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bpf: generalize is_branch_taken to handle all conditional jumps in one place
Make is_branch_taken() a single entry point for branch pruning decision making, handling both pointer vs pointer, pointer vs scalar, and scalar vs scalar cases in one place. This also nicely cleans up check_cond_jmp_op(). Acked-by: Eduard Zingerman <eddyz87@gmail.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/r/20231102033759.2541186-15-andrii@kernel.org Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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@ -14188,6 +14188,19 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *vstate,
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}));
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}
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/* check if register is a constant scalar value */
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static bool is_reg_const(struct bpf_reg_state *reg, bool subreg32)
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{
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return reg->type == SCALAR_VALUE &&
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tnum_is_const(subreg32 ? tnum_subreg(reg->var_off) : reg->var_off);
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}
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/* assuming is_reg_const() is true, return constant value of a register */
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static u64 reg_const_value(struct bpf_reg_state *reg, bool subreg32)
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{
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return subreg32 ? tnum_subreg(reg->var_off).value : reg->var_off.value;
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}
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/*
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* <reg1> <op> <reg2>, currently assuming reg2 is a constant
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*/
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@ -14429,12 +14442,20 @@ static int is_pkt_ptr_branch_taken(struct bpf_reg_state *dst_reg,
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static int is_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_state *reg2,
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u8 opcode, bool is_jmp32)
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{
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struct tnum reg2_tnum = is_jmp32 ? tnum_subreg(reg2->var_off) : reg2->var_off;
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u64 val;
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if (!tnum_is_const(reg2_tnum))
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if (reg_is_pkt_pointer_any(reg1) && reg_is_pkt_pointer_any(reg2) && !is_jmp32)
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return is_pkt_ptr_branch_taken(reg1, reg2, opcode);
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/* try to make sure reg2 is a constant SCALAR_VALUE */
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if (!is_reg_const(reg2, is_jmp32)) {
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opcode = flip_opcode(opcode);
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swap(reg1, reg2);
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}
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/* for now we expect reg2 to be a constant to make any useful decisions */
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if (!is_reg_const(reg2, is_jmp32))
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return -1;
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val = reg2_tnum.value;
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val = reg_const_value(reg2, is_jmp32);
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if (__is_pointer_value(false, reg1)) {
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if (!reg_not_null(reg1))
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@ -14915,27 +14936,7 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
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}
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is_jmp32 = BPF_CLASS(insn->code) == BPF_JMP32;
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if (BPF_SRC(insn->code) == BPF_K) {
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pred = is_branch_taken(dst_reg, src_reg, opcode, is_jmp32);
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} else if (src_reg->type == SCALAR_VALUE &&
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is_jmp32 && tnum_is_const(tnum_subreg(src_reg->var_off))) {
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pred = is_branch_taken(dst_reg, src_reg, opcode, is_jmp32);
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} else if (src_reg->type == SCALAR_VALUE &&
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!is_jmp32 && tnum_is_const(src_reg->var_off)) {
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pred = is_branch_taken(dst_reg, src_reg, opcode, is_jmp32);
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} else if (dst_reg->type == SCALAR_VALUE &&
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is_jmp32 && tnum_is_const(tnum_subreg(dst_reg->var_off))) {
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pred = is_branch_taken(src_reg, dst_reg, flip_opcode(opcode), is_jmp32);
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} else if (dst_reg->type == SCALAR_VALUE &&
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!is_jmp32 && tnum_is_const(dst_reg->var_off)) {
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pred = is_branch_taken(src_reg, dst_reg, flip_opcode(opcode), is_jmp32);
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} else if (reg_is_pkt_pointer_any(dst_reg) &&
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reg_is_pkt_pointer_any(src_reg) &&
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!is_jmp32) {
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pred = is_pkt_ptr_branch_taken(dst_reg, src_reg, opcode);
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}
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pred = is_branch_taken(dst_reg, src_reg, opcode, is_jmp32);
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if (pred >= 0) {
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/* If we get here with a dst_reg pointer type it is because
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* above is_branch_taken() special cased the 0 comparison.
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