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bpf/verifier: refactor checks for range computation
Split range computation checks in its own function, isolating pessimitic range set for dst_reg and failing return to a single point. Signed-off-by: Cupertino Miranda <cupertino.miranda@oracle.com> Acked-by: Eduard Zingerman <eddyz87@gmail.com> Cc: Yonghong Song <yonghong.song@linux.dev> Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com> Cc: David Faust <david.faust@oracle.com> Cc: Jose Marchesi <jose.marchesi@oracle.com> Cc: Elena Zannoni <elena.zannoni@oracle.com> Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com> bpf/verifier: improve code after range computation recent changes. Link: https://lore.kernel.org/r/20240506141849.185293-3-cupertino.miranda@oracle.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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@ -13878,6 +13878,50 @@ static void scalar_min_max_arsh(struct bpf_reg_state *dst_reg,
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__update_reg_bounds(dst_reg);
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}
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static bool is_safe_to_compute_dst_reg_range(struct bpf_insn *insn,
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const struct bpf_reg_state *src_reg)
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{
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bool src_is_const = false;
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u64 insn_bitness = (BPF_CLASS(insn->code) == BPF_ALU64) ? 64 : 32;
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if (insn_bitness == 32) {
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if (tnum_subreg_is_const(src_reg->var_off)
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&& src_reg->s32_min_value == src_reg->s32_max_value
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&& src_reg->u32_min_value == src_reg->u32_max_value)
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src_is_const = true;
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} else {
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if (tnum_is_const(src_reg->var_off)
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&& src_reg->smin_value == src_reg->smax_value
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&& src_reg->umin_value == src_reg->umax_value)
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src_is_const = true;
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}
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switch (BPF_OP(insn->code)) {
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case BPF_ADD:
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case BPF_SUB:
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case BPF_AND:
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return true;
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/* Compute range for the following only if the src_reg is const.
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*/
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case BPF_XOR:
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case BPF_OR:
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case BPF_MUL:
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return src_is_const;
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/* Shift operators range is only computable if shift dimension operand
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* is a constant. Shifts greater than 31 or 63 are undefined. This
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* includes shifts by a negative number.
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*/
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case BPF_LSH:
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case BPF_RSH:
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case BPF_ARSH:
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return (src_is_const && src_reg->umax_value < insn_bitness);
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default:
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return false;
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}
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}
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/* WARNING: This function does calculations on 64-bit values, but the actual
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* execution may occur on 32-bit values. Therefore, things like bitshifts
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* need extra checks in the 32-bit case.
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@ -13888,51 +13932,10 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
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struct bpf_reg_state src_reg)
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{
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u8 opcode = BPF_OP(insn->code);
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bool src_known;
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s64 smin_val, smax_val;
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u64 umin_val, umax_val;
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s32 s32_min_val, s32_max_val;
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u32 u32_min_val, u32_max_val;
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u64 insn_bitness = (BPF_CLASS(insn->code) == BPF_ALU64) ? 64 : 32;
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bool alu32 = (BPF_CLASS(insn->code) != BPF_ALU64);
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int ret;
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smin_val = src_reg.smin_value;
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smax_val = src_reg.smax_value;
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umin_val = src_reg.umin_value;
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umax_val = src_reg.umax_value;
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s32_min_val = src_reg.s32_min_value;
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s32_max_val = src_reg.s32_max_value;
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u32_min_val = src_reg.u32_min_value;
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u32_max_val = src_reg.u32_max_value;
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if (alu32) {
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src_known = tnum_subreg_is_const(src_reg.var_off);
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if ((src_known &&
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(s32_min_val != s32_max_val || u32_min_val != u32_max_val)) ||
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s32_min_val > s32_max_val || u32_min_val > u32_max_val) {
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/* Taint dst register if offset had invalid bounds
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* derived from e.g. dead branches.
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*/
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__mark_reg_unknown(env, dst_reg);
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return 0;
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}
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} else {
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src_known = tnum_is_const(src_reg.var_off);
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if ((src_known &&
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(smin_val != smax_val || umin_val != umax_val)) ||
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smin_val > smax_val || umin_val > umax_val) {
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/* Taint dst register if offset had invalid bounds
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* derived from e.g. dead branches.
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*/
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__mark_reg_unknown(env, dst_reg);
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return 0;
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}
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}
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if (!src_known &&
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opcode != BPF_ADD && opcode != BPF_SUB && opcode != BPF_AND) {
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if (!is_safe_to_compute_dst_reg_range(insn, &src_reg)) {
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__mark_reg_unknown(env, dst_reg);
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return 0;
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}
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@ -13989,46 +13992,24 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
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scalar_min_max_xor(dst_reg, &src_reg);
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break;
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case BPF_LSH:
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if (umax_val >= insn_bitness) {
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/* Shifts greater than 31 or 63 are undefined.
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* This includes shifts by a negative number.
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*/
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__mark_reg_unknown(env, dst_reg);
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break;
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}
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if (alu32)
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scalar32_min_max_lsh(dst_reg, &src_reg);
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else
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scalar_min_max_lsh(dst_reg, &src_reg);
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break;
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case BPF_RSH:
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if (umax_val >= insn_bitness) {
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/* Shifts greater than 31 or 63 are undefined.
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* This includes shifts by a negative number.
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*/
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__mark_reg_unknown(env, dst_reg);
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break;
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}
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if (alu32)
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scalar32_min_max_rsh(dst_reg, &src_reg);
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else
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scalar_min_max_rsh(dst_reg, &src_reg);
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break;
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case BPF_ARSH:
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if (umax_val >= insn_bitness) {
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/* Shifts greater than 31 or 63 are undefined.
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* This includes shifts by a negative number.
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*/
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__mark_reg_unknown(env, dst_reg);
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break;
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}
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if (alu32)
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scalar32_min_max_arsh(dst_reg, &src_reg);
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else
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scalar_min_max_arsh(dst_reg, &src_reg);
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break;
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default:
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__mark_reg_unknown(env, dst_reg);
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break;
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}
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