -1;
-
- switch (opcode) {
- case BPF_JEQ:
- return 0;
- case BPF_JNE:
- return 1;
- default:
- return -1;
- }
- }
-
- if (is_jmp32)
- return is_branch32_taken(reg1, reg2, opcode);
- return is_branch64_taken(reg1, reg2, opcode);
-}
-
static int flip_opcode(u32 opcode)
{
/* How can we transform "a <op> b" into "b <op> a"? */
@@ -14442,6 +14400,48 @@ static int is_pkt_ptr_branch_taken(struct bpf_reg_state *dst_reg,
return -1;
}

+/* compute branch direction of the expression "if (<reg1> opcode <reg2>) goto target;"
+ * and return:
+ * 1 - branch will be taken and "goto target" will be executed
+ * 0 - branch will not be taken and fall-through to next insn
+ * -1 - unknown. Example: "if (reg1 < 5)" is unknown when register value
+ * range [0,10]
+ */
+static int is_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_state *reg2,
+ u8 opcode, bool is_jmp32)
+{
+ struct tnum reg2_tnum = is_jmp32 ? tnum_subreg(reg2->var_off) : reg2->var_off;
+ u64 val;
+
+ if (!tnum_is_const(reg2_tnum))
+ return -1;
+ val = reg2_tnum.value;
+
+ if (__is_pointer_value(false, reg1)) {
+ if (!reg_not_null(reg1))
+ return -1;
+
+ /* If pointer is valid tests against zero will fail so we can
+ * use this to direct branch taken.
+ */
+ if (val != 0)
+ return -1;
+
+ switch (opcode) {
+ case BPF_JEQ:
+ return 0;
+ case BPF_JNE:
+ return 1;
+ default:
+ return -1;
+ }
+ }
+
+ if (is_jmp32)
+ return is_branch32_taken(reg1, reg2, opcode);
+ return is_branch64_taken(reg1, reg2, opcode);
+}
+
/* Adjusts the register min/max values in the case that the dst_reg is the
* variable register that we are working on, and src_reg is a constant or we're
* simply doing a BPF_K check.
--
2.34.1