From aced132599b3c8884c050218d4c48eef203678f6 Mon Sep 17 00:00:00 2001 From: Song Liu Date: Wed, 25 Jun 2025 09:40:24 -0700 Subject: bpf: Add range tracking for BPF_NEG Add range tracking for instruction BPF_NEG. Without this logic, a trivial program like the following will fail volatile bool found_value_b; SEC("lsm.s/socket_connect") int BPF_PROG(test_socket_connect) { if (!found_value_b) return -1; return 0; } with verifier log: "At program exit the register R0 has smin=0 smax=4294967295 should have been in [-4095, 0]". This is because range information is lost in BPF_NEG: 0: R1=ctx() R10=fp0 ; if (!found_value_b) @ xxxx.c:24 0: (18) r1 = 0xffa00000011e7048 ; R1_w=map_value(...) 2: (71) r0 = *(u8 *)(r1 +0) ; R0_w=scalar(smin32=0,smax=255) 3: (a4) w0 ^= 1 ; R0_w=scalar(smin32=0,smax=255) 4: (84) w0 = -w0 ; R0_w=scalar(range info lost) Note that, the log above is manually modified to highlight relevant bits. Fix this by maintaining proper range information with BPF_NEG, so that the verifier will know: 4: (84) w0 = -w0 ; R0_w=scalar(smin32=-255,smax=0) Also updated selftests based on the expected behavior. Signed-off-by: Song Liu Acked-by: Eduard Zingerman Link: https://lore.kernel.org/r/20250625164025.3310203-2-song@kernel.org Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) (limited to 'kernel/bpf/verifier.c') diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f403524bd215..2ff22ef42348 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -15182,6 +15182,7 @@ static bool is_safe_to_compute_dst_reg_range(struct bpf_insn *insn, switch (BPF_OP(insn->code)) { case BPF_ADD: case BPF_SUB: + case BPF_NEG: case BPF_AND: case BPF_XOR: case BPF_OR: @@ -15250,6 +15251,13 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, scalar_min_max_sub(dst_reg, &src_reg); dst_reg->var_off = tnum_sub(dst_reg->var_off, src_reg.var_off); break; + case BPF_NEG: + env->fake_reg[0] = *dst_reg; + __mark_reg_known(dst_reg, 0); + scalar32_min_max_sub(dst_reg, &env->fake_reg[0]); + scalar_min_max_sub(dst_reg, &env->fake_reg[0]); + dst_reg->var_off = tnum_neg(env->fake_reg[0].var_off); + break; case BPF_MUL: dst_reg->var_off = tnum_mul(dst_reg->var_off, src_reg.var_off); scalar32_min_max_mul(dst_reg, &src_reg); @@ -15473,7 +15481,14 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn) } /* check dest operand */ - err = check_reg_arg(env, insn->dst_reg, DST_OP); + if (opcode == BPF_NEG) { + err = check_reg_arg(env, insn->dst_reg, DST_OP_NO_MARK); + err = err ?: adjust_scalar_min_max_vals(env, insn, + ®s[insn->dst_reg], + regs[insn->dst_reg]); + } else { + err = check_reg_arg(env, insn->dst_reg, DST_OP); + } if (err) return err; -- cgit v1.2.3