[bpf-next,v1,1/5] bpf: Make every prog keep a copy of ctx_arg_info

Commit Message

Amery Hung Feb. 14, 2025, 4:45 p.m. UTC

Currently, ctx_arg_info is read-only in the view of the verifier since
it is shared among programs of the same attach type. Make each program
have their own copy of ctx_arg_info so that we can use it to store
program specific information.

In the next patch where we support acquiring a referenced kptr through a
struct_ops argument tagged with "__ref", ctx_arg_info->ref_obj_id will
be used to store the unique reference object id of the argument. This
avoids creating a requirement in the verifier that "__ref" tagged
arguments must be the first set of references acquired [0].

[0] https://lore.kernel.org/bpf/[e-mail]/

Signed-off-by: Amery Hung <[e-mail]>
Acked-by: Eduard Zingerman <[e-mail]>
---
 include/linux/bpf.h   |  7 +++++--
 kernel/bpf/bpf_iter.c | 13 ++++++-------
 kernel/bpf/syscall.c  |  2 ++
 kernel/bpf/verifier.c | 25 +++++++++++++++----------
 4 files changed, 28 insertions(+), 19 deletions(-)

Comments

Martin KaFai Lau Feb. 15, 2025, 12:20 a.m. UTC | #1

On 2/14/25 8:45 AM, Amery Hung wrote:
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index c420edbfb7c8..598f19e6ebd2 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -2315,6 +2315,8 @@ static void __bpf_prog_put_noref(struct bpf_prog *prog, bool deferred)
>   	kfree(prog->aux->kfunc_tab);
>   	if (prog->aux->attach_btf)
>   		btf_put(prog->aux->attach_btf);
> +	if (prog->aux->ctx_arg_info)

A small nit. NULL check is not needed.

Acked-by: Martin KaFai Lau <[e-mail]>

> +		kfree(prog->aux->ctx_arg_info);

Alexei Starovoitov Feb. 15, 2025, 2:41 a.m. UTC | #2

On Fri, Feb 14, 2025 at 8:45 AM Amery Hung <[e-mail]> wrote:
>
>
> +int bpf_prog_ctx_arg_info_init(struct bpf_prog *prog,
> +                              const struct bpf_ctx_arg_aux *info, u32 cnt)
> +{
> +       prog->aux->ctx_arg_info = kcalloc(cnt, sizeof(*info), GFP_KERNEL);

could have been kmalloc_array.

> +       if (!prog->aux->ctx_arg_info)
> +               return -ENOMEM;
> +
> +       memcpy(prog->aux->ctx_arg_info, info, sizeof(*info) * cnt);

Please use kmemdup().
Otherwise cocci fans will send a patch for this tomorrow.
imo kmalloc+memcpy is fine, but, sigh, cocci.

pw-bot: cr

Amery Hung Feb. 15, 2025, 4:39 a.m. UTC | #3

On Fri, Feb 14, 2025 at 6:42 PM Alexei Starovoitov
<[e-mail]> wrote:
>
> On Fri, Feb 14, 2025 at 8:45 AM Amery Hung <[e-mail]> wrote:
> >
> >
> > +int bpf_prog_ctx_arg_info_init(struct bpf_prog *prog,
> > +                              const struct bpf_ctx_arg_aux *info, u32 cnt)
> > +{
> > +       prog->aux->ctx_arg_info = kcalloc(cnt, sizeof(*info), GFP_KERNEL);
>
> could have been kmalloc_array.
>
> > +       if (!prog->aux->ctx_arg_info)
> > +               return -ENOMEM;
> > +
> > +       memcpy(prog->aux->ctx_arg_info, info, sizeof(*info) * cnt);
>
> Please use kmemdup().
> Otherwise cocci fans will send a patch for this tomorrow.
> imo kmalloc+memcpy is fine, but, sigh, cocci.
>

Thanks for pointing out. I will replace it with kmemdup.

> pw-bot: cr

Patch

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f3f50e29d639..f4df39e8c735 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1507,7 +1507,7 @@  struct bpf_prog_aux {
 	u32 max_rdonly_access;
 	u32 max_rdwr_access;
 	struct btf *attach_btf;
-	const struct bpf_ctx_arg_aux *ctx_arg_info;
+	struct bpf_ctx_arg_aux *ctx_arg_info;
 	void __percpu *priv_stack_ptr;
 	struct mutex dst_mutex; /* protects dst_* pointers below, *after* prog becomes visible */
 	struct bpf_prog *dst_prog;
@@ -1945,6 +1945,9 @@  static inline void bpf_struct_ops_desc_release(struct bpf_struct_ops_desc *st_op
 
