[PATCH v6 bpf-next 02/12] bpf: Handle BPF_UPTR in verifier

[Martin KaFai Lau <martin.lau@linux.dev>]

From: Kui-Feng Lee <thinker.li@gmail.com>

This patch adds BPF_UPTR support to the verifier. Not that only the
map_value will support the "__uptr" type tag.

This patch enforces only BPF_LDX is allowed to the value of an uptr.
After BPF_LDX, it will mark the dst_reg as PTR_TO_MEM | PTR_MAYBE_NULL
with size deduced from the field.kptr.btf_id. This will make the
dst_reg pointed memory to be readable and writable as scalar.

There is a redundant "val_reg = reg_state(env, value_regno);" statement
in the check_map_kptr_access(). This patch takes this chance to remove
it also.

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
---
Changes in v5:
  - The "if (kptr_field->type == BPF_UPTR)" addition in v4 in 
    map_kptr_match_type() is removed. It will not be reached.
    meta->kptr_field is for kptr only.
  - Use btf_field_type_name() for the verbose() log in check_map_access().
  - Directly use t->size in mark_uptr_ld_reg. "t" must be a struct.

 kernel/bpf/verifier.c | 39 +++++++++++++++++++++++++++++++++------
 1 file changed, 33 insertions(+), 6 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f514247ba8ba..1bd0c3f41f2f 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5485,6 +5485,22 @@ static u32 btf_ld_kptr_type(struct bpf_verifier_env *env, struct btf_field *kptr
 	return ret;
 }
 
+static int mark_uptr_ld_reg(struct bpf_verifier_env *env, u32 regno,
+			    struct btf_field *field)
+{
+	struct bpf_reg_state *reg;
+	const struct btf_type *t;
+
+	t = btf_type_by_id(field->kptr.btf, field->kptr.btf_id);
+	mark_reg_known_zero(env, cur_regs(env), regno);
+	reg = reg_state(env, regno);
+	reg->type = PTR_TO_MEM | PTR_MAYBE_NULL;
+	reg->mem_size = t->size;
+	reg->id = ++env->id_gen;
+
+	return 0;
+}
+
 static int check_map_kptr_access(struct bpf_verifier_env *env, u32 regno,
 				 int value_regno, int insn_idx,
 				 struct btf_field *kptr_field)
@@ -5513,9 +5529,15 @@ static int check_map_kptr_access(struct bpf_verifier_env *env, u32 regno,
 		verbose(env, "store to referenced kptr disallowed\n");
 		return -EACCES;
 	}
+	if (class != BPF_LDX && kptr_field->type == BPF_UPTR) {
+		verbose(env, "store to uptr disallowed\n");
+		return -EACCES;
+	}
 
 	if (class == BPF_LDX) {
-		val_reg = reg_state(env, value_regno);
+		if (kptr_field->type == BPF_UPTR)
+			return mark_uptr_ld_reg(env, value_regno, kptr_field);
+
 		/* We can simply mark the value_regno receiving the pointer
 		 * value from map as PTR_TO_BTF_ID, with the correct type.
 		 */
@@ -5573,21 +5595,26 @@ static int check_map_access(struct bpf_verifier_env *env, u32 regno,
 			case BPF_KPTR_UNREF:
 			case BPF_KPTR_REF:
 			case BPF_KPTR_PERCPU:
+			case BPF_UPTR:
 				if (src != ACCESS_DIRECT) {
-					verbose(env, "kptr cannot be accessed indirectly by helper\n");
+					verbose(env, "%s cannot be accessed indirectly by helper\n",
+						btf_field_type_name(field->type));
 					return -EACCES;
 				}
 				if (!tnum_is_const(reg->var_off)) {
-					verbose(env, "kptr access cannot have variable offset\n");
+					verbose(env, "%s access cannot have variable offset\n",
+						btf_field_type_name(field->type));
 					return -EACCES;
 				}
 				if (p != off + reg->var_off.value) {
-					verbose(env, "kptr access misaligned expected=%u off=%llu\n",
+					verbose(env, "%s access misaligned expected=%u off=%llu\n",
+						btf_field_type_name(field->type),
 						p, off + reg->var_off.value);
 					return -EACCES;
 				}
 				if (size != bpf_size_to_bytes(BPF_DW)) {
-					verbose(env, "kptr access size must be BPF_DW\n");
+					verbose(env, "%s access size must be BPF_DW\n",
+						btf_field_type_name(field->type));
 					return -EACCES;
 				}
 				break;
@@ -6953,7 +6980,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
 			return err;
 		if (tnum_is_const(reg->var_off))
 			kptr_field = btf_record_find(reg->map_ptr->record,
-						     off + reg->var_off.value, BPF_KPTR);
+						     off + reg->var_off.value, BPF_KPTR | BPF_UPTR);
 		if (kptr_field) {
 			err = check_map_kptr_access(env, regno, value_regno, insn_idx, kptr_field);
 		} else if (t == BPF_READ && value_regno >= 0) {
-- 
2.43.5