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Message-Id: <20231018061746.111364-7-zhouchuyi@bytedance.com>
Date: Wed, 18 Oct 2023 14:17:44 +0800
From: Chuyi Zhou <zhouchuyi@...edance.com>
To: bpf@...r.kernel.org
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
martin.lau@...nel.org, tj@...nel.org, linux-kernel@...r.kernel.org,
Chuyi Zhou <zhouchuyi@...edance.com>
Subject: [RESEND PATCH bpf-next v6 6/8] bpf: Let bpf_iter_task_new accept null task ptr
When using task_iter to iterate all threads of a specific task, we enforce
that the user must pass a valid task pointer to ensure safety. However,
when iterating all threads/process in the system, BPF verifier still
require a valid ptr instead of "nullable" pointer, even though it's
pointless, which is a kind of surprising from usability standpoint. It
would be nice if we could let that kfunc accept a explicit null pointer
when we are using BPF_TASK_ITER_ALL_{PROCS, THREADS} and a valid pointer
when using BPF_TASK_ITER_THREAD.
Given a trival kfunc:
__bpf_kfunc void FN(struct TYPE_A *obj);
BPF Prog would reject a nullptr for obj. The error info is:
"arg#x pointer type xx xx must point to scalar, or struct with scalar"
reported by get_kfunc_ptr_arg_type(). The reg->type is SCALAR_VALUE and
the btf type of ref_t is not scalar or scalar_struct which leads to the
rejection of get_kfunc_ptr_arg_type.
This patch add "__nullable" annotation:
__bpf_kfunc void FN(struct TYPE_A *obj__nullable);
Here __nullable indicates obj can be optional, user can pass a explicit
nullptr or a normal TYPE_A pointer. In get_kfunc_ptr_arg_type(), we will
detect whether the current arg is optional and register is null, If so,
return a new kfunc_ptr_arg_type KF_ARG_PTR_TO_NULL and skip to the next
arg in check_kfunc_args().
Signed-off-by: Chuyi Zhou <zhouchuyi@...edance.com>
Acked-by: Andrii Nakryiko <andrii@...nel.org>
---
kernel/bpf/task_iter.c | 7 +++++--
kernel/bpf/verifier.c | 13 ++++++++++++-
2 files changed, 17 insertions(+), 3 deletions(-)
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index faa1712c1df5..59e747938bdb 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -976,7 +976,7 @@ __diag_ignore_all("-Wmissing-prototypes",
"Global functions as their definitions will be in vmlinux BTF");
__bpf_kfunc int bpf_iter_task_new(struct bpf_iter_task *it,
- struct task_struct *task, unsigned int flags)
+ struct task_struct *task__nullable, unsigned int flags)
{
struct bpf_iter_task_kern *kit = (void *)it;
@@ -988,14 +988,17 @@ __bpf_kfunc int bpf_iter_task_new(struct bpf_iter_task *it,
switch (flags) {
case BPF_TASK_ITER_ALL_THREADS:
case BPF_TASK_ITER_ALL_PROCS:
+ break;
case BPF_TASK_ITER_PROC_THREADS:
+ if (!task__nullable)
+ return -EINVAL;
break;
default:
return -EINVAL;
}
if (flags == BPF_TASK_ITER_PROC_THREADS)
- kit->task = task;
+ kit->task = task__nullable;
else
kit->task = &init_task;
kit->pos = kit->task;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index fcdf2382153a..e9bc5d4a25a1 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10332,6 +10332,11 @@ static bool is_kfunc_arg_refcounted_kptr(const struct btf *btf, const struct btf
return __kfunc_param_match_suffix(btf, arg, "__refcounted_kptr");
}
+static bool is_kfunc_arg_nullable(const struct btf *btf, const struct btf_param *arg)
+{
+ return __kfunc_param_match_suffix(btf, arg, "__nullable");
+}
+
static bool is_kfunc_arg_scalar_with_name(const struct btf *btf,
const struct btf_param *arg,
const char *name)
@@ -10474,6 +10479,7 @@ enum kfunc_ptr_arg_type {
KF_ARG_PTR_TO_CALLBACK,
KF_ARG_PTR_TO_RB_ROOT,
KF_ARG_PTR_TO_RB_NODE,
+ KF_ARG_PTR_TO_NULL,
};
enum special_kfunc_type {
@@ -10630,6 +10636,8 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env *env,
if (is_kfunc_arg_callback(env, meta->btf, &args[argno]))
return KF_ARG_PTR_TO_CALLBACK;
+ if (is_kfunc_arg_nullable(meta->btf, &args[argno]) && register_is_null(reg))
+ return KF_ARG_PTR_TO_NULL;
if (argno + 1 < nargs &&
(is_kfunc_arg_mem_size(meta->btf, &args[argno + 1], ®s[regno + 1]) ||
@@ -11180,7 +11188,8 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
}
if ((is_kfunc_trusted_args(meta) || is_kfunc_rcu(meta)) &&
- (register_is_null(reg) || type_may_be_null(reg->type))) {
+ (register_is_null(reg) || type_may_be_null(reg->type)) &&
+ !is_kfunc_arg_nullable(meta->btf, &args[i])) {
verbose(env, "Possibly NULL pointer passed to trusted arg%d\n", i);
return -EACCES;
}
@@ -11205,6 +11214,8 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
return kf_arg_type;
switch (kf_arg_type) {
+ case KF_ARG_PTR_TO_NULL:
+ continue;
case KF_ARG_PTR_TO_ALLOC_BTF_ID:
case KF_ARG_PTR_TO_BTF_ID:
if (!is_kfunc_trusted_args(meta) && !is_kfunc_rcu(meta))
--
2.20.1
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