bpf: Enable bpf_iter targets registering ctx argument types

Commit b121b341e598 ("bpf: Add PTR_TO_BTF_ID_OR_NULL
support") adds a field btf_id_or_null_non0_off to
bpf_prog->aux structure to indicate that the
first ctx argument is PTR_TO_BTF_ID reg_type and
all others are PTR_TO_BTF_ID_OR_NULL.
This approach does not really scale if we have
other different reg types in the future, e.g.,
a pointer to a buffer.

This patch enables bpf_iter targets registering ctx argument
reg types which may be different from the default one.
For example, for pointers to structures, the default reg_type
is PTR_TO_BTF_ID for tracing program. The target can register
a particular pointer type as PTR_TO_BTF_ID_OR_NULL which can
be used by the verifier to enforce accesses.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200513180221.2949882-1-yhs@fb.com

5 files changed, 32 insertions, 6 deletions

diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index 644f8626b2c0..dd612b80b9fe 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -308,6 +308,11 @@ bool bpf_iter_prog_supported(struct bpf_prog *prog)
 	}
 	mutex_unlock(&targets_mutex);
 
+	if (supported) {
+		prog->aux->ctx_arg_info_size = tinfo->reg_info->ctx_arg_info_size;
+		prog->aux->ctx_arg_info = tinfo->reg_info->ctx_arg_info;
+	}
+
 	return supported;
 }
 
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index dcd233139294..58c9af1d4808 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3694,7 +3694,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
 	struct bpf_verifier_log *log = info->log;
 	const struct btf_param *args;
 	u32 nr_args, arg;
-	int ret;
+	int i, ret;
 
 	if (off % 8) {
 		bpf_log(log, "func '%s' offset %d is not multiple of 8\n",
@@ -3790,10 +3790,15 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
 		return true;
 
 	/* this is a pointer to another type */
-	if (off != 0 && prog->aux->btf_id_or_null_non0_off)
-		info->reg_type = PTR_TO_BTF_ID_OR_NULL;
-	else
-		info->reg_type = PTR_TO_BTF_ID;
+	info->reg_type = PTR_TO_BTF_ID;
+	for (i = 0; i < prog->aux->ctx_arg_info_size; i++) {
+		const struct bpf_ctx_arg_aux *ctx_arg_info = &prog->aux->ctx_arg_info[i];
+
+		if (ctx_arg_info->offset == off) {
+			info->reg_type = ctx_arg_info->reg_type;
+			break;
+		}
+	}
 
 	if (tgt_prog) {
 		ret = btf_translate_to_vmlinux(log, btf, t, tgt_prog->type, arg);
diff --git a/kernel/bpf/map_iter.c b/kernel/bpf/map_iter.c
index c6216a5fe56e..c69071e334bf 100644
--- a/kernel/bpf/map_iter.c
+++ b/kernel/bpf/map_iter.c
@@ -87,6 +87,11 @@ static const struct bpf_iter_reg bpf_map_reg_info = {
 	.init_seq_private	= NULL,
 	.fini_seq_private	= NULL,
 	.seq_priv_size		= sizeof(struct bpf_iter_seq_map_info),
+	.ctx_arg_info_size	= 1,
+	.ctx_arg_info		= {
+		{ offsetof(struct bpf_iter__bpf_map, map),
+		  PTR_TO_BTF_ID_OR_NULL },
+	},
 };
 
 static int __init bpf_map_iter_init(void)
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index bd7bfd83d9e0..a9b7264dda08 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -312,6 +312,11 @@ static const struct bpf_iter_reg task_reg_info = {
 	.init_seq_private	= init_seq_pidns,
 	.fini_seq_private	= fini_seq_pidns,
 	.seq_priv_size		= sizeof(struct bpf_iter_seq_task_info),
+	.ctx_arg_info_size	= 1,
+	.ctx_arg_info		= {
+		{ offsetof(struct bpf_iter__task, task),
+		  PTR_TO_BTF_ID_OR_NULL },
+	},
 };
 
 static const struct bpf_iter_reg task_file_reg_info = {
@@ -320,6 +325,13 @@ static const struct bpf_iter_reg task_file_reg_info = {
 	.init_seq_private	= init_seq_pidns,
 	.fini_seq_private	= fini_seq_pidns,
 	.seq_priv_size		= sizeof(struct bpf_iter_seq_task_file_info),
+	.ctx_arg_info_size	= 2,
+	.ctx_arg_info		= {
+		{ offsetof(struct bpf_iter__task_file, task),
+		  PTR_TO_BTF_ID_OR_NULL },
+		{ offsetof(struct bpf_iter__task_file, file),
+		  PTR_TO_BTF_ID_OR_NULL },
+	},
 };
 
 static int __init task_iter_init(void)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2a1826c76bb6..a3f2af756fd6 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10652,7 +10652,6 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 		prog->aux->attach_func_proto = t;
 		if (!bpf_iter_prog_supported(prog))
 			return -EINVAL;
-		prog->aux->btf_id_or_null_non0_off = true;
 		ret = btf_distill_func_proto(&env->log, btf, t,
 					     tname, &fmodel);
 		return ret;