Commit c697289e authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
Browse files

bpf: move is_branch_taken() down 



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: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231102033759.2541186-14-andrii@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent c3153426

kernel/bpf/verifier.c

+42 −42
Original line number Diff line number Diff line
@@ -14358,48 +14358,6 @@ 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"? */








@@ -14461,6 +14419,48 @@ 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.