[OFFLIST,RFC,3/4] bpf: Support bpf_kptr_xchg into local kptr

Commit Message

Amery Hung July 19, 2024, 5:21 p.m. UTC

From: Dave Marchevsky <[e-mail]>

Signed-off-by: Dave Marchevsky <[e-mail]>
---
 kernel/bpf/verifier.c | 42 ++++++++++++++++++++++++++++--------------
 1 file changed, 28 insertions(+), 14 deletions(-)

Comments

Alexei Starovoitov July 23, 2024, 12:18 a.m. UTC | #1

On Fri, Jul 19, 2024 at 05:21:18PM +0000, Amery Hung wrote:
> From: Dave Marchevsky <[e-mail]>
> 
> Signed-off-by: Dave Marchevsky <[e-mail]>

Amery,
please add your SOB after Dave's when you're sending patches like this.

Remove OFFLIST in subject... and resend cc-ing bpf@vger.

Add proper commit log.

> -	if (meta->func_id == BPF_FUNC_kptr_xchg && type_is_alloc(type)) {
> +	if (meta->func_id == BPF_FUNC_kptr_xchg && type_is_alloc(type) && regno > 1) {

I don't understand the point of regno > 1. Pls explain/add comment.

Patches 1 and 2 make sense.

Amery Hung July 24, 2024, 12:08 a.m. UTC | #2

On Mon, Jul 22, 2024 at 5:18 PM Alexei Starovoitov
<[e-mail]> wrote:
>
> On Fri, Jul 19, 2024 at 05:21:18PM +0000, Amery Hung wrote:
> > From: Dave Marchevsky <[e-mail]>
> >
> > Signed-off-by: Dave Marchevsky <[e-mail]>
>
> Amery,
> please add your SOB after Dave's when you're sending patches like this.
>
> Remove OFFLIST in subject... and resend cc-ing bpf@vger.
>
> Add proper commit log.

Got it.

>
> > -     if (meta->func_id == BPF_FUNC_kptr_xchg && type_is_alloc(type)) {
> > +     if (meta->func_id == BPF_FUNC_kptr_xchg && type_is_alloc(type) && regno > 1) {
>
> I don't understand the point of regno > 1. Pls explain/add comment.
>
> Patches 1 and 2 make sense.

I believe this patchset is incomplete, and it will trigger a refcount
bug when running local_kptr_stash/local_kptr_stash_simple. I will
finish and resend this individual series.

Thank you,
Amery

Patch

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 06ec18ee973c..39929569ae58 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7664,29 +7664,38 @@  static int process_kptr_func(struct bpf_verifier_env *env, int regno,
 			     struct bpf_call_arg_meta *meta)
 {
 	struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
-	struct bpf_map *map_ptr = reg->map_ptr;
 	struct btf_field *kptr_field;
+	struct bpf_map *map_ptr;
+	struct btf_record *rec;
 	u32 kptr_off;
 
+	if (type_is_ptr_alloc_obj(reg->type)) {
+		rec = reg_btf_record(reg);
+	} else { /* PTR_TO_MAP_VALUE */
+		map_ptr = reg->map_ptr;
+		if (!map_ptr->btf) {
+			verbose(env, "map '%s' has to have BTF in order to use bpf_kptr_xchg\n",
+				map_ptr->name);
+			return -EINVAL;
+		}
+		rec = map_ptr->record;
+		meta->map_ptr = map_ptr;
+	}
+
 	if (!tnum_is_const(reg->var_off)) {
 		verbose(env,
 			"R%d doesn't have constant offset. kptr has to be at the constant offset\n",
 			regno);
 		return -EINVAL;
 	}
-	if (!map_ptr->btf) {
-		verbose(env, "map '%s' has to have BTF in order to use bpf_kptr_xchg\n",
-			map_ptr->name);
-		return -EINVAL;
-	}
-	if (!btf_record_has_field(map_ptr->record, BPF_KPTR)) {
-		verbose(env, "map '%s' has no valid kptr\n", map_ptr->name);
+
+	if (!btf_record_has_field(rec, BPF_KPTR)) {
+		verbose(env, "R%d has no valid kptr\n", regno);
 		return -EINVAL;
 	}
 
-	meta->map_ptr = map_ptr;
 	kptr_off = reg->off + reg->var_off.value;
-	kptr_field = btf_record_find(map_ptr->record, kptr_off, BPF_KPTR);
+	kptr_field = btf_record_find(rec, kptr_off, BPF_KPTR);
 	if (!kptr_field) {
 		verbose(env, "off=%d doesn't point to kptr\n", kptr_off);
 		return -EACCES;
@@ -8260,7 +8269,12 @@  static const struct bpf_reg_types func_ptr_types = { .types = { PTR_TO_FUNC } };
 static const struct bpf_reg_types stack_ptr_types = { .types = { PTR_TO_STACK } };
 static const struct bpf_reg_types const_str_ptr_types = { .types = { PTR_TO_MAP_VALUE } };
 static const struct bpf_reg_types timer_types = { .types = { PTR_TO_MAP_VALUE } };
-static const struct bpf_reg_types kptr_xchg_dest_types = { .types = { PTR_TO_MAP_VALUE } };
+static const struct bpf_reg_types kptr_xchg_dest_types = {
+	.types = {
+		PTR_TO_MAP_VALUE,
+		PTR_TO_BTF_ID | MEM_ALLOC
+	}
+};
 static const struct bpf_reg_types dynptr_types = {
 	.types = {
 		PTR_TO_STACK,
@@ -8331,7 +8345,7 @@  static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
 	if (base_type(arg_type) == ARG_PTR_TO_MEM)
 		type &= ~DYNPTR_TYPE_FLAG_MASK;
 
-	if (meta->func_id == BPF_FUNC_kptr_xchg && type_is_alloc(type)) {
+	if (meta->func_id == BPF_FUNC_kptr_xchg && type_is_alloc(type) && regno > 1) {
 		type &= ~MEM_ALLOC;
 		type &= ~MEM_PERCPU;
 	}
@@ -8424,7 +8438,7 @@  static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
 			verbose(env, "verifier internal error: unimplemented handling of MEM_ALLOC\n");
 			return -EFAULT;
 		}
-		if (meta->func_id == BPF_FUNC_kptr_xchg) {
+		if (meta->func_id == BPF_FUNC_kptr_xchg && regno > 1) {
 			if (map_kptr_match_type(env, meta->kptr_field, reg, regno))
 				return -EACCES;
 		}
@@ -8735,7 +8749,7 @@  static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 		meta->release_regno = regno;
 	}
 
-	if (reg->ref_obj_id) {
+	if (reg->ref_obj_id && base_type(arg_type) != ARG_KPTR_XCHG_DEST) {
 		if (meta->ref_obj_id) {
 			verbose(env, "verifier internal error: more than one arg with ref_obj_id R%d %u %u\n",
 				regno, reg->ref_obj_id,