 #endif
 
+int bpf_prog_ctx_arg_info_init(struct bpf_prog *prog,
+			       const struct bpf_ctx_arg_aux *info, u32 cnt);
+
 #if defined(CONFIG_CGROUP_BPF) && defined(CONFIG_BPF_LSM)
 int bpf_trampoline_link_cgroup_shim(struct bpf_prog *prog,
 				    int cgroup_atype);
@@ -2546,7 +2549,7 @@  struct bpf_iter__bpf_map_elem {
 
 int bpf_iter_reg_target(const struct bpf_iter_reg *reg_info);
 void bpf_iter_unreg_target(const struct bpf_iter_reg *reg_info);
-bool bpf_iter_prog_supported(struct bpf_prog *prog);
+int bpf_iter_prog_supported(struct bpf_prog *prog);
 const struct bpf_func_proto *
 bpf_iter_get_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog);
 int bpf_iter_link_attach(const union bpf_attr *attr, bpfptr_t uattr, struct bpf_prog *prog);
diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index 106735145948..380e9a7cac75 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -335,7 +335,7 @@  static void cache_btf_id(struct bpf_iter_target_info *tinfo,
 	tinfo->btf_id = prog->aux->attach_btf_id;
 }
 
-bool bpf_iter_prog_supported(struct bpf_prog *prog)
+int bpf_iter_prog_supported(struct bpf_prog *prog)
 {
 	const char *attach_fname = prog->aux->attach_func_name;
 	struct bpf_iter_target_info *tinfo = NULL, *iter;
@@ -344,7 +344,7 @@  bool bpf_iter_prog_supported(struct bpf_prog *prog)
 	int prefix_len = strlen(prefix);
 
 	if (strncmp(attach_fname, prefix, prefix_len))
-		return false;
+		return -EINVAL;
 
 	mutex_lock(&targets_mutex);
 	list_for_each_entry(iter, &targets, list) {
@@ -360,12 +360,11 @@  bool bpf_iter_prog_supported(struct bpf_prog *prog)
 	}
 	mutex_unlock(&targets_mutex);
 
-	if (tinfo) {
-		prog->aux->ctx_arg_info_size = tinfo->reg_info->ctx_arg_info_size;
-		prog->aux->ctx_arg_info = tinfo->reg_info->ctx_arg_info;
-	}
+	if (!tinfo)
+		return -EINVAL;
 
-	return tinfo != NULL;
+	return bpf_prog_ctx_arg_info_init(prog, tinfo->reg_info->ctx_arg_info,
+					  tinfo->reg_info->ctx_arg_info_size);
 }
 
 const struct bpf_func_proto *
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index c420edbfb7c8..598f19e6ebd2 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2315,6 +2315,8 @@  static void __bpf_prog_put_noref(struct bpf_prog *prog, bool deferred)
 	kfree(prog->aux->kfunc_tab);
 	if (prog->aux->attach_btf)
 		btf_put(prog->aux->attach_btf);
+	if (prog->aux->ctx_arg_info)
+		kfree(prog->aux->ctx_arg_info);
 
 	if (deferred) {
 		if (prog->sleepable)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9971c03adfd5..a41ba019780f 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -22377,6 +22377,18 @@  static void print_verification_stats(struct bpf_verifier_env *env)
 		env->peak_states, env->longest_mark_read_walk);
 }
 
+int bpf_prog_ctx_arg_info_init(struct bpf_prog *prog,
+			       const struct bpf_ctx_arg_aux *info, u32 cnt)
+{
+	prog->aux->ctx_arg_info = kcalloc(cnt, sizeof(*info), GFP_KERNEL);
+	if (!prog->aux->ctx_arg_info)
+		return -ENOMEM;
+
+	memcpy(prog->aux->ctx_arg_info, info, sizeof(*info) * cnt);
+	prog->aux->ctx_arg_info_size = cnt;
+	return 0;
+}
+
 static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
 {
 	const struct btf_type *t, *func_proto;
@@ -22457,17 +22469,12 @@  static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
 		return -EACCES;
 	}
 
-	/* btf_ctx_access() used this to provide argument type info */
-	prog->aux->ctx_arg_info =
-		st_ops_desc->arg_info[member_idx].info;
-	prog->aux->ctx_arg_info_size =
-		st_ops_desc->arg_info[member_idx].cnt;
-
 	prog->aux->attach_func_proto = func_proto;
 	prog->aux->attach_func_name = mname;
 	env->ops = st_ops->verifier_ops;
 
-	return 0;
+	return bpf_prog_ctx_arg_info_init(prog, st_ops_desc->arg_info[member_idx].info,
+					  st_ops_desc->arg_info[member_idx].cnt);
 }
 #define SECURITY_PREFIX "security_"
 
@@ -22917,9 +22924,7 @@  static int check_attach_btf_id(struct bpf_verifier_env *env)
 		prog->aux->attach_btf_trace = true;
 		return 0;
 	} else if (prog->expected_attach_type == BPF_TRACE_ITER) {
-		if (!bpf_iter_prog_supported(prog))
-			return -EINVAL;
-		return 0;
+		return bpf_iter_prog_supported(prog);
 	}
 
 	if (prog->type == BPF_PROG_TYPE_LSM) {