bpf: split check_reg_sane_offset() in two parts

check_reg_sane_offset() is used when verifying operations like:

  dst_reg += src_reg
  ^          ^
  |          '-------- scalar
  '------------------- pointer

To verify range for both dst_reg and src_reg. Split it in two parts:
- one to check a pointer offset
- another to check scalar offset

This would be useful for further refactoring.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260212-ptrs-off-migration-v2-1-00820e4d3438@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 27 insertions, 12 deletions

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index edf5342b982f..3bf72eacbec2 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -14426,9 +14426,9 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 	return 0;
 }
 
-static bool check_reg_sane_offset(struct bpf_verifier_env *env,
-				  const struct bpf_reg_state *reg,
-				  enum bpf_reg_type type)
+static bool check_reg_sane_offset_scalar(struct bpf_verifier_env *env,
+					 const struct bpf_reg_state *reg,
+					 enum bpf_reg_type type)
 {
 	bool known = tnum_is_const(reg->var_off);
 	s64 val = reg->var_off.value;
@@ -14440,12 +14440,6 @@ static bool check_reg_sane_offset(struct bpf_verifier_env *env,
 		return false;
 	}
 
-	if (reg->off >= BPF_MAX_VAR_OFF || reg->off <= -BPF_MAX_VAR_OFF) {
-		verbose(env, "%s pointer offset %d is not allowed\n",
-			reg_type_str(env, type), reg->off);
-		return false;
-	}
-
 	if (smin == S64_MIN) {
 		verbose(env, "math between %s pointer and register with unbounded min value is not allowed\n",
 			reg_type_str(env, type));
@@ -14461,6 +14455,27 @@ static bool check_reg_sane_offset(struct bpf_verifier_env *env,
 	return true;
 }
 
+static bool check_reg_sane_offset_ptr(struct bpf_verifier_env *env,
+				      const struct bpf_reg_state *reg,
+				      enum bpf_reg_type type)
+{
+	s64 smin = reg->smin_value;
+
+	if (reg->off >= BPF_MAX_VAR_OFF || reg->off <= -BPF_MAX_VAR_OFF) {
+		verbose(env, "%s pointer offset %d is not allowed\n",
+			reg_type_str(env, type), reg->off);
+		return false;
+	}
+
+	if (smin >= BPF_MAX_VAR_OFF || smin <= -BPF_MAX_VAR_OFF) {
+		verbose(env, "%s pointer offset %lld is not allowed\n",
+			reg_type_str(env, type), smin);
+		return false;
+	}
+
+	return true;
+}
+
 enum {
 	REASON_BOUNDS	= -1,
 	REASON_TYPE	= -2,
@@ -14874,8 +14889,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
 	dst_reg->type = ptr_reg->type;
 	dst_reg->id = ptr_reg->id;
 
-	if (!check_reg_sane_offset(env, off_reg, ptr_reg->type) ||
-	    !check_reg_sane_offset(env, ptr_reg, ptr_reg->type))
+	if (!check_reg_sane_offset_scalar(env, off_reg, ptr_reg->type) ||
+	    !check_reg_sane_offset_ptr(env, ptr_reg, ptr_reg->type))
 		return -EINVAL;
 
 	/* pointer types do not carry 32-bit bounds at the moment. */
@@ -15004,7 +15019,7 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
 		return -EACCES;
 	}
 
-	if (!check_reg_sane_offset(env, dst_reg, ptr_reg->type))
+	if (!check_reg_sane_offset_ptr(env, dst_reg, ptr_reg->type))
 		return -EINVAL;
 	reg_bounds_sync(dst_reg);
 	bounds_ret = sanitize_check_bounds(env, insn, dst_reg);